How to operate opamp on two different voltages

[djc]

Hi,
Can anybody tell me how to opearte opamp on two different voltages. Like in battery charger circuit. Battery charging should be ON at 9.50 V and should be OFF on 14V. Will it work for solar charging with MPPT and using PWM controller UC3844. Plz help.

 

[chuckey]

Do you mean that the Vcc of the opamp can be either 9.5 or 14V? One way is to use a zener diode and a resistor to stabilise its supply at less then 9.5 V, say use a 6V zener, or use a proper stabiliser like a 7805, to give 5V.
Frank

 

[Audioguru]

You DO NOT want to operate the opamp on two voltages, instead you want it to detect the two voltages at its inputs then switch its output to turn on or turn off the battery charger.
Use the opamp in a simple comparator circuit but you must reduce the input voltages with a voltage divider.

 

[mike.zhang]

Generate A lower power voltage for AMP.

 

[djc]

what is the concept of schimitt trigger circuit. It can operate on two different voltages, so that it can be used in avoiding relay chattering too. But i think that voltage range is within .5v, so can we increase this range difference to 5 or 6 volt.

 

[schmitt trigger]

I'm with audioguru on his response.

What you are looking is at a way to compare two different voltage thresholds, not to actually feed the opamp with these two voltages.

Use a LM393 comparator. Search its datasheet and it shows many application circuits.

 

[Audioguru]

What is the concept of a schimitt trigger circuit?

A Schmitt Trigger circuit uses a little hysteresis (positive feedback) to produce a "snap action" at its output. If the input voltage is rising then it must rise a little higher than the threshold voltage for the output to abruptly switch and if the input voltage is falling then it must fall a little lower than the threshold voltage for the output to abruptly switch. So the input has a voltage gap where the comparator output does not switch.