Switching power supply device

Abstract

To provide a switching power supply device capable of securely transmitting occurrence of abnormality, which is detected on a secondary side, to a primary side while the device has a configuration which minimizes increases in manufacturing cost and a component mounting space.SOLUTION: A secondary side circuit 12A of a switching power supply device 10A includes: a mismatch detection part 13 which detects a degree of mismatch in a level corresponding to output voltage with respect to a preset target level; a photocoupler PC which feeds back the detected degree of mismatch to a control part IC; an overcurrent detection part 15 which detects occurrence of overcurrent; and a level change part 14 which compulsorily raises the level corresponding to output voltage which is referred to when the mismatch detection part 13 detects the degree of mismatch when occurrence of overcurrent is detected. The control part IC controls switching operation of a transistor Q1 so that mismatch becomes less based on the degree of mismatch, which is fed back by the photocoupler PC.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switching power supply device comprising a primary circuit including a switching element connected to a primary winding of a transformer and a control unit that controls the switching operation of the element, and a secondary circuit including a secondary rectifying and smoothing unit that rectifies and smoothes a voltage induced in a secondary winding of the transformer to generate an output voltage. [Background technology]

[0002] Conventionally, various switching power supply devices have been used, each of which includes a primary circuit including a switching element connected to a primary winding of a transformer and a control unit that controls the switching operation of the element, and a secondary circuit including a secondary rectifying and smoothing unit that rectifies and smoothes a voltage induced in a secondary winding of the transformer to generate an output voltage. Typically, the control unit of the primary circuit maintains the output voltage at a target voltage by appropriately controlling the switching operation of the switching element based on information about the output voltage level transmitted from the secondary circuit. Furthermore, this information about the output voltage level is often transmitted via a photocoupler.

[0003] Depending on the needs of the user, an abnormality detection unit may be provided to detect the occurrence of various abnormalities such as overcurrent in the secondary circuit (see, for example, Patent Document 1). In this case, information regarding the occurrence of an abnormality is usually transmitted to the control unit of the primary circuit via a photocoupler separate from the above-mentioned photocoupler. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-144243 Summary of the Invention [Problem to be solved by the invention]

[0005] Adding a photocoupler to notify the primary side of various abnormalities that have occurred on the secondary side increases manufacturing costs and the space required for mounting components.

[0006] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide a switching power supply device that can reliably transmit the occurrence of an abnormality detected on the secondary side to the primary side, while having a configuration that minimizes increases in manufacturing costs and component mounting space. [Means for solving the problem]

[0007] In order to solve the above problems, a switching power supply device according to the present invention is a device comprising: a primary side circuit including a switching element connected to a primary winding of a transformer and a control unit that controls the switching operation of the element; and a secondary side circuit including a secondary side rectifying and smoothing unit that rectifies and smoothes a voltage induced in a secondary winding of the transformer by the switching operation to generate an output voltage, wherein the secondary side circuit comprises a mismatch detection unit that detects the degree of mismatch of a level corresponding to the output voltage with respect to a preset target level; a feedback unit that feeds back the degree of mismatch detected by the mismatch detection unit to the control unit; an abnormality detection unit that detects the occurrence of an abnormality; and a level change unit that, when the abnormality detection unit detects the occurrence of an abnormality, forcibly raises the level corresponding to the output voltage that the mismatch detection unit uses when detecting the degree of mismatch, and the control unit controls the switching operation to reduce the mismatch based on the degree of mismatch fed back by the feedback unit.

[0008] In this configuration, in order to maintain the output voltage constant, the degree of mismatch of the level corresponding to the output voltage from a preset target level is fed back to the control unit by the feedback unit. Also, in this configuration, when the abnormality detection unit detects the occurrence of an abnormality, the degree of mismatch is forcibly increased by the level change unit, and the increased degree of mismatch is fed back to the control unit by the feedback unit. Therefore, with this configuration, there is no need to add a feedback unit to notify the control unit of the occurrence of an abnormality.

