CN102361402B - Switching power supply circuit - Google Patents
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- CN102361402B CN102361402B CN 201110323717 CN201110323717A CN102361402B CN 102361402 B CN102361402 B CN 102361402B CN 201110323717 CN201110323717 CN 201110323717 CN 201110323717 A CN201110323717 A CN 201110323717A CN 102361402 B CN102361402 B CN 102361402B
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Abstract
The invention discloses a switching power supply circuit, which comprises a starting circuit, a pulse width modulation (PWM) controller, a starting turn-off circuit, a main power tube and a main transformer, wherein the starting turn-off circuit comprises a first resistor, a turn-off triode, a charging capacitor, a first voltage sharing resistor and a second voltage sharing resistor; a connection point between the current sampling end of the PWM controller and a source of the main power tube is connected to the voltage reference end of the starting circuit through the first resistor; one circuit of the output end of the PWM controller is connected to the voltage reference end of the starting circuit through the charging capacitor and the other circuit of the output end of the PWM controller is connected to the voltage reference end of the starting circuit through the first voltage sharing resistor and the second voltage sharing resistor sequentially; a connection point between the first voltage sharing resistor and the second voltage sharing resistor is connected to a base of the turn-off triode; a collector of the turn-off triode is connected to the control end of the starting circuit; and an emitter of the turn-off triode is connected to the voltage reference end of the starting circuit.
Description
Technical field
The present invention relates to a kind of switching power circuit, particularly a kind ofly can when output short-circuit, produce the switching power circuit of less short-circuit dissipation.
Background technology
In the power electronic systems such as photovoltaic DC-to-AC converter, high voltage converter, all need accessory power supply output low-voltage DC to its control section power supply, and the non-constant width of power input voltage range of this system, be low to moderate one or two hectovolt, up to upper kilovolt.For the like this wide Switching Power Supply of power input voltage range, the more difficult design of its start-up circuit, because the start-up time will take into account the low pressure input time, startup line loss during normal operation, and the indexs such as short-circuit dissipation during output short-circuit.
As shown in Figure 1, in prior art, a kind of switching power circuit that is used in high pressure, wide voltage input occasion, comprise start-up circuit A1, filtering output circuit A2, start switch off control circuit A3, PWM controller, main power tube Qa, diode D2 and main transformer T1.
Start-up circuit A1 comprises power consumption resistance R 1, divider resistance R2, voltage stabilizing didoe ZD1, voltage stabilizing didoe ZD2, high-voltage MOS pipe Q2, diode D4 and filter capacitor C1, the end of divider resistance R2 is connected to the negative electrode of voltage stabilizing didoe ZD2, the other end is connected to the drain electrode of high-voltage MOS pipe Q2 by power consumption resistance R 1, the utmost point of deleting of high-voltage MOS pipe Q2 is connected with the negative electrode of voltage stabilizing didoe ZD2, the source electrode of high-voltage MOS pipe Q2 is connected to the anode of voltage stabilizing didoe ZD2 successively by diode D4 and voltage stabilizing didoe ZD1, wherein diode D4 is connected with the negative electrode of voltage stabilizing didoe ZD1, filter capacitor C1 and voltage stabilizing didoe ZD1 are in parallel, the voltage input end VIN that the tie point of divider resistance R2 and power consumption resistance R 1 is switching power circuit, the Voltage Reference end that the anode of voltage stabilizing didoe ZD2 is switching power circuit, the control end that the grid of high-voltage MOS pipe Q2 is start-up circuit A1, the output that the negative electrode of voltage stabilizing didoe ZD1 is start-up circuit A1.
