JP5444896B2 - Isolated switching power supply - Google Patents

Description

  The present invention relates to an isolated switching power supply including a composite transformer having a primary-secondary power transmission / voltage conversion function, a primary-secondary signal transmission function, and the like.

  Patent Document 1, Patent Document 2, and Patent Document 3 disclose a composite transformer that can be regarded as independent from each other using a pair of cores and an insulating switching power supply using the composite transformer.

  1A and 1B show wiring examples when the composite transformer shown in the second embodiment of Patent Document 3 is formed on a printed board. 2A shows the magnetic path of the signal transmission transformer unit, and FIG. 2B shows the magnetic path of the power transmission transformer unit. FIG. 1A is a plan view of a double-sided substrate 100a, and FIG. 1B is a plan view of a double-sided substrate 100b, which are stacked to form a four-layer substrate. 1A and 1B show cross sections of magnetic leg portions 106aa, 106ab, 106b, 106ca, 106cb of a five-leg transformer core (E-I shape or EE shape). ing. Around the center magnetic leg 106b, a three-turn spiral primary coil 101a is formed on the double-sided substrate 100a. A two-turn spiral secondary coil 103a is formed on the double-sided substrate 100b. Therefore, when the double-sided boards 100a and 100b are stacked coaxially, a power transmission transformer of primary side 3 turns: secondary side 2 turns is configured.

  On the double-sided boards 100a and 100b, a coil wound in one turn around the magnetic leg 106aa and the magnetic leg 106ab is connected in series to form the primary coil 102a and the secondary coil 104a of the first signal transmission transformer unit. Has been. Since the magnetic leg 106aa and the magnetic leg 106ab have the same distance from the central magnetic leg 106b and the same cross-sectional area, the voltage induced in the coil wound around the magnetic leg 106aa by the power transmission transformer and the magnetic leg 106ab are wound. The voltages induced in the coils are opposite in polarity and have the same voltage value and cancel each other. Accordingly, the voltage induced by the power transmission transformer does not appear at the output terminal of the primary coil 102a and the secondary coil 104a of the first signal transmission transformer unit. On the other hand, the magnetic flux generated in the coil wound around the magnetic leg 106aa of the first signal transmission transformer unit and the magnetic flux generated in the coil wound around the magnetic leg 106ab are in opposite directions and the amount of magnetic flux is equal. The magnetic legs 106b at the center cancel each other. By the above-described operation, the power transmission transformer unit and the first signal transmission transformer unit operate as if they seem to be independent from each other.

  Based on the same principle, a second signal transmission transformer formed of a primary coil 122a and a secondary coil 123a wound around the magnetic leg 106ca and the magnetic leg 106cb by turns in opposite directions, a power transmission transformer unit, Appear to be independent of each other. Further, since the first signal transmission transformer unit and the second signal transmission transformer unit are formed so as to be separated from each other, they hardly affect each other. Based on such a principle, a pair of cores can form an apparently independent one power transmission transformer unit and two signal transmission transformer units.

JP 2000-260639 A JP 2004-349293 A International Publication No. 2007/066943 Pamphlet

  Although Patent Document 3 mentions application to protection circuits such as output overvoltage protection, output undervoltage protection, and overheat protection circuit, a specific configuration example is not shown.

  An object of the present invention is to provide a specific circuit configuration of a protection circuit for an insulated switching power supply using a composite transformer.

The present invention is configured as follows to solve the above-described problems.
The isolated switching power supply of the present invention has an input / output isolated by a power transmission transformer, and has at least one power switch on the primary side to switch input power, at least one rectifier on the secondary side, and an output Comprising a filter and supplying power to the load device,
A power transformer unit and a signal transmission transformer unit, which are substantially independent of each other, are provided with a composite transformer integrally formed by sharing a pair of cores,
An abnormality detection circuit for detecting an abnormality of the isolated switching power supply or the load circuit, and a signal in a normal state from the secondary side to the primary side via the signal transmission transformer unit when the abnormality detection circuit detects an abnormality. An abnormal condition signal transmission circuit for transmitting different abnormal condition signals is provided on the secondary side,
In response to the abnormal state signal, the primary side is provided with a protection operation execution circuit that performs protection operation of the isolated switching power supply or the load device.

In another insulation type switching power supply of the present invention, the input / output is insulated by a power transmission transformer, and at least one power switch is provided on the primary side to switch the input power, and at least one power switch is provided on the secondary side. A rectifier and an output filter are provided to supply power to the load device,
A power transformer unit and a signal transmission transformer unit, which are substantially independent of each other, are provided with a composite transformer integrally formed by sharing a pair of cores,
An abnormality detection circuit that detects an abnormality of the isolated switching power supply or the load circuit, and a protection operation execution circuit that performs a protection operation of the isolated switching power supply or the load device when the abnormality detection circuit detects an abnormal state. In preparation for
When the abnormality detection circuit detects an abnormality, an abnormality state signal transmission circuit for transmitting an abnormality state signal different from a normal state signal from the primary side to the secondary side via the signal transmission transformer unit is provided on the primary side. ,
An alarm signal output circuit that outputs an alarm signal when the abnormal state signal is generated is provided on the secondary side.

Still another isolated switching power supply according to the present invention has an input / output isolated by a power transmission transformer and includes at least one power switch on the primary side to switch input power and at least one rectifier on the secondary side. And an output filter to supply power to the load device,
A power transformer unit and a signal transmission transformer unit, which are substantially independent of each other, are provided with a composite transformer integrally formed by sharing a pair of cores,
An abnormal state of the isolated switching power supply or an abnormality of the load circuit is detected, and in the case of an abnormality, an abnormal state signal different from a normal state signal is excited in the signal transmission transformer unit, and the signal excited in the signal transmission transformer Comprises an anomaly detection transmission circuit for bi-directional transmission from the primary side to the secondary side and from the secondary side to the primary side,
In response to the abnormal state signal, the primary side is provided with a protection operation execution circuit that performs the protection operation of the isolated switching power supply or the load device.

  The abnormality detection circuit is provided on the primary side or the secondary side as necessary, and detects an abnormal state in the insulated switching power supply. An abnormal state in an isolated switching power supply is an input undervoltage state, input overvoltage state, output undervoltage state, output overvoltage state, input current overcurrent state, output current overcurrent state, or circuit element It is at least one of overheating conditions.

  Further, when it is determined as an abnormal state, a protection operation execution circuit for protecting the isolated switching power supply and the load device by reducing the duty of the power switch, stopping the latch of the power switch, or hiccup operation is provided on the primary side.

  If necessary, an alarm signal output circuit is provided on the primary side or the secondary side, and when the abnormality detection circuit detects an abnormal state of the insulating switching power supply, an alarm signal is output to the outside of the insulating switching power supply.

  When the abnormality detection circuit, the protection operation execution circuit, and the alarm signal output circuit can be arranged only on the primary side or only on the secondary side, signal transmission between the primary and secondary is not necessary. . However, when the abnormality detection circuit, the protection operation execution circuit, or the alarm signal output circuit is arranged separately between the primary and secondary, the exchange of signals related to the protection operation between the primary and secondary Is required. In the present invention, signals related to the protection operation are exchanged using the signal transmission transformer unit of the composite transformer.

The present invention has the following effects.
Abnormality detection circuit, protection operation execution circuit, alarm signal output circuit can be separated between primary and secondary as necessary, and parts that may cause abnormality can be directly detected, so highly accurate abnormality detection Is possible.

  Regardless of the location where an abnormality is detected, an alarm signal can be output to either the primary side or the secondary side, which is convenient for protection and maintenance of the isolated switching power supply and its peripheral circuits.

  Since the maximum use temperature is limited to about 100 ° C., and it is not necessary to use a photocoupler having CTR deterioration over time for primary-secondary signal transmission, high reliability can be ensured.

  By using a composite transformer in which a coil is formed with a substrate pattern, a small and low-cost isolated switching power supply can be realized.

  Unlike a photocoupler, a signal transmission transformer can perform bidirectional transmission from the secondary side to the primary side, and from the primary side to the secondary side, so that the degree of freedom in designing the protection circuit is increased.

  Furthermore, since the composite transformer shown in the second embodiment of Patent Document 3 can form a plurality of signal transmission transformer units in addition to the power transmission transformer unit, the other signal transmission transformer units can be driven by a synchronous rectifier. It can be used for output voltage stabilization control. As a result, a highly functional isolated switching power supply can be realized.

FIGS. 1A and 1B are diagrams showing an example of wiring when the composite transformer shown in the second embodiment of Patent Document 3 is formed on a printed circuit board. 2A is a diagram illustrating a magnetic path of the signal transmission transformer unit, and FIG. 2B is a diagram illustrating a magnetic path of the power transmission transformer unit. It is a circuit diagram of the insulation type switching power supply 91 which concerns on 1st Embodiment. 3 is a waveform diagram of each part. It is a circuit diagram of the insulation type switching power supply 92 which concerns on 2nd Embodiment. 5 is a waveform diagram of each part.

