CN103066825A - A kind of power off method and power supply - Google Patents
A kind of power off method and power supply Download PDFInfo
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- CN103066825A CN103066825A CN2012105584999A CN201210558499A CN103066825A CN 103066825 A CN103066825 A CN 103066825A CN 2012105584999 A CN2012105584999 A CN 2012105584999A CN 201210558499 A CN201210558499 A CN 201210558499A CN 103066825 A CN103066825 A CN 103066825A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
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- H02M1/36—Means for starting or stopping converters
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Abstract
The embodiment of the invention discloses a power supply shutdown method, which comprises the following steps: receiving a shutdown signal, and changing the conduction time of a primary side main switch of the transformer or changing the switching frequency of the primary side main switch; detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer, or detecting the switching frequency of the primary main switch on the secondary side of the transformer; and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product or the switching frequency of the primary side main switch. The invention can effectively avoid self-oscillation when in shutdown, does not need to add extra circuit elements, and has the advantages of small circuit area, simple structure and low cost.
Description
Technical Field
The invention relates to the field of power supplies, in particular to a power supply shutdown method and a power supply.
Background
The synchronous rectification technology has remarkable efficiency advantage in the low-voltage and high-current field compared with the diode asynchronous rectification, so that the synchronous rectification technology is widely applied to a switching power supply. However, when the primary side Pulse Width Modulation (PWM) control is applied to the isolated dc power supply, the driving signal of the secondary side synchronous rectification circuit needs to be transmitted from the primary side to the secondary side, and after the primary side shutdown control unit is shutdown, the secondary side synchronous rectification circuit loses control. When the isolated direct-current power supply uses a secondary side synchronous rectification technology, the current in the output inductor can be bidirectional, and the output inductor current can become negative when the load is light. If the synchronous drive of the secondary side is not controlled when the direct-current isolation power supply is shut down, the circuit is easy to generate uncontrollable self-oscillation after the primary side is shut down, and therefore the stress of circuit elements is increased. In some cases, the self-oscillation can last for a long time or even last all the time, and influence the next start-up. Fig. 1 is a waveform diagram before and after shutdown of a secondary side follow current tube of a conventional forward active clamp dc converter. As shown in fig. 1, when t is 550 μ s, the power supply is turned off, and the waveform after the power supply is very dense, just because the synchronous rectification circuit in the power supply has self-oscillation.
In order to solve the problem of self-oscillation of the synchronous rectification circuit after shutdown, in the prior art, a photo coupler or a driving transformer is generally used on a shutdown control loop of secondary side synchronous driving to transmit a shutdown signal from a primary side. Fig. 2 is a schematic diagram of a conventional shutdown using an optocoupler control circuit, and as shown in fig. 2, after a shutdown signal is transmitted to a secondary control circuit through an optocoupler or other isolation device, the secondary control circuit shuts off a synchronous rectification circuit. However, no matter the optical coupler or other isolation devices are used to transmit the shutdown signal, additional circuit elements are required in the circuit. And because the optical coupler or other isolating devices need to meet the requirement of safety creepage distance, the element area is larger. These add to the bulk and cost of the circuit. In addition, the shutdown time of the conventional primary-side PWM shutdown control unit is random, that is, the shutdown time can occur at any time within a switching period, so that even if the delay time for transmitting a shutdown signal by using an optocoupler or other isolating devices is negligibly short, the current in the secondary-side output inductor may still be reversed during light-load shutdown, thereby causing overvoltage or even avalanche breakdown of the secondary-side synchronous switching tube during shutdown.
Disclosure of Invention
The technical problem to be solved by the embodiments of the present invention is to provide a power shutdown method and a power supply. Self-oscillation can be effectively avoided during shutdown.
In a first aspect, an embodiment of the present invention provides a power shutdown method, which may include: receiving a shutdown signal, and changing the conduction time of a primary side main switch of the transformer; detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on a secondary side of the transformer; and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product so as to realize the power supply turn-off.
In a second aspect, an embodiment of the present invention provides another power shutdown method, which may include: receiving a shutdown signal, and changing the switching frequency (or switching period) of a primary side main switch of the transformer; detecting the switching frequency (or switching period) of the primary side main switch on the secondary side of the transformer; and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency (or switching period) of the primary side main switch.
In a third aspect, an embodiment of the present invention provides a power supply, which may include: the shutdown control unit is used for receiving a shutdown signal and changing the conduction time of a primary side main switch of the transformer; the control value acquisition unit is used for detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer; and the secondary side control unit is used for controlling the on and off of the synchronous rectifier of the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product.
In a fourth aspect, an embodiment of the present invention provides another power supply, which may include: the shutdown control unit is used for receiving a shutdown signal and changing the switching frequency (or switching period) of a primary side main switch of the transformer; a frequency detection unit (or a period detection unit) for detecting a switching frequency (or a switching period) of the primary side main switch on a secondary side of the transformer; and the secondary side control unit is used for controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency (or switching period) of the primary side main switch.
According to the power supply shutdown method and the power supply provided by the embodiment of the invention, the on-time of the primary side main switch of the transformer is changed or the switching frequency of the primary side main switch is changed by receiving the shutdown signal; detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product or the switching frequency of the primary main switch on the secondary side of the transformer; and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product or the switching frequency of the primary side main switch, adjusting the switching circuit to a state most favorable for turn-off, and then turning off the synchronous rectification circuit on the primary side circuit and the secondary side according to a preset optimal turn-off time sequence, thereby achieving the purpose of effectively avoiding turn-off oscillation and turn-off stress. And a new circuit element is not required to be added, so that the size and the cost of the circuit are saved, the structure is simple, the cost is low, and the reliability and the stability of the power supply are improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a waveform diagram before and after shutdown of a secondary side follow current tube of a conventional forward active clamp dc converter;
FIG. 2 is a schematic diagram of a prior art shutdown using an optocoupler control circuit;
fig. 3 is a schematic flowchart of a power shutdown method according to an embodiment of the present invention;
FIG. 4a is a flowchart illustrating another power shutdown method according to an embodiment of the invention;
FIG. 4b is a flowchart illustrating a power shutdown method according to another embodiment of the invention;
FIG. 5 is a flowchart illustrating a power shutdown method according to another embodiment of the present invention;
FIG. 6 is a schematic diagram of a logic structure of a power supply according to an embodiment of the present invention;
FIG. 7 is a schematic circuit diagram of a shutdown control unit in a power supply according to an embodiment of the invention;
FIG. 8 is a schematic diagram of a logic structure of another power supply according to an embodiment of the present invention;
FIG. 9 is a schematic diagram of a logic structure of another power supply according to an embodiment of the present invention;
FIG. 10 is a schematic diagram of a logic structure of another power supply according to an embodiment of the present invention;
FIG. 11 is a signal timing diagram illustrating the power supply shown in FIG. 10;
FIG. 12 is a schematic diagram of a logic structure of another power supply according to an embodiment of the present invention;
fig. 13 is a flowchart of another power shutdown method according to an embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Here, it should be further noted that, in order to avoid obscuring the present invention by unnecessary details, only the device structure closely related to the scheme according to the present invention is shown in the drawings, and other details not closely related to the present invention are omitted.
