Linear power supply for ham radio! - Page 1
Forum section: electronics / projects

author: Bortmoun
author_rank: Newbie
timestamp: September 19, 2025, 12:59:41 am
content: Hi!I am currently designing a linear bench power supply to use alongside my TS-2000 ham radio. Was using a general pourpose SMPS but it's too noisy.So, I have already set some points and ideas. It's important to mention that I do NOT live in a first world country (so no fancy chips, op amps, LDO and alien technology), and that I will use what I have at hand in my workshop, so no need to buy some parts. Also buying already assembled PS is not an option, as there is NONE national ham industry, NONE, zero. Cannot import too without spending a kidney worth of money.My rig sinks at most 21A at full Tx power, at 13,8V nominal. I am planning the PS to have a headroom so it can operate between design boundaries. The output will be 13,8V and 25A max.Design topics below:1) For that I have already choosen a custom made toroidal transformer, 50A sencondary with something figuring around 12~14VAC (power section, 600~700 VA). With it I will use a smaller transformer, for logic and to set the reference voltage (see below), something around 1~2A, 15VAC . Of course, I will join both grounds after rectification and filtering.2) Speaking about those, I will use a capacitor bank built with 10x 4700uF, 50V caps, of good quality. I also added in my designs an inrush limiting resistor on the transformer secondary winding (82R 20W). There is no need to charge the bank fast. I do not care if I have to wait seconds or even a couple of minutes for the voltage to settle. Added discharging resistor too. By my calculations it will take less than 20 seconds to charge.3) The bridge rectifier will be composed of discrete diodes on a big active cooled heatsink; they were choosen having in mind the peak inrush current if there was none inrush limit mitigation. By my calculations, something capable of 70A continuous will be more than enough.4) I have also added protection against core magnetization inrush current, as the main transformer is not that small, in the primary. Both limitations (secondary and primary) will be removed from the circuitry by means of relay operation (hundreds of miliseconds in the primary, 20 seconds at the secondary).5) There is also another relay between the capacitor bank output and the regulation block. Added just because why not...With that in mind I think I have covered most os the aspects of transformer, bridge and capacitor bank.6) The regulation section will be composed of a op-amp amplifying the reference voltage of a LM336-5V0 to the desired level. It will have to take in consideration the emitter-follower topology voltage drops. This section will be feed up by the second transformer, so I can have plenty headroom to account for a not rail-to-rail op-amps etc and so I don't waste too much energy as heat. Could use a TL-431, too...7) As mentioned, the regulation of the crude capacitor bank voltage will be done through an emitter-follower topology, with 10x 2N3055 (or similar BJTs) that I have stocked. As the op amp cannot output the necessary base current to drive these transistors, another BJT will be used, maybe a darlington. By my calculations, each power BJT would have to handle something around 10-15W dissipation (2,5A each, 3~5V drop), accordingly with the load and the voltage in the main transformer secondary. Will add 0,1R balancing power resistors to the emitters too. I do not have means of getting myself MOSFETs, and I already own the BJTs, so I am saving money here.8 ) Overvoltage, overcurrent, undervoltage etc protections will be handled by an Arduino, also fed by the second transformer after correcting the voltage level. The relays operation will also be handled by the MCU.9) Finally, will add two analogic panel meters, for voltage and current measurements.I DO KNOW that I will need a big heatsink to cool the BJTs. For that I will use a thick aluminun heatsink with almost 30 cm lenght by 10 cm wide, active cooled. Take note that 80% of the time I Tx with at most 20W, so I think that the setup will be running cool most of the time. There is no need for high efficiency here.Would like some insights about this project, what I could design better.Thank you!

author: moffy
author_rank: Super Contributor
timestamp: September 19, 2025, 01:24:41 am
content: A simple schematic would be helpfull, easier to interpret rather than words, should help you also. With such a linear supply heatsinking will be as important as the design.

