CN111614062A - Short circuit protection circuit of multiple output power supply - Google Patents

Abstract

The invention discloses a short-circuit protection circuit of a multi-channel output power supply, comprising a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor; a base of the first triode The electrode is connected to the first voltage terminal of the multi-output power supply through the first resistor, the collector of the first triode is connected to the base of the second triode through the second resistor, and is connected to the second triode through the third resistor. The emitter of the first triode is connected to the ground through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-output power supply; the collector of the second triode is connected to the PWM output control terminal of the multi-output power supply connected and the emitter is grounded; the first triode and the second triode are converted from the off state to the on state when the first voltage end of the multi-channel output power supply is reduced by the influence of the output end short circuit; the present invention is used in the multi-channel output When any output terminal of the power supply is short-circuited, it can effectively protect the multi-output power supply.

Description

Short circuit protection circuit of multiple output power supply

technical field

The invention relates to the technical field of circuit protection, in particular to a short-circuit protection circuit for multiple output power supplies.

Background technique

A typical flyback power supply is shown in Figure 5. The flyback power supply consists of a startup circuit, a power management chip, a feedback circuit and a coupling transformer. The feedback circuit consists of an optocoupler and a TL431 device. The main output winding in the multi-output power supply The output voltage is detected by the feedback circuit, and forms a voltage loop control with the power management chip. When the main output winding is short-circuited or under light and heavy load, a closed-loop control is formed through the feedback circuit to achieve the function of a stable power supply protection circuit. In a traditional multi-output flyback circuit, under ideal conditions, if one of the outputs is short-circuited, the other windings will be scaled according to the actual number of turns, and the auxiliary winding will also reduce the voltage. When the undervoltage point is reached, the power chip will It will restart, so as to achieve short-circuit protection at the output until the short-circuit disappears. However, in practice, due to factors such as line impedance and leakage inductance between windings, all output short circuits are not scaled according to the turns ratio, which will cause the following problems: one of them may be short-circuited and the power supply is still working. , until the output burns out.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a short circuit protection circuit for multiple output power supplies, so as to effectively protect the multiple output power supplies when any output terminal of the multiple output power supplies is short-circuited.

In order to solve the above-mentioned technical problems, the technical scheme adopted in the present invention is:

The short-circuit protection circuit of the multi-channel output power supply includes a first transistor, a second transistor, a first resistor, a second resistor, a third resistor and a charging capacitor;

The base of the first triode is connected to the first voltage terminal of the multi-output power supply through the first resistor, and the collector of the first triode is connected to the second third through the second resistor. The base of the transistor is connected to the emitter of the second transistor through the third resistor, the emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the The second voltage terminal of the multi-channel output power supply is connected;

The collector of the second transistor is connected to the PWM output control terminal of the multi-output power supply, and the emitter is grounded;

The first triode is a PNP triode, and the second triode is an NPN triode;

The first triode and the second triode are converted from an off state to an on state when the first voltage terminal of the multi-channel output power supply is lowered due to the influence of the output terminal short circuit.

The beneficial effects of the present invention are: the short-circuit protection circuit of the multi-channel output power supply, when the multi-channel output power supply works normally, the charging capacitor is charged by the second voltage terminal of the multi-channel output power supply until the stable voltage is reached; When any output terminal of the power supply is short-circuited, the first voltage terminal of the multi-channel output power supply changes, so that the first transistor is converted from the off state to the on state. At this time, since the first transistor is a PNP transistor, Therefore, the charging capacitor connected to the emitter of the first triode begins to discharge, and driven by the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that it is connected to the collector of the second triode. The PWM output control terminal of the connected multi-output power supply starts to discharge to the ground, so that the voltage of the PWM output control terminal starts to drop, thereby cutting off the output of the PWM output terminal, so as to effectively protect the multi-output power supply. That is, the present invention solves the influence of different factors such as leakage inductance and equivalent resistance between the transformer windings on the output short circuit by building a circuit at low cost, so that when any output end of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be short-circuited. The output power is effectively protected.

Description of drawings

1 is a schematic diagram of the coordinated connection between a short-circuit protection circuit of a multi-channel output power supply and a multi-channel output power supply according to an embodiment of the present invention;

FIG. 2 is a specific circuit schematic diagram of the cooperative connection between the short-circuit protection circuit of the multi-channel output power supply and the start-up circuit, the power management chip and the feedback circuit of the multi-channel output power supply according to the embodiment of the present invention;

3 is a schematic diagram of the cooperative connection between a short-circuit protection circuit of a multi-channel output power supply and a multi-channel output power supply according to another embodiment of the present invention;

4 is a specific circuit schematic diagram of the cooperative connection between the short-circuit protection circuit of the multi-output power supply and the start-up circuit, the power management chip, and the feedback circuit of the multi-output power supply according to another embodiment of the present invention;

FIG. 5 is a schematic circuit diagram of a multi-channel output power supply in the prior art.

