JP2013240240A - Secondary side discharge circuit for power conversion device, and power conversion device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To electrically discharge a secondary side smoothing capacitor to a predetermined charge voltage or less within a specified time while avoiding compromising standby power.SOLUTION: In a power conversion device having a primary side smoothing capacitor 6 disposed on a transformer primary side to smooth a rectified voltage of an AC voltage, a converter transformer 1 for converting primary side power to secondary side power, a rectification circuit 15 for rectifying a voltage induced on a secondary side, and a secondary side smoothing capacitor 19 for smoothing the voltage rectified by the rectification circuit 15, a secondary side discharge circuit 18 is provided for the secondary side smoothing capacitor 19. The secondary side discharge circuit 18 is connected in parallel with the secondary side smoothing capacitor 19, and is inoperative when the AC voltage on the transformer primary side is on and operative to electrically discharge the secondary side smoothing capacitor 19 to a predetermined voltage or less within a specified time when the AC voltage is off.

Description

  The present invention relates to a power converter such as a switching power supply that converts power from a converter transformer primary side using a converter transformer, and then smoothes and outputs from a converter transformer secondary side through a rectifier circuit using a secondary side smoothing capacitor. The present invention relates to a secondary-side discharge circuit that rapidly discharges a charging voltage charged in a secondary-side smoothing capacitor, and a power conversion device such as a switching power supply including the secondary-side discharge circuit.

  In general, a switching power supply rectifies the AC voltage on the primary side of the transformer and smoothes the voltage with a smoothing capacitor on the primary side, and then controls the switching frequency of the switching transistor connected to the primary winding of the transformer with a control circuit, thereby controlling the primary voltage. The side power is converted to the converter transformer secondary side, and further smoothed by the secondary side smoothing capacitor via the transformer secondary side rectifier circuit, and a required DC voltage is supplied to the load and output.

  Some of such switching power supplies can be set to a standby mode. For example, the switching power supply disclosed in Patent Document 1 includes a main power supply and a standby-dedicated sub-power supply. When the main power supply is stopped and the sub-power supply is driven to enter a standby mode, a high charge is applied to the primary-side smoothing capacitor of the main power supply. The discharge circuit provided in parallel to the primary side smoothing capacitor is driven so that the primary side smoothing capacitor is rapidly discharged.

  On the other hand, unlike the standby mode method in the switching power supply of Patent Document 1, a switching transistor is provided so that the standby mode can be set in an AC voltage ON state in which an AC voltage is input on the transformer primary side without providing a standby dedicated sub power source. There is a switching power supply that lowers the switching frequency to reduce loss and reduce power consumption to the required power (standby power) or less.

  With respect to such a standby mode type switching power supply, the primary side smoothing capacitor can be rapidly discharged by using the discharge circuit of Patent Document 1 when the AC voltage is turned off and no AC voltage is input on the transformer primary side. When the load is, for example, no load, the charging voltage of the secondary side smoothing capacitor remains without being discharged.

  In such a switching power supply, when the AC voltage is turned off and the charging voltage remaining in the secondary smoothing capacitor is discharged within a specified time, for example, a discharge resistor is connected in parallel to the secondary smoothing capacitor. It is proposed to discharge the charge of the secondary side smoothing capacitor through the discharge resistor within the specified time.

JP 2011-135702 A

  However, when the AC voltage is off and the secondary smoothing capacitor is rapidly discharged by the discharge resistor, the power consumption is always continued by the discharge resistor even when the standby mode is set when the AC voltage is on. There was a problem that electric power deteriorated.

  The present invention has been made in view of the above circumstances, and in a power converter that can be in a standby mode when the AC voltage is on, the charging voltage of the secondary-side smoothing capacitor is within a specified time when the AC voltage is off. It is an object of the present invention to provide a secondary side discharge circuit that enables discharge of a secondary side smoothing capacitor while avoiding deterioration of standby power in a steady state when discharging below a predetermined voltage.

  The present invention also provides a power conversion device that allows a primary side smoothing capacitor to discharge via a converter transformer by the secondary side discharge circuit when the secondary side smoothing capacitor rapidly discharges in the secondary side discharge circuit. The purpose is.

