CN111614062A - Short-circuit protection circuit of multi-output power supply - Google Patents
Short-circuit protection circuit of multi-output power supply Download PDFInfo
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- CN111614062A CN111614062A CN202010419056.6A CN202010419056A CN111614062A CN 111614062 A CN111614062 A CN 111614062A CN 202010419056 A CN202010419056 A CN 202010419056A CN 111614062 A CN111614062 A CN 111614062A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
- H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
- H02H7/1213—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC converters
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Abstract
The invention discloses a short-circuit protection circuit of a multi-path output power supply, which comprises a first triode, a second triode, a first resistor, a second resistor, a third resistor and a charging capacitor, wherein the first triode is connected with the charging capacitor; the base electrode of the first triode is connected with the first voltage end of the multi-path output power supply through a first resistor, the collector electrode of the first triode is connected with the base electrode of the second triode through a second resistor and is connected with the emitter electrode of the second triode through a third resistor, the emitter electrode of the first triode is grounded through a 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 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 influenced by the short circuit of the output end and is reduced; the invention can effectively protect the multi-path output power supply when any output end of the multi-path output power supply is short-circuited.
Description
Technical Field
The invention relates to the technical field of circuit protection, in particular to a short-circuit protection circuit of a multi-output power supply.
Background
As shown in fig. 5, a typical flyback power supply is composed of a starting circuit, a power management chip, a feedback circuit and a coupling transformer, wherein the feedback circuit is composed of a photocoupler and a TL431 device, a main output winding in a multi-output power supply detects output voltage through the feedback circuit, and forms voltage loop control with the power management chip, and when the main output winding is short-circuited or lightly loaded, closed-loop control is formed through the feedback circuit, so as to achieve the effect of stabilizing the power protection circuit. Traditional multiplexed output flyback circuit, under ideal condition, if one of them output short circuit, other windings will zoom according to actual turn ratio, and auxiliary winding will reduce voltage equally, and when reaching the undervoltage point, power chip will restart to reach output short circuit protection effect, until the short circuit disappears. However, in practical situations, due to factors such as line impedance and leakage inductance between windings, short circuit of all output terminals is not scaled according to the turn ratio, which causes the following problems: one of the paths may be short-circuited, and the power supply still works until the output end is burnt.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the short-circuit protection circuit of the multi-path output power supply is provided, so that when any output end of the multi-path output power supply is short-circuited, the multi-path output power supply can be effectively protected.
In order to solve the technical problems, the invention adopts the technical scheme that:
the short-circuit protection circuit of the multi-path output power supply 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.
The invention has the beneficial effects that: when the multi-output power supply works normally, the charging capacitor is charged by a second voltage end of the multi-output power supply until the stable voltage is reached; when any output end of the multi-path output power supply is in short circuit, the first voltage end of the multi-path output power supply changes, so that the first triode is switched from a cut-off state to a conduction state, at the moment, because the first triode is a PNP triode, the charging capacitor connected with the emitting electrode of the first triode starts to discharge, the second diode starts to be conducted under the driving of the voltage of the charging capacitor and the third resistor, so that the PWM output control end of the multi-path output power supply connected with the collecting electrode of the second triode starts to discharge to the ground, the voltage of the PWM output control end starts to fall, and the output of the PWM output end is cut off, so that the multi-path output power supply is effectively protected. The invention solves the problem of influence of different factors such as leakage inductance and equivalent resistance among windings of the transformer on output short circuit by constructing a circuit with low cost, thereby effectively protecting the multi-path output power supply when any output end of the multi-path output power supply is short-circuited.
Drawings
Fig. 1 is a schematic diagram illustrating a matching connection between a short-circuit protection circuit of a multi-output power supply and the multi-output power supply according to an embodiment of the present invention;
fig. 2 is a schematic circuit diagram illustrating a short-circuit protection circuit of a multi-output power supply, a start circuit of the multi-output power supply, a power management chip, and a feedback circuit in a matching connection manner according to an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating the matching connection between the short-circuit protection circuit of the multi-output power supply and the multi-output power supply according to another embodiment of the present invention;
fig. 4 is a schematic circuit diagram illustrating a specific circuit of the short-circuit protection circuit of the multiple output power supply, the start circuit of the multiple output power supply, the power management chip, and the feedback circuit in a matching connection according to another embodiment of the present invention;
fig. 5 is a circuit diagram of a prior art multi-output power supply.
