CN101800467B - Protection circuit of switch power supply - Google Patents

Protection circuit of switch power supply Download PDF

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Publication number
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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China
Prior art keywords
output
power supply
signal
level
voltage
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CN 201010123855
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CN101800467A (en
Inventor
吴德钦
贾立刚
李国军
巫炜
刘伟
林雄杰
战·阮
布鲁斯·弗格森
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MICROSEMI Corp TAIWAN OFFICE
BCD Semiconductor Manufacturing Ltd
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MICROSEMI Corp TAIWAN OFFICE
BCD Semiconductor Manufacturing Ltd
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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

A kind of protective circuit of Switching Power Supply
Technical field
The present invention relates to field of switch power, relate in particular to a kind of protective circuit of Switching Power Supply.
Background technology
Being widely used of DC/DC Switching Power Supply.As shown in Figure 1, be the output interlock circuit structure in the Switching Power Supply, wherein, the tie point between main switch 11 and the synchro switch pipe 12 is the output SW of Switching Power Supply.When using Switching Power Supply, generally the output SW with Switching Power Supply passes through outputting inductance L and output capacitance C ground connection, and the tie point between outputting inductance L and the output capacitance C is as the actual output VOUT of Switching Power Supply.
In order to prevent that the Switching Power Supply voltage overshoot that the output voltage V out generation of actual output VOUT output is larger when starting, the electric current among the outputting inductance L from producing larger surge current, can in Switching Power Supply, add soft start control, so that output voltage V out and inductive current slowly change to a certain preset value.A kind of control method commonly used is: the reference voltage that slowly is promoted to preset value since 0 is set, gradually is increased to preset value so that output voltage is followed reference voltage from 0 by the loop adjustment, to avoid the overshoot of output voltage.
But in actual applications, may there be residual voltage in actual output VOUT, so that output voltage V out rises since 0.Because start-up course belongs to closed-loop control, when detecting output feedback signal and be higher than the reference voltage of described slow rising, control circuit can be by conducting synchro switch pipe 12 to drag down output voltage V out, can open for a long time synchro switch pipe 12 like this, make output voltage V out through outputting inductance L and 12 continuous discharges of synchro switch pipe.
In this case, the 12 long-time conductings of synchro switch pipe, the reverse current that flows through synchro switch pipe 12 is very large, has increased the loss of synchro switch pipe 12, so that surpass its thermal limit, can damage synchro switch pipe 12 when serious.
In order to address this problem, a kind of soft start protective circuit commonly used connects the negative-phase input of the first comparator 21 with the output feedback end FB of Switching Power Supply as shown in Figure 2 at present, and normal phase input end connects a reference voltage SSREF who slowly changes.When Switching Power Supply prepare to start, output feedback signal and reference voltage SSREF are compared, if output feedback signal less than reference voltage SSREF, Switching Power Supply normally starts; If output feedback signal, then turn-offs main switch 11 and synchro switch pipe 12 greater than reference voltage SSREF, at this moment, reference voltage SSREF still normally rises, until when being higher than output feedback signal, Switching Power Supply enters start-up course, main switch 11 and synchro switch pipe 12 alternate conduction.
But, the voltage that prestores on actual output VOUT is lower than the predetermined output voltage of Switching Power Supply, and when output feedback signal is greater than reference voltage SSREF in the start-up course, then the starting stage main switch 11 of soft start and synchro switch pipe 12 turn-off simultaneously, until reference voltage SSREF is when rising to greater than output feedback signal, just normal alternate conduction main switch 11 and synchro switch pipe 12, thereby so that there is the switching of two states in the soft start-up process of Switching Power Supply, cause easily the output voltage V out waveform of actual output VOUT unsmooth; And, when if the voltage that prestores on the actual output VOUT is higher than the preset value of output voltage, in whole soft-start period, main switch 11 and synchro switch pipe 12 turn-off simultaneously, soft-start period just can be adjusted to preset value with output voltage V out by the loop adjustment after finishing, and still may occur the problem of output voltage V out overshoot in the adjustment process.Based on above problem as can be known, existing soft start protective circuit also can't guarantee that switch power soft-start arrives the smooth transition of normal operation.
Summary of the invention
In view of this, the technical problem to be solved in the present invention is, a kind of protective circuit of Switching Power Supply is provided, and can realize that switch power soft-start arrives the smooth transition of normal operation.
