CN101800467B - Protection circuit of switch power supply - Google Patents
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- CN101800467B CN101800467B CN 201010123855 CN201010123855A CN101800467B CN 101800467 B CN101800467 B CN 101800467B CN 201010123855 CN201010123855 CN 201010123855 CN 201010123855 A CN201010123855 A CN 201010123855A CN 101800467 B CN101800467 B CN 101800467B
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Abstract
The invention discloses a protection circuit of switch power supply, comprising a detection unit which is used for comparing output feedback signal of the switch power supply with the preset standard voltage and generating high level or low level signal according to comparison result, a control unit which is used for generating a control signal according to the level signal generated by the detection unit and an enable signal of the switch power supply and a discharging unit which is used for controlling on-off of ground discharge access corresponding to the actual output terminal of the switch power supply. The switch power supply protection circuit can realize smooth transition from soft starting of switch power supply to normal operation.
Description
Technical Field
The invention relates to the field of switching power supplies, in particular to a protection circuit of a switching power supply.
Background
The application of the DC/DC switching power supply is wide. As shown in fig. 1, the output related circuit structure in the switching power supply is shown, wherein a connection point between the main switch tube 11 and the synchronous switch tube 12 is an output end SW of the switching power supply. When the switching power supply is used, the output terminal SW of the switching power supply is generally grounded through the output inductor L and the output capacitor C, and a connection point between the output inductor L and the output capacitor C is used as the actual output terminal VOUT of the switching power supply.
In order to prevent the output voltage VOUT output by the actual output terminal VOUT from generating a large voltage overshoot and the current in the output inductor L from generating a large inrush current when the switching power supply is started, a soft start control is added to the switching power supply to make the output voltage VOUT and the inductor current slowly change to a certain preset value. One commonly used control method is: the reference voltage which is slowly increased from 0 to the preset value is set, and the output voltage is gradually increased from 0 to the preset value along with the reference voltage through loop adjustment so as to avoid overshoot of the output voltage.
However, in practical applications, there may be a residual voltage at the actual output terminal VOUT, such that the output voltage VOUT does not start to rise from 0. Since the starting process is closed-loop control, when the output feedback signal is detected to be higher than the reference voltage which is slowly increased, the control circuit turns on the synchronous switch tube 12 to pull the output voltage Vout low, so that the synchronous switch tube 12 is turned on for a long time, and the output voltage Vout is continuously discharged through the output inductor L and the synchronous switch tube 12.
In this case, the synchronous switch tube 12 is turned on for a long time, and the reverse current flowing through the synchronous switch tube 12 is very large, which increases the loss of the synchronous switch tube 12 to exceed the thermal limit thereof and may damage the synchronous switch tube 12 in a severe case.
In order to solve this problem, a commonly used soft-start protection circuit is shown in fig. 2, in which an output feedback terminal FB of the switching power supply is connected to a negative phase input terminal of the first comparator 21, and a positive phase input terminal thereof is connected to a slowly changing reference voltage SSREF. When the switching power supply is ready to be started, comparing the output feedback signal with a reference voltage SSREF, and if the output feedback signal is smaller than the reference voltage SSREF, normally starting the switching power supply; if the output feedback signal is greater than the reference voltage SSREF, the main switching tube 11 and the synchronous switching tube 12 are turned off, and at this time, the reference voltage SSREF still normally rises until the output feedback signal is higher, the switching power supply enters a starting process, and the main switching tube 11 and the synchronous switching tube 12 are alternately turned on.
However, when the pre-stored voltage at the actual output terminal VOUT is lower than the predetermined output voltage of the switching power supply, and the output feedback signal is greater than the reference voltage SSREF in the starting process, the main switching tube 11 and the synchronous switching tube 12 are turned off at the same time in the initial stage of the soft start, and the main switching tube 11 and the synchronous switching tube 12 are normally and alternately turned on until the reference voltage SSREF rises to be greater than the output feedback signal, so that the switching between two states exists in the soft start process of the switching power supply, and the waveform of the output voltage VOUT at the actual output terminal VOUT is easily unsmooth; moreover, if the pre-stored voltage at the actual output terminal VOUT is higher than the preset value of the output voltage, the main switch tube 11 and the synchronous switch tube 12 are turned off simultaneously during the whole soft start period, and the output voltage VOUT is adjusted to the preset value through loop adjustment after the soft start period is over, so that the problem of output voltage VOUT overshoot may still occur during the adjustment process. Based on the above problems, the existing soft start protection circuit cannot ensure the smooth transition from the soft start to the normal operation of the switching power supply.
