Need help with OP AMP having adjustible pull in & adjustabile drop out.

Discussion in 'General Electronics Chat' started by cyclops2, Mar 14, 2012.

  1. cyclops2

    Thread Starter New Member

    Mar 14, 2012
    4
    0
    Would like to use something like a single or dual internally compensated 741 that can have a adjustabile 6 to 7 volt pull in point & about a .3 vdc lower drop out point . It will be used to control a 12 vdc relay that pulls .3 amps when energized.

    This will controll the charging on 2 small gasoline motors battery charging. They have alternators & rectifiers. But no control of the battery being over charged. So the SPST relay needs a adjustible pull in setpoint & a adjustabile drop out setpoint.
    A website with a diagram would be fine.


    Thank you for any help.
    Rich
     
  2. cyclops2

    Thread Starter New Member

    Mar 14, 2012
    4
    0
    A 555 operating in the bistable mode is closer to what I need ?
     
  3. crutschow

    Expert

    Mar 14, 2008
    12,972
    3,219
    You could use a comparator, such as the LM339 or LM393. You set their trip point by a resistor divider and hysteresis feedback. Here's an article on that.

    Depending on the required relay coil current you may need to add a transistor driver at the comparator output. Also be sure you add a transient suppressor diode across the relay coils (cathode to positive end).

    What's the supply voltage? If it's the battery voltage itself, then you will need to add a resistor and zener diode to provide a stable V reference voltage.
     
  4. cyclops2

    Thread Starter New Member

    Mar 14, 2012
    4
    0
    You site is excellent. The 555 has too large of a hysterisis minimum range.

    Are there OP AMPS with onboard reference supplies that will survive being powered by the extreme variations of a Lead acid battery in a boat or mower enviroment ? With voltages from 0 volts..dead battery... to 14.5 vdc maximum fully charged?
    I will add a transistor booster stage for the relay, 300 ma. load operating on a 14.5 volt battery.

    Thank you.
    Rich
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    656
    I think you need a comparator, not an op amp. There are lots of comparators with built-in references.Give us more details of what you are trying to do if you want design help.
     
  6. cyclops2

    Thread Starter New Member

    Mar 14, 2012
    4
    0
    I came across this 5 amp regulator. Will fly with it.

    Thank you both for the helping to get a old brain going again.

    Best wishes to both of you.
    Rich
     
Loading...