Prevent the circuit that restarts after the active hoop DC/DC inverter shutdown
Technical field:
The present invention relates to a kind of circuit of restarting after the active hoop DC/DC inverter shutdown of preventing.
Background technology:
Synchronous rectification is the key technology of low-voltage, high-current DC/DC converter, secondary (secondary) at the DC/DC converter, adopt synchronous rectification MOS transistor (MOSFET) to replace Schottky (Schottky) diode to carry out rectification, can effectively reduce on-state loss.But for the rectifying tube SR1 and the continued flow tube SR2 of synchronous rectification MOS transistor, its gate pole needs corresponding driving pulse to encourage.And in active-clamp (Active clamp) topology, the voltage waveform of its power transformer winding can be directly comes to provide excitation to rectifying tube SR1 and continued flow tube SR2 as the driving pulse of correspondence, realized the self-driven of synchronous rectification MOS transistor effectively, easily, so the active-clamp synchronous rectifier converter has obtained in low-voltage, high-current DC/DC using widely.
Clamp circuit in the active clamping circuir is composed in series by active device and clamping capacitance, is connected in parallel on the winding two ends of main switch or transformer.Active device can be a N type MOS transistor (N-MOSFET), also P type MOS transistor (P-MOSFET).Fig. 1 a is the industry using active clamp circuit commonly used and the DC/DC converter of synchronous rectification, wherein, S1 is former limit main switch (is called for short and is responsible for), SR1 and SR2 are respectively secondary synchronous rectifier and continued flow tube, Cc and S2 constitute original edge clamp circuit, are connected in parallel on to be responsible for two ends, and wherein clamper tube S2 is a P type MOS transistor, when Vg2 is negative level, the S2 conducting; When Vg2 was zero level or positive level, S2 turn-offed.The PWM2 signal provides pumping signal for clamper tube S2 by a paraphase drive circuit of being made up of C2, D1 and R1.
The main signal waveform of circuit is shown in Fig. 1 b among Fig. 1 a, and when UVP was high level, the PWM main control circuit produced two paths of signals PWM1, the PWM2 that dirt has fixed timing relationship, drive signal is provided for respectively S1, S2; When input supply voltage Vin was lower than under-voltage protection point Uuv, UVP was a low level, and control circuit is not worked.The operation principle of main circuit is: in the t1 moment, PWM2 is a high level, charges to C2 by the loop of C2, D1, and the last electromotive force of a C2 left side is high right low.Because the D1 conducting, the Vg2 signal is approximately zero level, and then clamper tube S2 turn-offs; And then t2 constantly, the PWM1 signal is a high level, then Vg1 also be high, is responsible for the S1 conducting, the former limit of transformer winding voltage Vp is for just, this voltage is coupled to the secondary winding and provides excitation to SR1, rectifying tube SR1 conducting, SR2 shutoff; In the t3 moment, the PWM1 signal is a low level, and then Vg1 also is low, is responsible for S1 and turn-offs; And then at t4 moment PWM2 signal also low level, because of being filled with the high right low voltage in an electromotive force left side on the C2, when PWM2 signal vanishing level, Vg2 signal instant reverse is a negative level, clamper tube S2 conducting, clamping capacitance Cc went up voltage and deducted input supply voltage and be the former limit of transformer winding voltage Vp this moment, and this voltage makes transformer realize magnetic reset for negative, this voltage is coupled to the secondary winding simultaneously, make rectifying tube SR1 turn-off, continued flow tube SR2 conducting, electric current is by the SR2 afterflow in the inductance L; In the t5 moment, the PWM2 signal is high, enters following one-period.
This circuit utilizes P type MOS transistor to constitute the clamp switch pipe, the shutoff voltage of being responsible for S1 is clamped on voltage on the capacitor C c, and in the magnetic reset of realizing transformer, Transformer Winding voltage provides excitation to secondary synchronous rectifier.Circuit is simple, and transducer effciency is higher.