Referring to fig. 3, a method flow diagram of a power shutdown method according to an embodiment of the present invention is shown, where the power shutdown method is applicable to a self-driven synchronous rectification power supply. As shown, the method includes:
s101, receiving a shutdown signal, and changing the conduction time of a primary side main switch of the transformer.
Alternatively, the switching period of the primary side main switch may or may not be changed.
And S102, detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer.
Alternatively, the corresponding control value of the volt-second product may be a voltage value or a current value.
Specifically, the reason why the volt-second product is used as the detection parameter is that the volt-second product parameter can be simply obtained according to the input voltage and the on-time of the secondary side, the circuit structure is simple, and calculation and judgment are convenient. Of course, a timing counter may be provided in the circuit to detect the values of parameters such as the frequency, period, and pulse width of the PWM signal as reference conditions for determining whether to shut down the power supply.
And S103, controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product.
Therefore, the power supply shutdown method provided by the embodiment of the invention changes the volt-second product of the input voltage detected by the secondary side by changing the conduction time of the primary side main switch, so that the switching circuit is adjusted to the state most favorable for shutdown, and then the synchronous rectification circuit of the primary side circuit and the secondary side is turned off according to the preset optimal shutdown time sequence, thereby achieving the purpose of eliminating shutdown oscillation and shutdown stress. And a new circuit element is not required to be added, so that the volume and the cost of the circuit are saved.
Fig. 4a is a schematic flow chart of a power shutdown method according to an embodiment of the present invention. In this embodiment, the method comprises the steps of:
s201, receiving a shutdown signal, and shortening the conduction time of a primary side main switch of the transformer.
Specifically, there are several ways to shorten the on-time of the primary side main switch of the transformer, but not limited to the following ways: at least one switching period before the primary side main switch of the transformer is turned off can be shortened, and the on-time of the switch after the switching period is shortened is shorter than the on-time of the switch before the switching period is shortened. The pulse width may also be shortened during at least one switching cycle before the primary side main switch of the transformer is turned off. At least one switching period before the primary side main switch of the transformer is turned off can be shortened, one or more of the shortened switching periods are selected, and the pulse width is shortened in the one or more shortened switching periods.
Preferably, the pulse width can be shortened in the last cycle before the primary side main switch is turned off. The specific implementation is to shorten the high level of the pulse to achieve a shortening of the last on-time before the switch is turned off. The pulses here may be PWM pulses.
It should be noted that, the time of the change of various parameters can be completed at the moment when the primary side main switch is turned off, but is measured by the switching period, which is beneficial for counting the detection value by taking the period as a unit during the subsequent detection.
And S202, detecting a volt-second product of the primary side input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer.
The control value corresponding to the volt-second product may be a voltage value or a current value.
Specifically, the reason why the volt-second product is used as the detection parameter is that the volt-second product parameter can be simply obtained according to the input voltage and the on-time of the secondary side, the circuit structure is simple, and calculation and judgment are convenient. Of course, a timing counter may be provided in the circuit to detect the values of parameters such as the frequency, period, and pulse width of the PWM signal as reference conditions for determining whether to shut down the power supply.
And S203, when the volt-second product or the control value corresponding to the volt-second product is smaller than or equal to a preset value, turning off the synchronous rectifier on the secondary side.
Specifically, the preset value may be set with reference to a steady voltage-second product when the power supply is not turned off and the circuit is normally operating, and the preset value may be set to be smaller than the steady voltage-second product according to a change trend of the switching period and/or the pulse width.
Fig. 4b is a schematic flow chart of a power shutdown method according to an embodiment of the present invention. In this embodiment, the method comprises the steps of:
s301, receiving a shutdown signal, and prolonging the conduction time of a primary side main switch of the transformer;
specifically, there are several ways to lengthen the on-time of the primary main switch of the transformer, but not limited to the following ways: at least one switching period before the primary side main switch of the transformer is turned off can be prolonged, and the on-time of the switch after the switching period is prolonged is longer than the on-time of the switch before the switching period is prolonged; or, the pulse width is increased in at least one switching period before the primary side main switch of the transformer is turned off; or lengthening at least one switching period before the primary side main switch of the transformer is turned off, selecting one or more switching periods from the lengthened at least one switching period, and lengthening the pulse width in the lengthened one or more switching periods.
Preferably, the pulse width may be increased in the last cycle before the primary side main switch turns off. Specifically, the high level of the pulse is lengthened to achieve a prolonged last on-time before the switch is turned off. The pulses here may be PWM pulses.
It should be noted that, the time of the change of various parameters can be completed at the moment when the primary side main switch is turned off, but is measured by the switching period, which is beneficial for counting the detection value by taking the period as a unit during the subsequent detection.
S302, detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer;
and S303, when the volt-second product or a control value corresponding to the volt-second product is greater than or equal to a preset value, turning off the synchronous rectifier on the secondary side.
Specifically, the preset value here may be set to be larger than the steady-state volt-second product accordingly.
Therefore, the power supply shutdown method provided by the embodiment of the invention utilizes the original transmission path of the PWM signal or other signals of the circuit, before shutdown, a group of shutdown pulses different from the shutdown pulse in the normal operation state is sent from the primary side to the secondary side, so that the detection and identification of the secondary side circuit are facilitated, meanwhile, the group of special shutdown pulses is utilized to adjust the switching circuit to the state most favorable for shutdown, and then the synchronous rectification circuit of the primary side circuit and the secondary side is shut down according to the preset optimal shutdown time sequence, so that the purposes of eliminating shutdown oscillation and shutdown stress are achieved. And a new circuit element is not required to be added, so that the volume and the cost of the circuit are saved. The switching period and/or the pulse width are/is changed to form various modes, one parameter can be changed independently or two parameters can be changed simultaneously, and only the shutdown pulse sent by the primary side is required to be different from the pulse in the normal operation state.
