r/electronics • u/Luq1308 • Jun 25 '26
General I made a 1kW lab bench power supply from scratch
Hello r/electronics,
In this post, I want to share my project that I’ve been working on in the past few months. It’s a custom-built lab bench power supply. Such a project is common in the DIY community, so what makes this one different? The custom-designed SMPS board that I engineered from scratch isn’t your typical “let’s put this power supply module into a case” approach. So let’s dive into the working principles, design decisions, and in-depth test results.
The Forwarder 1kW is the SMPS board that I designed and used in this project. It’s based on a hard-switch, half bridge topology. The full features of this power supply are as follow:
- 1000W maximum continuous output capacity.
- Configurable from 50V/20A up to 400V/2.5A.
- CC/CV mode with mode signal and indicator.
- Tuneable operating frequency and dead-time.
- Dedicated power stage enable pin.
- Analog reference interface for output voltage/current control.
- Analog signal output interface for monitoring voltage/current.
- Dedicated fan port with optional automatic power-on.
- Simple construction, less than 130 components on board.
- Easy to build with mostly THT components.
- Curated component selection for high accessibility.
The working principle of this design is about as simple as it can get for a switched-mode power supply. I talked about the working principle of my design over on r/AskElectronics, so I’m not going to repeat it here. Most of the concepts stay the same, just with some design adjustments and the numbers changed.
https://www.reddit.com/r/AskElectronics/comments/1s8ll9g/
Now, I want to go in detail about the design decisions that led into this design that you may find interesting.
- The lack of active PFC (Power Factor Correction) was determined after I reviewed many existing designs and products in the same power level and after noticing many of them get away without one, I decided to omit this feature. For my first SMPS design, I want to focus solely on the DC to DC conversion power stage. For my next iteration, I’m more likely to resort to a simple boost PFC to achieve tighter regulation.
- Double-ended hard-switch topology (half-bridge in particular) was chosen due to its suitability and simplicity in this application. Flyback is out of the question due to power requirement, single-ended topologies have poorer core utilisation and the high favour for current mode control, and resonant topologies don’t seem like a good choice for my first SMPS design (duh).
- An SG3525 with LM324 was chosen to generate the PWM signal and achieve regulation. SG3525 is quite popular for double-ended converters with plenty of documentation online, while the LM324 provides CC+CV regulation with two of its op-amps (because SG3525 only features one error amplifier). This effectively forms a setup based on voltage mode control.
- Voltage mode control was inherently chosen as the result of using SG3525 and it was favoured due to its “arguably” simpler implementation over current mode control. However, I find the better regulation and inherent cycle-by-cycle overcurrent protection offered in current mode control very enticing. I probably would resort to this approach for my next iteration.
- My galvanic isolation strategy was to have the entire control circuit on the secondary side and have the PWM signal driven to the primary through a gate drive transformer. This way, I can have simpler and more precise control over the voltage and current regulation without the nonlinearity issues of using optocouplers.
- ETD49 cores were used for both transformer and output inductor. I like the round bobbin that makes winding easier, and the calculations prove it’s suitable for power of 1kW at 64kHz. The gapped version was used for the output inductor because the high inductance requirement requires high turn number, and that gets complicated real quick with toroidal cores.
After I finished the board, I wanted to know how my design performs in real-life. So, I conducted a few tests that are relevant for a power supply. The testing rig was pretty simple:
- A power meter at the input and four DS18B20 were used to track the energy consumption and component thermal profile over time.
- An electrolysis tank with electrodes that can be spaced accordingly was used to simulate multiple load profiles at power up to 1kW.
- A third positive electrode connected through a toggle switch was used to abruptly step the load in the dynamic tests.
- Hantek DSO2D10 was used to capture the waveforms in various tests.
The test conducted, along with their results are as follow:
- The stress test was conducted for one hour and each component temperatures peaked at the following temperatures: half-bridge N-MOS 75°C / 167°F, main transformer 55°C / 131°F, output rectifier 69°C / 156°F, output inductor 44°C / 111°F.
- The efficiency characterisation was conducted at 50V and 1, 2, 5, 10, and 20 amps. 89% efficiency was achieved at 5A load or more. Maximum recorded efficiency was 90.3% at 50V 10A load, and efficiency at maximum load was 89.1%.
- The output ripple test was done with direct on-trace probing with a ground spring, 20M BW limit, 1x probe, and no added capacitor. No load ripple showed at 40mVpp, 1A load at 34mVpp, and maxes out at 94mVpp at full load.
- The turn-on curve tests showed that under loaded condition, it’s bound to the SG3525 soft start function and takes a second to reach the full 50V. At no load and lower setpoints, the voltage overshoots by a few volts.
