There is a very "cheap" solutions for the problem... not terribly elegant,
but it works great in my Harris 3230... fuses and transorbs. The FB fuses
solve the current spikes, and the transorbs (across the D-S of the mosfets)
catch the voltage spikes (basically short).
With that said... If someone wants to design the next round of amp
protection boards for SS devices.... I'd be willing to help!
Sincerely,
Dr. William J. Schmidt, II K9HZ
Trustee of the North American QRO - Central Division Club - K9ZC
"Collector of Edison Wind-up Phonographs... Do you have one for me?"
Email: bill@wjschmidt.com
Alternate Email: wmschmidt@charter.net
WebPage: www.wjschmidt.com
----- Original Message -----
From: "Steve Thompson" <g8gsq@qsl.net>
To: <amps@contesting.com>
Sent: Tuesday, December 16, 2003 9:03 AM
Subject: Re: [Amps] Really Big Solid State Power Amplifiers
> Larry Kayser wrote:
>
> > For me, my concerns with solid state is to have an effective
> > controller that will protect my investment. After some consideraton
> > what I want is a G3SEK type box that will look after my dollar
> > investment in solid state RF modules.
>
> Very tricky, unless the operating conditions are chosen to keep the device
> within survival limits either all the time, or at least long enough for
> protection to kick in. More often than not, the ultimate cause of a device
> blowing is the die overheating, whether that's caused by bad load VSWR, or
> spurious oscillation, or whatever. Under bad fault conditions, the die
will
> heat to destruction in the order of 100us. Detecting a fault and removing
> power in that sort of timescale while maintaining proper lf decoupling is
> not so simple.
> >
> > I am basing this on my experience in the LF world, 136 KHz where I had
> > an ex Decca amplifier, MosFets at up to 100V and 30 Amps and more, yet
> > it was unconditionally protected, antenna ON or OFF it did not matter
> > - the amplifier was protected by a wonderful protection design.
>
> I'd guess that the choice of output transistor was more significant than
the
> complexity of the protection circuitry - it's the combination of the two
> that delivers.
>
> Steve
>
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