I'm hoping someone can help or shed some light. Having issues with an Op amp + Mosfet current source Circuit. When RL is in Circuit I only get about 16mv, and Op amp Pin2 drops to the same value, when Rl is out of circuit(disconnected) then I get 1V at mosfet Source and top of R2 and D2 and pin 2 of Op Amp. I need 1V and 100ma at RL but not getting it. Any Suggestions appreciated. TY

 

Vcc = ???????????????????????????????????

 

What op-amp? TL741. Is it a LM741? What is VEE and VCC? While doing these tests what is connected to U& "CC Output"?

 

Sorry, +12 / -12 and yes LM741 (typo) nothing is connected to CC output

 

What do you have connected to your output connector for testing?

 

I just use multimeter to check the voltage at different points. but nothing is connected there.

 

I just use multimeter to check the voltage at different points. but nothing is connected there.

That explains a lot.
If you are trying to make a constant-current source, you'd be hard pressed to make 100mA flow though an open circuit from a 12V supply.
You'd need at least enough voltage for the spark to jump the gap between the connector pins.

 

But Without 1V at RL I'll never have 100ma across it.

 

Assuming that your MOSFET was fully switched on, how much voltage would you expect across the 10Ω resistor from a 12V supply? You have a 100k/10Ω potential divider.

 

so when the mosfet is switched on, it gives ~9V, with that divider I won't get much ~1ma, but by changing 100K to 1K then I'd get about 90mA

 

You must have a low value load plugged into U7. A short will also work.

 

But Without 1V at RL I'll never have 100ma across it.

And the only path for the current to get to RL is the 100kΩ resistor, R18.
That means you need 10,000 volts across R18.
Or a short or low resistance load between pins 1 and 2 of U7.

What is supposed to be connected to U7?

 

Changing the 100k resistor to 1k now works correctly, Op amp pin2 is stable at 1V and I get the 1V that I'm supposed to at RL. Kelvin probe connected to U7