voltage gain amplifier

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radium98
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voltage gain amplifier

Post by radium98 » Sun Oct 31, 2021 6:47 pm

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
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Re: voltage gain amplifier

Post by Albert H » Mon Nov 01, 2021 3:32 am

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!
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radium98
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Re: voltage gain amplifier

Post by radium98 » Tue Nov 02, 2021 9:23 pm

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 ?
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Albert H
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Re: voltage gain amplifier

Post by Albert H » Fri Nov 05, 2021 12:45 pm

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.
"Why is my rig humming?"
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