[0009] The primary side circuit of the switching power supply device may include a control power supply rectifying and smoothing unit that rectifies and smoothes the voltage induced in the tertiary winding of the transformer to generate a power supply voltage for the control unit, and an abnormality detection and determination unit that determines whether an abnormality has been detected based on the magnitude relationship between the generated power supply voltage and a preset threshold voltage, wherein the abnormality detection and determination unit determines that an abnormality has been detected when the power supply voltage falls below the threshold voltage, and the control unit executes predetermined abnormality control when the abnormality detection and determination unit determines that an abnormality has been detected.

[0010] This configuration can prevent each part from continuing to operate while an abnormality is occurring by performing control during abnormality occurrence. Note that a typical control during abnormality occurrence is to stop the switching operation of the switching element.

[0011] The feedback section of the switching power supply device includes, for example, one photocoupler.

[0012] The abnormality detection unit of the switching power supply device may include a first abnormality detection unit that detects the occurrence of a first abnormality and a second abnormality detection unit that detects the occurrence of a second abnormality different from the first abnormality. In this case, the level change unit must forcibly increase the level corresponding to the output voltage when the occurrence of at least one of the first abnormality and the second abnormality is detected. An example of the first abnormality is an overcurrent, and an example of the second abnormality is a temperature abnormality, but the first abnormality and the second abnormality are not limited to these.

[0013] The mismatch detection unit of the switching power supply device may include, for example, a resistive voltage divider that generates a level according to the output voltage by resistive voltage division, and a shunt regulator having a reference terminal connected to the voltage division point of the resistive voltage divider.

[0014] The level changer of the switching power supply device may include, for example, a variable resistance unit formed by connecting a resistance element and a switch element in series, the variable resistance element being connected in parallel to some of the plurality of resistance elements constituting the resistive voltage divider. In this case, the switch element must be configured so that its conduction state changes depending on whether an abnormality is detected by the abnormality detection unit or not. [Effects of the Invention]

[0015] According to the present invention, it is possible to provide a switching power supply device that can reliably transmit the occurrence of an abnormality detected on the secondary side to the primary side while minimizing increases in manufacturing costs and component mounting space. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing the configuration of a switching power supply device according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a diagram illustrating the operation of the switching power supply device according to the first embodiment of the present invention. [Figure 3] FIG. 10 is a diagram showing the configuration of a switching power supply device according to a second embodiment of the present invention. [Figure 4] FIG. 10 is a diagram showing the configuration of a switching power supply device according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of a switching power supply device according to the present invention will be described with reference to the accompanying drawings.

[0018] [First Example] 1 shows a switching power supply device 10A according to a first embodiment of the present invention. As shown in the figure, the switching power supply device 10A includes a transformer To including a primary winding T1, a secondary winding T2, and a tertiary winding T3, a primary side circuit 11, and a secondary side circuit 12A.

[0019] The primary side circuit 11 includes input terminals T1H and T1L, a smoothing capacitor C1, a transistor Q1, and a control unit IC.

[0020] The input terminal T1H is connected to one end of the primary winding T1 via a first high-side line HL1. One output terminal of a diode bridge circuit (not shown) is connected to the input terminal T1H. The input terminal T1L is connected to the other end of the tertiary winding T3 via a first low-side line LL1. The other output terminal of the aforementioned diode bridge circuit (not shown) is connected to the input terminal T1L.

[0021] The smoothing capacitor C1 is an electrolytic capacitor. The anode of the smoothing capacitor C1 is connected to the first high-side line HL1, and the cathode of the smoothing capacitor C1 is connected to the first low-side line LL1. The smoothing capacitor C1, together with the aforementioned diode bridge circuit (not shown), constitutes a primary-side rectifying and smoothing circuit.

[0022] The transistor Q1 is an N-type MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). The drain of the transistor Q1 is connected to the other end of the primary winding T1, and the source of the transistor Q1 is connected to the first low-side line LL1. The gate of the transistor Q1 is connected to the control signal output terminal OUT of the control unit IC. The transistor Q1 corresponds to the "switching element" of the present invention.

[0023] In addition to the control signal output terminal OUT mentioned above, the control unit IC has a power supply terminal VCC, a ground terminal GND, a feedback signal input terminal FB, and a latch signal input terminal LAT. The power supply terminal VCC is connected to the third high-side line HL3. The ground terminal GND is connected to the first low-side line LL1. The feedback signal input terminal FB and the latch signal input terminal LAT will be explained later.

