Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site umcp-cs.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!sdcsvax!sdcrdcf!hplabs!hao!seismo!umcp-cs!chris From: chris@umcp-cs.UUCP (Chris Torek) Newsgroups: net.analog Subject: Re: Big Capacitors and now power supplies Message-ID: <1701@umcp-cs.UUCP> Date: Fri, 7-Dec-84 19:10:54 EST Article-I.D.: umcp-cs.1701 Posted: Fri Dec 7 19:10:54 1984 Date-Received: Mon, 10-Dec-84 02:34:16 EST References: <1812@sun.uucp> <1215@hou4b.UUCP> <6171@brl-tgr.ARPA> <10102@watmath.UUCP> <259@umd5.UUCP> <549@voder.UUCP> Organization: U of Maryland, Computer Science Dept., College Park, MD Lines: 24 Yes, but.... 7805s are only rated at 1 amp. Now I know you can pull about 1.5 amps through most of these suckers before they melt (have *you* ever seen the thermal overload protect *work*?), and that you can get 3 and 5 amp versions of essentially the same thing, but you are still current limited by the things. Also, just having a 7805 doesn't do a whole lot of good. You still need quite a bit of capacitance, somewhere. In fact, with most real computers you need lots of caps sprinkled about the boards near each of the ICs, 'cause when those suckers switch, they want CURRENT. (Not much actual power, but over a very short time period, so lotsa current.) If you have lots of switching, you also need lots of capacitance BEHIND the regulator (that is on the rippled DC input side) so that it can recharge all the little caps even if the AC cycle is well below 5 volts (actually, with 7805s, you need about 6.5V min before regulation, but that's beside the point). -- (This line accidently left nonblank.) In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (301) 454-7690 UUCP: {seismo,allegra,brl-bmd}!umcp-cs!chris CSNet: chris@umcp-cs ARPA: chris@maryland