CN100433489C - Overpower protector of self-excitation power supply - Google Patents

Abstract

The present invention relates to an overpower protective apparatus of a self-excited power supplier. The present invention comprises a flexibility startup unit, an adjustment unit and a timing unit, wherein the flexibility startup unit is used for generating a compensation signal. The pulse width modulation unit of the self-excited power supplier generates a switching signal in order to control the output power of the self-excited power supplier. The flexibility startup unit is coupled with the adjustment unit. When the output terminal of the self-excited power supplier has short circuit and overload, the adjustment unit drives the flexibility startup unit to further drive the pulse width modulation unit to modulate the switching signal in order to reduce the pulse wave width of the switching signal and reduce the output power of the self-excited power supplier, and the timing unit counts simultaneously. If the output power is too large for a period of time, the timing unit drives the self-excited power supplier to stop supplying powder.

Description

The overpower protection of self-excitation power supply device

Technical field:

The invention relates to a kind of overpower protection, be meant the overpower protection of self-excitation power supply device especially.

Background technology:

Press, in the power supply unit of present desktop computer, the self-excitation power supply device is used widely, so that stable output voltage and the electric current of adjusting to be provided.The self-excitation power supply device is main application circuit with auto-excitation type semi-bridge type power supply unit, and its circuit diagram as shown in Figure 1.Known auto-excitation type semi-bridge type power supply unit includes a primary side circuit, a main transformer T ₁, a secondary side circuit, an overpower circuit for detecting and a driving transformer T ₂, wherein the primary side circuit includes an electric capacity of voltage regulation C ₁, an electric capacity of voltage regulation C ₂, one go up bridge power transistor Q ₃, one go up bridge drive circuit 32, a following bridge power transistor Q ₄, following bridge drive circuit 42 and one intercepts capacitor C _BThe secondary side circuit then includes an outputting inductance L ₀, an output capacitance C ₀, a divider resistance R ₀₁, a divider resistance R ₀₂, a PWM controller 100 and a resonant earthed system, resonant earthed system includes a compensating resistance R _CWith a building-out capacitor C _CThe overpower circuit for detecting then has a filtered diode 22, a filter capacitor C _PD, a divider resistance R _P1With a divider resistance R _P2

Auto-excitation type semi-bridge type power supply unit uses the bipolar transistor with high pressure characteristics (to go up bridge power transistor Q ₃With following bridge power transistor Q ₄) as the power switched switch, and use the auto-excitation type type of drive to drive bridge power transistor Q ₃With following bridge power transistor Q ₄, again by main transformer T ₁Energy is delivered to outlet side by primary side, and the auto-excitation type type of drive is to utilize the driving transformer T with current transformer characteristic ₂Reach, this type of drive is called ratio again and drives (proportional drive).

Please refer to Fig. 2 A, it is the circuit diagram of known auto-excitation type semi-bridge type power supply unit between the starting period.Cooperate shown in Figure 3ly, auto-excitation type semi-bridge type power supply unit is in starting moment, and PWM controller 100 is sent of high level and switched signal S ₂Make a transistor Q ₂Conducting, a supply power voltage V _DDSee through a diode 12 and a resistance R _DTo driving transformer T ₂Winding N _22BCharge.Because winding N _22BWith N _11APolarity identical, winding N _11ASense positive potential and produce base current I _B3, this base current I _B3See through power transistor and have the characteristic of amplification, and the corresponding primary side current I that produces _P=h _Fe* I _B3, and h _FeBe transistorized current gain, be meant bridge power transistor Q here especially ₃

Please refer to Fig. 2 B, it is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during power conversion.Last bridge power transistor Q ₃Be high voltage transistor, its current gain h _FeLess, thereby need bigger base current I _BCould drive.Type of drive is to utilize the driving transformer T with current transformer characteristic ₂, and the mode of using the oneself to drive is reached the auto-excitation type driving.Driving transformer T ₂Sensing winding N _PBe in order to detecting main transformer T ₁Primary side current I _P, see through winding N _11AWith sensing winding N _PTurn ratio relation can obtain:

$I_B=I_P\×\frac{N_{11A}}{N_P}---\left(1\right)$

Winding N _11AWith sensing winding N _PHave the directly proportional relation, and primary side current I _PFlow through sensing winding N _PCan obtain bigger base current I _B, this base current I _BAlso produce bigger primary side current I relatively _P, this similar regenerative mechanism makes and goes up bridge power transistor Q ₃Conducting fully.Cooperate shown in Figure 3, this moment switching signal S ₃Be high level, the base current I of this moment _B3* h _Fe＞I _P, main transformer T ₁Promptly deliver power to outlet side.

