KR20020048246A - Switching mode power supply with high efficiency - Google Patents

Abstract

PURPOSE: A high efficiency switching mode power supply(SMPS) is provided to reduce the loss of power by distributing a current through a plurality of current paths. CONSTITUTION: A switching signal generating unit(11) outputs a switching signal having a predetermined frequency. At least two switching devices perform ON/OFF operation according to the switching signal. A power converting device(15) is connected between the switching devices and an input direct current power terminal and generates a square wave signal according to ON or OFF state of the switching device. An output rectifying unit(17) receives the square wave signal generated from the power converting device(15) and rectifies it to output a DC(Direct Current) power. The power converting device(15) is provided corresponding to each of the switching devices.

Description

Switching mode power supply with high efficiency

The present invention relates to a switched mode power supply, and more particularly, to a switched mode power supply capable of minimizing energy loss.

At the Switching Mode Power Supply (SMPS), an attempt is made to reduce the energy loss due to the resistance of the coil by reducing the size of the transformer by increasing the switching frequency fs as much as possible and reducing the number of turns of the coil. However, it can be said that losses due to transistors, transformers, etc. used as components of the power supply still remain an inevitable problem.

The technical problem to be achieved by the present invention is to provide a switching mode power supply that can minimize the power loss by multiplexing and dispersing the passage of current flowing therein.

1 is a view showing the configuration of a forward type switching mode power supply apparatus according to an embodiment of the present invention.

2 is a view showing the configuration of a flyback type switching mode power supply according to another embodiment of the present invention.

3 is an example of configuration diagram of the PWM control circuit illustrated in FIG. 1 or 2.

4 is a block diagram showing a schematic configuration of a switched mode power supply device applied to the present invention.

Switching mode power supply according to the present invention for achieving the above object,

A switching signal generator for outputting a switching signal having a predetermined frequency; At least two switching elements configured to perform an on or off operation according to the switching signal; A power conversion element connected between the switching elements and an input DC power source and configured to generate a square wave signal by passing current or blocking depending on an on or off state of the switching element; And an output rectifying unit for receiving the square wave signal generated by the power conversion element and rectifying the square wave signal to output a DC power source.

Another switching mode power supply according to the present invention for achieving the above object,

A switching signal generator for outputting a switching signal having a predetermined frequency; A switching element performing an on or off operation according to the switching signal; At least two power conversion elements connected between the switching element and an input DC power source and configured to generate a square wave signal by passing current or blocking depending on an on or off state of the switching element; And an output rectifier for rectifying the square wave signal generated by the power conversion elements and outputting the DC power.

Each switching element is composed of a transistor, a source terminal of each transistor is commonly connected, a switching signal output from the switching signal generator is input to each gate terminal, and a drain terminal thereof is connected to the power conversion element. The transistors may be configured to be simultaneously turned on or off by the switching signal so as to interrupt a current flowing through the power conversion element, and the output rectifier forms one output voltage for each power conversion element or at least two. It is preferable to form one output voltage from the power conversion element of or at least two output voltages from one power conversion element.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the present invention.

4 is a block diagram illustrating a schematic configuration of a switching mode power supply according to the present invention. DC power is input to this power supply, and if the original power is AC, DC power will be received through the rectifier.

The switching controller 42 operates at a predetermined frequency to generate a switching signal for chopping the input DC voltage V _in with a square wave of high frequency, and the inverter unit 44 supplies the input DC power V _in . A square wave is generated according to the switching frequency of the switching controller 42. The current feedback unit 48 detects the output current of the inverter unit 44 and feeds it back to the switching controller 42. In addition, the final output voltage V _out of the output rectifier 47 is fed back to the switching controller 42. The switching controller 42 compares these feedback signals with the reference signal to adjust the pulse phase of the switching signal to adjust the level (size) of the current and voltage (PWM control). This keeps the voltage at the final output of the power supply constant. The high potential square wave signal output from the inverter unit 44 is rectified by the output rectifying unit 47 after the voltage level is adjusted to provide DC power.

Sources of energy loss in switched-mode power supplies include transistors, transformers, diodes, and PWM ICs. In case of FET transistor, by internal resistance component R _{DS (ON)} , in case of transformer, by DC resistance component, in case of diode, by forward voltage (V _F ) component, in case of PWM IC, switching signal Energy loss may occur due to the output current of the.

