What a very confusing way to draw a schematic.
The emitters of the optos should be connected to ground
the -ve of your 24V source and the FET gates should be connected to the collector of the FETs.
But I still got problems:
QuoteBut I still got problems:I think you may save a lot of time / money by buying a ready-made board.
"I cant believe that I have so much trouble assembling such a simple circuit..."
But then I wouldn't learn anything
Isnt the FET gate same as opto's emitter, since the two are connected?Do you mean drain by collector?
Do you mean to the - of the 24V?
But that makes all three optos connected, if one opens all three FETs open.
Transistors work with current flow
This is kind-of ambiguous, because every component "works with" current flow
I mean:-The emitters of the optos should be connected to ground, the -ve of your 24V source and the FET gates should be connected to the collector of the FETs.
The circuit as you drew it is just not going to work. Transistors work with current flow, there is no where for the current to flow if you connect the emitter directly to the FET's gate because a FET has such a high input impedance.
The gate is like a capacitor, so while a small amount of current will flow into it to build up that charge, no current will flow through the gate once it's built up, and the MOSFET will still conduct.
For an opto-coupler that pulls the gate up to turn it on (N-channel FET) you need to also keep a pull-down to ground to the gate, so that the gate turns off when the opto-coupler is not transmitting current. Perhaps a 2 kOhm pull-down will be sufficient, if you're not trying to switch the FETs at too high an on/off frequency.
The transistor in an opto coupler can only pull down, so there is nothing to supply the voltage to the FETs gate.
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