Leigh, the idea of having a device without external means for protection
is intriguing.
A device that can sustain such repetitive abuse and continue to operate
is really something.
As you said stated it could be done with standard methods, however they
do marginal
SWR, and high current shutdown. If you've seen the test video of the
NXP device on Youtube,
the power output never shuts down, just simply sits in ready for the
mismatch to clear.
73,
George, K4GVT
On 3/9/2013 9:13 PM, Leigh Turner wrote:
I'm always intrigued and puzzled why so many hams place so much reliance on
inherent brute force device survival per se when placing their amplifiers
through this kind of severe load and phase angle mismatch test.
With appropriate design and implementation of ancillary load impedance
sensing, protection, and fast acting shut-down circuitry then less rugged,
lower VDS breakdown QRO MOSFET devices will readily survive any VSWR load
you can throw at them. Existing MOSFET RF devices are more than capable.
Inadequate thermal design issues that don't keep the actual device flange
temperature low enough are far more likely to be the underlying cause of
premature device failure in practical SS amplifiers.
Leigh
VK5KLT
-----Original Message-----
From: Amps [mailto:amps-bounces@contesting.com] On Behalf Of George
Sent: Sunday, 10 March 2013 11:13 AM
To: Paul Decker
Cc: amps@contesting.com
Subject: Re: [Amps] Freescale LDMOS devices
Very nice Paul, have you put it through the ringer regarding mismatch,
open, or short.
73,
George, K4GVT
On 3/9/2013 6:46 PM, Paul Decker wrote:
I don't know how the freescale parts are, but the NXP BLF578XR seems to be
holding up well for me. with 4 watts I can drive it to about 1450W output
with 52V @ 42A. I've been running it ~45% duty cycle 45s on 75s off with
wsjt on 2m without issues.
Paul,
KG7HF
Date: Sat, 09 Mar 2013 09:23:52 -0500
From: George
To: jtml@vla.com
Cc: amps@contesting.com, John Lyles
Subject: Re: [Amps] Freescale LDMOS devices
Message-ID: <513B45F8.1090306@comcast.net>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
John, sounds like a great commercial project with quite an end result
most Hams will never see. I am very curious about your testing.
Be very interested if you had any fault history for the MRFE6VP61K25H.
Have you pushed it to extremes.
73,
George, K4GVT
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