Description of reference numerals:
C1-C5 are all capacitors, wherein C1 is the first capacitor; c2, a charging capacitor;
D1-D6 are all diodes, wherein D1 is a first diode; D2/D4, a second diode; d3, a third diode;
q1, the first triode; q2, the second triode;
R1-R19 are resistors, wherein R1/R9 is the first resistor; r2, a second resistor, R3 and a third resistor; r4, fourth resistor; r5, fifth resistor; r6, sixth resistor; r7, seventh resistor; r8, eighth resistor;
u1, photoelectric coupler; u2, TL431 devices; u3, power management chip;
V1/V2, branch output end of the multi-path output power supply; v3, a main output end of a multi-output power supply; vcc, supply voltage; vin, input direct current high voltage.
Detailed Description
In order to explain technical contents, achieved objects, and effects of the present invention in detail, the following description is made with reference to the accompanying drawings in combination with the embodiments.
Referring to fig. 1 to 4, the short-circuit protection circuit of the multi-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 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.
From the above description, the beneficial effects of the present invention are: when the multi-path output power supply works normally, the second voltage end of the multi-path output power supply charges the charging capacitor until the stable voltage is reached; when any output end of the multi-path output power supply is in short circuit, the first voltage end of the multi-path output power supply changes, so that the first triode is switched from a cut-off state to a conduction state, at the moment, because the first triode is a PNP triode, the charging capacitor connected with the emitting electrode of the first triode starts to discharge, the second diode starts to be conducted under the driving of the voltage of the charging capacitor and the third resistor, so that the PWM output control end of the multi-path output power supply connected with the collecting electrode of the second triode starts to discharge to the ground, the voltage of the PWM output control end starts to fall, and the output of the PWM output end is cut off, so that the multi-path output power supply is effectively protected. The invention solves the problem of influence of different factors such as leakage inductance and equivalent resistance among windings of the transformer on output short circuit by constructing a circuit with low cost, thereby effectively protecting the multi-path output power supply when any output end of the multi-path output power supply is short-circuited.
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.
As can be seen from the above description, after the charging capacitor is charged to the steady-state voltage, since the voltage is smaller than the voltage across the sixth resistor in the normal state of the multi-output power supply, and the sixth resistor is disposed at the base of the first transistor, for the PNP transistor, when the multi-output power supply is operating normally, the first transistor is in the off state. When any output end is in short circuit, the power supply voltage of the power supply voltage end of the multi-path output power supply is pulled down according to the equivalent voltage calculation of the turn ratio, but the problems of leakage inductance, equivalent impedance and the like exist in each output end, so that the power supply voltage can be pulled down to an undervoltage protection point when all the output ends are in short circuit; at this moment, the power supply voltage starts to be pulled down, so that the voltages at two ends of the sixth resistor start to drop, because the steady-state voltage of the charging capacitor is greater than the voltage at two ends of the sixth resistor, which is short-circuited at the output end of the multi-output power supply, the first triode is enabled to be conducted, the charging capacitor starts to discharge, and the second diode starts to be conducted under the driving of the voltage of the charging capacitor and the third resistor, so that the power supply voltage end connected with the collector electrode of the second triode starts to discharge rapidly to the ground, wherein the driving voltage end of the power management chip of the multi-output power supply is connected with the power supply voltage end, so that the voltage of the power supply voltage end triggers the undervoltage protection point of the driving voltage end of the power management chip, thereby cutting off the output of the PWM output end and.
Further, 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 multiple output power supply in the normal state and larger than the power supply voltage/(X +1) of the multiple output power supply when any one output power supply is short-circuited.
As can be seen from the above description, when the steady-state voltage of the charging capacitor is limited to be less than the supply voltage/(X +1) of the multiple output power supplies in the normal state and greater than the supply voltage/(X +1) of the multiple output power supplies in the short circuit of any output power supply, that is, assuming that the supply voltage of the multiple output power supplies in the normal state is 16V, the supply voltage of the multiple output power supplies in the short circuit of any output power supply is 12V, and the resistance ratio of the first resistor and the sixth resistor is 2, the steady-state voltage of the charging capacitor is less than 5.33V and greater than 4V, so as to ensure that the voltages of the base and the emitter of the first transistor change during the short circuit of any output power supply, so as to convert the first transistor from the off state to the.
Furthermore, a power supply voltage end of the multi-output power supply is also 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.
