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lab power supply

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not1xor1:

--- 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.

glinjik:
thankyou for you reply but could you explain your point? ie constructivly point out problems errors 
--- 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 ---
the cicuit is a well know one its all ove the intenet im trying to adapt it to suit me i keep changing things and all is working so far all the parts are recovered for old stuff except bd140, 2n3055, and bd140 oh and the volt monitor, my next problem is restricting the voltage to fan contol i put in a zener 12v but its getting vey hot is the wattage to low? or is there a better way to achive 12v it needs to come from the rectifier so it wont disrupt any other part of the circuit and when the circuit is switched off the fan will keep running untill components are cool that is indicated by the led and the i can switch off the mains input

MarkF:

--- 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).

george.b:

--- Quote from: glinjik on December 20, 2019, 10:28:12 am ---my next problem is restricting the voltage to fan contol i put in a zener 12v but its getting vey hot is the wattage to low?

--- End quote ---

Why don't you check your Zener diode's datasheet? Then you'll have your answer.


--- Quote ---or is there a better way to achive 12v

--- End quote ---

Yes. Use a 7812, or use a transistor as a buffer for the Zener.

glinjik:


Why don't you check your Zener diode's datasheet? Then you'll have your answer.

that indeed would be a great idea.....but im using recovered parts and there are no markings on the zener i obviously checked its voltage but thats all i can go on other than its physical size

i like the little circuit but i dont have the parts so what i think is il put in a lm715 circuit with a fixed voltage (i have lm315's

i did move the zener to just restrict the voltage to the fan but its still getting to hot like i can smell it

my problem is i live off the beaten track a bit and getting parts is a lot of trouble so i take apart junk to recover what i can but thank you for your answer all the various opinions are greatly apprieciated the fan control circuit works well no parts over heating apart from the zener the whole circuit can push 3 amps no problems just this little fan control that doing me in |O



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