1 is a view showing the configuration of a switching mode power supply according to an embodiment of the present invention, an example of a forward type power supply. The power supply device in this example includes an input filter 10, a PWM control circuit 11, an inverter unit 15, a current feedback unit 13 and an output rectifier unit 17, to increase the efficiency and energy In order to save power, a connection method of controlling a plurality of switching transistors Q ₁ , Q ₂ , Q ₃ and a plurality of inverter transformers T ₁ , T ₂ , T ₃ by one PWM control circuit 11 is provided. Adopted. The input filter 10 is formed as a low pass filter in which the capacitors Ci1, Ci2, Ci3 and the inductor Li1 are connected in a pie form to remove noise included in the input DC power supply Vin.

In the present embodiment, a circuit for generating a high frequency square wave power supply by a switching operation includes a PWM control circuit 11 for generating a switching signal, transistors Q ₁ , Q ₂ , and Q ₃ , and transformers T ₁ and T. ₂ , T ₃ ) and a current sensing transformer T _s . The transistors Q ₁ , Q ₂ , and Q ₃ have their source terminals connected in common, and as each gate terminal, a switching signal SWout output from the PWM control circuit 11 is input. Transistors Q ₁ , Q ₂ , and Q ₃ are simultaneously connected to the primary windings of T ₁ , T ₂ , and T ₃ by a switching signal SW _out generated from the PWM control circuit 11. On or off, the current flowing through the primary windings of the transformers T ₁ , T ₂ , and T ₃ are interrupted. When the transistors Q ₁ , Q ₂ and Q ₃ are turned on, a current is charged in the primary windings of the transformers T ₁ , T ₂ and T ₃ and then the transistors Q ₁ , Q ₂ and Q ₃ . When turned off, the current charged in the primary winding is transmitted to the secondary winding, and voltage is induced across the secondary winding according to the turns ratio of the transformers T ₁ , T ₂ , and T ₃ .

Although FIG. 1 illustrates a case where a plurality of switching transistors and a plurality of transformers are provided and one transformer is connected to one switching transistor, respectively, a plurality of transformers are connected or a plurality of switching transistors corresponding to one switching transistor. It will be readily understood by those skilled in the art that the energy saving effect in the present invention can be achieved even though one transformer is connected in response to the transformer, which can be arbitrarily selected by those skilled in the art according to the operating conditions or the environment of the power supply. It's a kind of specification. This also applies to the power supply illustrated in FIG. 2.

Meanwhile, the current feedback unit 13 is connected between the common source terminal of the transistors Q ₁ , Q ₂ , and Q ₃ and the negative terminal of the input power source, so that the transistors Q ₁ , Q ₂ , and Q _{3 are} connected. The signal generated according to the current at this time is fed back to the PWM control circuit 11. The current feedback unit 13 senses a change in the input side current according to a change in current or a change in the output side load (load) caused by a potential change _{in the} input side voltage V _in , and returns it to the PWM control circuit 11. In order to compensate for the phenomenon caused by the same current variation, the PWM control circuit 11 controls the switching operation according to the sensing signal.

The current feedback unit 13 detects a change in the current Ipp flowing through the transistors according to the change in the input voltage V _in or the load, converts it into a voltage signal, and then converts it into a voltage signal. Feedback. The PWM control circuit 11 controls the output voltage to be constant by adjusting the pulse period of the positive phase of the switching signal SW _out by reflecting the variation of the input voltage V _in or the variation of the load. . If the current I _pp is increased, the current sensing voltage detected by the current feedback unit 13 and fed back to the PWM control circuit 11 is increased, and the PWM control circuit 11 is based on the current sensing voltage. _pp ) adjusts the pulse interval of the switching signal SW _out to be controlled in the decreasing direction.

When the transistors Q ₁ , Q ₂ and Q ₃ are turned on, current is induced in the secondary winding by the current flowing in the primary winding of the current-coupling transformer T _s . The resistor R1 converts the current induced in the transformer T _S into a voltage signal, and the voltage applied to the sensing terminal SENSE is determined by adjusting the resistance value of the variable resistor R ₂ . The capacitors C ₂ and C ₃ are used for ripple and noise removal, and the diode D ₃ converts and rectifies the detected square wave signal into a DC signal. The current-coupling transformer T _S detects a change in the current flowing in the primary windings of the transformers T ₁ , T ₂ , and T ₃ by the transformer T _S , thereby controlling the PWM control circuit 11. And the inverter unit 15 are electrically isolated. By doing so, even if it operates as a high frequency switching signal, a phenomenon in which oscillation is prevented can be prevented, and the circuit structure which can obtain the square wave signal switched by the high frequency in the inverter part 15 becomes possible.

