CN103605035A - No-load detection circuit structure of self-adaptive switching power supply - Google Patents

No-load detection circuit structure of self-adaptive switching power supply Download PDF

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CN103605035A
CN103605035A CN201310637760.9A CN201310637760A CN103605035A CN 103605035 A CN103605035 A CN 103605035A CN 201310637760 A CN201310637760 A CN 201310637760A CN 103605035 A CN103605035 A CN 103605035A
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switching tube
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田剑彪
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SHAOXING DEVECHIP MICROELECTRONICS CO Ltd
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Abstract

The invention relates to a no-load detection circuit structure of a self-adaptive switching power supply. The no-load detection circuit structure comprises a switching power supply circuit, an error amplifier, a no-load detection comparer, a drive circuit and a no-load threshold voltage generating circuit. The first input end of the error amplifier is connected with the output end of the switching power supply circuit, the second input end of the error amplifier is connected with reference voltage, the output end of the no-load threshold voltage generating circuit is connected with the second input end of the no-load detection comparer, and the input end of the no-load threshold voltage generating circuit is connected with the input end of the switching power supply circuit. By means of the no-load detection circuit structure of the self-adaptive switching power supply, the no-load threshold voltage generating circuit and a down-conversion threshold voltage generating circuit can be added on the basis of the prior art, the no-load voltage threshold and down-conversion points can be automatically adjusted according to input voltage, no-load detection can be accurate without a sampling resistor, accurate no-load detection is achieved based on efficiency improvement, cost is lowered, and the application range is wider.

Description

The no load detection circuit structure of self-adaption switch electric power source
Technical field
The present invention relates to field of switch power, relate in particular to Switching Power Supply load detecting field, specifically refer to a kind of no load detection circuit structure of self-adaption switch electric power source.
Background technology
Whether in mobile device, after load removes, system generally will enter standby mode, reduces system power dissipation, increases portable power source flying power, therefore need to detect load and remove, unloaded.The unloaded detection technique of traditional switching power source chip has two kinds of methods: (1) resistance that resistance is less of connecting in load path, detects the pressure drop at these resistance two ends, as Fig. 1 (take booster type as example, voltage-dropping type is similarly); (2) detect the output of error amplifier, as Fig. 2 (take booster type as example); When load lightens, the output meeting step-down of error amplifier.
Yet all there is certain defect in two schemes.Scheme (1) increases a sampling resistor R in load path s, the consideration of need trading off of the value of resistance, value is crossed conference affects efficiency, the little difficult detection of value.For Switching Power Supply, efficiency is a very important index, so R sresistance can not obtain too large.If R swhen resistance value is very little, this just requires testing circuit to have very high precision, and the difficult design of high-precision testing circuit and cost are high, and the cost of the resistance that resistance is very little in addition itself is also high.Therefore always difficult selection between efficiency and cost of employing scheme (1).
Whether unloaded by the output detections of detection error amplifier EA in scheme (2).The schematic diagram of typical case's peak point current pwm pattern step-up switching power supply transducer as shown in Figure 3.The output V of EA eAwith current sample voltage V sENSErelatively produce pwm signal, pwm signal coordinates with osc signal, alternately closes and actuating switch pipe M.Whether continuous according to inductive current, transducer is divided into two kinds of mode of operations: continuous mode (CCM) and discontinuous mode (DCM), generally, system approaches when unloaded, transducer is operated in discontinuous mode, concrete waveform as shown in Figure 4, V now eAexpression formula be:
V EA = k ( 2 I load ( V o - V I ) T ηL ) R on ;
V wherein ifor input voltage, V ofor output voltage, T is switch periods, and L is inductance value, the efficiency that η is transducer, I loadfor load current, R onfor switching tube conduction impedance, k is amplifier multiple.From formula, can find out V eAwith
Figure BDA0000428094920000012
be directly proportional, therefore in other parameters fixedly time, can be according to V eAthe weight of size judgement load.But this scheme is existent defect also: under (1) same load current and under output voltage, switch power supply no-load detection threshold V eAalong with input voltage V ivariation and change V iincrease V eAreduce identical V eAcorresponding load current changes with input voltage, so no-load current thresholding is also with input voltage variation, cannot accurately determine unloaded thresholding; (2), when unloaded, load current is very little, only has tens mA, high efficiency Switching Power Supply R onalso very little, only have tens m Ω, so V eAcan be very little, be difficult for detecting, affect precision.
