which OP-Amp to provide 100mA

StefanL38

Hello,

I would like to build a circuit for basic electronic experiments.
Therefore I want to have 3 to 8 voltagesources with each providing 100mA of current at 5V

The precicision is not much important. So I came up with the idea to use some kind of DACs
and connect the DAC-output to OP-amps working as voltagefollowers and impedance-changers
to get a set of easy adjustable voltage-supplies with low impedance.

What kind of OP-amp would you recommend for this purpose?

best regards

Stefan

Phil Pilgrim (PhiPi)

Since you only need to source current, not sink it, just about any op amp will work (including the lowly LM358) when paired with an NPN emitter follower transistor output stage.

-Phil

kwinn

If you want adjustable power supplies, as long as you do not need less than 1.2V you may want to consider using an adjustable 3 terminal linear regulator and have the op amp output connected to ground/adjustment pin of the regulator.

StefanL38

OK I have to be more precise:

I want to adjust the output-voltage through the propeller-chip using one or maybe two or three IO-pins.

example creating a PWM-signal that is averaged through an RC-circuit and an OPAmp voltage-follower with capacitors between outputvoltage and ground.

From a LM358 you can get 20 to 30mA. But I would like to have 100mA.
As it is for very basic experiments like voltagedividers and measuring voltages and currents on a transistor to understand the basic function of transistors
the precicision has to be only medium. Of course there are 8-16 bit DAC some of them providing 50mA. But I want to keep it very low-cost accepting a lower precicision.

If somebody has a schematic handy for this I would appreciate if he/she can post it here.

Thanks in advance.

best regards

Stefan

Phil Pilgrim (PhiPi)

StefanL38 said...
From a LM358 you can get 20 to 30mA. But I would like to have 100mA.

And that's why I said you need to use a transistor follower:



The RC input filters the DUTY mode output from the Prop. The voltage divider will determine the overall range of your output. The transistor needs to be rated for both the current and the power it will dissipate. The supply voltage for both the transistor and op-amp will depend on the output voltage range of the op-amp, which needs to be at least 0.6V higher than your maximum output voltage, due to the base-emitter voltage drop of the transistor. BTW, the base resistor is not entirely necessary and can usually be omitted.

So get some parts and experiment!

-Phil