Start the A3 that switches off control circuit and comprise resistance R a, triode Q1, diode D1, resistance R 3, resistance R 4, voltage-stabiliser tube ZD3 and filter capacitor C2, power input VCC mono-tunnel of PWM controller is connected to the output of start-up circuit A1, and another road is connected to the Same Name of Ends of the auxiliary winding Nt of main transformer T1 successively by diode D1 and diode D2, and wherein the anode of diode D1 is connected with the negative electrode of D2, the negative electrode of diode D2 is leaded up to filter capacitor C2 and is connected to the emitter of triode Q1, another road is successively by voltage-stabiliser tube ZD3, resistance R 4 and resistance R 3 are connected to the emitter of triode Q1, wherein voltage-stabiliser tube ZD3 is connected with the negative electrode of diode D2, the tie point of resistance R 3 and resistance R 4 is connected to the base stage of triode Q1, the collector electrode of triode Q1 is connected to the control end of start-up circuit A1, the source electrode of main power tube Qa is connected to the anode of voltage stabilizing didoe ZD2 by resistance R a, the output OUTPUT of PWM controller is connected with the grid of main power tube Qa, the current sampling end CS of PWM controller is connected to the source electrode of main power tube Qa, the Voltage Reference end GND of PWM controller, the different name end of the emitter of triode Q1 and auxiliary winding Nt all is connected to the anode of voltage stabilizing didoe ZD2, the drain electrode of main power tube Qa is connected to the Same Name of Ends of the former limit of main transformer T1 winding Np, the different name end of the former limit of main transformer T1 winding Np is connected to the tie point of divider resistance R2 and power consumption resistance R 1, the secondary winding Ns of main transformer T1 is the output of switching power circuit, and it also can be exported by filtering output circuit A2.The said PWM controller can adopt the PWM that existing model is UC3843 to control the PWM controller that has above-mentioned pin function in IC or prior art.
The operation principle of switching power circuit shown in Fig. 1 is as follows:
The operation principle of start-up circuit A1 is as be: after voltage input end VIN powers on, power supply provides voltage by divider resistance R2 to voltage stabilizing didoe ZD2, the voltage of voltage stabilizing didoe ZD2 drives high-voltage MOS pipe Q2 conducting, two branch roads is arranged by the work of filter capacitor C1 charge initiation PWM controller: the one, and power supply passes through power consumption resistance R 1, high-voltage MOS pipe Q2, diode D4 charge to filter capacitor C1; The 2nd, the auxiliary winding Nt of main transformer T1 is by diode D2, D1 to filter capacitor C1 charging, and when the Switching Power Supply output short-circuit, auxiliary winding Nt no-output, therefore only have last branch road to charge to filter capacitor C1.After the voltage of filter capacitor C1 rises to the cut-in voltage point of PWM controller, the PWM controller is started working, its output OUTPUT output pulse width modulation voltage.The size of power consumption resistance R 1 and filter capacitor C1 has determined that the power input VCC voltage of PWM controller reaches the time of its cut-in voltage.In addition, the start-up circuit of this switching power circuit also can adopt other circuit forms that comprise above-mentioned start-up circuit A1 function in prior art, as high-voltage MOS pipe Q2 adopts triode, substitutes, and it realizes that principle is with noted earlier identical, and this is no longer going to repeat them.
The operation principle that starts the A3 that switches off control circuit is: after the cut-in voltage point of the voltage arrival PWM controller that start-up circuit A1 provides, the PWM controller is started working, its output OUTPUT output pulse width modulated voltage signal.When pulse width modulation voltage is high level, main power tube Qa conducting, the former limit winding Np voltage of main transformer T1 is upper just lower negative, according to transformer Same Name of Ends relation, secondary winding Ns voltage be upper negative under just, not conducting of diode D5, a main transformer T1 energy storage, no-output; When pulse width modulation voltage is low level, main power tube Qa turn-offs, the former limit winding Np voltage of main transformer T1 become upper negative under just, according to main transformer T1 Same Name of Ends relation, secondary winding Ns voltage is upper just lower negative, diode D5 conducting, and main transformer T1 releases energy, voltage is provided to output circuit and auxiliary winding Nt, starts working thereby drive starts the A3 that switches off control circuit.Now, the auxiliary output voltage climbed of winding Nt after diode D2 and filter capacitor C2 rectifying and wave-filtering, after its voltage is greater than the voltage stabilizing value of voltage-stabiliser tube ZD3, triode Q1 conducting, thereby drag down the grid potential of high-voltage MOS pipe Q2, high-voltage MOS pipe Q2 turn-offs, cut off start-up circuit A1, diode D4 can prevent the breakdown damage of high-voltage MOS pipe Q2, at this moment the supply power voltage of PWM controller is provided by auxiliary winding Nt, start-up circuit A1 disconnects fully, and start-up circuit A1 does not produce loss when normal operation.
