Short-circuit protection circuit for multiple output power supplies

Abstract

The invention discloses a short-circuit protection circuit for 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; the base of the first triode is connected to a first voltage terminal of the multi-channel 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 emitter of the second triode through the third resistor, the emitter of the first triode is grounded through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-channel output power supply; the collector of the second triode is connected to a PWM output control terminal of the multi-channel output power supply and the emitter is grounded; the first triode and the second triode are converted from a cut-off state to a conducting state when the first voltage terminal of the multi-channel output power supply is reduced due to an output terminal short circuit; the invention can effectively protect the multi-channel output power supply when any output terminal of the multi-channel output power supply is short-circuited.

Description

Technical Field

[0001] The present invention relates to the technical field of circuit protection, and in particular to a short-circuit protection circuit for a multi-channel output power supply. Background Art

[0002] A typical flyback power supply is Figure 5 As shown in the figure, the flyback power supply consists of a startup circuit, a power management chip, a feedback circuit and a coupling transformer, wherein the feedback circuit consists of an optocoupler and a TL431 device. The main output winding in the multi-channel output power supply detects the output voltage through the feedback circuit and forms a voltage loop control with the power management chip. When the main output winding is short-circuited or lightly or heavily loaded, a closed-loop control is formed through the feedback circuit to achieve the function of a stable power supply protection circuit. In the traditional multi-channel output flyback circuit, under ideal conditions, if one of the output ends 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 restart, thereby achieving the output end short-circuit protection function until the short circuit disappears. However, in actual situations, due to factors such as line impedance and leakage inductance between the windings, all output end short circuits are not scaled according to the turns ratio, which will cause the following problems: one of the output ends may be short-circuited, and the power supply is still working until the output end burns out. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a short-circuit protection circuit for a multi-channel output power supply, so as to effectively protect the multi-channel output power supply when any output end of the multi-channel output power supply is short-circuited.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A short-circuit protection circuit for a multi-channel output power supply comprises a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor;

[0006] The base of the first transistor is connected to the first voltage terminal of the multi-output power supply through the first resistor, the collector of the first transistor is connected to the base of the second transistor through the second resistor and 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 second voltage terminal of the multi-output power supply;

[0007] The collector of the second transistor is connected to the PWM output control terminal of the multi-channel output power supply and the emitter is grounded;

[0008] The first transistor is a PNP transistor, and the second transistor is an NPN transistor;

[0009] The first transistor and the second transistor are switched from a cut-off state to a conducting state when the first voltage terminal of the multi-output power supply is reduced due to an output terminal short circuit.

[0010] The beneficial effects of the present invention are as follows: 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 a stable voltage is reached; when any output terminal of the multi-channel output power supply is short-circuited, the first voltage terminal of the multi-channel output power supply changes, so that the first triode is converted from a cut-off state to a conducting state, at this time, since the first triode is a PNP triode, the charging capacitor connected to the emitter of the first triode begins to discharge, and under the drive of the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that the PWM output control terminal of the multi-channel output power supply connected to the collector of the second triode begins to discharge to the ground, so that the voltage of the PWM output control terminal begins 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 between each winding of the transformer and equivalent resistance on the output short circuit by building a circuit at a low cost, so that when any output terminal of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be effectively protected. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 A schematic diagram of the coordinated connection between the short-circuit protection circuit of the multi-channel output power supply and the multi-channel output power supply according to an embodiment of the present invention;

[0012] Figure 2 A schematic diagram of a specific circuit for the coordinated connection between a short-circuit protection circuit of a multi-output power supply and a startup circuit, a power management chip, and a feedback circuit of the multi-output power supply according to an embodiment of the present invention;

[0013] Figure 3 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 another embodiment of the present invention;

[0014] Figure 4 A schematic diagram of a specific circuit for the coordinated connection between a short-circuit protection circuit of a multi-output power supply and a startup circuit, a power management chip, and a feedback circuit of the multi-output power supply according to another embodiment of the present invention;

[0015] Figure 5 The figure is a circuit diagram of a multi-channel output power supply in the prior art.