Referring to fig. 5, an embodiment of the present invention further provides a power shutdown method, including:
s401, receiving a shutdown signal, and changing the switching frequency of a primary side main switch of the transformer.
The on time of the switch may be prolonged, may be maintained unchanged, or may be shortened, which is not limited in this embodiment of the present invention.
S402, detecting the switching frequency of the primary side main switch on the secondary side of the transformer;
and S403, controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch.
In one implementation, the switching frequency of the primary side main switch of the transformer is increased after receiving the shutdown signal. The secondary side holds a preset value of the switching frequency, which can be set slightly higher than the switching frequency of the power supply in the normal state. The secondary side detects the switching frequency, compares the switching frequency with the preset value, and turns off the synchronous rectifier of the secondary side when the detected switching frequency is higher than or equal to the preset value.
In another implementation, the switching frequency of the primary side main switch of the transformer is reduced after the shutdown signal is received. The secondary side holds a preset value of the switching frequency, which may be set slightly lower than the switching frequency of the power supply in the normal state. And after the secondary side detects the switching frequency, comparing the switching frequency with the preset value, and turning off the synchronous rectifier on the secondary side when the detected switching frequency is lower than or equal to the preset value.
Of course, it will be understood by those skilled in the art that varying the switching frequency is in fact equivalent to varying the switching period. The implementation of detecting the switching frequency or detecting the switching period is common knowledge of those skilled in the art, and will not be described herein. In addition, the technical scheme for changing the conduction time and the technical scheme for changing the switching frequency provided by the embodiment of the invention can be realized at the same time, and the same purpose can be achieved as long as the corresponding detection mode and the preset value are set on the secondary side.
Fig. 6 is a schematic circuit diagram of a power supply according to an embodiment of the invention. Fig. 6 shows a half-bridge rectifier circuit. It will be appreciated by those skilled in the art that this is merely exemplary and not limiting and that the present invention may also be applied to full bridge rectifier circuits or current doubler rectifier circuits. In the circuit of the present embodiment, the power supply includes:
the shutdown control unit 101 is configured to receive a shutdown signal and change on-time of a primary side main switch of the transformer TX 1;
in one implementation, the shutdown control unit 101 is configured to shorten the on-time of the primary side main switch of the transformer.
Specifically, there are several implementations as follows: at least one switching period before a primary side main switch of the transformer is turned off is shortened; or, the pulse width is shortened in at least one switching cycle before the primary side main switch of the transformer is turned off; or, at least one switching period before the primary side main switch of the transformer is turned off is shortened, one or more of the shortened switching periods is selected, and the pulse width is shortened in the one or more shortened switching periods.
In another implementation, the shutdown control unit 101 is configured to lengthen the conduction time of the primary side main switch of the transformer.
Specifically, there are several implementations as follows: lengthening at least one switching period before a primary side main switch of the transformer is turned off; or, the pulse width is increased in at least one switching period before the primary side main switch of the transformer is turned off; or lengthening at least one switching period before the primary side main switch of the transformer is turned off, selecting one or more switching periods from the lengthened at least one switching period, and lengthening the pulse width in the lengthened one or more switching periods.
A control value acquisition unit 102 configured to acquire a control value corresponding to a volt-second product or a volt-second product of a primary input voltage of the transformer in the on time;
in an implementation manner, the control value obtaining unit 102 detects a control value corresponding to a volt-second product of the primary input voltage Vins in the on-time at the secondary side of the transformer TX 1; in other implementations, a timing counter may be provided in the circuit to detect the value of parameters such as frequency, period, pulse width, etc. of the PWM signal as a reference condition for determining whether to shut down the power supply.
And the secondary side control unit 103 is used for controlling the on and off of the synchronous rectifier on the secondary side of the transformer TX1 according to the volt-second product or a control value corresponding to the volt-second product.
In an implementation manner, when the volt-second product or a control value corresponding to the volt-second product is less than or equal to a preset value, the synchronous rectifier on the secondary side is turned off to realize power shutdown.
For example, the shutdown control unit 101 shortens at least one switching cycle before the primary main switch Q1 of the transformer TX1 is turned off, the volt-second product detected by the control value acquisition unit 102 or the control value corresponding to the volt-second product is less than or equal to a preset value, and at this time, the secondary control unit 103 closes the synchronous rectification circuit on the secondary side to complete shutdown.
For another example, when the shutdown control unit 101 lengthens at least one switching cycle before the primary main switch Q1 of the transformer TX1 is turned off, the volt-second product detected by the control value acquisition unit 102 or the control value corresponding to the volt-second product is greater than or equal to a preset value, and at this time, the secondary control unit 103 closes the synchronous rectification circuit on the secondary side to complete shutdown.
As shown in fig. 6, the power supply circuit further includes: the circuit comprises a modulation signal generator 104, a transformer TX1, a primary side main switch Q1, a first secondary side switch Q2, a second secondary side switch Q3 and an LC filter; the switches Q1, Q2, and Q3 may be MOS transistors or other active switches.
The modulation signal generator 104 is electrically connected to the shutdown control unit 101, and is configured to modulate the primary-side input voltage Vin; the modulation signal generator 104 may be a pulse width modulation signal generator or a pulse frequency modulation signal generator.
The shutdown control unit 101 is electrically connected with the primary side main switch Q1; the primary side main switch Q1 is used for controlling the closed circuit and the open circuit of the primary side circuit loop.
One end of the primary side main switch Q1 is connected with a primary side input voltage end Vin through a primary coil P1 of the transformer TX1, and the other end of the primary side main switch Q1 is grounded;
the control value acquisition unit 102 is connected between a secondary side voltage input end Vins and the secondary side control unit;
the secondary side control unit 103 is connected to the first secondary side switch Q2 and the second secondary side switch Q3;
the first secondary switch Q2 and the second secondary switch Q3 are connected with the LC filter;
the primary side main switch Q1, the first secondary side switch Q2 and the second secondary side switch Q3 are insulated gate field effect transistors. Of course, other suitable switching devices are possible.
