CN103475217A - DC-DC circuit and overcurrent protection method thereof - Google Patents

Abstract

The invention discloses a DC-DC circuit and an overcurrent protection method thereof. The DC-DC circuit is connected with loads, and comprises an input power supply, an input filtration module, a PWM control module and a switch module, wherein the PWM control module comprises a PWM controller which comprises a voltage detection unit and a drive control unit. In the DC-DC circuit, the input power supply provides input voltages, the alternating components in the switch module generate ripple voltages when flowing through the input filtration module, the voltage detection unit detects the ripple voltages in the input filtration module, the difference value of the input voltages and the ripple voltages is compared with a preset reference voltage, the output of the output currents is controlled according to the comparative results, therefore, detection on the output currents can be achieved by detecting the ripple voltages, so that when overcurrent occurs to the DC-DC circuit, the output of the currents is cut off, and the purpose of overcurrent protection is achieved.

Description

DC-DC circuit and over-current protection method thereof

Technical field

The present invention relates to power technique fields, relate in particular to a kind of DC-DC circuit and over-current protection method thereof.

Background technology

At present, DC-to-DC (DC-DC) circuit of voltage-dropping type (BUCK) topological structure is widely used in electron trade.Common BUCK topology DC-DC circuit has two kinds of concrete forms: a kind of PWM of being controller and metal-oxide-semiconductor become one (or PWM controller only integrated upper metal-oxide-semiconductor), as shown in Figure 1; Another kind is PWM controller integrated MOS pipe not fully, need to use in the outside of PWM controller upper and lower two metal-oxide-semiconductors, as shown in Figure 2.

For the overcurrent protection of DC-DC circuit in Fig. 1, the designer tends at the inner integrated current detection circuit of PWM controller, by the electric current of flowing through between drain electrode, source electrode in metal-oxide-semiconductor Q11 on this current detection circuit direct-detection or lower metal-oxide-semiconductor Q12.When finding upper metal-oxide-semiconductor Q11 or lower metal-oxide-semiconductor Q12 overcurrent, will start overcurrent protection.But, for the DC-DC circuit of external metal-oxide-semiconductor in Fig. 2, just can't carry out by the current detection circuit that is integrated in PWM controller inside the electric current in metal-oxide-semiconductor Q21 on direct-detection or lower metal-oxide-semiconductor Q22.

Summary of the invention

Main purpose of the present invention is to propose a kind of DC-DC circuit and over-current protection method thereof, and the voltage detection unit be intended to by being integrated in PWM controller inside detects ripple voltage, realizes the detection to output current, realizes overcurrent protection.

In order to achieve the above object, the present invention proposes a kind of DC-DC circuit, this DC-DC circuit is connected with load, comprise input power, input filter module, PWM control module and switch module, described PWM control module comprises the PWM controller, and described PWM controller comprises voltage detection unit and driving control unit;

Described input power is connected with the input of described voltage detection unit, the input of described switch module respectively via described input filter module; The output of described voltage detection unit is connected with the control end of described driving control unit, the input of described driving control unit is connected with the output of described switch module, the output of described driving control unit is connected with the control end of described switch module, and the output of described switch module is connected with described load;

Described voltage detection unit detects the ripple voltage in described input filter module; the input voltage that described input power is provided and the difference of described ripple voltage and default reference voltage compare; and according to comparative result output overcurrent guard signal; control described driving control unit and whether drive described switch module, whether export to control output current.

Preferably, described PWM control module also comprises feeder ear and sample resistance; One end of described sample resistance is connected with described feeder ear and is connected with the reference edge of described voltage detection unit, the other end ground connection of described sample resistance.

Preferably, described voltage detection unit comprises constant-current source and the first voltage comparator; The in-phase input end of described the first voltage comparator is connected with described feeder ear via described constant-current source and via described sample resistance ground connection, the inverting input of described the first voltage comparator is connected with described input filter module with described input power respectively, and the output of described the first voltage comparator is connected with the control end of described driving control unit.

Preferably, described driving control unit comprises reference voltage source, operational amplifier, saw-toothed wave generator, second voltage comparator, triple gate, homophase device and inverter;

The in-phase input end of described operational amplifier is connected with described reference voltage source, the inverting input of described operational amplifier is connected with the output of described switch module, and the output of described operational amplifier is connected with the in-phase input end of described second voltage comparator; The inverting input of described second voltage comparator is connected with the signal output part of described saw-toothed wave generator, and the output of described second voltage comparator is connected with the input of described triple gate; The control Enable Pin of described triple gate is connected with the output of described the first voltage comparator, the output of described triple gate is connected with the input of described homophase device, the input of described inverter respectively, and the output of described homophase device, the output of described inverter all are connected with the control end of described switch module.