Summary of the invention
The object of the invention is to overcome the shortcoming of above-mentioned prior art, provide a kind of and can realize the problem that solves switch power supply no-load detection threshold in prior art and change greatly with input voltage and be difficult for detecting, do not need sampling resistor, accurately detector switch power supply zero load on the basis of guaranteed efficiency, there is the no load detection circuit structure of the self-adaption switch electric power source of broader applications scope.
To achieve these goals, the no load detection circuit structure of self-adaption switch electric power source of the present invention has following formation:
The no load detection circuit structure of this self-adaption switch electric power source, its principal feature is that described circuit structure comprises:
Switching power circuit;
Error amplifier, first input end is connected with the output terminal of described switching power circuit, and the second input end of described error amplifier is connected with reference voltage;
Unloaded detection comparator, first input end is connected with the output terminal of described error amplifier;
Driving circuit, input end is connected with the output terminal of described unloaded detection comparator, and the output terminal of described driving circuit is connected with the gauge tap of described switching power circuit;
Unloaded gate voltage limit generative circuit, in order to also to export according to the input voltage regulation threshold voltage of described switching power circuit, the output terminal of described unloaded gate voltage limit generative circuit is connected with the second input end of described unloaded detection comparator, and the input end of described unloaded gate voltage limit generative circuit is connected with the input end of described switching power circuit.
Preferably, described circuit structure also comprises the first output resistance and the second output resistance, the first end of the first described output resistance is connected with the positive terminal of the output terminal of described switching power circuit, the second end of the first described output resistance is connected with the first input end of the first end of described the second output resistance and described error amplifier respectively, and the second end of the second described output resistance is connected with the negative pole end of the output terminal of described switching power circuit.
Preferably, described unloaded gate voltage limit generative circuit comprises the first operational amplifier, the first switching tube, the first input resistance, second switch pipe, the second input resistance, the 3rd input resistance, the second operational amplifier, the 3rd switching tube, the 4th switching tube, the 4th input resistance, the 5th switching tube, the 6th switching tube, the 7th switching tube, the 8th switching tube, the 5th input resistance and the 6th input resistance, the first input end of the first described operational amplifier is connected with reference voltage, the output terminal of the first described operational amplifier is connected with the first described switching tube, the first described switching tube is connected between described second switch pipe and the first input resistance, the first end of the first described input resistance is connected with the second input end of described switching tube and described the first operational amplifier respectively, between the input end of the first switching tube described in described second switch pipe is connected in and described switching power circuit, described second switch Guan Yu eight switching tubes connect for base stage, the first end of the second described input resistance is connected with the input end of described switching power circuit, the second end of the second described input resistance is connected with the 3rd input resistance with the first input end of described the second operational amplifier respectively, the 4th described switching tube is connected between described the 3rd switching tube and the 4th input resistance, the first end of the 4th described input resistance is connected with the 3rd switching tube with the second input end of described the second operational amplifier respectively, the 5th described switching tube is connected with the 4th switching tube common base, the 6th described switching tube the 7th switching tube common base connects, the 5th described switching tube is connected between the input end and the 6th switching tube of described switching power circuit, the 8th described switching tube is connected between the described input end of switching power circuit and the first end of the 5th input resistance, the second end of the 5th described input resistance is connected with the 7th switching tube with the 6th described input resistance respectively, the first end of the 5th described input resistance is connected with the second input end of described unloaded detection comparator.
More preferably, described unloaded gate voltage limit generative circuit also comprises frequency reducing threshold voltage generation unit, described circuit structure also comprises frequency reducing comparer, between the second input end of the input end of the switching power circuit described in described frequency reducing threshold voltage generation unit is connected in and described frequency reducing comparer, the first input end of described frequency reducing comparer is connected with the output terminal of described error amplifier, and the output terminal of described frequency reducing comparer is connected with described driving circuit.
Further, described frequency reducing threshold voltage generation unit comprises the 9th switching tube, the tenth switching tube, the 7th input resistance and the 8th input resistance, the 9th described switching tube is connected with the 7th described switching tube common base, the tenth described switching tube is connected between described the 7th first end of input resistance and the input end of switching power circuit, the second end of the 7th described input resistance is connected with the 8th input resistance with the 9th described switching tube respectively, the first end of the 7th described input resistance is connected with described the tenth switching tube and the second input end of frequency reducing comparer respectively.
Further, described unloaded detection comparator and frequency reducing comparer are PWM error comparator.