As can be seen from the above description, by limiting the discharge constant, the speed of discharging the voltage across the charging capacitor to the ground through the first transistor, the second resistor and the third resistor is slower than the speed of discharging the power supply voltage to the ground through the fourth resistor to the undervoltage protection point of the driving voltage end of the voltage triggered 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.
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.
As can be seen from the above description, the steady-state voltage of the charging capacitor is limited such that the voltage difference between the emitter and the base of the first transistor is smaller than the turn-on voltage and is in the off state in the normal state of the multi-output power supply. When any output end is in short circuit, one of the second diodes is conducted, so that the base voltage of the first diode is rapidly reduced, the first diode is conducted at the moment because the steady-state voltage of the charging capacitor is greater than the conduction voltage between the emitter and the base of the first triode, so that the base voltage of the second diode is rapidly increased, and then the second diode is conducted, so that the photoelectric coupler is in saturated conduction, and the PWM output end of the original power management chip is switched off. Then, the main output end of the multi-path output power supply rapidly drops, the charging capacitor discharges the first resistor, the second resistor and the third resistor to maintain the conduction of the second diode, and therefore the auxiliary power supply is turned off for a period of time; when the voltage of the charging capacitor is reduced to a value which can not lead the first triode to be conducted, the auxiliary power is restarted, if the short circuit condition of the multi-path output power supply still exists, the charging capacitor is charged to a value above the conducting voltage of the first triode, the PWM output end of the power supply management chip is closed again, the power supply enters a restarting state again, and then the power supply enters a hiccup protection mode after repeated restarting; and when the short circuit condition of the multi-output power supply is eliminated, the power supply is restarted, and the voltage of the charging capacitor is charged to be higher than the conducting voltage of the first triode due to charging delay, the branch voltage is raised, so that the first diode and the second diode are kept in an off state, and the auxiliary power can be started normally and work.
Further, the ninth resistance is greater than the eighth resistance.
As is apparent from the above description, the discharge constant between the charge capacitor and the ninth resistor is thus larger than the charge constant of the charge capacitor and the eighth resistor to slow down the discharge speed of the charge capacitor.
Further, the power supply further comprises a third diode, and the connection of the emitter of the first triode and one end of the charging capacitor, one end of the seventh resistor and one end of the eighth resistor is 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.
As can be seen from the above description, after the main output terminal is powered off, the third diode cuts off a discharge channel of the charging capacitor, so as to slow down the discharge 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, and c is the conduction voltage of the third diode.
As can be seen from the above description, when the third diode is added, the state of the first transistor needs to be changed in consideration of the on-voltage of the diode.
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 transistor can be turned on quickly in the event of a short-circuit fault.
Further, a discharge constant formed between the charging capacitor and the ninth resistor is between 0.1 second and 10 seconds.
From the above description, it can be known that selecting reasonable charge capacitor and ninth resistance to cooperate makes the discharge speed of charge capacitor slower to maintain reasonable hiccup time, reduce the loss.
The following two embodiments are provided for the difference in the connection position of the PWM output control terminal.
Referring to fig. 1 to fig. 2, a first embodiment of the present invention is:
the short-circuit protection circuit of the multiple 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 protection of the circuit is realized by monitoring the power supply voltage Vcc of the power management chip U3.
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, a first diode D1, a fourth resistor R4, a fifth resistor R5, and a sixth resistor R6; the base of a first triode Q1 is connected with the power supply voltage end of the multi-output power supply through a first resistor R1, the collector of a first triode Q1 is connected with the base of a second triode Q2 through a second resistor R2 and is connected with the emitter of a second triode Q2 through a third resistor R3, the emitter of the first triode Q1 is connected with one end of a charging capacitor C2 and one end of a fifth resistor R5 at the same time, the other end of the charging capacitor C2 is grounded and is connected with the base of the first triode Q1 through a sixth resistor R6, the other end of the fifth resistor R5 is connected with the cathode of a first diode D1, and the anode of the first diode D1 is connected with the reference voltage end VREF of a power management chip U3 of the multi-output power supply; the collector of the second triode Q2 is connected with the power supply voltage end of the multi-path output power supply through a fourth resistor R4, and the emitter of the second triode Q2 is grounded; the first transistor Q1 is switched from the off state to the on state when the supply voltage terminal of the multi-output power supply is reduced due to the short circuit at the output terminal.
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-output power supply, that is, the power supply voltage Vcc corresponding to fig. 2; the second voltage terminal is a reference voltage terminal VREF of the power management chip U3 of the multi-output power supply.