[0024] The control unit IC controls the switching operation of the transistor Q1 by outputting a switching control signal (PWM signal) from the control signal output terminal OUT to the gate of the transistor Q1. In this example, the control unit IC used is a switching power supply control IC "FA8A87N" manufactured by Fuji Electric.

[0025] The primary side circuit 11 further includes a rectifier diode D1, a smoothing capacitor C2, a resistor R6 and capacitors C5 and C6 associated with a feedback signal input terminal FB of the control unit IC, and an abnormality detection and determination unit 16.

[0026] The rectifier diode D1 has an anode connected to one end of the tertiary winding T3 and a cathode connected to the third high-side line HL3.

[0027] The smoothing capacitor C2 is an electrolytic capacitor. The anode of the smoothing capacitor C2 is connected to the third high-side line HL3, and the cathode is connected to the first low-side line LL1. The smoothing capacitor C2 and a rectifier diode D1 form a rectifying and smoothing circuit. The rectifying and smoothing circuits D1 and C2 rectify and smooth the voltage induced in the tertiary winding T3 by the switching operation of the transistor Q1, thereby generating a power supply voltage to be supplied to the control unit IC. The rectifying and smoothing circuits D1 and C2 correspond to the "rectifying and smoothing unit for control power supply" of this invention.

[0028] One end of the resistor R6 is connected to the feedback signal input terminal FB of the control unit IC. One end of the capacitor C5 is connected to the feedback signal input terminal FB of the control unit IC and the other end is connected to the first low-side line LL1. One end of the capacitor C6 is connected to the other end of the resistor R6 and the other end is connected to the first low-side line LL1.

[0029] The abnormality detection determination unit 16 includes resistance elements R15 and R16, a Zener diode ZD, a capacitor C8, and an NPN transistor Q5.

[0030] One end of the resistor R15 is connected to the third high-side line HL3. The cathode of the Zener diode ZD is connected to the other end of the resistor R15. One end of the capacitor C8 is connected to the anode of the Zener diode ZD and the other end is connected to the first low-side line LL1. Furthermore, one end of the resistor R16 is connected to the anode of the Zener diode ZD and the other end is connected to the first low-side line LL1.

[0031] The base of the transistor Q5 is connected to the anode of the Zener diode ZD, and the emitter is connected to the first low-side line LL1. The transistor Q5 is turned on when the voltage across the smoothing capacitor C2 is higher than the set voltage of the Zener diode ZD. Conversely, the transistor Q5 is turned off when the voltage across the smoothing capacitor C2 is lower than the set voltage of the Zener diode ZD. The set voltage of the Zener diode ZD corresponds to the "predetermined threshold voltage" of this invention.

[0032] The abnormality detection determination unit 16 further includes resistance elements R17, R18, R19, R20, and R21, capacitors C9, C10, and C11, an NPN transistor Q6, and a PNP transistor Q4.

[0033] One end of the resistor R17 is connected to the third high-side line HL3 and the other end is connected to the collector of the transistor Q5. One end of the resistor R18 is connected to the collector of the transistor Q5 and the other end is connected to the first low-side line LL1. One end of the capacitor C9 is connected to the collector of the transistor Q5 and the other end is connected to the first low-side line LL1. The base of the transistor Q6 is connected to the collector of the transistor Q5 and the emitter is connected to the first low-side line LL1.

[0034] One end of the resistor R20 is connected to the third high-side line HL3. One end of the resistor R21 is connected to the other end of the resistor R20 and the other end is connected to the collector of the transistor Q6. One end of the capacitor C11 is connected to the third high-side line HL3 and the other end is connected to the other end of the resistor R20. The emitter of the transistor Q4 is connected to the third high-side line HL3 and the base is connected to the other end of the resistor R20. The collector of the transistor Q4 is connected to the latch signal input terminal LAT of the control unit IC.

[0035] One end of the resistor R19 is connected to the collector of the transistor Q4 and the other end is connected to the first low-side line LL1. One end of the capacitor C10 is also connected to the collector of the transistor Q4 and the other end is connected to the first low-side line LL1.

