What should be the deadtime for Hbridge circuit???

[billu8660]

Thread closed due to this being an example of an unisolated power supply that is permanently "live" and consequently potentially lethal. Such topics are against the rules for your safety,


diyAudio Rules

hi,
i am building a Hbridge SMPS with SG3525 and IR2110, the MOSFETS are IRFP460 i need to know what will be the sufficient deadtime for 50khz frequency???

Because MOSFETs are exploding with 880ns deadtime, is deadtime the problem because it works fine with 60Vdc as input but when i apply 310Vdc booooom

[RJM1]

#1 depends on what MOSFETs you are using and their turn off delay. A schematic would be useful? The turn on delay for the IRFP460 is 18uS, you probably want to be a bit longer than that.
#2 depends on your gate drive circuit.

[SemperFi]

What kind of monster are u building?
Drain voltage squared is a factor in switching losses, so u dont need to increase the voltage before it goes too far. You need to increase the voltage slower and observe when the devices temp gets critical.
Can you place current transformers in series with drai and gate to check currents? You'd be able to tweak DT that way. Assuming you have a good o-scope.

[SemperFi]

More possibilities:
Could it be spikes becoming too high as the voltage is increased killing the MOSFET?

[MarianB]

IRFP460 are quite sturdy MOSfet's but they have a rather large Ciss witch if not charged fast enough it causes slow turn on and so the power dissipated on the mosfets increases with increasing voltage and they cand be destroyed by this, so you need to be sure you have enough gate current for them. Anyway a schematic is the only way for us to determin what is your problem, so do show us what it is.

[palstanturhin]

Or:
Is your flux walking? How did you prevent that in your circuit?

[QUOTE=RJM1;3268831]A schematic would be useful?[QUOTE]

[SemperFi]

Originally Posted by MarianB

IRFP460 are quite sturdy MOSfet's but they have a rather large Ciss witch if not charged fast enough it causes slow turn on and so the power dissipated on the mosfets increases with increasing voltage and they cand be destroyed by this, so you need to be sure you have enough gate current for them. Anyway a schematic is the only way for us to determin what is your problem, so do show us what it is.

yep. perhaps the duty cycle is becoming too short as the voltage is increased, so short it is not turning the FET on properly....?

[MarianB]

That too could be the reason for failing, but fet's are verry fast devices and 50Khz does not seam that high a freq, if they would have enough gate current deadtime should not be a problem. But until we do not see the exact schematic used all we can do is suppose things.

[billu8660]

hi all,
here is the schematic

[palstanturhin]

Are you actually using MUR1560 at the output?
Are you sure you have not blown those already and that is the cause of problems?