As can be seen from fig. 2 and the above description, 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 supply start voltage, and the flyback power supply starts to operate, in this embodiment, the input dc high voltage Vin is a fixed voltage 16V, and the reference voltage end VREF of the power management chip U3(UC2845BD) of the multi-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 at the two ends of the charging capacitor C2 is 5V; meanwhile, 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 off state. When any output end is in short circuit, the power supply voltage Vcc can be pulled down according to the calculation of the turn ratio equivalent voltage, but because each output end has the problems of leakage inductance, equivalent impedance and the like, the power supply voltage Vcc can be pulled down to an undervoltage protection point when all output ends are in short circuit. Taking the worst case as an example, when the power supply voltage Vcc is pulled down to 12V, and the voltage across the sixth resistor R6 is 4V, the first transistor Q1 will be turned on, and the second transistor Q2(0.6A/60V) will also be turned on under the driving of the charging capacitor C2 and the second resistor R2(5k/0603), and the power supply voltage Vcc will be rapidly discharged to ground through the fourth resistor R4(100 Ω/0805) and the second transistor Q2, wherein the discharging constant formed among the charging capacitor C2, the second resistor R2 and the third resistor R3 is greater than 10 times of the discharging constant formed among the first capacitor C1 and the fourth resistor R4, so that the speed of discharging the voltage across the charging capacitor C2 to ground through the first transistor Q1 and the third resistor R3 is slower than the driving point of the undervoltage power supply voltage 3 of the power supply management chip through the fourth resistor R4 to ground, the undervoltage protection point of the driving voltage end VI of the power management chip U3 can be triggered by the power supply voltage Vcc of the power supply voltage end, so that the OUTPUT of the PWM OUTPUT end OUTPUT is cut off, and the multi-path OUTPUT power supply is effectively protected.
In the present 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 the normal state, and 12V in the 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 smaller than the supply voltage Vcc/(X +1) of the multi-output power supply in the normal state and larger than the supply voltage Vcc/(X +1) of the multi-output power supply when any one of the multi-output power supplies is short-circuited.
Referring to fig. 3 to 4, a second embodiment of the present invention is:
the short-circuit protection circuit of the multiple output power supply corresponds to the second protection circuit in fig. 3, wherein the second protection circuit of this embodiment is connected to the photocoupler U1, and the protection of the circuit is realized by monitoring the output end voltage of the photocoupler U1.
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, second diodes D2/D4, a seventh resistor R7, an eighth resistor R8 and third diodes D3, which correspond to the number of auxiliary power supply branches of the multi-output power supply; the base electrode of the first triode Q1 is connected with one end of a first resistor R9, the other end of the first resistor R9 is simultaneously connected with the anodes of a plurality of second diodes D2/D4, and the cathode of each second diode D2/D4 is respectively connected with the branch output end V1/V2 of an auxiliary power supply branch of the multi-output power supply; a collector of the first triode Q1 is connected with a base of the second triode Q2 through a second resistor R2 and is connected with an emitter of the second triode Q2 through a third resistor R3, the emitter of the first triode Q1 is connected with one end of a charging capacitor C2 and a cathode of a third diode D3, an anode of the third diode D3 is connected with one end of a seventh resistor R7 and one end of an eighth resistor R8, the other end of the charging capacitor C2 and the other end of the seventh resistor R7 are grounded simultaneously, and the other end of the eighth resistor R8 is connected with a main output end V3 of the multi-output power supply; a collector of the second triode Q2 is connected with an optocoupler detection output voltage end of the multi-path output power supply, and an emitter of the second triode Q2 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 an optocoupler detection output voltage terminal of the multiple output power supply, that is, the fourth terminal of the optocoupler U1 in fig. 4; the first voltage end is a branch output end V1/V2 of an auxiliary power supply branch of the multi-output power supply; the second voltage end is a main output end V3 of the multi-output power supply.
As can be seen from fig. 4 and the above description, 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 voltages of all the 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 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 typically 0.7V, and the turn-on voltage c of the third diode D3(150mA/100V) is typically 0.7V.
At this time, the voltage of the charging capacitor C2 is limited to be below 6.4V by the voltage division of the eighth resistor R8(2k/0603) and the seventh resistor R7(1.5k/0603), and in other embodiments, the voltage of the charging capacitor C2 is higher than a + C, i.e., higher than 1.4V, and may be actually set to be above 2V, so that the first transistor Q1 can be turned on when the two auxiliary power supply branches are short-circuited.
