From: "R. Lewis"
Subject: Re: Batt Charger 7905 discussion
Date: Mon, 16 Dec 2002 22:55:26 -0000
Organization: Nextra UK
NNTP-Posting-Date: Mon, 16 Dec 2002 22:55:23 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
wrote in message
> In sci.electronics.design Watson 'Atto Parsec' Name
> > I made up this constant current charger after some design on the web.
> > But I used a 7905 instead of a 7805, because I've got a lot of 'em
> > laying around from scrapped SMPSes. And I've seldom needed a negative
> > 5V supply. It works pretty good. I can switch between 50 or 150 mA.
> > But one question. Should the output lead to the battery have a 1N4002
> > in series to keep the battery's 6v from going back thru the regulator?
> > After a short while, the batts should charge up the cap in the wall wart
> > and no further current should flow. But when it charges up, it'll be
> > thru the regulator chip. In reverse.
> Read the datasheet of the 7905.
> I'm unsure exactly what will happen when you do this, I don't think you'd
> see any damage, but there might be a few milliamps of current
> drawn as the circuitry inside the 7905 gets powered.
> There is no reason that current will flow back through the 7905, though
> it might.
For a couple of reasons put a diode across your regulator - diode anode to
output, diode cathode to input of your regulator. A 1n400(x) is all that is