Interface problem

[xinya101]

I am trying to connect a non-inverting amplifier (op-amp 741) output to a relay. The amplifier gives me the output that I need which is about 7V. However, the moment I connect this to the relay input, the voltage drops to about 2V and thus the relay does not switch. I'm using a electromechanical relay which is normally open(6V relay). Why is this happening?

Is a 2V relay available in the market?If yes, please let me know where.

Thank you.

 

[panic mode]

this is normal... 741 is not designed to provide big output current.
it was designed to have big gain. nowdays, thins are a bit different
so there are OpAmps that can handle much more current.
another thing is that realys are not normally driven by OpAmp.
You need digital (on/off type) signal to operate relay properly.
If the 741 output is working like that in your application, all you need
is a transistor to get the current big enough to turn on relay.
if you need more help, try posting your circuit.

 

[xinya101]

Thank you for your quick reply.

I'm a little unsure about whether a relay is turned on by voltage or current or both voltage and current?

Do you mean I have to use a transistor to amplify the output current from the 741 op-amp?

What models of op-amp will provide me a larger current?

Thank you.

 

[thisistausif]

panic mode wrote

a transistor to get the current big enough to turn on relay.

i agree with this ,the tran should be good enough
you can use simply AC 187 and no need to change op-amp

 

[David Bridgen]

I'm a little unsure about whether a relay is turned on by voltage or current or both voltage and current?

Thank you.

A relay's specifications will include the coil's resistance and the nominal operating voltage, or small range of voltages.

It is the current through the coil's winding ( caused by applying the voltage across it ) which produces the magnetic field necessary for the relay's operation.

 

[audioguru]

The mention of using an AC187 transistor brings back fond memories.
It's an old germanium transistor in a cylindrical metal case!
It doesn't even need base current to turn on, just warm it a bit.
You want to know what "thermal runaway" is? Ask an AC187, its the expert.