Background technology
In recent years, the expansion of switching device kind, performance parameters improves, and circuit topology is perfect, so the soft switch circuit development is very fast.Power MOSFET is the first-selection in low-voltage, the frequency applications, and in high voltage, medium-high frequency converter, the superiority of IGBT becomes increasingly conspicuous, and becomes the main flow device.Because IGBT is a multiple device, the MOS in turn off process in the equivalent electric circuit turn-offs fast, causes V
CeRise rapidly, stored charge can not be extracted out from the mos gate utmost point in the equivalent transistor, and a part is by the compound elimination in inside, and another part is at V
CeDriving under force extraction by transistor collector current, form the hangover electric current, this hangover electric current produces bigger turn-off power loss with the collector voltage that raises.Soft switch technique can reduce switching loss greatly, and has many advantages that the hard switching technology is not had, and is the effective ways that overcome IGBT frequency applications obstacle.
The soft switch technique kind is a lot, as resonant switch technology, zero switching technique and branch on zero technology etc., wherein the branch on zero converter is owing to adopt the resonant process of auxiliary network control resonant element, when keeping the pwm converter advantage, realized soft switch, reduce switching loss, become the research focus of field of power electronics.But because auxiliary network has also been introduced the switching loss of auxiliary tube accordingly, if auxiliary tube is operated in the hard switching state, the switching loss of generation is also influential to the efficient of whole converter, and as the MOSFET of auxiliary tube with high pressure, then device cost is very high.Also adopt IGBT as auxiliary tube, be responsible for IGBT high voltage, high-power output requirement to adapt to, then auxiliary tube soft commutation break-make is also very important, and the effect of soft switch can also improve the functional reliability of switching device except reducing switching loss.Consider that from the reliability angle auxiliary tube also should adopt soft switch technique.
Summary of the invention
The purpose of this invention is to provide a kind of soft switching buck DC-DC converter, it has realized that by auxiliary network the zero-voltage zero-current of main switch turn-offs, the zero current break-make of auxiliary switch, and the zero current of fly-wheel diode is connected.
The present invention is achieved in that a kind of soft switching buck DC-DC converter, comprises by main switch Q, sustained diode
0, inductance L
0, filter capacitor C
0And resistance R
0The buck DC converter of forming is by auxiliary switch Q
1, resonant inductance L
r, resonant capacitance C
R1, C
R2, diode D
1, D
2, D
3The auxiliary resonant net of forming is characterized in that: described resonant capacitance C
R2One end, diode D
2Negative pole and the collector electrode of main switch Q be connected with positive source; Described resonant capacitance C
R2The other end and diode D
2Positive pole, diode D
3Negative pole, resonant inductance L
rAn end be connected; Described resonant inductance L
rThe other end and resonant capacitance C
R1An end be connected; Described resonant capacitance C
R1The other end and diode D
1Negative pole, auxiliary switch Q
1Collector electrode be connected; Described diode D
1Positive pole and emitter-base bandgap grading, the auxiliary switch Q of main switch Q
1Emitter-base bandgap grading, sustained diode
0Negative pole, inductance L
0An end be connected; Described inductance L
0The other end and filter capacitor C
0An end, resistance R
0An end be connected; Described filter capacitor C
0, resistance R
0, sustained diode
0And diode D
3Positive pole be connected with the negative pole of power supply.
The present invention has that switching loss is little, soft-switching range is wide, reliability is high, can be applicable to high voltage, occasion such as high-power.
Embodiment
The present invention will be further described below in conjunction with drawings and Examples.
As shown in Figure 1, the invention provides a kind of soft switching buck DC-DC converter, comprise by main switch Q, sustained diode
0, inductance L
0, filter capacitor C
0And resistance R
0The buck DC converter of forming is by auxiliary switch Q
1, resonant inductance L
r, resonant capacitance C
R1, C
R2, diode D
1, D
2, D
3The auxiliary resonant net of forming is characterized in that: described resonant capacitance C
R2One end, diode D
2Negative pole and the collector electrode of main switch Q be connected with positive source; Described resonant capacitance C
R2The other end and diode D
2Positive pole, diode D
3Negative pole, resonant inductance L
rAn end be connected; Described resonant inductance L
rThe other end and resonant capacitance C
R1An end be connected; Described resonant capacitance C
R1The other end and diode D
1Negative pole, auxiliary switch Q
1Collector electrode be connected; Described diode D
1Positive pole and emitter-base bandgap grading, the auxiliary switch Q of main switch Q
1Emitter-base bandgap grading, sustained diode
0Negative pole, inductance L
0An end be connected; Described inductance L
0The other end and filter capacitor C
0An end, resistance R
0An end be connected; Described filter capacitor C
0, resistance R
0, sustained diode
0And diode D
3Positive pole be connected with the negative pole of power supply.