In addition, because driving transformer T ₂Winding N _22BWith N _11BPolarity opposite, winding N _11BPromptly sense negative potential, following bridge power transistor Q ₄End, therefore, primary side current I _PFlow direction is by electric capacity of voltage regulation C ₁Anode to last bridge power transistor Q ₃, through driving transformer T ₂Sensing winding N _PTo main transformer T ₁, again through intercepting capacitor C _BGet back to electric capacity of voltage regulation C at last ₁Negative terminal, the energy of input is by main transformer T ₁Be converted to outlet side.

In addition, driving transformer T ₂Sensing winding N _PExcept can be in order to detecting primary side current I _P, also have the parameter and the characteristic of detecting output current simultaneously, therefore can be used as the sensing element of restriction output current, see through filter (filtered diode 22 and filter capacitor C _PD) can obtain overpower detection voltage V _PD:

$V_{\mathrm{PD}}=V_B\×\frac{N_{22}}{N_{11}}=I_P\×\frac{N_{11}}{N_P}\×Z_B\×\frac{N_{22}}{N_{11}}---\left(2\right)$

V _BBe winding N _11AOr N _11BThe voltage at two ends; N ₁₁Be winding N _11AOr N _11BN ₂₂Be winding N _22AOr N _22BZ _BBe last bridge power transistor Q ₃With following bridge power transistor Q ₄Input impedance, obtain overpower and detect voltage V _PDAfter, see through divider resistance R again _P1With R _P2, promptly can obtain overpower signal V _OP

Cooperate Fig. 3, please refer to Fig. 2 C, it is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during flywheel.Send the switching signal S of high level simultaneously when PWM controller 100 ₂With S ₁The time, will make transistor Q simultaneously ₁With Q ₂Conducting, driving transformer T ₂Winding N _22AWith N _22BForm short circuit, winding N _11AWith N _11BCan't respond to and produce the base current I that drives usefulness _B, while sensing winding N _PAlso can't detect primary side current I _PTherefore, last bridge power transistor Q ₃With following bridge power transistor Q ₄Be cut-off state.Cooperate shown in Figure 3ly, switch signal S ₃With S ₄Be low level, at this moment, main transformer T ₁Can't deliver power to outlet side.

Cooperate Fig. 3, please refer to Fig. 2 D, it is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during power conversion.Send the switching signal S of high level when PWM controller 100 ₁Make transistor Q ₁Conducting is because driving transformer T ₂Winding N _22AWith N _11BPolarity identical, winding N _11BSense positive potential and produce base current I _B4, then see through winding N _11BWith sensing winding N _PThe number of turn recently obtain bigger base current I _B4, thereby following bridge power transistor Q ₄Conducting fully.Cooperate shown in Figure 3ly, switch signal S ₄Be high level, the base current I of this moment _B4* h _Fe＞I _P, main transformer T ₁Promptly deliver power to outlet side.

In addition, because driving transformer T ₂Winding N _22AWith N _11APolarity opposite, winding N _11ASense negative potential, last bridge transistor Q ₃End, promptly switch signal S ₃Be low level, following bridge power transistor Q ₄After the conducting, primary side current I _PFlow direction is by electric capacity of voltage regulation C ₂Anode to intercepting capacitor C _B, through main transformer T ₁To driving transformer T ₂Sensing winding N _P, pass through bridge power transistor Q down again ₄Arrive electric capacity of voltage regulation C at last ₂Negative terminal, the energy of input is by main transformer T ₁Be passed to outlet side.

Above-mentioned cooperation Fig. 3 explanation, the PWM controller 100 of known auto-excitation type semi-bridge type power supply unit are to switch signal S ₂, just having begun the startup signal that moves as power supply unit, the PWM controller 100 of known auto-excitation type semi-bridge type power supply unit can also switch signal S ₁Just begin the startup signal that moves as power supply unit, and switched signal S this moment ₂Be the low level signal.