Preferably, described input filter module comprises input filter capacitor; One end of described input filter capacitor is connected with the positive pole of described input power, and with the inverting input of the first voltage comparator, the input of described switch module, be connected respectively, the other end ground connection of described input filter capacitor, the minus earth of described input power;

Described switch module comprises the first metal-oxide-semiconductor and the second metal-oxide-semiconductor; The grid of described the first metal-oxide-semiconductor is connected with the output of described homophase device, the drain electrode of described the first metal-oxide-semiconductor is connected with the common port of described input filter capacitor and described input power, and the source electrode of described the first metal-oxide-semiconductor is connected with the drain electrode of described the second metal-oxide-semiconductor and is connected with described load; The grid of described the second metal-oxide-semiconductor is connected with the output of described inverter, the source ground of described the second metal-oxide-semiconductor.

Preferably, the loaded work piece voltage of described DC-DC circuit output is Vout, the input voltage that described input power provides is Vin, the ripple voltage that described voltage detection unit detects is Δ V, described voltage detection unit is by detecting described ripple voltage, detect the average output current of described DC-DC circuit, the relational expression of Io and Δ V is as follows:

$\mathrm{\ΔV}=\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\frac{\mathrm{Vout}}{\mathrm{Vin}}\×\frac{1}{f},$

Wherein, the capacitance that Cin is described input filter capacitor, the switching frequency that f is described DC-DC circuit.

Preferably; the difference of described input voltage and described ripple voltage is Vm; described reference voltage is Vp, and when the difference of described input voltage and described ripple voltage equals described reference voltage, the over-current protection point critical current of described DC-DC circuit equals average output current:

$\mathrm{Io}=\frac{(\mathrm{Vin}-\mathrm{Vm})\×\mathrm{Vin}\×f\×\mathrm{Cin}}{\mathrm{Vout}}.$

Preferably, described DC-DC circuit also comprises output filtering module and output feedback module, described output filtering module is connected between the output and described load of described switch module, and described output feedback module is connected between the input of the output of described output filtering module and described driving control unit;

Described output filtering module comprises filter inductance and output filter capacitor; One end of described filter inductance is connected with the output of described switch module, and the other end of described filter inductance is connected via described output filter capacitor ground connection and with described load;

Described output feedback module comprises the first feedback resistance and the second feedback resistance; One end of described the first feedback resistance is connected with the common port of described filter inductance and described output filter capacitor, and the other end of described the first feedback resistance is connected with the input of described driving control unit and via described the second feedback resistance ground connection.

The DC-DC circuit that the present invention proposes; in the inner integrated voltage detection unit of PWM controller and driving control unit; detect the ripple voltage in the input filter module by voltage detection unit; the input voltage that input power is provided and the difference of ripple voltage and default reference voltage compare; and according to comparative result output overcurrent guard signal; control whether driving switch module of driving control unit, whether export thereby control output current.Because ripple voltage is that in switch module, the alternating component of the electric current input filter module of flowing through produces; therefore output current and the ripple voltage of the output of DC-DC circuit are relevant; thereby can just can detect output current by detecting ripple voltage; the detection of realization to output current, reach the purpose of overcurrent protection.

The present invention also proposes a kind of over-current protection method of DC-DC circuit, and this over-current protection method comprises the following steps:

Voltage comparison unit detects the ripple voltage in the input filter module;

The difference of input voltage and the described ripple voltage that detects and default reference voltage are compared and obtain comparative result;

Whether the overcurrent protection signal that will be generated by comparative result is sent to driving control unit, to control output current, export.

Whether preferably, the described overcurrent protection signal that will be generated by comparative result is sent to driving control unit, with the control output current, export and be specially:

When the difference of input voltage and ripple voltage is greater than default reference voltage, generate low level overcurrent protection signal and be sent to driving control unit, to control output current, normally export;

When the difference of input voltage and ripple voltage is less than default reference voltage, the overcurrent protection signal that generates high level is sent to driving control unit, to cut off the output of output current.

