Summary of the invention
Technical problem to be solved by this invention is at low output voltage, High Output Current application scenario, has proposed ZVS and has realized that a kind of synchronous rectification drive signal of utilizing of wide ranges latchs leakage inductance energy full-bridge soft-switching DC converter.
The present invention is for solving the problems of the technologies described above by the following technical solutions:
A kind of full-bridge soft-switching DC converter comprises the former limit of transformer circuit, transformer secondary circuit, and described former limit circuit comprises the input power supply, first to fourth switching tube, the former limit of isolating transformer winding; Wherein said first switching tube and the 3rd switching tube, second switch pipe and the 4th switching tube are formed two half-bridge circuits respectively, the two ends of two half-bridge circuits are connected with positive pole, the negative pole of input power supply respectively, and the two ends of the former limit of described isolating transformer winding connect the mid point of two half-bridge circuits respectively; Be connected in series first, second clamping switch tube successively between two brachium pontis of described two half-bridge circuits.
Preferably, full-bridge soft-switching DC converter of the present invention, first to fourth switching tube, first to second clamping switch tube include its parasitic diode, parasitic capacitance.
Preferably, full-bridge soft-switching DC converter of the present invention, secondary circuit comprises isolating transformer secondary winding, first to the second synchronous rectification switch pipe, outputting inductance, output filter capacitor, load constitutes; Wherein an end of isolating transformer secondary winding is connected with the source electrode of the first synchronous rectification switch pipe, the drain electrode of the first synchronous rectification switch pipe is connected with an end of outputting inductance, the drain electrode of the second synchronous rectification switch pipe respectively, and the source electrode of the second synchronous rectification switch pipe is connected with the other end of isolating transformer secondary winding; The other end of described outputting inductance is connected with an end of output filter capacitor, an end of load respectively, and the other end of described output filter capacitor, the other end of load are connected with the mid point of isolating transformer secondary winding respectively.
Preferably, full-bridge soft-switching DC converter of the present invention, first, second synchronous rectification switch pipe includes its parasitic diode, parasitic capacitance.
The present invention adopts above technical scheme compared with prior art, has following technique effect:
Full-bridge soft-switching DC converter of the present invention has ZVS and realizes reliable and wide ranges, the advantage that duty-cycle loss is low.The auxiliary switch that increases is operated under the ZCS condition, and its drive signal is consistent with the synchronous rectification switch pipe signal of secondary, and circuit is realized simpler.This embodiment need not to increase extra resonant inductance, and the ZVS realization condition does not rely on external variables such as input voltage and load current, helps converter and realizes high power density, high efficiency.Particularly, in each switch periods, the leakage inductance energy of isolating transformer is collected and releases energy at Dead Time, has overcome the voltage oscillation spike that produces when the former limit of conventional full bridge converter switching tube turn-offs, and has improved the reliability of converter.
The present invention realizes ZVS by increasing by two auxiliary switches on the former limit of isolating transformer, and the drive signal of auxiliary tube directly adopts secondary synchronous rectification drive signal simultaneously, have simple in structure, reliability is high, the reliable advantage of ZVS realization condition.
Embodiment
Below in conjunction with accompanying drawing technical scheme of the present invention is described in further detail:
As shown in Figure 1, the full-bridge soft-switching DC converter is by input power supply V
In, switching tube Q1-Q4, isolating transformer TX1, auxiliary switch Q5-Q6, secondary synchronous rectification switch pipe Q7-Q8, outputting inductance L1, output filter capacitor C1, load R1 constitutes.The drive waveforms of auxiliary switch is consistent with the drive signal of secondary synchronous rectification switch pipe, and for duty ratio is to be similar to 50% complementary square-wave signal, the insertion dead band is common to prevent between the auxiliary switch.D among Fig. 1
Q5, C
Q5Be parasitic diode and the parasitic capacitance of switching tube Q5, D
Q6, C
Q6Be switching tube Q6 parasitic diode and parasitic capacitance.It is to be noted to have identical parasitic parameter among the switching tube Q1-Q4, for simplify describe not shown.
