Adjustable Dual Polarity Power Supply

Hi Flemming,

There are schematics (and board CAD files as soon as I upload them - let me know if you need them anytime soon) for a dual-rail supply here:

Building a Linear Power Supply Module

It is fixed voltage, but can be made adjustable by swapping R2 and R6 out for variable resistors (and put a small resistance in series with them too).

If you need some help figuring out the values, let me know.

It is only a 200mA dual rail supply, or optionally 3-rail.

I created it for future op-amp and headphone amplifier projects, so it was intended to be a fixed rail supply.

If you wanted something with through-hole components, there is nothing wrong with a LM317 supply by the way, it will still serve you well.

I have an old homemade LM317 supply myself (I used a couple of LM317, for dual output), and I still use it.

Photo here next to a paperback book for size comparison. I didn't do a great assembly job.

Also if you search for jw0752 content he has blogged about some power supplies he has constructed, so you can see some ideas for how to build them.

Maybe you can check out

Hiland DIY USB Boost Single Turn Dual Power Linear Regulator Multiple Output Kit

available on many sites...although it is more of a DC-DC converter.

There's loads you could do to make it more interesting than just an LM317/LM337 based supply depending on how flexible you want your supply to be.

For example, if you want to increase the efficiency you could create a switching regulators for the positive and negative rails and then use the LM317/LM337 as a post regulator smooth out the output by rejecting the switching noise.

If your output will be a symmetric voltage then you could experiment with something like a flybuck topology to generate the +ve and -ve rails from a coupled inductor placed in the usual output inductor location of a standard buck converter. Again use the lineatr regs as a post regulator to smooth the output.

There's so many choices you could make which would make a fun power supply build. What are your required specs for this?

Best Regards,

Rachael

Also check out all the power supply build related projects that jw0752 has blogged about, there are lots of really cool power supply projects in his blogs!

Hi Flemming,

What are your current resources. Do you have a source of parts. To build a dual bench supply you will need a transformer or two, some way to rectify the AC from the transformers secondary, a filter capacitor to smooth out the rectified current and then you will need a circuit to control the voltage and current to your outputs. Finally  you will need the extra touches such as  a case, Volt and Amp meters, power switch, power indicator, and output jacks. Building a power supply from parts and available kits and circuits can be fun and rewarding. Start putting your concept together on paper and then begin to collect parts and solve problems until you have built what you want.

John

Thank you for the reply.

I am ahead of you

I got a 2*15 V, 0.5 Amp. ring transformer, 1 amp. rectifier bridges and large capacitors ( might be too big ), the case would be part of a 3 unit high 19" rack case from Shcroff

so must of the exterior is sorted

Volt and amp. meters is necessary, not sure what i use, depend on the space on the front panel.

The concept is just about planned, even a multi funktion power indicator.

I have been looking around at other homemade power supply, one thing is a puzzle to me, why do you all use small knobs for your adjustment, it's much easier to control with a BIG knob.

The most important part is missing -the regulator circuit

Thank you

Could be intersting

Hi Flemming,

When I want better control I use a 10 turn pot. Most of the time I use smaller controls as that is what fits on my panels and looks good. If you haven't already looked at it here is a link to the last dual bench supply that I built. I used salvage parts and case and my net cost for this unit was about $35. US.

https://www.element14.com/community/people/jw0752/blog/2017/02/11/oh-no-not-another-power-supply

I have built one more dual supply since this one and for a cool modification I used a MOSFET controller and MOSFETs to rectify the AC instead of diodes. This gave me about 2 more volts output and cut the energy usually lost in the diode drops.

https://www.element14.com/community/people/jw0752/blog/2017/03/03/incorporating-the-lt-4320-ideal-bridge-in-the-linear-bench-supply

Take a look at the power supply board that I am using. It comes as a kit for about $7.00 from Banggood. You have to provide a proper heat sink for the output transistor but when properly heat sunk it will handle 3 Amps. I also has current limiting and zero voltage adjustment. As I mentioned I will often use a ten turn pot on the voltage control. I usually leave the current control stock as this isn't as critical.

John

Hi John

A very fine "box" you put together there. Looking good on the inside too.

I do agree with your thoughts on that -why reinvent the wheel again.

I might have used a different layout on the front, placing the units on top of each other instead of beside each other, that would have made room for bigger knobs

I found those boards too and along with some other interesting kits, still waiting for delivery.

Flemming

Hi Flemming,

I really look forward to seeing your power supply. It is always interesting to see the creativity and innovation that each engineer brings to these builds.

John