CN103795036B - A kind of input undervoltage protection circuit of switch power controller - Google Patents

Abstract

The present invention proposes the input undervoltage protection circuit of a kind of switch power controller, including: current detection circuit, comprise controller built-in resistor R2 and external resistance R1, the resistance of R2 is much smaller than R1；Reference voltage generating circuit, comprises built-in resistor R3 and reference current source Iref, R3 and R2 are the internal same type of resistance of controller；UVP signal produces circuit, comprises comparator comp；Pulse output control circuit；A protection point input voltage vin (p) meets formula:When the input voltage vin of Switching Power Supply drops below protection point input voltage vin (p), the outfan UVP of comparator comp produces UVP signal, controls pulse output control circuit and turns off the pulse output of controller GATE pin.The present invention simplifies the peripheral circuit of controller, is lost little, and meanwhile, the precision of input undervoltage protection is high, little by process deviation.The present invention also proposes the input undervoltage protection circuit of a kind of band feedforward compensation, its feedforward compensation electric current I_comProportional to input voltage, precision is high, little by process deviation.

Description

A kind of input undervoltage protection circuit of switch power controller

Technical field

The present invention relates to the input undervoltage protection circuit of a kind of switch power controller, and the input undervoltage relating to band feedforward compensation is protected Protection circuit.

Background technology

As it is shown in figure 1, be the typical switch power converter not comprising feedforward compensation circuit (or referred to as Overpower compensating circuit) Application circuit, GATE pin be controller driving output；CS pin is come by the voltage of detection current sampling resistor RCS Determine to flow through the electric current of power MOS pipe, frequently referred to current loop；By design RI pin to " " resistance Ri can set Determine the operating frequency of controller；UVP is input undervoltage defencive function, designs a protection magnitude of voltage below minimum input voltage, When input voltage is less than this value, controller GATE stops output, because input voltage is the least, the transformator when maximum power output It is easily saturated and burns out power supply.Switching Power Supply typically has the restriction of peak power output, the most usually sets in switch power controller Count overpower protection, as output V_OUTWhen the load carried has exceeded peak power output, power supply can enter overpower protection pattern, Prevent the running of long-term overpower from causing power supply to burn out.But, when change range of input voltage is relatively wide, controller controls time delay Existence cause input high-low pressure overpower limit point different.As in figure 2 it is shown, be under different input voltages, Fig. 1 to adopt Sample resistance R_CSOn voltage waveform, V_HRefer to the actual value of peak inrush current, V under high input voltage_LRefer at low input electricity The actual value of pressure peak inrush current.V_OCIt is the threshold voltage of the overcurrent protection of controller inner setting, T_dIt it is controller CS end The voltage of mouth reaches V_OCIn time, start until power MOS turns off produced delay time, for a controller, T_dIt is substantially constant.Exactly because the existence of this time delay and R_CSOn different (this slope k=V of voltage slope_in/ L, V_in Being power input voltage, L is transformer primary inductance value), cause R within identical time delay_CSOn voltage rising value differ Sample.R when crossing stream_CSOn virtual voltage be:

$V_{R_{\mathrm{CS}}}=V_{\mathrm{OC}}+\frac{V_{\mathrm{in}}}{L}{T}_d{R}_{\mathrm{CS}}...\left(1\right)$

Visible, input voltage is the highest, sampling resistor R_CSOn maximum peak voltage actual value the highest, cause at different input voltages Lower maximum output current is different.The overpower of high-low pressure limits the inconsistent volume also resulting in transformator of point and becomes big, if because When mistake flow point during high input voltage is probably low input if not compensating several times, meet specified merit during low input The output of rate, then several times when peak power output is low input when high input voltage, at this moment transformator is easy for satisfying With, saturated in order to ensure that transformator does not enter, the volume of transformator will do more.If overpower during input high-low pressure Point is consistent, then transformator avoid the need for said before so big just so that in full voltage input range transformator Do not enter saturated.In order to ensure to detect resistance R under different input voltages_CSOn mistake flow point consistent, frequently with Fig. 3 Shown feed forward circuit.By meeting the resistance R of input voltage_inIntroducing feedforward current, it is at R_LCOne little compensation electricity of upper generation Pressure, due to R_CSRelative to R_LCAnd R_inFor be negligible, therefore compensate voltage be about:

$V_{R_{\mathrm{LC}}}=\frac{R_{\mathrm{LC}}}{R_{\mathrm{in}}}{V}_{\mathrm{in}}...\left(2\right)$

Like this, R when crossing stream after compensation_CSOn virtual voltage become:

${V^{\′}}_{R_{\mathrm{CS}}}=V_{\mathrm{OC}}+(\frac{R_{\mathrm{CS}}{T}_d}{L}-\frac{R_{\mathrm{LC}}}{R_{\mathrm{in}}})V_{\mathrm{in}}...\left(3\right)$

If it can be seen that regulation R_LC/R_inRatio the value of (3) formula round bracket just can be made equal to zero, it is possible to make in difference R when input voltage descended stream_CSOn virtual voltage be invariable value V_OC.Patent No. 201310301104.1 illustrates A kind of side that overpower point compensates when realizing inputting high-low pressure when static exciter by the negative voltage of sampling auxiliary winding Method so that cross flow point during input high-low pressure consistent.But in the Switching Power Supply of the DCDC of the big electric current of some low inputs, electricity Sensibility reciprocal is the least, and required feedforward compensation electric current is very big, and dutycycle is the least, when namely turning on when underloading or zero load Between the least, utilize the method described in patent in the shortest excitation time be difficult to produce bigger compensation electric current rapidly, and Turning on and off of relatively large compensation electric current is easy to disturb current detecting.

Input undervoltage protection in Fig. 3 be input voltage pass through after resistance R1 and R2 dividing potential drop again with the reference voltage ratio in controller Relatively, the highest precision can be accomplished.But input undervoltage protection is separated from each other with feedforward compensating function, not only makes the electricity of periphery Resistance is many, and the biggest by the loss of resistance.If peripheral circuits, resistance R2 is made in inside controller, but half Resistance precision in semiconductor process is poor, temperature coefficient big, by very poor for the precision causing input undervoltage to be protected.

Summary of the invention

The technical problem to be solved, it is simply that provide the input undervoltage protection circuit of a kind of switch power controller, will adopt Sample resistance R2 is made in inside controller, peripheral circuits, reduces loss, and meanwhile, the precision of input undervoltage protection is high.

Solving above-mentioned technical problem, the present invention takes following technical scheme:

A kind of input undervoltage protection circuit of switch power controller, including:

Current detection circuit, comprises controller built-in current sampling resistor R2, and its one end is connected with node A, other end ground connection, Node A is connected with the VIN pin of controller；It is provided with controller external resistance R1, this resistance R1 one end connecting valve power supply Input voltage vin, the other end connects the VIN pin of controller, and the resistance of described built-in resistor R2 is much smaller than external resistance R1；

Reference voltage generating circuit, comprises controller built-in resistor R3 and reference current source Iref, this reference current source Iref's Outfan is connected with one end of built-in resistor R3, and the node of connection is B, the other end ground connection of this resistance R3, this resistance R3 and Resistance R2 is the internal same type of resistance of controller；

UVP signal produces circuit, comprises comparator comp, the comparison input of this comparator comp and current detecting electricity The node A on road is connected, and reference input is connected with the node B of reference voltage generating circuit, and outfan UVP exports under-voltage protection Signal；

Pulse output control circuit, its control end connects the outfan UVP of comparator comp, and its outfan connects controller GATE pin；

Controller built-in resistor R2 resistance external with controller R1 connects dividing potential drop, the voltage swing reflection input voltage that dividing potential drop obtains Size.Resistance precision within controller is very poor and temperature coefficient is very big, and the voltage on built-in resistor R2 can not be accurately Reflection input voltage size, but the resistance that the resistance of built-in resistor R2 is much smaller than external resistance R1, so passing through built-in resistor The electric current of R2 approximates input voltage vin divided by external resistance R1, and the voltage on resistance R2 is about this electric current and is produced by resistance R2 Raw pressure drop.The present invention designs a reference current source Iref, its current flowing resistance R3, owing to resistance R3 with resistance R2 is The internal same type of resistance of controller, so the voltage on resistance R2 is equivalent to flow through compared with the voltage on resistance R3 Electric current on built-in resistor R2 is compared with reference current Iref, and the electric current flow through on built-in resistor R2 approximates input voltage Vin is divided by external resistance R1, and precision is high, temperature coefficient is little, and reference current source Iref precision is the highest and temperature coefficient is the least simultaneously, So, the present invention can accurately sampled input voltage, when input voltage arrives the voltage of the under-voltage protection point set, will produce Input undervoltage protection signal realizes accurately protection.

A protection point input voltage vin (p) meets formula:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2 and resistance R3 is the internal same type of resistance of controller, and the resistance of built-in resistor R2 is much smaller than outward Put resistance R1.

Although resistance R2 and resistance R3 is controller built-in resistor, low precision, temperature coefficient are big, but owing to R2 and R3 is The internal same type of resistance of controller, is mated by resistance domain, and the error of resistance ratio R3/R2 can be accomplished less than thousand points One of precision；R1 is external resistance, and precision is high, temperature coefficient is little；Reference current source Iref same accuracy is the highest, temperature Degree coefficient is the least.Thus, it is achieved the high accuracy of input undervoltage protection point.Further, the value of external resistance R1, i.e. scalable are regulated The value of protection point input voltage.