Disclosure of Invention
In view of the above, the technical problem to be solved by the present invention is to provide a protection circuit for a switching power supply, which can realize smooth transition from soft start to normal operation of the switching power supply.
Therefore, the embodiment of the invention adopts the following technical scheme:
the embodiment of the invention provides a protection circuit of a switching power supply, which is characterized by comprising the following components:
the detection unit is used for comparing an output feedback signal of the switching power supply with a preset reference voltage and correspondingly generating a high-level or low-level signal according to a comparison result;
the control unit is used for generating a control signal according to the level signal generated by the detection unit and the enable signal of the switching power supply;
and the discharging unit is used for controlling the on or off of the ground discharging path corresponding to the actual output end of the switching power supply according to the control signal generated by the control unit.
Wherein, the detecting element is specifically used for: when the output feedback signal is smaller than the preset reference voltage, generating a high level signal; and when the output feedback signal is greater than the preset reference voltage, generating a low-level signal.
The control unit is specifically configured to:
when the detection unit generates a high-level signal and the enable signal is a low-level signal, generating a low-level control signal; when the detection unit generates a low level signal and the enable signal is a low level signal, a high level control signal is generated.
The discharge unit is specifically configured to:
when the control signal is at a high level, controlling the ground discharge path corresponding to the actual output end to be conducted; and when the control signal is at a low level, controlling the ground discharge path corresponding to the actual output end to be switched off.
The detection unit is realized by a second comparator, the positive phase input end of the second comparator is connected with the preset reference voltage, and the negative phase input end of the second comparator is connected with the output feedback end of the switching power supply; and the output end of the second comparator outputs the level signal.
The control unit comprises an RS latch and a NOT gate; wherein,
the S end of the RS latch is connected with the output end of the detection unit, the R end of the RS latch is connected with an enabling signal, the output end of the RS latch is connected with the input end of the NOT gate, and the output end of the NOT gate outputs the control signal.
The control unit comprises a D trigger and a NOT gate; wherein,
the D end of the D trigger is connected with a power supply voltage, the CLK end is connected with the output end of the detection unit, the R end is connected with an enable signal, the output end is connected with the input end of the NOT gate, and the output end of the NOT gate outputs the control signal.
The discharge unit includes: the first switch tube, the third resistor and the output inductor; wherein,
the grid electrode of the first switching tube is connected with the output end of the control unit, the source electrode of the first switching tube is grounded, and the drain electrode of the first switching tube is connected with the output end of the switching power supply through a third resistor; the output end of the switching power supply is connected with the actual output end of the switching power supply through an output inductor.
The technical effect analysis of the technical scheme is as follows:
the protection circuit of the switching power supply enables the switching power supply to work under the complete closed-loop control in the whole starting process, and can detect the output voltage Vout in the actual output end VOUT and discharge the charges stored in the actual output end VOUT through the output end SW of the switching power supply before the switching power supply is started, so that the output voltage Vout of the actual output end VOUT can be normally and completely started from 0, and the stable transition from the soft start to the normal work of the switching power supply is realized; moreover, the protection circuit is relatively simple to implement and easy to implement.
Drawings
FIG. 1 is a schematic diagram of an output related circuit in a prior art switching power supply;
FIG. 2 is a schematic diagram of a soft-start protection circuit of a prior art switching power supply;
fig. 3 is a schematic structural diagram of a switching power supply protection circuit according to an embodiment of the invention;
fig. 4 is a schematic diagram of an implementation structure of the switching power supply protection circuit according to the embodiment of the invention;
fig. 5 is a schematic diagram of another implementation structure of the switching power supply protection circuit according to the embodiment of the invention.
Detailed Description
The following describes the implementation of the switching power supply protection circuit according to the embodiment of the present invention in detail with reference to the accompanying drawings.