The over-current protection method of the DC-DC circuit that the present invention proposes; at first detect the ripple voltage in the DC-DC circuit; secondly the difference of input voltage and ripple voltage and default reference voltage are compared; then according to comparative result output overcurrent guard signal; control output current by this output overcurrent guard signal and whether export, reach the purpose of overcurrent protection.

The accompanying drawing explanation

Fig. 1 is the electrical block diagram of existing DC-DC circuit one embodiment;

Fig. 2 is the electrical block diagram of existing another embodiment of DC-DC circuit;

The theory diagram that Fig. 3 is DC-DC circuit of the present invention preferred embodiment;

The electrical block diagram that Fig. 4 is DC-DC circuit of the present invention preferred embodiment;

The current waveform that Fig. 5 is voltage waveform that in Fig. 4, A, PH are ordered and the first metal-oxide-semiconductor, the second metal-oxide-semiconductor, filter inductance branch road;

The electrical block diagram that Fig. 6 is driving control unit in DC-DC circuit of the present invention;

The schematic flow sheet of the over-current protection method preferred embodiment that Fig. 7 is DC-DC circuit of the present invention.

The realization of the object of the invention, functional characteristics and advantage, in connection with embodiment, are described further with reference to accompanying drawing.

Embodiment

Further illustrate technical scheme of the present invention below in conjunction with Figure of description and specific embodiment.Should be appreciated that specific embodiment described herein, only in order to explain the present invention, is not intended to limit the present invention.

The present invention proposes a kind of DC-DC circuit.

With reference to Fig. 3, the theory diagram that Fig. 3 is DC-DC circuit of the present invention preferred embodiment.

In preferred embodiment of the present invention, DC-DC circuit 10 is connected with load 20, comprise input power 11, input filter module 12, PWM control module 13 and switch module 14, this PWM control module 13 comprises PWM controller 131, and this PWM controller 131 comprises voltage detection unit 1311 and driving control unit 1312.

Input power 11 is connected with the input of voltage detection unit 1311, the input of switch module 14 respectively via input filter module 12; The output of voltage detection unit 1311 is connected with the control end of driving control unit 1312, the input of driving control unit 1312 is connected with the output of switch module 14, the output of driving control unit 1312 is connected with the control end of switch module 14, and the output of switch module 14 is connected with load 20; The ripple voltage that voltage detection unit 1311 detects in input filter module 12; the input voltage that input power 11 is provided compares with the difference of the ripple voltage detected and default reference voltage; and according to comparative result output overcurrent guard signal; control whether driving switch module 14 of driving control unit 1312, whether export to control output current.

In the present embodiment, input power 11 provides input voltage, produce ripple voltage when in switch module 14, the alternating component of electric current is flowed through input filter module 12, in the inner integrated voltage detection unit 1311 of PWM controller 131 and driving control unit 1312, the ripple voltage detected in input filter module 12 by voltage detection unit 1311, the difference of input voltage and ripple voltage and reference voltage are compared, when the difference of input voltage and ripple voltage is greater than reference voltage, the overcurrent protection signal of output low level, control output current and normally export; When the difference of input voltage and ripple voltage is less than reference voltage, the overcurrent protection signal of output high level, cut off the output of output current.Because the ripple voltage alternating component that is electric current in switch module 14 the input filter module 12 of flowing through produces; therefore output current and the ripple voltage of 10 outputs of DC-DC circuit are relevant; when overcurrent condition appears in DC-DC circuit 10; the ripple voltage that voltage detection unit 1311 detects surpasses the predeterminated voltage value; thereby can just can detect output current by detecting ripple voltage; the detection of realization to output current, reach the purpose of overcurrent protection.

In the present embodiment, DC-DC circuit 10 also comprises output filtering module 15 and output feedback module 16, output filtering module 15 is connected between the output and load 20 of switch module 14, and output feedback module 16 is connected between the input of the output of output filtering module 15 and driving control unit 1312.15 pairs of output currents of output filtering module carry out filtering and process rear output loading operating voltage to load 20 power supplies; the loaded work piece voltage that 16 pairs of feedback modules of output are exported is sampled and is fed back a feedback voltage to driving control unit 1312; driving control unit 1312 generates square-wave signal according to this feedback voltage; according to the overcurrent protection signal of voltage detection unit 1311 outputs, control this square wave signal and whether export with driving switch module 14 again.

Refer again to Fig. 4, the electrical block diagram that Fig. 4 is DC-DC circuit of the present invention preferred embodiment, the DC-DC circuit shown in Fig. 4 is the improvement in Fig. 2, existing DC-DC circuit is done.