In this embodiment, it is preferable to use an insulated gate field effect transistor as a switch for explanation.
As shown in fig. 6, the LC filter circuit includes an output inductor L1 and a filter capacitor C1. One end of the output inductor L1 is connected with the secondary side voltage input end Vins, the other end is connected with the output voltage end Vo, and the output voltage end Vo is grounded through the filter capacitor C1. The primary side main switch Q1 has its source connected to ground, its gate connected to the power-off control unit 101, and its drain connected to the primary side voltage input Vin via the primary winding P1. The source of the first secondary switch Q2 is grounded, the gate is connected to the secondary control unit 103, and the drain is connected to the secondary input voltage terminal Vins through the secondary winding S1. The source of the second secondary switch Q3 is grounded, the gate is connected to the secondary control unit 103, and the drain is connected to the output voltage Vo through the output inductor L1.
When shutdown is required, the shutdown control unit 101 receives a shutdown signal, and changes a switching period and/or a pulse width in at least one period before the primary side main switch Q1 of the transformer TX1 is turned off according to the requirement. Here, we choose to shorten the pulse width for the explanation. Because the pulse width is shortened, the on-time Ton of the primary side main switch Q1 is shortened. In the shortened on-time Ton, the primary side input voltage Vin continues to induce the secondary side input voltage Vins on the secondary side, and the control value obtaining unit 102 receives the secondary side input voltage Vins and calculates the volt-second product of the secondary side input voltage Vins in the on-time Ton, that is, calculates the volt-second product of the primary side input voltage Vin in the on-time Ton in proportion to the secondary side input voltage Vins. The control value obtaining unit 102 may directly perform the determination according to the volt-second product, or perform corresponding calculation according to the volt-second product to obtain control values corresponding to the volt-second product one to one. In this embodiment, the control value obtaining unit 102 outputs the control value Vvs corresponding to the volt-second product of the primary input voltage Vin in the on-time Ton. Here, the control value Vvs may be a voltage value as shown in fig. 6, but may be a current value according to the design requirements of the circuit. In this embodiment, since the shutdown control unit 101 shortens the pulse width, the on-time Ton of the primary side main switch Q1 is reduced, so that the volt-second product of the secondary side input voltage Vins in the on-time Ton is reduced, and the corresponding control value Vvs is reduced. The secondary side control unit 103 detects the control value Vvs, and when the volt-second product is less than or equal to a preset value, the corresponding control value is also less than or equal to a certain preset value, and the secondary side control unit 103 is triggered to send a control instruction to turn off the first secondary side switch Q2 and the second secondary side switch Q3, so that a loop of the synchronous rectification circuit is broken, and the power supply is completely shut down.
It should be noted that, when the power supply is in normal operation, the voltage-second product of the primary input voltage Vin in the on-time Ton is kept at a fixed value, which is proportional to the output voltage Vo. In this embodiment, the voltage-second product when the power supply is operating normally is set to the steady-state voltage-second product. In setting the preset value, the setting may be made according to a steady state volt-second product. In this embodiment, the preset value may be set to be smaller than the control value corresponding to the steady-state volt-second product. When the power supply normally works, the primary side does not send a shutdown signal, the shutdown control unit 101 does not work on a loop of the primary side circuit, the conduction time of the primary side main switch Q1 is kept in a normal state, at this time, the voltage-second product of the primary side input voltage Vin in the conduction time Ton is a steady voltage-second product, the secondary side control unit 103 detects that the control value at this time is larger than the preset value, and the closed circuit or the open circuit of the loop of the synchronous rectification circuit is normally controlled. When the power supply is to be shut down, the primary side sends out a shutdown signal, the shutdown control unit receives the shutdown signal, the pulse width is shortened, and the conducting time Ton of the primary side main switch Q1 is shortened, so that the volt-second product of the primary side input voltage Vin in the conducting time Ton is reduced to be smaller than a preset value, and then the secondary side control unit 103 does not perform normal control operation on the synchronous rectification circuit any more, but directly sends out an instruction to control the first secondary side switch Q2 and the second secondary side switch Q3 to be turned off, so that the synchronous rectification circuit is disconnected, and the power supply is completely shut down.
Correspondingly, when the switching period is shortened (i.e., the switching frequency is increased) or both the switching period and the pulse width are shortened, the case is as described above;
when the switching period is prolonged or the switching period and the pulse width are prolonged simultaneously, the on-time Ton of the primary side main switch Q1 is prolonged, the volt-second product of the secondary side input voltage Vins in the on-time Ton is increased, the control value Vvs is increased, and when the volt-second product is greater than or equal to the preset value, the secondary side control unit 103 sends a command to control the first secondary side switch Q2 and the second secondary side switch Q3 to be turned off, so that the synchronous rectification circuit is switched off, and the power supply is completely shut down. At this time, the preset value is larger than the control value corresponding to the steady-state volt-second product. When the power supply normally works, the primary side does not send out a shutdown signal, the shutdown control unit 101 does not work on a primary side circuit loop, the conduction time Ton of the main switch Q1 keeps a normal state, the voltage-second product of the primary side input voltage Vin in the conduction time Ton is a steady-state voltage-second product, the secondary side control unit 103 detects that the control value at the moment is smaller than the preset value, and the closed circuit or the open circuit of the synchronous rectification circuit loop is normally controlled. As described above, when the power supply is to be shut down, the primary side sends a shutdown signal, and the shutdown control unit intentionally increases the on-time of the main switch in response to the shutdown signal, so that the volt-second product of the primary side input voltage in the on-time increases, and the control value Vvs increases to be greater than the predetermined value, so that the secondary side control unit does not perform normal control operation on the synchronous rectification circuit any more, but sends a command to open the synchronous rectification circuit, and the power supply is completely shut down.
Of course, there may be a case where the two parameters of the switching period and the pulse width are changed reversely, and it is only necessary to determine which parameter is dominant at this time.
The power supply provided by the invention can effectively avoid self-oscillation generated when the power supply is switched off, and does not need to add a new circuit element, so that the circuit area is small, the structure is simple, the cost is low, and the reliability and the stability of the power supply are improved.
Fig. 7 is a schematic circuit diagram of a shutdown control unit in a power supply according to an embodiment of the invention.
