CN203056919U - Low-power BOOST low-voltage output circuit for LED light source - Google Patents

Abstract

The utility model provides a low-power BOOST low-voltage output circuit for an LED light source. The low-power BOOST low-voltage output circuit solves the problem that a conventional low-voltage new-energy power converter is high in power consumption, low in efficiency and poor in reliability. The low-power BOOST low-voltage output circuit for an LED light source comprises an input power supply and an output protection circuit. The follow current inductor of the low-power BOOST low-voltage output circuit is differential-mode symmetric inductors arranged on the negative end of the output terminal of the input power supply. A width modulated pulse control circuit is a PWM controller, and two output terminals Ao, Bo of the PWA controller are respectively connected to a set of input terminals of a driving signal synthesis circuit. A reverse isolation circuit employs a common-cathode diode. An energy storage filter circuit employs a capacitor, of which the positive terminal is connected to the positive terminal of a load, and the negative terminal is connected to the negative terminal of the load.

Description

Led light source low-power consumption BOOST low-voltage output circuit

Technical field

The present invention relates to a kind of low-power consumption BOOST low-voltage output circuit, belong to power supply switch technology field.

Background technology

In recent years, the renewable new energy resources system of AC low-tensions such as photovoltaic generation, wind power generation, storage battery power supply, dc low-voltage power supply is widely used, and the power supplying efficiency, power supply quality, the power supply reliability that improve low pressure new energy system are imperative.

The basic employing of present power supply conversion known in this field:

1, exchange (AC) input, adopting full-wave rectifier is input AC (AC) power rectifier direct current (DC) power supply, carries out DC/DC again and is converted to direct current (DC) output.This kind scheme has solved the transfer problem than high input voltage AC power and small-power power.But when the input of low-voltage AC power and large power supply conversion, because the voltage drop of AC/DC rectification circuit is higher, and produce very high power consumption, make the power supply changeover device conversion efficiency very low.

2, direct current (DC) input is directly carried out DC/DC and is converted to direct current (DC) output.This kind scheme has solved the permanent plant powerup issue.But dependability is lower, especially at mobility equipment, often need reconnect the equipment of input power supply, connects anti-situation in case electric power polarity occurs, will produce the input short circuit accident.Therefore the higher equipment of ask for something reliability adds the directed rectification circuit of direct current at the transducer input.When the straight power supply input of low-voltage and large power supply conversion, higher because direct current is identified the voltage drop of directed rectification circuit, and produce very high power consumption, make the power supply changeover device conversion efficiency very low.

3, in order to improve low-voltage power supply efficient, to reduce line current and generally adopt boost type (BOOST) direct current (DC) supply power mode.Boost type (BOOST) direct current (DC) power supply is when output generation short trouble, and the BOOST circuit function lost efficacy when output voltage was lower than input voltage, and the input power supply is directly to load short circuits, and it is very big that difficulty is controlled in big electric current (high-power) system short-circuit protection.

Be that example describes with conventional rectification (identification directed) circuit being input as low pressure new forms of energy power supply, input voltage Ui=10V (AC, DC), input current Ii=20A, input power Pi=10 * 20=200W, rectification (identification is directed) circuit pressure drop Ud=2V, rectification (identification is directed) circuit consumption is: Pd=2 * 20=40W, power output Po=200-40=160W, its rectification (identification is directed) efficient is: E=160/200=0.8, this shows that conventional rectification (identification is directed) circuit is when being input as low pressure new forms of energy power supply, power consumption is very big, and efficient is very low.

Summary of the invention

The invention provides a kind of led light source with low-power consumption BOOST low-voltage output circuit, solved mainly that existing low pressure new forms of energy power supply changeover device power consumption height, efficient are low, the problem of poor reliability.

Concrete technical solution of the present invention is as follows:

This led light source low-power consumption BOOST low-voltage output circuit, comprise the input power supply, the output of described input power supply is connected with the input of afterflow inductance and the input of input current sample circuit respectively, the output of afterflow inductance is connected with the input of VMOS switching circuit, the input of VMOS switching circuit also is connected with the output of control circuit, and the output of VMOS switching circuit is connected with load with output protection circuit by reverse isolation circuit, energy storage filter circuit successively;

