Dear Steve,
You raise a very good point in your question about what happens to a
switching P/S
in an arc situation.
In a Class A power supply (ferroresonant, etc., ) there's a chance the
filter cap(s) might puncture the dielectric (and their case(s) ), the
rectifier
diodes might open or short, the "glitch" resistor might explode violently,
etc., etc.
In a switching power supply all bets are off.
In the Telco world, seeing HV (ESD) and lightning damage to
switching supplies for several years has led to the following observations:
The microprocessor rectifier-controller gets wiped out and one result is
a +24 volt switcher bank pushes +58 VDC into a set of VRLA battery cells,
cracking them open and pushing out caustic goo, the radios on line all
frying
from more than their rated input. All new gear needed.
Another observation was that the switchers just went all dead like there
was no a.c. input. The microprocessor controller (MCA) looked the same way.
The radios all worked until the batteries depleted. Since the MCA was dead
there was no Low Voltage Disconnect operation until the battery voltage
couldn't
keep the solenoid magnets pulled in: All new batteries, rectifiers and MCA.
Yet another scenario seen in Syracuse: The switchers shorted out and the
resulting overvoltage boiled out the floating cells and the hydrogen gas
ignited and caused a Halon discharge. The fuses blew in the radios because
they were ancient. Modern radios would have fried.
Hal
W4HBM
Tom W8JI wrote:
>> I'm aiming for a floating supply as the current project is a tetrode
>> running with the screen at ground potential. I initially thought about a
>> dc supply where the switching frequency can be filtered to a minimal
>> level, but then I thought about using the ac (more or less square wave)
>> instead for simplicity. Capacitive coupling from the heater to the
>> cathode is quite high impedance, and the cathode is bypassed to ground
>> so I figure that the likelyhood of heater voltage getting transferred
>> onto cathode-control grid bias voltage is low.
>
>
> How will a switching supply handle a HV to ground fault if the tube arcs?
For what I have in mind, the heater supply will come from the secondary
of a fully isolated transformer. 5kV insulation is easy to achieve and
fault current shouldn't flow through the heater. I don't see any major
difference from what happens with a regular mains transformer.
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