Hi, I need to build a power amplifier to amplify a signal from a function generator. I need to give it a sine wave of about 20 Hz and amplify that to a 100 V amplitude. The application is for a langmuir probe diagnostic on a plasma generated by a hollow cathode. I need to sweep voltage from 0 to 100 in about 100 milliseconds. Can anyone tell me if a power amplifier is indeed what i need? Does anyone know what the basic circuit design would look like?
Thank you!
What are the electrical characteristics of the load?
Will the function generator do the required amplitude modulation?
Bob
You can use a HV op-amp. Is that 100 vrms ?
greg
Guessing a step up transformer + National amp module. A common power supply 50Hz/60Hz transformer could be used. The idea gets crappy if you need more load regulation or drawing lots of power.
D from BC British Columbia Canada.
What kind of "standard" amplifier gives you 100V output?
Bob
At 20Hz you can just use a standard audio power amplifier.
Here's something that maybe of interest.
Jan 4, 2008 on the datasheet...Huh...Could be new?
D from BC British Columbia Canada.
For higher rails try Apex or TI for complete HV op-amps.
greg
Perhaps home amplifiers can probably be put in series for more voltage. Just 2 or 3 might do it.. Depends though..
Or something to try might be bridging a stereo amp. R channel out of phase with L channel.
D from BC British Columbia Canada.
Look at the chart.....
The whole idea of a Langmuir probe is to measure the local voltage in a plasma by looking for rectification--the electrons carry most of the current, so you can tell from the I-V curve when you start repelling them. It's a bit like an AC Wheatstone bridge. You do have to watch for capacitance, though, because usually there's a whole lot of 13 MHz RF running around--like 100 W to 1.5 kW in general.
Cheers,
Phil Hobbs
The 20Hz has a period of 50ms and you intend to ramp it up in 100ms or two periods? Maybe you should provide a link to a description of the application.
Something based on the CRT cathode drivers in a PC monitor might be a possible starting point.
This usually consists of a cascode stage - which is a high voltage common base transistor whose emitter is driven by a low voltage common emitter stage. The base voltage for the common base stage can be conveniently provided by an 8 or 12V 3-terminal regulator.
If you salvage the amplifier(s) from a scrap monitor, a good quality high resolution display will also have a complementary emitter-follower pair output stage on the cascode, for driving the high capacitance of CRT cathodes.
It would look like a highvoltage op amp. Similar to some audio amplifiers.
Bob
A transformer for 20 hz gets quite large for any appreciable power.
Bob
you can always run output transistors in series.
Bob
Depends on how much power he needs. You can still buy "Hi Fi" output transformers. Hook one up backwards, that is with the "PLATE" winding to the load, drive the 16 Ohm winding. 10 - 20 W units aren't all that expensive. I saw some in either the Mouser or Digikey catalog recently.
Tam
One with a step-up transformer on the output. A PA amp with 100V line output has one built in.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
100V line output transformers are cheaper and easier to find.
-- Service to my country? Been there, Done that, and I\'ve got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
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