Abstract: Recommended one kind of resonance to reposition the double switch to stir up the DC/DC converter. It not only overcame the resonance to reposition the single switch to stir up the converter switching voltage stress to be big and conversion efficiency low shortcoming, moreover had the dutyfactor to be possible to be bigger than 50% merits. Therefore, this converter may apply in the high input voltage, the width range of variation, the high efficiency request situation. Have carried on the detailed description to this analysis situs’s principle of work and the characteristic. Finally confirmed this analysis situs above merit through the experiment.
Key word: Resonant replacement; Double switch; Is stirring up the converter
1 outline
The resonance repositions the single switch to stir up the converter, as shown in Figure 1, is one kind of structure is quite simple, the application very widespread DC/DC converter. It carries on the replacement through the resonant electric capacity Cr on voltage to the transformer, this resetting voltage may be bigger than the input voltage, therefore, this converter’s dutyfactor may be bigger than 50%, suits in the wide input range situation. But the usual single switch is stirring up the converter to be the same, its switching voltage stress is quite big, is about input voltage 2 times, uses in the high input voltage the situation having certain difficulty. Moreover, before each time switch S clear, on Cr the voltage is the input voltage, when the S clear, not only on S parasitic capacity’s energy CossVin2/2 consumption on switch, simultaneously also Cr on energy CrVin2/2 consumption on S. But Cr is also outside and the resonant electric capacity, its value possibly by far is bigger than switch’s parasitic capacity, therefore, may think that this converter’s equivalent switching loss increases greatly, the efficiency will come under the serious influence.
The double switch was stirring up the converter to overcome the main switch voltage stress big shortcoming, its each switch’s voltage stress was equal to the input voltage, was about single switch violent half, was suitable in the high-pressured input situation. Moreover the double switch is stirring up the converter is carries on the replacement using the input voltage to the transformer, in the structure is also quite simple, the initiation energy and the leakage inductance energy back coupling arrives at the input side, the transfer efficiency is quite high. Therefore, this kind of double switch is stirring up the DC/DC analysis situs widely to apply in the industrial world, is not only the high-pressured input situation. But, this kind of double switch is stirring up the converter to have its prominent shortcoming, namely can only work in the dutyfactor is smaller than 50% conditions, therefore, is not suitable to use to transform the scope very wide situation.
This article recommended one kind of resonance to reposition the double switch to stir up the converter, it synthesized the single switch resonance to stir up with the double switch violent merit, not only might work in the dutyfactor is bigger than 50% conditions, moreover used the double switch structure, reduced switch’s voltage stress greatly. Therefore, this converter is suitable for the high voltage input, the width range of variation situation.
2 principles of work
The resonance repositions the double switch to stir up converter’s electric circuit as shown in Figure 2. Figure 2 Coss1, Coss2, Coss3 respectively for the switch S1, S2, S3 parasitism output capacity, Cr is the resonant electric capacity, it is parallel, in S2 leaks between the source, because Cr is bigger than switching valve’s parasitic capacity far, therefore Coss2 may neglect. Lm is the initiation inductance. As the simplified analysis, output capacity Co was considered the infinity, but replaces by constant pressure source Vo, and supposed the electric circuit already to enter the stable state.
This converter’s switching period may divide into 6 working stages, distinction like chart 3 6 equivalent circuits shows. Corresponding work profile as shown in Figure 4, t1-t3 is dead time td1, t5-t6 is dead time td2, these time are in fact short, in chart to indicate clearly, draws quite in a big way them. 6 working stage’s principle of work describes as follows separately.
1) stage 1(t0, t1) like chart 3 (a) and shown in Figure 4, at the same time this stage S1 and S2 the breakover, adds on the transformer primary side the voltage for input voltage Vin, the excitation circuit linearity rise. Simultaneously vice-side rectification diode DR1 breakover, after flow diode DR2 closure, on inductance L electric current iL linearity rise.
2) the stage 2(t1, t2)t1 time, like Figure 3(b) and shown in Figure 4, S1 and S2 also shut off, convert to the primary side load current and the excitation circuit together to the Coss1 charge, causes Coss3 to discharge, on Coss3 voltage vds3 rapid drop. Because resonant electric capacity Cr is big, in such a short time on the Cr voltage nearly has not risen, approximate is zero. Therefore vT on approximately equal vds3, also drops rapidly. But on this stage transformer’s voltage vT was still positive, therefore vice-side DR1 still breakover.
3) stage 3(t2, t3)t2 time vT drops the zero hour, vice-side diode DR1 cuts off, the DR2 breakover, iL through the DR2 after flow, the linearity drops under the output voltage Vo function. In the primary side, initiation inductance Lm and the resonant electric capacity Cr resonance, the resonance voltage which produces on Cr according to the sine change rise, at the same time this resonance voltage carries on the replacement to the transformer, the resonance current winds through S3 the body diode, like Figure 3(c) and shown in Figure 4.
4) the stage 4(t3, t4)t3 time, S3 gate driving signal vgs3 changes high extremely, S3 clears under the zero potential condition, Lm and Cr continue the resonance, on the Cr sine resonance voltage continue to the transformer to carry on the replacement, the resonance current wind through S3, like Figure 3(d) and shown in Figure 4.
5) stage 5(t4, t5) like chart 3(e) and shown in Figure 4, on Cr series resonance after the zero, the excitation circuit flows through S2 the body diode, but S3 still the breakover, by now the transformer primary side’s voltage was zero, the excitation circuit maintains invariable. Vice-side was still the DR1 closure, the DR2 breakover, the inductance electric current continues to drop.
