Hello.
I've built a constant current source based on an LM324 op amp.
(schematic attached)
I'm trying to turn on and off the LM324 with a transistor (T1).
What I expect is when i cut off power to the base of T1, the output of the LM324 (pin 1) becomes 0V, but the voltage actually goes up.
Hello.
I've built a constant current source based on an LM324 op amp.
(schematic attached)
I'm trying to turn on and off the LM324 with a transistor (T1).
What I expect is when i cut off power to the base of T1, the output of the LM324 (pin 1) becomes 0V, but the voltage actually goes up.
You’ve observed a very normal behaviour of a device that stays connected to +supply and the –supply is missing, or is dis-connected, AND all other stuff is referenced to –supply.
Try to make the opposite: use PNP transistor and remove the +supply from the opamp ..
You’ve observed a very normal behaviour of a device that stays connected to +supply and the –supply is missing, or is dis-connected, AND all other stuff is referenced to –supply.
Try to make the opposite: use PNP transistor and remove the +supply from the opamp ..
Thank you.
But the base will be controlled by a PIC microcontroller (5V max input).
Since the supply voltage to the LM324 is 12V, does that mean the only way to do this is with two transistors?
Yep -- did some googling, and I guess i have to use an NPN on the base of the PNP.