Further, described driving circuit is rest-set flip-flop, the R end of described rest-set flip-flop is connected with the described output terminal of unloaded detection comparator or the output terminal of frequency reducing comparer, the S end of described rest-set flip-flop is connected with osc signal, and the output terminal of described rest-set flip-flop is connected with the gauge tap of described switching power circuit.
The no load detection circuit structure that has adopted the self-adaption switch electric power source in this invention, has following beneficial effect:
The present invention has increased the generative circuit of unloaded gate voltage limit and frequency reducing threshold voltage on the basis of existing technology, realized according to input voltage and automatically regulated no-load voltage thresholding and frequency reducing point, neither need sampling resistor, can accurately detect zero load again, on the basis of guaranteed efficiency, realized unloaded detection accurately, also reduced cost, there is range of application widely simultaneously.
Accompanying drawing explanation
Fig. 1 utilizes sampling resistor to detect the circuit structure diagram of load in prior art.
Fig. 2 is the circuit structure diagram that available technology adopting error amplifier detects load.
Fig. 3 is the circuit structure diagram that the converter using error amplifier of Peak Current-Mode Controlled Circuit in prior art detects load.
Fig. 4 is the working waveform figure of the transducer of Peak Current-Mode Controlled Circuit in prior art.
Fig. 5 is the circuit structure diagram of the no load detection circuit structure of self-adaption switch electric power source of the present invention.
Fig. 6 is the curve that unloaded gate voltage limit of the present invention changes with input voltage.
Fig. 7 is the circuit structure diagram that unloaded gate voltage limit of the present invention generates.
Fig. 8 is the curve that frequency reducing threshold voltage of the present invention changes with input voltage.
Fig. 9 is the circuit structure diagram that unloaded gate voltage limit of the present invention and frequency reducing threshold voltage generate.
Embodiment
In order more clearly to describe technology contents of the present invention, below in conjunction with specific embodiment, conduct further description.
The present invention proposes a kind of unloaded detection scheme of novelty, this scheme does not need sampling resistor, can accurately detect zero load again, has realized so unloaded detection accurately on the basis of guaranteed efficiency, has reduced cost simultaneously yet.
Be illustrated in figure 5 actual block diagram of the present invention.Circuit structure of the present invention mainly comprises a unloaded detection comparator COMP1, a raw circuit V of unloaded gate limited production tHgenerater, a frequency reducing comparator C OMP2, an error amplifier EA.
In order to obtain a unloaded threshold that detects accurately, the present invention is based on scheme of the prior art (2) from the viewpoint of two:
(1) design one according to input voltage V iautomatically the V regulating tH.V in scheme (2) eAwith a V tHcompare and judge whether to enter zero load, thresholding V tHhow to confirm is the unloaded key detecting, by V eAexpression formula obtain, V TH = k ( 2 I TH ( V o - V I ) T ηL ) R on , Order K = k ( 2 I TH T ηL ) R on , ? V TH = K V O - V I , The unit of K is
Figure BDA0000428094920000044
v tHwith V ithe curve changing as the curve in Fig. 6 1. as shown in, V iMIN, V iMAXbe respectively minimum value and the maximal value of input voltage.Due to
Figure BDA0000428094920000045
on circuit, accurately realize cost prohibitive, the present invention with one at V iMINand V iMAXbetween approximate replacement of straight line, as the curve in Fig. 6 2. as shown in, the equation of straight line can be written as
V TH = K ( V O - V IMIN - V O - V IMIAX ) V IMAX - V IMIN V I + K ( V IMAX V O - V IMIN - V IMIN V O - V IMIAX ) V IMAX - V IMIN ;
According to straight-line equation, V tHcircuit realize as shown in Figure 7.In the circuit structure of Fig. 7, produce one and with input voltage, increase the unloaded gate voltage limit V reducing tH.
In Fig. 7, supply voltage is input voltage V i, V ithrough resistance R 2and R 3dividing potential drop, then by amplifier OP2, be converted into electric current and flow out from M8 branch road, V tHexpression formula is
V TH = - R 3 R 6 ( R 2 + R 3 ) R 4 V I + V REF ( R 5 + R 6 ) R 1 ;
By resistance and the V of design resistance rEFvalue, make
R 3 R 6 ( R 2 + R 3 ) R 4 = K ( V O - V IMIN - V O - V IMIAX ) V IMAX - V IMIN ;
V REF ( R 5 + R 6 ) R 1 = K ( V IMAX V O - V IMIN - V IMIN V O - V IMIAX ) V IMAX - V IMIN ;
Thereby obtain the V changing with input voltage tHvalue, so unloaded threshold I tHjust with input voltage, do not change.Input voltage range is less, and approximate error is also less.
