Post by thread:25v at 5 Amp ????

you can get standard 3amp devices and i think i've seen a spec that parallels the outputs to increase the amperes. michael You may leave the list at any time by writing "SIGNOFF PICLIST" in the body of a message to spam_OUTLISTSERVTakeThisOuTMITVMA.MIT.EDU. -----Original Message----- From: Ricardo Ponte G <.....rniniverKILLspam@spam@CANTV.NET> To: PICLISTKILLspamMITVMA.MIT.EDU <.....PICLISTKILLspam.....MITVMA.MIT.EDU> Date: Friday, December 11, 1998 5:26 PM Subject: 25v at 5 Amp ???? Hi Picers: I«m not sure if it«s a dream or not but: Some out there have deal or have saw some regulators like 7805 with 25v at 5 or more Amps in its output ???? Thanks for sharing your expericence.

Michael Hagberg wrote: > you can get standard 3amp devices and i think i've seen a spec that > parallels the outputs to increase the amperes. It is probably easier to use one or more PNP power transistors (MJ2955 or similar/ better) with emitter to unregulated supply, base to input of the regulator, and collector to output of the regulator which is the main regulated output. A 0.3 ohm resistor from emitter to base causes 2 amps to be passed by the regulator before the transistor(s) conducts; the remainder of the 25 amps is passed by the transistors. If more than one are paralleled, 0.02 ohm resistors are put in each separate emitter lead to equalise their contributions. This arrangement defeats the current and thermal limiting features of the regulator, though the latter will still occur if it is mounted on the same heatsink and close to the transistors. -- Cheers, Paul B.

On Fri, 11 Dec 1998 07:09:17 -0400 Ricardo Ponte G <EraseMErniniverspam_OUTTakeThisOuTCANTV.NET> writes: > Some out there have deal or have saw some regulators like 7805 >with 25v = >at >5 or more Amps in its output ???? Such IC's are made, but they're kind of expensive. A simple and cheap approach is to combine a standard 1.5A 3-terminal regulator with an external power transistor to boost the current. Unfortunately with this circuit, the transistor is not protected from burning out in case of an overload. A more complicated version adds another transistor to limit the current through the current-boosting transistor. Both circuits are described in the application circuits in the back of most regulator data sheets. Any linear regulator with 5A of current flowing through it is going to dissipate quite a bit of heat. It is likely that the heat sink will be the most expensive and unweildly part of the project. For that reason, switching regulators are very popular for these higer powers. The new all-in-one switching IC's are reasonably easy to use. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]