# Can differential op amps operate without any supply?

1. Jul 12, 2014

### amit016

Just want to amplify the difference of inputs.

Last edited by a moderator: Jul 12, 2014
2. Jul 12, 2014

### Simon Bridge

Welcome to PF;
Have you tried wiring one up to see?

3. Jul 12, 2014

### Averagesupernova

Curious what you mean by 'supply'. You cannot expect anything if you don't hook up the power supply pins.

4. Jul 12, 2014

### MrSparkle

The OP should look at the circuit diagram of an opamp. Like this one.

5. Jul 12, 2014

### amit016

Simon Bridge: No, that is the reason I am asking you people it is practically possible or not ???

6. Jul 12, 2014

### amit016

Averagesupernova : Supply means Vs other than input voltage. I want to amplify difference of input voltages that was the reason i had gone for differential op amp. I dont want to feed any supply voltage to it.

7. Jul 12, 2014

### amit016

MrSparkle: I understand, but its fully differential op amp or a simple demonstration of op amps???

I should make you people clear,,, I need to amplify millivolt (20 n more) to 5 volts but i dont want to go for any comparator op amps which requires Vs or supply. So i wanted to know ,,, does a differential op amp requires Vs because I found it in texas instrument's circuits,,, that is why I am confused right now.

1. differential op amp without supply (possible or not)

if yes

2. then please suggest me some IC numbers

8. Jul 12, 2014

### AlephZero

Averagsupernova already gave you the answer. There are no op amp chips of any type that will work without a power supply.

9. Jul 12, 2014

### MrSparkle

amit016, you don't understand the basic principle of amplification. When you take a small signal and want to amplify it up to say 5 volts, you take a 5 volt power supply and modify it by sending some percentage of it to ground, proportional(or inversely proportional) to the strength of the small signal. The supply voltage is absolutely critical to amplification.

10. Jul 12, 2014

### Staff: Mentor

An op amp is supposed to draw (nearly) no currents from its inputs, but it should be able to deliver a current at its output.
Without a power supply, that would violate energy conservation.

If you can draw large currents from the input and don't need large currents at the output, this is a DC-DC-converter, those work without external power supplies.

11. Jul 12, 2014

### Simon Bridge

... and finally:
... it is a simple, safe, and cheap, experiment - why not try it for yourself and see?

You description of what you tried would provide insight into how best to help you.

Note: all op-amps are "differential op amps", so what is true of general op-amps is true for them also.
See also:
http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar6.html

... but I think you have your answer.
Were you thinking of connecting the +Vs and -Vs pins to the input pins or something?

12. Jul 12, 2014

### jim hardy

Amplifying a signal without adding power from someplace would be perpetual motion .
You have to hook up the power terminals.

It's a common mistake for beginners.

13. Jul 13, 2014

### amit016

Thanks everyone for their precious time and making me more aware about op amps.

DC TO DC converters will work for me.

good day

14. Jul 13, 2014

### jim hardy

Last edited by a moderator: May 6, 2017
15. Jul 13, 2014

### sophiecentaur

The very word "amplifier" implies the control of power from a power source by a low power input signal, in order to provide a higher power output signal. Hence, a transformer (no external power supplied) is not an amplifier, even though it may produce more output volts than input volts. The output power from a transformer will never be more than the input (signal) power.

Last edited: Jul 13, 2014
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