I designed the current sinking circuit to test out a bunch of these 3V Lithium coin cell batteries that I have.
The battery is rated for 620mA-h.
I built my circuit and for the life of me I cannot get it to work. I am not even getting the 6.2V drop on pin 3 of the mosfet.
Can anyone help

 

Your battery voltage is only 3 volts.

 

I can make the voltage divider give 1V hence, 100 mA.

 

You're never going to get 6.2v from a 3v battery...lower the voltage divider reference to get 1.5v or less...

 

I didn't think this right. In my head i kept thinking because pin 3 is 6.2V that will make pin 2 6.2V.
But the feedback is the op-amp driving the output hard to get inputs the same.
I think i answered my own question.

I got the circuit to work with the modifications that I have attached. I am running 100 mA into the battery.
I guess how will I know when the battery is depleted?
What voltage will be across The battery when the circuit is on?

Well the battery just blew up. is the - of battery supposed to be connected to Drain of mosfet or the +?

 

The battery will discharge down to 1v approx, at switch on it will be 3v.

The battery positive is to the Drain, the Negative to the source.

 

I am not sure why it blew up???

 

100 mA is a high demand to put on a coin cell already, that may be what's blowing up your battery. Have you measured the actual current with a DVM? Could it be more than you expect?

 

well I set the Current limit on the 9V power supply to 200 mA. What's odd is when I was measuring voltage from Drain to ground I was getting like 7V. I thought that was strange.

 

Um, is everyone else seeing a posted circuit that I am not seeing?

Bob

 

Yes, it was a pdf, must have deleted it.