The ratio of the primary winding to the secondary winding of the transformer T _S is preferably about 1:50 to 200. For example, for a small power of less than 10 watts, the transformer T _S when the continuius current (I _PDC ) flowing in the primary coil of the transformers T ₁ , T ₂ , T ₃ is 1.0 A or less. It is preferable that the first winding is once and the second winding is 100 times. The core of the transformer T _S may be made of the same material as the core of the transformers T ₁ , T ₂ , and T ₃ .

The PWM control circuit 11 receives the output voltage (+ FB) of the converter and receives the sensing voltage SENSE generated by the input side current, thereby turning on / off the switching transistors Q ₁ , Q ₂ , and Q ₃ . The switching signal SWout is generated for the off operation. A detailed configuration thereof will be described with reference to FIG. 3.

On the other hand, the magnetic bias circuit for supplying the operating power supply (Vcc) to the electronic device (see output amplifier 35 in Fig. 3) constituting the output portion of the switching signal (SW _out ) in the PWM control circuit 11 is a transformer (T). _first feedback winding (N _FB) of the primary winding of a), and the like or a diode (D1). The voltage induced by the auxiliary winding N _FB on the primary side of the transformer T ₁ is applied to the Vcc terminal of the PWM control circuit 11 via the diode D1. Here, the capacitor C ₁ is for removing ripple. Then, power is supplied to the elements in the PWM control circuit 11 other than the switching output section in the PWM control circuit 11 by the input power supply V _in .

The characteristics and number of transistors for minimizing heat loss due to internal resistance of switching transistors will be described. First, suppose that the maximum allowable heat loss of each transistor is set to 35 mW so that it can be designed without a separate heat sink. When the circuit design exceeds the maximum allowable heat loss, the transistors must be connected in parallel.

Heat Loss by R _{DS (ON)} of One Transistor And current flowing through the transistor Is calculated as

Where current Denotes a continuous current of the switching current signal, also called a direct current, and is distinguished from the peak current Ipp. In other words, the heat loss of the transistor is calculated by converting the current to 0.4 times the peak current.

For example, if a mobile phone power supply that requires 5W output is required, assuming that the input battery voltage is 12V, the operating current of the switching transistor is as follows.

When selecting a transistor component, it is preferable to use one having a low input gate capacitance C _GS and an internal resistance R _{DS (ON)} and one having a high withstand voltage BV _DS between the drain and the source. If a transistor with internal resistance of 0.075 ohms is used, the heat loss with one transistor is calculated as follows.

Calculate the number of transistors (N) to be connected in parallel because they exceed the maximum heat loss tolerance of 35 mW.

Therefore, by distributing current by connecting three transistors in parallel, the heat loss by each transistor can be made lower than the maximum allowable value. If the transistor is composed of three transistors, the current I _Pdc and the heat loss P _LOSS flowing through each transistor are as follows.

Therefore, the total heat loss P _TotalLOSS due to the three transistors is as follows.

Therefore, it can be seen that the energy loss can be greatly reduced by using a parallel connection as compared to using one switching transistor.

Meanwhile, a method of saving energy by minimizing heat loss caused by a transformer will be described. Reducing the number of turns of the coil wound around the switching transformer and increasing the thickness of the coil reduces the internal resistance of the coil to reduce heat loss due to resistance, and also reduces energy loss by reducing the current flowing through the coil. have. As described above, it has already been described that the switching transistors can be connected in parallel and the transformers can be connected to each transistor to reduce the current flowing through each transformer. Therefore, even if the coil resistance of the transformer is the same, it is possible to reduce the heat loss. As the current flowing in the coil decreases, it is sometimes necessary to increase the number of turns of the coil, which can reduce the number of turns of the coil by increasing the switching frequency.

The inductance Lp, the number of turns Np, and the core size of the primary coil of the switching transformer of the inverter may be expressed by the following equation.

The following characteristics can be obtained when two switching transistors and transformers are used in designing a 5W output power supply using the above relation.

