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Variable power supply circuit

Variable power supply circuit board

I always wanted to build a variable power supply circuit. Every time I build something I have to cobble together something to power it. I’ve got veroboards all over the place with bits of rectifier circuits and regulators with bits of metal bolted to them. Loads of left over transformers and all sorts of bits are lying half used and forgotten. Next project I’ll do the whole thing again make something else temporary,

How to make a variable power supply.

I don’t think I need or can justify the cost of some of the bench power supplies. Why do they cost so much? What do I actually need? Most of the stuff I build needs 12 to 15 volts. The musical projects tend to use that but with positive and negative rails for op amps and stuff. Oh and some projects use 5 volts and now I think about it 9 volts is common as well.

Dual power supply circuit.

I think if I build something that provides a variable output and build two of them in a box to provide dual rails that will do the job, as long as it’s not too expensive.

Variable power supply circuit using LM317.

While looking around at what parts to use to build a variable power supply unit the LM317 variable regulator stood out. As I about to build LM317 circuit on Vero board I stumbled upon this Velleman power supply kit. This looks about perfect for what I was wanting. It’s small and cheap so getting two in a box won’t be too difficult. That will give plenty of space for the heat sinks and a transformer. The boards have a pre-set on them to set the voltage so I plan to just replace it with a front panel mounted variable resistor.

You will need to get heat sinks for the LM317. I’ll be honest with you although I studied electronics at college and polytechnics I never bothered with the working out for the heat sink you need. I just get one that looks “big enough”. It usually works fine and if I ever have a regulator that burns out the heat sink wasn’t big enough.

From all the other power supply projects that I had previously knocked up I took a hefty transformer to power the boards. You can see it in the pictures below.

One of the left over transformers from all the previous "temporary" power supply circuits.

I also decided to use two sets of binding posts to make it easier to connect to projects and both boards were linked together using a 0 volts terminal giving a dual rail supply instead of two separate power supplies. You can see the arrangement in the picture below.

variable power supply circuit terminals

LM317 variable power supply

Whilst building this project I found some cheap panel voltage meters which I thought would be excellent to fit on the front panel to indicate the voltage output.

The panel volt meters that I found on Amazon.

They just display the voltage that it fed into them with no need for a separate voltage supply to them. As yet I have not had time to cut holes in the panel for them but all in all they should complete it nicely to finally give me a variable bench power supply with dual rails, voltage display all in a box and at a very reasonable price from a simple variable power supply circuit.