JP2012090466A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply device with higher output voltage accuracy while surge breakdown voltage is improved with a simple structure.SOLUTION: The switching power supply device including a primary side circuit and a secondary side circuit includes: a detection circuit detecting output voltage of the secondary side circuit; and a relay circuit feeding back a detection result of the detection circuit to the primary side circuit in a state where the circuit is electrically insulated from the primary side circuit and the secondary side circuit. The detection circuit includes a first light emitting element emitting light in a light volume corresponding to the detected output voltage. The relay circuit includes a first light receiving element receiving light from the first light emitting element and generating current corresponding to the light volume; and a second light emitting element emitting the light in the light volume corresponding to a size of the current generated by the first light emitting element. The primary side circuit has a second light receiving element receiving light from the second light emitting element and generating the current corresponding to the light volume. The primary side circuit on/off-controls the current of primary winding based on the size of the current generated by the second light receiving element.

Description

  The present invention relates to a switching power supply device that converts an AC power supply voltage into a DC power supply voltage, and more particularly to a switching power supply device that can increase a surge withstand voltage between a primary side circuit and a secondary side circuit.

  In recent years, switching power supply devices are used in various electronic devices. The switching power supply device includes a rectifier circuit connected to an AC power supply (commercial power supply), a smoothing capacitor that smoothes the rectified output from the rectifier circuit, a transformer that is supplied with a DC voltage from the smoothing capacitor, and a smoothing capacitor. Switching element to which the direct current voltage is supplied via the primary winding of the transformer. The switching element is ON / OFF controlled by a switching control circuit, and the energy stored in the primary winding during the OFF period of this switching element is excited in the secondary winding during the ON period of the switching element and is generated in the secondary winding. DC voltage output is obtained by rectifying the voltage. In order to obtain a stable DC voltage output, the fluctuation of the DC voltage output is monitored and fed back to the switching control circuit to control the on / off time of the switching element. For monitoring and feedback of fluctuations in DC voltage output, a photocoupler is used for the purpose of maintaining insulation between the primary side circuit and the secondary side circuit (for example, Patent Document 1).

JP 2009-153234 A

  As described above, the switching power supply device outputs a predetermined voltage required by the device, and is usually connected to a commercial power supply. Therefore, it is designed to conform to various safety standards. For example, in a configuration such as Patent Document 1, a high withstand voltage (for example, a surge withstand voltage between the primary side circuit and the secondary side circuit conforms to the safety standard (for example, 5 kV), a dielectric breakdown voltage between the primary side circuit and the secondary side circuit is guaranteed. When switching power supplies are used in equipment that requires constant power supply, such as telephone exchanges and servers, a particularly high level of reliability is required, and the surge withstand voltage is higher than the surge withstand voltage required by safety standards. However, in the configuration of Patent Document 1, since the surge withstand voltage depends on the withstand voltage of the photocoupler, only the withstand voltage of the photocoupler can be guaranteed.

  As a method of increasing the surge withstand voltage, it is possible to monitor and feed back the voltage generated in the primary side auxiliary winding without using a photocoupler, but the configuration that directly monitors the voltage of the secondary side circuit that varies depending on the load Therefore, the accuracy of the output voltage is worse than the configuration using the photocoupler.

  The present invention has been made to solve the above problems. That is, an object of the present invention is to provide a switching power supply device with high breakdown voltage and high output voltage accuracy.

  In order to achieve the above object, a switching power supply device according to the present invention includes a primary winding, a switching element connected to the other end of the primary winding for turning on / off a current flowing in the primary winding, and an on / off switching element. A switching power supply comprising: a primary side circuit having a control circuit for controlling OFF; a secondary side circuit having a secondary winding; and a DC circuit for rectifying and smoothing a voltage generated in the secondary winding. A detection circuit for detecting an output voltage of the DC circuit, and a relay circuit for feeding back a detection result of the detection circuit to the control circuit in a state of being electrically insulated from the primary side circuit and the secondary side circuit; And the detection circuit includes a first light emitting element that emits light of a light amount corresponding to the detected output voltage, and the relay circuit receives the incident light and generates a current corresponding to the light amount. 1 light receiving element and the first light receiving element And a second light emitting element that is connected in series with the optical element and emits light of a light amount corresponding to the magnitude of the current generated by the first light receiving element, and the control circuit includes the second light emitting element The control circuit has a second light receiving element that receives light from the light and generates a current corresponding to the light amount, and the control circuit turns on / off the switching element based on the magnitude of the current generated by the second light receiving element. And the relay circuit receives the light from the first light emitting element.