For this reason, the embodiment of the invention adopts following technical scheme:
The embodiment of the invention provides a kind of protective circuit of Switching Power Supply, it is characterized in that, comprising:
Detecting unit is used for output feedback signal and the preset reference voltage of Switching Power Supply are compared, according to the corresponding generation high level of comparative result or low level level signal;
Control unit is used for generating control signal according to the level signal of detecting unit generation and the enable signal of Switching Power Supply;
Discharge cell is used for the control signal according to the control unit generation, conducting or the shutoff of the corresponding over the ground discharge path of actual output of control switch power supply.
Wherein, detecting unit specifically is used for: when output feedback signal during less than preset reference voltage, generate high level signal; When output feedback signal during greater than preset reference voltage, generate low level signal.
Control unit specifically is used for:
When detecting unit generates high level signal, when described enable signal is low level signal, generate low level control signal; When detecting unit generates low level signal, when described enable signal is low level signal, generate the control signal of high level.
Described discharge cell specifically is used for:
When described control signal is high level, control the conducting of the corresponding over the ground discharge path of actual output; When described control signal is low level, controls the corresponding over the ground discharge path of actual output and turn-off.
Described detecting unit is realized that by the second comparator the normal phase input end of described the second comparator connects described preset reference voltage, the output feedback end of negative-phase input connecting valve power supply; The output of described the second comparator is exported described level signal.
Described control unit comprises RS latch and not gate; Wherein,
RS latch S end connects the output of detecting unit, and the R end connects enable signal, and the output of RS latch connects the input of described not gate, and the output of described not gate is exported described control signal.
Described control unit comprises d type flip flop and not gate; Wherein,
The D end of d type flip flop connects supply voltage, and the CLK end connects the output of detecting unit, and the R end connects enable signal, and output connects the input of described not gate, and the output of described not gate is exported described control signal.
Described discharge cell comprises: the first switching tube, the 3rd resistance and outputting inductance; Wherein,
The grid of the first switching tube connects the output of described control unit, source ground, and drain electrode connects the output of described Switching Power Supply by the 3rd resistance; The output of described Switching Power Supply is by the actual output of outputting inductance connecting valve power supply.
Technique effect for technique scheme is analyzed as follows:
The protective circuit of Switching Power Supply of the present invention makes Switching Power Supply all be operated under the complete closed-loop control in whole start-up course, and, before starting, Switching Power Supply namely can detect the output voltage V out among the actual output VOUT and the output SW by Switching Power Supply discharges to the electric charge that actual output VOUT stores, so that the output voltage V out of actual output VOUT can since 0 normal complete startup, realize that switch power soft-start is to the smooth transition of normal operation; And this protective circuit realizes relatively simple, is easy to realize.
Description of drawings
Fig. 1 is output interlock circuit structural representation in the prior art Switching Power Supply;
Fig. 2 is a kind of soft start protective circuit structural representation of prior art Switching Power Supply;
Fig. 3 is embodiment of the invention protective circuit of switch power source structural representation;
Fig. 4 is a kind of implementation structure schematic diagram of embodiment of the invention protective circuit of switch power source;
Fig. 5 is the another kind of implementation structure schematic diagram of embodiment of the invention protective circuit of switch power source.
Embodiment
Below, be described with reference to the accompanying drawings the realization of embodiment of the invention protective circuit of switch power source.
Fig. 3 is embodiment of the invention protective circuit of switch power source structural representation, and as shown in Figure 3, this circuit comprises:
Detecting unit 310 is used for output feedback signal and the preset reference voltage of Switching Power Supply are compared, according to the corresponding generation high level of comparative result or low level level signal.
Concrete, detecting unit 310 can be used for: when output feedback signal during less than preset reference voltage, generate high level signal; When output feedback signal during greater than preset reference voltage, generate low level signal.
This reference voltage should be set to one as far as possible close to 0 value so that so that Switching Power Supply can begin to start from the magnitude of voltage close to 0.
Control unit 320 is used for generating control signal according to the level signal of detecting unit 310 generations and the enable signal of Switching Power Supply.
Control unit 320 specifically is used for: when detecting unit 310 generates high level signal, when described enable signal is low level signal, generate low level control signal; When detecting unit 310 generates low level signal, when described enable signal is low level signal, generate the control signal of high level.
