CN110611292A - PFC circuit and protection circuit thereof - Google Patents
PFC circuit and protection circuit thereof Download PDFInfo
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- CN110611292A CN110611292A CN201911026934.1A CN201911026934A CN110611292A CN 110611292 A CN110611292 A CN 110611292A CN 201911026934 A CN201911026934 A CN 201911026934A CN 110611292 A CN110611292 A CN 110611292A
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- 239000003990 capacitor Substances 0.000 claims description 105
- 238000005070 sampling Methods 0.000 claims description 37
- 238000007599 discharging Methods 0.000 claims description 4
- 230000000052 comparative effect Effects 0.000 claims 1
- 230000035484 reaction time Effects 0.000 abstract description 2
- 238000010586 diagram Methods 0.000 description 4
- 238000001514 detection method Methods 0.000 description 2
- 230000001052 transient effect Effects 0.000 description 2
- 230000005856 abnormality Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 230000003139 buffering effect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
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- 230000001105 regulatory effect Effects 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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Classifications
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/08—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/42—Circuits or arrangements for compensating for or adjusting power factor in converters or inverters
- H02M1/4208—Arrangements for improving power factor of AC input
- H02M1/4225—Arrangements for improving power factor of AC input using a non-isolated boost converter
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
According to the PFC circuit and the overcurrent short-circuit protection circuit thereof, the control circuit outputs a conducting signal to the switch circuit when the current output by the PFC circuit is smaller than the current threshold value, and the switch circuit is conducted so that the PFC circuit can normally supply power to a load; when the current output by the PFC circuit is larger than the current threshold value, a turn-off signal is output to the switching circuit, and the switching circuit is switched off so as to turn off the PFC circuit, so that the PFC circuit is protected. Through setting up first inductance, when PFC circuit output short circuit in the twinkling of an eye, first inductance can let short circuit instantaneous current increase gradually, rather than the heavy current short circuit in the twinkling of an eye, provides sufficient reaction time for control circuit and switching circuit.
Description
Technical Field
The invention relates to the field of PFC circuits, in particular to a PFC circuit and a protection circuit thereof.
Background
The PFC technology can effectively solve the problem of current harmonics in power electronic equipment, so that the utilization rate of electric energy is improved. And some devices, such as projectors, light speed lamps and the like, need to directly use the output 380V (between 370V and 390V) of the PFC circuit to bring the devices into operation. Once these loads are failed, aged or short-circuited, the PFC circuit is directly short-circuited or over-current, and an over-current protection and short-circuit protection device is required to prevent the PFC circuit from being damaged. The current limiting output of the conventional PFC circuit is realized by detecting current through a PFC control chip, but sudden high-voltage load short circuit or overcurrent occurs, so that the chip detection circuit cannot respond in time and a PFC main power device is burnt out.
Disclosure of Invention
The application provides a PFC circuit and a protection circuit thereof, which are used for protecting the PFC circuit.
An embodiment provides a protection circuit of a PFC circuit, including:
the first inductor is used for being connected with the output end of the PFC circuit in series;
the switch circuit is used for being connected with the output end of the PFC circuit in series and is switched on and off according to a signal output by the control circuit;
the control circuit is used for detecting the current output by the PFC circuit, comparing the current output by the PFC circuit with a current threshold value, and outputting a turn-off signal to the switching circuit when the current output by the PFC circuit is greater than the current threshold value so as to control the switching circuit to be switched off; and when the current output by the PFC circuit is smaller than the current threshold, outputting a conduction signal to the switch circuit to control the switch circuit to be conducted.
The protection circuit, wherein the control circuit includes:
the sampling resistor is connected with the output end of the PFC circuit in series;
a first capacitor having one end connected to an external power supply and the other end grounded;
the first comparison control sub-circuit is used for comparing the voltage of the first capacitor with a first voltage threshold value, and outputting a conducting signal to the switch circuit to control the switch circuit to be conducted when the voltage of the first capacitor is greater than the first voltage threshold value; when the voltage of the first capacitor is smaller than the first voltage threshold value, outputting a turn-off signal to the switch circuit to control the switch circuit to be switched off;
the second comparison control sub-circuit is used for comparing the voltage of the sampling resistor with a second voltage threshold value, and when the voltage of the sampling resistor is larger than the second voltage threshold value, discharging the first capacitor to enable the voltage of the first capacitor to be smaller than the first voltage threshold value; when the voltage of the sampling resistor is smaller than a second voltage threshold value, stopping discharging the first capacitor;
the first input end of the second comparison control sub-circuit is connected with the sampling resistor to obtain the voltage of the sampling resistor; the output end of the second comparison control sub-circuit is connected with one end of the first capacitor and the first input end of the first comparison control sub-circuit; the output end of the first comparison control sub-circuit is connected with the control end of the switch circuit.