author: DLJ
author_rank: Contributor
timestamp: September 19, 2025, 01:39:19 am
content: I use a Farnell B30/20 to power my radios. It is an OLD school linear psu. You might like to look at the manual to see how they did it back in the day.Good luck.

author: floobydust
author_rank: Super Contributor
timestamp: September 19, 2025, 01:58:55 am
content: One approach is using a battery to supply the high TX currents. I've also seen this in big car stereo displays, a car battery there so they can use a smaller PSU to recharge it.I think your design is on the right track. It's just that linear at this power level has so much heat to dissipate. Very expensive, big, heavy.Maybe look at some existing schematics,Pyramidor theAltronand there is cheapolaSamlex.this is vanillaPS-52KschematicMost are cookie-cutter uA723 designs, 8-9 pass transistors, weight 50+lbs.I'd recommend using a triple-emitter follower. You probably need 4-wire (sense wires) at 50A. not really an SCR crowbar, just pull power to the transformer maybe, if a pass transistor shorts.SMPS can be made to work... in a decent metal enclosure and with extra/double EMI filters.Newer designs from Pyramid have gone this way.

author: CaptainBucko
author_rank: Regular Contributor
timestamp: September 19, 2025, 03:10:13 am
content: I've done something very similar, albeit a bit bigger as it is a 50amp continuous 13v8 supply.In summary, my supply uses:- Massive EI core transformer (probably from old welder), would probably be rated to 100Amps at 35v but only using 50A- 75000uF 75v electros for smoothing- Soft start ramp up on primary switched with relay- Separate supply/transformer running control board and Atmel MCU for house keeping- Negative rail regulated using LM337 with 6 x 2n3771 pass transistors (common collector) - this has significant benefits over a common emitter positive rail regulation buts take a little time to get your head around (ie: regulating the negative rail with all collectors of pass devices tied to GND but it works, and works really well except you rarely see people use the design). You can learn more here:https://ludens.cl/Electron/Ps20/Ps20.html- 4 x FET series switch controlling output enable- Discrete stud diode bridge rectifier- Amtel MCU controls soft start, monitors electro voltage, output voltage, fet switch, temperature & fans, drives discrete LED display via SPI bus and RS-232 diagnostics- Analog V and I meters- Home made (Ink Jet printer artwork->etched) PCBs mixture of through hole and surface mountIt has run continuously since 2001 with occasional offline periods. Happy to share more info if you want.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 19, 2025, 05:37:17 am
content: Quote from: CaptainBucko on September 19, 2025, 03:10:13 amYes, if you are using exposed metal can transistors, eliminating the insulator both helps thermal resistance and reduces the risk of bare wires hitting the case.

author: jfet
author_rank: Contributor
timestamp: September 19, 2025, 07:00:20 am
content: https://www.repeater-builder.com/astron/pdf/50a-service-manual.pdfAstron Linear Power Supply 37A RMS and 50A Peak at 13.8Vandhttps://bama.edebris.com/download/astron/all/astron_all_v6.pdfschematics to a lot of Astron power supplies

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 19, 2025, 08:51:50 am
content: Quote from: Bortmoun on September 19, 2025, 12:59:41 amThese days, you might consider MOSFET drivers for lower drop bridges. These parts turn on the mosfets when the diodes would be conducting, to give much lower drops.You can get MOSFET-Bridge drivers that manage 4 MOSFETS, or you may find 4 x ideal diode controllers are cheaper and easier to apply.Look at LM74680 etc

author: CaptainBucko
author_rank: Regular Contributor
timestamp: September 19, 2025, 09:45:50 am
content: Quote from: PCB.Wiz on September 19, 2025, 05:37:17 amAnd the largest mechanical component of the design, the heatsink, is at GND potential.

author: mtwieg
author_rank: Frequent Contributor
timestamp: September 19, 2025, 12:00:11 pm
content: If the only issue with the SMPS is that it's "noisy," then it might be a lot easier to add filters or shielding to tame the noise than invent a completely new power supply. Could you share the model number?