[0036] When transistor Q5 is in the ON state, that is, when the voltage appearing across smoothing capacitor C2 (= power supply voltage for control IC) is higher than the set voltage of Zener diode ZD, transistors Q6 and Q4 are both in the OFF state. In this case, a latch signal of "L" level is input to the latch signal input terminal LAT of the control IC. Conversely, when transistor Q5 is in the OFF state, that is, when the voltage appearing across smoothing capacitor C2 is lower than the set voltage of Zener diode ZD, transistors Q6 and Q4 are both in the ON state. In this case, a latch signal of "H" level is input to the latch signal input terminal LAT of the control IC.

[0037] As will be explained in detail later, the voltage appearing across smoothing capacitor C2 falls below the set voltage of Zener diode ZD when an abnormality is detected on the secondary side. Also, as described above, abnormality detection determination unit 16 outputs an "H" level latch signal when the voltage appearing across smoothing capacitor C2 falls below the set voltage of Zener diode ZD. From these facts, it can be said that abnormality detection determination unit 16 is a circuit that determines whether or not an abnormality has been detected based on the voltage appearing across smoothing capacitor C2, and outputs an "H" level latch signal when it determines that an abnormality has been detected.

[0038] The secondary circuit 12A includes output terminals T2H and T2L, a rectifier diode D2, a smoothing capacitor C3, a photocoupler PC, a mismatch detection unit 13, a level change unit 14, and an overcurrent detection unit 15.

[0039] The output terminal T2H is connected to the second high-side line HL2 via a resistive element R11 that constitutes the overcurrent detection unit 15. A load (not shown) is connected to the output terminal T2H. The output terminal T2L is connected to the other end of the secondary winding T2 via a second low-side line LL2. The aforementioned load (not shown) is connected to the output terminal T2L.

[0040] The rectifier diode D2 has an anode connected to one end of the secondary winding T2 and a cathode connected to the second high-side line HL2.

[0041] The smoothing capacitor C3 is an electrolytic capacitor. The anode of the smoothing capacitor C3 is connected to the second high-side line HL2, and the cathode is connected to the second low-side line LL2. The smoothing capacitor C3 and a rectifier diode D2 form a rectifying and smoothing circuit. The rectifying and smoothing circuits D2 and C3 rectify and smooth the voltage induced in the secondary winding T2 by the switching operation of the transistor Q1, thereby generating an output voltage to be supplied to the aforementioned load (not shown). The rectifying and smoothing circuits D2 and C3 correspond to the "secondary-side rectifying and smoothing unit" of the present invention.

[0042] The mismatch detection unit 13 includes resistance elements R1, R2, R3, R4, and R5, a capacitor C4, and a shunt regulator SR.

[0043] One end of the resistor R1 is connected to the second high-side line HL2. One end of the resistor R2 is connected to the other end of the resistor R1, and the other end is connected to the second low-side line LL2. The resistors R1 and R2 correspond to the "resistive voltage divider" of the present invention. The connection point P of the resistors R1 and R2 corresponds to the "voltage dividing point" of the present invention. When the voltage of the second high-side line HL2 relative to the second low-side line LL2, i.e., the output voltage generated by the rectifying and smoothing circuits D2 and C3, is V11, the voltage at the connection point P is V11 × the resistance value of R2 / (the resistance value of R1 + the resistance value of R2). The voltage at the connection point P corresponds to the "level according to the output voltage" of the present invention.

[0044] One end of the resistor R4 is connected to the second high-side line HL2. One end of the resistor R5 is connected to the other end of the resistor R4. The shunt regulator SR has a cathode connected to the other end of the resistor R5 and an anode connected to the second low-side line LL2. The shunt regulator SR has a reference terminal connected to the connection point P.

[0045] One end of the resistor R3 is connected to the other end of the resistor R5. One end of the capacitor C4 is connected to the other end of the resistor R3, and the other end is connected to the connection point P.

[0046] The photocoupler PC includes a photodiode PD and a phototransistor QP. The photocoupler PC corresponds to the "feedback unit" of the present invention.

[0047] The photodiode PD has an anode connected to one end of the resistor R5 and a cathode connected to the other end of the resistor R5, that is, the photodiode PD is connected in parallel to the resistor R5.