(2) increase the unloaded current detecting I that detects tHcorresponding V tHvalue.From expression formula
Figure BDA0000428094920000054
can find out under identical output and input voltage, by increasing k, R on, T or reduce L and can make V tHincrease, but excessive k can make the output V of fully loaded work time error amplifier eAthe common-mode input range that surpasses PWM comparer, increases R oncan affect efficiency, when reducing L and can make to work, inductive current ripple be excessive.Therefore only have by increasing switch periods (cycle of oscillator in Fig. 3) T and increase V tH, i.e. frequency reducing although it is also can inductive current ripple excessive to increase T, can increase switch periods when load is lighter, can not affect normal operation like this.From expression formula, can find out V tHwith be directly proportional.When load reduces, V eAreduce, work as V eAbe reduced to frequency reducing thresholding V tH_LFtime, switching frequency reduces, and can reduce to original half or 1/4.Equally, V tH_LFalso will consider the impact that input voltage changes, frequency reducing point place transducer is generally operational in continuous mode, so V eAexpression formula be
Figure BDA0000428094920000056
a given load current frequency reducing point I tH_LF, V TH _ LF = k ( V O I TH _ LF η V I + V I ( V O - V I ) 2 V O L T ) R on , V tH_LFwith input voltage change curve as shown in Figure 8.
Equally with the approximate V of straight line iMINand V iMAXbetween curve, on the basis of Fig. 7 circuit, increase by a road and produce V tH_LFcircuit, can obtain the V automatically regulating according to input voltage tH_ lF, complete circuit as shown in Figure 9, produces one and with input voltage, increases the unloaded gate voltage limit V reducing tH, produce a frequency reducing threshold voltage V who changes with input voltage simultaneously tH_LF, V in circuit tH_LFexpression formula be:
V TH _ LF = - R 3 R 8 ( R 2 + R 3 ) R 4 V I + V REF ( R 7 + R 8 ) R 1 ;
Above on the basis of circuit by R is set 7and R 8value can produce the V wanting tH_LFcurve.
The no load detection circuit structure that has adopted the self-adaption switch electric power source in this invention, has following beneficial effect:
The present invention has increased the generative circuit of unloaded gate voltage limit and frequency reducing threshold voltage on the basis of existing technology, realized according to input voltage and automatically regulated no-load voltage thresholding and frequency reducing point, neither need sampling resistor, can accurately detect zero load again, on the basis of guaranteed efficiency, realized unloaded detection accurately, also reduced cost, there is range of application widely simultaneously.
In this instructions, the present invention is described with reference to its specific embodiment.But, still can make various modifications and conversion obviously and not deviate from the spirit and scope of the present invention.Therefore, instructions and accompanying drawing are regarded in an illustrative, rather than a restrictive.

Claims (7)

1. a no load detection circuit structure for self-adaption switch electric power source, is characterized in that, described circuit structure comprises:
Switching power circuit;
Error amplifier, first input end is connected with the output terminal of described switching power circuit, and the second input end of described error amplifier is connected with reference voltage;
Unloaded detection comparator, first input end is connected with the output terminal of described error amplifier;
Driving circuit, input end is connected with the output terminal of described unloaded detection comparator, and the output terminal of described driving circuit is connected with the gauge tap of described switching power circuit;
Unloaded gate voltage limit generative circuit, in order to also to export according to the input voltage regulation threshold voltage of described switching power circuit, the output terminal of described unloaded gate voltage limit generative circuit is connected with the second input end of described unloaded detection comparator, and the input end of described unloaded gate voltage limit generative circuit is connected with the input end of described switching power circuit.
2. the no load detection circuit structure of self-adaption switch electric power source according to claim 1, it is characterized in that, described circuit structure also comprises the first output resistance and the second output resistance, the first end of the first described output resistance is connected with the positive terminal of the output terminal of described switching power circuit, the second end of the first described output resistance is connected with the first input end of the first end of described the second output resistance and described error amplifier respectively, the second end of the second described output resistance is connected with the negative pole end of the output terminal of described switching power circuit.