[0016] Description of labels:

[0017] C1-C5 are all capacitors, among which C1 is the first capacitor; C2 is the charging capacitor;

[0018] D1-D6 are all diodes, among which D1 is the first diode; D2 / D4 is the second diode; D3 is the third diode;

[0019] Q1, the first transistor; Q2, the second transistor;

[0020] R1-R19 are all resistors, among which R1 / R9 is the first resistor; R2 is the second resistor; R3 is the third resistor; R4 is the fourth resistor; R5 is the fifth resistor; R6 is the sixth resistor; R7 is the seventh resistor; R8 is the eighth resistor;

[0021] U1, optocoupler; U2, TL431 device; U3, power management chip;

[0022] V1 / V2, branch output terminal of multi-channel output power supply; V3, main output terminal of multi-channel output power supply; Vcc, supply voltage; Vin, input DC high voltage. DETAILED DESCRIPTION

[0023] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0024] Please refer to Figures 1 to 4 , 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;

[0025] The base of the first transistor is connected to the first voltage terminal of the multi-output power supply through the first resistor, the collector of the first transistor is connected to the base of the second transistor through the second resistor and 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 second voltage terminal of the multi-output power supply;

[0026] The collector of the second transistor is connected to the PWM output control terminal of the multi-channel output power supply and the emitter is grounded;

[0027] The first transistor is a PNP transistor, and the second transistor is an NPN transistor;

[0028] The first transistor and the second transistor are switched from a cut-off state to a conducting state when the first voltage terminal of the multi-output power supply is reduced due to an output terminal short circuit.

[0029] From the above description, it can be seen that the beneficial effects of the present invention are: 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 multi-channel output power supply is short-circuited, the first voltage terminal of the multi-channel output power supply changes, so that the first triode is converted from a cut-off state to a conducting state, at this time, since the first triode is a PNP triode, the charging capacitor connected to the emitter of the first triode begins to discharge, and under the drive of the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that the PWM output control terminal of the multi-channel output power supply connected to the collector of the second triode begins to discharge to the ground, so that the voltage of the PWM output control terminal begins 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 each winding of the transformer on the output short circuit by building a circuit at a low cost, so that when any output terminal of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be effectively protected.

[0030] Furthermore, 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 power supply voltage terminals of the multi-channel output power supply;

[0031] The fourth resistor is connected between the collector of the second transistor and the power supply voltage terminal of the multi-output power supply;

[0032] The emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-channel output power supply in the following specific manner:

[0033] The emitter of the first transistor is connected to one end of the charging capacitor and one end of the fifth resistor at the same time, the other end of the charging capacitor is grounded and connected to the base of the first transistor through the sixth resistor, 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;

[0034] The steady-state voltage of the charging capacitor is smaller than the voltage across the sixth resistor in a normal state of the multi-output power supply and is larger than the voltage across the sixth resistor when the output end of the multi-output power supply is short-circuited.

[0035] From the above description, it can be seen that after the charging capacitor is charged to a steady-state voltage, since it is smaller than the voltage across the sixth resistor in the normal state of the multi-output power supply, and the sixth resistor is set at the base of the first transistor, therefore, for the PNP transistor, when the multi-output power supply works normally, the first transistor is in a cut-off state. When any output terminal is short-circuited, the supply voltage at the supply voltage terminal of the multi-channel output power supply will be pulled down according to the calculation of 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 the supply voltage can be pulled down to the undervoltage protection point when all output terminals are short-circuited. At this time, the supply voltage begins to be pulled down, so that the voltage at both ends of the sixth resistor begins to drop. Since the steady-state voltage of the charging capacitor is greater than the voltage at both ends of the sixth resistor when the output terminal of the multi-channel output power supply is short-circuited, 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 be turned on, so that the supply voltage terminal connected to the collector of the second transistor starts to discharge rapidly to the ground. Among them, the driving voltage terminal of the power management chip of the multi-channel output power supply is connected to the supply voltage terminal, so that the voltage at the supply voltage terminal triggers the undervoltage protection point of the driving voltage terminal of the power management chip, thereby cutting off the output of the PWM output terminal to effectively protect the multi-channel output power supply.

[0036] Furthermore, the resistance ratio of the first resistor to the sixth resistor is X, and the steady-state voltage of the charging capacitor is less than the supply voltage of the multi-output power supply in a normal state / (X+1) and greater than the supply voltage of the multi-output power supply when any one of the output power supplies is short-circuited / (X+1).