The protection circuit, wherein the first comparison control sub-circuit includes: a first transistor, and a first operational amplifier or a first comparator; a first voltage threshold is input to a non-inverting input end of the first operational amplifier or the first comparator, and an inverting input end of the first operational amplifier or the first comparator is a first input end of the first comparison control sub-circuit and is connected with one end of the first capacitor; the output end of the first operational amplifier or the first comparator is connected with the control end of the first transistor, and the first electrode of the first transistor is the output end of the first comparison control sub-circuit and is connected with the control end of the switch circuit; the second pole of the first transistor is grounded.
The protection circuit, wherein the second comparison control sub-circuit includes: a second capacitor, a second transistor, and a second operational amplifier or a second comparator; one end of the second capacitor is a first input end of a second comparison control sub-circuit and a non-inverting input end which is connected with the sampling resistor and the second operational amplifier or the second comparator; the other end of the second capacitor is grounded; a second voltage threshold is input to the inverting input end of the second operational amplifier or the second comparator; the output end of the second operational amplifier or the second comparator is connected with the control end of the second transistor, and the first electrode of the second transistor is the output end of the second comparison control sub-circuit and is connected with one end of the first capacitor; the second pole of the second transistor is grounded.
The protection circuit further comprises a controllable precise voltage-stabilizing source circuit for outputting a stable reference voltage; the second comparison control sub-circuit further comprises a first resistor and a second resistor; the output end of the controllable precise voltage-stabilizing source circuit is connected with the non-inverting input end of the first operational amplifier or the first comparator and one end of the first resistor; the other end of the first resistor is connected with the inverting input end of the second operational amplifier or the second comparator, and is grounded through the second resistor.
The protection circuit, wherein, the switch circuit includes the third transistor, the control pole of third transistor is the control end of switch circuit, connects the first pole of first transistor.
The protection circuit, wherein the first comparison control sub-circuit further comprises a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a third capacitor and a fourth capacitor; one end of the first capacitor is connected with an external power supply through the third resistor; one end of the fourth resistor is connected with the output end of the controllable precise voltage-stabilizing source circuit, and the other end of the fourth resistor is connected with the non-inverting input end of the first operational amplifier or the first comparator and is grounded through a third capacitor; the inverting input end of the first operational amplifier or the first comparator is connected with the output end of the first operational amplifier or the first comparator through a fifth resistor; the output end of the first operational amplifier or the first comparator is connected with the control end of the first transistor, one end of the seventh resistor and one end of the fourth capacitor through the sixth resistor; the other end of the seventh resistor and the other end of the fourth capacitor are both grounded; the first pole of the first transistor is connected with an external power supply through an eighth resistor and a ninth resistor respectively, and the first pole of the first transistor is connected with a sampling resistor through a tenth resistor.
The protection circuit, wherein the second comparison control sub-circuit further includes an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifth capacitor and a sixth capacitor; one end of the second capacitor is connected with the sampling resistor through an eleventh resistor, and the inverting input end of the second operational amplifier or the second comparator is grounded through a fifth capacitor; the non-inverting input end of the second operational amplifier or the second comparator is connected with the output end of the second operational amplifier or the second comparator through a twelfth resistor; the output end of the second operational amplifier or the second comparator is connected with the control end of the second transistor, one end of the sixth capacitor and one end of the fourteenth resistor through the thirteenth resistor; the other end of the sixth capacitor and the other end of the fourteenth resistor are both grounded.
The protection circuit, wherein, controllable accurate steady voltage source circuit includes: the voltage regulator comprises a controllable precise voltage-stabilizing source, a first diode, a seventh capacitor, an eighth capacitor and a third operational amplifier or a third comparator; the anode of the first diode and one end of the fifteenth resistor are both connected with an external power supply; the negative electrode of the first diode is connected with the positive electrode of a power supply of the third operational amplifier or the third comparator and one end of a seventh capacitor, and the other end of the seventh capacitor and the negative electrode of the power supply of the third operational amplifier or the third comparator are both grounded; the reference electrode of the controllable precise voltage-stabilizing source is the output end of the controllable precise voltage-stabilizing source circuit, the other end of the fifteenth resistor, the cathode of the controllable precise voltage-stabilizing source circuit and one end of the eighth capacitor; the anode of the controllable precise voltage-stabilizing source circuit and the other end of the eighth capacitor are both grounded; the first transistor and the second transistor are both NPN triodes, the base electrodes of the NPN triodes are control electrodes corresponding to the transistors, the collector electrodes of the NPN triodes correspond to the first electrodes of the transistors, and the emitter electrodes of the NPN triodes correspond to the second electrodes of the transistors; the third transistor is an N-channel MOS transistor, and the grid electrode of the N-channel MOS transistor is the control electrode of the third transistor; the first voltage threshold is smaller than the voltage output by the external power supply; the reference voltage is a first voltage threshold.