But simultaneous problem is: after supply voltage disconnected, Vin voltage began to reduce, and at t6 constantly, after Vin was reduced to under-voltage some Uuv of input of converter, main control circuit was closed PWM1, PWM2 signal; After the PWM1 signal is low level, is responsible for S1 and turn-offs, output voltage V out slowly discharges; After PWM2 is low level, because the voltage on the capacitor C 2 will slowly discharge, cause the Vg2 signal to keep negative level always, the long-term conducting of clamp switch pipe S2, then clamping capacitance Cc and static exciter inductance generation resonance, at this moment, voltage Vp is a sine wave as shown in the figure on the winding of the former limit of transformer, this sine voltage is coupled to the secondary winding, provides excitation to secondary synchronous rectifier, makes synchronous rectifier SR1, SR2 still keep the alternation state.Because shutdown back synchronous rectifier SR1, SR2 are still at the alternation state, the energy on the output capacitance to the feedback of former limit, causes Vin voltage to raise again by transformer; If energy is bigger on the output capacitance, the energy that feeds back to former limit makes Vin voltage be elevated to the under-voltage recovery point of converter, the UVP signal is again a high level, open PWM1, PWM2 signal again at t7 moment main control circuit, converter enters and restarts, this exception procedure is reacted to and then shows as output voltage on the waveform of output voltage V out occurred voltage bounce again in postboost decline process, can not satisfy the sequential requirement.
Summary of the invention:
Purpose of the present invention is exactly in order to overcome the above problems, and a kind of circuit of restarting after the active hoop DC/DC inverter shutdown of preventing is provided, and guarantees dull decline of shutdown back output voltage, satisfies the requirement of sequential.
For achieving the above object, the present invention proposes a kind of circuit of restarting after the active hoop DC/DC inverter shutdown of preventing, it is characterized in that comprising: the resonance signal testing circuit, and the former limit of described active hoop DC/DC inverter winding voltage signal is used to sample; Main circuit working state signal sample circuit, the operating state of the described active hoop DC/DC inverter that is used to sample; The useful signal summation circuit, be used for when described active hoop DC/DC inverter is in abnormal work state or off position, the former limit winding voltage signal that accumulation resonance signal testing circuit is sampled, generate accumulating signal, and, when in setting-up time, not receiving former limit winding voltage signal, accumulating signal is resetted; Decision circuitry is used for control signal of output when described accumulating signal reaches set point, and this control signal is used to turn-off the PWM main control circuit of active hoop DC/DC inverter.
Described resonance signal testing circuit comprises the auxiliary winding of responding in the former limit of converter winding and the unidirectional conduction device that is series at auxiliary winding; Main circuit working state signal sample circuit comprises transistor, its control utmost point is connected to the PWM main control circuit of converter, its main electric current break-over utmost point is connected between the output and ground of unidirectional conduction device, the useful signal summation circuit comprises charging capacitor and the discharge resistance in parallel with it, is connected to after the two parallel connection between the output and ground of unidirectional conduction device; Described decision circuitry comprises comparator, and two input connects reference voltage respectively and charging capacitor is far held, its output termination converter PWM main control circuit.
Owing to adopted above scheme, the height of accumulating signal level has reflected the situation of shutdown back converter input supply voltage indirectly.The energy of storing on output capacitance after the shutdown is many to former limit feedback, then the main circuit resonance time is long, input supply voltage and accumulating signal all raise often, turn-off to the PWM main control circuit that makes that to a certain degree will make converter and accumulating signal is high, therefore because the rising of the input supply voltage that resonance causes can not cause converter to enter to restart, output voltage waveforms just can not have a rebound yet.By adjusting in time resetting of accumulating signal, also can the falling situation of analog input supply voltage after resonance stops, making the described comparator circuit PWM main control circuit cut-off signals that in time overturns, but main control circuit is in operating state.Circuit structure of the present invention is simple, and cost is low, the efficient height.
Description of drawings:
Fig. 1 a is an active clamping circuir commonly used in the prior art;
Fig. 1 b is active clamping circuir operate as normal and postboost oscillogram commonly used in the prior art;
Fig. 2 a is that of the present invention preventing restarts circuit embodiments after the active clamping circuir shutdown;
Fig. 2 b is exemplary operation figure of the present invention.