As shown in Figure 4, PWM control module 13 also comprises feeder ear VCC and sample resistance RS; The end of sample resistance RS is connected with feeder ear VCC and is connected with the reference edge of voltage detection unit 1311, the other end ground connection of sample resistance RS.The present embodiment obtains reference voltage by sample resistance RS, and be input to the reference edge of voltage detection unit 1311, according to actual needs, determine the resistance of the sample resistance RS that will select, thereby the reference edge of voltage detection unit 1311 receives a default reference voltage.

Particularly, voltage detection unit 1311 comprises constant-current source IR and the first voltage comparator U1; The in-phase input end of the first voltage comparator U1 is connected with feeder ear VCC via constant-current source IR and via sample resistance RS ground connection, the inverting input of the first voltage comparator U1 is connected with input filter module 12 with input power 11 respectively, and the output of the first voltage comparator U1 is connected with the control end of driving control unit 1312.

In voltage detection unit 1311, constant-current source IR obtains a constant current by the supply power voltage of feeder ear VCC input, this constant current with flowing through the sample resistance RS flow direction, produce sampling voltage on sample resistance RS, due to constant-current source IR output is constant current, therefore this sampling voltage is also constant, this sampling voltage is input to the reference edge of voltage detection unit 1311 as reference voltage, thereby be input to the reference voltage Vp=Iref * Rcs of the in-phase input end of the first voltage comparator U1, the constant current that wherein Iref is constant-current source IR output, the resistance that Rcs is sample resistance RS.

Refer again to Fig. 6, the electrical block diagram that Fig. 6 is driving control unit in DC-DC circuit of the present invention.

As shown in Figure 6, driving control unit 1312 comprises reference voltage source U3, operational amplifier U4, saw-toothed wave generator U5, second voltage comparator U2, triple gate U6, homophase device U7 and inverter U8.

The in-phase input end of operational amplifier U4 is connected with reference voltage source U3, and the inverting input of operational amplifier U4 is connected with the output of switch module 14, and the output of operational amplifier U4 is connected with the in-phase input end of second voltage comparator U2; The inverting input of second voltage comparator U2 is connected with the signal output part of saw-toothed wave generator U5, and the output of second voltage comparator U2 is connected with the input of triple gate U6; The control Enable Pin of triple gate U6 is connected with the output of the first voltage comparator U1, the output of triple gate U6 is connected with the input of homophase device U7, the input of inverter U8 respectively, and the output of homophase device U7, the output of inverter U8 all are connected with the control end of switch module 14.

In Fig. 4, input filter module 12 comprises input filter capacitor C1; The end of input filter capacitor C1 is connected with the positive pole of input power 11, and is connected respectively the other end ground connection of input filter capacitor C1, the minus earth of input power 11 with the inverting input of the first voltage comparator U1, the input of switch module 14.

Switch module 14 comprises the first metal-oxide-semiconductor M1 and the second metal-oxide-semiconductor M2, and in the present embodiment, the first metal-oxide-semiconductor M1, the second metal-oxide-semiconductor M2 are the NMOS pipe; The grid of the first metal-oxide-semiconductor M1 is connected with the output of homophase device U7, and the drain electrode of the first metal-oxide-semiconductor M1 is connected with the common port of input power 11 with input filter capacitor C1, and the source electrode of the first metal-oxide-semiconductor M1 is connected with the drain electrode of the second metal-oxide-semiconductor M2 and is connected with load 20; The grid of the second metal-oxide-semiconductor M2 is connected with the output of inverter U8, the source ground of the second metal-oxide-semiconductor M2.

Particularly, output filtering module 15 comprises filter inductance L1 and output filter capacitor C2; The end of filter inductance L1 is connected with the output of switch module 14, with the source electrode of the first metal-oxide-semiconductor M1, is connected, and the other end of filter inductance L1 is connected via output filter capacitor C2 ground connection and with load 20.

Further, output feedback module 16 comprises the first feedback resistance RF1 and the second feedback resistance RF2; The end of the first feedback resistance RF1 is connected with the common port of output filter capacitor C2 with filter inductance L1, the other end of the first feedback resistance RF1 is connected with the input of driving control unit 1312, with the inverting input of operational amplifier U4, be connected, and the other end of the first feedback resistance RF1 is via the second feedback resistance RF2 ground connection.