Under normal conditions, the emitter voltage of the first transistor Q1 is lower than the base voltage, the collector-emitter terminal of the first transistor Q1 is kept in an off state, and the collector-emitter terminal of the second transistor Q2(0.6A/60V) is also kept in an off state, so that the protection circuit has no influence on the photoelectric coupler U1.
When any one of the auxiliary power supply branches is short-circuited, the second diode D2(150mA/100V) or D4(150mA/100V) is conducted, the base voltage of the first triode Q1 is rapidly reduced to cause the first triode Q1 to be turned on, after the base voltage of the second triode Q2 is rapidly increased, the second triode Q2 is conducted, then the photoelectric coupler U1(K1010-4C-1) is conducted in a saturated mode, and the PWM OUTPUT end OUTPUT of the original power management chip U3(UC2845BD) is switched off. Then, the voltage of the main output terminal V3 rapidly drops, but the charging capacitor C2(22uF/16V) discharges the second resistor R2(15k/0603), the third resistor R3(100k/0603) and the first resistor R9(49.9k/0603) more slowly, so that the conduction of the second triode Q2 can be maintained, and therefore, the auxiliary power is turned off for a period of time, wherein a discharging channel of the charging capacitor C2 is blocked by the third diode D3 to slow down the discharging speed of the charging capacitor C2.
When the voltage of the charging capacitor C2 drops to a level that the first triode Q1 cannot be turned on, for example, the voltage drops below 1V, the auxiliary power is restarted, if the short-circuit condition of the multi-OUTPUT power still exists, the charging capacitor C2 is charged to a level above 1.4V, the PWM OUTPUT terminal OUTPUT of the power management chip U3 is turned off again, the power enters a restart state again, and then the power is restarted repeatedly, so that the power enters a hiccup protection mode;
when the short circuit condition of the multi-output power supply is eliminated, the power supply is restarted, the voltage of the charging capacitor C2 is gradually charged to be more than 1.4V under the limitation of the eighth resistor R8, the voltages of the branch voltage ends V1 and V2 are already increased, the first diode D1 and the second diode D2/D4 are kept in an off section, and the auxiliary power supply is normally started and works.
In this embodiment, b is 5V, and a is 0.7V, the steady-state voltage of the charging capacitor is further limited to be greater than 3.4V to 4.4V, for example, about 3.9V, so as to ensure that the first transistor Q1 can be turned on quickly in the event of a short-circuit fault, thereby protecting the circuit quickly.
In this embodiment, the capacity of the charging capacitor C2 is 22uF, and the resistances 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 capacitance of the charging capacitor C2 is larger, and the resistance difference between the first resistor R9 and the eighth resistor R8 is larger, so that 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 second and 10 seconds (e.g., about 0.25 s), i.e., in the order of seconds, and at this time, the charge constant of the charging capacitor C2 and the eighth resistor R8 is controlled to be tens of milliseconds (e.g., about 50 ms); in the embodiment, when the first resistor R9 and the second resistor R2 are 49.9k and 15k, respectively, the eighth resistor R8 is 2k, and the seventh resistor R7 is 1.5 k. Therefore, 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 are reasonably selected to slow down the discharging speed of the charging capacitor C2, maintain reasonable hiccup time and reduce loss; meanwhile, the phenomenon that auxiliary power cannot be restarted due to too fast charging is avoided.
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 photocoupler U1 and the TL431 device U2 in fig. 2 will be described.
Wherein, the PWM circuit comprises a resistor R10(10k Ω/0603), a resistor R11(470 Ω/0603), a capacitor C3(1uF/0603), a diode D5(150mA/150V), a diode D6(150mA/150V) and a power management chip U3(UC2845BD), a first pin of the power management chip U3 is electrically connected with an anode of the diode D6 and a first end of the photocoupler U1 respectively, an eighth pin of the power management chip U3 is electrically connected with one end of the resistor R10 and a cathode of the diode D5 respectively, an anode of the diode D5 is electrically connected with the other end of the resistor R10, one end of the capacitor C3 and a cathode of the diode D6 respectively, the other end of the capacitor C3 is electrically connected with one end of the resistor R11, the other end of the capacitor C3 and one end of the resistor R11 are both grounded, the other end of the resistor R11 is electrically connected with a second end of the photocoupler U1, when the second end of the resistor U1 is equivalent to be larger, the first pin of the power management chip U3 keeps high level, so that the sixth pin of the power management chip U3 outputs PWM control signal with large duty ratio, and the voltage of the main output terminal V3 continuously rises; when the voltage of the main output end V3 rises to near the predetermined value, the equivalent resistances of the first end and the second end of the photocoupler U1 become small, the level of the first pin of the power management chip U3 decreases, so that the duty ratio of the PWM signal output from the sixth pin of the power management chip U3 becomes small, and the voltage of the main output end V3 is stabilized at the preset value.