When the input voltage vin of Switching Power Supply drops below protection point input voltage vin (p), the voltage of node A is less than knot The voltage of some B, the outfan UVP of comparator comp produces UVP signal, controls pulse output control circuit and turns off control The pulse output of device GATE pin, it is achieved accurately under-voltage protection.

In a preferred embodiment, above-mentioned current detection circuit also comprises electrical switch and resistance R5, this resistance R5 and electricity Resistance R2 series connection, described electrical switch is attempted by the two ends of resistance R5, and the control end of this electrical switch connects UVP signal and produces Comparator comp outfan UVP in raw circuit；

When the input voltage vin of Switching Power Supply is in normal input voltage scope, the level letter of comparator comp outfan UVP Number control electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5,

A protection point input voltage vin (p ') meets formula:

$V_{\mathrm{in}\left(p^{\′}\right)}\≈\frac{R3}{R2+R5}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2, resistance R5 and resistance R3 are the internal same type of resistance of controller, built-in resistor R2 and built-in The resistance sum of the resistance R5 resistance much smaller than external resistance R1；

When the input voltage vin of Switching Power Supply drops below a protection point input voltage vin (p '), comparator comp exports End UVP produces UVP signal, controls electrical switch conducting, and sampling resistor is resistance R2,

A protection point input voltage vin (p) meets formula:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2 and resistance R3 is the internal same type of resistance of controller, and the resistance of built-in resistor R2 is much smaller than outward Put resistance R1；

When the input voltage vin of Switching Power Supply rises above protection point input voltage vin (p), comparator comp outfan UVP cancels UVP signal, and electrical switch disconnects, and recovers normal operating conditions.

When normal input voltage scope, electrical switch disconnects, and sampling resistor is the series resistance (R2+R5) of R2 Yu R5, sends out After raw input undervoltage protection, electrical switch turns on, and sampling resistor is mono-resistance of R2, so only rising to when input voltage Time higher, just can make at node A big at voltage ratio node B, comparator comp cancels input undervoltage protection signal, is just recovering Often duty.Thus, set under-voltage protection point input voltage vin (p ') and again recover normal work protection point input electricity The return difference value of pressure Vin (p), and this return difference value=Vin (p)-Vin (p '), it is to avoid near under-voltage protection point, controller frequently opens Dynamic, it is ensured that controller is reliable and stable.

In one embodiment, above-mentioned electrical switch comprises not gate not, N-channel MOS pipe MN3, above-mentioned UVP signal Producing the comparator comp of circuit, it compares input is positive input terminal, and reference input is negative input end, and not gate not's is defeated Enter the end control end for electrical switch, connect comparator comp outfan UVP, the outfan of this not gate not and metal-oxide-semiconductor MN3 Grid be connected, one end of resistance R5 is connected with the drain electrode of metal-oxide-semiconductor MN3 and one end of resistance R2, the other end of resistance R2 Being connected with node A, the source electrode of metal-oxide-semiconductor MN3 and the other end of resistance R5 are all connected to the ground；

When comparator comp outfan UVP output low level UVP signal, metal-oxide-semiconductor MN3 turns on, and electrical switch turns on, Sampling resistor is resistance R2, and when comparator comp outfan UVP exports the normal working signal of high level, metal-oxide-semiconductor MN3 ends, Electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5.

The input undervoltage protection circuit of a kind of switch power controller of the present invention, also includes:

Feedforward compensation current generating circuit, comprises voltage follower and current mirror CM1, and this voltage follower comprises operational amplifier Amp1, N-channel MOS pipe MN1 and compensation current replication resistance R4, the positive input terminal of operational amplifier amp1 is connected with node A, Negative input end is connected with the source electrode of MN1 and one end of resistance R4, the other end ground connection of resistance R4, the input of current mirror CM1 End is connected with the drain electrode of metal-oxide-semiconductor MN1, and the outfan of this current mirror CM1 is through built-in resistor R_LCConnect controller CS pin, or The outfan of this current mirror CM1 is directly connected to controller CS pin, and this controller CS pin concatenates external resistance R_LC；

The feedforward compensation electric current Icom of current mirror CM1 outfan output meets formula:

$I_{\mathrm{com}}\≈\frac{V_{\mathrm{in}}}{R1}\·\frac{\mathrm{Ra}}{R4}\·n$

Wherein: resistance Ra is the sampling resistor between node A and ground, the resistance of this resistance Ra is much smaller than external resistance R1, should Resistance Ra and resistance R4 is the internal same type of resistance of controller, and the current ratio coefficient of current mirror CM1 is 1:n.