[0037] From the above description, it can be seen that when the steady-state voltage of the charging capacitor is less than the power supply voltage of the multi-output power supply in a normal state / (X+1) and greater than the power supply voltage of the multi-output power supply when any one of the output power supplies is short-circuited / (X+1), that is, assuming that the power supply voltage of the multi-output power supply in a normal state is 16V, the power supply voltage when any one of the output power supplies is short-circuited is 12V, and the resistance ratio of the first resistor to the sixth resistor is 2, then the steady-state voltage of the charging capacitor is less than 5.33V and greater than 4V, so as to ensure that when any one of the output power supplies is short-circuited, the voltages of the base and emitter of the first transistor change to convert the first transistor from a cut-off state to a conducting state.

[0038] Furthermore, the supply voltage terminal of the multi-output power supply is also connected to a first capacitor, and a discharge constant formed between the charging capacitor, the second resistor and the third resistor is greater than 10 times a discharge constant formed between the first capacitor and the fourth resistor.

[0039] From the above description, it can be seen that by limiting the discharge constant, the voltage at both ends of the charging capacitor is discharged to the ground through the first transistor, the second resistor and the third resistor at a speed slower than the power supply voltage is discharged to the ground through the fourth resistor to the voltage triggering the undervoltage protection point of the driving voltage end of the power management chip, so as to ensure that the power supply voltage at the power supply voltage end can trigger the undervoltage protection point of the driving voltage end of the power management chip.

[0040] Furthermore, 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 an optocoupler detection output voltage terminal of the multi-channel output power supply;

[0041] The base of the first transistor is connected to the first voltage terminal of the multi-channel output power supply through the first resistor as follows:

[0042] The base of the first transistor is connected to one end of the first resistor, the other end of the first resistor is simultaneously connected to the anodes of the plurality of second diodes, and the cathode of each of the second diodes is respectively connected to a branch output end of an auxiliary power supply branch of the multi-output power supply;

[0043] The emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-channel output power supply in the following specific manner:

[0044] The emitter of the first transistor 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, the other end of the charging capacitor and the other end of the seventh resistor are 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;

[0045] 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 lowest value of the normal voltages of all auxiliary power supply branches of the multi-output power supply.

[0046] From the above description, it can be known that the steady-state voltage of the charging capacitor is limited so that in the normal state of the multi-channel output power supply, the voltage difference between the emitter and the base of the first transistor is less than the conduction voltage and is in the cut-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. Since the steady-state voltage of the charging capacitor is greater than the conduction voltage between the emitter and the base of the first transistor, the first diode is turned on at this time, causing the base voltage of the second diode to rise rapidly, and then the second diode is turned on, so that the photoelectric coupler is saturated and turned on, and the original PWM output terminal of the power management chip is cut off. Subsequently, the main output end of the multi-channel output power supply drops rapidly, and the charging capacitor discharges the first resistor, the second resistor and the third resistor to maintain the conduction of the second diode, so the auxiliary power will be closed for a period of time; and when the voltage of the charging capacitor drops to a level that makes it impossible to conduct the first transistor, 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 a level above the conduction voltage of the first transistor, and the PWM output end of the power management chip will be closed again, and the power supply will enter the restart state again, and will be restarted repeatedly later, and the power supply will enter the "hiccup" protection mode; and when the short circuit of the multi-channel output power supply has been eliminated, the power supply is restarted. Due to the charging delay, when the voltage of the charging capacitor is charged to a level above the conduction voltage of the first transistor, the branch voltage has risen, so that the first diode and the second diode remain off, and the auxiliary power can start and work normally.

[0047] Furthermore, the ninth resistor is greater than the eighth resistor.

[0048] It can be seen from the above description that the discharge constant between the charging capacitor and the ninth resistor is greater than the charge constant between the charging capacitor and the eighth resistor, so as to slow down the discharge speed of the charging capacitor.

[0049] Furthermore, a third diode is included, and 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. Specifically:

[0050] The emitter of the first transistor 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 connected to one end of the seventh resistor and one end of the eighth resistor at the same time.

[0051] It can be seen from the above description that after the main output end is powered off, a discharge channel of the charging capacitor is blocked by the third diode to slow down the discharge speed of the charging capacitor.

[0052] Furthermore, 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.

[0053] It can be seen from the above description that when the third diode is added, the conduction voltage of the diode needs to be considered to change the state of the first transistor.

[0054] Furthermore, the steady-state voltage of the charging capacitor is greater than a+0.4b+c and less than a+0.6b+c.

[0055] It can be seen from the above description that 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 transistor can be quickly turned on in the event of a short circuit fault.