Label description:

C1-C5 are all capacitors, among which, C1, the first capacitor; C2, the charging capacitor;

D1-D6 are all diodes, wherein D1, the first diode; D2/D4, the second diode; D3, the third diode;

Q1, the first transistor; Q2, the second transistor;

R1-R19 are all resistors, among which, R1/R9, the first resistor; R2, the second resistor, R3, the third resistor; R4, the fourth resistor; R5, the fifth resistor; R6, the sixth resistor; R7, the first resistor Seven resistors; R8, eighth resistors;

U1, optocoupler; U2, TL431 device; U3, power management chip;

V1/V2, branch output terminal of multi-channel output power supply; V3, main output terminal of multi-channel output power supply; Vcc, power supply voltage; Vin, input DC high voltage.

Detailed ways

In order to describe in detail the technical content, achieved objects and effects of the present invention, the following descriptions are given with reference to the embodiments and the accompanying drawings.

Please refer to FIG. 1 to FIG. 4 , the short-circuit protection circuit of the multi-channel output power supply includes a first transistor, a second transistor, a first resistor, a second resistor, a third resistor and a charging capacitor;

The base of the first triode is connected to the first voltage terminal of the multi-output power supply through the first resistor, and the collector of the first triode is connected to the second third through the second resistor. The base of the transistor is connected to the emitter of the second transistor through the third resistor, the emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the The second voltage terminal of the multi-channel output power supply is connected;

The collector of the second transistor is connected to the PWM output control terminal of the multi-output power supply, and the emitter is grounded;

The first triode is a PNP triode, and the second triode is an NPN triode;

The first triode and the second triode are converted from an off state to an on state when the first voltage terminal of the multi-channel output power supply is lowered due to the influence of the output terminal short circuit.

It can be seen from the above description that the beneficial effects of the present invention are: when the multi-channel output power supply is working normally, the charging capacitor is charged by the second voltage terminal of the multi-channel output power supply until a stable voltage is reached; when any one of the multi-channel output power supply When the output terminal is short-circuited, the first voltage terminal of the multi-channel output power supply changes, so that the first transistor is converted from the off state to the on state. At this time, since the first transistor is a PNP transistor, the The charging capacitor connected to the emitter of a triode begins to discharge. Driven by the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that the multiplexer connected to the collector of the second triode starts to conduct. The PWM output control terminal of the output power supply starts to discharge to the ground, so that the voltage of the PWM output control terminal starts to drop, thereby cutting off the output of the PWM output terminal, so as to effectively protect the multi-channel output power supply. That is, the present invention solves the influence of different factors such as leakage inductance and equivalent resistance between the transformer windings on the output short circuit by building a circuit at low cost, so that when any output end of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be short-circuited. The output power is effectively protected.

Further, it also includes a first diode, a fourth resistor, a fifth resistor and a sixth resistor, and the first voltage terminal and the PWM output control terminal are both the power supply voltage terminals of the multi-channel output power supply;

The fourth resistor is connected between the collector of the second transistor and the supply voltage terminal of the multi-output power supply;

The emitter of the first triode is grounded through the charging capacitor, and the connection between the charging capacitor and the second voltage terminal of the multi-channel output power supply is as follows:

The emitter of the first triode is connected to one end of the charging capacitor and one end of the fifth resistor at the same time, and the other end of the charging capacitor is grounded and connected to the first triode through the sixth resistor The base of the tube is connected, the other end of the fifth resistor is connected to the cathode of the first diode, and the anode of the first diode is connected to the reference voltage terminal of the power management chip of the multi-output power supply connect;

The steady-state voltage of the charging capacitor is smaller than the voltage at both ends of the sixth resistor in the normal state of the multi-channel output power supply and is greater than the two ends of the sixth resistor short-circuited at the output end of the multi-channel output power supply Voltage.

It can be seen from the above description that when the charging capacitor is charged to the steady-state voltage, the sixth resistor is set at the base of the first triode because it is smaller than the voltage across the sixth resistor in the normal state of the multi-output power supply. , therefore, for the PNP triode, when the multi-channel output power supply works normally, the first triode is in an off state. When any output terminal is short-circuited, according to the equivalent voltage calculation of the turns ratio, the power supply voltage of the power supply voltage terminal of the multi-output power supply will be pulled down. However, due to the leakage inductance and equivalent impedance of each output terminal, it is not guaranteed. When all the output terminals are short-circuited, the power supply voltage can be pulled down to the undervoltage protection point; at this time, the power supply voltage starts to be pulled down, so that the voltage across the sixth resistor begins to drop, because the steady-state voltage of the charging capacitor is greater than that of the sixth resistor at The output terminal of the multi-channel output power supply is short-circuited to the voltage at both ends, that is, the first transistor is turned on, and the charging capacitor starts to discharge. Driven by the voltage of the charging capacitor and the third resistor, the second diode starts to conduct. , so that the power supply voltage terminal connected to the collector of the second triode begins to discharge rapidly to the ground, wherein the driving voltage terminal of the power management chip of the multi-channel output power supply is connected to the power supply voltage terminal, so that the voltage of the power supply voltage terminal triggers the power management The under-voltage protection point of the driving voltage end of the chip cuts off the output of the PWM output end to effectively protect the multi-channel output power supply.

