HV Capacitor Discharge Circuit - Page 1
Forum section: electronics / projects

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 26, 2014, 01:04:31 pm
content: Working on some power supplies last night and discharging caps like I have always done with a short or resistor which is not really my preferred way I would like to do this. I whipped up this discharge circuit this morning over coffee using some of the parts I have laying around. Have not built it yet, just in the simulator. Seems that it would work up to 300V or even a bit more. Let me know what you think.

author: SeanB
author_rank: Super Contributor
timestamp: January 26, 2014, 01:20:05 pm
content: I would suggest a 10-15V zener diode across the gate junction, as even if the device has built in ESD protection it will not be good to rely on them to protect against high voltage on the gate.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 26, 2014, 01:25:09 pm
content: Quote from: SeanB on January 26, 2014, 01:20:05 pmGood point, I thought about that but did not add it. Thanks!

author: dannyf
author_rank: Super Contributor
timestamp: January 26, 2014, 02:19:27 pm
content: A CCS built around a mosfet + resistor would be good for this.

author: kripton2035
author_rank: Super Contributor
timestamp: January 26, 2014, 03:05:26 pm
content: I recently bought this and it does the job for cheap.Link @ dx.com

author: sync
author_rank: Frequent Contributor
timestamp: January 26, 2014, 03:09:23 pm
content: I don't like it in this form. When the cap is connected with opposite polarity or the battery is empty the LED don't lit up. Not something I would trust.

author: kripton2035
author_rank: Super Contributor
timestamp: January 26, 2014, 03:34:31 pm
content: Quote from: sync on January 26, 2014, 03:09:23 pmthis is the first test I did when I received the tester : the led lits and discharges the cap even on opposite probes. but I did not try it with 300v dc ... I can test it.

author: sync
author_rank: Frequent Contributor
timestamp: January 26, 2014, 03:44:26 pm
content: Quote from: kripton2035 on January 26, 2014, 03:34:31 pmSorry, i meant Terabyte2007's circuit.btw: Is this DealExtreme thing battery powered?

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 26, 2014, 03:59:53 pm
content: Might be a good idea to tear it down and/or have Photonicinduction "review" it... Some newer multimeters have a low impedance mode that can be used for discharging caps, rated to the CAT rating of the meter itself.I just use an incandescent light bulb, followed by checking with a multimeter.Here's an interesting capacitor discharge circuit:http://www.repairfaq.org/sam/smpsfaq.htm#smpscapdi

author: SeanB
author_rank: Super Contributor
timestamp: January 26, 2014, 04:07:38 pm
content: I just use a 56k 10W metal film resistor ( I have a lot of them in a box) for that. Simple, cheap and I have preformed the leads to fit the capacitors i most often test. The resistor stays in the box with the insulation tester. It does not even get warm. A small spark on connection to 2kV and that is all.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: January 26, 2014, 04:10:39 pm
content: You mentioned high voltage , I need higher 2,000 - 4,000 for ham radio amps ?Currently using chicken stick with resistor .

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 26, 2014, 04:39:53 pm
content: Quote from: sync on January 26, 2014, 03:09:23 pmAdding a battery check and a polarity reversal circuit would be easy enough. Sure I could buy the one from DealExtreme which is probably similar in concept but what would be the fun in that? Keep in mind, I was bored and sketched this up over a cup of coffee. I have not refined it yet. Your comment is appreciated though, thank you.

author: Terabyte2007
author_rank: Frequent Contributor
timestamp: January 26, 2014, 06:00:16 pm
content: Quote from: KD0CAC John on January 26, 2014, 04:10:39 pmProbably not a bad idea with that kind of voltage! I'm only talking 300-400 volts max.

author: kripton2035
author_rank: Super Contributor
timestamp: January 26, 2014, 06:34:52 pm
content: Quote from: sync on January 26, 2014, 03:44:26 pmthey dont mention any battery inside, and the thing is glued so I dont think there is any battery insideI must break it if I want to make a teardown review !

author: sync
author_rank: Frequent Contributor
timestamp: January 26, 2014, 11:25:38 pm
content: Quote from: Terabyte2007 on January 26, 2014, 04:39:53 pmI would not trust one from DX (without teardown). DIY is good.

author: BiOzZ
author_rank: Regular Contributor
timestamp: January 27, 2014, 04:36:18 pm
content: make sure that primary switch is well isolated

author: mcinque
author_rank: Unknown
timestamp: January 27, 2014, 06:56:43 pm
content: Just to ask: a thing like this won't do the job?