Voltage Amplification of Thermopile?

Thread Starter


Joined Jan 24, 2020
I have a thermopile which produces a very small voltage (about 0.4-0.6 mV). I would like to amplify this up to about 0.4-0.6 volts if possible.

From what I have read, an OpAmp shoule be suitable for this. I have a LM308N OpAmp but I can't seem to get it to do anything with my small voltage, although I am sure, I have it wired correctly, i am using a inverted amplification circuit wwith R_1 = 22k and R_f = 220k but i cant achieve the amplification.

Should I continue working with LM308 or try it with another OPAMP?


Joined Oct 2, 2009
You can amplify a signal with an opamp assuming that the opamp is receiving power from another power source.

If you want to increase the voltage from a generating source there are two ways to do that (1) with a step-up transformer and (2) with a boost switching power supply. In both cases, there is a loss in power because no converter is 100% efficient.

Look up energy harvesting devices.
LTC3108 will harvest down to 20mV.


Audioguru again

Joined Oct 21, 2019
If your signal source has an output impedance less than about 1k ohms then your 220k feedback resistor and 22k input resistor for the opamp produces a voltage gain of only 10 times. You want a gain of 1000 times.

The very old LM308 is an obsolete antique that has not been made for many years. It is too noisy (hisss) to use a gain of 1000.
Use a modern audio opamp instead.

Thread Starter


Joined Jan 24, 2020
@Audioguru again i am using it for 3 times the same circuit to get a gain of 1000 but what can i observed is a a voltage of 0.73V at the output. it does not change even when the input source (Thermopile) is connected or disconnected.

Any other solution, which OPAMP can be successful. According to Pspice Simulation, every opamp is good but implementing it physically, the results are totally different when compared with simulations.


Joined Mar 14, 2008
To amplify a nominal 0.5mV DC signal, the op amp input offset should be less than that, so you need a very low offset unit.
An auto-zero op amp such as the OPA317, which has a typical offset of 20μV, would be an example.
You can get all the gain you need with one op amp.