[0048] The phototransistor QP operates in response to the amount of light emitted by the photodiode PD. The collector of the phototransistor QP is connected to a feedback signal input terminal FB of the control unit IC, and the emitter is connected to the first low-side line LL1.

[0049] When the output voltage fluctuates due to factors such as fluctuations in the load connected to the output terminals T2H and T2L, causing a mismatch between the preset reference voltage and the voltage at node P, the anode-cathode voltage of the shunt regulator SR increases or decreases depending on the degree of mismatch, thereby increasing or decreasing the amount of light emitted by the photodiode PD. In this way, the degree of mismatch is fed back to the feedback signal input terminal FB of the control unit IC. Upon receiving the feedback, the control unit IC adjusts the on-duty of the switching control signal output to the gate of transistor Q1 in a direction that resolves the mismatch, or stops outputting the switching control signal to stop the switching operation of transistor Q1. The reference voltage corresponds to the "preset target level" in this invention.

[0050] Specifically, when the voltage at node P becomes lower than the reference voltage, the light emission from the photodiode PD decreases, the current flowing through the phototransistor QP decreases, and the voltage at the feedback signal input terminal FB of the control unit IC increases. In this case, the control unit IC increases the on-duty of the switching control signal. Conversely, when the voltage at node P becomes higher than the reference voltage, the light emission from the photodiode PD increases, the current flowing through the phototransistor QP increases, and the voltage at the feedback signal input terminal FB of the control unit IC decreases. In this case, the control unit IC decreases the on-duty of the switching control signal. As a result of this feedback control, the output voltage remains constant.

[0051] The overcurrent detection unit 15 corresponds to the "abnormality detection unit" of the present invention, and includes a comparator CP, resistance elements R7, R8, R9, R10, and R11, and a diode D3.

[0052] One end of the resistor R7 is connected to the second high-side line HL2 and one end of the resistor R11. One end of the resistor R8 is connected to the other end of the resistor R7 and the other end is connected to the second low-side line LL2. The connection point of the resistors R7 and R8 is connected to the non-inverting input terminal (+) of the comparator CP.

[0053] One end of the resistor R9 is connected to the output terminal T2H and the other end of the resistor R11. One end of the resistor R10 is connected to the other end of the resistor R9 and the other end is connected to the second low-side line LL2. The connection point of the resistors R9 and R10 is connected to the inverting input terminal (-) of the comparator CP.

[0054] The comparator CP is made up of an operational amplifier, and the output terminal of the comparator CP is connected to the level changer 14 via a diode D3 connected in the forward direction.

[0055] The comparator CP is configured to output an "L" level when an overcurrent, which is a type of abnormality, is not occurring, i.e., when the voltage appearing across the resistor element R11 is relatively small, and to output an "H" level when an overcurrent is occurring, i.e., when the voltage appearing across the resistor element R11 is relatively large.

[0056] The level changer 14 includes resistive elements R12, R13, and R14, a capacitor C7, an NPN transistor Q2, and a PNP transistor Q3.

[0057] One end of the resistor R12 is connected to the second high-side line HL2. One end of the resistor R13 is connected to the other end of the resistor R12. The collector of the transistor Q2 is connected to the other end of the resistor R13, and the emitter is connected to the second low-side line LL2. The base of the transistor Q2 is connected to the overcurrent detection unit 15. More specifically, the base of the transistor Q2 is connected to the output terminal of the comparator CP via a diode D3.

[0058] The capacitor C7 has one end connected to the second high-side line HL2 and the other end connected to the other end of the resistor R12, that is, the capacitor C7 is connected in parallel to the resistor R12.

[0059] The transistor Q3 has an emitter connected to the second high side line HL2 and a base connected to the other end of the resistor R12. The transistor Q3 corresponds to the "switch element" of the present invention.

[0060] The resistor R14 has one end connected to the collector of the transistor Q3 and the other end connected to the connection point P of the mismatch detector 13.