Further, the resistance ratio of the first resistor and the sixth resistor is X, and the steady-state voltage of the charging capacitor is less than the power supply voltage of the multi-channel output power supply in a normal state/(X+1) and It is greater than the supply voltage/(X+1) of the multi-channel output power supply when any one of the output power supplies is short-circuited.

It can be seen from the above description that when the steady-state voltage of the limiting charging capacitor is less than the power supply voltage of the multi-channel output power supply in the normal state/(X+1) and greater than the supply voltage of the multi-channel output power supply when any output power supply is short-circuited/(X +1), that is, assuming that the power supply voltage of the multi-channel output power supply is 16V in normal state, the supply voltage when any output power supply is short-circuited is 12V, and the resistance ratio of the first resistor and the sixth resistor is 2, then the charging capacitor The steady-state voltage is less than 5.33V and greater than 4V, to ensure that any output power supply is short-circuited, and the voltage of the base and emitter of the first transistor changes, so as to convert the first transistor from the off state to the on state. .

Further, the power supply voltage terminal of the multi-channel output power supply is also connected with a first capacitor, and the discharge constant formed between the charging capacitor, the second resistor and the third resistor is greater than the first capacitor and the third resistor. 10 times the discharge constant formed between the fourth resistors.

It can be seen from the above description that by limiting the discharge constant, the voltage across the charging capacitor discharges to the ground through the first triode, the second resistor and the third resistor is slower than the power supply voltage discharges to the ground through the fourth resistor To the undervoltage protection point of the driving voltage terminal of the voltage-triggered power management chip, to ensure that the power supply voltage of the power supply voltage terminal can trigger the undervoltage protection point of the driving voltage terminal of the power management chip.

Further, it also includes a second diode, a seventh resistor and an eighth resistor corresponding to the number of auxiliary power supply branches of the multi-channel output power supply, and the PWM output control terminal is the light of the multi-channel output power supply. Coupling detection output voltage terminal;

The connection between the base of the first transistor and the first voltage terminal of the multi-channel output power supply through the first resistor is as follows:

The base of the first triode is connected to one end of the first resistor, and the other end of the first resistor is connected to the anodes of the plurality of second diodes at the same time, each of the second diodes The cathodes are respectively connected with the branch output ends of an auxiliary power supply branch of the multi-output power supply;

The emitter of the first triode is grounded through the charging capacitor, and the connection between the charging capacitor and the second voltage terminal of the multi-channel output power supply is as follows:

The emitter of the first transistor is simultaneously connected to one end of the charging capacitor, one end of the seventh resistor, and one end of the eighth resistor, and the other end of the charging capacitor is connected to the seventh resistor. The other end is grounded at the same time, and the other end of the eighth resistor is connected to the main output end of the multi-output power supply;

The steady-state voltage of the charging capacitor is greater than a and less than a+b, where a is the conduction voltage between the emitter and the base of the first transistor, and b is the multi-channel output power supply The lowest value of the normal voltage of all auxiliary power supply branches.

It can be seen from the above description that the steady-state voltage of the charging capacitor is limited, so that in the normal state of the multi-output power supply, the voltage difference between the emitter and the base of the first triode is less than the on-voltage and is in the off-state. When any output terminal is short-circuited, one of the second diodes is turned on, causing the base voltage of the first diode to drop rapidly, because the steady-state voltage of the charging capacitor is greater than the emitter and base of the first transistor. If the conduction voltage between the poles is high, the first diode is turned on at this time, so that the base voltage of the second diode rises rapidly, and then the second diode is turned on, so that the optocoupler is saturated and turned on, Turn off the PWM output of the original power management chip. Subsequently, the main output terminal of the multi-output power supply drops rapidly, and the first resistor, the second resistor and the third resistor are discharged by the charging capacitor to maintain the conduction of the second diode, so the auxiliary power will be turned off for a period of time. ; When the voltage of the charging capacitor drops to the point where the first transistor cannot be turned on, the auxiliary power is restarted. If the short circuit of the multi-channel output power supply still exists, the charging capacitor will be charged to the conduction of the first transistor. When the voltage is above, the PWM output of the power management chip is turned off again, the power supply enters the restart state again, and then restarts repeatedly, the power supply enters the "hiccup" protection mode; and when the short-circuit condition of the multi-output power supply has been eliminated, the When the power supply is restarted, due to the charging delay, when the voltage of the charging capacitor is charged above the turn-on voltage of the first triode, the branch voltage has risen, so that the first diode and the second diode remain off, and the auxiliary energy Starts normally and works.

Further, the ninth resistance is greater than the eighth resistance.