The voltage output circuit comprises a photocoupler U1, a resistor R19(10k omega/0603), a resistor R18(38k omega/0603), a resistor R12(10k omega/0603), a resistor R14(1k omega/1206), a resistor R13(100k omega/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 with one end of the resistor R19, a first pin of the TL431 device U2 and one end of the resistor R19 are grounded, a second pin of the TL431 device U2 is respectively electrically connected with 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, the other end of the capacitor C5 is electrically connected with one end of the resistor R13, the other end of the resistor R2 is respectively electrically connected with one end of the resistor R5856, one end of the resistor R8653 and one end of the resistor R12, the third pin 8653 and the resistor R431, The collector of the second triode Q2 is electrically connected with the fourth end of the photoelectric coupler U1, the other end of the resistor R18 is electrically connected with the other end of the resistor R12, one end of the resistor R14 and the main output end V3 respectively, and the other end of the resistor R14 is electrically connected with the third end of the photoelectric coupler U1. After the power supply is started, before the voltage of the main output end V3 rises to a preset value, the voltage of the second pin of the TL431 device U2 is divided by the resistors R18 and R19 to be less than 2.5V, and the second pin of the U2 outputs higher voltage, so that the current between the third end and the fourth end of the photoelectric coupler U1 is small, and the first end and the second end of the photoelectric coupler U1 keep higher equivalent resistance; when the main output end V3 rises to a predetermined value, the voltage of the second pin of the TL431 device U2 is close to 2.5V through the divided voltages of the resistors R18 and R19, and the output voltage of the second pin of the U2 decreases, so that the current between the third end and the fourth end of the photocoupler U1 becomes large, and the equivalent resistances of the first end and the second end of the photocoupler U1 become small.
In summary, in the short-circuit protection circuit of the multi-output power supply provided by the invention, when the multi-output power supply normally works, the charging capacitor is charged by the second voltage end of the multi-output power supply until the stable voltage is reached; when any output end of the multi-path output power supply is in short circuit, the first voltage end of the multi-path output power supply changes, so that the first triode is switched from a cut-off state to a conduction state, at the moment, because the first triode is a PNP triode, the charging capacitor connected with the emitting electrode of the first triode starts to discharge, the second diode starts to be conducted under the driving of the voltage of the charging capacitor and the third resistor, so that the PWM output control end of the multi-path output power supply connected with the collecting electrode of the second triode starts to discharge to the ground, the voltage of the PWM output control end starts to fall, and the output of the PWM output end is cut off, so that the multi-path output power supply is effectively protected. The invention solves the problem of influence of different factors such as leakage inductance and equivalent resistance among windings of the transformer on output short circuit by constructing a circuit with low cost, thereby effectively protecting the multi-path output power supply when any output end of the multi-path output power supply is short-circuited. The first embodiment of the 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 a proper charging capacitor, a first resistor, a sixth resistor, a third resistor and a fourth resistor. For the second embodiment, reasonable charging capacitors, a first resistor, a second resistor, a third resistor, a seventh resistor and an eighth resistor are selected, so that the discharging speed of the charging capacitors is slower, reasonable hiccup time is maintained, and loss is reduced; meanwhile, the problem that auxiliary power cannot be restarted due to too fast charging is avoided; in addition, after the main output end is powered off, a discharge channel of the charging capacitor is cut off through the third diode, so that the discharge speed of the charging capacitor is reduced.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all equivalent changes made by using the contents of the present specification and the drawings, or applied directly or indirectly to the related technical fields, are included in the scope 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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| CN202010419056.6A CN111614062A (en) | 2020-05-18 | 2020-05-18 | Short-circuit protection circuit of multi-output power supply |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112134257A (en) * | 2020-09-24 | 2020-12-25 | 深圳市信锐网科技术有限公司 | Short-circuit protection circuit of direct-current power supply |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112134257A (en) * | 2020-09-24 | 2020-12-25 | 深圳市信锐网科技术有限公司 | Short-circuit protection circuit of direct-current power supply |
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