  With such a configuration, the light of the first light emitting element is relayed between the first light receiving element and the second light emitting element of the relay circuit and sent to the second light receiving element for feedback control. That is, since the primary side circuit and the secondary side circuit are electrically insulated via the two sets of light emitting elements and light receiving elements, the surge withstand voltage is doubled as compared with the prior art. Further, since the output voltage is fed back to the primary circuit by the light emitting element and the light receiving element, the output voltage can be controlled with high accuracy.

  In addition, it is preferable that the relay circuit has a third winding insulated from the primary winding and the secondary winding. With such a configuration, the relay circuit can be easily configured.

  Further, it is preferable that the first light emitting element and the first light receiving element constitute a first photocoupler, and the second light emitting element and the second light receiving element constitute a second photocoupler.

  The first relay circuit receives N light from the first light emitting element and emits light toward the second relay circuit, and the nth (n is 2 or more). , An integer equal to or less than N−1) receives light from the (n−1) th relay circuit, emits light toward the (n + 1) th relay circuit, and the Nth relay circuit , (N-1) light from the relay circuit may be received to emit light toward the second light receiving element. By adopting such a configuration, the surge breakdown voltage can be further increased.

  Moreover, it is preferable that the impedance between the primary side circuit and the relay circuit is substantially equal to the impedance between the secondary side circuit and the relay circuit. In this case, a first resistor inserted between the ground of the primary circuit and the ground of the relay circuit, and a second resistor inserted between the ground of the secondary circuit and the ground of the relay circuit Further, the impedance of the first resistor is lower than the impedance between the primary circuit and the relay circuit, and the impedance of the second resistor is lower than the impedance between the secondary circuit and the relay circuit It is also good. By adopting such a configuration, it becomes possible to match the impedance when the relay circuit is viewed from the primary circuit and the impedance when the relay circuit is viewed from the secondary circuit, and a stable surge withstand voltage can be obtained. Obtainable.

  Alternatively, the primary side circuit may have a primary auxiliary winding, and the control circuit may be driven by a DC voltage obtained by rectifying and smoothing the voltage generated in the primary auxiliary winding. With such a configuration, the circuit can be simplified.

  As described above, according to the present invention, it is possible to provide a switching power supply device with high breakdown voltage and high output voltage accuracy.

1 is a circuit diagram showing a configuration of a switching power supply device according to a first embodiment of the present invention. It is a circuit diagram which shows the structure of the switching power supply device which concerns on the 2nd Embodiment of this invention.

  A switching power supply device according to an embodiment of the present invention will be described below.

  FIG. 1 is a circuit diagram of a switching power supply device 1 according to the first embodiment of the present invention. The switching power supply device 1 according to the present embodiment is a power supply device that converts AC power input to the primary side circuit by the transformer 400 and outputs constant DC power to the secondary side circuit. The transformer 400 includes a primary side winding 120, a primary side auxiliary winding 150, a secondary side winding 220, and an intermediate winding 320. The primary side circuit of the switching power supply 1 includes a diode bridge circuit 110, a capacitor 115, a primary side winding 120, an FET 125, resistors 126 and 127, a control IC 130, a primary side auxiliary winding 150, a diode 155, a capacitor 145, which will be described later. A second phototransistor 140 constituting the second photocoupler 205 is included. The secondary circuit of the switching power supply device 1 includes a secondary winding 220, a diode 210, a capacitor 215, resistors 225, 240 and 245, a shunt regulator 235, and a first light emitting diode 230. Further, the switching power supply device 1 includes an optical relay circuit 300 including an intermediate winding 320, a diode 310, a first phototransistor 330, a second light emitting diode 340, and a resistor 345. The first light emitting diode 230 and the first phototransistor 330 constitute a first photocoupler 200 (dotted line portion), and light emitted from the first light emitting diode 230 is received by the first phototransistor 330 and subjected to photoelectric conversion. The second light emitting diode 340 and the second phototransistor 140 constitute a second photocoupler 205 (dotted line portion), and light emitted from the second light emitting diode 340 is received by the second phototransistor 140 and subjected to photoelectric conversion. Is done. Note that the circuit of FIG. 1 is illustrated in a simplified manner for convenience of explanation.