An embodiment provides a PFC circuit including the protection circuit as described above.
According to the PFC circuit and the protection circuit thereof in the embodiment, the control circuit outputs the conducting signal to the switch circuit when the current output by the PFC circuit is smaller than the current threshold value, and the switch circuit is conducted so as to enable the PFC circuit to normally supply power to the load; when the current output by the PFC circuit is larger than the current threshold value, a turn-off signal is output to the switching circuit, and the switching circuit is switched off so as to turn off the PFC circuit, so that the PFC circuit is protected. Through setting up first inductance, when PFC circuit output short circuit in the twinkling of an eye, first inductance can let short circuit instantaneous current increase gradually, rather than the heavy current short circuit in the twinkling of an eye, provides sufficient reaction time for control circuit and switching circuit.
Drawings
Fig. 1 is a block diagram of an embodiment of a PFC circuit according to the present invention;
fig. 2 is a circuit diagram of an embodiment of a PFC circuit according to the present invention;
fig. 3 is a circuit diagram of a controllable precise voltage regulator circuit in the protection circuit of the PFC circuit according to the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following detailed description and accompanying drawings.
The invention increases the protection circuit in the prior PFC (power factor correction) circuit to improve the safety and stability of the PFC circuit. The PFC circuit has a wide range of applications, and the present invention is described by taking as an example its application to the PFC part of a power supply, which may be a switching power supply. As shown in fig. 1 and 2, the switching power supply includes an input interface (not shown in the figure), a filter circuit 30, a rectifier circuit 20, and a PFC circuit, which are connected in series in this order. The PFC circuit includes a PFC main circuit 10, a protection circuit 40, and an output interface 50. The PFC main circuit 10 is an existing PFC circuit.
The input interface is connected with alternating current, such as 220V or 110V mains supply.
The PFC main circuit 10 is used for transforming the ac power input from the input interface, for example, boosting the ac power through a transformer (not shown) so that the PFC circuit outputs the required voltage to the load. A fuse (fuse) is connected in series between the input interface and the PFC main circuit 10 to provide protection.
The rectifying circuit 20 rectifies the transformed alternating current.
Fig. 2 shows a partial circuit diagram of the PFC main circuit 10, which further includes a PWM controller (not shown in the figure) that outputs a PWM signal to a gate of the switching tube Q4, so that the dc power output by the rectifying circuit 20 can be adjusted by PWM, and the voltage and current output by the PFC main circuit can be controlled to implement power factor correction. Since the PFC main circuit 10 is a conventional PFC circuit, it is not described in detail.
The protection circuit 40 is located at the output stage of the PFC main circuit 10, monitors the current output by the PFC main circuit 10 in real time, and once the output current exceeds a preset current threshold, cuts off the load circuit to stop supplying power to a subsequent load, thereby implementing overcurrent protection. The current output by the PFC main circuit 10 is the current output by the PFC circuit provided by the present invention, and the current output by the PFC circuit is described in the following.
The output interface 50 serves as an output end of the PFC circuit and is used for being connected to a load, and the voltage output by the output interface 50 is 380V in this embodiment. The present invention mainly improves the existing PFC circuit, so the connections described herein are all electrical connections, which are not described in detail later. A fuse or the like is also connected in series between the PFC main circuit 10 and the output interface 50 to further protect the circuit.
The protection circuit 40 includes a first inductor L, a switching circuit 410, and a control circuit; wherein the first inductor L1 and the switch circuit 410 are both connected in series between the PFC main circuit 10 and the output interface 50, and further, in this embodiment, the first inductor L1 is connected in series between the switch circuit 410 and the output interface 50.
The first inductor L1 is connected in series in the power supply loop of the PFC circuit, and when the output of the PFC circuit is momentarily short-circuited, the first inductor L1 can gradually increase the short-circuited transient current, rather than the transient large-current short-circuit, thereby providing sufficient response time for the control circuit and the switch circuit 410. As shown in fig. 2, in the present embodiment, the second inductor L2 in the PFC main circuit 10 is connected in series between the rectifying circuit 20 and the positive electrode of the output interface 50, and L1 is connected in series between the rectifying circuit 20 and the negative electrode of the output interface 50, both inductors can slow the current rise time during overcurrent.