Please in the lump with reference to figure 4, it is the circuit diagram of the PWM controller of known auto-excitation type semi-bridge type power supply unit.PWM controller 100 includes a pulse-width modulation unit 110, error amplifier 120, a comparator 130 and a timer 140.This pulse-width modulation unit 110 includes two D flip- flops 1101 and 1102, oscillators 1103, two NAND gate 1104 and 1105 and comparators 1106 again.Oscillator 1103 is in order to produce a sawtooth waveforms signal V _SAWWith a time pulse signal CLK, this sawtooth waveforms signal V _SAWCan determine to switch signal S ₁With S ₂Switching frequency; The anode of error amplifier 120 is connected to a reference voltage V _R, negative terminal is connected to feedback holds FB, receives a back coupling signal V _FB, in order to export a compensating signature V _COMThe anode of comparator 1106 and negative terminal are connected to output and this oscillator 1103 of this error amplifier 120 respectively, receive this compensating signature V _COMWith this sawtooth waveforms signal V _SAW, via exporting the result after the comparison operation, see through the logical operation of D flip- flop 1101,1102 and NAND gate 1104,1105 again, export and determine this switching signal S ₁With S ₂Pulse bandwidth.

Based on meeting considering of safety (safety), power supply unit must provide the overpower protection circuit to come power-limiting output with protection power supply unit itself and power-supply system end, avoids the misoperation of short circuit and overload to take place.When the output of power supply unit is short-circuited when transshipping, output current and power can roll up, in order to the parameter of detecting output current and the primary side current I of characteristic _PAlso increase, further cause overpower signal V _OPIncrease.

Served as power signal V _OPSurpass critical signal V _TThe time, see through the comparison operation of comparator 130, the replacement end of the output of comparator 130 and timer 140 is a high level, this moment, timer 140 began to count, one section time of delay T _dAfter, the output of timer 140 will be sent the bolt-lock signal LATCH of high level, through the feasible signal S that switches of the protective circuit of PWM controller inside ₃With S ₄End fully.Above-mentioned T time of delay that is provided with _dPurpose be to change for fear of load moment to cause misoperation, this time of delay T _dMust be greater than the reaction time of dynamic load.

When the output short circuit of power supply unit, output voltage V ₀Descend the back coupling signal V that back coupling end FB receives _FBReduce, because reference voltage V _RBe a fixed voltage, and back coupling signal V _FBWith reference voltage V _RBetween voltage difference too big, therefore, feedback signal V _FBWith reference voltage V _RThrough the amplification of error amplifier 120, a very big compensating signature V will be exported _{COM (A)}Give comparator 1106, just compensating signature V _COMIncrease to V _{COM (A)}When overload took place power supply unit, power output increased, compensating signature V _COMAlso increase to V thereupon _{COM (A)}Compensating signature V _{COM (A)}With sawtooth waveforms signal V _SAWAfter seeing through the comparison operation output result of comparator 1106, pass through the logical operation of D flip- flop 1101,1102 and NAND gate 1104,1105 again, will export and switch signal S _{1 (A)}With S _{2 (A)}

By shown in Figure 3, switch signal S as can be known _{1 (A)}With S _{2 (A)}Pulse bandwidth compare S ₁With S ₂Pulse bandwidth little, so will produce the switching signal S of big pulse bandwidth _{3 (A)}With S _{4 (A)}, so will cause power transistor Q ₃With Q ₄Work period increase main transformer T simultaneously ₁Both end voltage V _T1Waveform will change V into _{T (A)}, and main transformer T ₁Both end voltage V _{T1 (A)}Work period greater than V _T1Work period, this kind situation will last till this section T time of delay _dFinish.Because this section T time of delay _dTo cause overpower protection to be difficult to control, and the power supply unit element must bear very big voltage and current stress, causes damage easily.

Therefore, therefore the present invention, in the overpower protection of self-excitation power supply device, can reach and decide Current Control and periodic current limliting, to address the above problem promptly at the overpower protection that proposes a kind of self-excitation power supply device at the problems referred to above.

Summary of the invention:

Main purpose of the present invention; be to propose a kind of overpower protection of self-excitation power supply device; when the output of self-excitation power supply device be short-circuited, when transshipping; by compensating signature is reduced; make and limit the work period reduction of bridge power transistor up and down to reach periodic current limliting and power output.