[0061] The transistor Q3 and the resistor element R14 correspond to the "variable resistor unit" of the present invention. When the overcurrent detection unit 15 does not detect the occurrence of an overcurrent, i.e., when the output of the comparator CP is at "L" level, the transistors Q2 and Q3 are in the off state. In this case, the resistance value of the variable resistor unit Q3 and R14 is infinite. Conversely, when the overcurrent detection unit 15 detects the occurrence of an overcurrent, i.e., when the output of the comparator CP is at "H" level, the transistors Q2 and Q3 are in the on state. In this case, the resistance value of the variable resistor unit Q3 and R14 is substantially equal to the resistance value of the resistor element R14.

[0062] Next, the operation of each unit when overcurrent detection unit 15 detects the occurrence of an overcurrent will be described in more detail with reference to Fig. 2. In the operation example shown in Fig. 2, it is assumed that overcurrent detection unit 15 detects the occurrence of an overcurrent at time t1.

[0063] Between times t0 and t1 when no overcurrent is occurring, the output voltage (the voltage appearing across smoothing capacitor C3 ≈ the voltage appearing at output terminals T2H and T2L) is maintained at the target voltage V11 by the feedback control described above. At this time, the output of comparator CP is at the "L" level, transistors Q2 and Q3 are off (i.e., the resistance values ​​of variable resistors Q3 and R14 are infinite), the voltage appearing across smoothing capacitor C2 is V11 × (number of turns N3 of tertiary winding T3 / number of turns N2 of secondary winding T2), transistor Q5 is on, transistors Q6 and Q4 are off, and the latch signal input to latch signal input terminal LAT is at the "L" level.

[0064] When the overcurrent detection unit 15 detects the occurrence of an overcurrent at time t1, the output of the comparator CP goes high, turning on the transistors Q2 and Q3 (i.e., the resistance value of the variable resistor unit Q3 and R14 connected in parallel to the resistor element R1 becomes the resistance value of the resistor element R14), forcing the voltage at the node P to rise significantly. This creates a large discrepancy between the reference voltage and the voltage at the node P. The control unit IC, which receives notification of the discrepancy via the photocoupler PC, stops the switching operation of the transistor Q1 to bring the voltage at the node P closer to the preset reference voltage. This causes the output voltage and the voltage appearing across the smoothing capacitor C2 to begin to drop.

[0065] At time t2, when the voltage across smoothing capacitor C2 falls below the set voltage of Zener diode ZD, transistor Q5 turns off, transistors Q6 and Q4 turn on, and the latch signal input to latch signal input terminal LAT goes to "H" level. In response to this, control unit IC starts counting the delay time Δt.

[0066] When the voltage at the connection point P matches the reference voltage at time t3, the control unit IC restarts the switching operation of the transistor Q1, thereby maintaining the output voltage at V12, which is lower than V11.

[0067] At time t4, a delay time Δt after time t2, the control unit IC stops the switching operation of transistor Q1. This causes the output voltage to begin to decrease toward zero. Meanwhile, the voltage appearing across smoothing capacitor C2 is maintained at an intermediate voltage between the original voltage and zero due to the latch function of the control unit IC.

[0068] In this embodiment, stopping the switching operation of transistor Q1 when delay time Δt has elapsed since the latch signal became “H” level and maintaining the voltage appearing across smoothing capacitor C2 at an intermediate voltage corresponds to the “control at the time of abnormality occurrence” of the present invention.

[0069] In this way, in the switching power supply 10A according to this embodiment, when an overcurrent occurs on the secondary side, this is transmitted to the control unit IC on the primary side via the photocoupler PC for maintaining the output voltage at the target voltage. Therefore, the switching power supply 10A can reduce manufacturing costs and component mounting space compared to when a photocoupler for transmitting the occurrence of an overcurrent is added.

[0070] [Second Example] 3 shows a switching power supply 10B according to a second embodiment of the present invention. As shown in the figure, switching power supply 10B differs from switching power supply 10A in that it includes a secondary side circuit 12B instead of secondary side circuit 12A, but is otherwise the same as switching power supply 10A.

[0071] The secondary-side circuit 12B includes output terminals T2H and T2L, a rectifier diode D2, a smoothing capacitor C3, a photocoupler PC, a mismatch detection unit 13, a level change unit 14, and a temperature abnormality detection unit 17. That is, the secondary-side circuit 12B differs from the secondary-side circuit 12A in that it includes the temperature abnormality detection unit 17 instead of the overcurrent detection unit 15, but is otherwise common to the secondary-side circuit 12A.

