The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Subject: Re: A protection problem
Date: Wed, 8 Jan 2003 11:14:59 +0000 (UTC)
NNTP-Posting-Date: Wed, 8 Jan 2003 11:14:59 +0000 (UTC)
User-Agent: tin/1.5.14-20020926 ("Soil") (UNIX) (Linux/2.4.20 (i686))
Ken Smith wrote:
> I'm currently working on a voltage regulator with a major protection
> problem. The specs are:
> Input voltage 23 to 28V. This is easy enough.
> Output voltage DAC controled 0 to 25V (doesn't need to boost make 25V when
> input is too low). This isn't too hard.
> Output current limited at 100mA. This isn't too hard.
> Some moron may hook a (+) or (-) 600V supply to the output. This 600V
> supply can supply a zillion amps so MOVs aren't the answer. PTC devices
> don't seem to be able to handle this case either.
Let's say the pass element is a P channel MOSFET with a 800V 500ma rating
in the positive rail.
This should cope with a brief connection to a -600V supply, though it
will explode into lots of little bits if the control circuitry doesn't shut
it off rapidly.
So, the remaining problem is +600V.
Can you put up with a diode drop?
Otherwise, a N channel depletion mode FET (do these exist?) on the drain
of the P channel one would let you turn things off from inside the 0-25V
supply, otherwise if you use an enhancement mode FET, you'd need a ~35V
low power supply.
You will need a zener diode and a resistor on the N-channel FETs gate, as
it won't really like -625V across it otherwise.
http://inquisitor.i.am/ | mailto:firstname.lastname@example.org | Ian Stirling.
If it can't be expressed in figures, it is not science, it is opinion.
-- Robert A Heinlein.
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup