LM358n issue

[sidring]

Hello All,

I am using LM358n for amplifying the the voltage and i am taking a 5 volt from arduino and giving to opamp as noniinverting amplifier and i am giving 12 volt to amplifier(+- ends). Using the formula Vo= (1+r1/r2)Vin. But my output voltage is restricted to 6 volts. i dont know what is wrong happening.
Could you please help me out.
Thanks
Siddharth

 

[davenn]

Hello All,

I am using LM358n for amplifying the the voltage and i am taking a 5 volt from arduino and giving to opamp as noniinverting amplifier and i am giving 12 volt to amplifier(+- ends). Using the formula Vo= (1+r1/r2)Vin. But my output voltage is restricted to 6 volts. i dont know what is wrong happening.
Could you please help me out.
Thanks
Siddharth

show us your circuit else we are only guessing

 

[Audioguru]

The datasheet of every opamp shows its output voltage swing. For an LM358 with a +12V supply and a load current of 10mA then its typical maximum output voltage is +10.5V. When the load current of a typical LM358 is about 35mA (about 171 ohms to ground) then its maximum output voltage is about 6V.

What is the output load resistance? Does the 12V supply stay at +12V?

 

[(*steve*)]

The answer to the problem is becoming clear...

Spoiler

 

[sidring]

Hello all
I am giving 5 volt input to opamp from arduino and you guys are right when check the output voltage from opamp it is near 6v and curreny is 33 amp.
And I am giving +-12volts to opamp from an adapter and I didn't checked it's configuration. I am new to electronics can you guys help how can I get the current in the range of 20amps and voltage near by 10volts at output.

Please help me out.

Thanks

 

[(*steve*)]

33 Amps? From an op-amp? You've got to be kidding.

Tell us what you are actually trying to do, not how you think it can be done.

 

[davenn]

Hello all
I am giving 5 volt input to opamp from arduino and you guys are right when check the output voltage from opamp it is near 6v and curreny is 33 amp.
And I am giving +-12volts to opamp from an adapter and I didn't checked it's configuration. I am new to electronics can you guys help how can I get the current in the range of 20amps and voltage near by 10volts at output.

Please help me out.

Thanks

as Steve said .... that isn't going to happen

and you still haven't done as I asked

 

[sidring]

I wrote by mistake 33amps actually it is 33 milli amps

 

[sidring]

33 Amps? From an op-amp? You've got to be kidding.

Tell us what you are actually trying to do, not how you think it can be done.

I am getting 33 milli amps.

 

[(*steve*)]

We can't do anything until you show us your circuit.

 

[Audioguru]

Most opamps are not power amplifiers, they cannot produce much output current. The datasheet for an LM358 shows that when the output current is 10mA then the maximum output voltage for a typical one is +10.5V when the supply is 12V and some LM358 opamps have more voltage loss.

A little transistor can easily produce an output current of 33mA so let the opamp drive a transistor emitter-follower that is connected inside the negative feedback loop of the opamp. Then the output of the opamp will be only 0.2mA but the output from the transistor will be 33mA. Then the maximum output voltage will be a little higher than +10V.

 

[davenn]

@sidring

you have been asked 3 times for your circuit

I am closing the thread till you respond in PM to either Steve or myself that you have a circuit that you can upload


Dave