The overpower protection of self-excitation power supply device of the present invention; it includes a flexible start unit; be received from a back coupling signal of excitation power supply supply; produce a compensating signature; a pulse-width modulation unit for the self-excitation power supply device produces the switching signal, switches the power of signal control self-excitation power supply device output.In addition, flexible start unit is connected with an adjustment unit, this adjustment unit receives an overpower signal and one second critical signal of this self-excitation power supply device, when the output of self-excitation power supply device is short-circuited and transships, and when making the overpower signal greater than the second critical signal, this adjustment unit orders about this flexibility start unit, and then orders about pulse-width modulation unit modulation switching signal.A timing unit, it receives this overpower signal and one first critical signal, and the overpower signal is during greater than the first critical signal, this timing unit is counted, after counting a period of time, will send a locking signal, make self-excitation power supply device stop supplies power supply.

Description of drawings:

Fig. 1 is the circuit diagram of known auto-excitation type semi-bridge type power supply unit;

Fig. 2 A is the circuit diagram of known auto-excitation type semi-bridge type power supply unit between the starting period;

Fig. 2 B is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during power conversion;

Fig. 2 C is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during flywheel;

Fig. 2 D is the circuit diagram of known auto-excitation type semi-bridge type power supply unit during power conversion;

Fig. 3 is the oscillogram of sawtooth waveforms signal, compensating signature, switching signal and the main transformer both end voltage of known auto-excitation type semi-bridge type power supply unit;

Fig. 4 is the circuit diagram of the PWM controller of known auto-excitation type semi-bridge type power supply unit;

Fig. 5 is the circuit diagram of the PWM controller of self-excitation power supply device of the present invention;

Fig. 6 is the starting resistor VSS of the overpower protection of self-excitation power supply device of the present invention and the oscillogram of overpower signal VOP;

Fig. 7 is the oscillogram of sawtooth waveforms signal, compensating signature, switching signal and the main transformer both end voltage of self-excitation power supply device of the present invention.

The figure number explanation:

12 diode 2101D D-flip flops

22 filtered diode 2102D D-flip flops

Bridge drive circuit 2103 oscillators on 32

42 times bridge drive circuit 2104 NAND gate

100PWM controller 2105 NAND gate

110 pulse-width modulation unit, 2106 comparators

1101D D-flip flop 220 flexible start units

1102D D-flip flop 2201 operational amplifiers

1103 oscillators, 2202 error amplifiers

1104 NAND gate, 2203 clamping diodes

1105 NAND gate, 2,204 first power supplys

1106 comparators, 230 timing units

120 error amplifiers, 2,301 first comparators

130 comparators, 2302 timers

140 timers, 240 adjustment units

200PWM controller 2,401 second comparators

210 pulse-width modulation unit, 2402 second sources

2,403 first switch RP1 divider resistances

2404 second switch RP2 divider resistances

C0 output capacitance S1 switches signal

C1 electric capacity of voltage regulation S1 (A) switches signal

C2 electric capacity of voltage regulation S1 (B) switches signal

CB intercepts electric capacity S2 and switches signal

CC building-out capacitor S2 (A) switches signal

CPD filter capacitor S2 (B) switches signal

CSS starts electric capacity S3 and switches signal

CLK time pulse signal S3 (A) switches signal

IB base current S3 (B) switches signal

IP primary side current S4 switches signal

N11A winding S4 (A) switches signal

N11B winding S4 (B) switches signal

N22A winding T1 main transformer

N22B winding T2 driving transformer

NP sensing winding VCOM compensating signature

Q1 transistor VCOM (A) compensating signature

Q2 transistor VCOM (B) compensating signature

The last bridge power transistor of Q3 VDD supply power voltage

Bridge power transistor VFB back coupling signal under the Q4

L0 outputting inductance VPD overpower detects voltage

R01 divider resistance V0 output voltage

R02 divider resistance VOP overpower signal

RC compensating resistance VR reference voltage

RD resistance VSAW sawtooth waveforms signal

The critical signal of VSS starting resistor VT

VT1 (A) main transformer two ends electricity VT1 (B) main transformer both end voltage