[0072] The temperature abnormality detection unit 17 corresponds to the "abnormality detection unit" of the present invention, and includes a thermistor TH as a temperature sensor, resistive elements R22, R23, R24, a capacitor C12, and a PNP transistor Q7.

[0073] The thermistor TH is a positive temperature coefficient thermistor, and one end of the thermistor TH is connected to the second high side line HL2.

[0074] One end of the resistor R22 is connected to the other end of the thermistor TH, and the other end is connected to the second low-side line LL2. The emitter of the transistor Q7 is connected to the second high-side line HL2, and the base is connected to the other end of the thermistor TH. The resistor R23 has one end connected to the collector of the transistor Q7. The capacitor C12 has one end connected to the other end of the resistor R23, and the other end connected to the second low-side line LL2. The resistor R24 ​​has one end connected to the other end of the resistor R23, and the other end connected to the second low-side line LL2. The other end of the resistor R23 is also connected to the level changer 14 (the base of the transistor Q2).

[0075] When the temperature is below a preset upper limit, i.e., when the resistance of thermistor TH is relatively small, transistor Q7 is in the OFF state. In this case, a low level signal is input to the base of transistor Q2, just as when overcurrent detection unit 15 of the first embodiment does not detect the occurrence of an overcurrent. Conversely, when the temperature is above the upper limit, i.e., when the resistance of thermistor TH is relatively high, transistor Q7 is in the ON state. In this case, a high level signal is input to the base of transistor Q2, just as when overcurrent detection unit 15 of the first embodiment detects the occurrence of an overcurrent.

[0076] When the temperature abnormality detection unit 17 does not detect the occurrence of a temperature abnormality, the resistance values ​​of the variable resistance units Q3 and R14 constituting the level change unit 14 are infinite. Conversely, when the temperature abnormality detection unit 17 detects the occurrence of a temperature abnormality, the resistance values ​​of the variable resistance units Q3 and R14 are substantially equal to the resistance value of the resistance element R14.

[0077] In the switching power supply device 10B according to this embodiment, if a temperature abnormality occurs on the secondary side, the occurrence of the temperature abnormality is transmitted to the control unit IC on the primary side via the photocoupler PC for maintaining the output voltage at the target voltage. Therefore, the switching power supply device 10B can reduce manufacturing costs and component mounting space compared to when a photocoupler for transmitting the occurrence of a temperature abnormality is added.

[0078] [Third Example] 4 shows a switching power supply 10C according to a third embodiment of the present invention. As shown in the figure, the switching power supply 10C differs from the switching power supply 10A in that it includes a secondary side circuit 12C instead of the secondary side circuit 12A, but is otherwise the same as the switching power supply 10A.

[0079] The secondary-side circuit 12C includes output terminals T2H and T2L, a rectifier diode D2, a smoothing capacitor C3, a photocoupler PC, a mismatch detection unit 13, a level change unit 14, an overcurrent detection unit 15, and a temperature abnormality detection unit 17. That is, the secondary-side circuit 12C differs from the secondary-side circuit 12A in that it further includes the temperature abnormality detection unit 17, but is otherwise common to the secondary-side circuit 12A. In this embodiment, the overcurrent detection unit 15 corresponds to the "first abnormality detection unit" of the present invention, and the temperature abnormality detection unit 17 corresponds to the "second abnormality detection unit" of the present invention.

[0080] When overcurrent detection unit 15 and temperature abnormality detection unit 17 do not detect the occurrence of an abnormality, i.e., when an "L" level is input to the base of transistor Q2, the resistance values ​​of variable resistance units Q3 and R14 that constitute level change unit 14 are infinite. Conversely, when at least one of overcurrent detection unit 15 and temperature abnormality detection unit 17 detects the occurrence of an abnormality, i.e., when an "H" level is input to the base of transistor Q2, the resistance values ​​of variable resistance units Q3 and R14 are substantially equal to the resistance value of resistive element R14.

