Amplifier for capacitative load

Hi,

Just a query. What kind of amplifier should you build to supply for a capacitative load? I think I might have enough voltage but not enough current for the frequency that I am going to build.

Thanks for oyur help!

Hi watertreader,

I made a project last year that was just like what you want. I made a Ripple current tester for capacitors.
The project is mainly a power amplifier with some control and a signal generator.
Through my experience with this project, you can build basically any power amplifier you find, but it can't has a feedback loop from the load to the input, because if it has one, it will oscillate for sure.

You have to remember that the impedance of the capacitor decays very quickly with the increase of the frequency, i.e., if you operate at high frequency, small voltages will generate very high currents. Take a look at some capacitor manufacturer website to learn about the capacitor´s behaviour.
Try www.epcos.com ; www.rubycon.com ; www.nichicon.co.jp.
They have very good basic information on their data books

If you have any further doubts, send me a message.

mcoster

Thanks for your help!

I think I have also found some rather interesting guide from www.apexmicrotech.com.

Btw, I am not quite clear on the feedback you are talking about... Wouldn't the output need to be reconnected back to the input?

Wouldn't the output need to be reconnected back to the input?

Click to expand...

Generally yes! You use feedbacks to make the gain of the amplifier stable (like in opamps theory) so they don´t change against frequency and/or output current, for example.

But in this particular case, when your load is capacitive, if you try to use feedback you will create a oscillator.

This was a problem in my project since i had to control the output current against variations on the capacitor's impedance. The way i found was to use the amplitude modulation function from the signal generator IC that i used. I couldn't make any kind of feedback to work.

I will try to digitalize the circuits i used and send to you, so you can take a look at.

hope i could help
mcoster

Generally yes! You use feedbacks to make the gain of the amplifier stable (like in opamps theory) so they don´t change against frequency and/or output current, for example.

But in this particular case, when your load is capacitive, if you try to use feedback you will create a oscillator.

This was a problem in my project since i had to control the output current against variations on the capacitor's impedance. The way i found was to use the amplitude modulation function from the signal generator IC that i used. I couldn't make any kind of feedback to work.