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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