author: johnboxall
author_rank: Unknown
timestamp: September 19, 2025, 12:13:25 pm
content: Google search for "VK Powermaster mark II".

author: Bortmoun
author_rank: Newbie
timestamp: September 19, 2025, 02:07:16 pm
content: Quote from: moffy on September 19, 2025, 01:24:41 amTrue! Today I gonna sit down and makee one, then post here!Quote from: floobydust on September 19, 2025, 01:58:55 amYep, I am already using the setup PSU+battery! The thing is my battery is only 60Ah, so it drops fastThis project is just conceptual at this point, as I am also considering shielding the SMPS and choking it's output with some ferrites, which would be much, much cheaper heheheQuote from: CaptainBucko on September 19, 2025, 03:10:13 amI am considdering this aproach too, about using common collector... It's a very nice idea. I was going to use a enclosed wind tunnel to cool the heatsink, so it wouldn't be exposed to outside surfaces, ergo I wouldn't need to isolate each BJT from the heatsink, as the collectors would be on the same voltage level, anways...Today afternoon I will post some schematics here! Thank you guys for the feedback!

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: September 19, 2025, 02:14:46 pm
content: Maybe I am confused. What is the voltage output of your big transformer ? Did you say 14 V?

author: Terry Bites
author_rank: Super Contributor
timestamp: September 19, 2025, 03:03:16 pm
content: https://sound-au.com/project77.htmAll easy to find cheap parts.To protect your rig, the crowbar is a must.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 20, 2025, 01:04:54 am
content: How about use a mixed design that has a buck converter in parallel with a small linear regulator? Set it so that at low current, the linear takes all the load and the buck converter stays off. The buck converter only starts operating when the linear regulator is not able to supply enough current. Check how much current the radio uses in receive and the linear regulator should current limit 20-50% higher than that.

author: xavier60
author_rank: Super Contributor
timestamp: September 20, 2025, 02:18:17 am
content: Quote from: CaptainBucko on September 19, 2025, 03:10:13 amWow! 47 years ago, I used near to exactly the same design to build a 3A variable bench PSU and then a 13.8V, 10A version for powering a 27MHz CB amplifier. One big advantage was not needing mica washers for the 2n3055's.At the time, I knew nothing about frequency compensation, but both were stable.The 10A PSU initially had some voltage overshoot while unloading which I cured by placing some low value resistor across b-E of the 2n3055's.

author: CaptainBucko
author_rank: Regular Contributor
timestamp: September 20, 2025, 02:42:51 am
content: Quote from: mtwieg on September 19, 2025, 12:00:11 pmHAM radio involves receiving weak signals. Trying to remove SMPS noise is a nightmare, especially below 50MHz. Its even worse because some SMPS vary in frequency with load, and so do their harmonics. It's a much better idea to use a quiet linear power supply, than try to tame a SMPS.

author: CaptainBucko
author_rank: Regular Contributor
timestamp: September 20, 2025, 02:45:51 am
content: Quote from: Bortmoun on September 19, 2025, 02:07:16 pmThat was my approach too, with fans that are temperature controlled, so they only operate when needed. You will still need to insulate the bridge rectifier diodes, and/or heatsink if they are stud mount type.

author: xavier60
author_rank: Super Contributor
timestamp: September 20, 2025, 03:24:19 am
content: A possible solution would be to have the SMPS operate only during transmit, and have a small linear PSU to power the receiver.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 20, 2025, 04:07:36 am
content: Quote from: xavier60 on September 20, 2025, 03:24:19 amThat's exactly what I proposed. An easy way to make that work is by setting the linear regulator to a slightly higher voltage.

author: xavier60
author_rank: Super Contributor
timestamp: September 20, 2025, 04:58:56 am
content: Quote from: NiHaoMike on September 20, 2025, 04:07:36 amThe idea might work with the existing SMPS.