The present invention uses resistance R4 to produce accurate feedforward compensation electric current.Operational amplifier amp1, N-channel MOS pipe MN1 group Voltage on sampling resistor Ra between node A and ground is copied on resistance R4 by the voltage follower become, and produces and flows through Ra The electric current of current in proportion, then the image current obtained after current mirror CM1 proportionally zooms in or out is just as feedforward Compensate electric current I_com, when the current detection circuit within controller only has resistance R2, the sampling resistor between node A and ground Ra=R2, when the current detection circuit within controller comprises resistance R2, resistance R5 and electrical switch, and electrical switch disconnects, Sampling resistor Ra=R2+R5 between node A and ground, owing to Ra Yu R4 is the internal same type of resistance of controller, resistance ratio Example Ra/R4 can be made very accurate, and R1 is external resistance, and precision is high, and temperature coefficient is little, current mirror CM1 proportionality coefficient n Error can also accomplish less than millesimal precision by the coupling of metal-oxide-semiconductor, thus, it is ensured that feedforward compensation electric current I_comBe with The precision current that input voltage vin is proportional.

Accompanying drawing explanation

Fig. 1 is existing to have input undervoltage defencive function but do not have the typical application circuit figure of feedforward compensation；

Fig. 2 is sampling resistor R in Fig. 1 under different input voltages_CSOn voltage waveform；

Fig. 3 is the typical application circuit figure of conventional external feedforward compensation；

Fig. 4 is the typical application circuit figure of the embodiment of the present invention one, embodiment two；

Fig. 5 is the embodiment of the present invention one circuit diagram；

Fig. 6 is the embodiment of the present invention two circuit diagram；

Fig. 7 is embodiment of the present invention three-circuit figure；

Fig. 8 is the application circuit of the embodiment of the present invention three.

Detailed description of the invention

Below in conjunction with the accompanying drawings the embodiment of the present invention is described in detail.

Embodiment one

As it is shown in figure 5, the embodiment of the present invention one includes:

Current detection circuit 101, comprises controller built-in current sampling resistor R2, and its one end is connected with node A, another termination Ground, node A is connected with the VIN pin of controller；It is provided with controller external resistance R1, this resistance R1 one end connecting valve electricity The input voltage vin in source, the other end connects the VIN pin of controller, and the resistance of described built-in resistor R2 is much smaller than external resistance R1；

Reference voltage generating circuit 102, comprises controller built-in resistor R3 and reference current source Iref, this reference current source Iref Comprising operational amplifier amp2, N-channel MOS pipe MN2 and current mirror CM2, the positive input termination of operational amplifier amp2 is internal Bandgap voltage reference Vref, negative input end is connected with source electrode and the controller RI pin of metal-oxide-semiconductor MN2, the RI of this controller Being connected external resistance Ri between pin with ground, the outfan of described operational amplifier amp2 is connected with the grid of metal-oxide-semiconductor MN2, The input of current mirror CM2 is connected with the drain electrode of metal-oxide-semiconductor MN2, the outfan of current source Iref on the basis of outfan；This benchmark The outfan of current source Iref is connected with one end of built-in resistor R3, and the node of connection is B, the other end ground connection of this resistance R3, This resistance R3 and resistance R2 is the internal same type of resistance of controller；

UVP signal produces circuit 104, comprises comparator comp, and the comparison input of this comparator comp is examined with electric current The node A of slowdown monitoring circuit is connected, and comparing input is positive input terminal, the node B phase of reference input and reference voltage generating circuit Even, reference input is negative input end, and outfan UVP exports UVP signal；

Pulse output control circuit 105, comprise agitator OSC and with door and, described is arteries and veins with a door and input Rush the control end of output control circuit, connect the outfan UVP of comparator comp, the input port of described agitator OSC and base In quasi-voltage generation circuit, the 3rd port of current mirror CM2 is connected, pulse signal input and the door and of this agitator OSC output Another input, the GATE that with the outfan that outfan is pulse output control circuit of door and, should connect controller draws Foot；When the outfan UVP of comparator comp produces low level UVP signal, persistently export low with the outfan of door and Level signal, turns off the pulse output of controller GATE pin.

