how to increase current output in a DA converter?

Google 'emitter follower'.
This is probably the simplest solution...effectively it is a single transistor current amplifier, you looses a tiny amount of voltage but gain loads of current.

Del

I tried to search for the emitter follower and I understood it how it works. But it's different from what I wanted to happen. My input voltage is varying from 0-5V with 0.25mA. I wanted to input some voltage and the output voltage should not change only the current output should change. Can you please suggest what kind of circuit can I use this this problem?

I see you want to convert a varying voltage to a varying current. I tought you just wanted to boost the current.

There are op amp feedback circuits to do this...try googling op amp voltage to current converter ?

Del

Thanks for the answers. I will try to search your suggestions and hopefully to make a simple circuit to solve my problem. Thanks and more power.

I have 2 Qs:

How much you know about electronics, are knowledgeable?

Have you any room for extra parts to install?

If you haven't then you have to find physically compatible op-amp that would fit in place of the one in it now with more current output.

How much output current would you need anyway?

Some op-amps are load protected and must make sure it churns out enough current before the limiter kicks in.

If you need plenty of juice then let me know and will give some more info.

Thanks for the reply. I'm not expert in electronics but I can understand basic electronics. For your second question, my ECU doesn't have a room to install extra parts. Right now I'm trying to make a circuit using op-amp and also I'm trying to make emitter follower circuit using transistor. I hope I could solve the problem. Thanks and more power.

Hi, I'm back.

I did not realize it b4 but you claim that you developed this circuit for your robot. To bost your current output all you need is a pair of complementary Qs (like BC 639 & DC 640) and tie each of their emitters and each of their bases together and connect the bases to your current output point an the emitters will be your new output. (These Qs operate in a push-pull arrangement because I assume you need the motor to run in both direction if not then only need one Q.)

Make sure that the feedback resistor at your present output is also transferred over to your new output (the emitters) and you don't need a resistor.

The collector of BC 639 (NPN) goes to your positive supply rail and the collector of BC 640 (PNP) goes to the negative supply rail therefore, your out voltage will be as high as now.

I don't think you need to worry about current limiting because the motor's DC resistance is typically 8ohms (better check) and if you supply is only 5volts then it's ok cos the Qs are 1Amp.

These transistor arrangements used to drive the early CD players disk-tracking (weather it was a motor or a linear arm) as well as focusing mechanizims.

Mr. Ohm says you cannot do that.

Given a fixed load resistance, the current into the load is going to be a function of the voltage across the load. You can't change one without changing the other.

I=E/R

Bill

GREAT MINDS??

That was my exact thought too!!

Bill

Yes you can use power opamps with a current feed back compared with the voltage output of your ECU. It is better if you build at least a PID loop so that surges can be compensated and static errors as well.