Described control circuit comprises the width modulation type pulse control circuit, drive signal synthesis circuit, VMOS switch driving circuit and afterflow voltage sampling circuit, the input of width modulation type pulse control circuit is connected with the output of input current sample circuit and the output of output current sample circuit respectively, the output of width modulation type pulse control circuit is connected with the input that drives signal synthesis circuit, the input that drives signal synthesis circuit also is connected with the output of afterflow voltage sampling circuit, the output that drives signal synthesis circuit is connected with the input of VMOS switching circuit by the VMOS switch driving circuit, and the input of afterflow voltage sampling circuit is connected with the output of VMOS switching circuit; The input of described output current sample circuit is connected with the output of energy storage filter circuit;

Described afterflow inductance is arranged on the differential mode symmetry inductance on the input power output end negative terminal; The width modulation type pulse control circuit is the PWM controller, and two output terminals A o, Bo of PWM controller are connected to the one group of input that drives signal synthesis circuit respectively; Described reverse isolation circuit adopts the common cathode diode; The energy storage filter circuit adopts an electric capacity, the positive termination load anode of this electric capacity, and the negative terminal of this electric capacity connects the load negative terminal;

Described output protection circuit comprises reference voltage source, comparator A, comparator B, triode N1 and voltage-stabiliser tube Z5; The input termination BOOST VD of this output protection circuit, the load of output termination, series connection is provided with VMOS pipe M5 and current-limiting resistance R24 on the major loop at described input and output place, wherein, the base stage of VMOS pipe M5 is connected to the negative terminal of described output through triode N1, and the base stage of triode N1 is connected to described reference voltage source; Described output is parallel with a filter capacitor and a feedback branch, is in series with divider resistance R14 and RC circuit on this feedback branch successively;

The normal phase input end of comparator A inserts this feedback branch, be connected to the anode of described output through divider resistance R14, the negative-phase input of comparator A connects reference voltage, and the output of comparator A is connected to the negative terminal of described input successively through resistance R 13, resistance R 27, the resistance R 22 of series connection;

The normal phase input end of comparator B inserts the series arm at resistance R 13, resistance R 27 and resistance R 22 places, and its access node is between resistance R 27 and resistance R 22; The negative-phase input of comparator B is connected to the negative terminal of described output through resistance R 6; The output of comparator B is connected to the base stage of triode N1.

The invention has the advantages that:

Led light source provided by the invention has XC/DC expansion (XC) shape, nonpolarity, many waveforms, the input of broadband power supply with low-power consumption BOOST low-voltage output circuit, DC (direct current) output, advantages such as auto polarity identification orientation, high conversion efficiency, High Power Factor, high reliability, high power density, low cost.

Added output protection circuit can guarantee that BOOST output adjusts automatically when load short circuits, current limliting output still guarantees low-power consumption simultaneously.

Description of drawings

Fig. 1 is schematic block circuit diagram of the present invention;

Fig. 2 is electrical block diagram of the present invention;

Monocycle oscillogram when Fig. 3 is the Ac sine wave for the input power supply.

Fig. 4 is the structural representation of output protection circuit of the present invention.

Embodiment

This led light source low-power consumption BOOST low-voltage output circuit, comprise the input power supply, the output of described input power supply is connected with the input of afterflow inductance and the input of input current sample circuit respectively, the output of afterflow inductance is connected with the input of VMOS switching circuit, the input of VMOS switching circuit also is connected with the output of control circuit, and the output of VMOS switching circuit is connected with load with the energy storage filter circuit by the reverse isolation circuit successively; Control circuit comprises the width modulation type pulse control circuit, drive signal synthesis circuit, VMOS switch driving circuit and afterflow voltage sampling circuit, the input of width modulation type pulse control circuit is connected with the output of input current sample circuit and the output of output current sample circuit respectively, the output of width modulation type pulse control circuit is connected with the input that drives signal synthesis circuit, the input that drives signal synthesis circuit also is connected with the output of afterflow voltage sampling circuit, the output that drives signal synthesis circuit is connected with the input of VMOS switching circuit by the VMOS switch driving circuit, and the input of afterflow voltage sampling circuit is connected with the output of VMOS switching circuit; The input of described output current sample circuit is connected with the output of energy storage filter circuit;

The afterflow inductance is arranged on the differential mode symmetry inductance on the input power output end negative terminal; The width modulation type pulse control circuit is the PWM controller, and two output terminals A o, Bo of PWM controller are connected to the one group of input that drives signal synthesis circuit respectively; The reverse isolation circuit adopts the common cathode diode; The energy storage filter circuit adopts an electric capacity, the positive termination load anode of this electric capacity, and the negative terminal of this electric capacity connects the load negative terminal.