It can be seen from the above description that the discharge constant between the charging capacitor and the ninth resistor is greater than the charging constant between the charging capacitor and the eighth resistor, so as to slow down the discharging speed of the charging capacitor.

Further, it also includes a third diode, and the emitter of the first triode is connected to one end of the charging capacitor, one end of the seventh resistor, and one end of the eighth resistor at the same time. Specifically:

The emitter of the first triode is connected to one end of the charging capacitor and the cathode of the third diode at the same time, and the anode of the third diode is simultaneously connected to one end of the seventh resistor and the cathode of the third diode. One end of the eighth resistor is connected.

As can be seen from the above description, after the main output end is powered off, a discharge channel of the charging capacitor is cut off by the third diode, so as to slow down the discharging speed of the charging capacitor.

Further, the steady-state voltage of the charging capacitor is greater than a+c and less than a+b+c, where c is the turn-on voltage of the third diode.

It can be seen from the above description that when the third diode is added, the on-voltage of the diode needs to be considered to change the state of the first transistor.

Further, the steady-state voltage of the charging capacitor is greater than a+0.4b+c and less than a+0.6b+c.

As can be seen from the above description, when the steady-state voltage of the charging capacitor is greater than a+0.4b+c and less than a+0.6b+c, the first triode can be quickly turned on in the event of a short-circuit fault.

Further, the discharge constant formed between the charging capacitor and the ninth resistor is between 0.1 seconds and 10 seconds.

It can be seen from the above description that a reasonable charging capacitor is selected to cooperate with the ninth resistor, so that the discharging speed of the charging capacitor is slow, so as to maintain a reasonable hiccup time and reduce losses.

The following two embodiments are provided for different connection positions of the PWM output control terminals.

Please refer to FIG. 1 to FIG. 2 , the first embodiment of the present invention is:

The short-circuit protection circuit of the multi-channel output power supply corresponds to the first protection circuit in FIG. 1, wherein the first protection circuit of this embodiment is connected to the power management chip U3, and the power supply voltage Vcc of the power management chip U3 is monitored to realize the protection. circuit protection.

As shown in FIG. 2 , the first protection circuit includes a first transistor Q1, a second transistor Q2, a first resistor R1, a second resistor R2, a third resistor R3, a charging capacitor C2, and a first diode D1 , the fourth resistor R4, the fifth resistor R5 and the sixth resistor R6; the base of the first transistor Q1 is connected to the supply voltage terminal of the multi-output power supply through the first resistor R1, and the collector of the first transistor Q1 The second resistor R2 is connected to the base of the second transistor Q2 and the third resistor R3 is connected to the emitter of the second transistor Q2. The emitter of the first transistor Q1 is connected to one end of the charging capacitor C2 at the same time. , One end of the fifth resistor R5 is connected, the other end of the charging capacitor C2 is grounded and connected to the base of the first transistor Q1 through the sixth resistor R6, and the other end of the fifth resistor R5 is connected to the cathode of the first diode D1 connected, the anode of the first diode D1 is connected to the reference voltage terminal VREF of the power management chip U3 of the multi-channel output power supply; wherein, the collector of the second transistor Q2 is connected to the power supply of the multi-channel output power supply through the fourth resistor R4 The voltage terminal is connected and the emitter is grounded; when the supply voltage terminal of the multi-channel output power supply is reduced by the short circuit of the output terminal, the first transistor Q1 is converted from the off state to the on state.

That is, in this embodiment, the first transistor Q1 is a PNP transistor, the second transistor Q2 is an NPN transistor, and the first voltage terminal and the PWM output control terminal are both the supply voltage terminals of the multi-channel output power supply, that is, the corresponding figure The power supply voltage Vcc of 2; the second voltage terminal is the reference voltage terminal VREF of the power management chip U3 of the multi-channel output power supply.

