Adding power to a DC signal


I my project, I want to supply a device with a DC tension from 0 to 12V.

I'm using a pwm output from the arduino, then an RC filter to have a DC signal from 0 to 5V. After that, I planed to use an Operational amplifier to have a signal from 0 to 12V.

But now I'm stuck. My device needs up to 1A of power, and the Operational amplifier won't provide such a current. Do you now an IC (like a transistor) that can can do that ?

Accuracy is not an issue here. 10% of error is ok.

Thanks for you help. Kaker.

Wire up a FET as a source follower on the output of the op-amp. That is gate to the amp, drain to +12V and source to your load.

Thank you.

I have some IRF520 N MOSFET.

Is my schematics correct ? Is it that simple ?


The easiest thing would be adding a emitter follower to the opamp. Also not that you need a supply voltage a bit higher than 12V, 15V would be adequate. The opamp should be set to a gain of 2.4 (=12/5)

op amp w emitter follower.JPG

Thank you nilton61.

I have IRF520 MOSFET and BD137 transistor. What is the best choice ?

Is my schematics correct ? Is it that simple ?

Yes it is that simple.

The easiest thing would be adding a emitter follower to the opamp.

No I would not do this because of two things:- 1) The voltage drop across the transistor will limit the top voltage to at least 0.7V less than the supply. 2) Transistors at about 1A are more expensive than FETs at the same current.

Thanks for all the information guys.

I have several BD 137 so I'll try with it first. If the tension drop is to high, I go for the FETs.

Have a nice day.

Voltage drop is not a big problem as long as you have a supply that can give more than 12V

You need feedback to come from the output after the MOSFET or BJT. If you use a P channel MOSFET, the Op Amp can run from 12V, but if it is an N channel, you'll need about 18V for the Op Amp.

If using a BJT, you may need Vcc for the transistor to be about 13V. For a MOSFET, the fully ON resistance can go so low that 12V will do.

Unfortunately, I only have 12V power supply and N-channel MOSFET... I understand that I won't be able to reach 12V on my load. Is 10V doable ? My OPAMPs are LM358. I can't fin a relation between Vcc and maximum output voltage in the datasheet.

What you are looking for is the parameter called output voltage swing. Its on the bottom of page 5 in this datasheet. I states Min 26v @ 30V supply voltage for Voh. Bipolar op amps have this behavior due to their technology. There are Rail to rail opamps that can swing within mV of supply voltage.

But those R-R outputs are not -really- R-R, as in they are not ideal components. They only get within a few tenths of a volt, and the more current drawn the further they get from the rail.

I am on my way to work, so I don't have time to sketch something up. A P channel MOSFET would work great, as the output of the LM358 would go -low- to cause the output to go high. You'd connect the feedback circuit from the output at the MOSFET drain to the -non-inverting input of the Op Amp, as the MOSFET is acting as an inverting amplifier.

You can use LM317 adjustable-voltage regulator

This is getting complicated!

There are a number of "power op amps" that deliver output currents in excess of 1 ampere. Many require dual power supplies but there are some single supply versions. For example, Power Amp Design's PAD117 can supply 15 amps with only a 1.5 volt drop from the power supply voltage. The PAD127 can do likewise with a 30 amp output.

TI, ST Micro and others also make power op amps, e.g.

Here it is. You should put ferrite beads on the leads of the MOSFET. And it wouldn’t be a bad idea to put a 10 ohm resistor between the Op Amp and the Gate, as close to the MOSFET as possible. These are to reduce the chances of oscillation.

This should take you right up to 12V, and be able to get down to 0V. Note that the Op Amp must run from the 12V supply.

Please note that, because the MOSFET is inverting, although the input is connected to the inverting input of the Op Amp, the entire circuit is noninverting. So 0V in is 0V out, and 5V in is 12V out.


Let’s see if I can embed this:

Nope. However, you can click on the link.

I'll test it as soon as I receive my new arduino (I burned the last one :roll_eyes:).

Thank you very much.

All the people must be aware of the basic idea of using amplifiers which are involved to take weak signal and increase their aptitude to drive speakers. A power amplifier is an electronic device which take electrical signals at input end. The power boost may be achieved by merely increasing input signal power. This power amplifiers has always been consumed to power output source of any stereo speaker, relay or motor.