Below the function of each important circuit is described:

Afterflow inductance: utilize inductance characteristic that the input power supply is boosted;

VMOS switching circuit: VMOS switching circuit conduction period, have electric current to pass through in the afterflow inductance; VMOS switching circuit blocking interval, the freewheeling circuit conducting makes electric current continuation conducting in the afterflow inductance, produces high pressure, and the energy storage filter circuit is charged, and the charging back is powered to load by the energy storage filter circuit;

The energy storage filter circuit: VMOS switching circuit blocking interval charges and load is powered;

VMOS switch driving circuit: VMOS switching signal and the VMOS afterflow signal that drives the signal synthesis circuit generation amplified processing;

Drive signal synthesis circuit: the PWM width modulation type pulse signal of width modulation type pulse control circuit generation, alternating current-direct current signal, both positive and negative polarity signal or afterflow signal and the power supply signal of voltage sampling circuit input are synthesized, generate composite signal (comprising polarity, interchange, direct current, accent bandwidth signals); Automatically distribute according to composite signal then, divide into VMOS switching signal and VMOS afterflow signal;

The width modulation type pulse control circuit: the current sampling signal according to input sampling circuit and/or the input of output sample circuit generates PWM width modulation type pulse signal;

The afterflow voltage sampling circuit: the current signal to VMOS switching circuit and freewheeling circuit is sampled, and produces alternating current-direct current signal, both positive and negative polarity signal or afterflow signal, and above-mentioned signal is inputed to the driving signal synthesis circuit;

The input current sample circuit: input is sampled through the electric current of afterflow inductance to the input power supply, generates sampled signal and sampled signal is offered the width modulation type pulse control circuit and handle;

Below in conjunction with accompanying drawing the present invention is described in detail:

IC1 (UCC28084 or other similar device), for the standard both-end is alternately exported the PWM controller, PWM transfers wide output by device 1 end (OC) control, output alternative P WM waveform P1, P2.

R1, R5, the afterflow waveform of C12, Z4 PA detect shaping, form waveform P3.Wherein, voltage-stabiliser tube Z4 keeps the voltage of P3 stable, and capacitor C 12 makes to make P3 continue high level when high level appears in PA in order to filtering.

R4, R3, the afterflow waveform of C11, Z3 PB detect shaping, form waveform P4.Wherein, voltage-stabiliser tube Z3 keeps the voltage of P4 stable, and capacitor C 11 makes to make P4 continue high level when high level appears in PB in order to filtering.

IC2 (CD4071 or other similar device) is standard 2 inputs or door, wherein: and Ao=A1+A2, Bo=B1+B2, Co=C1+C2, Do=D1+D2, carry out the synthetic back of logic to P1, P2, P3, P4 and form staggered output pwm waveform.

IC3, IC4 (IR442 or other similar device) are standard drive, wherein: Ao=Ai, Bo=Bi, VMOS is carried out the big current drives of high speed, improve conversion efficiency to reduce VMOS switch power consumption.

CS1, CS2, D4, D5, R21, C13 form current sense, discriminating, testing circuit, detect the PWM current waveform that the high-end VMOS of power supply passes through when opening automatically.Super its circuit has very low power consumption simultaneously, adopts current sense coefficient ﹤ 100, controlling of sampling voltage ﹤ 0.5V, and control power consumption Pe ﹤ 0.5 * IO * 0.01=0.005 * IO (IO is the conducting electric current) is when IO is 20A: Pe ﹤ 0.05 * 20=0.1W.

C7, C8, C9 are mainly used in further eliminating noise (burst pulse).

L1, D3, C14 form the LDC of BOOST booster circuit, in order to adapt to the asymmetry of importing power supply, for example unipolarity direct current, unipolarity square wave, unipolarity triangular wave etc., L1 adopts the differential mode symmetrical expression, also can be only inductance be set as L1 at anode or the negative terminal of input circuit.

Ao port and the Bo port of pwm control circuit (IC1) are alternately exported control signal P1, P2, and total the maintenance blanking time (corresponding to the high level of PA waveform) that is used for afterflow between P1, the P2.P3, P4 are by the PA in the input circuit, PB waveform dividing potential drop gained.P1, P2, P3, P4 insert the input port of triggering signal combiner circuit (IC2), carry out foregoing or logical operation after, drive through switch driver IC3, IC4 respectively again triggering signal added to two VMOS switching circuit groups (M1, M2 respectively; M3, M4), D3 has two inputs, is connected to anode and the negative terminal of input circuit respectively, and forward current charges through the C14 of reverse isolation circuit D3.