The method for transmitting the shutdown information has the advantages that the digital PWM control is simpler and easier to implement than the analog PWM control in the realization of the PWM controller. In digital PWM control, a more complex optimized shutdown pulse sequence can be easily programmed since both the PWM pulse width and period information before shutdown are known and can be stored in the controller. In the analog PWM control, it is difficult to implement a more complicated optimized shutdown pulse sequence by an analog circuit, so the shutdown pulse sequence is simplified and optimized as much as possible.
In this embodiment, the Shutdown control unit includes an RC series circuit, a Volt-Second clamp comparator Volt-Second clamp cam, and a Shutdown Pulse comparator Shutdown Pulse PWM.
The RC series circuit is connected between a primary side input voltage end Vin and the ground;
the Volt-Second clamp comparator Volt-Second Clam and the non-inverting input end of the Shutdown Pulse comparator Shutdown Pulse PWM are connected between a resistor Rvsc and a capacitor Cvsc of the RC circuit through a Volt-Second clamp pin VSCLAMP, and the threshold values of the Volt-Second clamp comparator Volt-Second Clam and the threshold value of the Shutdown Pulse comparator Shutdown Pulse PWM are different.
An external RC circuit can be connected to the primary side input voltage VIN on the primary side PWM shutdown control unit, and a slope voltage with the slope being proportional to the primary side input voltage VIN is generated on a volt-second clamp pin VSCLAMP of the shutdown control unit. When the circuit normally works, the peak value of the ramp voltage is controlled at a lower level by a feedback control loop or a Volt-Second clamp comparator Volt-Second Clam, the ramp voltage is allowed to rise to a higher level in the last period needing Shutdown, and a Shutdown Pulse comparator shut down Pulse PWM generates a Shutdown width Pulse with an increased Volt-Second product.
As shown in fig. 7, the threshold of Shutdown Pulse comparator Shutdown Pulse PWM at this time is 3V, and the threshold of Volt-Second clamp comparator Volt-Second cam is 2.5V. During normal operation, the ramp voltage on the VSCLAMP pin is limited by a Volt-Second clamp comparator Volt-Second Clam, and the general peak voltage works at about 1.5V-2V. The last lengthened Shutdown Pulse is generated by a Shutdown Pulse comparator Shutdown Pulse PWM, and the width of the generated Shutdown Pulse is 1.5-2 times of that of the normal working Pulse. The shutdown pulse width may be longer than a normal switching period. The length of the last Shutdown width Pulse with the increased volt-second product is determined not by the control loop and the volt-second clamp circuit, but by the comparison between the voltage of the volt-second clamp pin VSCLAMP and the 3V threshold level by the Shutdown Pulse comparator Shutdown Pulse PWM.
Of course, the detection of the secondary control value acquisition unit can also be realized by using a simple RC circuit and a voltage comparator based on the volt-second product detection principle.
It should be noted that the principles of the present invention are applicable to shutdown information transfer across isolated interfaces in all isolated power supplies, including DC/DC, AC/DC, DC/AC, AC/AC, and other isolated converters.
Of course, the principle of the invention is also applicable to the application of the PWM shutdown control unit on the secondary side and transmitting shutdown information from the secondary side to the primary side; and the principles of the present invention apply to both analog and digital control. Which inherently facilitates the implementation of an optimal shutdown PWM pulse sequence with digital control.
Fig. 8 is a circuit diagram of another power supply according to an embodiment of the invention.
In the present embodiment, another implementation form of the shutdown control unit 101 is specifically shown. The shutdown control unit 101 includes a control switch 1011, a driving unit 1012, a charge and discharge unit 1013, a comparator 1014, and a logic unit 1015. The control switch 1011 is connected between the output terminal of the modulation signal generator 104 and the input terminal of the driving unit 1012, and is closed or opened in response to a control signal from the logic unit 1015. The driving unit 1012 is configured to receive the modulation signal of the modulation signal generator 104 via the control switch 1011 and output the modulation signal to the control terminal of the primary side main switch Q1. The charging and discharging unit 1013 is connected between the control terminal of the primary side main switch Q1 and the ground, and is configured to perform charging according to the on-time of the primary side main switch Q1 and to supply an output value corresponding to the charging result to the comparator 1014. The comparator 1014 is configured to receive the output value of the charge and discharge unit 1013, compare the output value with a reference value, and output the comparison result to the modulation signal generator 104 to control the operation of the modulation signal generator 104 on the one hand, such that the modulation signal generator 104 is turned off when the output value of the charge and discharge unit 1013 is greater than the reference value, and output the comparison result to the logic unit 1015 on the other hand. The logic unit 1015 is configured to output a control signal according to the shutdown signal, the output of the comparator 1014, and the signal at the input of the driving unit 1012, such that the control switch 1011 is turned off when the shutdown signal indicates that the power supply is to be turned off, and such that the input of the driving unit 1012 has a high level when the control switch 1011 is turned off, so as to charge the charging and discharging unit 1013, and such that the control switch 1011 is turned on when the output value of the charging and discharging unit 1013 is greater than a reference value, so as to have a low level when the input of the driving unit 1012 has a low level, so as to turn off the primary side main switch. It can be seen that when the power supply is to be shut down, the primary side sends a shutdown signal, the shutdown control unit 101 responds to the shutdown signal, turns off the control switch 1011, charges the charge-discharge unit 1013, and makes the charging time longer than the charging time in the normal state of the power supply, when the output value corresponding to the charging result is greater than the reference value, the control switch 1011 is turned on, at this time, the input of the driving unit 1012 is pulled to a low level by the off modulation signal, the primary side main switch Q1 is turned off, and thus the on time Ton of the main switch Q1 is increased. According to an example of the present invention, the reference value Vref may be set according to design parameters of the circuit, such that the output value output by the charging and discharging circuit 1013 is less than the reference value Vref when the power supply normally operates, and the output value output by the charging and discharging circuit 1013 is greater than the reference value Vref when the power supply is to be shut down. As described above, when the power supply is to be shut down, the primary side sends a shutdown signal, and the shutdown control unit 101 intentionally increases the on-time of the main switch through the charging and discharging unit 1013 in response to the shutdown signal, so that the voltage-second product of the primary side input voltage in the on-time increases, and the control value Vvs increases to be greater than the predetermined value, so that the secondary side control unit does not perform normal control operation on the synchronous rectification circuit any more, but sends a command to shut down the synchronous rectification circuit, and the power supply is completely shut down.
