HV AC Function Generator for Biology Experiment  - Page 1
Forum section: electronics / projects

author: charlescurt
author_rank: Newbie
timestamp: October 16, 2019, 10:56:04 pm
content: Hi All,I have a biology device that we wish to do a test on. We are currently using a 700Vpp 45kHz signal to perform the function but wish to determine if other values are better.I am trying to find (without luck) an AC to AC amplifier could hook up to a waveform generator to allow me to create a test that output the following specs:0 - 1kV0 - a few MHzAnother alternative would be to get an AC generator with those specs but I also haven't found those.There is basically no load since it is a field-effect device so it doesn't need high power. I would like to buy something off the shelf, anyone know a device that is close to this? If not I'll go the custom route if that's the case can anyone suggest something off the shelf that solves any part of this?

author: dom0
author_rank: Super Contributor
timestamp: October 17, 2019, 12:06:37 am
content: 1 kVpp at a "few MHz" (3) requires a slew rate on the order of about 10 kV/µs. That in itself would be possible with very high speed, off the shelf devices, but not at a 1 kVpp swing. I wouldn't expect this to be feasible solid state only, unless you are not talking about an actual analog amplifier but rather something like a pulse generator.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 17, 2019, 03:14:15 am
content: Look here,http://www.trekinc.com/products/HV_Amp.aspHowever those are expensive instruments and dont even meet your specs. Luckily in electronics one can get away with fast pulses to create harmonic content instead of pure sinewaves, but in your case, a biologocal experiment, that may be different

author: KaneTW
author_rank: Frequent Contributor
timestamp: October 17, 2019, 04:53:42 am
content: I would generate a low-voltage sine at the desired frequency and then run it through a step-up transformer. You'll have a lower frequency bound, so for low-frequency you'd have to use something else.

author: Berni
author_rank: Super Contributor
timestamp: October 17, 2019, 05:33:20 am
content: Yeah i think the best way is to get a amplifier similar to this:https://www.newtons4th.com/products/laboratory-power-amplifiers/lpa01/And then design your own ferrite core transformer to boost the output up to the desired voltage. Tho getting it to work bellow 1kHz might be difficult as the transformer could start getting large.

author: charlescurt
author_rank: Newbie
timestamp: October 17, 2019, 05:11:04 pm
content: Thanks for the suggestion guys I understand it sounds naive to say "a few MHz" but the test is to try out a large variety of frequencies for more data points but I appreciate your suggestions.Let me describe the actual application since you all were nice enough to respond. We are running cells and "drops" through a microfluidics chip and merging them. This is where this field effect voltage is located. At the site of the merge, the polarity of the surface of these cells and drops prevent them from combining but if you apply a field to the surface of the drops they have the same polarity and it allows them to absorb into each other for the brief moment we pass them through the field.Basically, we are doing tiny chemical reactions on individual cells and this signal "mixes" them. I tried a DC field but this actually sheds the cells due to the force exerted upon them. Playing with a wide variety of voltages and frequencies would allow us to find an optimal value to maximize successful merges.Another thing this implies is that this signal can be nasty, all I care about is that the signal is symmetric so it causes no force on the cells.- dom0"That in itself would be possible with very high speed, off the shelf devices, but not at a 1 kVpp swing." So you know of a device near these values? I was looking for more of a complete package but I'll probably start with Kane's idea if not.- MasterTech"one can get away with fast pulses to create harmonic content instead of pure sinewaves"I didn't actually know of this, I described the actual application above, would that idea be nearly a full custom application?- KaneTWThis is what I was thinking if I couldn't find something off the shelf. I'd have to make a few devices for the frequency ranges for this single test (barf). But this is how the current board is working so I at least have something to work off of at least.- BerniThis is a new suggestion I haven't seen before, thank you!

author: Kleinstein
author_rank: Super Contributor
timestamp: October 17, 2019, 06:22:40 pm
content: One problem with a DC flied is likely electrolysis. So one could consider a series capacitor to avoid DC current.I don't think it would need so high frequencies and the actual waveform should no be so critical. So I would prefer an transformer as a relatively low cost solution.

author: PartialDischarge
author_rank: Super Contributor
timestamp: October 17, 2019, 08:17:54 pm
content: Quote from: charlescurt on October 17, 2019, 05:11:04 pmIt may be worth the try, it is easier and cheaper to generate high frequency HV pulses than HV sinewaves, this is how HV probes are calibrated for example.https://www.behlke.commakes Hv pulsers than can even exceed your voltage and frequency specs and at a lower cost than linear HV amplifiers

author: Marco
author_rank: Super Contributor
timestamp: October 18, 2019, 04:59:35 pm
content: A FSWP 3 MHz multi-kV squarewave generator will run you4302$.A wideband high insulation RF transformer might not be an easy find, might have to make it custom, so if squarewave suffices the Behlke seems the quickest solution.

author: dom0
author_rank: Super Contributor
timestamp: October 18, 2019, 05:13:04 pm
content: Quote from: charlescurt on October 17, 2019, 05:11:04 pmDSL line drivers achieve differential amplitudes on the order of 30-40 Vpp at more than 100 MHz bandwidth (e.g. THS6022). G.fast drivers are at least twice as fast (see e.g. THS6301). These give you a lot of speed, but not the amplitude.A linear amplifier (i.e. not a pulse generator) will have to use a special transformer to step the output voltage up. Turns ratio of at least ~1:30 would perhaps make it possible to use one of these line drivers to drive that transformer. Since DC operation doesn't seem to matter after all no separate LF path is needed. I'm not sure but I think the biggest challenge for that transformer is probably winding self-capacitance on the HV side, followed by inter-winding capacitance (due to the high slew rate on the secondary); a low drive impedance should be able to fix the latter, but will not help with the HF roll off of the former. Going from, say, a few kHz at the LF point to a few MHz at the HF point might be a real challenge due to that. I barely know anything about transformers, so take that with a big grain of salt.

author: jbb
author_rank: Super Contributor
timestamp: October 19, 2019, 06:55:13 am
content: An RF step-up transformer at those frequencies and voltages would be quite hard. With a high turns ratio the output winding capacitance makes the output impedance quite low, which mangles the waveforms.

author: Marco
author_rank: Super Contributor
timestamp: October 20, 2019, 11:31:07 am
content: If you do want to DIY something, how about a class A amplifier with NDFPD1N150CG low side and a current source based on the same high side? You're going to need to put them on a good heatsink and run them toasty because even though they have pretty low Coss at 9 pF that's still quite a lot and will presumably swamp the load. I don't think there's anything in that voltage range with significantly lower output capacitance, for lower voltages there are ... but for stacks you need isolated gate drives and that will quickly increase complexity.Lets say 2 MHz 10 pF, going to need to run with a quiescent current of ~60 mA, which will burn 30W in each transistor.PS. actually that's a bit beyond the SOA, a IXTH02N250 could do it.PPS. going to need a beefy gate drive of course.

author: TimFox
author_rank: Super Contributor
timestamp: October 20, 2019, 02:10:17 pm
content: At the "MHz" end of the spectrum, one could run a class-C non-linear or class-B linear vacuum tube amplifier into a resonant load, and get kV sine waves directly across the resonant circuit, with high voltage applied to the circuit. This would be equivalent to a ham-band transmitter, and you might have to worry about RF interference to your neighbors.

author: coppercone2
author_rank: Super Contributor
timestamp: October 20, 2019, 11:30:45 pm
content: what is it that you are making?