M1 alternation in parallel with M2, M3 alternation in parallel with M4 (each VMOS switch itself has diode connected in parallel with it).

Negative just down on the positive half cycle of waveform or input direct current are at input AC, when one of the control signal P1 of pwm control circuit (IC1) output and P2 are in high level, this XC/DC automatic orientation BOOST circuit is in the PWM conducting state, electric current from anode flow through successively first group of VMOS switching circuit group (M1, M2), second group of VMOS switching circuit group (M3, M4), flows back to negative terminal then in input circuit; Because D3 plays the reverse isolation effect, the energy storage on the C14 can reverse flow not be fed back into the loop.

As the control signal P1 of pwm control circuit (IC1) output, when P2 is low level, then there is not triggering signal on M1, the M2, therefore M1, not conducting of M2, but because the existence of afterflow inductance L 1, and the diode among M3, the M4 can form the conducting loop of holding certainly to the input circuit negative terminal, thereby the afterflow that produces because of the afterflow inductance in the circuit is charged through the C14 of D3 from the anode of input circuit, and via load, second group of VMOS switching circuit group (M3, M4) of output loop, flow back to negative terminal then simultaneously.In fact, in case there is above-mentioned afterflow in the circuit, namely PA is that high level, PB are low level, thereby make P1, P2, P3, P4 carry out or logical operation after produce triggering signal, make M3, M4 conducting, because the resistance of M3, M4 is very little, therefore, the power consumption that produces in the afterflow process is still very little.And the output itself of boosting can reduce line loss.Such as, Ui=10 (V), the back Uo=50 (V) that boosts is then according to P=U ²/ R as can be known, line loss only is original 1/5.

Illustrate low-power consumption of the present invention: adopt R in the circuit _DS=0.001 Ω low on-resistance N raceway groove VMOS pipe, the staggered conducting of M1, M2 during PWM opens, VMOS conducting resistance R _DS=0.001 Ω, the two-tube paralleling and interleaving conducting of M3, M4, VMOS conducting resistance R _DS=0.001 Ω/2=0.0005 Ω, if still import the 20A electric current, then conducting voltage is: U1=0.001 * 20=0.02V, U2=0.0005 * 20=0.01V, identify directed power consumption and be: Pe=20 * (0.02+0.01)=0.6W; End shutoff, the two-tube paralleling and interleaving conducting of M3, M4 afterflow, VMOS conducting resistance R at PWM blocking interval M1, M2 _DS=0.001 Ω/2=0.0005 Ω, if the 20A freewheel current, then conducting voltage is: U2=0.0005 * 20=0.01V, identify directed power consumption and be: Pe=20 * 0.01=0.2W.Compare to the power consumption of the rectification identification directional circuit 40W of prior art, XC/DC of the present invention identifies directed BOOST circuit power consumption automatically and significantly reduces.

If reverse isolation circuit D3 also adopts synchronous VMOS switching circuit (synchronous waveform of its triggering signal and PA and PB), then can utilize the little characteristic of VMOS switching circuit resistance further to reduce line loss.Especially the raising of conversion efficiency is more remarkable when BOOST output is low.

The VMOS switch is under the triggering signal effect, can realize conducting forward or backwards according to institute's making alive polarity, based on this characteristic, be negative timing down at input AC at waveform negative half period or input direct current, the course of work of this XC/DC automatic orientation BOOST circuit and above-mentioned conducting, afterflow Principle of Process are identical, and because first group of VMOS switching circuit group (M1, M2) adopts the symmetric circuit structure with second group of VMOS switching circuit group (M3, M4), be completely reversibility in the VMOS conducting of Ui negative half period and afterflow.Such as, as the control signal P1 of pwm control circuit (IC1) output, when P2 is low level, then do not have triggering signal on M3, the M4, so M3, not conducting of M4, and realize the afterflow process by first group of VMOS switching circuit group (M1, M2).

As seen, this BOOST circuit can be finished the automatic identification orientation to bipolar power supply (exchanging just profound ripple, square wave, triangular wave, AC power frequency, intermediate frequency, low frequency, ultralow frequency) automatically; Reach the automatic identification orientation to unipolarity power supply (direct current, direct current square wave, direct current triangular wave etc.), exchange bipolar power supply and direct current unipolarity power supply and can be regardless of positive and negative any access.