Refer again to Fig. 5, the current waveform that Fig. 5 is voltage waveform that in Fig. 4, A, PH are ordered and the first metal-oxide-semiconductor, the second metal-oxide-semiconductor, filter inductance branch road.

In Fig. 5, V _afor the voltage waveform that in Fig. 4, voltage input end A is ordered, V _pHfor the voltage waveform that PH in Fig. 4 is ordered, I _m1be the drain electrode of the first metal-oxide-semiconductor M1, the electric current between source electrode, i.e. electric current in the first metal-oxide-semiconductor M1, I _m2be the drain electrode of the second metal-oxide-semiconductor M2, the electric current between source electrode, i.e. electric current in the second metal-oxide-semiconductor M2, I _lfor the electric current in filter inductance L1, be the output current of DC-DC circuit 10, Io is average output current, and

minimum current when wherein I1 is the first metal-oxide-semiconductor M1 conducting, maximum current when I2 is the first metal-oxide-semiconductor M1 conducting.The switching frequency of the DC-DC circuit 10 shown in Fig. 4 is f, and the cycle is T, and duty ratio is D, and the first metal-oxide-semiconductor M1 ON time is Ton, and $\mathrm{Ton}=D\×T,T=\frac{1}{f},D=\frac{\mathrm{Vout}}{\mathrm{Vin}},$ The loaded work piece voltage that wherein Vout is 10 outputs of DC-DC circuit, the input voltage that Vin provides for input power 11.

In Fig. 4, the electric current I in the first metal-oxide-semiconductor M1 _m1in the alternating component electric current will be all by input filter capacitor C1, flow to ground.If input filter capacitor C1 selects ESR(Equivalent Series Resistance, equivalent series resistance) very little ceramic condenser, the electric current I in the first metal-oxide-semiconductor M1 so _m1in the alternating component electric current when the input filter capacitor C1, will on input filter capacitor C1, produce ripple voltage.During due to the first metal-oxide-semiconductor M1 conducting, the electric current I in the first metal-oxide-semiconductor M1 _m1to increase to gradually I2 from I1, at this moment input filter capacitor C1 discharges, voltage on input filter capacitor C1 progressively drops to the lowest point, therefore can calculate the upper ripple voltage produced of input filter capacitor C1, the ripple voltage that voltage input end A is ordered (ripple voltage that voltage detection unit 1311 detects):

$\mathrm{\ΔV}=\frac{1}{\mathrm{Cin}}{\∫}_0^{\mathrm{Ton}}{I}_{M1}\mathrm{dt}$

$=\frac{1}{\mathrm{Cin}}\×S_{\mathrm{HLKJ}}$

$=\frac{1}{\mathrm{Cin}}\×(I1+I2)\×\mathrm{Ton}\×\frac{1}{2}.$

$=\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\mathrm{Ton}$

In above formula, the capacitance that Cin is input filter capacitor C1, S _hLKJarea for trapezoidal HLKJ in Fig. 5.

As can be seen here, the ripple voltage Δ V that average output current Io and voltage input end A are ordered is relevant, and voltage detection unit 1311, by detecting ripple voltage, detects the average output current of DC-DC circuit 10, and the relational expression of Io and Δ V is as follows:

$\mathrm{\ΔV}=\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\mathrm{Ton}=\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\frac{\mathrm{Vout}}{\mathrm{Vin}}\×\frac{1}{f},$

Therefore as long as voltage detection unit 1311 detects the ripple voltage that voltage input end A orders, just can the indirect detection average output current, thus at ripple voltage, occur can detecting the output current overcurrent of now exporting when abnormal, can realize overcurrent protection thus.

When the voltage of input power 11 reaches hour, be input to the voltage of the inverting input of the first voltage comparator U1:

$\mathrm{Vm}=\mathrm{Vin}-\mathrm{\ΔV}=\mathrm{Vin}-\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\mathrm{Ton},$

And due to the reference voltage of the in-phase input end that is input to the first voltage comparator U1:

Vp=Iref×Rcs。

Therefore, when Vm is less than Vp, the overcurrent protection signal Voc of the first voltage comparator U1 output is high level, and when Vm is greater than Vp, the overcurrent protection signal Voc of the first voltage comparator U1 output is low level.