Switching frequency

Output Power of Each Transformer

Core size

Primary Coil Turns 4 (T)

Secondary coil turns 5 (T)

Primary coil current 0.54 A

Current of secondary side coil 0.55 A

Primary and Secondary Coil Thickness (Diameter) 0.14

Therefore, the heat loss due to the internal resistance of the coil of the transformer is also negligibly small by increasing the switching frequency, and an energy saving effect can be obtained.

Referring back to FIG. 1, the switching transistors Q ₁ , Q ₂ , and Q ₃ operate as switching elements that are turned on or off in accordance with the switching signal SWout output from the PWM control circuit 11. Transformers T ₁ , T ₂ , and T ₃ have a primary winding N _p connected between the input DC power supply V _in and the transistors Q ₁ , Q ₂ , Q ₃ so that the switching signal is turned on or off. By generating a high frequency square wave power supply to the primary winding by the power supply to the secondary winding. The current feedback unit 13 detects a current flowing in the primary windings of the transformers T ₁ , T ₂ , and T ₃ according to the on / off operation of the switching transistors Q ₁ , Q ₂ , and Q ₃ . It returns to the PWM control circuit 11. Here, the number of transistors and transformers can be appropriately selected depending on the number of outputs, rated power, and the like.

The PWM control circuit 11 receives the output DC power supply (+ FB) and current feedback the operating current of the inverter unit 15 which is changed in accordance with the error signal and the input voltage (V _in ) or the load change compared with the reference signal. The on / off duration of the switching signal SW _out is controlled according to the voltage level detected by the unit 13 to control the amount of current flowing in the primary winding. In addition, an output rectifying unit 17 connected to the secondary windings of the transformers T ₁ , T ₂ , and T ₃ to convert a square wave power source into a DC power source may be provided to obtain one or more constant voltage outputs.

Next, the configuration of the output rectifying unit 17 connected to the secondary windings of the transformers T ₁ , T ₂ , and T ₃ will be described. The output rectifying unit 17 may include one or more rectifying modules for obtaining each unit output voltage, and may be configured differently according to the output voltage level or rated power, and examples thereof are illustrated in the drawings. In addition, the connection of the output module may be variously implemented in response to the plurality of transformers provided in the inverter unit 15.

The output rectifier 17 is connected to the secondary windings of the transformers T ₁ , T ₂ , and T ₃ . That is, the first rectification module 171 is connected to the secondary winding of the transformer T ₁ to output the first output voltage V _out1 , and the second and third rectifications are provided to the secondary winding of the transformer T ₂ . The modules 172 and 173 are connected to output the second and third output voltages V _out2 and V _out3 , and the third rectifying module 174 is connected to the secondary winding of the transformer T ₃ to output the fourth output. Output the voltage (V _out4 ). Each rectifier module can be configured differently according to the output power rating. In other words, the output rectifier 17 may form one output voltage for each transformer, one output voltage from at least two transformers, or at least two output voltages from one transformer. .

The first rectifying module 171 represents an example in which the transistor is used as a rectifying element, and the second and third rectifying modules 172 and 173 represent an example in which a diode is used as the rectifying element, and the fourth rectifying module ( 174 illustrates an example in which the output terminals of the first rectifying module 171 are connected in parallel.

The first rectifying module 171 is a transformer T1 according to on / off of the rectifying transistors Q6 and Q7 and the transistors Q6 and Q7 that are turned on and off according to the square wave signal transmitted from the transformer T1. Including the transformer (T5) and the capacitor (Co1) that is charged and discharged by the current transmitted from the) to generate an output voltage.

In the first rectifying module 171, the transistors Q6 and Q7 are alternately turned on / off according to the switching signal transmitted to the secondary winding side of the transformer T ₁ to charge and discharge electric charges in the transformer T5 and output the same. Get the voltage. First, when transistor Q6 is turned on and transistor Q7 is turned off, charge is charged in the primary winding No of transformer T5. When the transistor Q6 is turned off and the transistor Q7 is turned on, the output voltage is represented by the charge charged in the primary winding No of the transformer T5, and the charge is charged in the secondary winding Ns. When the transistor Q6 is turned on again and the transistor Q7 is turned off, the output voltage appears due to the charge charged in the secondary winding Ns of the transformer T5. This process can be repeated to obtain the output voltage.