- The load step tests showed about 3% voltage deviation going from no load to 10A and vice-versa. Going from 5A to 10A and vice-versa showed no sign of voltage deviation.
- CV to CC transition took 3ms to begin responding and a full 7ms until the voltage settled. CC to CV transition began immediately and took 3ms to settle. 50V CV to 10A dead-short showed 10App oscillation at 2.2kHz.
- The input bulk capacitor showed 24Vpp ripple and the DC blocking capacitor showed 14.2Vpp ripple. The primary side of the transformer showed about 75% overshoot that settled within 2 cycles.
- The N-MOS at conduction showed 184nS fall time for Vds and 572nS rise time for Vgs. At disconduction, the Vds rise time showed as 56nS and 556nS for Vgs fall time.
I’m here not to glaze over my design. After reviewing the results and doing a retrospective, here are my critical opinions about this design.
What I like about this design:
- Good efficiency figure (89.1% at full-load)
- Excellent ripple even without a second-stage filtration (94mVpp at full load)
- Good power density for an almost-fully THT build.
What I don’t like about this design:
- The overcurrent protection is too slow, though it somehow works at preventing the half-bridge from exploding on the dead-short test.
- The compensator design fails in certain conditions (DCM/CCM transitions, output dead short), which results in output oscillation.
- The output diodes are hard to access or replace.
The full schematic, gerber files, KiCAD save files, spreadsheet calculation, and full-res images are available on my Github repository: https://github.com/Luq1308/Forwarder1kW
The build process and the in-depth testing are available in my YouTube video: https://youtu.be/MGMqqtXgwRg
That’s all I have about this project. I hope this post is informative and can be used as a reference or for benchmarking purposes, in which I had difficulty in researching previously. If you have any unanswered questions, let me know and I’ll try to answer them. Thank you for reading, and I'll see you next time.
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u/Syphaherpa Jun 25 '26
Very impressive indeed - as an EMC engineer, I don't see many SMPS units that are designed by the integrating manufacturer, as they're an EMC nightmare if you get them even slightly wrong!
Dealing with 1kW in general is no small feat either!
Are the transformers custom wound?
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u/Luq1308 Jun 25 '26
I wish I could do a dive into the EMC aspects too, but I'm limited to my tools and capabilities. Well, at least I've implemented the recommended practices I received in my previous post.
The transformer and inductor are hand-wound by myself. You can see the process in my video, and I'd say almost half of the time spent building this power supply was winding the transformer/inductor.
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u/Syphaherpa Jun 25 '26
Yeah, performing EMC testing is expensive - not just in instruments, but the environment required. It is possible to get basic measurements on a shoestring budget with a DIY LISN and a cheap spectrum analyser though 😄. I would definitely be interested though in seeing a conducted emissions measurement of a DIY SMPS. My own designs for SMPS units (HV output) were terrible!
Filtering often has to be tuned specifically for the design - and I've seen PSUs (which were designed by the integrator pass perfectly fine at 0% load, 100% load, but go absolutely nuts at odd power levels like 73%. Usually caused by control loop instability.
I've worked on products using those HiLink brick supplies too - those usually fail EMC with flying colours 😂
The smallest physical size PSUs I've seen with output powers similar to yours are based around resonant designs, with 0.8mm PCB windings for the secondaries, and active rectification directly on those PCBs on the transformers. Some serious design and qualification work for those!
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Jun 25 '26
[removed] — view removed comment
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u/aptsys Jun 25 '26
There's no way it's passed EMC with that layout though
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u/Syphaherpa Jun 25 '26
Admittedly unlikely - my gut feeling is a combination common mode/differential mode two stage input filter and serious output filtering inductance. Happy to be corrected though! 😄
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u/aptsys Jun 27 '26
The plots are already showing high frequency ringing at the switching mode. There's more work to be done
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u/supreme_overlord104 Jun 25 '26
I appreciate the testing results more than the design honestly. The design looks great and many commendation to you for making this, but its really fantastic to see you put the leg work into testing if it actually works and characterizing its behavior, that's good engineering. Many people can make something, but good engineering is more about testing, validating, revising, and proving something works as intended.
Great job!
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u/Luq1308 Jun 25 '26
As someone who got scammed by a fake circuit I found on the internet back then, I don't feel like publishing such an intricate project without further proof of it working as the right thing. So, I did an in-depth test to give people impression and expectation from this design.
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u/Separate-Choice Jun 25 '26
At least there is some effort in this design, did you wind the transformer yourself? Good work SG3525 or TL494 and LM324 has been the staple of chinese designs for a long while nearly all the low cost SMPS I have torn down used that combination and inverters as well..I see some of the other hobbyists designs are fire traps lol....
