Review self-made quad channel programmable power supply for digital designs - Page 1
Forum section: electronics / projects

author: alexk195
author_rank: Newbie
timestamp: October 01, 2024, 02:07:54 pm
content: I've built a programmable power supply and I'm wondering if this would be of any use for other makers. I'm doing sw for business, so this is my "most complex" electronic project so far and for sure not very polished. I would appreciate any comments about design/features and whether it makes sense to offer it on tindie or lectronz. Also what is a reasonable price tag for this. Thanks!More info onel08.de/pps1

author: squadchannel
author_rank: Frequent Contributor
timestamp: October 03, 2024, 06:18:22 am
content: There are several areas for improvement.What purpose IC8 used for? It looks like a power switch, but the circuit is not used as a switch.The DC jack has a center positive and center negative. It is very easy to make a mistake. I need a diode and fuse for reverse polarity protection.The resistor divider for voltage detection seems to output 3V when 12V is applied. Perhaps the MCU is 3.3V.As a pitfall, is the VDD voltage selectable as the reference voltage for the internal ADC? Some microcontrollers are not selectable.Also, in the unlikely event of a fault that causes 12V to be applied, the MCU will be damaged. Please add a zener or diode clamp.Large capacitors are used in places, such as 22uF. Considering the voltage and other factors, the size seems small.Considering DC bias, 22uF would be good for about 1206inch.The current sensor seems to be an analog output type. I would like to see an LPF on the output.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 03, 2024, 07:27:34 am
content: It´d be kind of a shame to have a USB-C socket on the PCB but no power delivery capability.I know that it´s intended for computer communication, and few computers have PD sourcing capabilities. Maybe you can add a second USB-C socket just for power supply.It seems you want a "no frills" design, but I think you should spend a few $ on a small status display. Configuration per SCPI is absolutely okay for that purpose, but it should also be possible to switch it on with default values without a computer connection. I would define a SCPI-command that stores the actual settings as defaults in the eeprom.Are you sure you want to operate this converter without any EMI filters? I´d definitely spend more decoupling caps and some ferrites in the outputs. A common mode choke for the input could also be useful but requires an adapted ground plane design.

author: alexk195
author_rank: Newbie
timestamp: October 03, 2024, 06:27:05 pm
content: Thanks for your honest opinion. I try to answer them.The IC8 is used as "ideal diode". So that XIAO chip can get power either from his USB or from LDO which converts 12V to 5V.The ADC pins accepts up to 3.3V. So with 1:4 divider I have max of 13.2V. I've added some margin because 12v supplies might output more. Yes the zener would protect the input event if higher voltage is applied, it was just a cost-driven decision to skip them in the first version.I've defined all passives to be in 0805 size, just because I have a lot of them at home for all R and C values ( just in the case of manual rework). For this board I've decided to use local pcb manufacturer to do also full assembly (SMD and TH), and i wanted to be prepared for rework. Actually no rework was needed so far. BTW for 3 boards I've paid about 400 EUR, which seems to be quite high...Sorry I don't understand the reason behind the sentence:QuoteLPF (Low pass filter?) was skipped for cost reasons. I do averaging in software instead.The DC jack looked easy solution at first glance but turned out to be a mistake. Different polarity and 4 different sizes of plugs varying by fractions of mm are big source of issues. I already selected a USB-PD board which will replace DC-Jack, it will be a second USB-C receptacle instead of DC-Jack. No wrong polarity and no wrong sizes any more. It will be ADA5807 from Adafruit. The uC will request correct input voltage from USB-PD via i2C.A nice small OLED i2C display would be great, but intended usage was actually remote control. I probably can add support for a certain display in uC and then detect if it's attached. So someone can just add it to the client board.At the moment it's actually like in the second review: There is a command *SAV which saves current settings to eeprom.On startup I wait until supply voltage is above some threshold, than power up channels according to saved values automatically if master switch was saved as "on".There is also a button to switch on/off master switch. In the future I want to add support for second eeprom(with different address) on the client board, so that if it is present the correct settings for this client board are applied. Than you can actually connect the power board to different client boards without having to re-configure the voltages. The eeprom on the power board is always used to read the calibration values.The EMI is a complex thing. As I'm a sw guy, I decided to ignore this and put everything in aluminum enclosure, so at least emmisions are low :-). I also have no equipment to do a intense measure on this. Just a simple 100Mhz scope. At least the output voltage seems to have very small ripple.I thought I could sell it on Tindie or Lectronz, but I’m not sure if it's a good idea.To cover the costs, I would need to charge about 100EUR+Shipping for this, what seems to be quite expensive...