The switch circuit 410 is a circuit having two states of "on (on)" and "off, and performs on-off switching, that is, switching of two states of on and off, according to a signal output from the control circuit.
The control circuit detects the current output by the PFC circuit and compares the current output by the PFC circuit with a current threshold value, wherein the current threshold value is a reference for judging whether overcurrent protection is started or not and is preset. Under the normal condition of the circuit, the current output by the PFC circuit is smaller than or equal to the current threshold value, so that the control circuit outputs a conducting signal to the switch circuit 410 when the current output by the PFC circuit is smaller than or equal to the current threshold value so as to control the switch circuit 410 to be conducted, and the PFC circuit continuously supplies power to a load; when the current output by the PFC circuit is greater than the current threshold, a turn-off signal is output to the switch circuit 410 to control the switch circuit 410 to be turned off, thereby implementing overcurrent protection.
Further, the control circuit includes a sampling resistor R, a first capacitor C1, a first comparison control sub-circuit 420, and a second comparison control sub-circuit 430. The sampling resistor R is connected in series between the PFC main circuit 10 and the output interface 50, and is used to detect the current output by the PFC circuit, that is, the current output by the PFC circuit is the current on the sampling resistor R. One end of the first capacitor C1 is connected to an external power supply, and the other end is grounded. The external power supply is relative to the protection circuit, and actually the external power supply may belong to a part of the PFC circuit, for example, a direct current output by a rectifying circuit 20 is taken to step down, that is, the external power supply may be used, the power supply is mainly used for supplying power to the protection circuit, specifically, for supplying power to each operational amplifier or comparator of the protection circuit, and the voltage of the power supply is represented by VCC, which is a direct current of 15V in this embodiment.
The first comparison control sub-circuit 420 is configured to compare the voltage of the first capacitor C1 with a first voltage threshold V1, and output a turn-on signal to the switch circuit 410 to control the switch circuit 410 to turn on when the voltage of the first capacitor is greater than the first voltage threshold V1; when the voltage of the first capacitor C1 is less than or equal to the first voltage threshold V1, a turn-off signal is output to the switch circuit 410 to control the switch circuit to turn off.
The second comparison control sub-circuit 430 is configured to compare the voltage of the sampling resistor R with a second voltage threshold V2, and when the voltage of the sampling resistor R is greater than the second voltage threshold V2, discharge the first capacitor C1 to make the voltage of the first capacitor smaller than the first voltage threshold V1; when the voltage of the sampling resistor R is less than or equal to the second voltage threshold V2, the first capacitor C1 stops being discharged. In this embodiment, the first capacitor C1 is discharged by grounding the first capacitor C1.
A first input end of the second comparison control sub-circuit 430 is connected with the sampling resistor R to obtain the voltage of the sampling resistor R; the output end of the second comparison control sub-circuit 430 is connected with one end of the first capacitor C1 and the first input end of the first comparison control sub-circuit 420; the output terminal of the first comparison control sub-circuit 420 is connected to the control terminal of the switch circuit 410.
In this embodiment, the PFC circuit outputs a regulated voltage of 380V (370V-390V DC) after being powered on, and supplies power to the rear device load through pins 1 and 3 of the output interface 50. The external power supply can simultaneously output VCC voltage to supply power to the protection circuit. When the power is on, the external power supply charges the first capacitor C1, and when the charging is started, the voltage of the first capacitor C1 is smaller than the first voltage threshold, so that the first comparison control sub-circuit 420 turns off the output of the PFC circuit through the switch circuit 410, and after the voltage of the first capacitor C1 is charged to be higher than the first voltage threshold, the output of the PFC circuit is turned on through the switch circuit 410, thereby achieving the delayed power-on and buffering the power-on. The magnitude of the first voltage threshold determines the time for delaying power-on, which is smaller than the voltage provided by the external power source, and can be specifically set according to requirements.
In view of the characteristic that the voltage and the current can be converted, the voltage of the sampling resistor R divided by the resistance of the sampling resistor R is the current output by the PFC circuit, and correspondingly, the second voltage threshold divided by the resistance of the sampling resistor R is the current threshold. That is, in this embodiment, whether the PFC circuit is over-current is determined in a form of detecting a voltage and determining a threshold, where a voltage of the sampling resistor R is greater than a second voltage threshold indicates that the current is too large, and a voltage of the sampling resistor R is less than or equal to the second voltage threshold indicates that the current is substantially normal.
