[Amps] Freescale LDMOS devices / load mismatch survival

[George]

Very nice project, nicely built and quite the survival test.
Thank you for sharing the data and great pictures.

73,
George, K4GVT

On 3/11/2013 4:14 AM, Peter Frenning [OZ1PIF] wrote:
> Den 11-03-2013 09:01, Steve Thompson skrev:
>> The video is, indeed, impressive - but it could also give a false 
>> impression. The transistor operating spec. is 100us pulses at 20% 
>> duty cycle - 100us on, 400us off. Looking at the current drawn during 
>> the variable load pull test, it's not running cw. Also, the test is 
>> being done at 200MHz and ruggedness doesn't necessarily translate to 
>> lower frequencies for those thinking of hf applications.
>>
>> At 100us long pulses, the die inside probably isn't reaching the peak 
>> temperature for any given dissipation which makes high VSWR survival 
>> easier.
>>
>> F1JRD tested Freescale devices with all phases of high load VSWR 
>> running 10ms pulses, low duty cycle. They survived, so a trip circuit 
>> acting faster than that should protect them. I'd expect NXP parts to 
>> be similar.
>>
>> Steve
> I, inadvertently, tested mine when the output coax relay gave up it's 
> ghost, see the pictures toward the bottom of the page:
> http://www.frenning.dk/OZ1PIF_HOMEPAGE/LDMOS_SSPA.html
> The LDMOS survived! I was running Digimode at about the 750W level 
> when it failed.
>