Bench top power supply

[churchjw]

One of my other hobbies is electrical work so I built a dual negative and positive adjustable power supply. It has some metal working on it (pop rivets, sheet metal, and some stamping) so I decided to post it here. Not a big project but fun to do. Also I think it looks cool, no reason a power supply has to be boring.



Jeff

 

[churchjw]

2 to 17 volts +- at around 2 amps max. Have a 1 amp fuse in it and most stuff I will be doing on it will need in 500mA range. It uses a LM317 for the positive and a LM337 for the negative supply. Both on huge heat sinks with a fan.

Jeff

 

[flatbelter]

Great power supply project.

I don't have anything that fancy, but if you jumper the middle green wire on an old computer power supply (ATX) to any black wire on the main cable bundle it will turn on the unit and delivers +3.3V, +5V, +12V and -12V (IIRC). The amperage it can deliver is pretty good for the price (free from junk computer), it's regulated and well filtered. Perfect for the home hobbyist. I use it to run my LiPo battery charger.

http://pinouts.ru/Power/atxpower_pinout.shtml

 

[yugami]

I bought an old power supply off of ebay years ago and it is one of the most useful purchases I've made (that and the nice soldering station with good heat control).

My old one has analog meters for both voltage and amperage and you can dial the voltage and a 2nd dial sets the current limit so you don't blow things up.

nice job on that one with the + and - setup much more useful for real electronics work (not just the limited stuff I play with)

 

[churchjw]

I have a few of power supplys made out of old computer supplies. They do work great. I would recommend anyone just getting into electronics to build one. I also have 3 heaver duty store bought ones including one I use for plating and electro cleaning



They have the current control as well as voltage. What I didn't have before is the +- option with a common ground and the ability to independently adjust the voltages on each. What would be cool is to have the current adjustment on my new one but that is still just outside my abilities to build and understand. Still a nub with electronics (even more than machining )) Next part of this is to start playing with opamps. A whole new world of stuff to learn. :biggrin:

Jeff

 

[75Plus]

Jeff, adding current limiting is easy. On the + side you will need another LM317 and a 5K pot. The new LM317 is added between the original LM317 and the output. I have a DPDT switch so the current limiting can be switched in and out of the circuit. I haven't used current limiting with a - (neg) supply but I am sure it would work the same.

On the positive side connect pin 2, the output, of the existing 317 to pin 3 of the new 317. Pin 1 of the new 317 is now the output. Connect the pot between pin 1 and 2 of the new 317. Add the switch if desired.

I built a 1.5 to 15 volt 1.5 amp, current limiting, bench supply back in 1987 and have been using it ever since. It is handy for charging a wide range of batteries of different chemistry's. I have the schematic around somewhere. I will dig it out if you are interested.

Joe

 

[churchjw]

Would love to see and pictures of the supply if you get a chance. Thanks. How does adding the second 317 limit the current? Sorry still new at electronics.

Jeff

 

[Rbeckett]

I think the lm317 is the + side and the LM337 is the - side of the voltage. 2amps is right up there near the limit on the Lm317, the 337 can run a little higher. I built an Elenco that has the same circuits as well as a 7805 for 4 amp 5 volts and 2-6.3 v AC taps too. I built this from the wiring diagram and the bill of materials in the assembly manual from the kit. I installed larger rectification diodes and 10K pots instead of 5 so I get nearly 20 volts with almost no ripple. Glad theres another electronics enthusiast around too. I'm still learning but I have Ohms law down cold and the rest is pretty easy so far. Amazing what you can do with a few books and a desire to try something new.
Bob

 

[flatbelter]

Here is a nice explanation of how to set up a constant current source. (and a little of how it works)

http://users.telenet.be/davshomepage/current-source.htm


@ Jeff,
Op amps are great to work with much simpler (I find) than transistor biasing. One thing to keep in mind most op amps have a limited current output so will need a power boost for driving large currents.

Here is an interesting vintage (1967) article on op amps.

http://www.rfcafe.com/references/el...onal-amplifier-aug-1967-electronics-world.htm


If you ever get the chance to take a circuit analysis course, do so. I comes in handy for situations where Ohms law just doesn't quite cut it.

Now if I could just make my own VFD ...

 

[Hawkeye]

The LM317T is actually designed for 1 amp with full heatsink. I believe the LM350 is the + VR good for 3 amps.

I picked up an old supply today at a thrift shop for $20. It works, but the ammeter seems to be dead. It will run up to 23 volts through a 2N3055 transistor. The ammeter is scaled to 3 amps.

BTW, you can get more current out of a 317-style VR by using it to drive a bigger output transistor, providing your supply transformer can source what you want.

Bench supplies are always worth having around, even if you aren't into electronics. I'm reconditioning a sealed lead acid battery by charging it every 24 to 48 hours through one of my supplies.