The secondary discharge circuit of the power converter according to the present invention includes a converter transformer that converts transformer primary power into transformer secondary power, a secondary rectifier circuit that rectifies the voltage induced on the transformer secondary side, A secondary-side smoothing capacitor for smoothing the voltage rectified by the secondary-side rectifier circuit, and enabling power saving by a standby mode when the AC voltage is input on the transformer primary side when the AC voltage is on In the conversion device, a secondary side discharge circuit for discharging the voltage of the secondary side smoothing capacitor,
The secondary-side discharge circuit is connected in parallel to the secondary-side smoothing capacitor, is inactive when the AC voltage is on, and operates when the AC voltage is off when no AC voltage is input on the transformer primary side. The operation of discharging the charging voltage of the capacitor is performed.

  In a preferred aspect of the present invention, the secondary-side discharge circuit performs an operation of discharging the charging voltage of the secondary-side smoothing capacitor to a predetermined voltage or less within a specified time when the AC voltage is off.

  In a preferred aspect of the present invention, the secondary discharge circuit includes a series circuit of a discharge resistor and a discharge switch connected in parallel to the secondary smoothing capacitor, and the discharge switch is turned on when the AC voltage is on. Open the secondary side discharge circuit so as not to operate, and short-circuit when the AC voltage is off, the secondary side discharge circuit is in an operating state, and the discharge resistor is connected in parallel to the secondary side smoothing capacitor. The charging voltage of the secondary side smoothing capacitor is discharged.

  In a preferred aspect of the present invention, the charging voltage of the primary side smoothing capacitor on the primary side of the transformer is discharged through the converter transformer.

A power converter according to the present invention includes a primary side rectifier circuit that rectifies an AC voltage on a transformer primary side, a primary side smoothing capacitor that smoothes a voltage rectified by the primary side rectifier circuit, and a transformer primary side power that is converted into a transformer. Converter transformer for converting to secondary side power, switching transistor connected to the primary winding of the converter transformer, control circuit for controlling the operating frequency of the switching transistor, and rectifying the voltage induced on the secondary side of the transformer A secondary side rectifier circuit and a secondary side smoothing capacitor for smoothing the voltage rectified by the secondary side rectifier circuit, and the control circuit receives an AC voltage on the transformer primary side. In the power converter that can be controlled to the standby mode in the steady state of the AC voltage on state,
A detection circuit for detecting an AC voltage off state where no AC voltage is input on the transformer primary side, a photocoupler that transmits a detection output of the detection circuit to the transformer secondary side, and the secondary discharge circuit of the present invention, Comprising at least
Control the operation of the photocoupler according to the detection signal of the detection circuit,
The secondary-side discharge circuit is inoperative when the AC voltage is on, and operates when the AC voltage is off, based on the operation state of the photocoupler, so that the charging voltage of the secondary-side smoothing capacitor is within a specified time. An operation of discharging to a predetermined voltage or less is performed.

  In a preferred aspect of the present invention, the control circuit performs control to lower the operating frequency of the switching transistor in the standby mode.

  In the power conversion device of the present invention, the secondary side discharge circuit is inoperative when the AC voltage is on and operates when the AC voltage is off to discharge the charging voltage of the secondary side smoothing capacitor. In standby mode, standby power is not consumed, and standby power can be prevented from deteriorating. At the same time, when the AC voltage is on, the charging voltage of the secondary side smoothing capacitor can be discharged to a predetermined voltage or less within a specified time. Further, when the converter transformer is in an operating state immediately after the AC voltage is turned off due to the remaining charging voltage of the primary side smoothing capacitor, the charging voltage of the primary side smoothing capacitor may be discharged by the secondary side discharging circuit via the converter transformer. it can.

  The secondary side discharge circuit for discharging the secondary side smoothing capacitor of the present invention is inactive when the AC voltage is on and operates when the AC voltage is off to discharge the charging voltage of the secondary side smoothing capacitor. It is possible to prevent the standby power from deteriorating in a steady state, and in addition, when the converter transformer is in an operating state when the AC voltage is off, the charge on the primary side smoothing capacitor can be discharged.

FIG. 1 is a schematic circuit diagram of a switching power supply according to an embodiment of the present invention.