The VT1 main transformer both end voltage VTH1 first critical signal

The VTH2 second critical signal

Embodiment:

Further understand and understanding for your auditor is had architectural feature of the present invention and the effect reached, sincerely help with preferred embodiment figure and cooperate detailed explanation, be described as follows:

Please refer to Fig. 5, it is the circuit diagram of the PWM controller of self-excitation power supply device of the present invention; Overpower protection of the present invention can be located at a PWM controller 200 of self-excitation power supply device, and is connected in a pulse-width modulation unit 210 of PWM controller 200, and overpower protection of the present invention also can not must be located at PWM controller 200.Overpower protection of the present invention includes a flexible start unit 220, a timing unit 230 and an adjustment unit 240.This flexibility start unit 220 includes an operational amplifier 2201, error amplifier 2202, a clamping diode 2203 and a charhing unit, and charhing unit includes one first power supply 2204 and one and starts capacitor C _SS, first power supply 2204 connects the startup capacitor C _SS, with to starting capacitor C _SSCharge.

Operational amplifier 2201, its anode receives a reference voltage V _R, negative terminal then is connected to the output and startup capacitor C of operational amplifier 2201 _SS, with as unity gain buffer, and then in the output output starting resistor V of operational amplifier 2201 _SSThe time, having pressure stabilization function is voltage regulation unit; Error amplifier 2202, its anode is connected to the startup capacitor C _SSWith the output of this operational amplifier 2201, receive starting resistor V _SS, the negative terminal of error amplifier 2202 is the back coupling end FB that are connected to the self-excitation power supply device, receives back coupling signal V _FB, the output of error amplifier 2202 then is connected to pulse-width modulation unit 210, and error amplifier 2202 receives starting resistor V _SSWith back coupling signal V _FB, in order to output compensating signature V _COMClamping diode 2203, it is connected between the negative terminal and output of error amplifier 2202, when the self-excitation power supply device starts, is used for strangulation compensating signature V _COMVoltage level.

Pulse-width modulation unit 210, it includes two D flip- flops 2101 and 2102, oscillators 2103, two NAND gate 2104 and 2105 and comparators 2106, and oscillator 2103 is in order to produce a time pulse signal CLK and a sawtooth waveforms signal V _SAW, can switch signal S in order to decision ₁With S ₂Switching frequency; The anode of comparator 2106 is connected to the output of the error amplifier 2202 of flexible start unit 220, receives compensating signature V _COM, and negative terminal is connected to this oscillator 2103, receives sawtooth waveforms signal V _SAW, via exporting the result after the comparison operation, see through the logical operation of D flip- flop 2101,2102 and NAND gate 2104,2105 again, export and determine this switching signal S ₁With S ₂Pulse bandwidth.

When the self-excitation power supply device is starting moment, first power supply 2204 can be to starting capacitor C _SSCharging, starting resistor V _SSBegin to rise by zero volt.Because operational amplifier 2201 is a unity gain buffer, so starting resistor V _SSMaximum be reference voltage V _RThe time, promptly enter normal condition.When originally the anode of error amplifier 2202 is zero volt, because of clamping diode 2203 has the effect of strangulation voltage level, so the output of error amplifier 2202 can be clamped at the conduction voltage drop V of clamping diode 2203 _F(generally about 0.7V), afterwards, the starting resistor V that receives along with the anode of error amplifier 2202 _SSRise the compensating signature V of error amplifier 2202 outputs gradually _COMAlso increase gradually, so in charging process, switch signal S ₁With S ₂Pulse bandwidth will be with starting resistor V _SSChange and change, up to starting resistor V _SSReach reference voltage V _R, switch signal S this moment ₁With S ₂Pulse bandwidth reach preset value, and the output voltage V of self-excitation power supply device ₀Will be along with starting resistor V _SSRising gradually and increase, set up output voltage V at last fully ₀, thereby reach the flexible effect that starts.

The first above-mentioned power supply 2204 is a current source, when being used for the startup of self-excitation power supply device, to starting capacitor C _SSCharging current is provided, makes starting resistor V _SSRise gradually, make the output voltage V of self-excitation power supply device ₀Increase gradually.Start capacitor C _SSCan be by the self capacity value in order to plan the start-up time of self-excitation power supply device, bigger startup capacitor C _SSTo increase start-up time, and it is specified to reduce the voltage and the electric current of power switch.Therefore, by reasonably selecting to start capacitor C _SSCapacitance, make starting the time of delay that moment causes can be in suitable scope.