[0056] Furthermore, a discharge constant formed between the charging capacitor and the ninth resistor is between 0.1 seconds and 10 seconds.

[0057] From the above description, it can be seen that by selecting a reasonable charging capacitor and the ninth resistor to cooperate, the discharge speed of the charging capacitor is slow, so as to maintain a reasonable hiccup time and reduce loss.

[0058] In view of the different connection positions of the PWM output control terminal, the following two embodiments are provided.

[0059] Please refer to Figure 1 to Figure 2 , Embodiment 1 of the present invention is:

[0060] Short-circuit protection circuit for multiple output power supplies, that is, corresponding Figure 1 The first protection circuit in the embodiment is connected to the power management chip U3, and the circuit is protected by monitoring the power supply voltage Vcc of the power management chip U3.

[0061] like Figure 2As shown, 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, a first diode D1, a fourth resistor R4, a fifth resistor R5 and a sixth resistor R6; the base of the first transistor Q1 is connected to the power supply voltage end of the multi-channel output power supply through the first resistor R1, 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, and the emitter of the first transistor Q1 is simultaneously connected to one end of the charging capacitor C2, 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, the other end of the fifth resistor R5 is connected to the cathode of the first diode D1, and the anode of the first diode D1 is connected to the reference voltage terminal VREF of the power management chip U3 of the multi-output power supply; wherein, the collector of the second transistor Q2 is connected to the power supply voltage terminal of the multi-output power supply through the fourth resistor R4 and the emitter is grounded; the first transistor Q1 is converted from a cut-off state to a conducting state when the power supply voltage terminal of the multi-output power supply is reduced due to the short circuit of the output terminal.

[0062] 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 power supply voltage terminals of the multi-channel output power supply, that is, corresponding to Figure 2 The second voltage terminal is the reference voltage terminal VREF of the power management chip U3 of the multi-channel output power supply.

[0063] pass Figure 2Combined with the above description, it can be known that at the moment of power-on, the input DC high voltage Vin charges the first capacitor C1 (100uF / 50V) through the resistors R15-R17 (200k / 3W) to reach the power startup voltage, and the flyback power supply starts working. 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 charges the charging capacitor C2 (10uF / 16V) through the first diode D1 (150mA / 100V) and the fifth resistor R5 (10k / 0603) 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 in a ratio of 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 the cut-off state. When any output terminal is short-circuited, the power supply voltage Vcc will be pulled down according to the turns ratio equivalent voltage calculation. However, due to the leakage inductance and equivalent impedance of each output terminal, it cannot be guaranteed that the power supply voltage Vcc can be pulled down to the undervoltage protection point when all outputs are short-circuited. Here, take the worst one as an example. When the power supply voltage Vcc is pulled down to 12V, the voltage across the sixth resistor R6 is 4V, and the first transistor Q1 will be turned on. At this time, the second transistor Q2 (0.6A / 60V) will also be turned on under the drive of the voltage of the charging capacitor C2 and the second resistor R2 (5k / 0603). The power supply voltage Vcc will be quickly discharged to the ground through the fourth resistor R4 (100Ω / 0805) and the second transistor Q2, wherein the discharge constant formed between the charging capacitor C2, the second resistor R2 and the third resistor R3 is greater than the first transistor. The discharge constant formed between the capacitor C1 and the fourth resistor R4 is 10 times, so that the voltage across the charging capacitor C2 is discharged to the ground through the first transistor Q1 and the third resistor R3 slower than the power supply voltage Vcc is discharged to the ground through the fourth resistor R4 to the voltage triggering the under-voltage protection point of the driving voltage terminal VI of the power management chip U3, so as to ensure that the power supply voltage Vcc at the power supply voltage end can trigger the under-voltage 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, so as to effectively protect the multi-channel output power supply.

[0064] In this embodiment, the resistance ratio of the first resistor R1 and the sixth resistor R6 is 2, and the steady-state voltage of the charging capacitor C2 is 5V, and the power supply voltage Vcc is 16V in a normal state and 12V in a 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 less than the power supply voltage Vcc / (X+1) of the multi-channel output power supply in a normal state and greater than the power supply voltage Vcc / (X+1) of the multi-channel output power supply when any one of the output power supplies is short-circuited.