Feedforward compensation current generating circuit 103, comprises voltage follower and current mirror CM1, and this voltage follower comprises computing and puts Big device amp1, N-channel MOS pipe MN1 and compensation current replication resistance R4, the positive input terminal of operational amplifier amp1 and node A Being connected, negative input end is connected with the source electrode of MN1 and one end of resistance R4, the other end ground connection of resistance R4, current mirror CM1 Input be connected with the drain electrode of metal-oxide-semiconductor MN1, the outfan of this current mirror CM1 is directly connected to controller CS pin, such as Fig. 4 Shown in, controller CS pin concatenates external resistance R_LC。

Fig. 4 is the typical application drawing of embodiment one, is the internal circuit diagram of Fig. 4 middle controller in Fig. 5 in thick line dotted line frame.As Shown in Fig. 5, Vin is the input voltage of Switching Power Supply, and internal resistance R2 connects with external resistance R1, then on R2 Voltage be:

$V_{R2}=\frac{R2}{R1+R2}\·V_{\mathrm{in}}...\left(4\right)$

The internal bandgap voltage reference V of controller_refBy by operational amplifier amp2, N-channel MOS pipe MN2, current mirror CM2(electricity Flow ratio example is k:1) trsanscondutance amplifier that forms is converted into reference current, constitutes reference current source Iref.

$I_{\mathrm{ref}}=\frac{V_{\mathrm{ref}}}{{\mathrm{kR}}_i}...\left(5\right)$

R_iBeing external resistance, its precision is high and temperature coefficient is little.

Protection point input voltage vin (p) is:

$V_{\mathrm{in}\left(p\right)}=\frac{R3}{R2}\·\frac{R1+R2}{R_i}\·\frac{V_{\mathrm{ref}}}{k}...\left(6\right)$

Owing to resistance R2 and resistance R3 is the internal same type of resistance of controller, mated by resistance domain, resistance ratio The error of R3/R2 can be accomplished less than millesimal precision；Similarly, the error of the proportionality coefficient k:1 of current mirror CM2 is led to The coupling crossing metal-oxide-semiconductor can also be accomplished less than one thousandth；V_refBeing bandgap voltage reference, it is determined by the band gap voltage of silicon Si, Precision is high, temperature coefficient is little.So the precision of under-voltage protection point input voltage vin (p) is mainly by proportionality coefficient (R1+R2)/R_i Determine, R1 and R_iBeing all external resistance, precision is high, temperature coefficient is little；R2 is controller internal resistance, low precision, temperature Coefficient is big；But the resistance of built-in resistor R2 is much smaller than external resistance R1, although its change in resistance is big, but changing value phase It is negligible for the value of (R1+R2).It is, (6) formula can be reduced to:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}...\left(7\right)$

Achieve the high accuracy of input undervoltage protection point.

When the input voltage vin of Switching Power Supply drops below protection point input voltage vin (p), the voltage of node A is less than knot The voltage of some B, the level signal of comparator comp outfan UVP is changed into low level from high level, i.e. produces low level under-voltage Protection signal, represents that input voltage is too low, and this low level UVP signal controls pulse output control circuit and turns off controller GATE The pulse output of pin, it is achieved accurately under-voltage protection.

The voltage follower of operational amplifier amp1, N-channel MOS pipe MN1 composition is by the sampling resistor R2 between node A and ground On voltage copy on resistance R4, the electric current of current in proportion producing with flowing through resistance R2, then become through current mirror CM1 As feedforward compensation electric current I after zooming in or out to ratio_com。

$I_{\mathrm{com}}=\frac{V_{\mathrm{in}}}{R1+R2}\·\frac{R2}{R4}\·n...\left(8\right)$

Wherein the current ratio coefficient of current mirror CM1 is 1:n, and resistance R2 and resistance R4 is the internal same type of electricity of controller Resistance, ratio can be made the most accurate.Because the resistance of built-in resistor R2 is much smaller than external resistance R1, (8) formula can be reduced to:

$I_{\mathrm{com}}\≈\frac{V_{\mathrm{in}}}{R1}\·\frac{R2}{R4}\·n...\left(9\right)$

As can be seen from the above equation, I_comBeing the precision current proportional to input voltage, our required feedforward compensation is electric the most just Stream.

The resistance R2 of embodiment one is to sense the electric current flow through on outer meeting resistance R1, as long as the resistance of R2 can relative to R1 To ignore, then the electric current flow through mainly is determined by R1.And in order to replicate accurately or current ratio relatively, be the electricity by same type Resistance R4, R3 match and realize.Reference voltage generating circuit 102 actually variable reference voltage produces circuit, is because head First can be by changing external resistance R_iChange the reference current I of generation_ref, thus change the pressure drop at node B, secondly The resistance accuracy of R3 is the highest, thus causes the change in voltage at node B relatively big, however R3 change in resistance and cause voltage at B Change eliminated by mating of R3 with R2.As long as so determining R_iResistance, be equivalent at B, set a benchmark Voltage, R_iResistance be by controller operating frequency determine, i.e. by set R_iAnd change I_oscSize control agitator The frequency of OSC.R_iResistance value changes R1 according to (7) formula after determining just can set the input voltage of under-voltage protection point easily.

