Electronics > Beginners
lab power supply
MarkF:
--- Quote from: not1xor1 on December 21, 2019, 06:31:58 am ---
--- Quote from: MarkF on December 20, 2019, 03:01:48 pm ---
--- Quote from: not1xor1 on December 20, 2019, 06:33:11 am ---
--- Quote from: glinjik on December 19, 2019, 09:30:49 am ---after looking at various ways to control a fan rather than just having it running found a little 555 timer fan control uses a npn transistor and thermistor so I’ve incorporated it into the scheme but before I build it in was wondering if any of you enlightened chaps might cast your eyes over the scheme so far oh i re drew the 555 to reflect it in reality rather than schematically its easyer to follow for me
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I'm sorry, but that circuit (I'm referring to the overall one, not just the fan control) just doesn't make any sense. It looks like a random assemblage of electronic components.
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Right, the OP introduced some errors into the last few versions.
Here is what I think it should be IHO (with a few unnecessary components removed).
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that circuit still doesn't make any sense. Both voltage regulation and current limit are really bad.
You can get similar results with just a potentiometer in parallel to a shunt regulator (e.g. TL431) plus a darlington to provide enough current for the power transistors.
And I' can't see any reason for not using just a BJT between the base and emitter of the power transistors.
Much better results might be achieved by several LM317 in parallel with ballast resistors (see the datasheet).
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I think this WHOLE design is poor.
I am working on a circuit where I was trying to limit the current by limiting the base current.
It worked. But NOT very well.
New design:
glinjik:
I believe D6 is intended for over-voltage protection on the output (i.e. The device being powered has a voltage on its power rails that is higher than this circuit is set for). It is only working for you because I suspect your wiring does not match the circuit diagram
thank you yes you are correct my drawing is in error it is actually wired correctly, i have removed the whole fan control circuit and the volt limiting 317 im looking for a way to control the in a different way i think the best and simplest way is in the following diagram although i dont have a bd139 i do have a great big igbt so im going to try than instead report back at next version
glinjik:
hi so my power pupply parts woes this morning got a knock at the door and a friend rought me this sack to see if i needed anything when i opened it woww its like early christmas maybe il find a fixed 12v volt regulator an awfull lot of transistors and big caps looks like computer power supplies or industrial power supplies, its nice to have friends of course im keeping the lot :-DD
glinjik:
after my windfall of components i finally finished the power supply its stable and functions well ive added heat sinks where i can tomorow i will put it in its case tomorow and do a few pics of the final product of course i will mod it at some point and add a amp meter im looking for a 0-5 a meter for now it will do hares the final scheme i know not perfect but im only a buiginer so thats my excuse merry christmas to you all in the wesern world here its not chrstmas till 6 jan but new year is the same
george.b:
Something's missing from your MOSFET's drain, no? :P
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