<< First Embodiment >>
FIG. 3 is a circuit diagram of the isolated switching power supply 91 according to the first embodiment, and FIG. 4 is a waveform diagram of each part of the isolated switching power supply 91.
The insulated switching power supply 91 of the first embodiment has a function of performing a hiccup protection operation and outputting an alarm signal to the outside when the output voltage drops below a standard value.

  3 includes a + input terminal “+ Vin”, a −input terminal “−Vin”, a + output terminal “+ Vout”, and a −output terminal “−Vout”. The insulating switching power supply 91 includes a remote control terminal RC for externally controlling the operation / stop of the insulating switching power supply, and an alarm signal output terminal for drawing current when the output voltage of the insulating switching power supply drops below a certain value. VALM is provided.

The insulating switching power supply 91 includes the following components.
Switch elements Q1, Q2, Q3, Q14, each of which is an N-channel MOSFET,
Diodes D1, D2, D3,
Capacitors C1, C2, C3, C4,
Resistors R1, R2, R3, R4, R5, R6, R7, R8,
Comparators CMP1, CMP2,
Multivibrators MV1, MV2, MV3 composed of NOR gates,
Transformers T1, T2, T3 configured in one composite transformer
Input filter 51,
Input low voltage monitoring and remote control circuit 52,
Hiccup control circuit 53,
Delay circuit 54,
Current / voltage amplification circuit 55,
Drive circuit 56 of the clamp switch Q2,
Zero voltage state detection circuit 57,
Output filter 58,
And an overcurrent protection circuit 59.

  The switch element Q1 is a power switch (main switch), and the switch element Q2 is a clamp switch. The diode D1 is a rectifier diode of the insulating switching power supply 91. The resistor R8 is an output current detection resistor. Each of the multivibrators MV1, MV2, and MV3 includes an oscillation / stop control terminal cnt and an output terminal out.

  The transformer T1 is a power transmission transformer, and includes a primary coil n11, a secondary coil n12, a tertiary coil n13, a quaternary coil n14, and a quintic coil n15. The transformer T2 is a first signal transmission transformer, and includes a primary coil n21 and a secondary coil n22. Furthermore, the transformer T3 is a second signal transmission transformer, and includes a primary coil n31 and a secondary coil n32.

4 shows an output voltage waveform (a) of the isolated switching power supply 91, a gate-source voltage waveform (b) of the power switch Q1, a drain-source voltage waveform (c) of the power switch Q1, a voltage transmission transformer unit. Current waveform of the primary coil n11 of T1 (= drain current waveform of the power switch Q1) (d), current waveform of the secondary coil n12 of the voltage transmission transformer T1 (= current waveform of the rectifier diode D1) (e), The input / output voltage waveform (f) of the first signal transmission transformer T2, the input / output voltage waveform (g) of the second signal transmission transformer T3, and the output voltage waveform (h) of the hiccup control circuit 53 are shown. .

  FIG. 4 shows a state where the output is short-circuited at point A and the overcurrent protection circuit 59 is activated, and as a result, the output voltage of the insulating switching power supply 91 drops.

  The hiccup control circuit 53 is composed of a monostable multivibrator, and after the pulse signal is input, the output voltage is set to the H level for a predetermined time. When the output voltage changes from the L level to the H level, free oscillation of the multivibrator MV1 stops and the switching operation stops.

  The isolated switching power supply 91 according to the first embodiment is a flyback converter that operates in a current critical mode and performs zero voltage switching. The DC power input between the input terminals “+ Vin” and “−Vin” of the insulated switching power supply 91 is switched by the power switch Q1 and converted to AC power. When the power switch Q1 is turned on, as shown by the waveform (d) in FIG. 4, the current of the primary coil n11 of the power transmission transformer unit T1 increases linearly, and electromagnetic energy is accumulated in the excitation inductance. When the power switch Q1 is turned off, a charge is charged in a parasitic capacitance that exists in parallel with Q1, and the drain-source voltage of the power switch Q1 increases. When the drain-source voltage of Q1 exceeds the voltage Vc1 across the capacitor C1, the parasitic diode of the clamp switch Q2 conducts and current flows into the capacitor C1, and the electromagnetic energy of the power transmission transformer T1 is the electrostatic energy of the capacitor C1. Is converted to

  Here, when the number of turns of the primary coil n1 is represented by n1 and the number of turns of the secondary coil is represented by n2, the voltage Vc1 across the capacitor C1 and the output voltage Vout of the insulated switching power supply 91 have the following relationship. Therefore, the rectifier diode D1 is turned on simultaneously with the conduction of the parasitic diode of the clamp switch Q2, and power is transmitted to the output filter 58.

Vc1≈n11 / n12 · Vout
The direct current supplied via the rectifier diode D1 is output from the + Vout and −Vout terminals after the ripple component is reduced by the output filter 58. When the clamp switch Q2 is turned on during the conduction period of the parasitic diode of the clamp switch Q2, the LC resonance continues even after all the electromagnetic energy of the power transmission transformer T1 is converted into the electrostatic energy of the capacitor C1, and the clamp switch Q2 Current flows from the drain to the source. The drive circuit 56 of the clamp switch Q2 has a time constant circuit therein, and turns off Q2 after a certain period of time has elapsed since the parasitic diode of the clamp switch Q2 is turned on.

  When the drive circuit 56 of the clamp switch Q2 turns off the clamp switch Q2, the capacitance of the capacitor that resonates with the inductance of the power transmission transformer unit T1 is “parasitic capacitance existing in parallel with Q1” + “capacitance of the capacitor C1”. It changes to “parasitic capacitance existing in parallel with Q1”. Therefore, the drain-source voltage of the power switch Q1 rapidly decreases.

  When the drain-source voltage of the power switch Q1 becomes approximately zero volts due to the LC resonance, the zero voltage state detection circuit 57 generates an H level pulse signal. When this pulse signal is applied to the multivibrator MV1 via the diode D2, the output of the multivibrator MV1 is inverted. As a result, the gate of the power switch Q1 is charged through the current / voltage amplification circuit 55, and the power switch Q1 is turned on.

  The zero voltage switching operation is repeated by the above-described operation, but the OFF timing of the power switch Q1 is defined by a pulse signal transmitted from the secondary side to the primary side via the first signal transmission transformer T2. .

By integrating the voltage of the rectifier diode D1 with the resistors R4 and R5 and the capacitor C2 , a ramp wave whose average value is proportional to the output voltage of the insulating switching power supply 91 is formed. The ramp wave is compared with the reference voltage Vref by the comparator CMP1, and when the ramp wave voltage exceeds the reference voltage Vref (timing), the output voltage of the comparator CMP1 is inverted from the H level to the L level.

  On the other hand, a voltage obtained by dividing the voltage of the fifth coil n15 of the power transmission transformer T1 by the resistors R2 and R3 is input to the multivibrator MV2 via the diode D3. Therefore, the multivibrator MV2 freely oscillates when the power switch Q1 is on and the output voltage of the comparator CMP1 becomes L level, and a pulse signal is generated from the out terminal.

  The pulse signal is transmitted from the secondary coil n22 to the primary coil n21 of the first signal transmission transformer T2, and turns on the switch element Q3. When the switch element Q3 is turned on, the multivibrator MV1 is inverted, the accumulated charge at the gate of the power switch Q1 is discharged via the current / voltage amplifier circuit 55, and the power switch Q1 is turned off. As described above, the timing at which Q1 is turned off is controlled by the comparator CMP1, so that the on-duty of the power switch Q1 is controlled and the output voltage is stabilized to be a substantially constant value.

In the insulated switching power supply 91, when the voltage is normal, the voltage divided by the resistors R6 and R7 is larger than the reference voltage Vref, so that the output voltage of the comparator CMP2 is at the L level. Therefore, the multivibrator MV3 freely oscillates and generates a rectangular wave-shaped pulse signal. This pulse signal is transmitted to the delay circuit 54 via the secondary coil n32 and the primary coil n31 of the second signal transmission transformer T3. (The state where the pulse signal is transmitted continues.)
While the pulse signal is applied to the hiccup control circuit 53 via the delay circuit 54, the output voltage of the hiccup control circuit 53 is maintained at the L level and does not hinder the oscillation operation of the multivibrator MV1, so that the power switch Q1 Switching operation is continued.

  As shown in the waveform (a) in FIG. 4, when the output of the isolated switching power supply is short-circuited at the point A, the voltage drop of the output current detection resistor R8 increases and the overcurrent protection circuit 59 causes the first signal The transmission timing of the pulse signal transmitted from the secondary side to the primary side by the transmission transformer is advanced, and the duty of the power switch Q1 is reduced.