But, there is following shortcoming in switching power circuit shown in Fig. 1: when the circuit output short-circuit, in switch periods each time, when the voltage that the PWM controller detects its current sampling end CS reaches its threshold voltage (UC3843 is 1V), the output that its output OUTPUT turn-offs the pulse width modulation voltage signal immediately, prevent the saturated and main power tube Qa overcurrent of main transformer T1.During due to output short-circuit, auxiliary winding Nt is also not output, so the upper no-voltage of filter capacitor C2, and triode Q1 can conducting, and start-up circuit A1 will work always, and the loss on power consumption resistance R 1 will be very high.The occasion of particularly inputting at high pressure, wide voltage, the accessory power supply that is the 100V-1000V direct current for input range, startup time expand while wanting to make the 100V input, be unlikely to excessive, power consumption resistance R 1 resistance need be got and is no more than 100K Ω, in the situation of 1000V input, the loss on power consumption resistance R 1 will reach like this
power consumption resistance R 1 must be selected the very large cement resistor of volume like this, its power consumption is excessive (under normal circumstances simultaneously, the short-circuit dissipation of accessory power supply need be controlled at about 1～2W), the short-circuit dissipation index while not meeting output short-circuit, affect the reliability of whole power electronic system.
Summary of the invention
The purpose of this invention is to provide a kind of switching power circuit, can when output short-circuit, produce less short-circuit dissipation.
The objective of the invention is to realize by following technical measures: a kind of switching power circuit, comprise start-up circuit, the PWM controller, startup switches off control circuit, main power tube and main transformer, input voltage is input to the power input of PWM controller by start-up circuit, the output output pulse width modulation signal of PWM controller, control main power tube work and pass through the main transformer output voltage, when the switching power circuit output short-circuit, start the control end of output cut-off signals to start-up circuit that switch off control circuit, described startup switches off control circuit and comprises the first resistance, turn-off triode, charging capacitor, the first divider resistance and the second divider resistance, the tie point of described PWM controller current sampling end and described main power tube source electrode is connected to the Voltage Reference end of described start-up circuit by the first resistance, the output of described PWM controller is leaded up to charging capacitor and is connected to the Voltage Reference end of described start-up circuit, another road is connected to the Voltage Reference end of described start-up circuit successively by the first divider resistance and the second divider resistance, the tie point of the first divider resistance and the second divider resistance is connected to the base stage of turn-offing triode, the collector electrode that turn-offs triode is connected to the control end of described start-up circuit, the emitter that turn-offs triode is connected to the Voltage Reference end of described start-up circuit.
In order to limit the electric current of described charging capacitor, described startup switches off control circuit and also comprises for limiting the second resistance of described charging capacitor charging current; The output of described PWM controller is connected to the tie point of described charging capacitor and the first divider resistance by the second resistance.
In order to cut off described startup, switch off control circuit to the interference of PWM controller output end, described startup switches off control circuit and also comprises the first diode described PWM controller output end disturbed for cutting off described startup breaking circuit; The first diode is connected between the output and described the second resistance of described PWM controller, and wherein the negative electrode of the first diode is connected with described the second resistance.
A kind of execution mode as invention, also comprise the filtering output circuit; The filtering output circuit is connected to the secondary winding two ends of main transformer.