In Fig. 6, the feedback voltage V f of output feedback module 16 outputs is input to the inverting input of operational amplifier U4, the reference voltage of reference voltage source U3 output is input to the in-phase input end of operational amplifier U4, after operational amplifier U4 amplifies feedback voltage V f, be input to the in-phase input end of second voltage comparator U2, in addition, the sawtooth signal of saw-toothed wave generator U5 output is input to the inverting input of second voltage comparator U2, after second voltage comparator U2 compares the feedback voltage V f after amplifying and sawtooth signal, the output square-wave signal is to the input of triple gate U6.

Because the overcurrent protection signal Voc of the first voltage comparator U1 output is input to the control Enable Pin of triple gate U6; and this triple gate U6 is Low level effective; therefore; when the overcurrent protection signal Voc of the first voltage comparator U1 output is low level; triple gate U6 enables, thereby the output of triple gate U6 is also exported square-wave signal.When this square wave signal is high level, homophase device U7 also exports high level, drives the first metal-oxide-semiconductor M1 conducting, inverter U8 output low level, the second metal-oxide-semiconductor M2 cut-off; When this square wave signal is low level, homophase device U7 is output low level also, the first metal-oxide-semiconductor M1 cut-off, and inverter U8 exports high level, drives the second metal-oxide-semiconductor M2 conducting.Hence one can see that, when the overcurrent protection signal Voc of the first voltage comparator U1 output is low level, and driving control unit 1312 output square-wave signals, driven the first metal-oxide-semiconductor M1, the second metal-oxide-semiconductor M2 conducting, make output current normally export.

When the overcurrent protection signal Voc of the first voltage comparator U1 output is high level; triple gate U6 is in high-impedance state; PWM controls and quits work; cut off the output of square-wave signal, can't drive the first metal-oxide-semiconductor M1 or the second metal-oxide-semiconductor M2 conducting, thereby there is no output current output; when overcurrent condition appears in DC-DC circuit 10; cut off the output of output current, also cut off the output of loaded work piece voltage, reach the purpose of overcurrent protection.

In summary, the over-current protection point critical current of DC-DC circuit 10 of the present invention meets:

$\left\{\begin{array}{c}\mathrm{Vm}=\mathrm{Vin}-\mathrm{\ΔV}=\mathrm{Vin}-\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\mathrm{Ton}\\ \mathrm{Vp}-\mathrm{Vm}\end{array}\right..$

Therefore, when the difference of input voltage and ripple voltage equals described reference voltage, the over-current protection point electric current of DC-DC circuit 10 equals average output current:

$\mathrm{Io}=\frac{(\mathrm{Vin}-\mathrm{Vm})\×\mathrm{Cin}}{\mathrm{Ton}}=\frac{(\mathrm{Vin}-\mathrm{Vm})\×\mathrm{Cin}}{\frac{\mathrm{Vout}}{\mathrm{Vin}}\×\frac{1}{f}}=\frac{(\mathrm{Vin}-\mathrm{Vm})\×\mathrm{Vin}\×f\×\mathrm{Cin}}{\mathrm{Vout}},$

The over-current protection point critical current that is DC-DC circuit 10 meets:

$\left\{\begin{array}{c}\mathrm{Vp}=\mathrm{Iref}\×\mathrm{Rcs}\\ \mathrm{Vm}=\mathrm{Vin}-\mathrm{\ΔV}=\mathrm{Vin}-\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\mathrm{Ton}\\ \mathrm{Vp}=\mathrm{Vm}\end{array}\right.,$

When the difference of input voltage and ripple voltage equals described reference voltage, the over-current protection point electric current of DC-DC circuit 10 is:

$\mathrm{Io}=\frac{(\mathrm{Vin}-\mathrm{Iref}\×\mathrm{Rcs})\×\mathrm{Cin}}{\mathrm{Ton}}=\frac{(\mathrm{Vin}-\mathrm{Iref}\×\mathrm{Rcs})\×\mathrm{Cin}}{\frac{\mathrm{Vout}}{\mathrm{Vin}}\×\frac{1}{f}}=\frac{(\mathrm{Vin}-\mathrm{Iref}\×\mathrm{Rcs})\×\mathrm{Vin}\×f\×\mathrm{Cin}}{\mathrm{Vout}}.$

From above formula; by different Rcs and Cin are set; different over-current protection point electric currents can be set; thereby in practical application according to the specific requirement of 10 pairs of overcurrent protections of DC-DC circuit; by choosing the value of suitable sample resistance RS and input filter capacitor C1, meet the specific requirement of 10 pairs of overcurrent protections of DC-DC circuit.