According to Figure 2 and the above description, at the moment of power-on, the first capacitor C1 (100uF/50V) is charged by the input DC high voltage Vin through the resistors R15-R17 (200k/3W) to reach the starting voltage of the power supply, and the flyback power supply starts. In this embodiment, the input DC high voltage Vin is a fixed voltage of 16V, and the reference voltage terminal VREF of the power management chip U3 (UC2845BD) of the multi-channel output power supply passes through the first diode D1 (150mA/100V), the fifth resistor R5 (10k/0603) charges the charging capacitor C2 (10uF/16V) until the voltage across the charging capacitor C2 is 5V; at the same time, the first resistor R1 (150k/0603) and the sixth resistor R6 (75k/0603) are set The ratio is 2:1; at this time, the voltage across the sixth resistor R6 is 5.33V, and the first transistor Q1 (0.6A/-60V) is in an off state. When any output terminal is short-circuited, the power supply voltage Vcc will be pulled down according to the equivalent voltage of the turns ratio. However, due to the leakage inductance and equivalent impedance of each output terminal, it cannot be guaranteed that when all outputs are short-circuited, the power supply voltage Vcc can be pulled down to the undervoltage protection point. Take the worst route as an example, when the power supply voltage Vcc is pulled down to 12V, the voltage at both ends of the sixth resistor R6 is 4V, the first transistor Q1 will be turned on, and the second transistor Q2 (0.6 A/60V) will also be turned on under the drive of the voltage of the charging capacitor C2 and the second resistor R2 (5k/0603), and the supply voltage Vcc will pass through the fourth resistor R4 (100Ω/0805) and the second transistor Q2 is rapidly discharged to the ground, wherein the discharge constant formed between the charging capacitor C2, the second resistor R2 and the third resistor R3 is greater than 10 times the discharge constant formed between the first capacitor C1 and the fourth resistor R4, so that the charging capacitor The speed at which the voltage across C2 is discharged to ground through the first transistor Q1 and the third resistor R3 is slower than the discharge of the supply voltage Vcc to the ground through the fourth resistor R4 to the voltage-triggered power supply management chip U3 driving voltage terminal VI To ensure that the power supply voltage Vcc of the power supply voltage terminal can trigger the undervoltage protection point of the driving voltage terminal VI of the power management chip U3, thereby cutting off the output of the PWM output terminal OUTPUT to effectively protect the multi-channel output power supply.

In this embodiment, the resistance ratio of the first resistor R1 and the sixth resistor R6 is 2, the steady-state voltage of the charging capacitor C2 is 5V, the power supply voltage Vcc is 16V in a normal state, and 12V in a load short-circuit state . In other equivalent embodiments, when the resistance ratio of the first resistor R1 and the sixth resistor R6 is X, the steady-state voltage of the charging capacitor C2 is lower than the supply voltage Vcc/(X+ 1) and is greater than the power supply voltage Vcc/(X+1) of the multi-channel output power supply when any output power supply is short-circuited.

Please refer to FIG. 3 to FIG. 4 , the second embodiment of the present invention is:

The short-circuit protection circuit of the multi-channel output power supply corresponds to the second protection circuit in FIG. 3 , wherein the second protection circuit of this embodiment is connected to the optocoupler U1, and the output terminal voltage of the optocoupler U1 is monitored to realize the protection. circuit protection.

As shown in FIG. 4 , the second protection circuit includes a first transistor Q1, a second transistor Q2, a first resistor R9, a second resistor R2, a third resistor R3, a charging capacitor C2, and a multi-channel output power supply. The number of auxiliary power supply branches corresponds to the second diode D2/D4, the seventh resistor R7, the eighth resistor R8 and the third diode D3; the base of the first transistor Q1 and one end of the first resistor R9 connection, the other end of the first resistor R9 is connected to the anodes of a plurality of second diodes D2/D4 at the same time, and the cathodes of each second diode D2/D4 are respectively connected to an auxiliary power supply branch of an auxiliary power supply branch of the multi-channel output power supply. The branch output terminals V1/V2 are connected; the collector of the first transistor Q1 is connected to the base of the second transistor Q2 through the second resistor R2 and is connected to the emitter of the second transistor Q2 through the third resistor R3 connected, the emitter of the first transistor Q1 is simultaneously connected to one end of the charging capacitor C2 and the cathode of the third diode D3, and the anode of the third diode D3 is simultaneously connected to one end of the seventh resistor R7 and the eighth resistor R8 The other end of the charging capacitor C2 and the other end of the seventh resistor R7 are grounded at the same time, and the other end of the eighth resistor R8 is connected to the main output terminal V3 of the multi-output power supply; the collector of the second transistor Q2 is connected to The optocoupler detection output voltage terminal of the multi-channel output power supply is connected and the emitter is grounded;

That is, in this embodiment, the first transistor Q1 is a PNP transistor, the second transistor Q2 is an NPN transistor, and the PWM output control terminal is the optocoupler detection output voltage terminal of the multi-channel output power supply, that is, the optoelectronic The fourth terminal of the coupler U1; the first voltage terminal is the branch output terminal V1/V2 of an auxiliary power supply branch of the multi-channel output power supply; the second voltage terminal is the main output terminal V3 of the multi-channel output power supply.

It can be seen from FIG. 4 combined with the above description that in this embodiment, it is assumed that the normal voltage of the main output terminal V3 of the multi-output power supply is 12V, and the minimum value b of the normal voltage of all auxiliary power supply branches of the multi-output power supply is 5V For example, the normal voltage of the branch output terminal V2 in FIG. 4 is b=5V, and the normal voltage of the branch output terminal V1 is 9V. The turn-on voltage a between the emitter and the base of the first transistor Q1 (0.6A/-60V) is generally 0.7V, and the turn-on voltage c of the third diode D3 (150mA/100V) is generally 0.7 V.

