1.2 Gain 350mA amplifier

[hpcycling2010]

Hello and please help!

I am trying to make an amplifier with a basic op amp and so far no luck.
I need a 1.2 gain for an input signal that ranges 0-10V. The output should be 0-12V and max 350mA needed.

I tried using a 741 OP AMP with a voltage divider (with a 1k and 5k resistor) and the output wont go above 0.3V I even flipped the resistors to get a different "division" and the output didnt change. Any ideas or components that I may be missing ?

I think that to get the desired current I'll use an NPN transistor. But first things first, I should get my signals working... :/

Thanks ahead of time

 

[ericgibbs]

hi,
What voltage are you using to power the 741.?

The 741 is a very old OPA with a very poor specification.

 

[hpcycling2010]

Using 12V and ground

 

[ericgibbs]

Using 12V and ground

hi,
The best you will get from a 741 with a 12V supply is approx 1.5V to 9V output.
Most OPA's will only go as high as their supply less about 2V.

To get a close to a 0V output and12V out you will need a 15V supply and modern OPA, say a LM358 or equivalent.

 

[audioguru]

You will not get more than about 9V at 20mA from the output of an opamp powered from 12V.
You need to add some power transistors to reach 7V at 350mA.

 

[Nigel Goodwin]

Perhaps if you told us exactly what you're trying to do we could offer more exact help?.

 

[hpcycling2010]

I am trying to convert a 0-10V signal to a 0-12V signal at a max 350mA. Any ideas? If its OPA's, Im going to need some help picking out components...

 

[ericgibbs]

I am trying to convert a 0-10V signal to a 0-12V signal at a max 350mA. Any ideas? If its OPA's, Im going to need some help picking out components...

hi,
You need a +15Vdc supply rated at 500mA also a OPA, say a LM358 and MOSFET.

I assume when you say a 0V to 10V signal ,its a signal that can any where fro 0 thru +10V, not just 0V or 10V...??


For an actual 0V out at 350mA, a -Vdc will also be required.

Tell us what the circuit is going to be used for.

 

[ericgibbs]

I am trying to convert a 0-10V signal to a 0-12V signal at a max 350mA. Any ideas? If its OPA's, Im going to need some help picking out components...

Hi,
This is one option.

The BD437 will need a heat sink.

 

[hpcycling2010]

Wow Eric. Thank you so much. I will try this and see how it goes.

And yeah, it was a full linear input and output. The current would also "follow" the voltage from 0-350mA

 

[hpcycling2010]

Whats the V+ and V- set at? +15 and -5V? Can I get away with 0 and 15V ? my circuit supply is Gnd and 24V.

 

[ericgibbs]

Whats the V+ and V- set at? +15 and -5V? Can I get away with 0 and 15V ? my circuit supply is Gnd and 24V.

Hi,
That circuit requires dual supplies in order to give the 0V thru 12V output.

 

[hpcycling2010]

Hi,
That circuit requires dual supplies in order to give the 0V thru 12V output.

Is there any way to get dual supplies from my 24V and Gnd? If its +15V and +5V I can do it, but if I need a -5 or -15 I dont know how to get there...

 

[ericgibbs]

Is there any way to get dual supplies from my 24V and Gnd? If its +15V and +5V I can do it, but if I need a -5 or -15 I dont know how to get there...

How is the 0 to +12V 350mA load connected to the amplifier,, basically what is the load.??

 

[hpcycling2010]

How is the 0 to +12V 350mA load connected to the amplifier,, basically what is the load.??

Its an proportional air valve, so the load is a coil/solenoid. The current/voltage sets how far it opens or closes to allow air through.

 

[ericgibbs]

Its an proportional air valve, so the load is a coil/solenoid. The current/voltage sets how far it opens or closes to allow air through.

OK.
So is the solenoid not connected to 0V in anyway.? its say, isolated ?

 

[hpcycling2010]

Correct. two wires coming out.

 

[ericgibbs]

Correct. two wires coming out.

Ok,
I will see what I can do with a single 24V supply, let you know.

BTW: the 0 to 10V input control, is that ground free.?

 

[hpcycling2010]

Ok,
I will see what I can do with a single 24V supply, let you know.

BTW: the 0 to 10V input control, is that ground free.?

It would have the same ground as the 24V supply.

 

[ericgibbs]

It would have the same ground as the 24V supply.

hi,
Look at this option.