Suggestions for Variable Linear DC Power Supply

Thread Starter

wraujr

Joined Jun 28, 2022
40
Looking for benchtop supply, variable LINEAR (not switching) dc power supply.
BUT, want to keep under $100, so suspect that will be single output.
Digital display/settings.
Do NOT need remote programming/control.
Want new, not used.
What have others bought and liked?
 

sghioto

Joined Dec 31, 2017
3,409
Been happy with my Zeny model 305D I bought on Amazon 6 years ago. No longer available but look for similar models like this on Amazon KORAD KD3005, 85.00. Rated 30 volts at 5 amps max.
1662505020442.png
 
Last edited:

Thread Starter

wraujr

Joined Jun 28, 2022
40
Yes, been looking at that one as its Linear and there are some teardowns on youtube showing generally good construction.
 

Thread Starter

wraujr

Joined Jun 28, 2022
40
Where I get confused, is I understand the diff between a linear supply and a switching supply and that a switcher might have more hi-freq noise in output. But then I saw there are switchers that have a linear output stage. How can you tell from Amazon listing what to get?
 

dl324

Joined Mar 30, 2015
15,113
switcher might have more hi-freq noise in output
Why does this concern you? High frequency noise isn't that difficult to filter. If you want lower noise, you can use a linear regulator on the switcher's output.

I used a power supply (linear) in a Heathkit ET-3100 that had 150mV of ripple that I didn't notice until I designed a analog circuit where the output swung close to the power rail and it didn't work correctly. But for 5V digital logic, it never caused any problems.
 

DickCappels

Joined Aug 21, 2008
9,317
It is far better to not generate noise in the first place than to make the noise and then filter it out. For most things I avoid switching supplies if possible.

Since the late 1970's I have used bench supplies made of an LM317 and an LM337, mainly because I rarely need much current. The regulators are well designed and nearly indestructible, and quiet enough for most work.
 

dl324

Joined Mar 30, 2015
15,113
I've been using this power supply for all of my breadboards, including rail-rail opamp circuits where inputs/outputs went to the rails, for a couple years now. Output noise/ripple has not been a problem.
1662648006557.png
The only thing I don't like about it is the order of the outputs. Earth ground being in the center, with no way to short to ground internally, makes all of my dual banana plug test leads useless. Back in the day, it would be on the outside near the ground terminal with a convenient shorting bar to put on the 2-way banana jacks to connect them.

One of these days, I'm going to open it up and see if I can change them to something that makes more sense. Like plus, minus, earth...

I would have like the jacks to be 2-way too, but it seems like none of the newer ones use them...
 

k1ng 1337

Joined Sep 11, 2020
683
It is far better to not generate noise in the first place than to make the noise and then filter it out. For most things I avoid switching supplies if possible.

Since the late 1970's I have used bench supplies made of an LM317 and an LM337, mainly because I rarely need much current. The regulators are well designed and nearly indestructible, and quiet enough for most work.
Do you have a schematic for a CC/CV LM317 power supply? There are some floating on the internet that look interesting, easy and cheap to build.
 

DickCappels

Joined Aug 21, 2008
9,317
As @atferrari indicated, I only used the examples in the datasheets, but used a full wave bridge and center-tapped transformer secondary to get positive and negative unregulated supplies to feed the regulators. I also had resistor-LED indicators for the unregulated input and each output so at a glance I could get an idea of the output voltage. With DVMs on the workbench I did not have a need for front panel voltmeters. I think that the resistor from the output to the adj terminal on the LM337 should be 120 ohms for better stability, so you should cut that adjustable resistor P2 in half. Revers diodes between the outputs and inputs help protect the pass transistors.

The circuit below is pretty close to what I made both times, not the differences mentioned above. Fuse the transformer primary and use a grounded AC plug with the option of connecting the GND connection to earth ground for safety. Oh yeah, and use metal boxes for fire safety.
1662666694270.png
Source: https://www.twovolt.com/power-supply/1-2v-to-37v-adjustable-dual-power-supply-using-lm317-lm337-3/

You can add an adjustable current limit by current limiting the inputs to the regulators by using the constant current source circuits recommended in the National Semiconductor (and later Texas Instruments) datasheets. I do not need them since the chips' internal current limit is adequate for my needs.
 
Top