Further, as shown in fig. 2, the first comparison control sub-circuit 420 includes a first operational amplifier U1 and a first transistor Q1. A first voltage threshold V1 is input to a non-inverting input terminal of a first operational amplifier U1, and an inverting input terminal of the first operational amplifier U1 is a first input terminal of the first comparison control sub-circuit 420 and is connected to one end of a first capacitor C1; the output end of the first operational amplifier U1 is connected with the control end of a first transistor Q1, the first pole of the first transistor Q1 is the output end of the first comparison control sub-circuit 420 and is connected with the control end of the switch circuit; the second pole of the first transistor Q1 is connected to ground. In this embodiment, the first transistor Q1 is an NPN transistor, a base of the NPN transistor is a control electrode of the first transistor Q1, a collector of the NPN transistor is a first electrode of the first transistor Q1, and an emitter of the NPN transistor is a second electrode of the first transistor Q1. In another embodiment, the first operational amplifier may be replaced by a first comparator, and since the connection relationship of the components in the first comparison control sub-circuit 420 using the comparator may be unchanged, the first comparison control sub-circuit 420 using the comparator is not described in detail.
The second comparison control sub-circuit 430 includes a second capacitor C2, a second operational amplifier U2, and a second transistor Q2; one end of the second capacitor C2 is a first input end of the second comparison control sub-circuit 430, and is connected with the sampling resistor R and a non-inverting input end of the second operational amplifier U2; the other end of the second capacitor C2 is grounded; the inverting input terminal of the second operational amplifier U2 inputs a second voltage threshold V2; the output end of the second operational amplifier U2 is connected to the control end of a second transistor Q2, and the first electrode of the second transistor Q2 is the output end of the second comparison control sub-circuit 430 and is connected to one end of a first capacitor; the second pole of the second transistor Q2 is grounded. In this embodiment, the second transistor Q2 is an NPN transistor, a base of the NPN transistor is a control electrode of the second transistor Q2, a collector of the NPN transistor is a first electrode of the second transistor Q2, and an emitter of the NPN transistor is a second electrode of the second transistor Q2. In another embodiment, the second operational amplifier may be replaced by a second comparator, and since the connection relationship of the components in the second comparison control sub-circuit 430 using the comparator may be unchanged, the second comparison control sub-circuit 430 using the comparator is not described in detail.
The switch circuit 410 includes a third transistor Q3, a control electrode of the third transistor Q3 is a control terminal of the switch circuit 410, and a first electrode of the first transistor Q1 is connected. A first pole of the third transistor Q3 is connected to one end of the resistor R, and a second pole of the third transistor Q3 is connected to one end of the first inductor L1. In this embodiment, the third transistor Q3 is an N-channel MOS, the gate of the N-channel MOS is the control electrode of the third transistor Q3, the source of the N-channel MOS is the first electrode of the third transistor Q3, and the drain of the N-channel MOS is the second electrode of the third transistor Q3. The first comparison control sub-circuit 420 can control the on-off of the source and drain of the N-channel MOS transistor by outputting a high-low level signal to the gate of the N-channel MOS transistor, thereby realizing the on-off control of the PFC circuit.
When the PFC circuit is powered on, a certain time is required for charging the first capacitor C1, so that the operational amplifier U1 outputs a high level, the high level drives the first transistor Q1, the third transistor Q3 is driven to be turned off, and the third transistor Q3 is turned off. With the charging time of the first capacitor C1 being longer, after the voltage is charged to be higher than the first voltage threshold V1, the operational amplifier U1 outputs a low level to drive the first transistor Q1, and the Q3 is turned off, so that the PFC circuit has a complete loop and normally supplies power to the load device. Once the load device is over-current or short-circuited, current flows through the first inductor L1 and the second inductor L2 to generate a voltage drop to the sampling resistor R, when the non-inverting input terminal of the operational amplifier U2 detects that the voltage of the sampling resistor R exceeds the second voltage threshold V2, the operational amplifier U2 outputs a high voltage to drive the second transistor Q2 to operate, and the Q2 pulls the voltage across the first capacitor C1 low, and when the voltage is lower than the first voltage threshold V1, the U1 outputs a high voltage, so that the Q3 is turned off by the Q1, and power supply to the load device is cut off. And the PFC power stage components are protected from being damaged. Therefore, the invention realizes real-time monitoring and protection of the output current of the PFC circuit through the circuit.