  Hereinafter, an example of a power conversion device according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the embodiment, description will be made by applying the present invention to a flyback switching power supply as a power conversion device. Any power conversion device can be used as long as it converts power on the transformer primary side with a converter transformer, and then smoothes and outputs from the secondary side of the converter transformer via a rectifier circuit and a secondary side smoothing capacitor.

  FIG. 1 is a circuit diagram of a flyback switching power supply according to an embodiment.

  The switching power supply according to the embodiment includes a converter transformer 1 for power conversion. Converter transformer 1 electrically insulates and separates the primary side and the secondary side. On the primary side of the converter transformer 1, an AC power source 3 is connected between the input terminals 2a and 2b of the switching power source.

  The AC power source 3 is, for example, a 100V commercial AC power source having a frequency of 50 Hz. Further, an AC voltage within a range of 95 to 105 V, for example, is applied due to an error. Of course, the voltage and frequency of the AC power source in the applicable country and region may be used.

  The AC voltage is applied to both inputs of the primary side rectifier circuit 5 including a full wave rectifier circuit via a pair of AC voltage lines 4 a and 4 b and is full wave rectified by the primary side rectifier circuit 5. Both outputs of the primary side rectifier circuit 5 are connected between the high level and low level voltage lines 4a and 4b, and the positive side rectified voltage of the primary side rectifier circuit 5 is smoothed by the primary side via the high level voltage line 4a. The voltage is applied to the plus side electrode of the capacitor 6 and smoothed by the primary side smoothing capacitor 6.

  The converter transformer 1 includes a primary winding L1 and an auxiliary winding L3 on the primary side, and a secondary winding L2 on the secondary side. The positive electrode of the primary side smoothing capacitor 6 is connected to the positive side terminal (black circle terminal) of the primary winding L1 through the high level voltage line 4a. The drain electrode of the n-channel MOSFET 7 (MOS field effect transistor), which is a switching transistor, is connected to the negative terminal (terminal without a black circle) of the primary winding L1. The type of MOSFET 7 is not particularly limited. Further, the switching transistor is not limited to the MOSFET 7, and may be another type transistor such as a bipolar type.

  The source electrode of the MOSFET 7 is connected to the low level voltage line 4 b and its gate electrode is connected to the control output unit 8 a of the control circuit 8. A switching operation voltage is supplied from the control output unit 8a to the gate electrode of the MOSFET 7. The control circuit 8 has a power supply receiving unit 8b. The AC voltage induced at the positive terminal (black circle terminal) of the auxiliary winding L3 of the converter transformer 1 is rectified by the rectifier diode 9, smoothed by the smoothing capacitor 10, and supplied to the power supply receiving unit 8b as a DC voltage. The

  The control circuit 8 includes a detection output input unit 8c, and the detection output input from the detection unit 11 on the secondary side of the converter transformer 1 is input to the detection output input unit 8c. The switching operation frequency of the MOSFET 7 can be controlled according to the detection output. For example, when the output voltage is higher or lower than a predetermined voltage, the on / off duty at the switching operation frequency is controlled so that the output voltage can be controlled to the constant predetermined voltage value. Such a control circuit 8 can be realized by a known control IC, and a detailed description of the internal configuration and operation is omitted.

  Although not shown, when a signal indicating whether the mode is the steady mode or the standby mode is input to the control circuit 8 from, for example, the output load 12 connected between the output terminals 20a and 20b, the control circuit 8 Corresponding to the standby mode, the switching operation frequency of the MOSFET 7 may be controlled. For example, in the standby mode, the control circuit 8 can reduce the loss by reducing the switching operation frequency of the MOSFET 7 and can reduce the power consumption below the required power (standby power). The standby mode is not limited to the above, and other standby mode methods may be used, such as increasing the off-duty of the MOSFET 7 that is a switching transistor. In this case, the signals of the steady mode and the standby mode input from the output load 12 side are arbitrary, and of course are not limited to the embodiment.

  Examples of the load 12 include various types of loads such as a liquid crystal television display device, a backlight LED driving device, and a backlight inverter circuit, and are not particularly limited. Of course, there is a case where no load is connected between the output terminals 20a and 20b.