Similarly, the power supply provided by the embodiment of the invention can be effectively turned off to avoid self-oscillation, and an optical coupling device is not required, so that the power supply has the advantages of small area, cost saving, simple structure and convenience in installation.
In the embodiment shown in fig. 9, it is specifically shown that the control value acquisition unit 102 may include a charging circuit 1021 and a discharging circuit 1022. The discharging circuit 1022 discharges the charging circuit 1021 at the start of the on-time of the main control switch, and thereafter the charging circuit 1021 charges for the on-time Ton, and takes the voltage value corresponding to the charging result as the control value Vvs at the end of the on-time Ton. Therefore, the control value acquiring unit 102 acquires the control value Vvs corresponding to the integrated value of the input voltage Vins with respect to time, and outputs the control value Vvs to the secondary control unit 103. The power shutdown principle of this embodiment is substantially the same as that of the previous embodiment, and is not described herein again.
Fig. 10 shows an embodiment of the shutdown control unit and the control value acquisition unit. In the present embodiment, the modulation signal generator 104 is a PWM modulation signal generator, but those skilled in the art will understand that a PFM (Pulse frequency modulation) modulation signal generator may also be used in the present embodiment according to different application requirements. The shutdown control unit 101 comprises a charge-discharge circuit composed of a resistor R3, a capacitor C4 and a diode, a comparator U2, an and gate U1, a control switch k1 and a driving unit U4, wherein R3 and C4 are connected in series between a control terminal of a primary side main switch Q1 and ground, and D1 is connected across the R3 for discharging C4. When the power supply normally works, the shutdown signal is at a low level, the and gate U1 outputs the low level, the switch k1 is controlled to be closed, and the PWM signal is transmitted to the driving unit through the switch k1 to drive the primary side main switch Q1. When the shutdown signal is high and the PWM modulation signal and U2 are also high, the and gate U1 outputs high, the control switch k1 is turned off, the input of the driving unit U4 remains high, and the output also remains high until the voltage of C4 is charged higher than Vref, the comparator U2 inverts to low, and the and gate outputs low again, and the switch k1 is closed. Meanwhile, since the comparator U2 is inverted to a low level, the PWM modulation signal generator is notified to stop operating by the change, so that the PWM modulation signal becomes a low level, the input of the driving unit U4 is pulled to a low level by the PWM modulation signal, and the primary side main switch Q1 is turned off. The time from when the shutdown signal is high to when the primary side main switch Q1 is turned off is the extended on-time ton, and how long the on-time is extended is determined by the time constant of the charge and discharge circuit R3C 4. Diode D1 is used to discharge capacitor C4. The capacitor C4 is constantly charged and discharged, forming a periodic sawtooth wave. When the device works normally, the amplitude of the sawtooth wave is not high, and the amplitude is obviously increased when the device is shut down.
In the present embodiment, the charging circuit 1021 in the control value obtaining unit 102 includes a first capacitor C2 and a first resistor R1 connected in series, while the discharging circuit 1022 includes a second capacitor C3 and a second resistor R2 connected in series, a branch where C3 and R2 are located is connected in parallel with a branch where R1 and C2 are located, and both C3 and R2 are connected to a control terminal of a switch Q4, and the switch Q4 is connected across the C2 for discharging the C2 when conducting.
In this embodiment, during the on-time Ton of the PWM modulation signal, the secondary winding S1 induces a secondary input voltage Vins proportional to the primary input voltage Vin, and when the voltage Vins is at a rising edge, a very narrow pulse is driven to the switch Q4 through a differential circuit formed by the capacitor C3 and the resistor R2, so that the Q4 is turned on for a moment, and the charge of the first capacitor C2 is discharged, and the voltage is pulled to 0V. The first capacitor C2 is charged via the first resistor R1 during the on-time Ton, and at the end of Ton, the first capacitor C2 is not charged any more, and the magnitude of the voltage Vvs represents the time integral of Vin in the Ton period, which is referred to as volt-second product. Waiting for the next on-time Ton, the control value obtaining unit 402 discharges and recharges again, and so on. When the power supply normally works, the integral of Vin with respect to time in the Ton period, namely the volt-second product, basically keeps a fixed value, and when the power supply is shut down, the volt-second product is also obviously increased due to the intentional obvious increase of the on-time Ton, and the control value Vvs is obviously increased. After the secondary side control unit 103 detects the significantly increased Vvs, it sends a command to turn off the switches Q2 and Q3 on the synchronous rectification circuit, so that the power supply is completely turned off, the current backflow is prevented, and the self-oscillation is suppressed. In this embodiment, the two drive signals (to drive switches Q2 and Q3) of the secondary control unit 103 are input from the secondary windings S2 and S3 of the transformer.
Fig. 11 is a signal timing diagram illustrating the self-driven synchronous rectified power supply shown in fig. 10.
Fig. 11 shows a timing chart of the voltage Vg1 of the control terminal of the main control switch Q1, the voltages Vg2 and Vg3 of the control terminals of the switches Q2 and Q3 of the synchronous rectification circuit on the secondary side, and the control value Vvs output by the control value acquisition unit 102. Referring to fig. 11, the last on time Ton (the last period when Vg1 is high) of the primary side main switch Q1 is longer than the previous on time because the power-off control unit 101 increases the on time Ton in response to the power-off signal at the time of power-off. As can be seen from fig. 11, during the increased on-time Ton, the control value Vvs output by the control value obtaining unit 102 increases to be greater than the control value Vvs in the normal state, exceeding a predetermined value. After the increased on-time Ton (i.e., the last period in which Vg1 is high), Vg1 becomes 0, so that the main switch Q1 is turned off, and the control value Vvs exceeds a predetermined value, so that the secondary-side control unit 103 detects a significantly increased Vvs, issues a command to control the levels of the control terminals of the switches Q2 and Q3 on the synchronous rectification circuit to turn off the switches Q2 and Q3, and the power supply is completely shut down without the occurrence of the self-oscillation phenomenon.
In the solution of the embodiment of the present invention, the shutdown signal may include, but is not limited to, a shutdown signal generated by triggering of actions such as remote shutdown, overcurrent protection, overvoltage protection, overtemperature protection, and undervoltage protection.