The second capacitor C2 is charged when the switch circuit 410 is turned on, and after the protection circuit starts the overcurrent protection to turn off the switch circuit 410, although the current of the resistor R becomes 0, the second capacitor C2 starts to discharge at this time, so that the voltage of the non-inverting input terminal of the second operational amplifier U2 is higher than the voltage of the inverting input terminal, and is maintained for a period of time, thereby prolonging the turn-off time of the switch circuit 410 and facilitating the overcurrent protection.
Referring to fig. 3, the protection circuit further includes a controllable precise voltage regulator circuit for outputting a stable reference voltage; in this embodiment, the reference voltage output by the controllable precise voltage regulator circuit is the first voltage threshold V1, in other words, the first voltage threshold is preset and is determined by the reference voltage output by the controllable precise voltage regulator circuit.
The second comparison control sub-circuit 430 further includes a first resistor R1 and a second resistor R2. The output end of the controllable precise voltage-stabilizing source circuit is connected with the non-inverting input end of the first operational amplifier U1 and one end of the first resistor R1; the other end of the first resistor R1 is connected to the inverting input terminal of the second operational amplifier U2 and is also connected to ground through a second resistor R2. In other words, the first resistor R1 and the second resistor R2 obtain the second voltage threshold V2 by dividing the reference voltage. The second voltage threshold V2 is also preset and is determined by the reference voltage outputted from the controllable precision regulator circuit, the first resistor R1 and the second resistor R2.
Further, the first comparison control sub-circuit 420 further includes a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a tenth resistor R10, a third capacitor C3, and a fourth capacitor C4. One end of the first capacitor C1 is connected to the external power source through the third resistor R3, i.e. the third resistor R3 is used to charge the first capacitor C1. One end of the fourth resistor R4 is connected with the output end of the controllable precision voltage-stabilizing source circuit, and the other end of the fourth resistor R4 is connected with the non-inverting input end of the first operational amplifier U1 and is grounded through a third capacitor C3; the inverting input end of the first operational amplifier U1 is connected with the output end of the first operational amplifier U1 through a fifth resistor R5; the output end of the first operational amplifier U1 is connected with the control end of the first transistor Q1, one end of a seventh resistor R7 and one end of a fourth capacitor C4 through a sixth resistor R6; the other end of the seventh resistor R7 and the other end of the fourth capacitor C4 are both grounded; the first pole of the first transistor Q1 is further connected to an external power source through an eighth resistor R8 and a ninth resistor R8, respectively, and the first pole of the first transistor Q1 is further connected to one end of a sampling resistor R through a tenth resistor R10; the other end of the sampling resistor R is grounded.
The second comparison control sub-circuit 430 further includes an eleventh resistor R11, a twelfth resistor R12, a thirteenth resistor R13, a fourteenth resistor R14, a fifth capacitor C5 and a sixth capacitor C6; one end of the second capacitor C2 is connected to the sampling resistor R through an eleventh resistor R11, and the inverting input terminal of the second operational amplifier U2 is connected to the ground through a fifth capacitor C5; the non-inverting input end of the second operational amplifier U2 is connected with the output end of the second operational amplifier U2 through a twelfth resistor R12; the output end of the second operational amplifier U2 is connected with the control end of the second transistor Q2, one end of a sixth capacitor C6 and one end of a fourteenth resistor R14 through a thirteenth resistor R13; the other end of the sixth capacitor C6 and the other end of the fourteenth resistor R14 are both grounded.
The controllable precise voltage-stabilizing source circuit comprises a controllable precise voltage-stabilizing source U4, a first diode D1, a third operational amplifier U3, a seventh capacitor C7 and an eighth capacitor C8; the anode of the first diode D1 and one end of a fifteenth resistor R15 are both connected with an external power supply; the negative electrode of the first diode D1 is connected with the positive electrode of a power supply of a third operational amplifier U3 and one end of a seventh capacitor C7, and the other end of the seventh capacitor C7 and the negative electrode of the power supply of the third operational amplifier U3 are both grounded; the reference electrode of the controllable precise voltage-stabilizing source U4 is the output end of the controllable precise voltage-stabilizing source circuit, the other end of the fifteenth resistor R15 is connected, the cathode of the controllable precise voltage-stabilizing source circuit and one end of the eighth capacitor C8; and the anode of the controllable precise voltage-stabilizing power supply circuit and the other end of the eighth capacitor C8 are both grounded. In this embodiment, the reference voltage output by the controllable precision voltage regulator U4 is 2.5V. In another embodiment, the third operational amplifier may be replaced by a third comparator, and since the connection relationship of the components in the controllable precise voltage regulator circuit using the comparator may be unchanged, the controllable precise voltage regulator circuit using the comparator is not described in detail.