As shown in the first rectifying module 171, a snubber circuit is provided around the transistor Q6. The RC element, consisting of a resistor (R _s1 ) and a capacitor (C _s1 ), is parasitic due to capacitance (C _GS ) between the leakage inductance (L _T ) of the primary coil of transformer (T1) and the gate-source of transistor (Q ₆ ). A first snubber circuit for preventing oscillation, the RC element composed of a resistor (R _S2 ) and a capacitor (C _S2 ) includes the leakage inductance (LT) of the primary coil of the transformer (T1) and the drain of the transistor (Q ₆ ). The second snubber circuit for preventing oscillation occurring between the capacitance (C _oss ) between the source and the source. A gate resistor (R _g) is connected to the gate terminal of the transistor (Q ₆₎ is added to ensure that the rise time of the square wave rise time (rising time) and the transistor (Q ₆₎ of the transfer from the transformer (T1) matches .

In the first snubber circuit, in order to prevent parasitic oscillation occurring between the leakage inductance of the primary coil of the transformer (10% of L _TL = Lp) and the capacitance C _GS between the input gate-source of transistor Q5. The values of each device can be designed as follows.

here,

In the second snubber circuit, the value of each element is prevented to prevent the parasitic oscillation generated between the leakage inductance of the primary coil of the transformer (10% of L _TL = Lp) and the output capacitance C _OSS of transistor Q5. Can be designed as follows.

The second rectifying module 172 may obtain an output voltage by charges charged in the inductor Lo2 while the diodes D5 and D6 are alternately turned on and off. When the "high" level signal is transmitted to the secondary winding Ns1 side of the transformer T2, the diode D5 is turned on and the diode D6 is turned off to charge the inductor Lo1. On the contrary, when the "low" level signal is transmitted to the secondary winding Ns1 side of the transformer T2, the diode D5 is turned off and the diode D6 is turned on to charge the inductor Lo1. The charge charged in the inductor Lo1 is discharged by the capacitor Co1 to represent the output voltage.

The fourth rectifying module 174 shows an example in which two first rectifying modules 171 are connected in parallel to the secondary winding side of the transformer T3 and the output terminals of two first rectifying modules having substantially the same configuration. By taking the structure of parallel connection in order to get more output power.

The primary windings of the transformers T ₁ , T ₂ , and T ₃ include a primary winding N _p and an auxiliary winding N _T , respectively. The auxiliary winding N _T stores energy while the switching transistors Q ₁ , Q ₂ and Q ₃ are off and outputs the stored energy when the transistors Q ₁ , Q ₂ and Q ₃ are on. By returning to, the energy of the down portion of the square wave, that is, the low level signal is transferred to the output side, thereby increasing the off signal level. On the other hand, the primary winding (N _p) is a transistor _{(Q 1, Q 2, Q} 3) of the stored energy when the stored energy while is on it is the transistors _{(Q 1, Q 2, Q} 3) and the off Pass it to the output.

The primary winding (N _p ) and the auxiliary winding (N _T ) are wound in opposite polarities, and the diode (D2) uses an ultra fast diode, and the primary winding (N _p ) and the auxiliary winding (N _T) Or between the auxiliary winding N _T and the negative terminal of the input power source to determine the direction of the current while the switching transistors Q ₁ , Q ₂ and Q ₃ are off. The thickness and the number of turns of the coil used for the auxiliary winding N _T are configured substantially the same as that of the basic winding N _p .

The functions of the coils connected to the primary side and the secondary side of the transformer T1 are summarized as follows. The basic winding N _p is connected between the positive terminal of the input power Vin and the drain terminal of the switching transistor to store power of the load and transmit it to the secondary coil. Auxiliary winding (N _T ) is a coil that serves to supply the storage energy to the filter coil of the output terminal in the forward converter, the winding winding polarity and the number of windings are reversed with the basic winding (N _p ). The feedback winding N _FB supplies power to an output transistor used to generate a switching signal in the PWM control circuit 11. The primary winding N _{G on} the secondary side serves to supply a square wave signal to the gate terminal of the transistor, which is a rectifying element at the output terminal of the synchronous rectification method, and the secondary winding N _S is a rectified DC applied to the load of the output terminal. As a coil for supplying voltage, the thickness of the coil is determined by the magnitude of the load current.

The design process of a transformer including such a winding will be described in turn. The current flowing through the primary coil and the inductance can be calculated by the following equations (2) and (9). The size of the core is determined by Equation 11, and the number of turns of the basic winding Np is determined by Equation 10, and the thickness of the coil is determined so that stability is based on the size of the continuous current I _PDC . Determine. The number of turns of the auxiliary winding N _T and the thickness of the coil are substantially the same as that of the basic winding N _p . The number of turns of the feedback winding N _FB is calculated as follows after determining the feedback voltage V _FB according to the voltage Vcc to be applied to the PWM control circuit 11.

The first winding N _{G on} the secondary side is calculated as follows according to the voltage V _GS between the gate and the source, which is the input voltage level of the rectifying transistor.

The second winding N _{S on} the secondary side is closely related to the output voltage V _out , and can be obtained by the following equation.

The value of the choke coil (L ₀ ) in the output rectifier module can be calculated as follows according to the output voltage (V _out ) and the off time (off time t _off of the switching transistor).

The inductance of the choke coil is determined by the magnitude of the output voltage and the current, and the magnitude of the core is determined by Equation (11). The number of turns of the choke coil is calculated from the inductance factor A _L at zero airgap according to the following formula, and the thickness of the core is determined by the magnitude of the output current Iout.

Meanwhile, the parameter for the primary winding N _o1 of the transformer T5 included in the first rectifying module 171 may be obtained by the above equations, and the number of turns of the secondary winding N _s1 may be obtained as follows. .

Then, the capacitance of the filter capacitor Co connected to the output terminal can be obtained as follows.

here,

On the secondary side of the transformer T ₂ , coils N _S1 and N _S2 , each of which has a different number of turns depending on different load output voltages, are wound. In particular, an output having a negative voltage polarity can be obtained by reversing the polarity of the rectifying diode like the third output voltage V _out3 .

2 is a view showing the configuration of a switching mode power supply according to another embodiment of the present invention, an example of a flyback power supply. The power supply device in this example includes an input filter 20, a PWM control circuit 21, an inverter unit 25, a current feedback unit 23 and an output rectifier 27, to increase the efficiency and energy In order to save power, a connection method of controlling the plurality of switching transistors Q ₁ , Q ₂ , Q ₃ and the plurality of inverter transformers T ₁ , T ₂ , T ₃ by one PWM control circuit 21 is described. The overall configuration is similar to that of the forward type power supply of Fig. 1, but there are some differences in the configurations of the transformers (T ₁ , T ₂ , T ₃ ) and the output rectifier. Accordingly, the input filter 20, the PWM control circuit 21, and the current feedback unit 23 are substantially similar to the input filter 10, the PWM control circuit 11, and the current feedback unit 13 shown in FIG. 1. Since the functions are the same, and the functions of the switching transistors Q ₁ , Q ₂ and Q ₃ are also substantially the same as those shown in FIG. 1, the detailed description thereof will be omitted.

On the other hand, in the case of transformers (T ₁ , T ₂ , T ₃ ), unlike FIG. 1, the auxiliary winding N _T is not connected to the primary side, and each output module of the output rectifying unit 27 is shown in FIG. 1. Otherwise choke coils are not required. In addition, an output module 271a and 271b are separately configured on each of the two transformers T1 and T2 and output terminals thereof are connected in parallel to generate a single output voltage V _out1 . Of course, one output voltage can be generated. In addition, it can also be configured by connecting two output modules to the secondary winding side of one transformer.

In the configuration of the flyback power supply shown in FIG. 2, a plurality of switching transistors and a plurality of transformers connected thereto are used to reduce the current flowing through each transistor and the transformer, thereby reducing the total power loss. Here, the peak current flowing in the primary windings of each transistor and transformer is expressed by the following equation.

The inductance of the primary coil of each transformer can be obtained as follows.

Compared with the circuit of FIG. 1, the peak current in the circuit of FIG. 2 is only about 1/2 of the peak current in the circuit of FIG. 1, so that the value of the transformer inductance Lp is lowered and the core of the transformer is lower. It also shrinks in size. Thus, the circuit of FIG. 2 is more economical and space-saving than the circuit of FIG.

The determination of core size in the design of the transformer is likewise applied to the formula applied to the circuit of FIG. However, the number of turns of the primary coil of the transformer can be obtained by the following formula.

Where the air gap ( ) Is as follows.

On the other hand, the number of coil turns of the feedback winding N _FB and the secondary winding of the transformer T ₁ can be calculated by the following equation.