Fig. 3 a, 3b, 3c are three kinds of circuit diagrams of the embodiment of the invention two.
Fig. 4 is the embodiment of the invention three schematic diagrames.
Embodiment:
Also the present invention is described in further detail in conjunction with the accompanying drawings below by specific embodiment.
As mentioned above, basic design of the present invention is, detect the resonance situation of active clamping circuir shutdown back main circuit LC, if shutdown back main circuit resonance times is more, then this testing circuit is by the pwm signal in the shielding main control circuit, make DC to DC converter can not reenter work in the short time, output voltage just can not rebound.
Embodiment one:
Fig. 2 a is an exemplary embodiments of the present invention.In this example, described useful signal summation circuit produces circuit by timing signal (Vsig) and forms, decision circuitry is made up of comparator circuit, main circuit working state signal sample circuit is made up of screened circuit, in other words, prevent to restart after active clamping circuir from shutting down circuit described in this example and comprise that resonance signal (Vres) testing circuit, timing signal (Vsig) produce circuit and comparator circuit.Described resonance signal (Vres) picks up from Transformer Winding by diode, described timing signal (Vsig) has reflected the resonance time of shutdown back main circuit LC, a timing signal (Vsig) and a reference voltage base (Vref) connect two inputs with comparator respectively, and comparator output terminal connects the operating state control input end of PWM main control circuit.The resonance signal (Vres) that picks up from Transformer Winding by diode is synchronized with pwm signal, and pwm signal shields resonance signal (Vres) when the converter operate as normal; Shutdown back resonance signal (Vres) raises timing signal (Vsig), and the PWM main control circuit is in " shutoff " state during main circuit resonance by comparator circuit.
Described resonance signal (Vres) testing circuit comprises auxiliary winding Vf of a transformer and diode D2; Described timing signal (Vsig) produces the timing circuit that circuit comprises that R5, R6, C3 form, and R3, R4, Q1 form screened circuit; Described comparator circuit adopts amplifier U1A in the present embodiment, this amplifier positive input terminal is a reference voltage base (Vref), the amplifier negative input end connects timing signal (Vsig), the operating state control input end of amplifier output termination PWM main control circuit, when amplifier output SHUT signal is high level, the PWM main control circuit can be worked, and when the SHUT signal was low level, the PWM main control circuit was in " shutoff " state.The Transformer Winding of described sampling resonance signal (Vres) can directly be utilized the accessory power supply winding, and reference voltage base (Vref) also can adopt the reference voltage in the PWM main control circuit.Described circuit is to not influence of converter work during the converter operate as normal.
The main signal waveform of circuit is shown in Fig. 2 b among Fig. 2 a, when the DC to DC converter operate as normal, at t1 constantly, PWM1 is a high level, is responsible for the S1 conducting, the former limit of transformer winding voltage waveform Vp is the forward level, at this moment, the auxiliary winding Vf waveform of transformer also is sensed as the forward level, but be high level because of PWM1 this moment, the Q1 conducting, timing signal Vsig is a low level; At t2 constantly, PWM1 is a low level, and Q1 turn-offs, and is responsible for S1 and turn-offs, and this moment, former limit winding voltage Vp and auxiliary winding voltage Vf were for negative, because the buffer action of D2, resonance signal Vres is a low level, and therefore this moment, timing signal Vsig still was a low level.So when operate as normal, Vsig keeps low level always, amplifier U1A output SHUT signal is a high level always, to the not influence of work of PWM main control circuit.At t3 constantly, after Vin was reduced to under-voltage some Uuv of input of converter, main control circuit was closed pwm signal, as previously mentioned, clamper tube S2 still keeps long-term conducting, clamping capacitance Cc and former limit magnetizing inductance begin resonance, and at t4 constantly, former limit winding voltage Vp and auxiliary winding voltage Vf resonance are to positive level, be closed because of the PWM1 signal this moment, Q1 turn-offs, and to capacitor C 3 chargings, timing signal Vsig begins to rise resonance signal Vres by resistance R 5; At t5 constantly, former