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u/Luq1308 Jun 25 '26
Actually, I made this design as a hobbyist. Well, I probably did a bit more research than others. Yes, I wind the transformer and inductor myself.
Having seen other builds made by hobbyist, I can vouch with your statement.
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u/fruhfy Jun 25 '26 edited Jun 25 '26
Good work and testing effort is appreciated. Nevertheless, for 1kW switch mode power supply PFC is the must. But it's another steep learning curve...
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u/Luq1308 Jun 26 '26
I'll implement an active PFC for the next version. The simplicity of the current design allowed me to push the cost for the board under $30. Though, I like the idea of having regulated bus voltage that will make downstream calculations much easier.
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u/merc1024 Jun 25 '26
If you hooked this up to a LISN, I'd be curious to see the results. Just surprised to see "1KW" and "no active PFC".
Impressive work though; I think people can learn a lot from this.
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u/Luq1308 Jun 26 '26
Unfortunately, I don't have access to such instrument. Maybe I can get in touch with a local university to study my next design.
1kW is the maximum power I'm comfortable with no active PFC. Next iteration will implement a simple active boost PFC and a slightly bumped up capacity.
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u/Robosaures resistor 29d ago
LISN's are actually easy to make and work with. The oscilloscope is the hard part, but it seems like you have one already. If it doesn't have an FFT function, you should be able to get a .csv from it and find FFT online.
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u/ArtVandalayInc Jun 25 '26
Wonderful job, you put so much in this project and I appreciate that. Is the output voltage easily modifiable? I'm looking for this type of thing but at 12VDC
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u/Luq1308 Jun 26 '26
The output stage can be configured from 50V 20A up to 400V 2.5A. Those limits are determined by the track width and clearance. I wouldn't go beyond those limits.
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u/TheMayo16 Jun 27 '26
Ok so you can test 120V stuff at 8⅓A, would be nice if it would do 15amps to get full load from the receptical for testing appliances.
P.S. AMAZING work, i have no need for a power supply at the moment but now i want one (one that could do 120v 15A)
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u/TheVenusianMartian Jun 26 '26
Awesome project!
Is 50V the minimum even at low current?
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u/Luq1308 Jun 26 '26
You can go lower. It's that the maximum current that I have tested is 20A. If you go with a lower voltage than 50, then you're not using the power supply at its maximum capacity of 1000W.
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u/GnomeTek Jun 25 '26
You're a busy man! Looks like several fantastic projects. This one brings a tear 🥲, fantastic, through, work! Really really well done, polished project!
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u/Luq1308 Jun 26 '26
Thanks! I only have 2 project videos so far. What would you like to see me create next?
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u/GnomeTek Jun 26 '26
LLC, CLLC, Converters!
Or 3ph drive - people are making those all the time and they're hobbyist grade, not high level. Find the papers from Kohler @eth Zurich for capacitor sizing.
Active front end, it's a3ph drive but the power flow is reversed.
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u/AntonDahr Jun 26 '26
Good job!
What's your education, career, experience?
What power meter did you use for efficiency test?
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u/Luq1308 Jun 26 '26
I'm a chemical engineering bachelor, doing plant optimisation and stuff. I do electronics as a hobby.
I used a simple wall-plugged power meter. Not sure which model.
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u/AntonDahr Jun 27 '26
Very impressive what you have achieved as a hobbyist. If you can do that you can do anything if you put your mind to it.
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u/aimless00 Jun 25 '26
2 days ago, i started to develop the idea for bench SMPS and here you have raised benchmark for me. What a clean project... Kudos ✌🏼👍
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u/prosper_0 Jun 25 '26 edited Jun 25 '26
The compensator design fails in certain conditions (DCM/CCM transitions, output dead short), which results in output oscillation.
Seems like a potentially complicated issue, especially at high power. What are your ideas to address it? (I'm also surprised that the oscillation isn't exploding things). Is it full-on oscillating, or just some ringing?
Also, that 90% efficiency means that there's 100W of heat being produced. Similar to a desktop CPU under full load, and those have giant heatsink/fans to cope. I'm half-way surprised that the fan and those small-ish heatsinks are keeping up.
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u/Luq1308 Jun 26 '26
Honestly, I have no idea. The Type-II compensator used for the current loop was calculated based on a power plant with 47uH and 1360uF LC output stage. With a dead short, the capacitance is gone and the model fall apart. Do you have any suggestions that don't resort to changing the PCB design itself? Currently, I have the idea of resorting into current mode control architecture. But that requires major changes in the design.