Cooperate Fig. 1, multiple with reference to figure 5, anode and negative terminal that timing unit 230 includes one first comparator 2301 and timer 2302, the first comparators 2301 receive overpower signal V respectively _OPWith the first critical signal V _TH1, and the output of first comparator 2301 is to be connected with the replacement end of timer 2302.Served as power signal V _OPBe lower than the first critical signal V _TH1The time, the replacement end of the output of first comparator 2301 and timer 2302 is a low level, and this moment, timer 2302 was not counted, and the bolt-lock signal LATCH that the output of timer 2302 is sent is a low level, the normal running of self-excitation power supply device.

When the output of self-excitation power supply device was short-circuited or transships, output current and power rolled up, in order to the parameter of detecting output current and the primary side current I of characteristic _PAlso increase, further cause overpower signal V _OPIncrease.Overpower signal V _OPSurpass the first critical signal V _TH1The time, the replacement end of the output of first comparator 2301 and timer 2302 is a high level, this moment timer 2302 begin the counting, one section time of delay T _dAfter, the bolt-lock signal LATCH that the output of timer 2302 is sent is a high level, through the protective circuit of PWM controller inside, makes and goes up bridge power transistor Q ₃With following bridge power transistor Q ₄End main transformer T fully ₁Can't deliver power to outlet side, i.e. self-excitation power supply device stop supplies power supply.

Multiple with reference to figure 5, anode and negative terminal that adjustment unit 240 includes one second comparator 2401, a second source 2402 and one first switch 2403, the second comparators 2401 receive overpower signal V respectively _OPWith the second critical signal V _TH2Second source 2402 is connected between first switch 2403 and the earth terminal, and first switch 2403 is connected to first power supply 2204 and starts capacitor C _SS

Equally when the output of self-excitation power supply device is short-circuited or transships, overpower signal V _OPIncrease, served as power signal V _OPSurpass the first critical signal V _TH1, timer 2302 can begin counting, if overpower signal V _OPAlso surpass the second critical signal V _TH2The time, through the comparison operation of second comparator 2401, the output of second comparator 2401 is a high level, orders about first switch 2403 and is conducting state, starts capacitor C _SSBegin discharge with fixing second source 2402.Though first power supply 2204 is still to starting capacitor C _SSCharging, but the discharge current value I of second source 2402 _DCHCharging current value I much larger than first power supply 2204 _CH, thereby cause as shown in Figure 6 starting resistor V _SSFastish discharge.

Because the self-excitation power supply device sees through to feedback a little delay is arranged necessarily, will cause as shown in Figure 6 overpower signal V _OPSurpass the second critical signal V _TH2The time still can continue a bit of time, this moment starting resistor V _SSDescend, timer 2302 is also still at counting.Comparatively speaking, because starting resistor V _SSThe output compensating signature V as shown in Figure 7 of error amplifier 2202 so descend _{COM (B)}, by illustrating compensating signature V as can be known _{COM (B)}Level be smaller than compensating signature V _COMLevel, so through after the comparison operation of comparator 2106, will make NAND gate 2104 and 2105, output is the switching signal S of pulse bandwidth greatly _{1 (B)}With S _{2 (B)}, and then produce the hungry signal S that switches of less pulse bandwidth _{3 (B)}With S _{4 (B)}, cause bridge power transistor Q ₃With following bridge power transistor Q ₄Work period reduce, reduce main transformer T ₁Both end voltage V _{T1 (B)}Work period, make overpower signal V _OPDescend.