At this time, the voltage of the charging capacitor C2 is limited to be less than 6.4V by dividing the voltage by the eighth resistor R8 (2k/0603) and the seventh resistor R7 (1.5k/0603). In other embodiments, the voltage of the charging capacitor C2 Higher than a+c, that is, higher than 1.4V, it may actually be set above 2V, so that when the two auxiliary power supply branches are short-circuited, the first transistor Q1 can be turned on.

Under normal circumstances, the emitter voltage of the first transistor Q1 is lower than the base voltage, the collector-emitter terminals of the first transistor Q1 remain in the off-segment state, and the second transistor Q2 (0.6A/ 60V) both ends of the collector-emitter also maintain the off-stage state, so that the protection circuit does not affect the optocoupler U1.

When any one of the auxiliary power supply branches is short-circuited, the second diode D2 (150mA/100V) or D4 (150mA/100V) is turned on, and the base voltage of the first transistor Q1 drops rapidly, resulting in the first transistor Q1. Q1 is turned on, after the base voltage of the second transistor Q2 rises rapidly, the second transistor Q2 is turned on, and then the photocoupler U1 (K1010-4C-1) is saturated and turned on, turning the original power management chip U3 ( The PWM output terminal OUTPUT of UC2845BD) is closed. Then the voltage of the main output terminal V3 drops rapidly, but the charging capacitor C2 (22uF/16V) has no effect on the second resistor R2 (15k/0603), the third resistor R3 (100k/0603), the first resistor R9 (49.9k/0603) The discharge is slow, and the conduction of the second transistor Q2 can be maintained, so the auxiliary power will be turned off for a period of time. Among them, a discharge channel of the charging capacitor C2 is blocked by the third diode D3 to slow down the charging capacitor C2 The discharge of speed.

When the voltage of the charging capacitor C2 drops to such an extent that the first transistor Q1 cannot be turned on, for example, it drops below 1V, the auxiliary power is restarted. If the short circuit of the multi-output power supply still exists, the charging capacitor C2 will be charged to When the voltage is above 1.4V, turn off the PWM output OUTPUT of the power management chip U3 again, the power supply will enter the restart state again, and then restart repeatedly, the power supply will enter the "hiccup" protection mode;

When the short circuit of the multi-channel output power supply has been eliminated, the power supply is restarted, and the voltage of the charging capacitor C2 is gradually charged to more than 1.4V under the limit of the eighth resistor R8, and the voltages of the branch voltage terminals V1 and V2 have been rising, so that the first diode D1 and the second diode D2/D4 remain off, and the auxiliary power starts and works normally.

Among them, in this embodiment, b=5V, a=c=0.7V, then the steady-state voltage of the charging capacitor is further limited to be greater than 3.4V to 4.4, such as about 3.9V, to ensure that the first transistor Q1 can be quickly turned on in the event of a short-circuit fault, so as to quickly realize the protection of the circuit.

Wherein, in this embodiment, the capacity of the charging capacitor C2 is 22uF, and the resistance values of the first resistor R9, the second resistor R2 and the third resistor R3 are 49.9k, 15k and 100k respectively. In other equivalent embodiments, the capacity of the charging capacitor C2 is larger, and the resistance difference between the first resistor R9 and the eighth resistor R8 is larger. Therefore, the charging capacitor C2 is different from the first resistor R9 and the second resistor R2. The discharge constant formed between the third resistor R3 and the third resistor R3 is between 0.1 seconds and 10 seconds (such as about 0.25s), that is, in the second level. At this time, the charging constant of the charging capacitor C2 and the eighth resistor R8 is controlled within a few seconds. Ten milliseconds (such as about 50ms); for example, when the first resistor R9 and the second resistor R2 are 49.9k and 15k respectively in this embodiment, the eighth resistor R8 is 2k, and the seventh resistor R7 is 1.5k. Therefore, through reasonable selection of the charging capacitor C2, the first resistor R9, the second resistor R2, the third resistor R3, the seventh resistor R7 and the eighth resistor R8, the discharge speed of the charging capacitor C2 can be slowed down and a reasonable hiccup can be maintained. Time, reduce loss; at the same time, avoid charging too fast and cause the auxiliary power to fail to restart.

Among them, as shown in FIG. 2, in order to facilitate understanding of the present invention, the PWM circuit composed of the power management chip U3 and the voltage output circuit composed of the optocoupler U1 and the TL431 device U2 in FIG. 2 are described.

