[Elecraft] Switched PS overvoltage

[K9MA]

It's far less likely that a switcher will fail to overvoltage. The 
switching transistor(s) under stress, and most likely to fail, will just 
cause the supply to die, as you have observed.

Still, I don't like entrusting the life of my K3 to one cheap resistor 
in the feedback loop. That comes of a career designing spacecraft 
electronics.

73,
Scott K9MA

On 6/10/2019 11:01, Bert wrote:
> I haven't experienced that a switched PS causes overvoltage. They 
> usually just die!
>
> Bert VE3NR
>
>
> On 6/10/2019 11:12 AM, K9MA wrote:
>> On 6/9/2019 23:16, Bert wrote:
>>> How would a switched PS take out a radio?
>>>
>>> Bert VE3NR 
>>
>> Most likely due to overvoltage. Linear supplies are particularly 
>> susceptible, as the series pass transistor is under stress and can 
>> short. Switching supplies can fail if the voltage feedback loop 
>> somehow opens up. I've not heard of it happening, but all it would 
>> take would be one failed resistor or solder joint. I use a switching 
>> supply for my K3, but I built an external overvoltage protector. Of 
>> course, the supply has never failed.
>>
>> BTW, I've found that the fan noise from the Samlex SEC-1235 is never 
>> audible above the K3 fans, except during long periods of receive, 
>> when the low speed supply fan is just barely audible. (I did the mod, 
>> so the supply fan runs at low speed all the time.) If I transmit long 
>> enough for the supply fan to switch to full speed, the K3 fans are 
>> already running fast enough to drown it out. Not to mention those in 
>> the KPA-1500.
>>
>> I'm very happy with the Samlex supply. I've never detected a trace of 
>> RFI from it.
>>
>> 73,
>>
>> Scott K9MA
>>
>
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-- 
Scott  K9MA

k9ma at sdellington.us