voltage regulator with crow bar protection

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spindown
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voltage regulator with crow bar protection

Post by spindown » Thu Sep 08, 2011 2:29 pm

I want to make a 12 volt d.c. power supply for my ham radio. Does anyone
know if a 12 volt regulator with crow bar protection is available and where?
Thanks Paul

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MrAl
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Re: voltage regulator with crow bar protection

Post by MrAl » Thu Sep 08, 2011 4:11 pm

Hi,

How much power you need, that is, how many amperes do you need to drive it?
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Re: voltage regulator with crow bar protection

Post by Robert Reed » Thu Sep 08, 2011 5:07 pm

Crowbar protection is relatively easy to add to most supplys. It involves an SCR. a fuse and a simple sense circuit. Need more info? Post whether you want to limit current or voltage. Generally speaking, a crowbar circuit limits over voltage by intentionally forcing a fuse to blow.

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dacflyer
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Re: voltage regulator with crow bar protection

Post by dacflyer » Fri Sep 09, 2011 1:29 pm

last time i ever saw a crowbar circuit was used on the outputs of a Peavey cs-800
it was designed to sense DC on the outputs and would short out and possibly blow the amp.
its design was to protect your speakers from DC voltage. because Peavey figured that it was cheaper to rebuild the amp, rather than replace expensive speakers.
and if the amp was putting out DC it was probably already damaged.
but on the good side. Peavey Amps like the CS-800 are almost indestructible. they are a true abusive work horse.
most i ever worked on , only needed a good dust blow out and volume control cleaning.
their is 2 drivers and 10 finals for this amp..and it is a simple design too.

here is a link to a schematic of a peavey.. if you look all the way to the right, you will see the crowbar circuit, perhaps it might be of use to you.

http://webpages.charter.net/eastwind_en ... S800-2.jpg

good luck..

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Re: voltage regulator with crow bar protection

Post by haklesup » Fri Sep 09, 2011 4:03 pm

Crowbar protection (shorting or opening the output when a fault situation is detected) is kind of old fashoned for low power supplies since there are now so many options for active regualtion of the output voltage or current. Flipping off the switch is generally not the preferred method of circuit protection aside from a fuse.

They still get used in HV or high current supplies because so much power is available at the output, active regulating circuits cannot operate fast enough to protect loads or even a regulated current is too much in a fault situation. They may also be desireable if you need all power to be removed immedietly when a fault is detected and wait for operator to reset it. (not unlike a circuit breaker but faster and more precise)

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Re: voltage regulator with crow bar protection

Post by Dean Huster » Fri Sep 09, 2011 4:38 pm

"Crowbar" is sometimes a misinterpreted term. As mentioned, a crowbar circuit is one that senses a fault (overcurrent, overvoltage, DC on an AC-only line, etc.) and throws a semiconductor component (usually an SCR) into a full-on condition from the power suppy rail to ground to blow a fuse back toward the source. It's a brutal but effective control but is a hassle for "oops" situations because of the fuse replacement. Paul, perhaps you're actually looking for current limiting (foldback is another term) in your supply. Most 3-terminal regulators already come with this feature, designed to current limit at their rated current. Most can be configured to provide a variable current limiting circuit within your supply.
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spindown
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Re: voltage regulator with crow bar protection

Post by spindown » Sat Sep 10, 2011 4:20 pm

Thanks for the responses. My concern is the voltage sensitive components in a modern day receiver of conventional or software defined receiver design and mostly concerned with over voltage sensitivity. My current needs would probably be in the 4-15 amp range. Paul

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Re: voltage regulator with crow bar protection

Post by Dean Huster » Sat Sep 10, 2011 6:57 pm

Good gosh! That kind of current for a receiver? What do they have, 500-watt audio power amps? Or are we realloy talking about transceivers and it's the transmitter that requires all the current?
Dean Huster, Electronics Curmudgeon
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Bob Scott
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Re: voltage regulator with crow bar protection

Post by Bob Scott » Sat Sep 17, 2011 4:24 pm

You might also consider reverse voltage protection in case someone wires the power leads backwards. That is just a rectifier diode wired (normally reversed biased) across the power supply terminals and AFTER the fuse.
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Re: voltage regulator with crow bar protection

Post by Lenp » Sun Sep 18, 2011 7:57 am

'AC Crowbar with sparks'
Years ago a local school system was having problems with boiler rooms flooding. When the water rose it submerged the low mounted computerized boiler controls. It destroyed them since they were under power and cooked for some time. I designed a water sensor that was below the controls. When it got wet it operated a high current relay to short the power line, tripping the breaker at the panel. This saved many controls.
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Re: voltage regulator with crow bar protection

Post by FOB » Sat Oct 01, 2011 6:42 pm

Back in the 80's and 90's most of the guys in the local Ham radio club would rely on the ASTRON brand of power supplies. Most models used the same pc board for voltage control, foldback current, and an SCR circuit (crowbar) to protect from catastrophic overvoltage. One of the guys designed a pc board that was electrically identical to the ASTRON board, we silkscreened about 500 of them and used them for about 5 or 6 years of "Construction Night" weekly meetings to teach, repair, and build power supplies for home use. I think one of those boards would be what the Original Poster had in mind, I may still have a few (I never throw anything away) and will supply one along with schematic info if he contacts me.

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