  The commercial power supply (AC 100 to 220 V) input (applied) to the diode bridge circuit 110 is rectified by the diode bridge circuit 110, smoothed by the capacitor 115, and generates a primary DC voltage V1 between the terminals of the capacitor 115. Note that the negative terminal side of the capacitor 115 is connected to the negative terminal side of the diode bridge circuit 110 and is at the ground level (GND1) of the primary side circuit. The primary DC voltage V <b> 1 is supplied to one end of the primary winding 120 of the transformer 400 and the VH terminal of the control IC 130.

  The other end of the primary winding 120 is connected to the drain terminal of the FET 125. Further, the source terminal of the FET 125 is connected to the GND1 (ground) of the primary circuit and the IS terminal of the control IC 130 via the resistors 126 and 127, and the gate terminal is connected to the OUT terminal of the control IC 130.

  The FET 125 is, for example, a power MOSFET (Metal-Oxide Semiconductor Field-Effect Transistor), and a current flowing between the drain terminal and the source terminal is controlled by a voltage input to the gate terminal. The FET 125 of this embodiment is an N-type MOSFET, and is configured such that a current flows (that is, turns on) between the drain terminal and the source terminal when the voltage input to the gate terminal rises.

  The control IC 130 is an IC for controlling on / off of the FET 125. The control IC 130 has a clock (not shown) inside, generates a switching pulse of a predetermined frequency, and outputs it from the OUT terminal of the control IC 130. When a switching pulse is input to the gate terminal of the FET 125, the FET 125 is turned on, and a current (primary current) caused by the primary DC voltage V1 passes through the primary side winding 120, the FET 125, and the resistor 126, and GND1 of the primary side circuit. (Ground). While the FET 125 is on, magnetic energy is stored in the primary winding 120 by the current flowing through the primary winding 120. When the FET 125 is turned off, the secondary side winding 220 and the primary side auxiliary winding are configured such that the magnetic energy stored in the primary side winding 120 has a polarity opposite to that of the primary side winding 120. 150 and the intermediate winding 320. That is, the FET 125 is intermittently turned on / off under the control of the control IC 130, thereby intermittent voltage is induced in the secondary winding 220, the primary auxiliary winding 150, and the intermediate winding 320.

  The voltage induced in the primary side auxiliary winding 150 is rectified by the diode 155, smoothed by the capacitor 145, and applied to the Vcc terminal (power supply terminal) of the control IC 130. In addition, since no voltage is induced in the primary side auxiliary winding 150 at the time of starting, a starting circuit (not shown) built in the control IC 130 supplies a current caused by the primary DC voltage V1 to the VH terminal of the control IC 130. The control IC 130 is activated by supplying the signal.

  The source terminal of the FET 125 is connected to the IS terminal of the control IC 130 via the resistor 127. The FET 125 and the resistor 126 constitute a so-called source follower, and the voltage at the source terminal of the FET 125 is proportional to the current flowing through the FET 125. The control IC 130 detects an overcurrent by monitoring the voltage applied to the IS terminal.

  The collector of the second phototransistor 140 is connected to the FB terminal of the control IC 130, and the emitter of the second phototransistor 140 is connected to GND1. As will be described later, the second phototransistor 140 receives light from the second light emitting diode 340 whose light amount varies depending on the voltage value of the secondary DC voltage V2 (DC output), and photoelectrically converts the light to the received light amount. Apply the appropriate current. The control IC 130 detects the voltage value of the secondary DC voltage V2 from the current flowing through the second light emitting diode 340 so that the voltage value of the secondary DC voltage V2 becomes constant (that is, flows through the second light emitting diode 340). The duty ratio of the switching pulse supplied to the FET 125 is changed so that the current becomes constant. As described above, controlling the duty ratio of FET 125 (i.e., the time during which it is turned on) is nothing but controlling the magnetic energy stored in the primary winding 120, so that the secondary winding is thereby controlled. The voltage induced in 220 can be controlled. As described above, the voltage value of the secondary DC voltage V2 is fed back to the electrically isolated primary circuit by the second light emitting diode 340 and the second phototransistor 140.