Purpose of the present invention also can realize by following technical measures:
A kind of switching power circuit, comprise start-up circuit, the PWM controller, startup switches off control circuit, main power tube and main transformer, input voltage is input to the power input of PWM controller by start-up circuit, the output output pulse width modulation signal of PWM controller, control main power tube work and pass through the main transformer output voltage, when the switching power circuit output short-circuit, start the control end of output cut-off signals to start-up circuit that switch off control circuit, described startup switches off control circuit and comprises the first resistance, turn-off triode, charging capacitor, the first divider resistance and the second divider resistance, the tie point of described PWM controller current sampling end and described main power tube source electrode is connected to the Voltage Reference end of described start-up circuit by the first resistance, the reference voltage terminal of described PWM controller is leaded up to charging capacitor and is connected to the Voltage Reference end of described start-up circuit, another road is connected to the Voltage Reference end of described start-up circuit successively by the first divider resistance and the second divider resistance, the tie point of the first divider resistance and the second divider resistance is connected to the base stage of turn-offing triode, the collector electrode that turn-offs triode is connected to the control end of described start-up circuit, the emitter that turn-offs triode is connected to the Voltage Reference end of described start-up circuit.
Than prior art, the present invention has following technique effect:
Owing to having adopted above-mentioned startup to switch off control circuit, by charging capacitor is set, the first divider resistance, the size of the second divider resistance, the holding time of voltage on charging capacitor during the controllable switch power circuit short, the drive circuit that voltage on charging capacitor forms by the first divider resistance and the second divider resistance is controlled and is turn-offed turning on and off of triode, thereby control turning on and off of start-up circuit, service time by shortening start-up circuit and reduce the average power consumption of start-up circuit when output short-circuit, and then reduce the short-circuit dissipation of whole Switching Power Supply, and not there will be in prior art when the switching power circuit output short-circuit, start-up circuit is because keeping opening the situation that causes producing severe attrition.So switching power circuit of the present invention is applicable to being applied in high pressure, wide voltage input occasion, and there are the characteristics of low output short-circuit power consumption, meet the short-circuit dissipation index of accessory power supply when output short-circuit, can guarantee the reliability of power electronic system work.
The accompanying drawing explanation
Below in conjunction with the drawings and specific embodiments, the present invention is described in further detail.
The circuit theory diagrams that Fig. 1 is the prior art switching power circuit;
The theory diagram that Fig. 2 is the embodiment of the present invention one;
The circuit theory diagrams that Fig. 3 is the embodiment of the present invention one;
Fig. 4 is for the switching power circuit for the embodiment of the present invention one under the input of 800V direct current, and the work period of its PWM controller schemes;
The circuit theory diagrams that Fig. 5 is the embodiment of the present invention two;
Embodiment
Fig. 2 and Fig. 3 show the switching power circuit of the embodiment of the present invention one, mainly comprise start-up circuit A1, filtering output circuit A2, start switch off control circuit A4, PWM controller, main power tube Qa and main transformer T1.Wherein: start-up circuit A1, filtering output circuit A2, main power tube Qa and main transformer T1 are identical with structure composition and the annexation of switching power circuit shown in Fig. 1, in this explanation no longer one by one.
Shown in the switching power circuit of the embodiment of the present invention one and Fig. 1, the difference of switching power circuit is: start the A4 that switches off control circuit and comprise the first resistance R a, the first diode D3, the second resistance R 7, turn-off triode Q3, charging capacitor C3, the first divider resistance R5 and the second divider resistance R6, the tie point of described PWM controller current sampling end CS and described main power tube source electrode is connected to the Voltage Reference end of described start-up circuit by the first resistance R a, it is the Voltage Reference end of switching power circuit, the output OUTPUT of described PWM controller is successively by the first diode D3, the second resistance R 7 and charging capacitor C3 are connected to the Voltage Reference end of described start-up circuit, wherein the negative electrode of the first diode D3 is connected with the second resistance R 7, the tie point A of the second resistance R 7 and charging capacitor C3 is connected to the Voltage Reference end of described start-up circuit successively by the second divider resistance R6 and the first divider resistance R5, the tie point of the first divider resistance R5 and the second divider resistance R6 is connected to the base stage of turn-offing triode Q3, the collector electrode that turn-offs triode Q3 is connected to the control end of described start-up circuit, it is the grid of high-voltage MOS pipe Q2, the emitter of triode is connected to the Voltage Reference end of described start-up circuit.