As shown in Figure 2, it has provided the sequential and the main waveform schematic diagram of the full-bridge soft-switching DC converter of example of the present invention.Fig. 2 waveform from top to bottom is respectively: the drive waveforms of switching tube Q1, Q4 in the full-bridge; The drive waveforms of switching tube Q2, Q3 in the full-bridge; The drive waveforms of auxiliary switch Q5 and synchronous rectifier Q7; Flow through parasitic diode D
Q6With the current waveform among the auxiliary switch Q5; The drive waveforms of auxiliary switch Q6 and synchronous rectifier Q8; Flow through parasitic diode D
Q5With the current waveform among the auxiliary switch Q6; Isolating transformer primary current i
pSynchronous rectification switch pipe Q7 current waveform; Synchronous rectification switch pipe Q8 current waveform; Outputting inductance current waveform i
LAs shown in Figure 2, auxiliary two-tube active clamp full-bridge soft-switching DC converter can mainly be divided into 6 kinds of switching modes in a switch periods, be respectively [t
0, t
1], [t
1, t
2], [t
2, t
3], [t
3, t
4], [t
4, t
5], [t
5, t
6], [t wherein
0, t
3] be the preceding half period, [t
3, t
6] be the later half cycle.The operation principle of converter when below briefly introducing each operation mode.
[t
0, t
1] mode (with reference to figure 3):
At t
0In the Dead Time constantly, the junction capacitance resonance among leakage inductance and switching tube Q1-Q4 and the auxiliary switch Q6, be latched in the auxiliary brachium pontis leakage inductance energy release and with the junction capacitance energy exchange.By designing suitable leakage inductance, the t in Fig. 2
0Constantly, but the DS both end voltage resonance of full-bridge switch pipe Q1, Q4 and auxiliary switch Q5 is 0, so full-bridge switch pipe Q1 and Q4 can realize that ZVS is open-minded.At t
0Constantly, because D
Q6The diode blocking-up, auxiliary switch Q5 conducting this moment does not have electric current to be flow through, simultaneously because the DS voltage at auxiliary switch Q5 two ends is 0, so Q5 is the ZVZCS(zero-voltage and zero-current switch) open-minded.Switching tube Q1, Q4 and synchronous rectification switch pipe Q7 conducting in the full-bridge converter, the isolating transformer exciting curent is linear to increase outputting inductance i
L1The storage power electric current is linear to rise.Limit, transformer Central Plains current i
pBy magnetizing inductance electric current and outputting inductance i
L1Convert the stack of primary current two parts and form, power supply is an electric.
[t
1, t
2] mode (with reference to figure 4):
The output voltage of full-bridge converter reaches the V of expectation
Out, the main switch Q1 and the Q4 of full-bridge converter close.Because the undercurrent that flows through in the transformer of former limit is to provide outputting inductance i
L1Required electric current, the conducting simultaneously of the body diode among synchronous rectification switch pipe Q7 and the synchronous rectification switch pipe Q8 provides load current, and isolating transformer is by short circuit.Because auxiliary switch Q5 is in conducting state, the transformer primary current is flowed through by parasitic diode D
Q6, the service bridge armlet road that constitutes of Q5 and winding two ends, the former limit of transformer, the leakage inductance energy of transformer is latched in the auxiliary brachium pontis.Outputting inductance i
L1Storage power is discharged into output, inductive current i through the body diode among synchronous rectification switch pipe Q7 and the synchronous rectification switch pipe Q8
L1Effect lower linear at output voltage descends.As shown in Figure 2, at [t
1, t
2] electric current that flows through the former limit of transformer during the mode changes very for a short time, the reason that electric current descends is that the part leakage inductance energy is consumed by the impedance in the auxiliary brachium pontis.Because the energy of leakage inductance is latched by auxiliary brachium pontis, significant voltage oscillation spike will can not appear in full-bridge switch pipe Q1, Q4 two ends when closing, and realize low EMI, and the reliability of switching tube also is improved.