  The primary side of the converter transformer 1 is provided with a detection circuit 13 that detects whether the AC voltage is not input and the AC voltage is OFF or the AC voltage is input. The detection circuit 13 has two input parts 13a and 13b and two output parts 13c and 13d, and the two input parts 13a and 13b are connected in parallel to the AC power source 3 to input an AC voltage, and one output part 13d. Is connected to the low level voltage line 4b, and the other output section 13c is connected to the cathode of the light emitting diode 14a of the photocoupler 14 as a signal output section.

  The detection circuit 13 outputs a low level detection signal from the signal output unit 13c in the steady state when the AC voltage is input and the AC voltage is input to the two input units 13a and 13b, and the AC voltage is not input. In the case of time, a high level detection signal can be output from the signal output unit 13c.

  The photocoupler 14 includes a light-emitting diode 14a and a light-receiving transistor 14b that receives light emitted from the light-emitting diode 14a and has a collector / emitter that is conductive. The anode of the light emitting diode 14a is connected to the plus side terminal of the auxiliary winding L3, and the low level and high level detection signals from the output part 13c of the detection circuit 13 are applied. When the detection signal is a low level detection signal, current is supplied to the light emitting diode 14a from the auxiliary winding L3 to conduct light, and this detection signal is a high level detection signal indicating that the AC voltage is off. The light emitting diode 14a becomes non-conductive and does not emit light. The light receiving transistor 14b of the photocoupler 14 is turned on when the light emitting diode 14a emits light, and is turned off when the light emitting diode 14a does not emit light.

  The anode of the rectifier diode 15, which is a secondary rectifier circuit, is connected to the negative terminal (the terminal without a black circle) of the secondary winding L2 of the converter transformer 1, and the cathode of the rectifier diode 15 is at a high level. The positive side electrode of the secondary side smoothing capacitor 19 is connected via the voltage line 16a, and the negative side electrode of the secondary side smoothing capacitor 19 is connected to the positive side terminal of the secondary winding L2 via the low level voltage line 16b. Connected to (black circle terminal). A resistance voltage dividing circuit 17 comprising a series connection circuit of first and second resistors 17a and 17b is connected between the secondary high-level voltage line 16a and the low-level voltage line 16b. The collector / emitter of the light receiving transistor 14b of the photocoupler 14 is connected in parallel to the second resistor 17b in the resistance voltage dividing circuit 17.

  In the present embodiment, a discharge circuit 18 is connected in parallel to the secondary side smoothing capacitor 19 between the high level voltage line 16a and the low level voltage line 16b on the secondary side of the converter transformer 1. The discharge circuit 18 is configured by connecting a discharge resistor 18a and a MOSFET 18b as a discharge switch. One end of the discharge resistor 18a is connected to the high level voltage line 16a, and the other end of the discharge resistor 18a is the drain of the MOSFET 18b. It is connected to the. A second resistor 17b of the resistor voltage dividing circuit 17 is connected between the gate and source of the MOSFET 18b.

  In the above configuration, in the AC voltage on steady mode, the AC voltage of the AC power supply 3 is full-wave rectified by the primary side rectifier circuit 5, and the rectified voltage is smoothed by the primary side smoothing capacitor 6. The voltage smoothed by the primary side smoothing capacitor 6 is applied to the plus side terminal of the primary winding L1 of the converter transformer 1. Then, the control circuit 8 causes the MOSFET 7 to perform a switching operation at a required switching operation frequency, and the smoothed voltage is converted into a predetermined voltage on the secondary side of the converter transformer 1 and induced between both ends of the secondary winding L2. Is done.

  The voltage induced across the secondary winding L2 is rectified by the rectifier diode 15 and smoothed by the secondary side smoothing capacitor 19 and supplied to the output load 12 as a DC voltage. In this case, since AC voltage is applied to the input parts 13a and 13b of the detection circuit 13, the detection circuit 13 detects that the AC voltage is on, and outputs a low level detection signal from the output parts 13c and 13d to the photocoupler 14. To the light emitting diode 14a. As a result, the light emitting diode 14a emits light, and the light receiving transistor 14b of the photocoupler 14 receives the light and conducts. When the light receiving transistor 14b becomes conductive, the gate-source voltage of the MOSFET 18b of the discharge circuit 18 becomes 0V, and the MOSFET 18b becomes non-conductive. As a result, the discharge resistor 18 a is not connected to the secondary side smoothing capacitor 19, and the charging voltage of the secondary side smoothing capacitor 19 is not discharged through the discharge circuit 18.