Embodiment two

As shown in Figure 6, for the circuit diagram of the embodiment of the present invention two: compared with embodiment one, the present embodiment current detection circuit 201 Also comprising electrical switch and resistance R5, electrical switch comprises not gate not, N-channel MOS pipe MN3, and the input of not gate not is The control end of electrical switch, connects comparator comp outfan UVP, the outfan of this not gate not and the grid of metal-oxide-semiconductor MN3 Being connected, one end of resistance R5 is connected with one end of the drain electrode of MN3 and resistance R2, and the other end of resistance R2 is connected with node A, The source electrode of metal-oxide-semiconductor MN3 and the other end of resistance R5 are all connected to the ground；Visible, resistance R5 and resistance R2 series connection, electrical switch Be equivalent to be attempted by the two ends of resistance R5, and the end that controls of electrical switch connects the comparator in UVP signal generation circuit Comp outfan UVP.

When comparator comp outfan UVP output low level UVP signal, metal-oxide-semiconductor MN3 turns on, and electrical switch turns on, Sampling resistor is resistance R2, and when comparator comp outfan UVP exports the normal working signal of high level, metal-oxide-semiconductor MN3 ends, Electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5.

When the input voltage vin of Switching Power Supply is in normal input voltage scope, the level letter of comparator comp outfan UVP Number control electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5,

A protection point input voltage vin (p ') meets formula:

$V_{\mathrm{in}\left(p^{\′}\right)}\≈\frac{R3}{R2+R5}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}$

Wherein: resistance R2, resistance R5 and resistance R3 are the internal same type of resistance of controller, built-in resistor R2 and built-in The resistance sum of resistance R5 is much smaller than external resistance R1, and the current ratio coefficient of current mirror CM2 is k:1；

When the input voltage vin of Switching Power Supply drops below a protection point input voltage vin (p '), comparator comp exports End UVP produces UVP signal, controls electrical switch conducting, and sampling resistor is resistance R2,

A protection point input voltage vin (p) meets formula:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}$

Wherein: resistance R2 and resistance R3 is the internal same type of resistance of controller, and the resistance of built-in resistor R2 is much smaller than outward The current ratio coefficient putting resistance R1, current mirror CM2 is k:1；

When the input voltage vin of Switching Power Supply rises above protection point input voltage vin (p), comparator comp outfan UVP cancels UVP signal, and electrical switch disconnects, and recovers normal operating conditions.

In actual application, after there is input voltage protection, input voltage is again restored to nominal input range controller often needs Again recovering normal work, the input voltage of the normal work of under-voltage protection voltage and again recovery has a return difference value.Such as, when Input voltage, less than entering under-voltage protection state during 10V, just recovers normal work when input voltage rises to 12V again.This reality Execute the place changed in example and set this hysteresis voltage exactly.Principle is: when normal input voltage scope, input undervoltage protection letter Number UVP is inactive level, i.e. high level, so what metal-oxide-semiconductor MN3 was off, at this moment sampling resistor is actually R2 and R5 Series resistance (R2+R5).And after there is input undervoltage protection, UVP is effective low level, and MN3 is open-minded, at this moment detects electricity Resistance has reformed into mono-resistance of R2, so only when input voltage rises to higher so that big at voltage ratio B at node A, Comparator comp just exports high level, cancels input undervoltage protection, recovers normal operating conditions.

From (7) formula, R2 with R5 connects as current sampling resistor, and input undervoltage protection point is:

$V_{\mathrm{in}\left(p^{\′}\right)}\≈\frac{R3}{R2+R5}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}=\frac{R3}{(1+\mathrm{\β})R_2}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}...\left(10\right)$

Because resistance R2, resistance R5 and resistance R3 are the same type of resistance in controller inside, their ratio can be made very Accurately.Above formula designs R5=β R2.When only R2 is as sampling resistor, input undervoltage protection point is exactly (7) formula, thus The input voltage return difference value recovered is:

${\mathrm{\ΔV}}_{\mathrm{in}}=V_{\mathrm{in}\left(p\right)}-V_{\mathrm{in}\left(p^{\′}\right)}=\frac{\mathrm{\β}}{1+\mathrm{\β}}\·\frac{R3}{R2}\·\frac{R1}{R_i}\·\frac{V_{\mathrm{ref}}}{k}={\mathrm{\βV}}_{\mathrm{in}\left(p^{\′}\right)}...\left(11\right)$

It can be seen that hysteresis voltage value is β times of input undervoltage protection point.Such as, design R5=0.2R2 in controller, if By the peripheral resistance R of regulation_iInput undervoltage protection point is made to be 10V with R1, then just to recover when input voltage rises to 12V again Normal work；If input undervoltage protection point is 20V, then just recover normal work when input voltage rises to 24V again.