[0065] Please refer to Figure 3 to Figure 4 , Embodiment 2 of the present invention is:

[0066] Short-circuit protection circuit for multiple output power supplies, that is, corresponding Figure 3 The second protection circuit in the embodiment is connected to the photocoupler U1, and the circuit is protected by monitoring the output voltage of the photocoupler U1.

[0067] like Figure 4 As shown, 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, a second diode D2 / D4 corresponding to the number of auxiliary power supply branches of the multi-channel output power supply, a seventh resistor R7, an eighth resistor R8 and a third diode D3; the base of the first transistor Q1 is connected to one end of the first resistor R9, the other end of the first resistor R9 is simultaneously connected to the anodes of multiple second diodes D2 / D4, and the cathode of each second diode D2 / D4 is respectively connected to the branch output end V1 / V2 of an auxiliary power supply branch of the multi-channel output power supply; the first transistor The collector of the 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. 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. The anode of the third diode D3 is simultaneously connected to one end of the seventh resistor R7 and one end of the eighth resistor R8. The other end of the charging capacitor C2 and the other end of the seventh resistor R7 are simultaneously grounded. The other end of the eighth resistor R8 is connected to the main output end V3 of the multi-channel output power supply. The collector of the second transistor Q2 is connected to the optocoupler detection output voltage end of the multi-channel output power supply and the emitter is grounded.

[0068] 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 an optocoupler detection output voltage terminal of the multi-channel output power supply, that is, Figure 4 The fourth terminal of the photoelectric coupler U1 in the multi-channel output power supply; 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.

[0069] pass Figure 4 Combined with the above description, it can be seen 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 lowest value b of the normal voltage of all auxiliary power supply branches of the multi-output power supply is 5V. Figure 4The normal voltage of the branch output terminal V2 is b=5V, and the normal voltage of the branch output terminal V1 is 9V. The conduction voltage a between the emitter and the base of the first transistor Q1 (0.6A / -60V) is generally 0.7V, and the conduction voltage c of the third diode D3 (150mA / 100V) is generally 0.7V.

[0070] At this time, the voltage of the charging capacitor C2 is limited to below 6.4V through the voltage division of the eighth resistor R8 (2k / 0603) and the seventh resistor R7 (1.5k / 0603). In other embodiments, the voltage of the charging capacitor C2 is higher than a+c, that is, higher than 1.4V, and 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.

[0071] 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 an off state, and the collector-emitter terminals of the second transistor Q2 (0.6A / 60V) also remain in an off state, so that the protection circuit has no effect on the photocoupler U1.

[0072] When any 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, causing the first transistor Q1 to turn on. After the base voltage of the second transistor Q2 rises rapidly, the second transistor Q2 is turned on, and then the optocoupler U1 (K1010-4C-1) is saturated and turned on, turning off the PWM output terminal OUTPUT of the original power management chip U3 (UC2845BD). Then the voltage of the main output terminal V3 drops rapidly, but the charging capacitor C2 (22uF / 16V) discharges slowly to the second resistor R2 (15k / 0603), the third resistor R3 (100k / 0603) and the first resistor R9 (49.9k / 0603), which can maintain the conduction of the second transistor Q2. Therefore, the auxiliary power will be turned off for a period of time, wherein a discharge channel of the charging capacitor C2 is blocked by the third diode D3 to slow down the discharge speed of the charging capacitor C2.

[0073] When the voltage of the charging capacitor C2 drops to a level that makes it impossible for the first transistor Q1 to conduct, for example, it drops below 1V, and the auxiliary power is restarted. If the short circuit of the multi-channel output power supply still exists, the charging capacitor C2 will be charged to above 1.4V, and the PWM output terminal OUTPUT of the power management chip U3 will be closed again, and the power supply will enter the restart state again, and then restart repeatedly, and the power supply will enter the "hiccup" protection mode;

[0074] When the short circuit of the multi-output power supply is eliminated, the power supply is restarted, and the voltage of the charging capacitor C2 is gradually charged to above 1.4V under the limitation of the eighth resistor R8, the voltage of the branch voltage terminals V1 and V2 has risen, so that the first diode D1 and the second diode D2 / D4 remain closed, and the auxiliary power can start and work normally.

[0075] Among them, in this embodiment, b=5V, a=c=0.7V, then the steady-state voltage of the charging capacitor is further limited to between greater than 3.4V and 4.4V, for example, about 3.9V, to ensure that the first transistor Q1 can be turned on quickly in the event of a short circuit fault, thereby quickly protecting the circuit.