author: squadchannel
author_rank: Frequent Contributor
timestamp: October 04, 2024, 12:48:12 am
content: It seems to be difficult to understand in translation.High dielectric MLCCs have DC bias characteristics.The higher the DC voltage, the lower the actual capacitance.Based on the size of the board image, I would guess 0805.For example, with this capacitor, 0805 22uF 25V (GRM21BR61E226ME44)When 12V is applied, the capacitance is lost by 82% and is only 3.96uF instead of 22uF.for this reason, use a low dielectric capacitor such as C0G or NP0. but there are no high capacitance ones.increase the actual size or use a larger capacitance considering the lower capacitance or use several in parallel.

author: Phil1977
author_rank: Frequent Contributor
timestamp: October 04, 2024, 06:53:36 am
content: Quote from: alexk195 on October 03, 2024, 06:27:05 pmUnfortunately do the RF waves not care about your educationThe Al-enclosure prevents direct emissions, but each cable you plug in gets an antenna. Especially if you do not have the knowledge and equipment to simulate or test it, you should implement the basic filter types on the PCB.That means:- Pi-LC-Filters on each output- Staged decoupling caps between the ground plane and all inputs and outputsI´ve just seen that the chip manufacturer sells an EVM for the converter chip:https://www.monolithicpower.com/en/documentview/productdocument/index/version/2/document_type/Datasheet/lang/en/sku/EVM54304-MN-01A/document_id/9460/I´d order this ($25,- is a very fair price) and copy the layout and the used filters as far as possible. Without engaging an expert you won't find a better design by yourself.

author: jonpaul
author_rank: Super Contributor
timestamp: October 04, 2024, 07:12:00 am
content: schematics?

author: ArdWar
author_rank: Frequent Contributor
timestamp: October 04, 2024, 08:35:04 am
content: I'm not sure how much demand for 0.5-5.5V supply are there. If it's for general hobbyist I'd design to cover 12V. But adapting the PMIC for that while maintaining programmability doesn't seem to be straightforward without buffering the FB pin.For the circuit design. The aforementioned DC bias effect is valid concern, although it should be easily tackled by simply adding large electrolytic cap at the input. EMI filter are in the "it depends" category, subject to actual implementation and requirement. LC filter is better, but design it wrong and you may end up worse. Low Z ferrite bead are hard to mess up, but give less attenuation.As for the board design, your input caps (C3, C4) straddle the wrong plane. Look at their aforementioned EVM and pay attention how their input caps (C1, C2) are positioned. There are very good reason why they were positioned that way, to the point that Vcc bypass and GPIO pulldown positioning are sacrificed. Your C9, C10 could be better but that's not that critical. You may also want to put your FB signal pickup point to be at least "after" the respective output caps instead of directly binding them with the OUTx pins.

author: alexk195
author_rank: Newbie
timestamp: October 04, 2024, 11:22:45 am
content: @jonpaul: schmematics is linked on the website:http://el08.de/pps1/schematics.pdfThe EVM was a good hint. They also use 0805 caps and no filters on output. So this should be ok, i think.@ArdWar: They also have large Cap C8 on input in EVM, which is not populated. So probably this would be enough for filtering.@ArdWar:Copy the full design is not possible as I don't want to use any components on the bottom side.If I would change the supply to USB-PD, is then any input filter needed?The layout was done by someone with much more experience, so I cannot explain the details behind it.My C3,C4 are close to the input pins of the chip. And are connected to ground plane. In the EVM they have put them on top and bottom, which is no option for me.The FB Pins are routed back at the place where decoupling capacitors are. This happens close to the chip. Then they are routed to the connector. Do you suggest to do feedback loop further away, closer to the connector?What do you suggest about C9,C10? Move them closer to the chip?

author: jonpaul
author_rank: Super Contributor
timestamp: October 04, 2024, 05:11:21 pm
content: poor des concept.EMI of SMPS cannot be cured by avg.Add EMI filters.j