Embodiment three

As it is shown in fig. 7, be the circuit diagram of the embodiment of the present invention three.Compared with embodiment two, feedforward compensation electric current in the present embodiment Produce and circuit 303 increases resistance R_LC, the outfan of current mirror CM1 is through built-in resistor R_LCConnect controller CS pin.

As in figure 2 it is shown, feedforward compensation is by delaying time of controller T_dTime delay produces, the R that under high low input, it is caused_CSEnd electricity Pressure reduction V_H-V_LRelative to V_OCFor be fraction ratio, through feedforward current I_comBuilt-in resistor R in 303_LCFormed is little After voltage compensation, ideal situation can make V_H-V_LVanishing.Although controller internal resistance low precision, it is impossible to by all products V_H-V_LVanishing, but also it can be controlled within the scope of accepting.By peripheral R_LCIncorporating resistor is to behind controller inside, no Only peripheral circuit is simpler, as shown in Figure 8, and CS pin and R_CSIt is joined directly together, is greatly improved the anti-dry of current sample Disturb ability.

Embodiment four

Unlike embodiment one: add feedforward resistance R in feedforward compensation current generating circuit_LC, current mirror CM1's is defeated Go out end through built-in resistor R_LCConnect controller CS pin.Circuit and the connection of other parts are identical with embodiment one, at this no longer Repeat.

Above-described embodiment one to embodiment four, UVP signal produces the comparator comp of circuit 104, and it compares input and is Positive input terminal, reference input is negative input end, and certainly, it is possible to exchange, comparing input is negative input end, reference input For positive input terminal, as the circuit connected with comparator comp outfan UVP, do and adjust accordingly.

Embodiments of the present invention are not limited to this, according to the foregoing of the present invention, utilize the ordinary technical knowledge of this area and are used to By means, without departing under the present invention above-mentioned basic fundamental thought premise, the present invention can also make other various ways amendment, Replace or change, within the scope of all falling within rights protection of the present invention.

Claims (6)

1. the input undervoltage protection circuit of a switch power controller, it is characterised in that including:

Current detection circuit, comprises controller built-in current sampling resistor R2, and its one end is connected with node A, other end ground connection, Node A is connected with the VIN pin of controller；It is provided with controller external resistance R1, this resistance R1 one end connecting valve power supply Input voltage vin, the other end connects the VIN pin of controller, and the resistance of described built-in resistor R2 is much smaller than external resistance R1；

Reference voltage generating circuit, comprises controller built-in resistor R3 and reference current source Iref, this reference current source Iref's Outfan is connected with one end of built-in resistor R3, and the node of connection is B, the other end ground connection of this resistance R3, this resistance R3 and Resistance R2 is the internal same type of resistance of controller；

UVP signal produces circuit, comprises comparator comp, the comparison input of this comparator comp and current detecting electricity The node A on road is connected, and reference input is connected with the node B of reference voltage generating circuit, and outfan UVP exports under-voltage protection Signal；

Pulse output control circuit, its control end connects the outfan UVP of comparator comp, and its outfan connects controller GATE pin；

A protection point input voltage vin (p) meets formula:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2 and resistance R3 is the internal same type of resistance of controller, and the resistance of built-in resistor R2 is much smaller than outward Put resistance R1；

When the input voltage vin of Switching Power Supply drops below protection point input voltage vin (p), the voltage of node A is less than knot The voltage of some B, the outfan UVP of comparator comp produces UVP signal, controls pulse output control circuit and turns off control The pulse output of device GATE pin.

Input undervoltage protection circuit the most according to claim 1, it is characterised in that described current detection circuit also comprises electronic cutting Closing and resistance R5, this resistance R5 and resistance R2 connect, described electrical switch is attempted by the two ends of resistance R5, this electrical switch The end that controls connect UVP signal and produce the comparator comp outfan UVP in circuit；

When the input voltage vin of Switching Power Supply is in normal input voltage scope, the level letter of comparator comp outfan UVP Number control electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5,

A protection point input voltage vin (p ') meets formula:

$V_{\mathrm{in}\left(p^{\′}\right)}\≈\frac{R3}{R2+R5}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2, resistance R5 and resistance R3 are the internal same type of resistance of controller, built-in resistor R2 and built-in The resistance sum of the resistance R5 resistance much smaller than external resistance R1；