In order to make those skilled in the art fully understand the present invention, cooperate Fig. 2 and Fig. 3 a~Fig. 3 g to be described further below, here to simplify the analysis, we suppose that all components and parts all are desirable in the circuit, output inductor L
0Enough big, use constant-current source I
0Replace input voltage V
InExpression.If t=t
0Before, resonant capacitance C
R1Voltage be-V
Crlmax, resonant capacitance C
R2Voltage be zero.Circuit has six kinds of operational modes a switch periods.
(1) pattern 1t
0Before shown in Fig. 3 a: main switch Q conducting, auxiliary switch Q
1Turn-off, auxiliary network is not worked, and circuit operates in conventional PWM mode.
(2) pattern 2 (t
0~t
1) t
0The time auxiliary switch Q
1Zero current passing, L
rWith C
R1And C
R2Resonance takes place, and shown in Fig. 3 b, inductive current is started from scratch to be increased by sinusoidal rule, and the electric current of main switch Q then reduces with sinusoidal rule, process
Behind the harmonic period, i
LrReach maximum, the main switch electric current drops to zero, and turn-off main switch this moment, realized the zero-current switching of main switch.
(3) mode 3 (t
1~t
2) t
1The time main switch Q turn-off main switch both end voltage V
CeRising, resonant capacitance C
R1, C
R2Voltage also raises gradually.Work as V
Cr2=V
InThe time, D
3Conducting, the resonance branch road is from Q
1, L
r, C
R1And C
R2Transfer to L
r, C
R1, Q
1, D
0And D
3The loop, shown in Fig. 3 c, the resonant inductance energy stored is to capacitor C
R1Shift resonant inductance L
rElectric current reduces gradually, sustained diode
0Electric current increases gradually, for zero current is connected.When the resonant inductance current i
LrWhen being zero, capacitor C
R1Both end voltage reaches maximum, D
3End, this resonance branch road stops resonance.C in the circuit
R2Both as resonant capacitance, again with D
3Constitute the resonant network change-over circuit, and by C
R2And D
3It is to guarantee resonant inductance L that the resonance branch road that constitutes shifts
rEnergy continues to capacitor C
R1Shift the key point that realizes the auxiliary switch zero-current switching.
(4) pattern 4 (t
2~t
3) t
2The time i
Lr=0, Chuan Lian auxiliary switch Q with it
1Electric current also is zero, from t
2Begin to turn-off auxiliary switch Q in the period to this section of being responsible for before connecting
1Can realize the zero-current switching of auxiliary tube.Auxiliary network quit work after auxiliary tube turn-offed, and circuit operates in the conventional PWM mode that the BUCK inductance is in the afterflow state, is the inductance afterflow stage, shown in Fig. 3 d.
(5) pattern 5 (t
1~t
4) t
1Main switch Q conducting constantly, circuit is on the one hand to inductance L
0The charging and to electric, be resonant element energy reseting procedure on the other hand, resonant inductance L
rWith C
R1And C
R2Resonance takes place, shown in Fig. 3 e, capacitor C
R2Both end voltage V
Cr2Reduce gradually.
(6) pattern 6 (t
4~t
5) t
4The time V
Cr2=0 o'clock, D
2Conducting, shown in Fig. 3 f, L
rWith C
R1Continue resonance, up to resonant inductance L
rCurrent i
Lr=0 o'clock, D in the resonant slots
1And D
2End, circuit stops resonance, and the resonant inductance energy is all transferred on the electric capacity, C
R1Voltage remains on-Vcrmax, C
R2Voltage remains zero, for next switch periods main switch zero-current switching is prepared.t
5Later on shown in Fig. 3 g: auxiliary network is not worked, and circuit is got back to conventional PWM operational mode again, repeats a switch periods job.
By above analysis as can be known, realize that the key of main switch zero-current switching is pattern 2, utilize L
rWith C
R1And C
R2Resonance makes the main switch electric current transfer to the resonance branch road gradually, and the prerequisite of generation current transfer is will certain original negative voltage is provided and carry out energy before each switch periods finishes to resonant capacitance to reset.When the auxiliary switch conducting, the resonance branch current increases gradually, and the main switch electric current reduces gradually, until i
cRealized zero-current switching at=0 o'clock; When the main switch conducting, carry out the reseting procedure of resonant energy, rebulid negative capacitance voltage, for the main switch zero-current switching of following one-period is prepared.
The key that realizes the auxiliary switch zero-current switching is in the mode 3 by C
R2And D
3The transfer of the resonance branch road that constitutes makes the resonant inductance energy of connecting with auxiliary switch be passed through D
3Continue to be discharged into zero, realize the zero-current switching of auxiliary switch.
The above only is preferred embodiment of the present invention, and all equalizations of being done according to the present patent application claim change and modify, and all should belong to covering scope of the present invention.