Among them, the PWM circuit includes resistor R10 (10kΩ/0603), resistor R11 (470Ω/0603), capacitor C3 (1uF/0603), diode D5 (150mA/150V), diode D6 (150mA/150V) and power management chip U3 ( UC2845BD), the first pin of the power management chip U3 is electrically connected to the anode of the diode D6 and the first end of the optocoupler U1 respectively, and the eighth pin of the power management chip U3 is respectively connected to one end of the resistor R10 and one end of the diode D5 ( The cathode is electrically connected, the anode of the diode D5 is electrically connected to the other end of the resistor R10, one end of the capacitor C3 and the cathode of the diode D6, the other end of the capacitor C3 is electrically connected to one end of the resistor R11, and the other end of the capacitor C3 is electrically connected to the resistor R11 One end of the resistor R11 is grounded, and the other end of the resistor R11 is electrically connected to the second end of the photocoupler U1. When the equivalent resistance of the first end and the second end of the photocoupler U1 is large, the first lead of the power management chip U3 The pin maintains a high level, so that the sixth pin of the power management chip U3 outputs a PWM control signal with a large duty ratio, and the voltage of the main output V3 continues to rise; when the voltage of the main output V3 rises to a predetermined value, the photoelectric The equivalent resistance of the first end and the second end of the coupler U1 becomes smaller, and the level of the first pin of the power management chip U3 decreases, so that the duty cycle of the PWM signal output by the sixth pin of the power management chip U3 becomes smaller , so that the voltage of the main output terminal V3 is stabilized at the preset value.

Among them, the voltage output circuit includes photocoupler U1, resistor R19 (10kΩ/0603), resistor R18 (38kΩ/0603), resistor R12 (10kΩ/0603), resistor R14 (1kΩ/1206), resistor R13 (100kΩ/0603) , capacitor C4 (220pF/0603), capacitor C5 (0.1uF/0603) and TL431 device U2 (TL431/SOT-89), the first pin of TL431 device U2 is electrically connected to one end of resistor R19 and the first pin of TL431 device U2 A pin and one end of the resistor R19 are both grounded, the second pin of the TL431 device U2 is electrically connected to the other end of the resistor R19, one end of the resistor R18, one end of the capacitor C4 and one end of the capacitor C5, and the other end of the capacitor C5 is electrically connected to One end of the resistor R13 is electrically connected, and the other end of the resistor R13 is respectively connected with the other end of the capacitor C4, one end of the resistor R12, the third pin of the TL431 device U2, the collector of the second transistor Q2 and the third pin of the photocoupler U1. The four terminals are electrically connected, the other end of the resistor R18 is electrically connected to the other end of the resistor R12, one end of the resistor R14 and the main output terminal V3, and the other end of the resistor R14 is electrically connected to the third terminal of the photocoupler U1. When the power is turned on, before the voltage of the main output terminal V3 rises to a predetermined value, the voltage of the second pin of the TL431 device U2 is less than 2.5V through the voltage division of the resistors R18 and R19, and the second pin of U2 outputs a higher voltage, so that The current between the third terminal and the fourth terminal of the optocoupler U1 is very small, and the first and second terminals of the optocoupler U1 maintain a high equivalent resistance; when the main output terminal V3 rises to a predetermined value, the TL431 device The voltage of the second pin of U2 is close to 2.5V through the voltage division of the resistors R18 and R19, and the output voltage of the second pin of U2 decreases, so that the current between the third and fourth ends of the optocoupler U1 becomes larger, and the photoelectric The equivalent resistance of the first end and the second end of the coupler U1 becomes smaller.

To sum up, in the short-circuit protection circuit of the multi-channel output power supply provided by the present invention, when the multi-channel output power supply works normally, the charging capacitor is charged by the second voltage terminal of the multi-channel output power supply until a stable voltage is reached; When any output terminal of the multiple output power supply is short-circuited, the first voltage terminal of the multiple output power supply changes, so that the first transistor is converted from the off state to the on state. At this time, since the first transistor is a PNP Therefore, the charging capacitor connected to the emitter of the first triode begins to discharge, and driven by the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that the second diode is connected to the second triode. The PWM output control terminal of the multi-output power supply connected to the collector starts to discharge to the ground, so that the voltage of the PWM output control terminal starts to drop, thereby cutting off the output of the PWM output terminal, so as to effectively protect the multi-output power supply. That is, the present invention solves the influence of different factors such as leakage inductance and equivalent resistance between the transformer windings on the output short circuit by building a circuit at low cost, so that when any output end of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be short-circuited. The output power is effectively protected. Among them, the first embodiment of the power supply voltage detection protection circuit and the second embodiment of the output voltage detection protection circuit are provided. For the first embodiment, the protection effect is ensured by selecting appropriate charging capacitors, first resistors, sixth resistors, third resistors, and fourth resistors. For the second embodiment, reasonable charging capacitors, first resistors, second resistors, third resistors, seventh resistors and eighth resistors are selected to make the discharge speed of the charging capacitors slower, so as to maintain a reasonable hiccup time and reduce At the same time, it avoids the problem that the auxiliary power cannot be restarted due to too fast charging; in addition, after the main output is powered off, a discharge channel of the charging capacitor is cut off by a third diode to slow down the discharging speed of the charging capacitor.

The above descriptions are only examples of the present invention, and are not intended to limit the scope of the present invention. Any equivalent transformations made by using the contents of the description and drawings of the present invention, or directly or indirectly applied in related technical fields, are similarly included in the within the scope of patent protection of the present invention.