[0081] In the switching power supply 10C according to this embodiment, if an overcurrent or temperature abnormality occurs on the secondary side, the occurrence of the overcurrent or temperature abnormality is transmitted to the control unit IC on the primary side via the photocoupler PC for maintaining the output voltage at the target voltage. Therefore, the switching power supply 10C can reduce manufacturing costs and component mounting space compared to when a photocoupler for transmitting the occurrence of an overcurrent or temperature abnormality is added.

[0082] Although several embodiments of the switching power supply according to the present invention have been described above, the configuration of the present invention is not limited to these.

[0083] For example, the control performed by the control unit when an abnormality occurs does not have to include control (latch function) to maintain the power supply voltage of the control unit at an intermediate voltage. Furthermore, the control performed by the control unit when an abnormality occurs may include control to maintain the output voltage at an intermediate voltage between the target voltage (V11 in FIG. 2) and zero, or control to reduce the output voltage to the intermediate voltage, instead of control to stop the switching operation and reduce the output voltage to zero. Furthermore, the control unit may end the control performed when an abnormality occurs when the abnormality is resolved, or may continue the control performed when an abnormality occurs even after the abnormality is resolved.

[0084] Furthermore, the secondary side circuit may include three or more abnormality detection units, and each detection unit may detect the occurrence of an abnormality other than an overcurrent or temperature abnormality (for example, an overvoltage). [Explanation of symbols]

[0085] 10A, 10B, 10C Switching Power Supply 11 Primary circuit 12A,12B,12C Secondary circuit 13 Mismatch detection unit 14 Level change section 15 Overcurrent detection section 16 Abnormality detection and judgment unit 17 Temperature abnormality detection unit IC control section

Claims

1. A switching power supply device comprising: a primary side circuit including a switching element connected to a primary winding of a transformer and a control unit that controls the switching operation of the element; and a secondary side circuit including a secondary side rectifying and smoothing unit that rectifies and smoothes a voltage induced in a secondary winding of the transformer by the switching operation to generate an output voltage, The secondary side circuit includes: a mismatch detection unit that detects the degree of mismatch of a level corresponding to the output voltage with respect to a preset target level; a feedback unit that feeds back the degree of the mismatch detected by the mismatch detection unit to the control unit; an abnormality detection unit that detects the occurrence of an abnormality; a level changing unit that, when the occurrence of the abnormality is detected by the abnormality detection unit, forcibly increases a level corresponding to the output voltage that is referenced by the mismatch detection unit when detecting the degree of the mismatch; Equipped with The control unit controls the switching operation based on the degree of the mismatch fed back by the feedback unit so as to reduce the mismatch. A switching power supply device characterized by:

2. The primary side circuit includes: a control power supply rectifying and smoothing unit that rectifies and smoothes a voltage induced in a tertiary winding of the transformer to generate a power supply voltage for the control unit; an abnormality detection determination unit that determines whether or not the occurrence of the abnormality has been detected based on the magnitude relationship between the power supply voltage and a preset threshold voltage; Equipped with the abnormality detection determination unit determines that the occurrence of the abnormality has been detected when the power supply voltage falls below the threshold voltage; The control unit executes a predetermined abnormality occurrence control when the abnormality detection determination unit determines that the abnormality has occurred.

2. The switching power supply device according to claim 1.

3. The feedback section includes one photocoupler.

3. The switching power supply device according to claim 1 or 2.

4. the abnormality detection unit includes a first abnormality detection unit that detects the occurrence of a first abnormality and a second abnormality detection unit that detects the occurrence of a second abnormality different from the first abnormality, The level changing unit forcibly increases the level when occurrence of at least one of the first abnormality and the second abnormality is detected.

3. The switching power supply device according to claim 1 or 2.

5. the mismatch detection unit includes a resistive voltage dividing unit that generates a level according to the output voltage by resistive voltage division, and a shunt regulator having a reference terminal connected to a voltage dividing point of the resistive voltage dividing unit; the level changing unit includes a variable resistance unit formed by connecting a resistance element and a switch element in series, the variable resistance unit being connected in parallel to some of the plurality of resistance elements constituting the resistance voltage dividing unit; The switch element changes its conduction state depending on whether the abnormality is detected by the abnormality detection unit or not.

3. The switching power supply device according to claim 1 or 2.

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