3. the no load detection circuit structure of self-adaption switch electric power source according to claim 1, it is characterized in that, described unloaded gate voltage limit generative circuit comprises the first operational amplifier, the first switching tube, the first input resistance, second switch pipe, the second input resistance, the 3rd input resistance, the second operational amplifier, the 3rd switching tube, the 4th switching tube, the 4th input resistance, the 5th switching tube, the 6th switching tube, the 7th switching tube, the 8th switching tube, the 5th input resistance and the 6th input resistance, the first input end of the first described operational amplifier is connected with reference voltage, the output terminal of the first described operational amplifier is connected with the first described switching tube, the first described switching tube is connected between described second switch pipe and the first input resistance, the first end of the first described input resistance is connected with the second input end of described switching tube and described the first operational amplifier respectively, between the input end of the first switching tube described in described second switch pipe is connected in and described switching power circuit, described second switch Guan Yu eight switching tubes connect for base stage, the first end of the second described input resistance is connected with the input end of described switching power circuit, the second end of the second described input resistance is connected with the 3rd input resistance with the first input end of described the second operational amplifier respectively, the 4th described switching tube is connected between described the 3rd switching tube and the 4th input resistance, the first end of the 4th described input resistance is connected with the 3rd switching tube with the second input end of described the second operational amplifier respectively, the 5th described switching tube is connected with the 4th switching tube common base, the 6th described switching tube the 7th switching tube common base connects, the 5th described switching tube is connected between the input end and the 6th switching tube of described switching power circuit, the 8th described switching tube is connected between the described input end of switching power circuit and the first end of the 5th input resistance, the second end of the 5th described input resistance is connected with the 7th switching tube with the 6th described input resistance respectively, the first end of the 5th described input resistance is connected with the second input end of described unloaded detection comparator.
4. the no load detection circuit structure of self-adaption switch electric power source according to claim 3, it is characterized in that, described unloaded gate voltage limit generative circuit also comprises frequency reducing threshold voltage generation unit, described circuit structure also comprises frequency reducing comparer, between the second input end of the input end of the switching power circuit described in described frequency reducing threshold voltage generation unit is connected in and described frequency reducing comparer, the first input end of described frequency reducing comparer is connected with the output terminal of described error amplifier, the output terminal of described frequency reducing comparer is connected with described driving circuit.
5. the no load detection circuit structure of self-adaption switch electric power source according to claim 4, it is characterized in that, described frequency reducing threshold voltage generation unit comprises the 9th switching tube, the tenth switching tube, the 7th input resistance and the 8th input resistance, the 9th described switching tube is connected with the 7th described switching tube common base, the tenth described switching tube is connected between described the 7th first end of input resistance and the input end of switching power circuit, the second end of the 7th described input resistance is connected with the 8th input resistance with the 9th described switching tube respectively, the first end of the 7th described input resistance is connected with described the tenth switching tube and the second input end of frequency reducing comparer respectively.
6. the no load detection circuit structure of self-adaption switch electric power source according to claim 4, is characterized in that, described unloaded detection comparator and frequency reducing comparer are PWM error comparator.
7. the no load detection circuit structure of self-adaption switch electric power source according to claim 4, it is characterized in that, described driving circuit is rest-set flip-flop, the R end of described rest-set flip-flop is connected with the described output terminal of unloaded detection comparator or the output terminal of frequency reducing comparer, the S end of described rest-set flip-flop is connected with osc signal, and the output terminal of described rest-set flip-flop is connected with the gauge tap of described switching power circuit.
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CN109613359A (en) * 2018-12-13 2019-04-12 张家港金盛莲能源科技有限公司 A kind of AC power supply device zero load detection device and detection method
CN109613359B (en) * 2018-12-13 2021-03-26 张家港金盛莲能源科技有限公司 No-load detection device and detection method for alternating current power supply equipment
CN110034535A (en) * 2019-03-29 2019-07-19 惠州汇能精电科技有限公司 Discharge equipment and its remained capacity circuit
CN111404402A (en) * 2020-03-02 2020-07-10 深圳固邦科技有限公司 Self-adaptive output no-load control circuit and voltage conversion circuit
CN111404402B (en) * 2020-03-02 2023-03-14 深圳固邦科技有限公司 Self-adaptive output no-load control circuit and voltage conversion circuit
CN111693888A (en) * 2020-08-04 2020-09-22 上海钧正网络科技有限公司 Power performance detection device
CN113252970A (en) * 2021-04-23 2021-08-13 长城电源技术有限公司 Load detection circuit and power supply system
CN113252970B (en) * 2021-04-23 2022-11-18 长城电源技术有限公司 Load detection circuit and power supply system

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