Discharge cell 330 is used for the control signal according to the control unit generation, conducting or the shutoff of the corresponding over the ground discharge path of actual output of control switch power supply.
Wherein, described discharge cell 330 specifically is used for: when control signal is high level, control the conducting of the corresponding over the ground discharge path of actual output; When control signal is low level, controls the corresponding over the ground discharge path of actual output and turn-off.
Fig. 4 is that a kind of concrete circuit of the described protective circuit of switch power source of Fig. 3 is realized, as shown in Figure 4, wherein, the output SW of Switching Power Supply is by outputting inductance L and output capacitance C ground connection.Tie point between outputting inductance L and the output capacitance C is the actual output VOUT of Switching Power Supply; Actual output VOUT is by the first resistance R 1 and the second resistance R 2 ground connection, and the tie point of the first resistance R 1 and the second resistance R 2 is the output feedback end FB of Switching Power Supply.Wherein, for the Switching Power Supply of fixing output, the first resistance R 1 and the second resistance R 2 are integrated in Switching Power Supply inside, and for the Switching Power Supply of adjustable output, the first resistance R 1 and 2 of the second resistance R are independently arranged by the user.As shown in Figure 4, described protective circuit comprises:
The output feedback end FB of Switching Power Supply is connected with the negative-phase input of the second comparator 41, to the output feedback signal of the negative-phase input input switch power supply of the second comparator 41; The normal phase input end of the second comparator 41 connects preset reference voltage REF, and the output of the second comparator 41 connects the S end of RS latch 42.Wherein, when the output feedback signal of output feedback end FB output is lower than preset reference voltage REF, the second comparator 41 output high level signals, when the output feedback signal of output feedback end FB output is higher than preset reference voltage REF, the second comparator 41 output low level signals.
The output of the second comparator 41 connects the S end of RS latch 42, and the Enable Pin EN of the R end connecting valve power supply of RS latch 42 receives enable signal; The output Q of RS latch 42 connects the input of not gate 43, and the output of not gate 43 connects the grid of the first switching tube 45.Wherein, when the second comparator 41 output high level signals, when the enable signal of described Enable Pin EN output was low level signal, RS latch 42 was exported high level signals, and then is converted to low level control signal by not gate 43; When the second comparator 41 generates low level signals, when described enable signal is low level signal, RS latch 42 output low level signals, and then be converted to the control signal of high level by not gate 43.
The output of the grid NAND gate 43 of the first switching tube 45 links to each other, source ground, and drain electrode is by the output SW of the 3rd resistance R 3 connecting valve power supplys.
Wherein, the circuit of described the second comparator 41 formations has been realized the function of detecting unit 310.The circuit that described RS latch 42 and not gate 43 form has been realized the function of described control unit 320, and the signal of telecommunication of not gate 43 outputs output is used for opening or turn-offing of control the first switching tube 45.And described the first switching tube 45, the 3rd resistance R 3 and outputting inductance L have consisted of the corresponding over the ground discharge path of described actual output VOUT in the described discharge cell 330.
More than the operation principle of protective circuit shown in Figure 4 be:
When the output feedback signal of output feedback end FB output is lower than reference voltage REF, the second comparator 41 output high level, RS latch 42 is output as high level, be converted to low level through not gate 43 after oppositely, this low level signal is controlled the first switching tube 45 and is turn-offed, thereby is turn-offed by the discharge path that the first switching tube 45, the 3rd resistance R 3 and outputting inductance L consist of; When the output feedback signal of output feedback end FB output is higher than reference voltage REF, the second comparator 41 output low levels, and then RS latch 42 output low levels, be converted to high level through not gate 43 after oppositely, this high level signal is controlled the first switching tube 45 and is opened, thereby by the discharge path conducting that the first switching tube 45, the 3rd resistance R 3 and outputting inductance L consist of, the electric weight that stores among the actual output VOUT is discharged over the ground by the 3rd resistance R 3 and outputting inductance L.
In addition; described control unit 320 can also be realized by d type flip flop and not gate; in the protective circuit of switch power source as shown in Figure 5; only be with protective circuit of switch power source difference shown in Figure 4: RS latch 42 is replaced with d type flip flop 44; wherein; d type flip flop 44 triggers for rising edge, R end high level zero clearing output, and low level is invalid.Concrete syndeton is:
The CLK end of d type flip flop 44 connects the output of the second comparator 41, and the R end connects Enable Pin EN, D termination power VIN, the input of output termination not gate 43.