  In the steady mode, when the standby mode is set, the control circuit 8 receives a standby mode signal from a circuit (not shown) or the output load 12 side. The control circuit 8 performs control to lower the switching frequency of the switching transistor 7 in response to the input of the standby mode signal. As a result, the standby mode is set, and the power is controlled to be reduced below the required standby power.

  In this case, in the steady mode, as described above, since the discharge circuit 18 is not operating, the charging voltage of the secondary side smoothing capacitor 19 is not discharged, and the standby power does not deteriorate.

  Next, when the AC voltage is turned off, this AC voltage off is detected by the detection circuit 13, and a high level detection signal is applied from the detection circuit 13 to the cathode of the light emitting diode 14a of the photocoupler 14, thereby causing the light emitting diode 14a to No current flows, and the light emitting diode 14a stops emitting light. When the light emitting diode 14a stops emitting light, the light receiving transistor 14b of the photocoupler 14 becomes non-conductive, and a divided voltage across the second resistor 17b of the resistor voltage dividing circuit 17 is applied between the gate and source of the MOSFET 18 of the discharge circuit 18. Will be. As a result, the MOSFET 18 of the discharge circuit 18 becomes conductive. As a result, the discharge resistor 18a of the discharge circuit 18 is connected in parallel to the secondary side smoothing capacitor 19, and the charge voltage of the secondary side smoothing capacitor 19 is the discharge resistance of the discharge circuit 18. 18a discharges below a predetermined voltage within a specified time.

  In this case, in order to discharge the charging voltage of the secondary side smoothing capacitor 19 to a predetermined voltage or less within a specified time, at the time of discharge consisting of the product of the capacitance value of the secondary side smoothing capacitor 19 and the resistance value of the discharge resistor 18a. The constant and the charging voltage of the secondary side smoothing capacitor 19 can be appropriately determined by experiments or the like.

  Further, the number of discharge resistors 18a is one in the embodiment, but the number is not limited to one, and a plurality of resistors may be connected in series and / or in parallel, or other discharge resistors 18a may be substituted. Of course, a discharge element may be used. Further, in the discharge circuit 18, the MOSFET 18 serving as a discharge switch is an n-channel type MOSFET, but may be other types of transistors such as a bipolar type.

  In this way, when the AC voltage is off, the charge of the secondary side smoothing capacitor 19 is discharged by the discharge circuit 18, but when a high charging voltage remains in the primary side smoothing capacitor 6 immediately after the AC voltage is turned off. The converter transformer 1 is in an operating state, and the charge on the primary side smoothing capacitor 6 is discharged by the discharge circuit 18 via the converter transformer 1.

  As described above, in this embodiment, the control circuit 8 controls the switching frequency of the MOSFET 7 to be lowered when the standby mode is entered when the AC voltage is in a steady state, and loss reduction and power consumption are required for the standby mode. In this case, since the discharge circuit 18 does not operate, the secondary side smoothing capacitor and the primary side smoothing capacitor are not discharged, and therefore the standby power does not deteriorate.

  In this embodiment, when the AC voltage is turned off, the discharge circuit 18 operates to discharge the charging voltage of the secondary side smoothing capacitor 19 to a predetermined voltage or less within a specified time, and at the same time, the primary side smoothing capacitor 6 The charged electric charge can be discharged by the discharge circuit 18 via the converter transformer 1, and the circuit configuration can be simplified.

  The standby power consumption in the standby mode in the conventional switching power supply (standby power before improvement) is compared with the standby power consumption in the standby mode in the switching power supply according to the present invention (standby power after improvement). While the power was 1.4 W, the standby power after improvement in the present invention was 0.45 W, and the standby power was greatly improved in the present invention.

  In the measurement of the standby power, the switching frequency of the MOSFET 7 by the control circuit 8 is 1.5 kHz, the AC voltage is 230 V, the frequency of the AC voltage is 50 Hz, and the resistance value of the discharge resistor 18 a of the discharge circuit 18 of the present invention is 33Ω. In the conventional switching power supply, a discharge resistor having the same resistance value as that of the discharge resistor 18a is connected in parallel to the secondary smoothing capacitor.