  When the output voltage droops due to the reduction of the on-duty of the power switch Q1, the voltage divided by the resistors R6 and R7 decreases. When the voltage falls below the reference voltage Vref, the output voltage of the comparator CMP2 changes from the L level to the H level. Invert to level. When the comparator CMP2 output voltage becomes H level, the oscillation of the multivibrator MV3 stops and the pulse signal is not output. At the same time, the switch element Q14 is turned on and a current is drawn from the alarm signal output terminal VALM, so that an alarm signal is output to the outside of the insulated switching power supply 91. The alarm signal is used for protection operation and maintenance of the load device.

  As described above, when the output voltage of the insulating switching power supply 91 decreases and the multivibrator MV3 does not oscillate, it is transmitted from the secondary side to the primary side via the second signal transmission transformer unit T3 in a normal state. Will not be transmitted. When the pulse signal is not output from the second signal transmission transformer T3, the output voltage of the hiccup control circuit 53 is inverted from the L level to the H level after the delay time defined by the delay circuit 54. When the output voltage of the hiccup control circuit 53 becomes H level, the oscillation of the multivibrator MV1 stops and the switching operation of the power switch Q1 stops.

  The hiccup control circuit 53 pauses the switching operation by setting the output voltage to the H level, and then inverts the output voltage from the H level to the L level again after a certain pause period. When the output voltage of the hiccup control circuit 53 is inverted from the H level to the L level, the multivibrator MV1 oscillates again. As a result, the switching operation of the power switch Q1 is resumed.

  If the output short circuit state is maintained even after the switching operation of the power switch Q1 is resumed, the output voltage is in a drooped state, so that the multivibrator MV3 does not oscillate and passes through the second signal transmission transformer T3. Pulse signal is not transmitted. Therefore, after the delay time defined by the delay circuit 54, the output voltage of the hiccup control circuit 53 (the cnt terminal voltage of the multivibrator MV1) is inverted from the L level to the H level, and the switching operation of the power switch Q1 is stopped again. .

  While the output short circuit state is maintained, the operation → stop → operation → stop is repeated according to the above-described cycle, and the hiccup protection operation is performed. When the short circuit state of the output is released, the output of the comparator CMP2 is inverted to the L level upon restarting. Therefore, the multivibrator MV3 oscillates to generate a pulse signal, and the pulse signal is transmitted from the secondary side to the primary side via the second signal transmission transformer unit T3. As a result, the normal switching operation is restored.

  When the input voltage of the insulation type switching power supply 91 is less than the specified value or when a signal for stopping the insulation type switching power supply 91 is inputted to the remote control terminal RC, the input low voltage monitoring and remote control circuit 52 becomes a multivibrator. The voltage at the cnt terminal of MV1 is set to H level. Therefore, the oscillation of multivibrator MV1 is stopped and the switching operation of power switch Q1 is not performed. When the input voltage becomes equal to or higher than the specified value and no stop signal is input to the remote control terminal RC, the power switch Q1 starts a switching operation.

  When the isolated switching power supply 91 is normally started and when the hiccup operation is restarted, the smoothing capacitor in the output filter 58 is charged, and the output voltage gradually increases. Below the threshold of the protection circuit. In addition, since a power source for driving the multivibrator MV3 is not formed on the secondary side immediately after startup, a delay time occurs even after the insulated switching power supply 91 is started until the multivibrator MV3 starts oscillating. If the delay time formed by the delay circuit 54 is set to be longer than the charging period of the smoothing capacitor and the start delay time of the multivibrator MV3, the output voltage of the hiccup control circuit 53 is L even immediately after the start. Maintained at level. Therefore, the oscillation operation of multivibrator MV1 is not hindered, and the switching operation of power switch Q1 is continued.

<< Second Embodiment >>
FIG. 5 is a circuit diagram of the isolated switching power supply 92 according to the second embodiment, and FIG. 6 is a waveform diagram of each part of the isolated switching power supply 92.
The insulated switching power supply 92 of the second embodiment has a protective operation function that stops latching when the temperature of the circuit element rises above a standard value. In addition, not only when the power switch that is the primary side circuit element is overheated, but also when the synchronous rectifier that is the secondary side circuit element is overheated, the latch is stopped. Can do.

  5 includes an + input terminal “+ Vin” of the isolated switching power supply, a −input terminal “−Vin” of the isolated switching power supply, a + output terminal “+ Vout” of the isolated switching power supply, an isolated type The output terminal “−Vout” of the switching power supply is provided with an auxiliary power input terminal Vcc for driving the primary control circuit.