Served as power signal V _OPDrop to and be lower than the second critical signal V _TH2The time, start capacitor C _SSDischarging action finish starting resistor V _SSMaintain a lower voltage level.This moment is because overpower signal V _OPStill be higher than the first critical signal V _TH1, timer 2302 also still at counting, has served as power signal V _OPDrop to and be lower than the second critical signal V _TH2The time, second comparator 2401 is stopped using, and first switch 2403 is a cut-off state, and at this moment, first power supply 2204 begins again starting capacitor C _SSCharge, then starting resistor V _SSBegin slow rising by a lower voltage level.Starting resistor V _SSSlow rising make to go up bridge power transistor Q ₃With following bridge power transistor Q ₄Work period also slowly increase, cause overpower signal V _OPSurpass the second critical signal V again _TH2

And then, the output of second comparator 2401 is a high level, and first switch 2403 is again a conducting state, starts capacitor C _SSBegin discharge again with fixing second source 2402, so carry out repetitive cycling discharge and recharge action up to one section time of delay T _dAfter, the bolt-lock signal LATCH that the output of timer 2 302 is sent is a high level, through the protective circuit of PWM controller inside, will make bridge power transistor Q ₃With following bridge power transistor Q ₄End fully.

When the output short circuit of self-excitation power supply device, output voltage V ₀Descend the back coupling signal V that back coupling end FB receives _FBReduce compensating signature V _COMAlso increase thereupon.When overload took place the self-excitation power supply device, power output increased, compensating signature V _COMAlso increase thereupon.Overpower protection of the present invention is by overpower signal V _OPIncrease, and see through to start capacitor C _SSDischarge reduce starting resistor V _SS, and then make error amplifier 2202 export less compensating signature V _{COM (B)}Give comparator 2106, just compensating signature V _COMBe reduced to V _{COM (B)}Compensating signature V _{COM (B)}With sawtooth waveforms signal V _SAWThrough the logical operation of comparator 2106, D flip- flop 2101,2102 and NAND gate 2104,2105, produce the switching signal S of less pulse bandwidth _{3 (B)}With S _{4 (B)}, cause bridge power transistor Q ₃With following bridge power transistor Q ₄Work period reduce main transformer T simultaneously ₁Both end voltage V _{T1 (B)}Work period reduce, and last till this section T time of delay _dFinish.

Because this section T time of delay _dStart the mechanism of overpower protection, reached the restriction of periodic current limliting and peak power output simultaneously.See through overpower protection of the present invention, can avoid when the output short circuit of self-excitation power supply device takes place with overload, exporting too high compensating signature V _COM, increase the power output of self-excitation power supply device, and use when of the present invention last bridge power transistor Q ₃With following bridge power transistor Q ₄Voltage and current rating can select lowlyer, therefore circuit cost also can reduce.

Multiple adjustment unit 240 more includes a second switch 2404 with reference to figure 5, and it is connected in the startup capacitor C _SSAnd between the earth terminal, second switch 2404 and startup capacitor C _SSBeing connected in parallel, is to be controlled by a replacement signal RST, in order to starting capacitor C _SSDischarge.When the self-excitation power supply device did not provide power output, the flexible start unit 220 of the present invention was from feedbacking end FB detection back coupling signal V _FB, through the protective circuit of PWM controller 200 inside, in order to export this replacement signal RST.Replacement signal RST enables, and can make the startup capacitor C _SSRepid discharge allows starting resistor V _SSReduce fast, and then cause compensating signature V _COMLevel descend.

Because compensating signature V _COMReduce compensating signature V fast _COMWith sawtooth waveforms signal V _SAWAfter seeing through the comparison operation of comparator 2106, make and the switching signal of output stage small wave width will cause bridge power transistor Q ₃With following bridge power transistor Q ₄Work period reduce, promptly reduce main transformer T ₁Both end voltage V _T1Work period.As starting resistor V _SSContinue to descend, and compensating signature V _COMAlso drop to and be lower than sawtooth waveforms signal V _SAWThe time, transistor Q ₁With Q ₂Conducting fully, last bridge power transistor Q ₃With following bridge power transistor Q ₄Almost completely end, thereby reach and reset and suitable protective effect.

In sum; the present invention proposes a kind of overpower protection; it is used in the self-excitation power supply device; when output is short-circuited with the situation of transshipping; can reduce the starting resistor that starts on the electric capacity by adjustment unit, and then reduce compensating signature, so can allow the bridge power transistor and the work period of following bridge power transistor reduce; and the work period of reducing the main transformer both end voltage, so can reach the restriction of periodic current limliting and peak power output.

The above, it only is preferred embodiment of the present invention, be not to be used for limiting scope of the invention process, all according to the described shape of the present patent application claim, structure, feature and principle etc. change and modify, all should be contained in the claim of the present invention.