  As described above, in the present embodiment, the secondary side discharge circuit 18 is inoperative when the AC voltage is on and operates when the AC voltage is off to discharge the charging voltage of the secondary side smoothing capacitor 19. Is in standby mode with the AC voltage on, standby power is not consumed, and standby power deterioration can be prevented. When the AC voltage is off, the charging voltage of the secondary side smoothing capacitor 19 can be discharged to a predetermined voltage or less within a specified time. When the converter transformer 1 is in an operating state immediately after the AC voltage is turned off due to the remaining charging voltage of the primary side smoothing capacitor 6, the charging voltage of the primary side smoothing capacitor 6 is supplied to the secondary side discharge circuit 18 via the converter transformer 1. Can be discharged.

DESCRIPTION OF SYMBOLS 1 Converter transformer 3 AC power supply 5 Full wave rectification circuit 6 Primary side smoothing capacitor 7 Switching transistor 8 Control circuit 12 Output load 13 Detection circuit 14 Photocoupler 17 Resistance voltage dividing circuit 18 Discharge circuit 19 Secondary side smoothing capacitor

Claims (6)

A converter transformer that converts transformer primary side power into transformer secondary side power, a secondary side rectifier circuit that rectifies the voltage induced on the transformer secondary side, and a voltage rectified by the secondary side rectifier circuit is smoothed In a power converter that includes a secondary-side smoothing capacitor to enable power saving in a standby mode when an AC voltage is input on the transformer primary side when the AC voltage is turned on.
A secondary side discharge circuit for discharging the voltage of the secondary side smoothing capacitor,
The secondary-side discharge circuit is connected in parallel to the secondary-side smoothing capacitor, is inactive when the AC voltage is on, and operates when the AC voltage is off when no AC voltage is input on the transformer primary side. The secondary side discharge circuit characterized by performing the operation | movement which discharges the charge voltage of a capacitor | condenser.   The secondary-side discharge circuit according to claim 1, wherein the secondary-side discharge circuit performs an operation of discharging a charging voltage of the secondary-side smoothing capacitor to a predetermined voltage or less within a specified time when the AC voltage is off. The secondary side discharge circuit is formed by connecting a series circuit of a discharge resistor and a discharge switch in parallel to the secondary side smoothing capacitor,
The discharge switch is opened when the AC voltage is on to deactivate the secondary-side discharge circuit, and is short-circuited when the AC voltage is off to place the secondary-side discharge circuit in an operating state so that the discharge resistance is The secondary side discharge circuit according to claim 1 or 2, wherein the secondary side smoothing capacitor is connected in parallel to discharge a charging voltage of the secondary side smoothing capacitor.   The secondary side discharge circuit according to any one of claims 1 to 3, wherein a charging voltage of a primary side smoothing capacitor on a transformer primary side is discharged through the converter transformer. A primary-side rectifier circuit that rectifies an AC voltage on the transformer primary side, a primary-side smoothing capacitor that smoothes the voltage rectified by the primary-side rectifier circuit, and a converter that converts the transformer primary-side power into transformer secondary-side power. A transformer, a switching transistor connected to a primary winding of the converter transformer, a control circuit for controlling an operating frequency of the switching transistor, a secondary side rectifier circuit for rectifying a voltage induced on the transformer secondary side, A secondary-side smoothing capacitor for smoothing the voltage rectified by the secondary-side rectifier circuit, and the control circuit is in a steady state in an AC voltage ON state where an AC voltage is input on the transformer primary side. In the power converter that can be controlled to the standby mode,
A detection circuit for detecting a state in which the AC voltage is off when no AC voltage is input on the primary side of the transformer;
A photocoupler for transmitting the detection output of the detection circuit to the transformer secondary side;
A secondary-side discharge circuit according to claim 1,
Control the operation of the photocoupler according to the detection signal of the detection circuit,
The secondary-side discharge circuit is inoperative when the AC voltage is on, and operates when the AC voltage is off, based on the operating state of the photocoupler, and sets the charging voltage of the secondary-side smoothing capacitor within a specified time. Perform the operation of discharging below the voltage,
The power converter characterized by the above-mentioned.   The power converter according to claim 5, wherein the control circuit performs control to reduce an operating frequency of the switching transistor in the standby mode.

Images