Electronics > Beginners

lab power supply

<< < (13/15) > >>

glinjik:
thank you for your reply please explain why d6 prevents current flowing and if it is wht am i getting 3 amps (when i crank it up) on the emmiters of 2n3055? here is the original drawing well i doubt its original but its where i got it

not1xor1:

--- 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

--- End quote ---

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.

--- End quote ---

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).


--- End quote ---

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).

not1xor1:

--- Quote from: MarkF on December 21, 2019, 02:57:01 am ---
--- Quote from: glinjik on December 20, 2019, 04:33:15 pm ---Well here is my latest incarnation fo your enjoyment i know its a bit odd adding a 317 just to regulate voltage to a fan circuit but it will work i only using what i have here so this is my solution now to build the last part circuit board is getting crowded bu here goes...

--- End quote ---

You have diode D6 in the wrong place.  No current will flow to the 2N3055 transistors where it is.

(Attachment Link)

--- End quote ---

BTW if the diode (in glinjik schematic) were correctly polarized it would not withstand currents greater than 1A (and would be useless).

glinjik:
im thinking that diode is not serving any purpose at all i might remove it and check results but the volt control and currnt control work very smoothly with no problems even shorting the output across a 15w resistor getts good results although i only tried that for a few seconds to see what amperage i could achive the only problem is getting 12 volts to the fan circuit and keeping the current low without using a transistor other than a lm317 or a volt regulator at the moment the lm317 and bd140 are getting too hot thinking of putting in a secondary transformer to achive the 12v low current power 4 is the latest as of now

MarkF:

--- Quote from: glinjik on December 21, 2019, 05:34:48 am ---thank you for your reply please explain why d6 prevents current flowing and if it is wht am i getting 3 amps (when i crank it up) on the emmiters of 2n3055? here is the original drawing well i doubt its original but its where i got it

--- End quote ---

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.


Your last circuit -- WRONG

How does the current go backward through the diode, D6, to the 2N3055?
NO collector current!




Your first circuit (Reply #7) -- RIGHT

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod