DIY SCPI programmable dual channel bench PSU 0-50V/3A
List of important changes
Update 2015-02-14: New power pre-regulator schematic is posted here.
Update 2015-02-26: Corrected bias power supply schematic (Sheet 1) and simplified post regulator schematic (without TLC555/relay based bias control) is posted here.
Update 2015-03-21: Spice models added for redesigned power post-regulator.
Update 2015-04-06: Modified post-regulator Spice model with new OE circuit is added.
Update 2015-04-08: New schematics for pre-regulator and post-regulator and new PCBs are presented here.
Update 2015-05-15: Mosfet pre-regulator board is assembled and tested.
Update 2015-06-20: Eagle files, BOM and Gerbers for Pre-regulator PCB r2B5 (06/2015).
Update 2015-07-29: New PCB for front panel designed as Arduino shield for Mega2560 or Due boards is introduced. An 3.2" color TFT touch-screen display replaces monochrome 128x64 LCD. This PCB makes obsolete previous MCU board, 4x4 keypad and BP PCB.
Update 2015-07-30: New AUX power supply with soft-start/stand-by is added that make previous one obsolete.
Update 2015-10-03: SMD version of Mosfet pre-regulator board and post-regulator are assembled and tested.
Update 2015-10-21: Eagle files, BOM and Gerbers for the Arduino Shield latest revision
Update 2015-11-01: A new thread about software support for this power supply is opened here.
Update 2015-11-10: A repository for hosting hardware design files and source code is created and now available on https://github.com/eez-open
Redesigned PSU with smaller enclosure and SMPS pre-regulator
Update 2016-03-04: New power board (pre- and post-regulator merged into one)
Update 2016-03-05: AUX PS with fan controller, Ethernet and USB connection
Update 2016-03-05: Arduino shield with W5500 Ethernet controller
Update 2016-06-17: Redesigned set of PCBs for lower profile enclosure and hybrid power modules is available on the GitHub. This revision will be used for planned group buy.
Update 2016-10-06: Firmware M2 is released.
Update 2016-12-29: Firmware M3 is released.
Update 2017-02-23: EEZ H24005 became a fully funded campaign on the CrowdSupply.
I’d like to present what I did until now trying to make a bench power supply that should have a solid “analog” core that can be enhanced by adding MCU for on-site or remote programming, monitoring and data logging. My understanding of analog circuits are basic and I tried to compile many ideas found on various places. Initial document was Agilent E3634A Service guide (Part No. E2634-90010, April 2000) and presentations found on i.e. Gerry’s and Ian’s blogs.
Presented work is still not backed by any simulation (I still wonder which one to choose, it that LTspice or something else, your recommendations are welcome). I can imagine that such simulation could save considerable amount of time and material.
There is many DIY power supply projects available (as cheap yet solid enough PSU that comes from various manufacturers) but I decide to try to make one by myself to learn a little about various circuits and parts that are now available on the market. The result of such quest is that I include many components that goes far beyond 2N3055 or LM317 based solutions but since we are in 21 century and logistics is amazing and since my budget is not so tight I think that I should proceed in that way. As a “reality check” to not end up with some really “esoteric” parts all what was selected has to be available through at least one of two European supplier (see below).
It’s also interesting that in DIY projects Vout of 30V is as some kind of magic threshold which is not cross over very often. Maybe it’s just a practical reason for that since most of today equipment do not need anything beyond 24V?
Situation with ideas about digital part and programming is better and many parts that is added on MCU board was inspired by my own view what kind of functionality programmable bench power supply should have. But this is a next step. The first one is to create solid core that can survive various testing torture and do not call into question safety/integrity of the various loads/equipment that could be connected somewhere in the future.
I spent many hours “breadboarding” and end up with complete mess (see picture of my desktop). Thanks to that many components was burned when I touch wrong wire or components or apply wrong voltage :( So, it’s high time to put what is done on PCB. PCBs (see below) will be successors of the first batch where I mainly tested SMPS functionality that was previously unknown to me. On the beginning I tried to test LM5005 for bias, LM5118 for pre-regulator and LM5119 for both functionality since it is dual channel. Unfortunately I never succeed to do any testing with the latest for the simple reason that soldering QFN without reflow oven which I still don’t have became mission impossible despite some encouraging videos such as this one. Maybe the reason for my failure is not using of a solder paste but even if I succeed I start to wonder what kind of nightmare that may be for the other people who eventually decide to follow this project. Fortunately soldering (with the right soldering tip) of even tiniest SMD ICs (such as 5-pin SOT-23) become surprisingly simple.
In this first post I’d like to present some basic facts about projects such as goals, features, schematic and PCBs that I’m going to order soon. I hope that will generate discussion that will further improve this project even if that not necessary simplify something that one can already found too complex :) Maybe we even ends up in not so distant future with group buy, who knows. Here we go:
Project goals list
Modules feature list
Schematic on Sheets 1/10 to 4/10
Most parts are tested. That also include basic ADC/DAC functionality (set Vout and Iout using DAC and measuring Vout/Iout using ADC). Require additional testing for pre-regulator tracker when pre-regulator enter buck-boost mode (Vin ≤ Vout). Currently design include a silly way of achieving power up and power down without overshooting regardless of the fact that load is connected or not. That is mainly because a bias supply with separate transformer (LM317/7805/LM339L) is used when experimenting and power-up sequencing is not correct (correct biasing comes too late despite of fact that pre-regulator has huge soft start of ~40ms).