The insulating switching power supply 92 includes the following components.
Switch elements Q1, Q4, Q5, Q6, which are N-channel MOSFETs, respectively.
NPN transistors Q7, Q10,
PNP transistors Q8, Q11,
Thyristor Q9,
Diodes D4, D5, D6,
First positive thermistor PTH1,
Second positive thermistor PTH2,
Capacitors C5, C6, C7, C8, C9, C10, C11,
Choke coil L1,
Resistors R9, R10, R11, R12, R13, R14, R15, R16, R17,
Transformers T1, T2, T3 configured in one composite transformer
PWM control IC 60,
And an alarm signal output circuit 61.

  The switch element Q1 is a power switch (main switch), the switch element Q4 is a rectification side synchronous rectifier, and the switch element Q5 is a commutation side synchronous rectifier.

The positive thermistor PTH1 is mounted in the vicinity of the power switch Q1, and detects the temperature of the power switch Q1. The positive thermistor PTH2 is mounted in the vicinity of the synchronous rectifiers Q4 and Q5, and detects the temperature of the synchronous rectifiers Q4 and Q5.
The capacitor C5 smoothes the input voltage, and the capacitor C10 smoothes the output voltage.

  The transformer T1 is a power transmission transformer, and includes a primary coil n11, a secondary coil n12, and a tertiary coil n13. The transformer T2 is a first signal transmission transformer, and includes a primary coil n21 and a secondary coil n22. Furthermore, the transformer T3 is a second signal transmission transformer, and includes a primary coil n31 and a secondary coil n32.

  The PWM control IC 60 includes an auxiliary power input terminal Vcc, a gate drive signal output terminal out of the power switch Q1, a ground terminal gnd, and a control terminal cnt for switching operation.

  When the voltage at the cnt terminal is at the H level, a gate drive signal is output from the out terminal. When the voltage at the cnt terminal becomes L level, the out terminal becomes the potential of the gnd terminal, and the power switch Q1 is kept off.

  In FIG. 6, the gate-source voltage waveform (a) of the power switch Q1 of the isolated switching power supply 92, the drain-source voltage waveform (b) of the power switch Q1, the primary coil n11 of the power transmission transformer unit T1. Current waveform (c), drain-source voltage (d) of the synchronous rectifier Q5, input / output voltage waveform (e) of the first signal transmission transformer T2, voltage across the first positive thermistor PTH1 (f), The voltage across the positive terminal 2 (g) of the positive thermistor PTH2, the input / output voltage waveform (h) of the second signal transmission transformer T3, and the voltage waveform (i) of the cnt terminal of the PWM control IC 60 are shown.

  In FIG. 6, the left half shows a state in which the power switch Q1 is overheated at point A and the resistance value of the positive thermistor PTH1 increases rapidly. The right half shows how the synchronous rectifier Q4 or Q5 is overheated at point B and the resistance of the positive thermistor PTH2 increases rapidly.

  The insulated switching power supply 92 according to the second embodiment is a resonant reset forward converter in which the rectifiers on the rectification side and the commutation side are configured by synchronous rectifiers. The DC power input between the input terminals “+ Vin” and “−Vin” of the insulated switching power supply 92 is smoothed by the capacitor C5, and then switched by the power switch Q1 to be converted to AC power. The AC power is transmitted from the primary coil n11 to the secondary coil n12 of the power transmission transformer T1, and is rectified by the rectification side synchronous rectifier Q4 and the commutation side synchronous rectifier Q5 that are driven at complementary timings. And it is smoothed by the output filter comprised by the choke coil L1 and the capacitor | condenser C10, and is output as direct-current power from between output terminal "+ Vout"-"-Vout".

  In the isolated switching power supply 92, the rectifying side synchronous rectifier Q4 is driven so as to be turned on during the on period of the power switch Q1 and turned off during the off period of the power switch by the voltage generated in the secondary coil n12 of the power transmission transformer unit T1. The

  The commutation side synchronous rectifier Q5 has a source of the switch element Q6 → the drain of the switch element Q6 → the tertiary coil n13 → commutation by a reset voltage generated in the tertiary coil n13 of the power transmission transformer T1 immediately after the power switch Q1 is turned off. A current flows through the gate path of the side synchronous rectifier Q5. Therefore, the input capacity of the commutation side synchronous rectifier Q5 is charged and the commutation side synchronous rectifier Q5 is turned on.