Protective circuit of switch power source specific works principle shown in Figure 5 is: the output initial state of the second comparator 41 is set to low level, when output feedback signal during greater than reference voltage REF, 41 outputs of the second comparator still are low level, d type flip flop 44 output low levels, through not gate 43 oppositely after control the first switching tube 45 open; When output feedback signal during less than reference voltage REF, the second comparator 41 output high level, d type flip flop 44 output high level, through not gate 43 oppositely after control the first switching tube 45 turn-off.
The protective circuit of Switching Power Supply of the present invention makes Switching Power Supply all be operated under the complete closed-loop control in whole start-up course; and; before starting, Switching Power Supply namely can detect the output voltage V out among the actual output VOUT and the output SW by Switching Power Supply discharges to the electric charge that actual output VOUT stores; the problem that described state of the prior art switches can not appear; and, the problem that overshoot may occur for output voltage V out in the described adjustment process can not appear yet.The output voltage V out of actual output VOUT in the embodiment of the invention can since 0 normal complete startup, realize the smooth transition of Switching Power Supply from soft start to normal operation; And this protective circuit realizes relatively simple, is easy to realize.
This method is discharged to the electric charge of the actual output VOUT storage of Switching Power Supply by outputting inductance L from the SW point, rather than directly by actual output VOUT discharge, has increased on the one hand the damping coefficient of discharge; The Switching Power Supply of having avoided on the other hand adjustable output does not have the VOUT port and can't be by the direct problem of discharge of actual output VOUT, so that this protective circuit can be applied to fixing output and two kinds of Switching Power Supplies of adjustable output simultaneously, range of application is more extensive.
The above only is preferred implementation of the present invention; should be pointed out that for those skilled in the art, under the prerequisite that does not break away from the principle of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (6)

1. the protective circuit of a Switching Power Supply is characterized in that, comprising:
Detecting unit is used for output feedback signal and the preset reference voltage of Switching Power Supply are compared, according to the corresponding generation high level of comparative result or low level level signal; Described preset reference voltage should be set to one close to 0 value so that so that Switching Power Supply can begin to start from the magnitude of voltage close to 0;
Control unit is used for generating control signal according to the level signal of detecting unit generation and the enable signal of Switching Power Supply;
Discharge cell is used for controlling the conducting of the corresponding over the ground discharge path of actual output when described control signal is high level; When described control signal is low level, controls the corresponding over the ground discharge path of actual output and turn-off;
Described discharge cell comprises: the first switching tube, the 3rd resistance and outputting inductance; Wherein, described the first switching tube is an external switch pipe that is independent of Switching Power Supply;
The grid of the first switching tube connects the output of described control unit, source ground, and drain electrode connects the output of described Switching Power Supply by the 3rd resistance; The output of described Switching Power Supply is by the actual output of outputting inductance connecting valve power supply.
2. circuit according to claim 1 is characterized in that, detecting unit specifically is used for: when output feedback signal during less than preset reference voltage, generate the level signal of high level; When output feedback signal during greater than preset reference voltage, generate low level level signal.
3. circuit according to claim 1 and 2 is characterized in that, control unit specifically is used for:
Level signal when detecting unit generation high level when described enable signal is low level signal, generates low level control signal; When detecting unit generates low level level signal, when described enable signal is low level signal, generate the control signal of high level.
4. circuit according to claim 2 is characterized in that, described detecting unit is realized that by the second comparator the normal phase input end of described the second comparator connects described preset reference voltage, the output feedback end of negative-phase input connecting valve power supply; The output of described the second comparator is exported described level signal.
5. circuit according to claim 3 is characterized in that, described control unit comprises RS latch and not gate; Wherein,
RS latch S end connects the output of detecting unit, and the R end connects enable signal, and the output of RS latch connects the input of described not gate, and the output of described not gate is exported described control signal.
6. circuit according to claim 3 is characterized in that, described control unit comprises d type flip flop and not gate; Wherein,
The D end of d type flip flop connects supply voltage, and the CLK end connects the output of detecting unit, and the R end connects enable signal, and output connects the input of described not gate, and the output of described not gate is exported described control signal.
CN 201010123855 2010-03-11 2010-03-11 Protection circuit of switch power supply Expired - Fee Related CN101800467B (en)

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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
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

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