During testing a LM5118 based pre-regulator was on the first PCB version. Power inductor in buck-boost can be under real stress and some of them (Bourns PM2110-820-K-RC1240) can reach, I believe due to the saturation (tested with Vin=40VAC and Vout=50V/3A), a temperature of 90oC or even more! The most flexible solution is playing with own inductor winded on the ETD ferrite core.
Low noise LDO (LT3030, TPS7A3001) in combination with SMPS pre-regulator (LM5574) was tested on breadboard only. That was pretty challenging and real performance (ripple rejection) was not possible to test.
For load/stability testing the following parts are used: 2 x 8R2/100W, 2 x 33/25W power resistors and 4 x 12V/35W halogen lamps. Tested with full 150W and beyond that (approx. 200W). Testing of two channels will be started when PCB arrived (then will be possible to test SMPS frequency sync and serial and parallel connection). I’d like to extend stability testing using 100R/25W resistor and DC motor (~100W).
Schematic on Sheets 5/10 to 7/10
Not tested, require PCB
Aux power (+5V) and AC input protection
Schematic on the Sheet 8/10
Not tested, require PCB
Schematic on the Sheet 9/10
Serial or parallel wiring of two Power boards without additional external cables using power relays
Sense to Output wiring without additional external cables using small signal relays
LED indication for mode of operation (serial/parallel) and Sense connection
MCU board is required for programming
LED and relay driver through 16-channel driver TI (TLC5925)
On-board protection against wrong programming to avoid simultaneous activation of serial and parallel relays (if serial mode is active parallel is automatically disabled)
DC outputs are guarded with combination of SAR, MOV and TVS
Proof of concept tested (i.e. SPI communication with TLC5925 and serial/parallel relay control), more testing when MCU board become functional and two Power boards are assembled
4 x 4 Keypad
Schematic on the Sheet 10/10
Proof of concept tested, more testing when MCU board become functional
Ethernet + USB sockets board
Schematic on the Sheet 8/10
Not tested, require PCB
Schematic as image files
Sheets from schematic (PDF) as separate image files ...
... and PCBs (for closer inspection click on image and then on option "View image" on right mouse click menu)...
Few LM5118 pre-regulator measurements ...
Here you can find some measurements done on pre-regulator (assembled on first PCB revision) with pure resistive load (two 8R2/100W in connected in series). Vin=40VAC therefore for the upper limit LM5118 is in buck-boost mode that generate more output ripple then is buck mode. For measurements are used simple short ground probing (no differential probing with two channels).
Channel color legend:
Yellow - Vout ripple (AC coupled)
Cyan - Vout (DC coupled)
Magenta - HI mosfet Gate
Blue - LO mosfet Gate
Power inductor is approx. 100uH (custom made on ETD29/16/10 ferrite core).
Step response using DAC programming ...
Additional possibly interesting measurement what I can provide in this moment is how PSU follow DAC instructions. Please note that measurement was performed with post-regulator section build on breadboard. DAC command was sent using Arduino in infinite loop sequence of three U_SET value each 5, 20 or 50ms long. Connected load was again 16R4 (2 x 8R2). As you can see there is no overshooting nor undershooting presents. Falling edge is possibly too slow. This is done with 100uF capacitor connected on the output. Channel color legend is the same as in the previous post. HI and LO gate signals frequency is too high to be seen correctly.
Very impressive and interesting! It is beyond my level of understanding (a little complex for my knowledge) but it looks as a top of the range PSU.
Looking forward for further progress.
BTW, you chose a high voltage level (50V) but you limit the current to only 3A, I think a higher current level would be more useful in a dual PS, in order to serve power amps' test for example.
If we stay strictly within buck region (Vin > Vout) with selected bias supply (low noise in 200KHz region LDO's as post-regulators) and N-ch MOSFET based main post-regulator which is very quiet it could be possible to ends up with Vout noise level acceptable for audio testing (due to that it was also highly on the list of requirements a no cooling fan solution to not kill a joy of listening performance of a connected preamp or smaller amp stage).
I'm agree that 3A is really not enough for some bigger amps testing but what I can preliminary say that it should reach easily 5A with proper transformer and MOSFET even with max Vout of 50V. Also don't forget that the project goal is dual channel unit with possibility for serial or parallel connection. The former gives you 0-100V range and the latest 6A (or hopefully 10A).
While waiting for PCBs I spent some time to organize my halogen lamps based dummy load in a proper way (holder of the first one was almost melted by high temperature). Here are some pictures if some find such approach useful. Ceramic lamp holder is HE01-150.
Front panel design excercise
I spent some time to test how is working Front Panel Designer (v4.41 for 64-bit linux) from Schaeffer AG. It's really nice and simple tool covering everything that I can imagine in this moment. Great feature is built-in price calculator. Unfortunately not so nice "feature" is the total cost of simple design :scared:. Here is what I have in mind for MCU controlled and manually controlled dual channel unit. I took as a reference dimensions of Modushop's Alu-cases (with front panel's of 320x115mm and 280x115mm respectively).
The first design costs 73.91EUR (87.95EUR incl. VAT, excl. S&H) and the second one 109.74EUR (130.59EUR incl. VAT, excl. S&H) :eek:. Does anybody recently made an order that can tell me how accurate is that price calculator?
100% accurate (excluding shipping costs back and forth if needed, of course).
They charge you based on the sum calculated by their app.
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