[Amps] Freescale LDMOS devices / load mismatch survival

[Leigh Turner]

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 at comcast.net] 
Sent: Sunday, 10 March 2013 11:56 PM
To: Leigh Turner
Cc: amps at 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 at contesting.com] On Behalf Of George
> Sent: Sunday, 10 March 2013 11:13 AM
> To: Paul Decker
> Cc: amps at 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 at vla.com
>> Cc: amps at contesting.com, John Lyles
>> Subject: Re: [Amps] Freescale LDMOS devices
>> Message-ID: <513B45F8.1090306 at 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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