Budget high voltage/frequency signal generator - Page 1
Forum section: electronics / testgear

author: J-R
author_rank: Super Contributor
timestamp: September 13, 2022, 11:25:20 pm
content: I've been using the "hack" of sig-gen-->amp-->transformer-->T&M for quite some time but of course that has the obvious shortcomings. A fully-featured calibrator seems to be out of the question, so is there another solution? I'd like to reach at least 300V RMS and 100kHz. High power isn't necessary, just want to feed some signals to various things.

author: slugrustle
author_rank: Frequent Contributor
timestamp: September 14, 2022, 12:25:00 am
content: Can the transformer you're using right now hit 300V RMS output at 100kHz? If so, please share details. Sorry I can't help with your original query, but you've piqued my interest.

author: MasterT
author_rank: Frequent Contributor
timestamp: September 14, 2022, 03:21:09 am
content: You can search "CRT TV Video buffer". Those things were able to drive 4 MHz at 300 V

author: J-R
author_rank: Super Contributor
timestamp: September 14, 2022, 03:39:54 am
content: Quote from: slugrustle on September 14, 2022, 12:25:00 amI have no way to drive the transformer that high. It's just some random one I pulled out of the parts bin.There are high-frequency transformers out there and I could also try to modify the amp to hit higher frequencies, but any kind of transformer setup is going to be limited due to the waveform required. So I'm not pursuing that path.

author: J-R
author_rank: Super Contributor
timestamp: September 14, 2022, 03:40:55 am
content: Quote from: MasterT on September 14, 2022, 03:21:09 amI'm not finding much under that search term, got a link?

author: MasterT
author_rank: Frequent Contributor
timestamp: September 14, 2022, 04:13:26 am
content: https://www.afiata.com/how-to-fix-crt-television-color-problem/

author: Zoli
author_rank: Frequent Contributor
timestamp: September 14, 2022, 05:03:22 am
content: Quote from: J-R on September 13, 2022, 11:25:20 pmLook for the LCD monitor/TV CCFL drivers; you can mod them to fit your requirements.Example:https://www.ebay.com/itm/164641398362?hash=item2655645e5a(not associated)And don't forget: safety first, because ultrasonic HV will leak, and will give you some nasty burns.Quote from: MasterT on September 14, 2022, 03:21:09 amThose generate 300Vp-ponly

author: Berni
author_rank: Super Contributor
timestamp: September 14, 2022, 05:13:42 am
content: There is also no mention of what output impedance you are looking for.If you are sticking to the classic 50Ohm impedance that signal generators have you will need an output buffer that can handle 1.8kW to hit 300 Vrms into 50Ohm. That would be getting into big ass boat anchor radio transmitter territory of amplifiers.In general if you are after building an amplifier like this the way to do it is to use a opamp with the output chained to a 10x gain power output stage made out of discrete transistors. The output amp gives the huge voltage swing and power while the opamp is doing the feedback loop to keep the output stable. However once you get to these kind of fast slewrates, careful design and compensation tuning will be required to keep it stable. Even then you might make it unstable by driving loads that are too reactive.

author: J-R
author_rank: Super Contributor
timestamp: September 14, 2022, 08:07:35 am
content: I am not looking to build something from scratch at this time. I do see some high voltage op amps out there. Anyone know of something ready-made?

author: Martinn
author_rank: Frequent Contributor
timestamp: September 14, 2022, 11:21:55 am
content: Maybe some amplifier from Apexhttps://www.apexanalog.com/support/linear_search.html?

author: Berni
author_rank: Super Contributor
timestamp: September 14, 2022, 02:44:40 pm
content: Yep Apex is famous for making the sort of analog chips that operate into the ridiculous levels of current and voltage.Tho be warned they don't come cheap. They know they are making pretty specialized components for a pretty 'specialized price'. Another reason is that these are typically not the usual single silicon die chip that you normally get as an opamp. A lot of these things are actually hybrids inside. A thermally conductive ceramic that hosts multiple devices on it, be it opamp dies, discrete transistor dies, or sometimes even fully packaged transistors. It is basically the discrete transistor solution packaged into a module for easy use.Due to the prices these things don't usually make sense for mass production. Exception is when used in products with eye watering price tags (like militairy) or for building very low volume things where the high price of the module justifies the time saved in design. Particularly because some of this analog stuff can be hard to get right and the people at Apex know how to do it.