150 amp Darlington power transistors variable PSU?? - Page 1
Forum section: electronics / beginners

author: medosa00
author_rank: Newbie
timestamp: April 11, 2016, 07:18:10 am
content: Hello everyone,I found the attached circuit herehttp://www.homemade-circuits.com/2015/03/100-amp-variable-voltage-power-supply.html,And i was wondering what you think of it?? could it be that simple?? and if you can think of any disadvantages or problems or whatever that would be great.Thanks.

author: johansen
author_rank: Super Contributor
timestamp: April 11, 2016, 07:55:31 am
content: no, not that simple.I have some darlington transistors that are rated 100 amps, or 600 volts, or about 600 watts continuous dissipation each. they are each about 4 inches by 1.5 inch wide. i have about 200 of them, bought them for a couple bucks each* on ebay. The packaged body diode with the transistor is worth as much as i paid, unfortunately.but this is child's play these days.* i don't recall spending that much either. anyhow, i've done the math a number of times. try finding a passive heatsink ready, 100 amp, 480v diode bridge for less than 20$.

author: danadak
author_rank: Super Contributor
timestamp: April 11, 2016, 11:07:54 am
content: Keep in mind thats NOT a regulated power supply, so load variationswill affect the output voltage. Its also not short circuit protected, nordoes it have matched current sharing thru each transistor. And verysensitive to temperature changes.Regards, Dana.

author: Dave
author_rank: Super Contributor
timestamp: April 11, 2016, 01:13:32 pm
content: You'd be hard pressed to get more than an amp out of this circuit. The bases need a substantial amount of current to let 150A through the circuit. A 10k pot and some resistors aren't going to provide that.And as others have already mentioned, this isn't a power supply. A power supply's job is to keep the output fairly stable, regardless of load and input variations, this circuit doesn't do any of this.

author: danadak
author_rank: Super Contributor
timestamp: April 11, 2016, 01:51:00 pm
content: Darlingtons have typical beta of 100 at design Ic, so for round numbersif you used 5, 150A total, thats 30A each / beta = Ib = 300 mA. Consultdatasheet for worst case.Beta also a strong f(temperature).Regards, Dana.

author: wraper
author_rank: Unknown
timestamp: April 11, 2016, 02:30:53 pm
content: This circuit is made by clueless person. Nor it can supply 150A, nor work well at all. Max current for TIP142 is 10 amp , so that 150A claim is just someone's dream. If one would look into TIP142 datasheet, would notice that at 30V voltage drop, their max safe operating current is 5A, so 6x5 = 30 A max current per all of them given ideal current sharing which will never happen, but that would be extreme for them too an would be valid with cold heatsink only. At 60V max current is 1A per transistor, so 6A for all circuit, again given ideal current sharing. Driving circuit is completely unsuited as well.

author: danadak
author_rank: Super Contributor
timestamp: April 11, 2016, 02:52:17 pm
content: @wrapper I am glad you picked that up on the TIP141, I completelymissed the P/N being used. But notice in an earlier post he is going towork with some 100A units he has already bought.But that does not negate the fact there is no current sharing implemented,short circuit protection, or just basic voltage regulation. Its a tinker-bellsupply, pixie dust and magic wands come to mind.Regards, Dana.

author: Audioguru
author_rank: Super Contributor
timestamp: April 11, 2016, 03:02:38 pm
content: I noticed that the author of this circuit which was designed by a "clueless person" lives in Mumbai which I never heard of so I looked it up. It was formerly called Bombay.

author: danadak
author_rank: Super Contributor
timestamp: April 11, 2016, 08:35:16 pm
content: Mumbai -https://en.wikipedia.org/wiki/2008_Mumbai_attacksRegards, Dana.

author: medosa00
author_rank: Newbie
timestamp: April 13, 2016, 07:03:59 am
content: Thanks everyone for your help.