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.
From: Winfield Hill
Subject: Re: High Voltage Input into 78xx
Date: 31 Oct 2002 06:47:21 -0800
Organization: Rowland Institute
X-Newsreader: Direct Read News 4.00
>"Shaun Davy" wrote ...
>> 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!! ...
>> The main suggestions so far seem to be use a switching regulator.
>> Would this be the simplest and most effective way?
Yes. Look at National Semi's simple switchers. An LM2575 will
probably work nicely for you. And they offer free samples!
>>> 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 the 250mA mark and if possable for
>>> future projects upto .5A or 1A.
> 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
> 16mA. This works OK for low power but the switcher is your best
> bet if you're looking for an Amp or so.
If one want to stick with a 7805 linear regulator powered from 35V
at up to 1A, then a series pre-regulator is preferred over a shunt,
. 60V FET or
. darlington _____ LM7805 5.0V
. IN o----+--/\/\--, ,-+------+--| |---+----+---o OUT
. | 1 ohm | | | s | | | | | to 1A
. | 10W _|_V_|_ === |_adj_| | ===
. 10k ----, 0.1 | | | | 10uF
. 1/2W | gnd gnd | |
. | | _ | gnd
. 15V zener
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup