JP2014117129A - Power supply device, and electronic apparatus having the same - Google Patents

Abstract

An object of the present invention is to make it difficult to destroy a current detection resistor even if an excessive voltage exceeding an assumed design voltage is applied so that a current interrupting means can function.
A current bypass circuit is provided in parallel with a current detection resistor. When an excessive voltage exceeding the design assumed voltage is applied from the commercial AC power supply 1 to the input unit 70, the current bypass circuit 15 is turned on, so that part of the current i1 flowing through the field effect transistor 7 is current bypassed. It flows into the circuit 15. As a result, the rate of increase in the voltage v1 across the current detection resistor 14 decreases, and the current detection resistor 14 is less likely to be destroyed. Further, since the increase in the current i1 is not hindered, the current fuse 30 can be blown. Thereby, explosion-proofing of the smoothing capacitor 4 can be suppressed.
[Selection] Figure 1

Description

  The present invention relates to a power supply device and an electronic apparatus including the power supply device.

  In general, the AC voltage supplied from the commercial AC power source to the electronic device differs depending on the country. For example, Japan, North America, etc. belong to the 100V range, and China, Europe, Australia, etc. belong to the 200V range. In some countries, such as Brazil, 100V system voltage and 200V system voltage coexist. In general, there are power supply devices used for electronic devices that can operate in either the 100 V range or the 200 V range, and those that can only be operated in either the 100 V range or the 200 V range. In particular, if a power supply device dedicated to the 100 V range is connected to a commercial AC power supply that supplies 200 V by mistake, a voltage exceeding the withstand voltage is applied to the smoothing capacitor of the converter. When a voltage exceeding the withstand voltage is applied to the smoothing capacitor for a long time, the electrolytic solution in the smoothing capacitor may be ejected. Since the electrolytic solution is made of a conductive material, there is a risk of shorting the electronic component. In order to solve this problem, when a power supply dedicated for 100V range is mistakenly connected to a voltage of 200V, protection is provided to stop the power supply from the commercial AC power supply by cutting off the fuse by supplying an overcurrent. A circuit has been proposed (Patent Document 1).

JP 2008-259375 A

  Generally, in an electronic device, a power converter that generates a secondary side low voltage by switching a primary side voltage smoothed by a smoothing capacitor is used. The control circuit that controls the switching element that performs switching monitors the current flowing from the current inflow terminal to the current outflow terminal of the switching element and executes the switching control. A current detection resistor for monitoring this current is inserted in series with the switching element.

  In order to connect a plurality of such power supply converters to one smoothing capacitor, the capacity of the smoothing capacitor must be increased. Further, by providing the protection circuit in one power converter among the plurality of power converters, the manufacturing cost may be reduced. In such a power supply device, when an excessive voltage exceeding the designed voltage is applied, an overcurrent flows only in the power converter provided with the protection circuit. Since the energy charged in the smoothing capacitor flows only into the power converter provided with the protection circuit, the discharge energy concentrates on the current detection resistor of the power converter. The current detection resistor has a withstand voltage set in accordance with the output of the power converter. Therefore, when excessive energy is applied, the current detection resistor is destroyed, and the current interrupting fuse provided in the input portion of the power supply device cannot be blown.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to make it possible to function a current interrupting means by making it difficult for a current detection resistor to be destroyed even when an excessive voltage exceeding an assumed design voltage is applied.

The present invention is, for example,
Input means for inputting AC voltage from a commercial AC power source;
A blocking means provided in the input means, for cutting off the AC voltage when an overvoltage is applied to the input means for a predetermined time or more;
Rectifying and smoothing means for rectifying and smoothing the AC voltage input to the input means;
Voltage converting means for converting the output voltage from the rectifying and smoothing means;
Switching means for switching the voltage conversion means;
A current detection resistor for detecting a current flowing through the switching means;
Control means for controlling the switching means within a range in which the value of the current detected by the current detection resistor does not exceed a predetermined limit value, and controlling the voltage output from the voltage conversion means to be a target voltage; ,
When detecting that the voltage supplied from the commercial AC power supply is an overvoltage, an overvoltage detection unit that forcibly turns on the switching unit and guides the blocking unit to block the AC voltage;
Provided in parallel with the current detection resistor is a power supply device comprising: bypass means that conducts when the overvoltage detection means detects an overvoltage, and bypasses the current detection resistance to flow current. .

  According to the present invention, since the bypass means is provided in parallel to the current detection resistor, even if an excessive voltage exceeding the designed voltage is applied, the current detection resistance is not easily destroyed, and the interruption means Be able to function.

The circuit diagram which shows an example of a power supply device. The figure explaining the outline of an operation | movement waveform. The circuit diagram which shows the other example of a power supply device. The figure explaining the outline of an operation | movement waveform. The figure which shows an example of the power supply device provided with the some converter. FIG. 14 illustrates an example of an electronic device.

  In FIG. 1, the power supplied from the commercial AC power supply 1 is input to the input unit 70 of the power supply device 100. The voltage of the commercial AC power supply 1 is Vin. The input unit 70 functions as input means for inputting AC from the commercial AC power source 1. The input unit 70 is provided with a current fuse 30, a filter 2 for removing noise, and a rectifier 3. The current fuse 30 functions as a cutoff unit that cuts off the AC voltage when a non-standard voltage (overvoltage that is not assumed in design: a voltage equal to or higher than a predetermined threshold) is applied to the input unit for a predetermined time or longer. The rectifier 3 and the smoothing capacitor 4 function as a rectifying / smoothing means that rectifies and smoothes the alternating current input to the input unit 70. In this way, the input voltage Vin that has been full-wave rectified by the rectifier 3 is smoothed by the smoothing capacitor 4. The smoothed input voltage Vin is applied to the voltage converter 50.

  The voltage converter 50 functions as voltage conversion means for converting the output voltage from the rectifying and smoothing circuit. The transformer 6 of the voltage converter 50 is voltage conversion means for electrically insulating the primary side and the secondary side and converting the primary side voltage to generate a secondary side voltage. The field effect transistor 7 is a switching unit that switches a current flowing on the primary side of the transformer 6 and controls a voltage generated on the secondary side to be a target voltage. A switching element different from the field effect transistor 7 may be employed. The current detection resistor 14 is a resistor for detecting the current i <b> 1 that is passed through the field effect transistor 7.

  The secondary side voltage of the transformer 6 that is switching-controlled by the field effect transistor 7 is rectified by the diode 8, smoothed by the smoothing capacitor 9, and the output voltage Vout is generated.

  The voltage control unit 13 is a circuit that controls the output voltage Vout to be a constant target voltage. The voltage control unit 13 generates a control signal based on the output voltage Vout and sends the control signal to the control circuit 12 provided on the primary side. The control circuit 12 controls the switching of the field effect transistor 7 according to the control signal. The output voltage Vout is divided by a voltage dividing circuit including a resistor 23 and a resistor 25. The voltage control unit 13 controls the current supplied to the light emitting diode of the photocoupler 24 so that the divided voltage matches the reference voltage of the shunt regulator 26. The resistor 22 is a limiting resistor for limiting the current flowing through the photocoupler 24 and the shunt regulator 26. An output transistor included in the photocoupler 24 is connected to the control circuit 12 and transmits a control signal output from the voltage control unit 13 to the control circuit 12.

  The control circuit 12 controls the field effect transistor 7 in a range where the current value i1 detected by the current detection resistor 14 does not exceed a predetermined limit value, so that the voltage output from the transformer 6 becomes the target voltage. It is a control means to control. Specifically, the control circuit 12 determines the control duty of the field effect transistor 7 based on the control signal from the voltage control unit 13 and generates a gate signal according to the determined control duty. The gate signal is input to the control terminal (gate) of the field effect transistor 7 through the gate resistor 29, the diode 16 and the capacitor 17. Thereby, the field effect transistor 7 is driven. When the output voltage Vout falls below the target voltage, the voltage divided by the resistors 23 and 24 becomes smaller than the reference voltage of the shunt regulator 26. As a result, the current flowing through the photocoupler 24 by the shunt regulator 26 is reduced. In this way, the control circuit 12 detects that the output voltage Vout has decreased. The control circuit 12 controls the field effect transistor 7 to increase the output voltage Vout by increasing the ON duty of the gate signal (that is, increasing the ON time). When the output voltage Vout increases from the target voltage, the voltage divided by the resistors 23 and 24 becomes larger than the reference voltage of the shunt regulator 26, so that the shunt regulator 26 increases the current flowing through the photocoupler 24. As a result, the control circuit 12 detects that the output voltage Vout has increased. The control circuit 12 controls the field effect transistor 7 to lower the output voltage Vout by reducing the on-duty of the pulsed gate signal (shortening the on-time).

  By performing such feedback control, the voltage converter 50 controls switching of the field effect transistor 7 so that the output voltage Vout always becomes a constant target voltage.

  The current detection resistor 14 detects a current i1 flowing through the field effect transistor 7, and converts the current i1 into a voltage v1. The voltage v1 is input to the control circuit 12. The control circuit 12 controls the on-duty (on time) so that the current i1 detected by the current detection resistor 14 does not exceed the limit value set by the control circuit 12. For example, when the supply of power from the commercial AC power supply 1 is started (at start-up), the control circuit 12 increases the on-duty of the gate signal (longens the on-time) by the control signal from the voltage control unit 13. . The control circuit 12 performs current limit control by comparing the limit value with the current i1 detected by the current detection resistor 14 so that the current i1 does not exceed the rated current of the field effect transistor 7. Since the current value i1 is detected as the voltage v1, the limit value is handled as the limit voltage Vlimit.

  When the overvoltage detection circuit 5 detects that the input voltage Vin supplied from the commercial AC power supply 1 is an overvoltage, the overvoltage detection circuit 5 forcibly turns on the field effect transistor 7 to cut off the AC voltage from the commercial AC power supply 1. It functions as an overvoltage detection means for leading the current fuse 30 to the current. When a voltage assumed by design is input to the power supply apparatus 100, the Zener diode 18 is not conducted, and the overvoltage detection circuit 5 does not perform a protection operation. On the other hand, when the voltage supplied from the commercial AC power supply 1 greatly exceeds the designed voltage, the Zener diode 18 becomes conductive, and the overvoltage detection circuit 5 starts the protective operation. For example, it is assumed that the designed input voltage for power supply device 100 is a 100V system voltage. In this case, when a 200V system voltage is input to the power supply device 100, the Zener diode 18 is turned on, and charging of the capacitor 27 is started. The withstand voltage of the Zener diode 18 of the power supply apparatus 100 is higher than the 100V system voltage and lower than the 200V system voltage in order to reduce the manufacturing cost. When the charging voltage of the capacitor 27 rises to the gate-on voltage of the field effect transistor 7, the field effect transistor 7 continues to conduct. The current i1 increases at an increase rate determined by the ratio between the primary inductance of the transformer 6 and the input voltage. The resistor 28 is a resistor that discharges the electric charge of the capacitor 27. The resistor 28 is provided to prevent the capacitor 27 from being charged by the leakage current of the Zener diode 18 or the like when the Zener diode 18 is not conducting. The diode 19 is provided to prevent the capacitor 27 from being charged by the gate signal from the control circuit 12 when an assumed design voltage is input (during normal operation). The diode 16 is provided to prevent the control circuit 12 from applying a voltage output from the overvoltage detection circuit 5 when the overvoltage detection circuit 5 operates. By connecting the diode 16 to the control circuit 12, the control circuit 12 cannot draw a current for turning off the field effect transistor 7 from the field effect transistor 7. Therefore, the capacitor 17 is connected in parallel to the diode 16 so that the control circuit 12 can turn off the field effect transistor 7.

  The current bypass circuit 15 is provided in parallel to the current detection resistor 14, and is turned on when the overvoltage detection circuit 5 detects an overvoltage, and functions as a bypass unit that bypasses the current detection resistor 14 and flows current. That is, by flowing a part of the current i1 flowing through the field effect transistor 7 to the current bypass circuit 15, the voltage across the current detection resistor 14 is reduced, and the breakdown of the current detection resistor 14 is suppressed. As described above, when an excessive voltage exceeding the assumed voltage is applied from the commercial AC power supply 1, the field effect transistor 7 continues to conduct, and the current i1 is increased at a rate determined by the ratio between the primary inductance of the transformer 6 and the input voltage. Will increase. The current i1 also flows through the current detection resistor 14. When the voltage v1 across the current detection resistor 14 becomes equal to or higher than the threshold voltage determined from the Zener diode 20 and the resistor 21, at least a part of the current i1 of the field effect transistor 7 flows to the current bypass circuit 15. The resistance value of the resistor 21 is sufficiently smaller than the resistance value of the current detection resistor 14. The Zener voltage of the Zener diode 20 is set to a value larger than the limit value Vlimit of the current detection resistor 14 corresponding to the current limit value set by the control circuit 12. Therefore, when a normal voltage Vnormal (eg, 100 V) is input, no current flows through the current bypass circuit 15. When an excessive voltage Vhigh is applied, the field effect transistor 7 continues to be conducted by the current bypass circuit 15. When the current flowing through the current fuse 30 exceeds the fusing capacity, the current fuse 30 is blown, and the input voltage Vin is not applied to the smoothing capacitor 4.

  FIG. 2 shows a schematic waveform of the current i1 flowing through the field effect transistor 7 and the voltage v1 applied to the current detection resistor 14. The vertical axis represents the amplitude of the waveform, and the horizontal axis represents time. From time t0 to time t1, the input voltage Vin is a normal voltage Normal assumed in design. From time t1 to time t3, the input voltage Vin is a voltage High that is significantly higher than a normal voltage assumed in design.

  When the normal voltage Normal is input from the commercial AC power supply 1 to the input unit 70 of the power supply device 100, the voltage v1 applied to the current detection resistor 14 is a limit voltage corresponding to the current limit value set by the control circuit 12. It is controlled so as to be equal to or lower than Vlimit. When the voltage control unit 13 is performing feedback control, the current i1 is controlled to be smaller than the current limit value, so that the voltage v1 is also controlled to be a value smaller than Vlimit.

  Assume that a high voltage High is input from the commercial AC power supply 1 at time t1. Here, in FIG. 2, Vin is shown as being switched from Normal to High, but in reality, High will be applied from the beginning. As described above, when a 200V voltage is input to the 100V power supply device 100, the field effect transistor 7 continues to be conductive. When the voltage v1 of the current detection resistor 14 reaches the Zener voltage Vz of the Zener diode 20 at time t2, the current bypass circuit 15 becomes conductive. As a result, at least a part of the current i1 flows through the current bypass circuit 15, so that the rate of increase of the voltage v1 decreases. Thus, the voltage v1 is clamped by the current bypass circuit 15. The current fuse 30 is blown when the current i1 applied to the field effect transistor 7 exceeds the blown capacity ifuse of the current fuse 30. As a result, the input power source Vin is not applied to the smoothing capacitor 4. When the current bypass circuit 15 is not provided, the voltage v1 of the current detection resistor 14 increases with a certain slope as shown by the dotted line, and the current detection resistor 14 may burn out.

  For example, when the power supply device 100 is a power supply device dedicated to the 100 V range, an electrolytic capacitor having a withstand voltage of 200 V is generally selected as the smoothing capacitor 4. When an AC voltage of 200V to 240V, which is a 200V system voltage, is applied from the commercial AC power supply 1, the voltage after smoothing is about 280V to 337V. For this reason, a voltage exceeding the withstand voltage is applied to the smoothing capacitor 4 of the power supply device dedicated to the 100 V range. In anticipation of such a situation, it is conceivable to use, for example, a capacitor having a withstand voltage of 400 V as the smoothing capacitor 4 of the power supply device 100 dedicated to the 100 V range. However, when the withstand voltage of a capacitor is doubled, the size and cost of the capacitor are greatly increased. Therefore, it is more advantageous in terms of size and cost to employ an electrolytic capacitor having a withstand voltage of about 200 V as the smoothing capacitor 4 of the power supply device 100 dedicated to the 100 V range.

  As described above, when a voltage High higher than the design assumption is input, the field effect transistor 7 is forcibly kept on. In particular, if the current bypass circuit 15 is not provided, an excessive voltage may be applied to the current detection resistor 14 or the control circuit 12 to which the voltage v1 is input before the current fuse 30 is blown, leading to destruction. If the current detection resistor 14 and the control circuit 12 are damaged, the current i1 does not flow and the current fuse 30 cannot be blown. As a result, the smoothing capacitor 4 is explosion-proof.

  On the other hand, in this embodiment, the current bypass circuit 15 guides the current fuse 30 to be blown by detecting that the voltage High higher than the normal voltage Normal is input. Thereby, voltage High exceeding the withstand voltage can be suppressed from being applied to the smoothing capacitor 4 for a long time, and explosion-proofing of the smoothing capacitor 4 can be suppressed. More specifically, since part of the current i1 flows through the current bypass circuit 15 and the voltage v1 is clamped by the Zener diode 20, the current detection resistor 14 and the control circuit 12 to which the detection voltage v1 is input are excessively applied. It becomes difficult to apply the voltage. Therefore, the current fuse 30 can be blown before the current detection resistor 14 and the control circuit 12 are damaged. Further, explosion-proofing of the smoothing capacitor 4 can be suppressed.

  In this embodiment, the Zener diode 18 is used as an element for detecting the input voltage Vin, but other elements capable of detecting the voltage, such as a varistor, may be employed. Although the Zener diode 20 is employed as the clamp element of the current bypass circuit 15, one diode or a series connection of a plurality of diodes may be employed. The resistor 21 may be short-circuited. In this case, there is an advantage that the resistor 21 can be omitted.

  FIG. 3 shows another example of the power supply device 100. Here, a different point from the power supply device 100 demonstrated using FIG. 1, 2 is demonstrated. As can be seen by comparing FIG. 1 and FIG. 3, the overvoltage detection circuit 5 and the current bypass circuit 15 are replaced with an overvoltage detection circuit 40 and a current bypass circuit 41, respectively.

  When the normal voltage Normal is input to the input unit 70 of the power supply device 100, the Zener diode 18 of the overvoltage detection circuit 40 is not conductive, and thus the overvoltage detection circuit 40 does not operate. When a high voltage High is input from the commercial AC power supply 1, the Zener diode 18 is turned on and charging of the capacitor 27 is started. Furthermore, charging of the capacitor 45 is also started according to a time constant determined by the resistor 44 and the capacitor 45. The resistor 44 and the capacitor 45 form a delay circuit. The zener diode 18 is a component having a withstand voltage higher than the assumed voltage Normal and lower than High. When the charging voltage of the capacitor 45 rises to the gate-on voltage of the field effect transistor 7, the field effect transistor 7 becomes conductive. Thereafter, the field effect transistor 7 continues to conduct, and the current i1 increases at a rate determined by the ratio between the primary inductance of the transformer 6 and the input voltage. The resistor 28 is a resistor that discharges the electric charges of the capacitors 27 and 45. The Zener diode 18 does not conduct when the normal voltage Normal is applied. When the Zener diode 18 is not conducting, the resistor 28 consumes the leakage current of the Zener diode 18 so that the capacitors 27 and 45 are not charged. The diode 19 functions so that the capacitors 27 and 45 are not charged by the gate signal from the control circuit 12.

  The current bypass circuit 41 is provided in parallel to the current detection resistor 14 and is turned on when the overvoltage detection circuit 40 detects an overvoltage, and functions as a bypass unit that bypasses the current detection resistor 14 and flows a part of the current i1. To do. The current bypass circuit 41 includes a field effect transistor 42 which is an example of a switch element, and a resistor 21 connected in series to the current inflow terminal or current outflow terminal of the field effect transistor 42.

  As described above, when the voltage High higher than the assumed voltage is input from the commercial AC power supply 1, charging of the capacitor 27 is started. When the charging voltage of the capacitor 27 rises to the gate-on voltage of the field effect transistor 42, the field effect transistor 42 continues to conduct. The resistor 43 is a gate resistance of the field effect transistor 42. When the field effect transistor 42 is turned on, at least part of the current i 1 of the field effect transistor 7 flows to the current bypass circuit 41. The resistance value of the resistor 21 is sufficiently smaller than the resistance value of the current detection resistor 14. The current detection resistor here is a combined resistance of the current detection resistor 14 and the resistor 21. When the normal voltage Normal is input, the field effect transistor 42 is not conductive, so that no current flows through the current bypass circuit 41. Therefore, the combined resistance of the current detection resistor is only the current detection resistor 14.

  Due to the time constants of the resistor 44 and the capacitor 45, the field effect transistor 42 is turned on before the field effect transistor 7 is forcibly turned on. This mechanism is as follows. The overvoltage detection circuit 40 outputs a drive signal (charging voltage of the capacitor 27) to the gate terminal of the field effect transistor 7 and the gate terminal of the field effect transistor 42 when an overvoltage is detected. The resistor 44 and the capacitor 45 form a kind of delay circuit. Therefore, the drive signal reaches the field effect transistor 42 before the field effect transistor 7. Thus, the resistor 44 and the capacitor 45 function as a delay circuit that delays the drive signal for forcibly turning on the field effect transistor 7. In this way, the field effect transistor 42 is turned on before the field effect transistor 7 is forcibly turned on, so that energization of the current bypass circuit 41 is started. When the current bypass circuit 41 is turned on, the current detection resistor for detecting the current i1 is a combined resistance of the current detection resistor 14 and the resistor 21. Therefore, the increase rate of the voltage v1 decreases. A part of the current i1 flows through the current bypass circuit 41.

  When the charging voltage of the capacitor 45 rises to the gate-on voltage of the field effect transistor 7, the field effect transistor 7 starts to conduct, and the current i1 increases at a rate of increase determined by the ratio between the primary inductance of the transformer 6 and the input voltage. When the current i1 of the field effect transistor 7 exceeds the blowing capacity ifuse of the current fuse 30, the current fuse 30 is blown and the input voltage Vin (= High) is not applied to the smoothing capacitor 4.

  FIG. 4 shows a schematic operation waveform of the energization current of the field effect transistor 7 and the voltage applied to the current detection resistor 14. When normal commercial AC power is input, control is performed below the current limit set by the control circuit 12. When feedback control is performed by the voltage control unit 13, control is performed with a value smaller than the current limit. When a different voltage, for example, a 200V system voltage is input from a commercial AC power supply to a 100V system power converter, the field effect transistor 42 is turned on, the combined resistance of current detection is reduced, and the applied voltage is reduced. . Thereafter, the field effect transistor 7 continues to conduct, and the current fuse 30 is blown when the current passed through the field effect transistor 7 exceeds the blown capacity of the current fuse 30 so that the input power supply is not applied to the smoothing capacitor 4. Become. In the absence of the current bypass circuit 41, the voltage applied to the current detection resistor 14 increases with a constant slope, as indicated by the dotted line.

  According to the present embodiment, the overvoltage detection circuit 40 detects that a high voltage High has been input to the input unit 70 of the power supply device 100, and the current bypass circuit 41 functions to blow the current fuse 30. Thereby, it is possible to suppress a voltage exceeding the withstand voltage from being applied to the smoothing capacitor 4 for a long time. Further, explosion-proofing of the smoothing capacitor 4 can be suppressed.

  When the overvoltage detection circuit 40 and the current bypass circuit 41 are not employed, the field effect transistor 7 continues to be forcibly turned on when a voltage higher than the designed voltage is input to the input unit 70. Therefore, the current detection resistor 14 and the control circuit 12 may be destroyed before the current fuse 30 is blown. If the current detection resistor 14 and the control circuit 12 are damaged, the current i1 cannot flow and the current fuse 30 cannot be blown. As a result, the smoothing capacitor 4 is explosion-proof.

  On the other hand, in the present embodiment, when a high voltage High is input to the input unit 70, the overvoltage detection circuit 40 turns on the field effect transistor 42 to reduce the current detection resistance. The delay circuit forcibly turns on the field effect transistor 7 later than the field effect transistor 42 by the delay circuit. Therefore, an excessive voltage is hardly applied to the current detection resistor 14 and the control circuit 12 to which the voltage v1 is applied, and the current fuse 30 is blown. Therefore, explosion-proofing of the smoothing capacitor 4 can be suppressed.

  Although the field effect transistor 42 is used as the switch element of the current bypass circuit 41, other types of switch elements such as bipolar transistors may be employed.

  FIG. 5 shows an example of a power supply device 100 including a plurality of voltage converters 50, 51, 52. The voltage converter 50 is a voltage converter that converts a voltage output from a rectifying and smoothing circuit including the rectifier 3 and the smoothing capacitor 4 and outputs a voltage Vout1. The voltage converter 51 is a voltage converter that converts a voltage output from a rectifying / smoothing circuit including the rectifier 3 and the smoothing capacitor 4 and outputs a voltage Vout2. The voltage converter 52 is a voltage converter that converts a voltage output from a rectifying and smoothing circuit having the rectifier 3 and the smoothing capacitor 4 and outputs a voltage Vout3. At least one of the voltage converters 50, 51, 52 has the converter circuit shown in FIG. 1 or FIG. The remaining two voltage converters may not include the overvoltage detection circuits 5 and 40 and the current bypass circuits 15 and 41. The voltages Vout1, Vout2, and Vout3 are, for example, + 24V, + 5V, + 3.3V, and the like. In addition, the voltage converter with which the power supply device 100 is provided may be one, two may be sufficient, and four or more may be sufficient. The number of voltage converters depends on how many types of voltage are required for an electronic device that is supplied with power from the power supply apparatus 100 and operates. The electronic device may be, for example, various devices such as an image forming device, a display device, a communication device, a recording / playback device, and an information processing device, and various household electric appliances. Hereinafter, an image forming apparatus equipped with the power supply apparatus 100 will be described as an example of an electronic device.

  In FIG. 6, an image forming apparatus 1000 is an electrophotographic printer that operates by supplying necessary power from the power supply apparatus 100. The photosensitive drum 122 is, for example, an organic photoconductor or an amorphous silicon photoconductor, and rotates clockwise at a predetermined peripheral speed (process speed) Vd. The charging roller 123 charges the peripheral surface of the photosensitive drum 122 to a uniform potential. The laser optical box 108 irradiates the peripheral surface of the photosensitive drum 122 with laser light modulated in accordance with image information input from an image signal generation device such as an image reading device or a computer. Thereby, an electrostatic latent image corresponding to the image information is formed. The exposure start timing in the sub scanning direction is determined by the sub scanning synchronization signal. That is, the laser optical box 108 functions as an image forming unit that forms an image on the image carrier with the synchronization signal as a starting point. The developing roller 121 develops the electrostatic latent image using toner to form a toner image.

  The paper feed roller 102 feeds the recording paper P from the paper cassette 101 to the transport path one by one. The paper cassette 101, the manual feed tray, and the like function as a storage unit that stores recording paper and supplies it to the conveyance path. The conveyance roller 103 and the registration roller 104 convey the recording paper P further downstream. The conveyance roller 103 and the registration roller 104 are an example of a plurality of conveyance units that convey the recording paper P from the paper cassette 101 to the transfer roller 106. The registration roller 104 is a conveying unit that is disposed closest to the transfer roller 106 among the plurality of conveying units. In the conveyance section from the registration roller 104 to the transfer roller 106, a top sensor 105 is disposed as a detection unit that detects the recording paper P. The top sensor 105 is disposed on the upstream side of the transfer roller 106 in the conveyance direction of the recording paper. Further, the conveyance roller 103 and the registration roller 104 are arranged on the upstream side of the transfer roller 106 in the conveyance direction of the recording paper. When the recording paper P passes through the transfer nip formed by the photosensitive drum 122 and the transfer roller 106, the toner image is transferred from the photosensitive drum 122. The transfer roller 106, the transfer blade, and the like function as a transfer unit that transfers an image formed on the image carrier onto a recording sheet. The thermal fixing device 130 includes a thermistor 131, a heater 132, a fixing film 133, and a pressure roller 134. The thermal fixing device 130 keeps the temperature of the heater 132 constant according to the temperature detected by the thermistor 131. The toner image is fixed to the recording paper P by the fixing film 133 and the pressure roller 134. The recording paper P is conveyed by the FU roller 110 and the FD roller 111 and discharged to the FD tray 113.

  The control circuits for controlling the various rollers and the image forming process described above are examples of loads that operate with power supplied from the power supply apparatus 100.

Claims (7)

Input means for inputting AC voltage from a commercial AC power source;
A blocking means provided in the input means, for cutting off the AC voltage when an overvoltage is applied to the input means for a predetermined time or more;
Rectifying and smoothing means for rectifying and smoothing the AC voltage input to the input means;
Voltage converting means for converting the output voltage from the rectifying and smoothing means;
Switching means for switching the voltage conversion means;
A current detection resistor for detecting a current flowing through the switching means;
Control means for controlling the switching means within a range in which the value of the current detected by the current detection resistor does not exceed a predetermined limit value, and controlling the voltage output from the voltage conversion means to be a target voltage; ,
When detecting that the voltage supplied from the commercial AC power supply is an overvoltage, an overvoltage detection unit that forcibly turns on the switching unit and guides the blocking unit to block the AC voltage;
A power supply apparatus, comprising: a bypass unit that is provided in parallel with the current detection resistor and that conducts when the overvoltage detection unit detects an overvoltage, and bypasses the current detection resistor to flow current.   The power supply according to claim 1, wherein the bypass unit includes an element that limits an increase in a voltage applied to the current detection resistor when the switching unit is forcibly turned on. apparatus.   The power supply device according to claim 1, wherein the bypass unit includes a Zener diode and a resistor connected in series to the Zener diode.   3. The power supply device according to claim 1, wherein the bypass unit includes a switch element and a resistor connected in series to a current inflow terminal or a current outflow terminal of the switch element. A delay circuit for delaying a drive signal for forcibly turning on the switching means among the drive signals output to the switching means and the switch element when the overvoltage detection means detects an overvoltage;
5. The power supply device according to claim 4, wherein when the overvoltage detection unit detects an overvoltage, the switch element is turned on before the switching unit. Input means for inputting AC voltage from a commercial AC power source;
A blocking means provided in the input means, for cutting off the AC voltage when an overvoltage is applied to the input means for a predetermined time or more;
Rectifying and smoothing means for rectifying and smoothing the AC voltage input to the input means;
A plurality of voltage converters connected to the rectifying / smoothing means and outputting different voltages, respectively;
At least one voltage converter of the plurality of voltage converters is
Voltage converting means for converting the output voltage from the rectifying and smoothing means;
Switching means for switching the voltage conversion means;
A current detection resistor for detecting a current flowing through the switching means;
Control means for controlling the switching means within a range in which the value of the current detected by the current detection resistor does not exceed a predetermined limit value, and controlling the voltage output from the voltage conversion means to be a target voltage; ,
When detecting that the voltage supplied from the commercial AC power supply is an overvoltage, an overvoltage detection unit that forcibly turns on the switching unit and guides the blocking unit to block the AC voltage;
A power supply apparatus, comprising: a bypass unit that is provided in parallel with the current detection resistor and that conducts when the overvoltage detection unit detects an overvoltage, and bypasses the current detection resistor to flow current. A power supply device according to any one of claims 1 to 6,
An electronic apparatus comprising: a load that operates with electric power supplied from the power supply device.