The said PWM controller can adopt the PWM that existing model is UC3843 to control the PWM controller that has above-mentioned pin function in IC or prior art.
In addition, the start-up circuit of this switching power circuit also can adopt other circuit forms that comprise above-mentioned start-up circuit A1 function in prior art, as high-voltage MOS pipe Q2 adopts triode, substitutes, and it realizes that principle is with noted earlier identical, and this is no longer going to repeat them.
The operation principle of the switching power circuit of the embodiment of the present invention one is:
After the cut-in voltage point of the voltage arrival PWM controller that start-up circuit A1 provides, the PWM controller is started working, the voltage of its output OUTPUT is given charging capacitor C3 charging by the first diode D3, the second resistance R 7, voltage on charging capacitor C3 drives by the second divider resistance R6 and the first divider resistance R5 the triode Q3 conducting work of turn-offing again, thereby drag down the grid potential of high-voltage MOS pipe Q2, high-voltage MOS pipe Q2 cut-off, start-up circuit A1 quits work.Because the output current of output OUTPUT is limited in one's ability, the effect of the second resistance R 7 is charging currents of restriction charging capacitor C3.When power supply works, the crest voltage of the output OUTPUT output pulse width modulated voltage signal that the voltage on charging capacitor C3 is the PWM controller, approximate the VCC magnitude of voltage of PWM controller, at this moment turn-off triode Q3 conducting, high-voltage MOS pipe Q2 cut-off, start-up circuit A1 does not work always, and start-up circuit does not have loss substantially.
When the switching power circuit output short-circuit, in switch periods each time, when the voltage that the PWM controller detects its current sampling end CS reaches its threshold voltage (UC3843 is 1V), output OUTPUT turn-offs the output of pulse width modulating signal immediately, thereby main power tube Qa cut-off, prevented that main power tube Qa overcurrent and main transformer T1 are saturated.Due to start-up circuit quit work and during output short-circuit auxiliary winding Nt do not export, so the voltage of the power input VCC of PWM controller meeting continuous decrease, when the VCC voltage drop during to under-voltage of PWM controller, the PWM controller quits work, the complete no-output of its output OUTPUT, owing to now on charging capacitor C3, still having voltage, so turn-off still conducting of triode Q3, but charging capacitor C3 noenergy supply, so the voltage of charging capacitor C3 can slowly descend, by the time the voltage on charging capacitor C3 drops to while being not enough to make to turn-off triode Q3 conducting, the grid potential of high-voltage MOS pipe Q2 returns to the voltage of voltage regulation of voltage stabilizing didoe ZD2, high-voltage MOS pipe Q2 conducting, start-up circuit A1 starts working again, voltage is provided to the power input VCC of PWM controller, and when VCC voltage reaches its cut-in voltage, the PWM controller starts again work, its output OUTPUT output pulse width modulation voltage provides voltage to charging capacitor C3, turn-off triode Q3 conducting, thereby again turn-off start-up circuit A1, simultaneously due to output short-circuit VCC voltage continuous decrease again, so repeat said process, until switching power circuit output breaks away from short-circuit condition, switching power circuit recovers normal operation.
In addition, the embodiment of the present invention one is identical with the operation principle of start-up circuit A1 in the switching power circuit shown in Fig. 1, does not repeat them here.
In the invention described above embodiment mono-, for the second resistance R 7 of limiting described charging capacitor charging current, can save, can realize equally the achieved purpose of the present invention of the embodiment of the present invention one, its principle is identical with the operation principle of above-described embodiment one.
