Is there a single part for DC over-voltage protection analogous to MOV 's which do the same job for AC?
Specific application: I have a particular power supply that reduces 12V down from 24V. I have heard that if one of the regulators fail in a common way that it passes 24V out. This 24V will likely damage a connected transceiver.
What can I put in line between the radio and power supply to protect against this possibility?
Are you sure it doesn't already have one? 24 to 12 inverters are common items in the trucking industry, and I would suspect any decent quality one would have some sort of over voltage protection built in.
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What you may want to do is look for a crowbar circuit.
It is a tried and true overvoltage protection method.
Just put a fuse between the supply and the load with the crowbar on load side of the fuse.
73, Sue
AF6LJ Conspiracy Theorists Are People
Who Question The Statements Made By Known Liars.
Here is a high-power zener. But usually an scr is used, tripped by a zener from output to gate. You may need a spike bypass cap to prevent brief switching transients from tripping the scr.
A fuse in series with the + followed by a stout Zener to - makes a quick and dirty effective Crowbar circuit.
Specify the Zener at 1W and its value should be a bit higher than the target overvoltage. For example, a 14V Zener should do well here.
Voltage exceeds Zener breakdown voltage, diode conducts and is a short to common, blowing the fuse...
73
What you describe is not a crowbar, it is simply a voltage clipper, set to whatever voltage the zener is. A 1 watt zener is not a good choice, unless the fuse is less than an amp. And the clip point should be a couple of volts above the nominal, or maybe 16 volts.
Sue has the riight idea. A true crowbar is a heavy duty SCR triggered by a zener. Once it fires, the SCR looks like a short, or has the effect of throwing a crowbar across the voltage, causing the series fuse to blow. You might download the schematic of an Astron RS35 PS and build a copy of their crowbar circuit, consists of a few parts, including an SCR and a zener, and a couple of other things.
Is there a single part for DC over-voltage protection analogous to the
Metal-Oxide Varistor (MOV) or Transient-Voltage-Suppression (TVS) diode used with Alternating Current (AC) circuits/designs ?
Specific application: I have a particular power supply that reduces 12V down from 24V.
I have heard that if one of the regulators fail in a common way that it passes 24V out. This 24V will likely damage a connected transceiver.
What can I put in line between the radio and power supply to protect against this possibility?
CORRECT.
In some Linear Power Supply designs (or in your case DC-to-DC converters) -- a failure of the NPN Pass transistors (e.g. 2N3055, 2N3771) or
the regulator (LM723) can result in full unregulated DC voltage appearing at the output terminals.
A Crowbar circuit, set for 14.5 to 15 VDC, is a common protection circuit for this these failures.
Another approach is to montior the output voltage and "cut in off" this high (or low) voltage, when a FAULT condition occurs. This approach is very useful with Field Day and emergency/portable situations
where the DC source may be from various power sources (e.g. solar, wind, inverters, gas generators, batteries).
Mike Bryce, WB8VGE of The Heathkit Shop designed and built ... The Protector, featured in June 2003 issue of QST magazine, page 55
Mike's circuit used an LM358, a Power FET, and a common automotive industry ISO relay rated to 40 amps
The was original for retro-fitting the Heathkit HP-1144 power supply that was sold with the SB-104(A) HF transceiver. http://p1k.arrl.org/pubs_archive/1225
What Is Used For DC Over-Voltage Circuit / Part
Originally Posted by KE3WD