Referring to fig. 12, another power supply is provided for the embodiment of the present invention, the power supply includes:
the shutdown control unit 11 is configured to receive a shutdown signal and change a switching frequency of a primary side main switch of the transformer;
the on time of the switch may be prolonged, may be maintained unchanged, or may be shortened, which is not limited in this embodiment of the present invention.
A frequency detection unit 12, configured to detect a switching frequency of the primary side main switch on a secondary side of the transformer;
and the secondary side control unit 13 is configured to control turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch.
In an implementation manner, the shutdown control unit 11 is specifically configured to increase a switching frequency of a primary side main switch of the transformer; the secondary control unit 13 is specifically configured to: and when the switching frequency of the primary side main switch is higher than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
In another implementation manner, the shutdown control unit 11 is specifically configured to: reducing the switching frequency of a primary side main switch of the transformer; the secondary control unit 13 is specifically configured to: and when the switching frequency of the primary side main switch is lower than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
The specific implementation may refer to corresponding method embodiments. It will be appreciated by those skilled in the art that varying the switching frequency is in fact equivalent to varying the switching period. It is common knowledge of those skilled in the art to implement the detection of the switching frequency or the detection of the switching period, that is, the frequency detection unit 12 can also be used for period detection, and accordingly, the preset value is set to a value corresponding to the switching period in the normal state of the power supply. The frequency detection and the period detection have various means, and the skilled person can select the frequency detection and the period detection according to the requirements.
Fig. 13 is a flow diagram of a method of shutting down a self-driven synchronous rectified power supply according to one embodiment of the present invention.
Referring to fig. 13, when the self-driven synchronous rectified power is to be shut down, the shutdown is performed as follows.
In step S11, the primary side sends out a shutdown signal, and the last on-time of the primary side main switch is increased on the primary side; in step S12, a voltage-second product of the primary input voltage within the on-time is detected on the secondary side; in step S13, when the volt-second product is greater than or equal to a predetermined value, the synchronous rectification circuit of the secondary side is turned off to shut down the power supply.
Through the description of the above embodiments, the present invention has the following advantages:
the original transmission path of a PWM signal or other signals of the circuit is utilized to send a group of shutdown pulses different from the normal operation state to the secondary side from the primary side before shutdown, or the frequency of a primary side switching tube is changed so as to facilitate the detection and identification of the secondary side circuit, thereby realizing the adjustment of the switching circuit to the state most beneficial to shutdown, and then switching off the synchronous rectification circuit of the primary side circuit and the secondary side according to the preset optimal shutdown time sequence, thereby achieving the purpose of eliminating shutdown oscillation and shutdown stress. And a new circuit element is not required to be added, so that the volume and the cost of the circuit are saved, the structure is simple, the cost is low, and the reliability and the stability of the power supply are improved. The switching frequency and the pulse width are changed to form various modes comprehensively, a certain parameter can be changed independently or two parameters can be changed simultaneously, and only the condition that the corresponding parameter (such as volt-second product or switching period) detected by the secondary side is different from the parameter in the normal operation state is required to be ensured.
It will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by a computer program, which can be stored in a computer-readable storage medium, and when executed, can include the processes of the embodiments of the methods described above. The storage medium may be a magnetic disk, an optical disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), or the like.
The above disclosure is only for the purpose of illustrating the preferred embodiments of the present invention, and it is therefore to be understood that the invention is not limited by the scope of the appended claims.
Claims (23)
1. A method for power shutdown, the method comprising:
receiving a shutdown signal, and changing the conduction time of a primary side main switch of the transformer;
detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on a secondary side of the transformer;
and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product.
2. The method of claim 1, wherein receiving the shutdown signal to change a conduction time of a primary side main switch of the transformer comprises:
receiving a shutdown signal, and prolonging the conduction time of a primary side main switch of the transformer;
the controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or the control value corresponding to the volt-second product specifically includes:
and when the volt-second product or the control value corresponding to the volt-second product is greater than or equal to a preset value, the synchronous rectifier on the secondary side is turned off.
3. The method of claim 2, wherein the lengthening the conduction time of the primary side main switch of the transformer comprises:
lengthening at least one switching period before a primary side main switch of the transformer is turned off; or,
lengthening the pulse width in at least one switching period before the primary side main switch of the transformer is turned off; or,
lengthening at least one switching cycle before a primary side main switch of the transformer is turned off, selecting one or more switching cycles from the lengthened at least one switching cycle, and lengthening a pulse width within the one or more lengthened switching cycles.
4. The method of claim 1, wherein receiving the shutdown signal to change a conduction time of a primary side main switch of the transformer comprises:
receiving a shutdown signal, and shortening the conduction time of a primary side main switch of the transformer;
the controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or the control value corresponding to the volt-second product specifically includes:
and when the volt-second product or the control value corresponding to the volt-second product is smaller than or equal to a preset value, the synchronous rectifier on the secondary side is turned off.
5. The method of claim 4, wherein reducing the conduction time of the primary side main switch of the transformer comprises:
at least one switching period before a primary side main switch of the transformer is turned off is shortened; or,
shortening the pulse width in at least one switching period before the primary side main switch of the transformer is turned off; or,
at least one switching period before a primary side main switch of the transformer is turned off is shortened, one or more of the shortened switching periods is selected, and the pulse width is shortened in the one or more shortened switching periods.
6. A method for power shutdown, the method comprising:
receiving a shutdown signal, and changing the switching frequency of a primary side main switch of the transformer;
detecting the switching frequency of the primary side main switch on the secondary side of the transformer;
and controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch.
7. The method of claim 6, wherein changing the switching frequency of the primary side main switch of the transformer comprises:
the switching frequency of a primary side main switch of the transformer is improved;
the controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch specifically includes:
and when the switching frequency of the primary side main switch is higher than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
8. The method of claim 6, wherein changing the switching frequency of the primary side main switch of the transformer comprises:
reducing the switching frequency of a primary side main switch of the transformer;
the controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch specifically includes:
and when the switching frequency of the primary side main switch is lower than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
9. A power supply, comprising
The shutdown control unit is used for receiving a shutdown signal and changing the conduction time of a primary side main switch of the transformer;
the control value acquisition unit is used for detecting a volt-second product of the primary input voltage in the conduction time or a control value corresponding to the volt-second product on the secondary side of the transformer;
and the secondary side control unit is used for controlling the on and off of the synchronous rectifier of the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product.
