Shon, Jim, and all,
with correctly designed switching power supplies there is a MUCH lower
risk to get an overvoltage at the output, than with linear supplies.
In a linear supply, the most common failure is one of the pass
transistors shorting out, and this results in the full unregulated
voltage appearing on the output. If there is overvoltage protection
included, fine, it will blow a fuse - but if not, the radios connected
are at severe risk.
In a switching power supply, instead, the failure of ANY of the power
devices, in ANY way (short or open), will always result in the voltage
going down, not up. This makes switchers much safer than linear supplies
ever can be.
In both types of power supply the voltage can go up if the control
circuitry fails, but since that's low power circuitry, it's easy to make
very reliable. Not all manufacturers do, though.
No matter how low I switched the DC Adjust dial (9-15 V), it just
> pegged itself it seemed even a bit higher than the max.
That smells like a potentiometer failure, along with poor design.
Potentiometers are notorious for failing with the wiper becoming
open-circuited. Depending on the circuit design, an open wiper in the
voltage setting potentiometer will result in either the voltage going
down, or up, or becoming undefined. I always make a point of designing
my circuits in such a way that an open potentiometer wiper will result
in the safest possible situation, and in a power supply that is: Voltage
going down.
I invite the electronically savvy among you to check the different power
supply designs on my website, and analyze what will happen if the wiper
of the potentiometers (trimpots in these cases) becomes disconnected.
And I encourage manufacturers and homebrewers reading this to do like I
do, and always consider the consequences of potentiometer failure in
their designs. Not just in power supplies, but everything else too.
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|