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| To: | DK7FC <rsgb_lf_group@blacksheep.org> |
|---|---|
| Subject: | Re: LF: Varistor spike management |
| From: | Chris Wilson <dead.fets@gmail.com> |
| Date: | Fri, 28 Apr 2017 12:36:26 +0100 |
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| In-reply-to: | <5901FD30.5010902@posteo.de> |
| References: | <1106627522.20170427150315@gmail.com> <5901FD30.5010902@posteo.de> |
| Reply-to: | rsgb_lf_group@blacksheep.org |
| Sender: | owner-rsgb_lf_group@blacksheep.org |
28th May 2017 Hi Stefan, remarkable work on VLF, congratulations!! I see these with all FET's but I acquired very cheaply some Wolfspeed FETs with a lot of overhead. These spikes sometimes kill lesser ones. If you follow these links you can see the normal gate and drain waveforms, and the drain waveform without a Varistor as an OPERA TX period ends, i took the latter from a series of screenshots showing the highest level the close TX spike reaches http://www.gatesgarth.com/wolfspeed-scope-capture-50v.jpg http://www.gatesgarth.com/wolfspeed-overshoot-50v.jpg http://www.gatesgarth.com/wolfspeed.pdf Best regards, Chris 2E0ILY mailto:chris@gatesgarth.com My part time LF grabber is at http://www.chriswilson.tv/grabber.html > Hi Chris, > Which type of FETs are you using? > The IRFP460A for example has a built in Z-diode which seems to handle > the spikes. Anyway i put a 150 Ohm / 220 pF (for LF) series RC paralell > to the Drain-Source... > 73, Stefan -- Best regards, Chris mailto:dead_fets@gmail.com |
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