SS switching of ~5kV - Page 1
Forum section: electronics / projects

author: garboui
author_rank: Regular Contributor
timestamp: June 08, 2016, 10:10:19 pm
content: Beginning to look at building a driver board for driving a corona generator electrode. The driver is to be having ~8 channels and all independently switched. While getting 5kV is not the problem, figuring out how to switch them is. There seem to be relays that are rated for the voltage and ~$30 a piece on digikey. While cost is not the biggest factor, the channels may be switched too fast for relays to be piratical. The search for HV mosfets or something begins. Seems that getting to 5kv in digikey is not possible (max 4.5kV and $30). Some searching brought up specialty companies that make HV stuff but is priced out of range. Am I missing something here, I feel like the part should exist, and inexpensively (<$20)?

author: ovnr
author_rank: Frequent Contributor
timestamp: June 08, 2016, 10:50:50 pm
content: Well, the easiest solution is to switch it on the primary side, not the secondary. Use separate supplies for each electrode.Actually switching multiple kV is not a simple task, nor is it common (in small-scale electronics anyhow). If you INSIST, you may be able to get something working with series transistors, gate driver transformers and some voltage balancing resistors, but it's going to be finicky.

author: garboui
author_rank: Regular Contributor
timestamp: June 09, 2016, 01:08:06 am
content: that may be what it ultimately comes down to. i may have to experiment with some other voltage multiplier typologies to see if the settling time could be made quick enough (sub millisecond). I would likely have to add an H-bridge to switch the primary at a higher frequencies too.

author: MarkL
author_rank: Unknown
timestamp: June 09, 2016, 01:27:18 am
content: Do a search for "high voltage mosfet stack". Here's a couple of papers that describe the strategy:http://www.mrc.uidaho.edu/~atkinson/IPPW/IPPW-5/Papers/p7_1_foun.pdfhttp://cmosedu.com/jbaker/papers/1992/RSI631992.pdf

author: Zeranin
author_rank: Regular Contributor
timestamp: June 09, 2016, 03:20:22 am
content: Quote from: garboui on June 08, 2016, 10:10:19 pmI'm often building multi-kv pulsers with rise/fall times down to a nanosecond, and these days I tend not to re-invent the wheel, and buy the switching module from Behlke (www.behlke.com) They are expensive, but relative to performance, maybe not. If you want to roll your own, then do you need switching of DC levels, or only pulsed, and what is the longest pulse width you need.Features - Switch Model Series HTSOperating voltage from 500 V to 150 kVPeak current from 15 to 16,000 Amps (pk)di/dt from 5 to 32 kA/µs (type depending)Rise times down to 0.8 ns (type depending)Short propagation delay time and low jitterCont. operating frequency up to 3 MHzBurst frequ. up to 10 MHz (type depending)Safe galvanic isolation up to 200 kVDCEasy control by simple TTL signal (3-6V)Active input filter for excellent EMC behaviorNo dangerous instabilities at short pulsesInternal clocks syncronized for low EMISafety circuit with fast thermotriggerFault signal output & inhibit input (TTL)Guaranteed temperature range -40...70 CVarious passive and active cooling optionsOn-off switches for fixed & variable on-timeHalf & full bridge switches (Push-Pull)Cost efficient discharge switchesAll switches can be made for DC and ACHighly reliable, 5 YEARS WARRANTY

author: daqq
author_rank: Super Contributor
timestamp: June 09, 2016, 05:49:22 am
content: Another thumbs up for Behlke. They even have a special offers page:http://www.behlke.com/special_offers.htm

author: Molenaar
author_rank: Regular Contributor
timestamp: June 09, 2016, 11:02:44 am
content: I don't know your requirements regarding rise time, but valves are still used for HV purposes. You might look into thyratrons if you only want to switch.