LM317 Power Supply questions?

[Guest]

A couple questions if I may...

I'm just starting to get into electronics and this will be my first project. I was hoping someone could lead me in the right direction. I'm working on a similar project which can be found at

www.uoguelph.ca/~atoon/circ/vps.htm

1) I have a 10,000uF cap on hand that I would like to use to give me good, low-ripple properties. With this (if I can use it) should I use a 6A, 8A or 10A bridge rectifier. Do I need to change any of the resistance values or for that matter and of the circuit? I plan on going with a 3W, 1.8K R1 due to predicted heat issues and for more reliability.

2) The bypass transistor looks interesting to me (saw this in the LM317 PSU post in the Projects Q/A forum). What exactly does this accomplish? Is it worth while putting it in and if so how would I connect it in the circuit?

3) I have a 24V ---> 2A centre tapped transformer I plan on using. To be honest I plan on working on circuits below the 21V mark so I'm not to concerned about the smaller voltage at the output. Why does everyone want a 24VDC and higher output voltage? How do I figure out my theoretical output (both V and A) using the above transformer?

4) I plan on making an additional circuit with a smaller transformer in paralell at the 120VAC input. This will be used to power a small muffin fan to blow across the LM317 heatsink and transistor (if I go this way).Hopefully this helps disipate the heat generated at the IC.

5) Where the 220 ohm resistor is, he talks of using a 240 ohm resistor. Which is better?

6) I plan on adding the two diodes to the output of the IC to drop the voltage down to 0V, if needed. (I see this being useful when driving a motor or if you have a circuit that needs a 0 reference).

If anyone has any upgrades or suggestions I'd love to hear them.

Thanks for all your help in advance.

Jay

[surajbarkale]

the posted link is not accessible can anybody else access it?

[Dazza]

Forbidden

You don't have permission to access /~atoon/circ/vps.htm on this server.


This is all I get.

[Guest]

Just went there. Try this:

http://www.uoguelph.ca/~antoon/circ/vps.htm

[darrins]

bitsdoo,

I actually built this power supply and use it all the time.

You shouldn't have to change too much. The most expensive parts are probably the transformer, the volt meter, and the box. You could probably use almost anything for the box, but if it is metal or has a metal bottom, make sure you ground it.

Some of the resistors are just to limit the current going a) the led and b) the volt meter. You should be able to calculate the resistance you need for both. You need the pot on the voltmeter for calibration.

Most likely you don't need a fan for the LM317 if you have a good heatsink and drill some holes in your box.

If you have an old power strip, you can recycle the cord and the switch from it. Don't forget to use a fuse.

With regard to your first question, its a good rule-of-thumb to always use components that are rated HIGHER than what you'll actually need.

This was my first project too.

I'll give you one more piece of advice. Make sure you give yourself some slack when it comes to the wiring, especially those parts that will be attached to the box. It makes putting it all together a lilttle easier. :)

If you decide to use the voltmeter, they usually have the cutout pattern on the back of the package. Don't throw it away. It will help you cut out the proper size opening on the box. I used a Dremel tool to do this.

Good luck.

Darrin

[ante]

Jay,

The data sheet for the LM317 has info on the 220/240R issue and even the bypass transistor circuit. Tony Van Roon:s page is also valuable info. If you need to go down to zero volts I would not recommend using diodes. It

[steven]

:) i hope this comes in handy

[steven]

:)