As shown in Figure 4, for the switching power circuit of the embodiment of the present invention one under the input of 800V direct current, the work period figure of its PWM controller.When the switching power circuit output short-circuit, in the one-period of PWM controller repeated priming, t0 start-up circuit A1 constantly starts the power input VCC charging to the PWM controller, after to t1, power input VCC voltage reaches PWM controller start-up point constantly, start working, power input VCC voltage reduces gradually afterwards, drop to the under-voltage point of PWM controller to t2 moment power input VCC voltage, the t3 upper voltage of charging capacitor C3 constantly is not enough to conducting shutoff triode Q3, and start-up circuit A1 starts again to charge to power input VCC, so the operating time of start-up circuit A1 is ta (ta=t1-t0), be tb+tc the opening time of start-up circuit A1, when the input voltage of the voltage input end VIN of switching power circuit is 800V, during the operating time of start-up circuit A1 ta, start-up circuit A1 power consumption is
so need guarantee tb+tc " ta just can make the average power consumption of start-up circuit A1 in zone of reasonableness, and ta is by cut-in voltage and the decision of under-voltage point of charging current, filter capacitor C1 and the PWM controller of start-up circuit A1, charging current is determined by input voltage, the power consumption resistance R 1 of voltage input end VIN, when power consumption resistance R 1 is got 100K ohm, the electric current on power consumption resistance R 1 is
be that charging current is 8mA, tb is by the current sinking of PWM controller work, the cut-in voltage of filter capacitor C1 value and PWM controller and under-voltage point determine, during work, the current sinking of PWM controller is also in 7～8mA left and right, so tb approximates ta under normal circumstances, so want tb+tc " ta, the time of tc is very crucial, and the value of tb+tc is by charging capacitor C3, the second divider resistance R6 and the first divider resistance R5 determine, charging capacitor C3 appearance value is larger, stored energy is more, its voltage is longer release time, the value of choose reasonable the second divider resistance R6 and the first divider resistance R5 under the condition that meets shutoff triode Q3 drive current, divider resistance R6 and divider resistance R5 are larger, the upper voltage of charging capacitor C3 is longer release time, the tb+tc time is longer, the average power consumption of start-up circuit A1 is less.So by the value of choose reasonable charging capacitor C3, the second divider resistance R6 and the first divider resistance R5, can determine the time of tb+tc, reduce the average power consumption of start-up circuit A1 during output short-circuit.In figure, can find out, " tb+tc, so its short-circuit dissipation is in tolerance interval for ta.
Fig. 5 shows the switching power circuit of the embodiment of the present invention two, comprises start-up circuit A1, filtering output circuit A2, starts switch off control circuit A5, PWM controller, main power tube Qa, the second diode D2 and main transformer T1.The embodiment of the present invention two is basic identical with the switching power circuit of embodiment mono-, and its annexation difference is: start in the A5 that switches off control circuit, the anodic bonding of the first diode D3 is to the reference voltage terminal Vref of PWM controller.The embodiment of the present invention two is basic identical with the operation principle of embodiment mono-, its difference is: when the voltage of power input VCC reaches the cut-in voltage of PWM controller, fixing 5V voltage of its reference voltage terminal Vref output can drag down the grid potential of high-voltage MOS pipe Q2 by the startup A5 that switches off control circuit, when the VCC lower voltage, during to under-voltage of PWM controller, the voltage of reference voltage terminal Vref can stop output.
Above content is in conjunction with concrete preferred implementation further description made for the present invention, can not assert that specific embodiment of the invention is confined to these explanations.For the general technical staff of the technical field of the invention, without departing from the inventive concept of the premise, can also make some simple deductions and replacement, all should be considered as protection scope of the present invention.
Claims (8)
1. a switching power circuit, comprise start-up circuit, the PWM controller, startup switches off control circuit, main power tube and main transformer, input voltage is input to the power input of PWM controller by start-up circuit, the output output pulse width modulation signal of PWM controller, control main power tube work and pass through the main transformer output voltage, when the switching power circuit output short-circuit, start the control end of output cut-off signals to start-up circuit that switch off control circuit, it is characterized in that: described startup switches off control circuit and comprises the first resistance, turn-off triode, charging capacitor, the first divider resistance and the second divider resistance, the tie point of described PWM controller current sampling end and described main power tube source electrode is connected to the Voltage Reference end of described start-up circuit by the first resistance, the output of described PWM controller is leaded up to charging capacitor and is connected to the Voltage Reference end of described start-up circuit, another road is connected to the Voltage Reference end of described start-up circuit successively by the first divider resistance and the second divider resistance, the tie point of the first divider resistance and the second divider resistance is connected to the base stage of turn-offing triode, the collector electrode that turn-offs triode is connected to the control end of described start-up circuit, the emitter that turn-offs triode is connected to the Voltage Reference end of described start-up circuit.
2. switching power circuit according to claim 1, it is characterized in that: described startup switches off control circuit and also comprises for limiting the second resistance of described charging capacitor charging current; The output of described PWM controller is connected to the tie point of described charging capacitor and the first divider resistance by the second resistance.
3. switching power circuit according to claim 2, it is characterized in that: described startup switches off control circuit and also comprises the first diode that switches off control circuit described PWM controller output end is disturbed for cutting off described startup; The first diode is connected between the output and described the second resistance of described PWM controller, and wherein the negative electrode of the first diode is connected with described the second resistance.
4. according to the described switching power circuit of arbitrary claim in claim 1～3, it is characterized in that: also comprise the filtering output circuit; The filtering output circuit is connected to the secondary winding two ends of main transformer.
5. a switching power circuit, comprise start-up circuit, the PWM controller, startup switches off control circuit, main power tube and main transformer, input voltage is input to the power input of PWM controller by start-up circuit, the output output pulse width modulation signal of PWM controller, control main power tube work and pass through the main transformer output voltage, when the switching power circuit output short-circuit, start the control end of output cut-off signals to start-up circuit that switch off control circuit, it is characterized in that: described startup switches off control circuit and comprises the first resistance, turn-off triode, charging capacitor, the first divider resistance and the second divider resistance, the tie point of described PWM controller current sampling end and described main power tube source electrode is connected to the Voltage Reference end of described start-up circuit by the first resistance, the reference voltage terminal of described PWM controller is leaded up to charging capacitor and is connected to the Voltage Reference end of described start-up circuit, another road is connected to the Voltage Reference end of described start-up circuit successively by the first divider resistance and the second divider resistance, the tie point of the first divider resistance and the second divider resistance is connected to the base stage of turn-offing triode, the collector electrode that turn-offs triode is connected to the control end of described start-up circuit, the emitter that turn-offs triode is connected to the Voltage Reference end of described start-up circuit.
6. switching power circuit according to claim 5, it is characterized in that: described startup switches off control circuit and also comprises for limiting the second resistance of described charging capacitor charging current; The reference voltage terminal of described PWM controller is connected to the tie point of described charging capacitor and the first divider resistance by the second resistance.
7. switching power circuit according to claim 6, it is characterized in that: described startup switches off control circuit and also comprises the first diode that switches off control circuit described PWM controller output end is disturbed for cutting off described startup; The first diode is connected between the reference voltage terminal and described the second resistance of described PWM controller, and wherein the negative electrode of the first diode is connected with described the second resistance.
8. according to the described switching power circuit of arbitrary claim in claim 5～7, it is characterized in that: also comprise the filtering output circuit; The filtering output circuit is connected to the secondary winding two ends of main transformer.
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| CN 201110323717 CN102361402B (en) | 2011-10-21 | 2011-10-21 | Switching power supply circuit |
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| CN 201110323717 CN102361402B (en) | 2011-10-21 | 2011-10-21 | Switching power supply circuit |
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