In summary, the PFC circuit provided by the present invention adds current detection in the PFC output stage to monitor the output current of the PFC circuit in real time. When the output current exceeds a set current value, the protection circuit cuts off the load circuit and stops supplying power to the subsequent load. And meanwhile, the inductor is added to serve as a current suppressor, and when the PFC output is in instant short circuit, the current suppressor can enable the short-circuit instant current to be gradually increased instead of instant large-current short circuit. This gives the protection circuit sufficient time to start protection.
The invention also provides a beam lamp, and a switch power supply of the beam lamp adopts the PFC circuit. The light speed lamp bulb is often damaged suddenly due to some reason to cause short circuit; the lighting board has the possibility of being bad, once the lighting board breaks down, large current is caused, or short circuit is caused, the 380V output of the power supply can be directly short-circuited; meanwhile, after the lamp bulb is used for a period of time, the aging phenomenon can occur, and excessive current or short circuit can be caused at the moment of switching on and switching off. The switching power supply with the PFC circuit is adopted as a power supply, and can respond in time when abnormality such as overcurrent occurs, so that the power supply board is protected from being burnt out, and the switching power supply can be recovered to work again after the fault is removed. Similarly, the switching power supply with the PFC circuit of the present invention can also be applied to a projector as a power supply for the projector.
The present invention has been described in terms of specific examples, which are provided to aid understanding of the invention and are not intended to be limiting. For a person skilled in the art to which the invention pertains, several simple deductions, modifications or substitutions may be made according to the idea of the invention.
Claims (10)
1. A protection circuit of a PFC circuit, comprising:
the first inductor is used for being connected with the output end of the PFC circuit in series;
the switch circuit is used for being connected with the output end of the PFC circuit in series and is switched on and off according to a signal output by the control circuit;
the control circuit is used for detecting the current output by the PFC circuit, comparing the current output by the PFC circuit with a current threshold value, and outputting a turn-off signal to the switching circuit when the current output by the PFC circuit is greater than the current threshold value so as to control the switching circuit to be switched off; and when the current output by the PFC circuit is smaller than the current threshold, outputting a conduction signal to the switch circuit to control the switch circuit to be conducted.
2. The protection circuit of claim 1, wherein the control circuit comprises:
the sampling resistor is connected with the output end of the PFC circuit in series;
a first capacitor having one end connected to an external power supply and the other end grounded;
the first comparison control sub-circuit is used for comparing the voltage of the first capacitor with a first voltage threshold value, and outputting a conducting signal to the switch circuit to control the switch circuit to be conducted when the voltage of the first capacitor is greater than the first voltage threshold value; when the voltage of the first capacitor is smaller than the first voltage threshold value, outputting a turn-off signal to the switch circuit to control the switch circuit to be switched off;
the second comparison control sub-circuit is used for comparing the voltage of the sampling resistor with a second voltage threshold value, and when the voltage of the sampling resistor is larger than the second voltage threshold value, discharging the first capacitor to enable the voltage of the first capacitor to be smaller than the first voltage threshold value; when the voltage of the sampling resistor is smaller than a second voltage threshold value, stopping discharging the first capacitor;
the first input end of the second comparison control sub-circuit is connected with the sampling resistor to obtain the voltage of the sampling resistor; the output end of the second comparison control sub-circuit is connected with one end of the first capacitor and the first input end of the first comparison control sub-circuit; the output end of the first comparison control sub-circuit is connected with the control end of the switch circuit.
3. The protection circuit of claim 2, wherein the first comparison control sub-circuit comprises: a first transistor, and a first operational amplifier or a first comparator; a first voltage threshold is input to a non-inverting input end of the first operational amplifier or the first comparator, and an inverting input end of the first operational amplifier or the first comparator is a first input end of the first comparison control sub-circuit and is connected with one end of the first capacitor; the output end of the first operational amplifier or the first comparator is connected with the control end of the first transistor, and the first electrode of the first transistor is the output end of the first comparison control sub-circuit and is connected with the control end of the switch circuit; the second pole of the first transistor is grounded.
4. The protection circuit of claim 3, wherein the second comparison control sub-circuit comprises: a second capacitor, a second transistor, and a second operational amplifier or a second comparator; one end of the second capacitor is a first input end of a second comparison control sub-circuit and a non-inverting input end which is connected with the sampling resistor and the second operational amplifier or the second comparator; the other end of the second capacitor is grounded; a second voltage threshold is input to the inverting input end of the second operational amplifier or the second comparator; the output end of the second operational amplifier or the second comparator is connected with the control end of the second transistor, and the first electrode of the second transistor is the output end of the second comparison control sub-circuit and is connected with one end of the first capacitor; the second pole of the second transistor is grounded.