limit winding voltage Vp and auxiliary winding voltage Vf resonance are to zero level, timing signal Vsig is by resistance R 6 discharges, because of the R6 resistance bigger, so it is slower to discharge, the discharge time constant of discharge resistance R6 and charging capacitor C3 formation is much larger than the charge constant of charging resistor R5 and charging capacitor C3 formation like this, perhaps also we can say, mean charging current on the charging resistor R5 is greater than the discharging current on the discharge resistance R6, thereby charging capacitor C3 its terminal voltage when charging repeatedly can constantly be accumulated.Continue as LC resonance in the main circuit, then capacitor C 3 is recharged repeatedly, and be higher than reference voltage base Vref constantly at t6, the upset of amplifier output SHUT signal is low level, the PWM main control circuit is in " shutoff " state, even after this energy that feeds back to former limit from secondary is lifted to Vin more than the Vuv level, DC to DC converter can not enter yet and restart, and guarantees dull decline the in output voltage waveforms shutdown back.When secondary output capacitance voltage descends near zero level, LC resonance also stops gradually in the main circuit, input terminal voltage Vin gradually the loop to Vuv, simultaneously, because of stopping back capacitor C 3, main circuit resonance no longer includes charging, so capacitor C 3 is discharged to below the Vref level gradually by resistance R 6, the upset of amplifier U1a output SHUT signal is high level, but PWM master control end is in operating state.
Embodiment two:
Shown in Fig. 3 a, 3b, 3c, this example is to do change on the basis of embodiment one slightly: will assist the direction of winding of winding reverse, thereby make the voltage that is produced on its voltage of responding to and the former limit winding just in time opposite, and can reach goal of the invention too.Need this moment the direction of diode D2 reverse, add inverter between the screened circuit Q1, and two inputs of comparator are exchanged.
As Fig. 3 a, winding is reverse, and diode is also reverse, then the resonance signal sample circuit adopt be a negative signal, then the benchmark of comparator also must be a negative benchmark, promptly Fu multilist more shows that resonance time is long more.Screened circuit Q1 will shield also more complicated of a negative signal, needs with a P channel MOS tube.
As Fig. 3 b, because of sampled signal has individual charge and discharge process, the Q1 shielding time is unnecessary very accurate, the signal of available PWM2 back.
As Fig. 3 c, if auxiliary winding is reverse, diode is not reverse, then is equivalent to adopt another wave head of resonance signal, as long as the control signal of screened circuit oppositely just can.
Embodiment three:
As shown in Figure 4, this example has been compared more different with embodiment one, two: it is that timing circuit is partly made into pure counter mode, and effective with rising or trailing edge, then D2 can save; With the size of count value decision upset, then comparator also can save, with PWM1 have or not the decision counting whether effective, then Q1 also can save.As seen, in this example, this two parts circuit of described useful signal summation circuit and decision circuitry is to be realized separately by counter circuit.
Patent disclosure of the present invention prevent that restarting circuit after the active clamping circuir shutdown is confirmed for testing, described circuit is used in the input of 36~75V direct current, 3.3V/20A in the DC/DC power supply of direct current output, under any input voltage waveform, under various environmental conditions, under various external output capacitance conditions, shutdown back output voltage all can be realized dull decline, and nothing restarts.
More than describe the present invention by embodiment, but the present invention also do not limit therewith, and is all in improvement or the replacement of saying work without prejudice to spirit of the present invention and content, should be regarded as belonging to protection scope of the present invention.Such as, though in an embodiment, main circuit working state signal sample circuit is realized by screened circuit, is not limited to this, and screened circuit has various ways again; In embodiment one, two, the useful signal summation circuit is realized by timing circuit, and in embodiment three, useful signal summation circuit and decision circuitry are integrally realized by counter circuit, but its implementation still is not limited to these two kinds, and so on.