author: iMo
author_rank: Super Contributor
timestamp: September 20, 2025, 07:23:03 am
content: A hint: do not over-engineer the supply, make it as simple as possible.. I saw such a PSU in our ham-club, made in late 70ties perhaps, 4 pass transistors on a similar sized heat-sink as you are planning, no fan, simple electronics inside (no need for fancy chips there, like 3-4 transistors and a zener will do). It is not a "laboratory power supply", you need 13.8V +/-15%, that's all..I would put there the crowbar protection as mentioned above - you would need a beefy thyristor/SCR there, also it needs some filtering at the SCR's gate such it not fires when picking up some RF when TXing (could be tricky, btw.), but fast enough to protect the 13.8V output when the pass transistors short itself.Also avoid the fake 2N3055s..PS: the crowbar - you have to experiment with the zener there - you need a zener which will fire up the SCR at around 16V at the output (it depends on the zener type/current and SCR's gate threshold). You should finetune it outside the PSU first..The pass transistors - you may add more transistors there in parallel (provided the driver there - ie. the BD135 in the example - can source enough current, thus with more transistors you may use a beefier driver)..

author: mtwieg
author_rank: Frequent Contributor
timestamp: September 20, 2025, 01:42:41 pm
content: Quote from: CaptainBucko on September 20, 2025, 02:42:51 amThe relative effort of switchmode vs linear depends greatly on the power level (especially current). At one amp, a linear supply is usually the obvious choice. At one hundred amps, not so much. If space/weight is limited, linear is sometimes just not an option, period. I've implemented switchmode supplies for use inside the bores of MRI scanners, where receiver sensitivity is typically on the order of -120dBm. In my experience adding shielding to a switchmode supply is far preferable to adding water cooling to a linear supply.Quote from: NiHaoMike on September 20, 2025, 04:07:36 amGating the transmit might work depending on the design of the power amplifier. Unfortunately most RFPA designs for HAM use probably won't respond well to gating. They typically are designed to run hot, and require seconds or more for their bias to stabilize due to thermal effects. This likely isn't an option for the OP, unless they are willing to hack their TS-2000.Another option often used in extremely noise-sensitive applications is rechargeable batteries directly supplying circuits. Again this depends on the system not being in continuous use; every now and then you need to top the batteries off. You would do this when the receivers are not in use. This is the absolute best option, as batteries have lower noise than even the fanciest linear regulators. Only disadvantage is that voltage regulation isn't amazing, but usually this is preferable to higher frequency noise.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 20, 2025, 05:28:55 pm
content: The manual for the TS-2000 lists 2.6A during receive, quite easy to do with a linear.

author: kite31
author_rank: Regular Contributor
timestamp: September 21, 2025, 12:02:04 am
content: Bortmoun, you mentioned that you currently use a 60A battery in parallel with a PSU. Your transmit max power is 21A and receive max 2.6A.What is your effective duty cycle for transmit/receive? What is the downtime (not in use)?What does your existing PSU supply?Adding another 60AH battery, or even assembling 200AH, may be a suitable solution depending on your average power demand and current or low cost alternative PSU.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 21, 2025, 01:48:28 am
content: Such a large battery would be considerably more expensive than a buck converter.

author: kite31
author_rank: Regular Contributor
timestamp: September 21, 2025, 02:22:45 am
content: True, but also least complexity. I like your buck converter solution as well, but it involves more than almost literally dropping in a single item.Edit to add: One of my interests in my post before this was to help to clarify the question or problem. At the moment it has a little of the XY characteristic where the problem to answer is not fully defined while solutions are pursued.It may be that a ripper of a linear supply is the optimal answer, but we do not fully know what it is answering.