10. The power supply of claim 9, wherein the shutdown control unit is specifically configured to: receiving a shutdown signal, and prolonging the conduction time of a primary side main switch of the transformer;
the secondary side control unit is specifically configured to: and when the volt-second product or the control value corresponding to the volt-second product is greater than or equal to a preset value, the synchronous rectifier on the secondary side is turned off.
11. The power supply of claim 10, wherein the shutdown control unit is specifically configured to:
receiving a shutdown signal, and lengthening at least one switching period before a primary side main switch of the transformer is turned off; or,
receiving a shutdown signal, and lengthening the pulse width in at least one switching period before a primary side main switch of the transformer is turned off; or,
the method comprises the steps of receiving a shutdown signal, lengthening at least one switching period before a primary side main switch of the transformer is turned off, selecting one or more switching periods from the lengthened at least one switching period, and lengthening pulse width in the lengthened switching period or periods.
12. The power supply of claim 9, wherein the shutdown control unit is specifically configured to: receiving a shutdown signal, and shortening the conduction time of a primary side main switch of the transformer;
the secondary side control unit is specifically configured to: and when the volt-second product or the control value corresponding to the volt-second product is smaller than or equal to a preset value, the synchronous rectifier on the secondary side is turned off.
13. The power supply of claim 12, wherein the shutdown control unit is specifically configured to:
receiving a shutdown signal, and shortening at least one switching period before a primary side main switch of the transformer is turned off; or,
receiving a shutdown signal, and shortening the pulse width in at least one switching period before a primary side main switch of the transformer is turned off; or,
and receiving a shutdown signal, shortening at least one switching period before a primary side main switch of the transformer is turned off, selecting one or more than one of the shortened switching periods, and shortening the pulse width in the one or more than one shortened switching period.
14. The power supply of claim 9, wherein the shutdown control unit comprises an RC series circuit, a volt-second clamp comparator, and a shutdown pulse comparator;
the RC series circuit is connected between the primary side input voltage end and the ground;
the same-phase input ends of the volt-second clamp comparator and the shutdown pulse comparator are connected between the resistor and the capacitor of the RC circuit through a volt-second clamp pin, and the threshold values of the volt-second clamp comparator and the shutdown pulse comparator are different.
15. The power supply of claim 14, further comprising: the device comprises a modulation signal generator, a transformer, a primary side main switch, a first secondary side switch, a second secondary side switch and an LC filter;
the modulation signal generator is electrically connected with the shutdown control unit and is used for modulating the primary side input voltage;
the shutdown control unit is electrically connected with the primary side main switch;
one end of the primary side main switch is connected with a primary side input voltage end through a primary coil of the transformer, and the other end of the primary side main switch is grounded;
the control value acquisition unit is connected between a secondary side voltage input end and the secondary side control unit;
the secondary side control unit is connected with the first secondary side switch and the second secondary side switch;
and the first secondary side switch and the second secondary side switch are connected with the LC filter.
16. The power supply according to claim 9, wherein the control value acquisition unit is provided on the secondary side of the transformer, receives a secondary side input voltage proportional to the primary side input voltage, and includes a discharge circuit and a charge circuit, the charge circuit including a first capacitor, the charge circuit charging the first capacitor for the on time after the discharge circuit discharges the first capacitor at the start of the on time, and taking a voltage value on the first capacitor as the control value at the end of the on time.
17. The power supply of claim 16, wherein the secondary control unit is configured to turn off the synchronous rectifier when the control value is greater than or equal to a predetermined value.
18. The power supply of claim 9, wherein the shutdown control unit comprises:
a control switch connected between an input terminal of the driving unit and an output terminal of the modulation signal generator, and turned on or off in response to a control signal;
a driving unit configured to receive the modulation signal of the modulation signal generator via the control switch and output the modulation signal to a control terminal of the primary side main switch;
the charging and discharging unit is connected between the control terminal of the primary side main switch and the ground, and is used for charging according to the conduction time of the primary side main switch and transmitting an output value corresponding to a charging result to the comparator;
a comparator configured to receive the output value of the charge and discharge unit, compare the output value with a reference value, and output the comparison result to the modulation signal generator to control the operation of the modulation signal generator on the one hand, such that the modulation signal generator is turned off when the output value of the charge and discharge unit is greater than the reference value, and output the comparison result to a logic unit on the other hand;
a logic unit configured to output a control signal according to the shutdown signal, the output of the comparator, and a signal of the input terminal of the driving unit, such that when the shutdown signal indicates that the power supply is to be shut off, the control switch is turned off, and such that when the control switch is turned off, the input terminal of the driving unit has a high level to charge the charge and discharge unit, and when the output value of the charge and discharge unit is greater than the reference value, the control switch is turned on, such that the input terminal of the driving unit has a low level to turn off the primary side main switch.
19. The power supply of claim 18, wherein the logic cell is an and gate.
20. The power supply of claim 18, wherein the shutdown signal is a shutdown signal triggered by a remote shutdown, an over-current protection, an over-voltage protection, an over-temperature protection, an under-voltage protection.
21. A power supply, characterized in that the power supply comprises:
the shutdown control unit is used for receiving a shutdown signal and changing the switching frequency of a primary side main switch of the transformer;
the frequency detection unit is used for detecting the switching frequency of the primary side main switch on the secondary side of the transformer;
and the secondary side control unit is used for controlling the turn-off of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the primary side main switch.
22. The power supply of claim 21, wherein the shutdown control unit is specifically configured to: the switching frequency of a primary side main switch of the transformer is improved;
the secondary side control unit is specifically configured to: and when the switching frequency of the primary side main switch is higher than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
23. The power supply of claim 21, wherein the shutdown control unit is specifically configured to: reducing the switching frequency of a primary side main switch of the transformer;
the secondary side control unit is specifically configured to: and when the switching frequency of the primary side main switch is lower than or equal to a preset value, the synchronous rectifier of the secondary side is switched off.
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Also Published As
| Publication number | Publication date |
|---|---|
| CN104319986A (en) | 2015-01-28 |
| CN103066825B (en) | 2016-03-09 |
| CN102437725A (en) | 2012-05-02 |
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