Electronics > Beginners
Constant current load Help needed
LukeB:
I put in a resistor there and it did nothing. The voltage across the resistor remains at 1.8v even if the set voltage is at 0v.
LukeB:
Ohh I think I am beginning to understand. If the common mode voltage range is 13v ish then that means that an input of within 2v of either end of the supply voltage will have funny results. Is that correct or am I just confusing myself?
That could explain why I have problems trying to get the voltage to go to 0v. It hovers at 1.8 no matter what the inputs. That 1.8 seems to correspond with the 2v ish range thingo.
xavier60:
--- Quote from: LukeB on September 24, 2018, 01:51:54 am ---Ohh I think I am beginning to understand. If the common mode voltage range is 13v ish then that means that an input of within 2v of either end of the supply voltage will have funny results. Is that correct or am I just confusing myself?
That could explain why I have problems trying to get the voltage to go to 0v. It hovers at 1.8 no matter what the inputs. That 1.8 seems to correspond with the 2v ish range thingo.
--- End quote ---
That's right. Now you need to find an op-amp that has a common mode range that includes the negative rail like the LM358, but in a single channel type if you want to use the same PCB layout. You could wire in an LM358 to prove that it's a fix for the range problem.
Someone here might already know of a suitable op-amp.
LukeB:
Oh ok thats all good, I will just breadboard a new one. Probably should have done that last time hehe. Oh well it was only a home etched one anyway so pretty cheap.
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