In the output rectifying unit 271 of FIG. 2, the second and second output modules 271a and 271b are connected to the second winding side of the first output module 271 and the transformer T3 to generate one output in parallel. 3 includes output modules 273 and 274. A transistor is used as the rectifying element of the first output module 271, whereas a diode is used in the second or third output modules 273 and 274.

Meanwhile, the diodes included in the second output module 273 and the third output module 274 are different from each other. That is, the diode D5 of the second output module 273 is connected to a terminal without a dot mark of the secondary winding NG3 of the transformer T3 while the diode D6 of the third output module 274 is connected. ) Is connected to a terminal marked with a dot of the secondary winding NG4 of the transformer T3. Therefore, the output Vout3 of the second output module 273 may output a positive voltage and the output Vout4 of the third output module 274 may output a negative voltage. In addition, in the configuration of the second or third output module, by connecting a plurality of diodes in parallel or by output capacitors in parallel, it is possible to use a device having a lower rating than when using a single diode or capacitor The volume or cost of the device can be lowered.

The first output module 271 is composed of an upper module 271a and a lower module 271b having substantially the same configuration as shown, and the (+) output terminal and the (-) output terminal of each module are common to each other. Is connected to generate one output voltage. An upper module (271a) and a lower module (271b) performs a rectifying operation by each operation of the transformer (T1) and a s are connected to the secondary winding of the transformer (T2) transistors (Q5, Q _5). In addition, a snubber circuit is provided around each of the transistors Q ₅ and Q ₆ . The first snubber circuit composed of the resistor R _s1 and the capacitor C _s1 and the second snubber circuit composed of the resistor R _s2 and the capacitor C _s2 are the snubber circuit described in FIG. The design criteria are substantially the same.

FIG. 3 illustrates a current-mode control scheme as an example of a configuration diagram of the PWM control circuit illustrated in FIG. 1 or 2. The power supply Vcc induced by the feedback winding N _FB on the primary side of the transformer T ₁ supplies power to the amplifier 35 which outputs the switching signal SW _out , and the clock generator 33 and the flip line. Circuits such as the flop 34, the error amplifier 31, the comparator 32, and the like are supplied with operating power from an input power source V _in applied through the regulator 37.

The error amplifier 31 compares and amplifies the output signal + FB and the reference voltage V _ref , and the error signal is input to the comparator 32. Then, the output current of the inverter is sensed and converted into a voltage, and then the sensing signal SENSE is input to the comparator 32. The comparator 32 inputs the detection signal SENSE according to the peak switch current to the RS flip-flop (latch) 34 by comparing it with an error signal related to the output signal. The clock generator 33 generates a clock signal which is a square wave signal corresponding to the switching frequency fs, and the RS flip-flop 34 receives the output of the comparator 32 and the clock signal to drive on / off of the switching element. To generate a switching signal SW _out . The switching signal turns on / off a switching element (transistor) connected at the rear end according to its logic level.

The main output voltage (+ FB) fed back from the final output stage is compared with the reference voltage (V _ref ) in the error amplifier 31, the current feedback signal (SENSE) is compared with the reference voltage (1.2V) in the comparator 32 The result is input to the flip flop 34. The flip-flop 34 increases or decreases the phase (or width) of the clock signal generated by the oscillator 33 according to the output signal of the comparator 32 (that is, the pulse width modulation in which the duty cycle of the clock signal is changed) By generating a PWM) signal to generate a switching signal SW _out , the current flowing through the transformer T ₁ may be increased or decreased according to the change of the input voltage and the load, thereby keeping the output voltage of the final output terminal constant.

As described above, according to the switching mode power supply apparatus according to the present invention, by using a plurality of switching transistors and / or a plurality of transformers to distribute the current flowing through the inverter in a plurality of paths to the transistors and / or transformers The transformer's size can be reduced while minimizing power loss. Therefore, even if there is no heat sink required to dissipate the heat generated by the energy loss can be operated stably, it is possible to greatly reduce the overall volume or size of the power supply. Such a power supply device may be usefully applied as a power supply device used in mobile phones, portable computers, electric toys, electronic devices of automobiles, and the like.