In addition, the output safety control circuit that adds before load comprises reference voltage source, comparator A, comparator B, triode N1 and voltage-stabiliser tube Z5; The input termination BOOST VD of this output safety control circuit, the load of output termination, series connection is provided with VMOS pipe M5 and current-limiting resistance R24 on the major loop at described input and output place, wherein, the base stage of VMOS pipe M5 is connected to the negative terminal of described output through triode N1, and the base stage of triode N1 is connected to described reference voltage source; Described output is parallel with a filter capacitor and a feedback branch, is in series with divider resistance R14 and RC circuit on this feedback branch successively;

The normal phase input end of comparator A inserts this feedback branch, be connected to the anode of described output through divider resistance R14, the negative-phase input of comparator A connects reference voltage, and the output of comparator A is connected to the negative terminal of described input successively through resistance R 13, resistance R 27, the resistance R 22 of series connection;

The normal phase input end of comparator B inserts the series arm at resistance R 13, resistance R 27 and resistance R 22 places, and its access node is between resistance R 27 and resistance R 22; The negative-phase input of comparator B is connected to the negative terminal of described output through resistance R 6; The output of comparator B is connected to the base stage of triode N1.

Draw a branch road and manage the source electrode of M5 to VMOS between the drain electrode of the base stage of VMOS pipe M5 and triode N1, this branch road is provided with voltage-stabiliser tube Z1.

Described reference voltage is provided by the 2.5V voltage-stabiliser tube of connecting with described reference voltage source.

The access node of the normal phase input end of comparator B also is connected to the negative terminal of described output by filter capacitor.

Comparator A and comparator B constitute a two encapsulation comparator.

The preferred LH2903 of this pair encapsulation comparator, LM2903 or other similar device.

IC5 is standard high-speed comparator circuit (dual comparator), and comparator B, N1, M5 form constant-current control circuit.B-terminal voltage V3=0V, the B+ terminal voltage is:

V2=R22×V1/(R22+R27)-Us

In the following formula, Us=Is * Rs=Is * R24

V1 voltage is controlled by comparator A, A-terminal voltage VR=2.5V, and the A+ terminal voltage is:

VL=UL×R7/(R7+R14)=RL×Is。

1, current-limited startup

During circuit start (powering on), VL ﹤ 2.5V, comparator A output is low, and then R13 inserts dividing potential drop.

Wherein: R13 ﹤ ﹤ R25, R13 ﹤ ﹤ R27, VR=2.5V;

V1≈VR×R13/(R13+R25)=2.5×R13/(R13+R25)

V2=R22×V1/(R22+R27)-Us=R22×(2.5×R13/(R13+R25))/(R22+R27)-Us=2.5×R22×R13/((R13+R25)(R22+R27))-Is×Rs

If: c1=2.5 * R22 * R13/ ((R13+R25) (R22+R27))

That is: V2=c1-Rs * Is

When V2=c1-Rs * Is ≦ 0, comparator B, N1, the output of M5 current limliting, cut-off current is: Is=c1/Rs.

Can guarantee that namely BOOST output starts with current limliting (Is=c1/Rs).

VL=UL×R7/(R7+R14)=RL×Is=c1×RL/Rs

Therefore, only need the corresponding resistance of configuration, when making BOOST load impedance less (short circuit), VL ﹤ 2.5V is operated under the safe limited current state.Such as, according to Is=c1/Rs, Is is set between routine value 1/4-1/10.

2, operating conventional current limliting

Comparator A output high (open circuit) when BOOST load impedance fault-free VL ≧ 2.5V, R13 disengaging dividing potential drop then, V2=2.5 * R22/ (R22+R27+R25)-Us;

If: c2=2.5 * R22/ (R22+R27+R25)

That is: V2=c2-Rs * IL

When V2=c2-Rs * IL ≦ 0, comparator B, N1, the output of M5 current limliting, cut-off current is: IL=c2/Rs,

Can guarantee that namely BOOST output works with current limliting (IL=c2/Rs).

Therefore, only need the corresponding resistance of configuration, make IL greater than running current, and VMOS is limited in the safe range of electric current, power.Usually, IL is set between 1.1 times to 1.5 times of conventional value.

3, the low-power consumption of operate as normal

During BOOST output operate as normal, output current is less than IL, and comparator (A, B) is exported high (open circuit), and P raceway groove VMOS (M5) is operated in ultralow conducting resistance (R _DS=0.005 Ω) under the state.

For example: power output 200W output voltage 50V, then output current is: Io=200/50=4A,

VMOS (M5) goes up pressure drop: 4 * 0.005=0.02,

VMOS (M5) control power consumption is: Pe=0.02 * 4=0.08W, as can be seen, the control power consumption when normally moving is very low.

