G'day folks.
I've been struggling with this for months now and not getting very far. I'm trying to build a plasma speaker from an old tv flyback (ac disc type)
Initially I was getting good results using 2x IRF250's driven from a 555 timer ic with a bc639/640 totem pole driver. Eventually it fried and I bought a bunch of IRF740's.
Since the current handling of the 740's is lower I decided to run 3 in parallel and found that the gate drive wasn't sufficient.
Now I'm running three totem pole drivers (639/640) and the 740's are running extremely hot. After 10 or so seconds, one invariably blows follwed closely by the remaining two.
The gate drive waveform is clean and it seems to run well at around 22Khz accept for the heating.
Totempole drivers are running at 12v and the gate resistors are 33ohm with a anti-parallel diode for gate discharge, back emf protection is a 12Kv diode from drain to source of all three fets.
My question is, could I be having problems with timing given the three seperate totem poles? Nothing else has changed since I had it running with "less robust" mosfets. My scope isn't a dso so how would I go about measuring and comparing the slew rates?
I haven't got a circuit diagram atm, but if it'll help I'll draw one up.
Thanks in advance, Any help would be greatly appriciated
sorry, also, I only have paint to draw a diagram atm, could someone give me some direction as to how to post the image? thanks
I've been struggling with this for months now and not getting very far. I'm trying to build a plasma speaker from an old tv flyback (ac disc type)
Initially I was getting good results using 2x IRF250's driven from a 555 timer ic with a bc639/640 totem pole driver. Eventually it fried and I bought a bunch of IRF740's.
Since the current handling of the 740's is lower I decided to run 3 in parallel and found that the gate drive wasn't sufficient.
Now I'm running three totem pole drivers (639/640) and the 740's are running extremely hot. After 10 or so seconds, one invariably blows follwed closely by the remaining two.
The gate drive waveform is clean and it seems to run well at around 22Khz accept for the heating.
Totempole drivers are running at 12v and the gate resistors are 33ohm with a anti-parallel diode for gate discharge, back emf protection is a 12Kv diode from drain to source of all three fets.
My question is, could I be having problems with timing given the three seperate totem poles? Nothing else has changed since I had it running with "less robust" mosfets. My scope isn't a dso so how would I go about measuring and comparing the slew rates?
I haven't got a circuit diagram atm, but if it'll help I'll draw one up.
Thanks in advance, Any help would be greatly appriciated
sorry, also, I only have paint to draw a diagram atm, could someone give me some direction as to how to post the image? thanks
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