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Subject: Re: High Voltage Input into 78xx
X-Newsreader: Microsoft Outlook Express 6.00.2800.1106
Date: Thu, 31 Oct 2002 13:57:14 GMT
NNTP-Posting-Date: Fri, 01 Nov 2002 00:57:14 EST
Organization: BigPond Internet Services (http://www.bigpond.net.au)
"Shaun Davy" wrote in message
> Basically the circuit runs off an input (upto 24VAC) that is switched on and
> off with triacs. The input also runs the circuit which requires +5V DC to
> switch on and off the triacs.
> Sorry i didn't really think about the fact the 1A needs to dissipate 30W!!
> Basically it needs to be around the 250mA mark but realistically up to .5A
> would be good for anything in future. 1A would be good to know if possible
> but really needed.
> The main suggestions so far seem to be use a switching regulator.
> Would this be the simplest and most effective way? if so is there a
> switching regulator that is fairly common, i guess the switching equivalent
> of the 78xx series?
> Thanks again
> "Shaun Davy" wrote in message
> > Just wondering if anyone could point me in the direction of how i could go
> > about running a +5V regulator off a 35V DC input (24VAC) and draw around
> > 250mA mark and if possable for future projects upto .5A or 1A.
> > Should i just use a normal 7805 and strap a big heatsink to it to
> > all that heat or is there a better more efficient way?
> > Thanks
> > Shaun
I've just finished doing something similar to feed a 78L05 from a 24V lighter socket
in a bus.
I used a 12V zenner diode as a shunt pre-regulator with 330R 1/2W series resistor.
Although my power requirements are a bit lower than yours, as my circuit only draws
This works OK for low power but the switcher is your best bet if you're looking for
an Amp or so.
Greg the Grog
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