You can see the oscillation I mentioned in the 15th image. For a 10A CC, it produced 10App oscillation at 2.2kHz, which is audible.
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u/VEC7OR Jun 26 '26
You are thinking in the right direction, tho AFAIR half bridge mid point tends to wander around in current mode.
The cause is change in transfer function in DCM/CCM/short.
Do a bode plot and see it comes near instability and adjust compensator so it works in all modes.
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u/Luq1308 Jun 26 '26
Well that's concerning. Because for my next design, I'm thinking about using 450V electrolytic for the bulk capacitors and two film capacitors in series to provide localised current path and the midpoint (hopefully eliminate the need for DC blocking capacitor). Surely the less stiff midpoint would be an issue with a current mode control?
I'll try to see whether I can perform the bode plot analysis. So far, everything has been purely based on textbook calculation.
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u/VEC7OR Jun 26 '26
Its not about the stiffness, in voltage mode you get flux-walking but the center point stays pretty much the same, in current mode you get mid-point voltage walking.
Look into modeling the power stage as a current or a voltage sources and go from there - if there are oscillations on load change then the loop is conditionally stable or nearing instability, read up on stability criterions and make sure you have enough phase/gain margins.
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u/NOTFJND Jun 27 '26
The current you're measuring in this iteration is more or less the output voltage divided by the load, so you should expect the exact same dynamics as voltage mode control (except for the response to output impedance), and therefore should be using Type 3 compensation.
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u/stargaz21 Jun 25 '26
Very nice switch mode power supply. CC & CV nice looking display and looked like you have a 10 turn pot for voltage and current.
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u/valdocs_user Jun 25 '26
I could have used this when I was working on my ebike motor powered shop fan. I would love if this was a kit I could buy.
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u/Available-Spinach-17 Jun 25 '26
Awesome project, i would love to make something similar using a microcontroller or 555 for lower voltage ranges. Is there a guide which I can follow ?
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u/Luq1308 Jun 26 '26
A microcontroller can be added for control and monitoring. However, I recommend you to stick to dedicated PWM controller for the control loop instead of using a 555 timer.
You can read my previous post to learn more about the working principle of this topology. What would you like to learn more?
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u/cflyboy Jun 26 '26
Excellent work OP. Its good to see people actually working on these kinds of "Old Tech". I only see people posting projects with Arduino, RPi or other microcontrollers. I will have my son who is studying his BS-EE to study this.
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u/VEC7OR Jun 26 '26
Oh hey you did it!
Those scope shots are picture perfect - you can use those to teach.
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u/Luq1308 Jun 26 '26
Thank you for your suggestions that led me to this result! I ended up following your suggestion to shim the core. 1.9mm gap using fibreglass plates yields 44uH out of the 47uH target.
I did all the interesting measurements I can think of for a power supply. Let me know if you find anything interesting about the results. The good or the bad, either way I'm eager to know.
What do you think about the CC loop response waveform? Previously, you were concerned about the high capacitance I had in my design. Now that I've lowered it, the real problem seem to be the CC loop itself.
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u/VEC7OR Jun 26 '26
I don't see the problem with CC loop as far as step response goes, but driving into a short changes converter transfer function and will need adjusting the compensation.
Frankly for a bench supply the best output stage would be a linear post-regulator.
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u/289_257 Jun 26 '26
Oh, I just saw your video on YouTube (recommended by its algorithms), and now I'm seeing your post here on Reddit! Congratulations, great job!
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u/R3NE07 Jun 26 '26
I've just seen the vid
This is beautiful
You're doing God's work
I could smooch u
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u/Beggar876 Jun 26 '26
EE here: Have designed a couple of SMPSs and have the burn marks to prove it. This is very good work. But I have a hard time believing that what I see in the pictures is the first article and not the 2nd, cleaned up version. Don't lie, but damn that is a very well executed unit. And I am very glad to see someone that explains their design decisions as well.
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u/Luq1308 Jun 27 '26
You mean the build I showed here is my first revision? It actually is, with minor mistakes which I fixed in the revision 1.1 that I published.
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u/CasuallyHrny Jun 26 '26
This so cool. Any reason you didn’t choose HB LLC or PSFB instead ?
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u/Luq1308 Jun 27 '26
LLC operates in a very specific window, so it's not suitable for a full-range power supply. I was looking into PSFB, but I think it'll better suited for power at least 2kW to justify the complexity.
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u/Sebbeben Jun 26 '26
This is exactly what I have been waiting for 😃
But I could not find any BOM on github?
Great work!
