Need help with component selection in a circuit.

[igidy]

Please view the attached circuit diagram. It is from a project I worked on several years ago and I have forgotten most everything about it since then (plus I was never really good with circuit design). I am working on a timing circuit whereby I control the pulse of an electromagnet with the use of an IR emitter/detector and a potentiometer. What I need to know is what specific components (PN & spec?)I need for my specific circuit for the following components: power transistor and D3.

Also, this is a really beginner question but... what voltage capacitors would be required for this particular circuit.

I know these are very basic questions but I had lots of help when designing this circuit originally and have fallen far out of contact with those that have helped me. Any help is appreciated. The following (3) links are the circuit diagram and (2) photos I found of the actual circuit.

http://i276.photobucket.com/albums/kk19/Igidy/timing.jpg

http://i276.photobucket.com/albums/kk19/Igidy/IMG_1152.jpg

http://i276.photobucket.com/albums/kk19/Igidy/IMG_1150.jpg

Thanks in advance for any help.

 

[Skogsgurra]

It is next to impossible to say if we do not know the resistance of the coil or what current it needs.

If optimum cost or performance isn't an issue, you can use any low voltage medium power NPN transistor.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[igidy]

the resistance of the coil will be 4 ohms with 3 amps. a higher performance power transistor would mean better current supply to the coil?

 

[Skogsgurra]

Select a bipolar transistor with Uce 30 - 50 V, Ic 5 -10 A and beta (hfe) better than around 100. No need to optimize. And those numbers are on the safe side.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[zzzjim]

Testing un-known remains like these I have seen the odd Darlington pair in a single package , if switching is not too fast , but plenty of gain is wanted !