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Re: LF: Varistor spike management

To: DK7FC <[email protected]>
Subject: Re: LF: Varistor spike management
From: Chris Wilson <[email protected]>
Date: Fri, 28 Apr 2017 12:36:26 +0100
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 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:[email protected]

 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:[email protected]


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