Help with Comparator and MOSFET Circuit!!

Discussion in 'General Electronics Chat' started by Joster, Sep 30, 2013.

  1. Joster

    Thread Starter Member

    Jun 12, 2013
    Hi All,

    I'm hoping someone can help me out with getting this circuit going. I'm trying to use a comparator to sense the voltage of a capacitor and then discharge it into a battery.

    I have the comparator set up but the output voltage range is not what I expected. I'm running the LM371 with a 9V battery and my out switches from 1.2V to 7.7V. I understand this is actually what the comparaotor output voltage looks like as it is not ideal.

    So I figured I would connected the output to an H11D1 and use 720 Ohms in series from the output of the comparator to the in of the H11D1 to only reach I(f) (which is 10mA) when the opamp goes high. This did work but the resistance between the collector and emitter of the H11D1 ranged from 300 Ohms to 3.7K. So I guess it's not being driven fully into saturation or cut off?

    I'm sure you can tell I'm pretty lost in this but I'm frustrated because its such a simple process and what I understand should be happening is not at all.

    I graduated from as an Electronics Technician with Honors 5 years ago so I'm pretty bummed that I can't figure this out.

    Any help would be great thanks!

  2. crutschow


    Mar 14, 2008
    Post a schematic.