  Even if the resonance reset voltage is no longer supplied from the power transmission transformer T1, if the switch element Q6 is turned off, the gate storage charge of the commutation side synchronous rectifier Q5 is not discharged and the commutation side synchronous rectifier Q5 is turned on. to continue. When a gate drive signal appears at the out terminal of the PWM control IC 60, a pulse signal is generated in the first signal transmission transformer T2 by the charging operation of the input capacitance of the power switch Q1 by the gate drive signal. This pulse signal is transmitted from the primary coil n21 to the secondary coil n22 of the first signal transmission transformer T2, and is applied between the gate and source of the switch element Q6, and the switch element Q6 is turned on. When the switch element Q6 is turned on, the charge accumulated in the gate of the commutation side synchronous rectifier Q5 is changed from the gate of the commutation side synchronous rectifier Q5 to the tertiary coil n13 of the power transmission transformer T1 → the drain of the switch element Q6 → the switch element Q6. And the commutation side synchronous rectifier Q5 is turned off.

By the operation described above, the commutation side synchronous rectifier Q5 is turned off immediately before the power switch Q1 is turned on, so that a short-circuit current due to the turn-off delay of the commutation side synchronous rectifier Q5 does not flow and power conversion can be performed with high efficiency.

  In FIG. 5, although not shown, an error signal generated by comparing the output voltage of the isolated switching power supply 92 with the reference voltage is fed back to the PWM control IC 60, and the PWM control IC 60 turns on the duty of the power switch Q1. By controlling, the output voltage is stabilized.

  In the switching power supply operating as described above, the temperatures of the power switch Q1 and the synchronous rectifiers Q4 and Q5 are kept sufficiently low during normal operation, and the positive thermistors PTH1 and PTH2 also have a low resistance value. The series circuit of the resistor R9, the capacitor C6, and the positive thermistor PTH1, and the series circuit of the resistor R14, the capacitor C9, and the positive thermistor PTH2 each form an RC snubber circuit. , R14 is smaller than the resistance value, and the fluctuation width of the voltage across the positive thermistors PTH1, PTH2 due to the fluctuation of the voltage across the power switch Q1 and commutation side synchronous rectifier Q5 is small, and the transistors Q7, Q10 maintain the off state. .

  If the temperature of the power switch Q1 rises at point A in FIG. 6 due to some abnormality, the resistance value of the positive thermistor PTH1 mounted in the vicinity of the power switch Q1 increases. Therefore, as shown in the waveform (f) in FIG. 6, a pulse voltage is generated across the positive thermistor PTH1 when the power switch Q1 is turned off.

  When the transistor Q7 is turned on by the pulse voltage, the transistor Q8 is turned on, and a current flows through the capacitor C7 to the primary coil n31 of the second signal transmission transformer T3. As a result, as shown in the waveform (h) in FIG. 6, a pulse voltage is generated in the second signal transmission transformer T3. Since this pulse voltage becomes a trigger and the thyristor Q9 is turned on, the cnt terminal voltage of the PWM control IC 60 is latched to the L level, and the insulating switching power supply 92 is latched and stopped.

  If the temperature of the synchronous rectifier Q4 or Q5 rises at point B in FIG. 6 due to some abnormality, the resistance value of the positive thermistor PTH2 mounted in the vicinity of the synchronous rectifiers Q4 and Q5 increases. Therefore, as shown in the waveform (f) in FIG. 6, when the power switch Q1 is turned off, a pulsed voltage is generated across the positive thermistor PTH2. When the transistor Q10 is turned on by this pulse voltage, the transistor Q11 is turned on, and a current flows through the capacitor C11 to the secondary coil n32 of the second signal transmission transformer T3. As a result, a pulse voltage is generated in the second signal transmission transformer T3 as shown by the waveform (h) in FIG. Since this pulse voltage becomes a trigger and the thyristor Q9 is turned on, the cnt terminal voltage of the PWM control IC 60 is latched to the L level, and the isolated switching power supply is latched and stopped.

  The diode D6 connected to the secondary coil n32 of the second signal transmission transformer unit T3 conducts a negative voltage immediately after the second signal transmission transformer unit T3 transmits a positive pulse signal, and the second signal transmission transformer unit T3 conducts the second voltage. The excitation of the signal transmission transformer unit T3 is reset.

  When the alarm signal output circuit 61 detects a pulse signal generated (or applied) in the secondary coil n32 of the second signal transmission transformer T3, the alarm signal output circuit 61 outputs the alarm signal to the outside. Since the second signal transmission transformer T3 transmits the abnormality detection signal in both directions, an alarm signal output circuit can be obtained by connecting an alarm signal output circuit to the primary coil n31 of the second signal transmission transformer T3. A circuit can also be provided on the primary side.