Claims (10)

1, a kind of overpower protection of self-excitation power supply device is characterized in that, includes:

A flexible start unit, receive a back coupling signal of this self-excitation power supply device, produce a compensating signature, switch signal for a pulse-width modulation unit generation of this self-excitation power supply device, this switching signal is controlled the power of this self-excitation power supply device output;

An adjustment unit, be coupled to this flexibility start unit, this adjustment unit receives an overpower signal and one second critical signal of this self-excitation power supply device, this overpower signal is during greater than this second critical signal, this adjustment unit orders about this flexibility start unit, and then order about this this switching signal of pulse-width modulation unit modulation, to reduce the output of this self-excitation power supply device;

A timing unit, receive this overpower signal and one first critical signal of this self-excitation power supply device, this overpower signal is during greater than this first critical signal, this timing unit is counted, after counting a period of time, to send a locking signal, make this self-excitation power supply device stop supplies power supply;

Wherein, the set point of the second critical signal is greater than the set point of the first critical signal.

2, the overpower protection of self-excitation power supply device as claimed in claim 1 is characterized in that, this flexibility start unit more includes:

A charhing unit produces a starting resistor;

A voltage regulation unit is coupled to this charhing unit, is used to stablize this starting resistor;

An error amplifier, its anode are coupled to this charhing unit and this voltage regulation unit, receive this starting resistor, and the negative terminal of this error amplifier receives this back coupling signal of this self-excitation power supply device, and the output of this error amplifier is exported this compensating signature;

A clamping diode is coupled between the output and negative terminal of this error amplifier.

3, the overpower protection of self-excitation power supply device as claimed in claim 2; it is characterized in that; this voltage regulation unit is a unit gain buffer cell; the anode of this unit gain buffer cell receives a reference voltage; the negative terminal of this unit gain buffer cell is coupled to output and this charhing unit of unit gain buffer cell; receive this starting resistor, the output of this unit gain buffer cell is coupled to the anode of error amplifier.

4, the overpower protection of self-excitation power supply device as claimed in claim 2; it is characterized in that; this voltage regulation unit is an operational amplifier; the anode of this operational amplifier receives a reference voltage; the negative terminal of this operational amplifier is coupled to output and this charhing unit of this operational amplifier; receive this starting resistor, the output of this operational amplifier is coupled to the anode of error amplifier.

5, the overpower protection of self-excitation power supply device as claimed in claim 2; it is characterized in that this charhing unit includes one first power supply and a startup electric capacity, this first supply coupling starts electric capacity in this; this is started the electric capacity charging, produce this starting resistor.

6, the overpower protection of self-excitation power supply device as claimed in claim 2; it is characterized in that; this adjustment unit is used to order about this flexibility start unit, and then orders about this adjustment unit of this pulse-width modulation unit this switching signal of modulation, and this adjustment unit includes:

A second source is coupled to an earth terminal;

One first switch is coupled between this charhing unit and this second source;

One second comparator, its anode and negative terminal receive this overpower signal and this second critical signal of this self-excitation power supply device respectively, this overpower signal is during greater than this second critical signal, the output of this second comparator is exported a signal, order about this first switch conduction, make this charhing unit discharge, reduce this starting resistor.

7, the overpower protection of self-excitation power supply device as claimed in claim 6; it is characterized in that; this adjustment unit more includes a second switch; it is coupled between this charhing unit and this earth terminal; this second switch receives a replacement signal and conducting; this charhing unit is discharged, reduce this starting resistor.

8, the overpower protection of self-excitation power supply device as claimed in claim 1; it is characterized in that; this timing unit includes one first comparator and a timer; this first comparator couples mutually with this timer; the anode of this first comparator and negative terminal receive this overpower signal and this first critical signal of this self-excitation power supply device respectively; this overpower signal is during greater than this first critical signal; this first comparator output high level signal counts this timer to this timer.

9, the overpower protection of self-excitation power supply device as claimed in claim 1; it is characterized in that; this overpower signal that this adjustment unit receives is during greater than this second critical signal; this adjustment unit orders about this flexibility start unit; reduce the level of this compensating signature, to reduce the output of this self-excitation power supply device.

10, the overpower protection of self-excitation power supply device as claimed in claim 1 is characterized in that, this overpower protection is located on the PWM controller of this self-excitation power supply device.

Images