  The voltage intermittently induced across the secondary winding 220 is rectified by the diode 210 and smoothed by the capacitor 215 to generate the secondary DC voltage V2. The secondary DC voltage V2 is supplied as a DC output to a load (not shown).

  The first light emitting diode 230, the shunt regulator 235, and the resistors 225, 240, and 245 constitute a secondary DC voltage monitor circuit.

  The shunt regulator 235 is an element that controls the current flowing through the shunt regulator 235 by the voltage of the reference terminal. The resistors 240 and 245 are inserted in series between the secondary DC voltage V2 and the GND2 (ground) of the secondary circuit, and the voltage at the connection point of the resistors 240 and 245 is applied to the reference terminal of the shunt regulator 235. . When the voltage at the reference terminal of the shunt regulator 235 is smaller than a predetermined value, the current flowing through the shunt regulator 235 decreases. Conversely, when the voltage at the reference terminal is larger than the predetermined value, the current flowing through the shunt regulator 235 is large. Become. Therefore, the current flowing through the first light emitting diode 230 via the resistor 225, that is, the light emission amount of the first light emitting diode 230 is controlled by the voltage at the reference terminal. In the case of the present embodiment, a voltage obtained by dividing the secondary DC voltage V2 by the resistors 240 and 245 is applied to the reference terminal of the shunt regulator 235, so that the first DC voltage V2 varies depending on the voltage value of the secondary DC voltage V2. The light emission amount of the light emitting diode 230 changes.

  The intermediate winding 320, the diode 310, the capacitor 315, the first phototransistor 330, the second light emitting diode 340, and the resistor 345 constitute the optical relay circuit 300. The intermediate winding 320 is a winding of the transformer 400 that is insulated from each of the primary side winding 120, the secondary side winding 220, and the primary side auxiliary winding 150. As described above, intermittent current flows through the primary winding 120, thereby inducing intermittent voltage across the intermediate winding 320. This voltage is rectified by the diode 310 and smoothed by the capacitor 315 to generate the intermediate DC voltage V3. A first phototransistor 330, a second light emitting diode 340, and a resistor 345 are inserted in series between the intermediate DC voltage V3 and its ground (GND3).

  The first phototransistor 330 passes a current substantially proportional to the light from the first light emitting diode 230. Then, this current flows into the GND 3 via the second light emitting diode 340 and the resistor 345. At this time, the second light emitting diode 340 emits light with a light amount corresponding to the current generated in the first phototransistor 330. Since the current generated in the first phototransistor 330 is based on the light quantity of the first light emitting diode 230, that is, the voltage value of the secondary DC voltage V2, the light quantity of the second light emitting diode 340 is equal to the secondary DC voltage V2. It represents the voltage value. The light emitted from the second light emitting diode 340 is received by the second phototransistor 140, and the feedback control described above is performed.

  As described above, in the switching power supply device 1 of the present embodiment, light having a light amount corresponding to the voltage value of the secondary DC voltage V <b> 2 is output from the first light emitting diode 230. The light emitted from the first light emitting diode 230 is relayed by the first phototransistor 330 and the second light emitting diode 340 (that is, the optical relay circuit 300) insulated from the primary side circuit and the secondary side circuit, Two phototransistors 140 are configured to be sent. That is, the primary side circuit and the secondary side circuit are electrically connected via two photocouplers (first photocoupler 200 and second photocoupler 205) inserted in series between the primary side circuit and the secondary side circuit. Is insulated. Therefore, the surge withstand voltage when a surge voltage is applied between the primary side circuit and the secondary side circuit is the sum of the surge withstand voltage of the first photocoupler 200 and the surge withstand voltage of the second photocoupler 205. Compared with the configuration in which the primary side circuit and the secondary side circuit are insulated by one photocoupler, the surge withstand voltage is doubled. Further, since the voltage value of the secondary DC voltage V2 is fed back to the primary side circuit by the photocoupler, the output voltage can be controlled with high accuracy.