Fig. 3 is a schematic structural diagram of a switching power supply protection circuit according to an embodiment of the present invention, and as shown in fig. 3, the circuit includes:
the detecting unit 310 is configured to compare the output feedback signal of the switching power supply with a preset reference voltage, and generate a high-level or low-level signal according to the comparison result.
Specifically, the detection unit 310 may be configured to: when the output feedback signal is smaller than the preset reference voltage, generating a high level signal; and when the output feedback signal is greater than the preset reference voltage, generating a low-level signal.
This reference voltage should be set to a value as close to 0 as possible in order to enable the switching power supply to start from a voltage value close to 0.
And a control unit 320 for generating a control signal according to the level signal generated by the detection unit 310 and the enable signal of the switching power supply.
The control unit 320 is specifically configured to: when the detection unit 310 generates a high level signal and the enable signal is a low level signal, a low level control signal is generated; when the detection unit 310 generates a low level signal and the enable signal is a low level signal, a control signal of a high level is generated.
And the discharging unit 330 is configured to control, according to the control signal generated by the control unit, on or off of a ground discharging path corresponding to the actual output terminal of the switching power supply.
The discharge unit 330 is specifically configured to: when the control signal is at a high level, controlling the conduction of a discharge path to the ground corresponding to the actual output end; and when the control signal is at a low level, controlling the ground discharge path corresponding to the actual output end to be switched off.
Fig. 4 is a specific circuit implementation of the protection circuit of the switching power supply shown in fig. 3, and as shown in fig. 4, an output terminal SW of the switching power supply is grounded through an output inductor L and an output capacitor C. The connection point between the output inductor L and the output capacitor C is the actual output end VOUT of the switching power supply; the actual output terminal VOUT is grounded through the first resistor R1 and the second resistor R2, and a connection point of the first resistor R1 and the second resistor R2 is an output feedback terminal FB of the switching power supply. The first resistor R1 and the second resistor R2 are integrated in the switching power supply for the switching power supply with fixed output, and the first resistor R1 and the second resistor R2 are set by a user independently for the switching power supply with adjustable output. As shown in fig. 4, the protection circuit includes:
an output feedback end FB of the switching power supply is connected with a negative phase input end of the second comparator 41, and an output feedback signal of the switching power supply is input to the negative phase input end of the second comparator 41; the non-inverting input terminal of the second comparator 41 is connected to the preset reference voltage REF, and the output terminal of the second comparator 41 is connected to the S terminal of the RS latch 42. When the output feedback signal output by the output feedback terminal FB is lower than the preset reference voltage REF, the second comparator 41 outputs a high level signal, and when the output feedback signal output by the output feedback terminal FB is higher than the preset reference voltage REF, the second comparator 41 outputs a low level signal.
The output end of the second comparator 41 is connected to the S end of the RS latch 42, and the R end of the RS latch 42 is connected to the enable end EN of the switching power supply, and receives an enable signal; the output end Q of the RS latch 42 is connected to the input end of the not gate 43, and the output end of the not gate 43 is connected to the gate of the first switching tube 45. When the second comparator 41 outputs a high-level signal and the enable signal output by the enable terminal EN is a low-level signal, the RS latch 42 outputs the high-level signal and further converts the high-level signal into a low-level control signal through the not gate 43; when the second comparator 41 generates a low level signal, and the enable signal is a low level signal, the RS latch 42 outputs the low level signal, and further converts the low level signal into a high level control signal through the not gate 43.
The gate of the first switch tube 45 is connected to the output of the nand gate 43, the source is grounded, and the drain is connected to the output SW of the switch power supply through the third resistor R3.
Wherein the second comparator 41 constitutes a circuit that implements the function of the detection unit 310. The RS latch 42 and the not gate 43 form a circuit to realize the function of the control unit 320, and the electrical signal output by the output terminal of the not gate 43 is used to control the first switch tube 45 to be turned on or off. The first switch tube 45, the third resistor R3 and the output inductor L form a discharge path to ground corresponding to the actual output terminal VOUT in the discharge unit 330.