With respect to prior art; DC-DC circuit 10 of the present invention is in the inner integrated voltage detection unit 1311 of PWM controller 131 and driving control unit 1312; detect ripple voltage by the first voltage comparator U1 in voltage detection unit 1311; realize the detection to average output current; thereby can be by detecting the ripple voltage in DC-DC circuit 10; whether the output current that judges DC-DC circuit 10 output overcurrent; with when the output current overcurrent; controlling driving control unit 1312 quits work; cut off the output of output current, realize overcurrent protection.

The present invention also proposes a kind of over-current protection method of DC-DC circuit.

With reference to Fig. 7, the schematic flow sheet of the over-current protection method preferred embodiment that Fig. 7 is DC-DC circuit of the present invention.

In preferred embodiment of the present invention, the over-current protection method of DC-DC circuit comprises the following steps:

Step S10: voltage comparison unit detects the ripple voltage in the input filter module.

Step S20: the difference of input voltage and the described ripple voltage that detects and default reference voltage are compared and obtain comparative result.

Whether step S30: the overcurrent protection signal that will be generated by comparative result is sent to driving control unit, to control output current, export.

The over-current protection method of the present embodiment is the over-current protection method corresponding with the DC-DC circuit of the invention described above, in the present embodiment, the input power of input voltage in the DC-DC circuit provides, when in the switch module of ripple voltage in the DC-DC circuit, the alternating component of electric current is flowed through the input filter module, produce, the DC-DC circuit is in the inner integrated voltage detection unit of PWM controller and driving control unit, detect the ripple voltage in the input filter module by voltage detection unit, the difference of input voltage and ripple voltage and default reference voltage are compared, and according to comparative result output overcurrent guard signal, whether by this output overcurrent guard signal, control output current exports, with when overcurrent condition appears in the DC-DC circuit, cut off the output of output current, reach the purpose of overcurrent protection.

Particularly, step S30 is specially:

When the difference of input voltage and ripple voltage is greater than default reference voltage, generate low level overcurrent protection signal and be sent to driving control unit, to control output current, normally export; When the difference of input voltage and ripple voltage is less than default reference voltage, the overcurrent protection signal that generates high level is sent to driving control unit, to cut off the output of output current.

Therefore; when the ripple voltage detected becomes large, the difference of input voltage and ripple voltage diminishes, when the output current overcurrent; the difference of input voltage and ripple voltage is less than reference voltage; the overcurrent protection signal generated is high level, cuts off the output of output current, thereby can be by detecting the ripple voltage in the DC-DC circuit; whether the output current that judges DC-DC circuit output overcurrent; with when the output current overcurrent, cut off the output of output current, realize overcurrent protection.

The foregoing is only the preferred embodiments of the present invention; not thereby limit the scope of the claims of the present invention; every equivalent structure or conversion of equivalent flow process that utilizes specification of the present invention and accompanying drawing content to do; or directly or indirectly be used in other relevant technical fields, all in like manner be included in scope of patent protection of the present invention.

Claims (10)

1. a DC-DC circuit, be connected with load, comprise input power, input filter module, PWM control module and switch module, it is characterized in that, described PWM control module comprises the PWM controller, and described PWM controller comprises voltage detection unit and driving control unit;

Described input power is connected with the input of described voltage detection unit, the input of described switch module respectively via described input filter module; The output of described voltage detection unit is connected with the control end of described driving control unit, the input of described driving control unit is connected with the output of described switch module, the output of described driving control unit is connected with the control end of described switch module, and the output of described switch module is connected with described load;

Described voltage detection unit detects the ripple voltage in described input filter module; the input voltage that described input power is provided and the difference of described ripple voltage and default reference voltage compare; and according to comparative result output overcurrent guard signal; control described driving control unit and whether drive described switch module, whether export to control output current.

2. DC-DC circuit as claimed in claim 1, is characterized in that, described PWM control module also comprises feeder ear and sample resistance; One end of described sample resistance is connected with described feeder ear and is connected with the reference edge of described voltage detection unit, the other end ground connection of described sample resistance.

3. DC-DC circuit as claimed in claim 2, is characterized in that, described voltage detection unit comprises constant-current source and the first voltage comparator; The in-phase input end of described the first voltage comparator is connected with described feeder ear via described constant-current source and via described sample resistance ground connection, the inverting input of described the first voltage comparator is connected with described input filter module with described input power respectively, and the output of described the first voltage comparator is connected with the control end of described driving control unit.

