Re: supercapacitors

Hello Todd,


Does anyone have experience with supercapacitors? What's the best way
to learn more about them and what they're useful for? Any good web
links with design examples?

We have a 1 kW transmitter for ultrasound that uses 12 electrolytic
capacitors (2200uF each) in a bank, for 26.4 mF total capacitance. The
ESR is very low so our system responds very well when transmitting
pings (lengths ranging 0.1-1.0 ms). The caps are buffering a 48V power
rail. I've thought about trying to scale the power rail down to 12 V
and beefing up the transformer by a factor of 4.


I wouldn't really call that a super capacitor. A few hundred uF or more per channel isn't that unusual. In my ultrasound designs the most important aspect was where the peak current would be coming from. This data plus ESR values is in the data sheets and if not you have to obtain it.


Has anyone used a supercapacitor in a transmitter?


Real super caps are in the Farad capacitance range, more like short-term backup supplies. They come in various flavors. As Pete said they can be high in ESR, for example if their market is RAM backup. You would need the ones that are marketed into the short-term power supply sector.

A kilowatt is nothing to sneeze at. Especially if it is Doppler and more than just one short pulse, be careful. I have seen electrolytics explode with gusto when exceeding the max ripple rate. A short pulse can be cushioned off with several high quality smaller caps but long pulse trains really can't.

--
Regards, Joerg

http://www.analogconsultants.com
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