  The impedance when the optical repeater circuit 300 is viewed from the primary circuit is considered to be the impedance between the second phototransistor 140 and the second light emitting diode 340, and the impedance when the optical repeater circuit 300 is viewed from the secondary circuit. The impedance is considered as the impedance between the first phototransistor 330 and the first light emitting diode 230. Accordingly, when the circuit arrangement and wiring conditions of the first photocoupler 200 and the second photocoupler 205 are substantially equal, both impedances are approximately equal, and when a surge voltage is applied between the primary side circuit and the secondary side circuit, This surge voltage is applied substantially equally between the first phototransistor 330 and the first light emitting diode 230 and between the second phototransistor 140 and the second light emitting diode 340. Therefore, no surge voltage is applied to one of the photocouplers, and the photocoupler is not destroyed.

  Next, as the second embodiment of the present invention, the impedance when the optical repeater circuit 300 is viewed from the primary circuit and the impedance when the optical repeater circuit 300 is viewed from the secondary circuit are matched. A switching power supply device will be described. The conditions such as circuit arrangement of the first photocoupler 200 and the second photocoupler 205 are different, the impedance when the optical repeater circuit 300 is viewed from the primary circuit, and the optical repeater circuit 300 when viewed from the secondary circuit. If the impedance is different, it is desirable to match both impedances.

  FIG. 2 is a circuit diagram showing a configuration of a switching power supply apparatus 1M according to the second embodiment of the present invention. The switching power supply device 1M according to the present embodiment is obtained by adding resistors 350 and 355 for matching impedance to the switching power supply device 1 according to the first embodiment shown in FIG. In FIG. 2, the same reference numerals as those in FIG. 1 are assigned to configurations common to the first embodiment.

  As shown in FIG. 2, in the switching power supply device 1M of the present embodiment, the ground terminal G1 (GND1) of the primary circuit and the ground terminal G3 (GND3) of the optical relay circuit 300 are connected via a resistor 355. The ground terminal G2 (GND2) of the secondary circuit and the ground terminal G3 of the optical relay circuit 300 are connected via a resistor 350.

  The resistor 350 is a resistor having an impedance lower than the impedance between the first phototransistor 330 and the first light emitting diode 230 (for example, about 1/10), and the resistor 355 is the second phototransistor 140 and the second light emitting diode. A resistor having an impedance lower than the impedance between 340 (eg, about 1/10). In this case, the impedance when the optical repeater circuit 300 is viewed from the primary circuit is considered to be a combined impedance of the impedance between the first phototransistor 330 and the first light emitting diode 230 and the impedance of the resistor 355. The impedance when the optical repeater circuit 300 is viewed from the secondary circuit is considered to be a combined impedance of the impedance between the second phototransistor 140 and the second light emitting diode 340 and the impedance of the resistor 350. Therefore, by adjusting the resistance values of the resistor 350 and the resistor 355, the impedance when the optical repeater circuit 300 is viewed from the primary circuit and the impedance when the optical repeater circuit 300 is viewed from the secondary circuit are accurately determined. Can be matched.

  As described above, according to the switching power supply device 1M of the present embodiment, the impedance when the optical repeater circuit 300 is viewed from the primary circuit and the impedance when the optical repeater circuit 300 is viewed from the secondary circuit are obtained. Since matching is possible, when a surge voltage is applied between the primary side circuit and the secondary side circuit, the surge voltage is applied between the first phototransistor 330 and the first light emitting diode 230, and between the second phototransistor 140 and the second phototransistor 140. And the second light emitting diode 340 are equally added. For example, when the withstand voltage of the first photocoupler 200 and the second photocoupler 205 is 5 kV, even if a surge voltage exceeding 5 kV is applied, these two photocouplers are connected in series, and therefore applied to each photocoupler. If the applied voltage falls below 5 kV, the photocoupler will not be damaged. That is, when there are two photocouplers, the maximum allowable surge voltage is 10 kV.