Claims (13)

A switching signal generator for outputting a switching signal having a predetermined frequency; At least two switching elements configured to perform an on or off operation according to the switching signal; A power conversion element connected between the switching elements and an input DC power source and configured to generate a square wave signal by passing current or blocking depending on an on or off state of the switching element; And Switching mode power supply characterized in that it comprises an output rectifying unit for receiving the square wave signal generated by the power conversion element to rectify it to output a DC power. The power conversion device of claim 1, wherein the power conversion device is provided corresponding to each of the at least two switching devices such that a current flowing between the input DC power source and the switching elements flows to each power conversion device. Switching mode power supply. A switching signal generator for outputting a switching signal having a predetermined frequency; A switching element performing an on or off operation according to the switching signal; At least two power conversion elements connected between the switching element and an input DC power source and configured to generate a square wave signal by passing current or blocking depending on an on or off state of the switching element; And Switching mode power supply characterized in that it comprises an output rectifier for receiving a square wave signal generated by the power conversion elements to rectify it to output a DC power. The switching device of claim 1 or 3, wherein each of the switching elements comprises a transistor, and source terminals of the transistors are commonly connected, and a switching signal output from the switching signal generator is input to each gate terminal thereof. The terminal is connected to the power conversion element, the switching mode power supply, characterized in that the transistors are simultaneously turned on or off by the switching signal to control the current flowing through the power conversion element. The method of claim 1 or 3, wherein the output rectifying unit Switching mode power supply, characterized in that for each of the power conversion element to form one output voltage, or to form one output voltage from at least two power conversion elements, or at least two output voltage from one power conversion element Feeder. The method of claim 1 or 3, wherein the output rectifying unit Comprising an output module for rectifying the square wave signal transmitted from the power conversion element to output a DC voltage, at least two output modules having substantially the same configuration as the output module is connected in parallel to form a single output voltage Switched mode power supply characterized in that. According to claim 1 or 3, wherein each of the power conversion element is a transformer, the primary side includes a coil winding and a winding winding in the opposite polarity of the same thickness and the number of turns of the coil substantially the same, The auxiliary winding and the auxiliary winding alternately store energy in accordance with the on-off operation of the switching element, and then transfer the stored energy to the secondary winding. The apparatus of claim 1, further comprising: a current feedback unit configured to detect a current flowing through the switching elements according to an on / off operation of each switching element, and return the current to the switching signal generator. The switching signal generator receives the current signal detected by the current feedback unit and the output DC voltage signal of the output rectifier and controls the output DC voltage to be constant by adjusting the pulse phase of the switching signal based on these feedback signals. Switching mode power supply, characterized in that. The method of claim 6, wherein the current feedback unit Connected between the negative pole of the input DC power supply and the switching elements, the current flowing through the power conversion element is supplied to the primary winding in accordance with the switching on and off of the switching elements to convert to a predetermined ratio to the secondary winding A current-coupled converter for supplying; And And a signal generator for generating a detection signal proportional to a current induced in the secondary winding of the current-coupling converter and feeding it back to the switching signal generator. The method of claim 1 or 3, wherein the output rectifying unit Two rectifying elements alternately turned on or off in accordance with a square wave signal transmitted from the power conversion element; An inductor for charging and discharging a current transferred from the power conversion element according to on / off of the transistors; And And a capacitor configured to generate an output voltage by being charged by the current discharged from the inductor. The method of claim 1 or 3, wherein the output rectifying unit A rectifier for operating on or off in accordance with a square wave signal transmitted from the power conversion device; And Switching mode power supply, characterized in that it comprises a capacitor that is charged by the current delivered through the rectifying element to generate an output voltage. The rectifying device of claim 10, wherein the rectifying element of the output rectifying unit comprises a transistor. Between the first terminal and the snubber circuit and the drain terminal and the source terminal for preventing the oscillation caused by the leakage inductance and the gate capacitance of the power conversion device between the gate terminal and the source terminal and the leakage inductance of the power conversion device between the drain and the source And a snubber portion including at least one of the second snubber circuits for preventing oscillation due to capacitance. The rectifying device of claim 11, wherein the rectifying element of the output rectifying unit comprises a transistor. Between the first terminal and the snubber circuit and the drain terminal and the source terminal for preventing the oscillation caused by the leakage inductance and the gate capacitance of the power conversion device between the gate terminal and the source terminal and the leakage inductance of the power conversion device between the drain and the source And a snubber portion including at least one of the second snubber circuits for preventing oscillation due to capacitance.