The working principle of the protection circuit shown in fig. 4 is as follows:
when the output feedback signal output by the output feedback terminal FB is lower than the reference voltage REF, the second comparator 41 outputs a high level, the output of the RS latch 42 is a high level, and is converted into a low level after being inverted by the not gate 43, and the low level signal controls the first switching tube 45 to be turned off, so that the discharge path formed by the first switching tube 45, the third resistor R3 and the output inductor L is turned off; when the output feedback signal output by the output feedback terminal FB is higher than the reference voltage REF, the second comparator 41 outputs a low level, and then the RS latch 42 outputs a low level, and the low level is inverted by the not gate 43 and then converted into a high level, and the high level signal controls the first switch tube 45 to be opened, so that a discharge path formed by the first switch tube 45, the third resistor R3 and the output inductor L is turned on, and the electric quantity stored in the actual output terminal VOUT is discharged to the ground through the third resistor R3 and the output inductor L.
In addition, the control unit 320 may also be implemented by a D flip-flop and a not gate, and as in the switching power supply protection circuit shown in fig. 5, the difference from the switching power supply protection circuit shown in fig. 4 is only that: the RS latch 42 is replaced by a D flip-flop 44, wherein the D flip-flop 44 is triggered by a rising edge, the high level of the R terminal is cleared and output, and the low level is invalid. The specific connection structure is as follows:
the CLK terminal of the D flip-flop 44 is connected to the output terminal of the second comparator 41, the R terminal is connected to the enable terminal EN, the D terminal is connected to the power source VIN, and the output terminal is connected to the input terminal of the not gate 43.
The specific working principle of the switching power supply protection circuit shown in fig. 5 is as follows: the output initial state of the second comparator 41 is set to be low level, when the output feedback signal is greater than the reference voltage REF, the output of the second comparator 41 is still low level, the D flip-flop 44 outputs low level, and the first switch tube 45 is controlled to be opened after the inversion of the not gate 43; when the output feedback signal is smaller than the reference voltage REF, the second comparator 41 outputs a high level, the D flip-flop 44 outputs a high level, and the high level is inverted by the not gate 43 to control the first switching tube 45 to turn off.
The protection circuit of the switching power supply enables the switching power supply to work under the complete closed-loop control in the whole starting process, and can detect the output voltage Vout in the actual output end VOUT and discharge the charges stored in the actual output end VOUT through the output end SW of the switching power supply before the switching power supply is started, so that the problem of state switching in the prior art can be solved, and the problem of overshoot of the output voltage Vout in the adjusting process can be solved. The output voltage Vout of the actual output end VOUT in the embodiment of the invention can start normal and complete starting from 0, and the smooth transition from soft starting to normal working of the switching power supply is realized; moreover, the protection circuit is relatively simple to implement and easy to implement.
The method discharges the charges stored at the actual output terminal VOUT of the switch power supply from the SW point through the output inductor L instead of directly discharging from the actual output terminal VOUT, so that the discharge damping coefficient is increased; on the other hand, the problem that the switching power supply with adjustable output cannot be directly discharged by the actual output end VOUT due to the fact that the VOUT port does not exist is solved, so that the protection circuit can be simultaneously applied to two switching power supplies with fixed output and adjustable output, and the application range is wider.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (6)
1. A protection circuit for a switching power supply, comprising:
the detection unit is used for comparing an output feedback signal of the switching power supply with a preset reference voltage and correspondingly generating a high-level or low-level signal according to a comparison result; the preset reference voltage should be set to a value close to 0 so as to enable the switching power supply to start from a voltage value close to 0;
the control unit is used for generating a control signal according to the level signal generated by the detection unit and the enable signal of the switching power supply;
the discharging unit is used for controlling the conduction of a ground discharging channel corresponding to the actual output end when the control signal is at a high level; when the control signal is at a low level, controlling the ground discharge path corresponding to the actual output end to be switched off;
the discharge unit includes: the first switch tube, the third resistor and the output inductor; wherein, the first switch tube is an external switch tube independent of the switch power supply;
the grid electrode of the first switching tube is connected with the output end of the control unit, the source electrode of the first switching tube is grounded, and the drain electrode of the first switching tube is connected with the output end of the switching power supply through a third resistor; the output end of the switching power supply is connected with the actual output end of the switching power supply through an output inductor.
2. The circuit according to claim 1, characterized in that the detection unit is specifically configured to: when the output feedback signal is smaller than the preset reference voltage, generating a high-level signal; and when the output feedback signal is greater than the preset reference voltage, generating a low-level signal.
