Your so right Leigh, isn't it nice to see a high power semiconductor
that gives you a moment to react before shutdown
or taking corrective action without destruction.
73,
George, K4GVT
On 3/10/2013 10:57 PM, Leigh Turner wrote:
Yes I do concur here George; that's an impressive device survivability
capability all right!
Nevertheless, as an amplifier designer using this device I'd still build-in
the aforementioned ancillary sensing and protection and shut down circuity
to safeguard against abnormal antenna load impedance, excessive Id current,
drain breakdown voltage, or adverse thermal conditions, etc.
This to me seems entirely reasonable to shut things down whenever parameters
go out of whack and deviate outside their safe zone limits. It's all too
easy to see right before your eyes a hard-earned thousand dollars or more
literally evaporating in milliseconds.... :-(
Consequently rugged and bullet-proof SS amplifiers are necessarily burdened
by fairly complex ancillary protection circuitry to try and avert mishap
fatalities from such inadvertent worst-case parameter excursions; the
inherent robustness of the MOSFET device notwithstanding...that's a bonus!
Leigh
VK5KLT
-----Original Message-----
From: George [mailto:K4GVT@comcast.net]
Sent: Sunday, 10 March 2013 11:56 PM
To: Leigh Turner
Cc: amps@contesting.com
Subject: Re: [Amps] Freescale LDMOS devices / load mismatch survival
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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