[0076] Among them, 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 relatively large, and the resistance difference between the first resistor R9 and the eighth resistor R8 is relatively large. Therefore, the discharge constant formed between the charging capacitor C2 and the first resistor R9, the second resistor R2 and the third resistor R3 is between 0.1 seconds and 10 seconds (such as about 0.25s), that is, in the second level, and at this time, the charging constant of the charging capacitor C2 and the eighth resistor R8 is controlled to be tens of 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, by reasonably selecting the charging capacitor C2 and 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, the reasonable hiccup time can be maintained, and the loss can be reduced; at the same time, it is avoided that the auxiliary power cannot be restarted due to over-fast charging.

[0077] Among them, Figure 2 As shown, in order to facilitate the understanding of the present invention, Figure 2 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 are explained.

[0078] The PWM circuit includes a resistor R10 (10kΩ / 0603), a resistor R11 (470Ω / 0603), a capacitor C3 (1uF / 0603), a diode D5 (150mA / 150V), a diode D6 (150mA / 150V) and a 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 photocoupler U1, respectively. The eighth pin of the power management chip U3 is electrically connected to one end of the resistor R10 and the cathode of the diode D5, respectively. 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, respectively. The other end of the capacitor C3 is electrically connected to the One end is electrically connected, and the other end of the capacitor C3 and one end of the resistor R11 are both grounded, and the other end of the resistor R11 is electrically connected to the second end of the photoelectric coupler U1. When the equivalent resistance of the first and second ends of the photoelectric coupler U1 is large, the first pin of the power management chip U3 maintains a high level, so that the sixth pin of the power management chip U3 outputs a PWM control signal with a large duty cycle, and the voltage of the main output terminal V3 continues to rise; when the voltage of the main output terminal V3 rises to near a predetermined value, the equivalent resistance of the first and second ends of the photoelectric coupler U1 decreases, 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 decreases, thereby stabilizing the voltage of the main output terminal V3 at a preset value.

[0079] The voltage output circuit includes an optocoupler U1, a resistor R19 (10kΩ / 0603), a resistor R18 (38kΩ / 0603), a resistor R12 (10kΩ / 0603), a resistor R14 (1kΩ / 1206), a resistor R13 (100kΩ / 0603), a capacitor C4 (220pF / 0603), a capacitor C5 (0.1uF / 0603) and a TL431 device U2 (TL431 / SOT-89), a first pin of the TL431 device U2 is electrically connected to one end of the resistor R19, and the first pin of the TL431 device U2 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 respectively, the other end of the capacitor C5 is electrically connected to one end of the resistor R13, the other end of the resistor R13 is electrically connected to 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 fourth end of the photocoupler U1 respectively, 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 respectively, and the other end of the resistor R14 is electrically connected to the third end of the photocoupler U1. After the power supply is started, 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 and fourth terminals of the photocoupler U1 is very small, and the first and second terminals of the photocoupler U1 maintain a relatively high equivalent resistance; when the main output terminal V3 rises to a predetermined value, the voltage of the second pin of the TL431 device 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 terminals of the photocoupler U1 becomes larger, and the equivalent resistance of the first and second terminals of the photocoupler U1 becomes smaller.

[0080] In summary, 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 multi-channel output power supply is short-circuited, the first voltage terminal of the multi-channel output power supply changes, so that the first triode is converted from a cut-off state to a conducting state, at this time, since the first triode is a PNP triode, the charging capacitor connected to the emitter of the first triode begins to discharge, and under the drive of the voltage of the charging capacitor and the third resistor, the second diode begins to conduct, so that the PWM output control terminal of the multi-channel output power supply connected to the collector of the second triode begins to discharge to the ground, so that the voltage of the PWM output control terminal begins 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 each winding of the transformer on the output short circuit by building a circuit at a low cost, so that when any output terminal of the multi-channel output power supply is short-circuited, the multi-channel output power supply can be effectively protected. Among them, an embodiment 1 of a power supply voltage detection protection circuit and an embodiment 2 of an output voltage detection protection circuit are provided. For the first embodiment, the protection effect is ensured by selecting a suitable charging capacitor, a first resistor, a sixth resistor, a third resistor, and a fourth resistor. For the second embodiment, a reasonable charging capacitor, a first resistor, a second resistor, a third resistor, a seventh resistor, and an eighth resistor are selected so that the discharge speed of the charging capacitor is slower to maintain a reasonable hiccup time and reduce losses; at the same time, the problem of the auxiliary power being unable to restart due to over-fast charging is avoided; in addition, after the main output end is powered off, a discharge channel of the charging capacitor is blocked by a third diode to slow down the discharge speed of the charging capacitor.