When the input voltage vin of Switching Power Supply drops below a protection point input voltage vin (p '), comparator comp exports End UVP produces UVP signal, controls electrical switch conducting, and sampling resistor is resistance R2,

A protection point input voltage vin (p) meets formula:

$V_{\mathrm{in}\left(p\right)}\≈\frac{R3}{R2}\·R1\·I_{\mathrm{ref}}$

Wherein: resistance R2 and resistance R3 is the internal same type of resistance of controller, and the resistance of built-in resistor R2 is much smaller than outward Put resistance R1；

When the input voltage vin of Switching Power Supply rises above protection point input voltage vin (p), comparator comp outfan UVP cancels UVP signal, and electrical switch disconnects, and recovers normal operating conditions.

Input undervoltage protection circuit the most according to claim 2, it is characterised in that described electrical switch comprises not gate not, N Channel MOS tube MN3, described UVP signal produces the comparator comp of circuit, and it compares input is positive input terminal, ginseng Examining input is negative input end, and the input of not gate not is the control end of electrical switch, connects comparator comp outfan UVP, The outfan of this not gate not is connected with the grid of metal-oxide-semiconductor MN3, one end of resistance R5 and the drain electrode of metal-oxide-semiconductor MN3 and resistance One end of R2 be connected, the other end of resistance R2 is connected with node A, the source electrode of metal-oxide-semiconductor MN3 and the other end of resistance R5 all with Ground is connected；

When comparator comp outfan UVP output low level UVP signal, metal-oxide-semiconductor MN3 turns on, and electrical switch turns on, Sampling resistor is resistance R2, and when comparator comp outfan UVP exports the normal working signal of high level, metal-oxide-semiconductor MN3 ends, Electrical switch disconnects, and sampling resistor is the series resistance of resistance R2 and resistance R5.

4. according to the input undervoltage protection circuit described in any one of claims 1 to 3, it is characterised in that described reference current source Iref Comprising operational amplifier amp2, N-channel MOS pipe MN2 and current mirror CM2, the positive input termination of operational amplifier amp2 is internal Bandgap voltage reference Vref, negative input end is connected with source electrode and the controller RI pin of metal-oxide-semiconductor MN2, the RI of this controller Being connected external resistance Ri between pin with ground, the outfan of described operational amplifier amp2 is connected with the grid of metal-oxide-semiconductor MN2, The input of current mirror CM2 is connected with the drain electrode of metal-oxide-semiconductor MN2, the outfan of current source Iref on the basis of outfan；

Reference current Iref meets formula:

$I_{\mathrm{ref}}=\frac{V_{\mathrm{ref}}}{{\mathrm{kR}}_i}$

Wherein: the current ratio coefficient of current mirror CM2 is k:1.

Input undervoltage protection circuit the most according to claim 4, it is characterised in that described pulse output control circuit comprises vibration Device OSC and with door and, the described control end that an input is pulse output control circuit with door and, connect comparator The outfan UVP of comp, the input port of described agitator OSC and the 3rd end of current mirror CM2 in reference voltage generating circuit Mouth is connected, the pulse signal input of this agitator OSC output and another input of door and, is somebody's turn to do the outfan with door and For the outfan of pulse output control circuit, connect the GATE pin of controller；

When the outfan UVP of comparator comp produces low level UVP signal, persistently export with the outfan of door and Low level signal, turns off the pulse output of controller GATE pin.

6. according to the input undervoltage protection circuit described in any one of claims 1 to 3, it is characterised in that also include:

Feedforward compensation current generating circuit, comprises voltage follower and current mirror CM1, and this voltage follower comprises operational amplifier Amp1, N-channel MOS pipe MN1 and compensation current replication resistance R4, the positive input terminal of operational amplifier amp1 is connected with node A, Negative input end is connected with the source electrode of MN1 and one end of resistance R4, the other end ground connection of this resistance R4, and current mirror CM1's is defeated Entering end to be connected with the drain electrode of metal-oxide-semiconductor MN1, the outfan of this current mirror CM1 is through built-in resistor R_LCConnect controller CS pin, Or the outfan of this current mirror CM1 is directly connected to controller CS pin, this controller CS pin concatenates external resistance R_LC；

The feedforward compensation electric current Icom of current mirror CM1 outfan output meets formula:

$I_{\mathrm{com}}\≈\frac{V_{\mathrm{in}}}{R1}\·\frac{\mathrm{Ra}}{R4}\·n$

Wherein: resistance Ra is the sampling resistor between node A and ground, the resistance of this resistance Ra is much smaller than external resistance R1, should Resistance Ra and resistance R4 is the internal same type of resistance of controller, and the current ratio coefficient of current mirror CM1 is 1:n.