For those that have a 24v power supply on the bed, using edirol’s opto-isolator/MOSFET controller, I have a question. When I build the circuit, I’m getting a small voltage on the MOSFET drain even when the power is not applied to the opto-isloator – maybe .3 to .5 volts. When connected to the bed, it shows zero volts (presumably because the bed is acting like a pull-down resistor) but when the bed is not connected to the drain of the MOFSET, it shows a little voltage. That makes me think that the bed is getting a tiny voltage (heat) all the time – has anyone tested their circuit this way? I’m thinking the drain should show 0 volts but I can’t get it to do that even after changing swapping in new I/C’s… Any thoughts?
In theory you shoudn’t get any voltage on the drain
but since semiconductors are semi-conductors wich are not ideal and have always very small leaking current you can measure a little voltage there
So no worry at all
note that Mosfets are very easy to damage with static electricity
you must handle them with care and they should be send to you in an proper esd package
[quote=“floris”]In theory you shoudn’t get any voltage on the drain
but since semiconductors are semi-conductors wich are not ideal and have always very small leaking current you can measure a little voltage there
So no worry at all
note that Mosfets are very easy to damage with static electricity
you must handle them with care and they should be send to you in an proper esd package[/quote]
Thanks, and I hear you re semiconductors – though I would expect the leakage to be much smaller… ?? Curious if anyone else has measured with a multimeter with the board disconnected to see how much flows to the drain?
You can measure if there is any voltage is on the gate of the hexfet wich is feeded by a voltagedevider with the optocoupler