[0081] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. Short-circuit protection circuit for multi-channel output power supply, Features: It includes a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor; The base of the first transistor is connected to the first voltage terminal of the multi-output power supply through the first resistor, the collector of the first transistor is connected to the base of the second transistor through the second resistor and 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 second voltage terminal of the multi-output power supply; The collector of the second transistor is connected to the PWM output control terminal of the multi-channel output power supply and the emitter is grounded; The first transistor is a PNP transistor, and the second transistor is an NPN transistor; The first transistor and the second transistor are switched from a cut-off state to a conducting state when the first voltage terminal of the multi-channel output power supply is reduced due to the short circuit of the output terminal; 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 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 power supply voltage terminal of the multi-output power supply; The emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-channel output power supply in the following specific manner: The emitter of the first transistor is connected to one end of the charging capacitor and one end of the fifth resistor at the same time, the other end of the charging capacitor is grounded and connected to the base of the first transistor through the sixth resistor, 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; The steady-state voltage of the charging capacitor is smaller than the voltage across the sixth resistor in a normal state of the multi-output power supply and is larger than the voltage across the sixth resistor when the output end of the multi-output power supply is short-circuited.

2. The short-circuit protection circuit of the multi-output power supply according to claim 1, Features: 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 supply voltage of the multi-output power supply in a normal state / (X+1) and is greater than the supply voltage of the multi-output power supply when any one of the output power supplies is short-circuited / (X+1).

3. The short-circuit protection circuit of the multi-output power supply according to claim 1, Features: The supply voltage end of the multi-output power supply is also connected to a first capacitor, and a discharge constant formed between the charging capacitor, the second resistor and the third resistor is greater than 10 times the discharge constant formed between the first capacitor and the fourth resistor.

4. The short-circuit protection circuit of a multi-output power supply according to any one of claims 1 to 3, Features: A discharge constant formed between the charging capacitor and the first resistor is between 0.1 seconds and 10 seconds.

5. Short-circuit protection circuit for multiple output power supplies, Features: It includes a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor; The base of the first transistor is connected to the first voltage terminal of the multi-output power supply through the first resistor, the collector of the first transistor is connected to the base of the second transistor through the second resistor and 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 second voltage terminal of the multi-output power supply; The collector of the second transistor is connected to the PWM output control terminal of the multi-channel output power supply and the emitter is grounded; The first transistor is a PNP transistor, and the second transistor is an NPN transistor; The first transistor and the second transistor are switched from a cut-off state to a conducting state when the first voltage terminal of the multi-channel output power supply is reduced due to the short circuit of the output terminal; 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 end is an optocoupler detection output voltage end of the multi-channel output power supply; The base of the first transistor is connected to the first voltage terminal of the multi-channel output power supply through the first resistor as follows: The base of the first transistor is connected to one end of the first resistor, the other end of the first resistor is simultaneously connected to the anodes of the plurality of second diodes, and the cathode of each of the second diodes is respectively connected to a branch output end of an auxiliary power supply branch of the multi-output power supply; The emitter of the first transistor is grounded through the charging capacitor, and the charging capacitor is connected to the second voltage terminal of the multi-channel output power supply in the following specific manner: The emitter of the first transistor 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, the other end of the charging capacitor and the other end of the seventh resistor are 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 lowest value of the normal voltages of all auxiliary power supply branches of the multi-output power supply.

6. The short-circuit protection circuit of the multi-output power supply according to claim 5, Features: The first resistor is greater than the eighth resistor.

7. The short-circuit protection circuit of the multi-output power supply according to claim 5, Features: A third diode is further included, and 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. Specifically: The emitter of the first transistor 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 connected to one end of the seventh resistor and one end of the eighth resistor at the same time.

8. The short-circuit protection circuit of the multi-output power supply according to claim 7, Features: 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.

9. The short-circuit protection circuit of the multi-output power supply according to claim 8, Features: 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 multi-output power supply according to any one of claims 5 to 9, Features: A discharge constant formed between the charging capacitor and the first resistor is between 0.1 seconds and 10 seconds.

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