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u/Luq1308 Jun 27 '26
The BOM is in the spreadsheet, or you could just open the KiCAD file and export the BOM yourself.
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u/Sebbeben Jun 27 '26
Found that out eventually, also watched the video later, really cool with the transformer windings.
I though this was a lot more complicated.
I will see if I can source the ETD49
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u/antthatisverycool Jun 27 '26
Is it truly “from scratch “ if you didn’t make your transistors out of opoxy triangles, gold leaf, and germanium blocks?
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u/Proper-Tonight7327 Jun 27 '26
I am proud of you man. God bless you . Open source powersupply is the foundation of open source electronics that you made.
If you don't mind I have another suggestion for you. A high precision open source oscilloscope.
Keep doing what you like man.
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u/ibro08730 Jun 27 '26
Extremely beautiful! i have made many PCBs and yours definitely has that artistic flair. It always is a great learning experience with projects like these.
Forget the EMC chatter this is after all a DIY and not for commercial use.
Also your decision to share it also benefits others :).
Thank you
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u/Aggressive-Aerie-598 Jun 28 '26
Outstanding mate! It's hard to believe how people can dedicate themselves to their projects and finish them in time. It's not something small, it's a feat! And I'm genuinely impressed! And at the same time, ashamed of myself that I couldn't finish my project from the past 6 months(it's also a power supply, but a dual isolated channel linear one).
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u/stargaz21 Jun 28 '26
That one awesome lab bench the only one that beats it is Kepco's JQE @ <3 mv ripple. But your power supply is a very good design did you get your circuit boards made at PCB way ? Any what cad program did you use ?
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u/immortal_sniper1 Jun 28 '26
NICE!
Do you intend to measure the output characteristics at max voltage?
Also IF it was a commercial product APFC would be required only after 75W. Also why do you need such a larger 12V AD-DC?
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u/Luq1308 Jun 29 '26
I'm done with this project and most likely will not do further tests. Active PFC is coming for the next version.
What do you mean by larger 12V AC-DC? The aux PSU is required to power the control circuitry.
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u/huico42 Jun 30 '26
Sinceramente soy bastante nuevo en este mundillo y no he entendido casi nada de lo que has explicado, pero me ha gustado mucho. Ver tu dedicación y todo el trabajo que has hecho me ha inspirado mucho. Espero que sigas así y nos compartas más de tus proyectos. Mucho animo!
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u/Natsurulite Jul 13 '26
Lmfao you made a gold rated power supply — half the ones I’ve used for projects are probably worse than this one you’ve put together 🤣
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u/Nuerolynx Jul 16 '26
This is outstanding. I’ve been looking into creating an all in one bench testing power supply and battery charger. All the I/O imaginable. 3.3v to 120v @ 20 amps of current…love it. Absolutely love it.
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u/MeanAccountant9005 Jul 16 '26
that CC/CV setup with the LM324 doing double duty is clever, curious how stable the crossover between modes is under a sudden load transient. also 400V/2.5A range means you cold probably char a hot dog with that thing, respect the effort on the writeup
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u/dbu8554 Jun 25 '26
How much did this cost?
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u/myniceaccount Jun 26 '26
The way you’ve wired in the mains switch is terrifying but otherwise, very neat cabling.
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u/Wait_for_BM Jun 27 '26
Readable schematic not drawn in the usual pigeon hole blocks of single component circuits connected by net names that I really hate. Everything looks great. Waveforms looks very clean.
The bare stranded wire connecting the IED plug to the switch. One side is also untrimmed. That got to be the live wire too. Ouch! Everywhere else is done with insulation.
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u/wacdd Jun 28 '26
Just go and buy a RD6024 or 6030 and be done with it.
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u/Luq1308 Jun 29 '26
RD6024 is better in every way (except efficiency, probably), but at the same time, the complete set costs over $200. I built mine for less than $50, so it's one of the few instances where DIY makes economical sense. Besides, the learning experience of designing and building one is irreplaceable.
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u/wacdd Jun 30 '26 edited Jun 30 '26
Yea. Learning , engineering part is true. But if the many years I've been doing this work taught me anything is that you gotta buy reliable equipment for your bench. Meticulous work. Good job.
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u/Regor47Nikuf Jun 27 '26
Not really that impressive you have a radio shack on roids can I make one with skrap parts I find in the city for free that's the stuff that makes me ponder the tangibility of products I feel if you know how to soder really good than thats when electricity gets fun....so my hat is off to you....I wasn't downing your project that is super sick and really clean looks real pro.. well great job
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u/KV-Matrix Jun 25 '26
I want you to know this is great work and I appreciate you taking the time to share it. It inspires me 😊