[t
2, t
3] mode (with reference to figure 5):
Switching tube Q1-Q4, auxiliary switch Q5-Q6, secondary synchronous rectification switch pipe Q7-Q8 are in closed condition in the full-bridge converter.Be latched in the meantime that leakage inductance energy in the auxiliary brachium pontis discharges and with the energy exchange of switching tube junction capacitance.The isolating transformer primary current descends under leakage inductance and switching tube junction capacitance resonance affects, and is shorter because of this section Dead Time, and primary current also can be similar to be thought and do not change.By designing suitable leakage inductance, the t in Fig. 2
3Constantly, but the DS voltage resonance of full-bridge switch pipe Q2, Q3 and auxiliary switch Q6 is 0, and primary current flows through in the parasitic body diode of Q2, Q3 to power feed, therefore at t
3Switching tube Q2, Q3 and Q6 can realize that ZVS is open-minded constantly.During this mode, former limit input current still is not enough to provide outputting inductance i
L1Required electric current, electric current is flow through in the conducting simultaneously of the parasitic body diode among the synchronous rectification switch pipe Q7-Q8, and isolating transformer is still by short circuit.
Later half cycle [t
3, t
6] switch operation mode and preceding half period [t
0, t
3] be identical, no longer analyze.
By above analysis as can be known, the work of we the drive signal control auxiliary switch Q5-Q6 by utilizing the synchronous rectification switch pipe is latched the leakage inductance energy of full-bridge transformer and is discharged constantly in the dead band constantly, and auxiliary switch is operated in the ZVZCS state simultaneously.Because Dead Time is less, with respect to traditional full-bridge converter soft switch technique, this method not only can make main switch Q1-Q4 be easy to realize the ZVS switch, and realization wider range of the soft switch of ZVS, and is not high with the relevance of load and input voltage.By such design, just can reduce the switching loss of power switch pipe in the full-bridge converter greatly, improved the efficient of converter, and the auxiliary switch switching loss that is operated under the ZVZCS state is also lower.And this method is owing to overcome the voltage oscillation spike that produces when the former limit of conventional full bridge converter switching tube turn-offs, and the reliability of converter also improves greatly.
The concrete parameter of example of the present invention is as follows: input voltage is 36VDC-75VDC; Output voltage 12VDC; Output current 15A; The transformer turn ratio is 2:1; Output inductor L1 is 15 μ H; Output filter capacitor C1 is 200 μ F; Full-bridge main switch, auxiliary switch, secondary synchronous rectification switch pipe are IPB108N15N3G, and its control chip is ISL6753, and the switching frequency of setting is 100kHz, and Dead Time is 500nS.
In sum, a kind of full-bridge soft-switching DC converter of the present invention, control the switch motion moment of two auxiliary switches of full-bridge converter by utilizing secondary synchronous rectification drive signal, the former limit transformer leakage inductance energy of collecting can be discharged in Dead Time, realizes the ZVS(zero voltage switch of full-bridge converter main switch) soft switch.The full-bridge soft-switching DC converter main switch ZVS condition that realizes by the auxiliary switch mode is subjected to the influence of input voltage and load variations less, can realize ZVS in the scope of broad, has promoted the efficient of converter.Simultaneously, can not produce on the former limit main switch of full-bridge converter because it closes the resonance spikes that causes the vibration between leakage inductance and junction capacitance to cause, the full-bridge switch pipe can be selected lower withstand voltage, has reduced cost, has improved the reliability of converter.In addition, because full-bridge converter is realized the ZVS switch easily in gamut, secondary adopts synchronous rectification, so the EMI interference is low, efficient is high.