Claims (10)

1. Short-circuit protection circuit of multiplexed output power supply, its characterized in that: the circuit comprises a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor;

the base electrode of the first triode is connected with the first voltage end of the multi-path output power supply through the first resistor, the collector electrode of the first triode is connected with the base electrode of the second triode through the second resistor and is connected with the emitter electrode of the second triode through the third resistor, the emitter electrode of the first triode is grounded through the charging capacitor, and the charging capacitor is connected with the second voltage end of the multi-path output power supply;

the collector of the second triode is connected with the PWM output control end of the multi-path output power supply, and the emitter of the second triode is grounded;

the first triode is a PNP triode and the second triode is an NPN triode;

and the first triode and the second triode are switched from a cut-off state to a conducting state when the first voltage end of the multi-path output power supply is reduced due to the influence of short circuit of the output end.

2. The short-circuit protection circuit of a multi-output power supply according to claim 1, wherein: the first voltage end and the PWM output control end are both power supply voltage ends of the multi-path output power supply;

the fourth resistor is connected between the collector of the second triode and the power supply voltage end of the multi-path output power supply;

the emitting electrode of the first triode is grounded through the charging capacitor, and the connection of the charging capacitor and the second voltage end of the multi-path output power supply specifically comprises the following steps:

an emitting electrode of the first triode is simultaneously connected with one end of the charging capacitor and one end of the fifth resistor, the other end of the charging capacitor is grounded and is connected with a base electrode of the first triode through the sixth resistor, the other end of the fifth resistor is connected with a cathode of the first diode, and an anode of the first diode is connected with a reference voltage end of a power management chip of the multi-output power supply;

the steady state voltage of the charging capacitor is smaller than the voltage of the sixth resistor at two ends of the multi-path output power supply in a normal state and is larger than the voltage of the sixth resistor at two ends of the output end of the multi-path output power supply in a short circuit state.

3. The short-circuit protection circuit of a multi-output power supply according to claim 2, wherein: the resistance ratio of the first resistor to the sixth resistor is X, and the steady-state voltage of the charging capacitor is smaller than the power supply voltage/(X +1) of the multi-path output power supply in a normal state and larger than the power supply voltage/(X +1) of the multi-path output power supply when any one path of output power supply is short-circuited.

4. The short-circuit protection circuit of a multi-output power supply according to claim 2, wherein: the power supply voltage end of the multi-path output power supply is further connected with a first capacitor, and a discharge constant formed among the charging capacitor, the second resistor and the third resistor is 10 times larger than a discharge constant formed among the first capacitor and the fourth resistor.

5. The short-circuit protection circuit of a multi-output power supply according to claim 1, wherein: the PWM output control end is an optical coupler detection output voltage end of the multi-path output power supply;

the base electrode of the first triode is connected with the first voltage end of the multi-path output power supply through the first resistor, and the connection specifically comprises the following steps:

the base electrode of the first triode is connected with one end of a first resistor, the other end of the first resistor is simultaneously connected with the anodes of a plurality of second diodes, and the cathode of each second diode is respectively connected with the branch output end of an auxiliary power supply branch of the multi-path output power supply;

the emitting electrode of the first triode is grounded through the charging capacitor, and the connection of the charging capacitor and the second voltage end of the multi-path output power supply specifically comprises the following steps:

an emitting electrode of the first triode is simultaneously connected with one end of the charging capacitor, one end of the seventh resistor and one end of the eighth resistor, the other end of the charging capacitor and the other end of the seventh resistor are simultaneously grounded, and the other end of the eighth resistor is connected with a main output end of the multi-path output power supply;

the steady state voltage of the charging capacitor is greater than a and less than a + b, wherein a is the conduction voltage between the emitter and the base of the first triode, and b is the lowest value of the normal voltage of all auxiliary power supply branches of the multi-output power supply.

6. The short-circuit protection circuit of a multi-output power supply according to claim 5, wherein: the ninth resistance is greater than the eighth resistance.

7. The short-circuit protection circuit of a multi-output power supply according to claim 5, wherein: still include the third diode, the projecting pole of first triode simultaneously with charge capacitor's one end, the one end of seventh resistance, the one end of eighth resistance is connected specifically:

and an emitting electrode of the first triode is simultaneously connected with one end of the charging capacitor and a cathode of the third diode, and an anode of the third diode is simultaneously connected with one end of the seventh resistor and one end of the eighth resistor.

8. The short-circuit protection circuit of a multi-output power supply according to claim 7, wherein: the steady-state voltage of the charging capacitor is greater than a + c and less than a + b + c, and c is the conduction voltage of the third diode.

9. The short-circuit protection circuit of a multi-output power supply of claim 8, wherein: the steady state voltage of the charging capacitor is greater than a +0.4b + c and less than a +0.6b + c.

10. The short-circuit protection circuit of a multiple-output power supply according to any one of claims 1 to 9, characterized in that: the discharge constant formed between the charging capacitor and the ninth resistor is between 0.1 second and 10 seconds.

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