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 21, 2025, 02:38:05 pm
content: Perhaps the easier solution would be to have the switching supply charge the battery during transmit and while the radio is not in use, only switching it off during receive?

author: iMo
author_rank: Super Contributor
timestamp: September 23, 2025, 07:57:30 am
content: .. out of curiosity - a beefier version of my above simple PSU made of discrete transistors - stability at 2A and 25A..Example only, may need some finetuning..PS: the resistors in series with C1 and C2 are their parasitic ESRs..

author: iMo
author_rank: Super Contributor
timestamp: September 23, 2025, 10:19:37 am
content: .. and an LM723 based simple PSU - a better design if you may get the LM723 handy..Example only..

author: MariuszD
author_rank: Regular Contributor
timestamp: September 23, 2025, 10:39:05 am
content: @iMo I was curious to see what the loop gain looks like for such a power supply using discrete transistors. As expected, the gain for DC is quite low.Can you attach the ASC file?

author: iMo
author_rank: Super Contributor
timestamp: September 23, 2025, 11:15:15 am
content: Here is the .asc of my simple discrete transistor PSU above (with the FRA)..Quote from: MariuszD on September 23, 2025, 10:39:05 am

author: MariuszD
author_rank: Regular Contributor
timestamp: September 23, 2025, 12:47:32 pm
content: It won't make a difference to the OP or the transmitting equipment, but I was wondering if I know a simple way to improve the gain.This is my attempt:

author: CaptainBucko
author_rank: Regular Contributor
timestamp: September 23, 2025, 10:56:15 pm
content: Quote from: iMo on September 23, 2025, 10:19:37 amGreat work on the simulations! What's the minimum drop out voltage of your two (discrete & LM723) high side regulator designs?The negative rail regulated LM741 from ludens is claimed to have only 0.6v drop out. I built the ludens design, but modified to use an LM337. I don't see this as any more or less complicated than a high side design, other than getting your head around the regulation of the negative rail to achieve 13v8 as opposed to the positive.Would be interesting to see a simulation for this topology to compare.

author: xavier60
author_rank: Super Contributor
timestamp: September 23, 2025, 11:04:54 pm
content: Quote from: CaptainBucko on September 23, 2025, 10:56:15 pmThe ludens design is actually true LDO. The drop-out voltage has nothing to do with junction forward drop, just C-E saturation voltage.

author: floobydust
author_rank: Super Contributor
timestamp: September 24, 2025, 03:39:31 am
content: I used a TL431 and triple EF for low parts count. Just need to add current limiting. This is on a Samlex dumpster rescue.A bit more schematicshttps://www.eevblog.com/forum/repair/jaycar-mp3098-20amp-linear-13-8v-she-dead

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: September 24, 2025, 12:49:21 pm
content: I know that the OP wants a 13.8 Volt PS. But here is a link to the adjustable Lab PS that I rebuilt using three OP Amps. It should work just fine at 13.8. It has voltage and current adjustments. I built this and it works. My criticism is that it wanders a few milli volts and the Zener is the most sensitive to temp changes.https://www.eevblog.com/forum/repair/lambda-linear-lab-supply-schematics-lp-414a-fm/msg5881048/#msg5881048

author: coromonadalix
author_rank: Super Contributor
timestamp: September 24, 2025, 03:42:20 pm
content: Quote from: Wallace Gasiewicz on September 24, 2025, 12:49:21 pmbut you miss any current overload, limiting or short protection ... take the schematics from an astron 50 amps psua 723 design can be very good, not perfect but good enough for ham radio, we see tons of theses designs in Pyramid, Astron and othersOP will never get a perfect solution, with some Ham rig you may need lots of juice when transmitting ...there are some smps psu's for ham rigs, can't recall the brand, their switching frequencies are calculated to produce less harmonics than normal psu's100khz 200khz i've seen 300khz switching on one i had, very small and had 20 amps of current at 12vdc, never heard anything bad in the riggo with linear ... sure you loose in thermals and can get heavy, use a toroïdal x-former, will be already better than a laminated one

author: floobydust
author_rank: Super Contributor
timestamp: September 24, 2025, 07:17:49 pm
content: It would help to know what is easy/hard to get in OP's Brazil. I think copper and iron are plentiful but not sure if the value-adds are done there (making ore into wire, laminations etc.) to make a big transformer not cost a lot. Compared with NA or Europe where they are very expensive now. They get OEM'd in china but shipping seems to make them expensive.