Dual tracking PSU circuit design or diagram - Page 1
Forum section: electronics / beginners

author: andy1969
author_rank: Newbie
timestamp: August 26, 2023, 06:03:09 am
content: Hi Guys & Gails,I am a hobby electronic newbie and looking to start by getting some bench equipment. I would like to build the normal newbie project of a bench power supply as I would like to concentrate on audio projects so a dual +- supply is a must. The minimum criteria are listed below:-Linear design30-0-30 volt minimumminimum 5amp per railMust be dual-tracking and/or independently adjustableI already have some knowledge of using LM317 and LM337 but the specific area I am having trouble with is integrating the voltage adjust, current adjust and the tracking ability. I already have a salvaged toroidal transformer which is 36-0-36 5amp so LM317 & LM337 are probably not the components of choice due to the voltage input.I have hunted the internet and just can't seem to find a suitable circuit. Does anyone have a circuit diagram of a simple dual-tracking linear PSU that would meet the criteria or point me to an old magazine article that has a suitable design?Thanks in advance

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: August 26, 2023, 07:53:30 am
content: Hi andy1969,in the "good old days" there where LM325 and RC4195 ICs for tracking-PSUs.But limited to +-15 or 18Volts i think.Are you sure you need +-30V 5A?Good luck

author: David Hess
author_rank: Super Contributor
timestamp: August 26, 2023, 08:21:47 am
content: HP/Harrison and Tektronix made such power supplies, albeit at lower voltages and currents, which are fully documented so can be studied. The Tektronix PS503A was +/-20 volts and 1 amp.Just a 30 volt 5 amp variable power supply is not trivial. Power dissipation can be up to 150 watts which will require multiple output devices in series-parallel and attention to thermal design, and 30 volts is just high enough to restrict the selection of operational amplifiers and require high voltage design. (1) The HP/Harrison designs bootstrapped the error amplifiers so could use low voltage operational amplifiers, but this requires floating auxiliary supplies to power the operational amplifiers.The LM317/LM337 may be a useful part of such a design; I would use them as thermally protected drivers for the output transistors. But at least one external control loop will be required for adjustable current limiting.(1) Standard parts operate up to 36 volts, but there are some older 40 and 44 volt operational amplifiers which could be used like the 741, LF355 (low power JFET), LF356 (JFET), LT1001 (OP-07 equivalent), and LT1006/LT1013/LT1014 (324 equivalents).

author: xavier60
author_rank: Super Contributor
timestamp: August 27, 2023, 05:41:21 am
content: If its current control loop works properly, this boosted LM317 design could be ganged with the negative LM337 version.Edit: I have a simple way to get the CC REF current across to the other side with Q7.Corrected some mistakes.

author: xavier60
author_rank: Super Contributor
timestamp: August 27, 2023, 11:23:34 am
content: I tested a mockup of the essential parts. CC wouldn't adjust to 0A. 10Ω in series with Q5 fixed that. R8 should be replaced by a constant current sink, an LM317LZ and resistor.The CC loop needed frequency compensation. A 330Ω in series with 100n between B-C of Q3 which I changed to a D45H11 for now.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: August 27, 2023, 10:21:39 pm
content: Quote from: David Hess on August 26, 2023, 08:21:47 amAlso look at the HP 6227B and 6228B.

author: armandine2
author_rank: Frequent Contributor
timestamp: August 29, 2023, 07:09:33 am
content: https://sound-au.com/articles/bench-supply.htmfor some sound advice

author: xavier60
author_rank: Super Contributor
timestamp: August 29, 2023, 08:00:18 am
content: Current and voltage tracking can be done without opamps.Q10 is optional. It reduces the positive rail if the negative rail gets overloaded only.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 29, 2023, 11:59:40 am
content: Off the shelf? Tenma 72-2640?Dont be to hasty to write off smps for precision audio work.Dont listen to old geezers.

author: Grandchuck
author_rank: Super Contributor
timestamp: August 29, 2023, 05:21:55 pm
content: The attached file might be helpful.

author: TimFox
author_rank: Super Contributor
timestamp: August 29, 2023, 09:28:23 pm
content: Quote from: Terry Bites on August 29, 2023, 11:59:40 amI was the old geezer at work who recommended against using smps with low-noise precision analog electronics.I admitted that it was possible to use them, but insisted that engineering time be in the budget to design and verify filtration.

author: David Hess
author_rank: Super Contributor
timestamp: August 29, 2023, 09:56:54 pm
content: The example shown below shows how simple a dual tracking regulator can be.Power supplies like the Tektronix PS503A allow the ratio of the outputs to be set while tracking, so asymmetrical tracking outputs are supported. I think the HP/Harrison power supplies can also do that, but they present a different set of user controls.What should happen when the current is limited on one side? Should the other side continue tracking the voltage on the current limited side? The PS503A has a separate current limit for each side and they are completely independent, and the outputs do not track while one is in current limiting, which works well enough. I am not sure any extra complexity here would be worth it.

author: xavier60
author_rank: Super Contributor
timestamp: August 30, 2023, 07:10:13 am
content: The problem with having a single VR is that if one output is overloaded, the other will increase.I see that some designs just have a dual Pot which would remove a lot of clutter from my experimental design.

author: David Hess
author_rank: Super Contributor
timestamp: August 30, 2023, 02:37:33 pm
content: Quote from: xavier60 on August 30, 2023, 07:10:13 amThat is a problem with the simple example I gave, but more complex designs operate each side independently, or perhaps tie them together so if one side falls, the other side tracks it. The Tektronix PS503A has three pots; two set the output voltages for each side, and a third which when engaged is the tracking control which varies both of the others from zero to full output.The PS503A schematic is shown below. I might use this design, but I would make changes like making the control amplifiers fixed gain so the bandwidth of the control loop does not vary with output voltage.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 30, 2023, 03:13:08 pm
content: You can, in principle, add tracking to any dual supply.Adding 2x Vcm to the feedback reference points will shift the regulation untill Vcm=0The attenuation+gain arrangement is needed to keep the opamp in range.