4, short-circuit protection

If in the BOOST circuit working process if fault such as output short-circuit takes place, cause VL ﹤ 2.5V, then comparator A output is low, make comparator B, N1, M5 current limliting output (referring to aforementioned the 1st kind of situation), circuit reenters clean boot (Is) state, after fault was eliminated, BOOST recovered normal output automatically.

Above-described embodiment is most preferred embodiment of the present invention, adopts this staggered PWM control mode to make M1, the M2 conducting that interlocks, and each VMOS switch operating frequency is 1/2 channel frequency, and the VMOS switch is being worked than under the low switching frequency, significantly reduces the switch power consumption; Correspondingly, the operating frequency of L, C device is 2 times of VMOS pipe frequencies in the circuit, and higher circuit work frequency has reduced the requirement to inductance in the lc circuit (L) amount and electric capacity (C), has reduced cost and technology difficulty.In fact, based on the basic principle of conducting of the present invention, afterflow, can consider that also each VMOS switching circuit group only adopts a VMOS switch, also is enough to embody technique effect of the present invention.Such as only keeping M1, M3, equally also can when input AC is negative just down on the positive half cycle of waveform or input direct current are, realize the conducting loop by M1, M3, realize continuous current circuit by M3; Be negative timing down at input AC at waveform negative half period or input direct current, realize the conducting loop by M1, M3, realize continuous current circuit by M1.Certainly, under this scheme, also can attempt allowing the operating frequency of each VMOS switch reduce by half, but this just need increase afterflow inductance, storage capacitor exponentially, satisfying the requirement of afterflow, thereby cause that cost is higher, the components and parts volume is big, power density reduces.

Claims (1)

1. a led light source is with low-power consumption BOOST low-voltage output circuit, comprise the input power supply, the output of described input power supply is connected with the input of afterflow inductance and the input of input current sample circuit respectively, the output of afterflow inductance is connected with the input of VMOS switching circuit, the input of VMOS switching circuit also is connected with the output of control circuit, and the output of VMOS switching circuit is connected with load with output protection circuit by reverse isolation circuit, energy storage filter circuit successively;

Described control circuit comprises the width modulation type pulse control circuit, drive signal synthesis circuit, VMOS switch driving circuit and afterflow voltage sampling circuit, the input of width modulation type pulse control circuit is connected with the output of input current sample circuit and the output of output current sample circuit respectively, the output of width modulation type pulse control circuit is connected with the input that drives signal synthesis circuit, the input that drives signal synthesis circuit also is connected with the output of afterflow voltage sampling circuit, the output that drives signal synthesis circuit is connected with the input of VMOS switching circuit by the VMOS switch driving circuit, and the input of afterflow voltage sampling circuit is connected with the output of VMOS switching circuit; The input of described output current sample circuit is connected with the output of energy storage filter circuit;

Described afterflow inductance is arranged on the differential mode symmetry inductance on the input power output end negative terminal; The width modulation type pulse control circuit is the PWM controller, and two output terminals A o, Bo of PWM controller are connected to the one group of input that drives signal synthesis circuit respectively; Described reverse isolation circuit adopts the common cathode diode; The energy storage filter circuit adopts an electric capacity, the positive termination load anode of this electric capacity, and the negative terminal of this electric capacity connects the load negative terminal;

Described output protection circuit comprises reference voltage source, comparator A, comparator B, triode N1 and voltage-stabiliser tube Z5; The input termination BOOST VD of this output protection circuit, the load of output termination, series connection is provided with VMOS pipe M5 and current-limiting resistance R24 on the major loop at described input and output place, wherein, the base stage of VMOS pipe M5 is connected to the negative terminal of described output through triode N1, and the base stage of triode N1 is connected to described reference voltage source; Described output is parallel with a filter capacitor and a feedback branch, is in series with divider resistance R14 and RC circuit on this feedback branch successively;

The normal phase input end of comparator A inserts this feedback branch, be connected to the anode of described output through divider resistance R14, the negative-phase input of comparator A connects reference voltage, and the output of comparator A is connected to the negative terminal of described input successively through resistance R 13, resistance R 27, the resistance R 22 of series connection;

The normal phase input end of comparator B inserts the series arm at resistance R 13, resistance R 27 and resistance R 22 places, and its access node is between resistance R 27 and resistance R 22; The negative-phase input of comparator B is connected to the negative terminal of described output through resistance R 6; The output of comparator B is connected to the base stage of triode N1.

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