5. The protection circuit of claim 4, further comprising a controllable precision regulator circuit for outputting a stable reference voltage; the second comparison control sub-circuit further comprises a first resistor and a second resistor; the output end of the controllable precise voltage-stabilizing source circuit is connected with the non-inverting input end of the first operational amplifier or the first comparator and one end of the first resistor; the other end of the first resistor is connected with the inverting input end of the second operational amplifier or the second comparator, and is grounded through the second resistor.
6. The protection circuit of claim 5, wherein the switch circuit comprises a third transistor having a control terminal coupled to the control terminal of the switch circuit and a first terminal coupled to the first transistor.
7. The protection circuit of claim 5, wherein the first comparison control sub-circuit further comprises a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a tenth resistor, a third capacitor, and a fourth capacitor; one end of the first capacitor is connected with an external power supply through the third resistor; one end of the fourth resistor is connected with the output end of the controllable precise voltage-stabilizing source circuit, and the other end of the fourth resistor is connected with the non-inverting input end of the first operational amplifier or the first comparator and is grounded through a third capacitor; the inverting input end of the first operational amplifier or the first comparator is connected with the output end of the first operational amplifier or the first comparator through a fifth resistor; the output end of the first operational amplifier or the first comparator is connected with the control end of the first transistor, one end of the seventh resistor and one end of the fourth capacitor through the sixth resistor; the other end of the seventh resistor and the other end of the fourth capacitor are both grounded; the first pole of the first transistor is connected with an external power supply through an eighth resistor and a ninth resistor respectively, and the first pole of the first transistor is connected with a sampling resistor through a tenth resistor.
8. The protection circuit of claim 5, wherein the second comparative control sub-circuit further comprises an eleventh resistor, a twelfth resistor, a thirteenth resistor, a fourteenth resistor, a fifth capacitor, and a sixth capacitor; one end of the second capacitor is connected with the sampling resistor through an eleventh resistor, and the inverting input end of the second operational amplifier or the second comparator is grounded through a fifth capacitor; the non-inverting input end of the second operational amplifier or the second comparator is connected with the output end of the second operational amplifier or the second comparator through a twelfth resistor; the output end of the second operational amplifier or the second comparator is connected with the control end of the second transistor, one end of the sixth capacitor and one end of the fourteenth resistor through the thirteenth resistor; the other end of the sixth capacitor and the other end of the fourteenth resistor are both grounded.
9. The protection circuit of claim 6, wherein the controllable precision regulator circuit comprises: the voltage regulator comprises a controllable precise voltage-stabilizing source, a first diode, a seventh capacitor, an eighth capacitor and a third operational amplifier or a third comparator; the anode of the first diode and one end of the fifteenth resistor are both connected with an external power supply; the negative electrode of the first diode is connected with the positive electrode of a power supply of the third operational amplifier or the third comparator and one end of a seventh capacitor, and the other end of the seventh capacitor and the negative electrode of the power supply of the third operational amplifier or the third comparator are both grounded; the reference electrode of the controllable precise voltage-stabilizing source is the output end of the controllable precise voltage-stabilizing source circuit, the other end of the fifteenth resistor, the cathode of the controllable precise voltage-stabilizing source circuit and one end of the eighth capacitor; the anode of the controllable precise voltage-stabilizing source circuit and the other end of the eighth capacitor are both grounded; the first transistor and the second transistor are both NPN triodes, the base electrodes of the NPN triodes are control electrodes corresponding to the transistors, the collector electrodes of the NPN triodes correspond to the first electrodes of the transistors, and the emitter electrodes of the NPN triodes correspond to the second electrodes of the transistors; the third transistor is an N-channel MOS transistor, and the grid electrode of the N-channel MOS transistor is the control electrode of the third transistor; the first voltage threshold is smaller than the voltage output by the external power supply; the reference voltage is a first voltage threshold.
10. A PFC circuit comprising the protection circuit of any one of claims 1-9.
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| CN201911026934.1A CN110611292B (en) | 2019-10-26 | 2019-10-26 | PFC circuit and protection circuit thereof |
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| CN201911026934.1A CN110611292B (en) | 2019-10-26 | 2019-10-26 | PFC circuit and protection circuit thereof |
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| CN110611292B (en) | 2024-03-12 |
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