6) stage 6(t5, t6) like chart 3(f) and shown in Figure 4, S3 shuts off in the t5 time, as soon as the excitation circuit carries on the charge to Coss3, vds3 is bigger than zero, vice-on the one hand rectification diode DR1 on the breakover, the excitation circuit flows to the transformer vice-on the other hand, but it is insufficient to maintain the load current, therefore after flow diode still breakover. As a result of DR1 and the DR2 breakover, on transformer’s voltage by the clip in zero, the excitation circuit maintains invariable. But on the switch S1 voltage by the clip on the Vin, S2 voltage is zero.
Figure 3
the t6 time, S1 and S2 also clear, S2 is the zero potential clear, but on the Coss1 electric charge puts rapidly through S1, the electric circuit enters to the next switching period stage 1, the load current winds through DR1.
By the above analysis may see that switch S1 and the S3 voltage stress is input voltage Vin, but the S2 voltage stress is the resetting voltage.
3 characteristic analyses
May see according to the above analysis, S1 and S3 are a pair of supplementary switch, on both parasitism output capacity’s sum of voltage vds1 and the vds3 is equal to input voltage Vin. Therefore, when vds1 (either vds3) is equal to the zero hour, vds3 (or vds1) is equal to Vin, obviously switch S1 and the S3 voltage stress is the input voltage.
The switch S2 source leaked parallel resonant electric capacity Cr, its value was bigger than S2 far parasitism output capacity Coss2, therefore, on the Cr voltage was the voltage which S2 must withstand. After S1 and S2 shutdown, initiation inductance Lm and resonant electric capacity Cr starts the resonance, produces a sinusoidal voltage on Cr to carry on magnetism replacement to the transformer. Therefore, the switch S2 voltage stress is this resetting voltage peak value.
Obviously, this converter’s switching voltage stress and the single switch are stirring up the converter to compare must be much smaller.
This converter’s another merit is may work, in the dutyfactor is bigger than under 50% conditions. As shown in Figure 4, when at the same time main switch S1 and S2 breakover, auxiliary switch S3 closure, add in the transformer primary side voltage to positively, the size is equal to the input voltage. When main switch S1 and S2 also cut off, when auxiliary switch S3 breakover, Lm and the Cr resonance the voltage which produces on Cr carries on magnetism replacement to the transformer. Through the choice small Cr value, this resetting voltage may be bigger than the input voltage, causes transformer’s resetting time is smaller than the forward breakover time, thus obtains one to be bigger than 50% dutyfactors. Such advantage is both may reduce a converter side the breakover loss, and may reduce two time side rectification diode’s voltage stress.
In addition, because on Cr series resonance after the zero, main switch S2 only then clears, therefore the resonant electric capacity cannot bring the extra loss, on the contrary caused S2 to realize the zero potential clear, its switching loss also greatly dropped. But S3 before the breakover is the body diode breakover, namely S3 is also the zero potential clear, the switching loss reduces greatly. Therefore, this converter’s transfer efficiency must stir up the converter the single switch resonance replacement to be much higher.
4 experimental results
Uses the resonance to reposition the double switch to stir up the DC/DC converter analysis situs the experiment prototype, has confirmed this analysis situs principle of work and the characteristic. This prototype’s specification and the main parameter are as follows:
Input voltage Vin250V~400V;
Output voltage Vo54V;
Output current Io0~5A;
Operating frequency f70kHz;
Main switch S1 and S2STP11NM60;
Auxiliary switch S3IRF830;
Rectification diode DR1HER1604PT;
After flow diode DR2B20200;
Transformer Tn=40∶20, Lm=3mH, Ls=15μH;
Filter inductance L130μH;
Resonant electric capacity Cr200pF.
Figure 5 is outputs when 4The main experiment profile. When its Chinese Library 5(a) is the input voltage is 250V, the transformer primary side’s voltage waveform, may see the dutyfactor is about 53%, proved that this converter may work in the dutyfactor is bigger than 50% conditions. Figure 5(b) is when the input is equal to 400V, the main switch S1 gate extremely slaving voltage and leaks the voltage waveform between the source, leaks the source voltage to the platform is 400V, happen to is being equal to the input voltage. Figure 5(c) is when the input is equal to 400V, the main switch S2 gate extremely slaving voltage and leaks the voltage waveform between the source, leaks the source voltage according to the sine change, its peak value is about 460V, this voltage carries on the replacement to the transformer. Meanwhile from the chart may see before the gate pole tension changes is high, vds2 already the resonance arrived at zero, S2 was the zero potential clear. Figure 5(d) is when the input is equal to 400V, the auxiliary switch S3 gate extremely slaving voltage and leaks the voltage waveform between the source, the source drain voltage to the platform is also 400V.
Figure 6 has given this converter in the different input voltage, under different load current transfer efficiency. The peak efficiency has achieved 95.3%.
5 conclusions
This article proposed the resonance repositions the double switch to stir up the converter, both inherited the resonance to reposition the single switch to stir up the converter dutyfactor to be possible to be bigger than 50% merits, and has displayed the double switch structure superiority, caused two main switch S1 and the S2 voltage stress respectively be the input voltage and the resetting voltage, but the auxiliary switch S3 voltage stress was the input voltage, thus reduced switch’s voltage stress greatly. Moreover, this converter’s switch S2 and S3 have realized ZVS, raised converter’s transfer efficiency greatly. Therefore, recommends the resonance repositions the double switch to stir up the converter to be possible to use in the high voltage input, the width range of variation, the high efficiency request situation.
