# High current high bandwidth

1. Dec 4, 2014

### Excom

Hi All

I hope that someone can help me. I have this thermal actuator with a resistance of ~1 Ohm that I want to operate at high frequencies, up to 100 kHz. In order to get the right amount of actuation I need to pass 1-2 A through the actuator.

Can anyone tell me what kind of circuit would be able to give this kind of performance?

Thanks

2. Dec 4, 2014

### phinds

I think you may need to restate the problem. Maybe it's just me, but what I am hearing is that you have a device that acts based on temperature and you want it to change states up to 100,000 times per second. I don't see how that's possible, so I'm assuming I don't really get what it is that you are asking.

3. Dec 4, 2014

### Excom

Well it is actually what I want to do. The actuators I am working with have a bandwidth of 3 kHz but at higher frequencies the amplitude starts to decrease as the time constant if the actuator is too long. However, by modulating the drive signal you can increase the bandwidth of the actuator. Put in another way. The flat region in a bode plot can be extended to higher frequencies.

4. Dec 4, 2014

### supamas

V=I*R. You already know the resistance and current needed. Sounds like all you're going to do is plug in a 1-2 Volt source and you'll have your circuit. Of course if that doesn't solve your problem you'll need to explain more of what is going on in the circuit and whether you are controlling anything or not.. etc.

5. Dec 4, 2014

### Excom

The problem/challenge is to get a high current at 100 kHz. Ideally I would like to drive my actuator using a DAQcard but a normal DAQcard is not capable of delivering a 2 A current.

So it is my plan control the signal to some extend.

At the moment my best option is a function generator or a DAQcard and non of them can deliver the needed current. Therefor I would like to build a circuit that can deliver teh current and I can then control the circuit using either a function generator a DAQcard. An option is to use an op amp but I can't find an op amp with the needed bandwidth and current range.

Last edited: Dec 4, 2014
6. Dec 5, 2014

### sophiecentaur

I think I am not the only one who is confused by your stated requirement. I can't think of any thermal device that can change at 100kHz rate - or is the 'thermal' word just incidental?
If you need 2A at 100kHz, I reckon you will need a buffer / driver between the OpAmp and your device. Not a problem, though.

7. Dec 5, 2014

### Excom

By thermal I do mean thermal as in heating. An example of a thermal actuator operating at 10 kHz can be found in this paper, see figure 11: In depth characterization and control of AFM cantilevers with integrated sensing and actuation. I can't go into too much details about what we are doing as the work is not published yet but I can assure you that we are beyond the 10 kHz. And in the end we need a circuit that can go faster than the actuator.

I will have a look at the buffer/driver idea. Thanks.

Last edited: Dec 5, 2014
8. Dec 5, 2014

### meBigGuy

Are you simply asking for a device that can drive 2A at 100Khz? Here is 1 example when I searched for 2A opamp. http://www.ti.com/product/OPA569/technicaldocuments

It can drive 1.2Mhz with 0dB gain.

You may want a peripheral board containing a completed design. I didn't stumble onto one.

9. Dec 8, 2014

### f95toli

I've used the aforementioned OPA569 for something similar, I used built a small voltage to current converter, this was used as an amplifier (well, a transducer) for the output of a DAQ.
So this is probably the easiest solution.

10. Dec 8, 2014

### Excom

Thanks for the replies.

An OPA569 seems like a good option. I will go for it.

Again thanks.