Quote:
Originally Posted by wasyoungonce
Funny enough I am at this moment getting some cct boards made for a FET driven 4 channel PWM dew heater I designed & prototyped up.
I found that many FET (or transistor) PWM dew heaters switched the heater thru Vcc rail. Thus when the output driver device was off there is Vcc (in most cases +12V DC) sitting on the outer shell of the heater connector. Some/many of these commercial dew heater use a metal RCA connector & +12V sitting on this outer shell is recipe for trouble.
So I designed up a FET cct that switches heater thru earth with the outer shell connected to earth, thus the outer shell is always earth.
I am tossing up whether to market these as I could pump them out at pretty much $100 Aust.
A low tech (cheap) solution indeed.
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Sounds good - can you give us some more info on the actual specs for your controller? A photo maybe? Max output currents, indicators, temperature controlled, under voltage protection/cutoff?
High-side switching - meaning you interrupt the 12V rather than the ground return - is the way to go and can avoid some EMC issues as well. Are the outputs in your controller short circuit proof? P-fets can be a bit sensitive and I have seen them go before the fuse at times.
Cheers,
Peter