thanks tahmid for reply
Tahmid said:
1) Where is the 311VDC coming from? Is it rectified from the mains? Did you use a sufficiently larger capacitance to filter it to produce clean DC?
311vdc is coming from another circuit that i have already made,it is regulated. i have used 47uf capacitor ,here is the image
one more thing i have noticed,when i apply 311vdc to hbridge and filter is not connected ,then there is no damage, as i connected my filter (lc 5mh, 0.22uf) and switch on my dc supply mosfets of hbridge blown out also the mosfets which were used in dc dc converter stage also blown out.
Tahmid said:
2) What is the voltage rating of the 0.22µF filter capacitor?
on the capacitor it is written 1000v.
Tahmid said:
3) When the MOSFETs blow out, do they get very hot?
as i connect filter and switch on my dc bus bus, mosfets blown out,,, and also they get very hot.
Tahmid said:
4) Do all the MOSFETs get damaged or is it just one or two or three? Which ones?
i dont think that all mosfets of hbridge get damaged ,,only two of them get very hot,,i m not sure whether it was high side or low side,,,but probably it was high side mosfet that gets hot
Tahmid said:
5) Did you test with no load? Or did you use a load? If so, what load?
I have tested it in both conditions separetly that is with load (60 watt bulb) and without load also. in both conditions i have got failure.
Tahmid said:
6) Try adding a soft-start to the program so that the microcontroller starts sending the pulses a while after power is turned on.
In one trial I first turned on my microcontroller and then i switched on my dc bus,
in second trial i connected my complete circuit i.e. i have connected my dc bus to hbridge stage and simultaneously switch on the complete circuit (hbridge+dc dc stage),,
i haven't tried giving dc to hbridge first and then turning on my microcontroller.
Tahmid said:
7) Did you replace the filter capacitor and the MOSFETs and try again?
yes tahmid ,i have replaced my mosfets as well as filter capacitor,, infact this is my 16th try of complete circuit, but i have repalced my capacitor only 3 times,,after that i only replaced the mosfets (all four mosfets) and use the same capacitor.
Tahmid said:
8) Add capacitors (filter and decoupling) across the VC and COM of the IR2110s, as well as between VDD and VSS lines of the microcontroller.
what is the role of these capacitor,,? i have made my 16th circuit on breadboard in which i have connected capacitors across VC and COM, i haven't tried this before,,
all the previous circuit that i have made are on veroboard , i haven't tried my 16th circuit yet ,,,tomorrow i will try ,,
one more thing tahmid
i have used 1k resistor from gate to source in each mosfets,,and i have used 22uf capacitor in my bootstrap circuit. this capacitor has to provide the gate voltage above 8v to 10ms time interval, but according to discharging equation of capacitor V=V0(e^(-t/RC)) , the 22uf capacitor will drop to approx 6.3volts ,which is less than the threshold voltage of the power mosfets, it should be greater than 8volts for the entire 10ms ,,
but i don't think that this is reason for the damaging of mosfets , because in this case mosfet will simply turn off as the voltage will drop below 8volts,, please through more light on this,,
also tell me where i am wrong ,i have tried again and again but didn't get success..