  As described above, when the power switch Q1 that is the primary side circuit element is overheated or the synchronous rectifiers Q4 and Q5 that are the secondary side circuit elements are overheated, the thyristor Q9 is turned on and the latch is stopped. Perform protective actions. In this way, since the temperatures of the plurality of circuit elements are monitored over the primary and secondary orders, a highly safe overheat protection operation can be performed.

  In addition, this invention is not limited to the above-mentioned embodiment, Various application expansion | deployment is possible. In addition to the output undervoltage state and the circuit element overheat state, the abnormal mode detected by the protection circuit includes an input undervoltage state, an input overvoltage state, an output overvoltage state, an input current overcurrent state, or It can be applied to an overcurrent state of the output current. Further, a signal indicating an abnormal state can be transmitted not only from the secondary side to the primary side but also from the primary side to the secondary side. Further, for example, it is possible to mix with a drive signal or feedback signal of a synchronous rectifier and transmit another signal by one pulse transformer, and to separate each signal after reception. Further, a signal indicating an abnormal state may be transmitted in the form of a digital signal.

CMP1, CMP2 ... comparator cnt ... control terminal D1 ... rectifier diode gnd ... ground terminal L1 ... choke coil MV1, MV2, MV3 ... multivibrator n11 ... primary coil n12 ... secondary coil n13 ... tertiary coil n14 ... quaternary coil n15 ... 5th coil n21 ... Primary coil n22 ... Secondary coil n31 ... Primary coil n32 ... Secondary coil out ... Output terminals PTH1, PTH2 ... Positive thermistor Q1 ... Switch element (power switch)
Q2 ... Switch element (clamp switch)
Q4 ... Rectification side synchronous rectifier Q5 ... Commutation side synchronous rectifier Q9 ... Thyristor R8 ... Output current detection resistor RC ... Remote control terminal T1 ... Power transmission transformer T2 ... First signal transmission transformer T3 ... Second signal transmission transformer Unit VAL ... alarm signal output terminal Vcc ... auxiliary power supply input terminal Vref ... reference voltage 51 ... input filter 52 ... input low voltage monitoring and remote control circuit 53 ... hiccup control circuit 54 ... delay circuit 55 ... current / voltage amplification circuit 56 ... clamp Switch Q2 drive circuit 57 ... Zero voltage state detection circuit 58 ... Output filter 59 ... Overcurrent protection circuit 60 ... PWM control IC
91, 92 ... Insulated switching power supply

Claims (4)

An input and an output are electrically isolated by a power transmission transformer, and at least one power switch is provided on a primary side of the power transmission transformer to switch input power; and at least one rectifier element on a secondary side; An isolated switching power supply that includes an output filter and supplies power to a load device,
A power transformer unit and a signal transmission transformer unit, which are substantially independent of each other, are provided with a composite transformer integrally formed by sharing a pair of cores,
An abnormality detection circuit for detecting an abnormality of the isolated switching power supply or the load device, and a signal in a normal state from the secondary side to the primary side via the signal transmission transformer unit when the abnormality detection circuit detects an abnormality. An abnormal condition signal transmission circuit for transmitting different abnormal condition signals is provided on the secondary side,
In response to the abnormal state signal, the primary side is provided with a protection operation execution circuit that performs protection operation of the isolated switching power supply or the load device ,
The abnormal state signal transmission circuit includes a pulse signal generation circuit that repeatedly generates a pulse signal in a normal state and supplies the pulse signal to the protection operation implementation circuit through the signal transmission transformer unit,
The protection operation execution circuit determines that the pulse signal is not detected as an abnormal state and performs the protection operation.
The protection operation implementation circuit includes a delay circuit that masks a period from immediately after the normal startup of the isolated switching power supply to when the pulse signal is generated so as not to reach the protection operation.
Isolated switching power supply.   The insulated switching power supply according to claim 1, further comprising an alarm signal output circuit that outputs an alarm signal when the abnormal state signal is generated on a primary side or a secondary side. The insulated switching power supply according to claim 1 or 2 , wherein the protection operation of the protection operation implementation circuit is performed by reducing the on-duty of the power switch, stopping the latching of the power switch, or hiccup operation. An abnormality of the isolated switching power supply detected by the abnormality detection circuit includes an input undervoltage state, an input overvoltage state, an output undervoltage state, an output overvoltage state, an input current overcurrent state, and an output current overcurrent state. The insulated switching power supply according to any one of claims 1 to 3 , wherein the insulated switching power supply is at least one of an overheated state of components of the insulated switching power supply.

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