4. DC-DC circuit as claimed in claim 3, is characterized in that, described driving control unit comprises reference voltage source, operational amplifier, saw-toothed wave generator, second voltage comparator, triple gate, homophase device and inverter;

The in-phase input end of described operational amplifier is connected with described reference voltage source, the inverting input of described operational amplifier is connected with the output of described switch module, and the output of described operational amplifier is connected with the in-phase input end of described second voltage comparator; The inverting input of described second voltage comparator is connected with the signal output part of described saw-toothed wave generator, and the output of described second voltage comparator is connected with the input of described triple gate; The control Enable Pin of described triple gate is connected with the output of described the first voltage comparator, the output of described triple gate is connected with the input of described homophase device, the input of described inverter respectively, and the output of described homophase device, the output of described inverter all are connected with the control end of described switch module.

5. DC-DC circuit as claimed in claim 4, is characterized in that, described input filter module comprises input filter capacitor; One end of described input filter capacitor is connected with the positive pole of described input power, and with the inverting input of the first voltage comparator, the input of described switch module, be connected respectively, the other end ground connection of described input filter capacitor, the minus earth of described input power;

Described switch module comprises the first metal-oxide-semiconductor and the second metal-oxide-semiconductor; The grid of described the first metal-oxide-semiconductor is connected with the output of described homophase device, the drain electrode of described the first metal-oxide-semiconductor is connected with the common port of described input filter capacitor and described input power, and the source electrode of described the first metal-oxide-semiconductor is connected with the drain electrode of described the second metal-oxide-semiconductor and is connected with described load; The grid of described the second metal-oxide-semiconductor is connected with the output of described inverter, the source ground of described the second metal-oxide-semiconductor.

6. DC-DC circuit as claimed in claim 5, it is characterized in that, the loaded work piece voltage of described DC-DC circuit output is Vout, the input voltage that described input power provides is Vin, the ripple voltage that described voltage detection unit detects is Δ V, described voltage detection unit, by detecting described ripple voltage, detects the average output current of described DC-DC circuit, and the relational expression of Io and Δ V is as follows:

$\mathrm{\ΔV}=\frac{1}{\mathrm{Cin}}\×\mathrm{Io}\×\frac{\mathrm{Vout}}{\mathrm{Vin}}\×\frac{1}{f},$

Wherein, the capacitance that Cin is described input filter capacitor, the switching frequency that f is described DC-DC circuit.

7. DC-DC circuit as claimed in claim 6; it is characterized in that; the difference of described input voltage and described ripple voltage is Vm; described reference voltage is Vp; when the difference of described input voltage and described ripple voltage equals described reference voltage, the over-current protection point critical current of described DC-DC circuit equals average output current:

$\mathrm{Io}=\frac{(\mathrm{Vin}-\mathrm{Vm})\×\mathrm{Vin}\×f\×\mathrm{Cin}}{\mathrm{Vout}}.$

8. DC-DC circuit as claimed in any of claims 1 to 7 in one of claims, it is characterized in that, described DC-DC circuit also comprises output filtering module and output feedback module, described output filtering module is connected between the output and described load of described switch module, and described output feedback module is connected between the input of the output of described output filtering module and described driving control unit;

Described output filtering module comprises filter inductance and output filter capacitor; One end of described filter inductance is connected with the output of described switch module, and the other end of described filter inductance is connected via described output filter capacitor ground connection and with described load;

Described output feedback module comprises the first feedback resistance and the second feedback resistance; One end of described the first feedback resistance is connected with the common port of described filter inductance and described output filter capacitor, and the other end of described the first feedback resistance is connected with the input of described driving control unit and via described the second feedback resistance ground connection.

9. the over-current protection method of a DC-DC circuit, is characterized in that, comprises the following steps:

Voltage comparison unit detects the ripple voltage in the input filter module;

The difference of input voltage and the described ripple voltage that detects and default reference voltage are compared and obtain comparative result;

Whether the overcurrent protection signal that will be generated by comparative result is sent to driving control unit, to control output current, export.

10. whether over-current protection method as claimed in claim 9, is characterized in that, the described overcurrent protection signal that will be generated by comparative result is sent to driving control unit, with the control output current, export and be specially:

When the difference of input voltage and ripple voltage is greater than default reference voltage, generate low level overcurrent protection signal and be sent to driving control unit, to control output current, normally export;

When the difference of input voltage and ripple voltage is less than default reference voltage, the overcurrent protection signal that generates high level is sent to driving control unit, to cut off the output of output current.

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