  As described above, in the first and second embodiments of the present invention, the light of the first light emitting diode 230 is transmitted through the one optical relay circuit 300 (that is, the first phototransistor 330 and the second light emitting diode 340). Although described as a configuration for relaying to two phototransistors 140, the present invention is not limited to this configuration, and a configuration in which a plurality of optical relay circuits 300 are provided so that light is sequentially propagated between a plurality of photocouplers. Also good. By adopting such a configuration, the surge withstand voltage between the primary and secondary is further increased. Even in this case, the impedance when the optical repeater circuit 300 is viewed from the primary circuit and the impedance when the optical repeater circuit 300 is viewed from the secondary circuit are substantially equal.

  In the first and second embodiments of the present invention, the control IC 130 has been described as operating by the voltage induced in the primary side auxiliary winding 150, but the present invention is limited to this configuration. It is not a thing. For example, the primary auxiliary winding may be eliminated and a control IC that operates with the primary DC voltage V1 may be used.

  Further, in the first and second embodiments of the present invention, the intermediate winding 320 is configured to have the same polarity as the secondary winding 220, but the present invention is not limited to this configuration. Absent. The intermediate winding 320 only needs to generate a voltage for driving the optical relay circuit 300 and may be configured to have the same polarity as the primary winding 120.

1, 1M switching power supply device 110 diode bridge circuit 115, 145, 215, 315 capacitor 120 primary winding 125 FET
130 IC for control
140 Second Phototransistor 150 Primary Auxiliary Winding 155, 210, 310 Diode 200 First Photocoupler 205 Second Photocoupler 220 Secondary Winding 126, 127, 225, 240, 245, 345, 350, 355 Resistor 230 First light emitting diode 235 Shunt regulator 300 Optical relay circuit 320 Intermediate winding 330 First phototransistor 340 Second light emitting diode 400 Transformer

Claims (7)

A primary side circuit comprising: a primary winding; a switching element connected to the other end of the primary winding for turning on / off a current flowing through the primary winding; and a control circuit for controlling on / off of the switching element. When,
A secondary side circuit having a secondary winding and a DC circuit for rectifying and smoothing a voltage generated in the secondary winding;
In a switching power supply device comprising:
A detection circuit for detecting an output voltage of the DC circuit;
A relay circuit that feeds back a detection result of the detection circuit to the control circuit while being electrically insulated from the primary circuit and the secondary circuit;
The detection circuit includes a first light emitting element that emits light of a light amount corresponding to the detected output voltage,
The relay circuit is connected to the first light receiving element in series with the first light receiving element that receives incident light and generates a current corresponding to the amount of light, and is generated by the first light receiving element. A second light emitting element that emits light of a light amount corresponding to the magnitude of the current,
The control circuit includes a second light receiving element that receives light from the second light emitting element and generates a current corresponding to the light amount;
The control circuit controls on / off of the switching element based on a magnitude of a current generated by the second light receiving element;
The switching power supply device, wherein the relay circuit receives light from the first light emitting element.   2. The switching power supply device according to claim 1, wherein the relay circuit includes a third winding insulated from the primary winding and the secondary winding.   The first light emitting element and the first light receiving element constitute a first photocoupler, and the second light emitting element and the second light receiving element constitute a second photocoupler. The switching power supply device according to claim 1 or 2. N relay circuits,
The first relay circuit receives light from the first light emitting element and emits light toward the second relay circuit;
The nth (n is an integer of 2 or more and N−1 or less) relay circuit receives light from the (n−1) th relay circuit and emits light toward the (n + 1) th relay circuit. And
The Nth relay circuit receives the light from the (n-1) th relay circuit and emits light toward the second light receiving element. Switching power supply.   5. The impedance between the primary side circuit and the relay circuit and the impedance between the secondary side circuit and the relay circuit are substantially equal to each other. The switching power supply device described in 1. A first resistor inserted between the ground of the primary circuit and the ground of the relay circuit;
A second resistor inserted between the ground of the secondary circuit and the ground of the relay circuit;
The switching power supply according to claim 5, further comprising: The primary side circuit has a primary auxiliary winding;
The switching power supply according to any one of claims 1 to 6, wherein the control circuit is driven by a DC voltage obtained by rectifying and smoothing a voltage generated in the primary auxiliary winding. .

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