[Amps] Freescale LDMOS devices / load mismatch survival

[George]

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 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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