[SOLVED] Dead time for IGBT bridge

[vinu gopalakrishnan]

Hi guys...
Trying to do build 3 phase inverter to drive induction motor.
Im using pic18f452 to give gating signals to IGBT bridge(3 legged) via TLP 250. So the confusion is that should i give dead time in the code?
My igbt is FGA15N120 having maximum Ton Toff delays 150ns (for high current). According to the c code, one instruction cycle takes more than this time...so should i give additional delay time between the switching?..What do you think???

this figure shows two pins giving complementary outputs, having no instructions in between...time taken between the instructions is 330ns...Is this delay enough?

 

[iop95]

It's not enough. Must be minim td(off) + tf, accordingly datasheet mean 310+60 = 370ns; adding same extra time for safety, to avoid cross conduction, I think you need to increase this time to 500-600ns.

 

[vinu gopalakrishnan]

What if i change the oscillator for pic...such that the time for one instruction cycle is made 600ns?

 

[iop95]

May be ok but are your sure that instruction cycle need near constant time or even don't decrease below 300-400ns cycle time? I think it's not safe to use cycle durations to design delays in system.

 

[urgentappliance]

It's not enough, you need more for it.

 

[ArNvC]

ya, as mentioned by urgentappliance you need more deadtime to ensure that the high and low side igbt's are never on at the same time , thus shorting the supply. It depends on how quickly you can turn on and off the switches that will dictate the dead time.

 

[vinu gopalakrishnan]

ok,, so i will include code for dead time..thanks everyone.

 

[davemaster]

Greetings,

Always try to post the schematic / diagram... thanks

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Greetings,

Always try to post the schematic / diagram... thanks