voltage gain amplifier

[radium98]

Hello , i am in need of a little design circuit wich can use eg S8050 or c945 transistors , that can work as a voltage gain amplifier.
my problem exist in , i have a few milli volts abt 160 mv that i need to amplify to level to activate a relay coil that can work between 5 and 12v.then 160 mv can go up to several volts to activate the relay

thanks

[Albert H]

160mV won't switch on a transistor - you need ~650mV. If your signal is that small, you'll need a DC-coupled op-amp circuit to get it up to a big enough voltage to operate a transistor.

However, if you've got such a tiny signal, and there's RF around, you'll have all sorts of problems!

[radium98]

thank you for the help and reply .
this circuit is what i want to implement between my low signal and theone that will activate the sensitivity of the realy that already will have a transistor .
what do you think , i have remove this circuit from a circuit similar to what i want
only difference it use ca3130 and what i am trying with is 741 and i think for such need there is no problem ?

[Albert H]

Your circuit should work, but an LM358 might be a better choice since it tolerates input and output voltages close to the rails.

Remember to RF filter the inputs of the op-amp and the base of the relay drive transistor. RF can get into anything and cause problems. Also be sure to put a reverse-biased diode across the relay coil, and filter the switching spikes off the supply rails.