3. The circuit according to claim 1 or 2, wherein the control unit is specifically configured to:
when the detection unit generates a high-level signal and the enable signal is a low-level signal, generating a low-level control signal; when the detection unit generates a low-level signal and the enable signal is a low-level signal, a high-level control signal is generated.
4. The circuit according to claim 2, wherein the detection unit is implemented by a second comparator, a positive phase input terminal of the second comparator is connected to the preset reference voltage, and a negative phase input terminal of the second comparator is connected to an output feedback terminal of the switching power supply; and the output end of the second comparator outputs the level signal.
5. The circuit of claim 3, wherein the control unit comprises an RS latch and a NOT gate; wherein,
the S end of the RS latch is connected with the output end of the detection unit, the R end of the RS latch is connected with an enabling signal, the output end of the RS latch is connected with the input end of the NOT gate, and the output end of the NOT gate outputs the control signal.
6. The circuit of claim 3, wherein the control unit comprises a D flip-flop and a NOT gate; wherein,
the D end of the D trigger is connected with a power supply voltage, the CLK end is connected with the output end of the detection unit, the R end is connected with an enable signal, the output end is connected with the input end of the NOT gate, and the output end of the NOT gate outputs the control signal.
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| CN 201010123855 CN101800467B (en) | 2010-03-11 | 2010-03-11 | Protection circuit of switch power supply |
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| CN 201010123855 CN101800467B (en) | 2010-03-11 | 2010-03-11 | Protection circuit of switch power supply |
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| CN101800467B true CN101800467B (en) | 2013-03-20 |
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Families Citing this family (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102594111A (en) | 2012-02-24 | 2012-07-18 | 中兴通讯股份有限公司 | Quick discharge circuit |
| CN103311892A (en) * | 2012-03-12 | 2013-09-18 | 上海华虹集成电路有限责任公司 | Protection circuit for switch power supply |
| CN103617995A (en) * | 2013-11-25 | 2014-03-05 | 苏州贝克微电子有限公司 | Power source voltage load dump protective circuit |
| CN106549641B (en) * | 2015-09-16 | 2021-07-06 | 中兴通讯股份有限公司 | Protective circuit |
| CN108107377B (en) * | 2017-12-27 | 2023-09-22 | 杰华特微电子股份有限公司 | Power supply monitoring circuit, monitoring method and switching power supply |
| CN109217259A (en) * | 2018-10-26 | 2019-01-15 | 成都英特格灵微电子技术有限公司 | It is a kind of for the feedback short circuit protection circuit of Buck and guard method |
| CN113391185B (en) * | 2020-03-12 | 2023-08-08 | 圣邦微电子（北京）股份有限公司 | Aging box |
| CN113067470B (en) * | 2021-06-02 | 2021-08-17 | 上海芯龙半导体技术股份有限公司 | Enabling circuit for switching power supply chip, switching power supply chip and control method |
| CN114583663B (en) * | 2022-03-11 | 2023-07-21 | 苏州浪潮智能科技有限公司 | Monitoring protection circuit and step-down type switch power supply circuit |
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| US7254000B1 (en) * | 2005-06-20 | 2007-08-07 | Nexem, Inc. | Over voltage protection scheme for synchronous buck converter |
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| JP3963794B2 (en) * | 2002-07-09 | 2007-08-22 | ローム株式会社 | DC / DC converter |
| US6922044B2 (en) * | 2002-09-06 | 2005-07-26 | Intersil Americas Inc. | Synchronization of multiphase synthetic ripple voltage regulator |
| US7466115B2 (en) * | 2005-09-19 | 2008-12-16 | Texas Instruments Incorporated | Soft-start circuit and method for power-up of an amplifier circuit |
| CN100592611C (en) * | 2007-08-24 | 2010-02-24 | 尼克森微电子股份有限公司 | Pulse width modulation controller for switch type voltage stabilizer |
| JP4979521B2 (en) * | 2007-09-12 | 2012-07-18 | ローム株式会社 | Inverter, control circuit therefor, control method, and light emitting device using the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US7254000B1 (en) * | 2005-06-20 | 2007-08-07 | Nexem, Inc. | Over voltage protection scheme for synchronous buck converter |
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