Universal PSU module - Suggestions and Ideas? - Page 1
Forum section: electronics / projects

author: ricko_uk
author_rank: Super Contributor
timestamp: August 04, 2020, 01:06:34 pm
content: Hi,I am thinking of making a little power supply module for whenever I need compact multiple supplies on the go and away from the lab, with the following specs:- input 4.5 to 15V- outputs: +/-3.3, +/-5, +/-12, + variable (trimmer set), - variable (trimmer set)- LEDs: Power in/on and over current (for the various regulators used)- input connector USB, DC barrel and screw terminal- output connector pin header and screw terminalTwo questions:1) would you add anything else?2) which regulators configuration and regulators would you use?Out of curiosity, is there anything already available on the market? I could only find this one which is somehow similar but delivery is Sept:https://www.amazon.co.uk/Single-Supply-Module-Regulator-Multiple/dp/B089RS1MJ8/ref=sr_1_10?dchild=1&keywords=dual+power+supply+module&qid=1596545395&sr=8-10Thank you

author: Pawelr98
author_rank: Regular Contributor
timestamp: August 04, 2020, 02:06:54 pm
content: Depends on how much output current you want.Rails separate or common ground ?Good independent regulation or rough ?In the 100-200mA range you can go with push-pull primary and multiple secondaries.Then LDO for proper regulation.

author: ricko_uk
author_rank: Super Contributor
timestamp: August 04, 2020, 07:31:22 pm
content: Thank you Pawelr98,I am thinking about at least 500mA, preferably 1A.All grounds common (although you now made me think that perhaps separate grounds is a better idea and then I can join them with a jumper/switch if and when needed).Good regulation but nothing extreme. something perhaps around 0.1V regulation.

author: Pawelr98
author_rank: Regular Contributor
timestamp: August 05, 2020, 02:07:33 am
content: Good efficiency or medicore ?With so many output voltages and negative/positive the push-pull configuration is something I would use.Classic 494 or many other IC's can handle the rough regulation.Then postregulation with LDO's that will just heat up.Input voltage of the LDO regulator shouldn't be too high as this would cause overheating problems.Should be simple to build. Find a core without a gap, such cores are used for Half-bridge or Forward topologies.Wind half of the primary, then secondaries, at last second half of the primary.With push pull configuration you want to wind bifilar primary winding in order to save time and make sure both parts are fairly similar.Just remember to connect those primary windings the right way.Then there's a small issue of low input voltage.A small boost regulator should boost the input voltage for the driver.Doesn't have to be anything fancy, it only carries small amount of power.Mosfet transistors are going to need that higher voltage for their gates.Unless good efficiency is required.Then it becomes tricky.Synchronous converters and other modern solutions.

author: ricko_uk
author_rank: Super Contributor
timestamp: August 05, 2020, 05:02:14 am
content: Thank you Powelr98,efficiency is not that important.More important is the fact that I haven't wound transformers before and am looking for a more "standard" solution that I can just design and make with off the shelf parts. Even if it involves more parts.Very busy so I need to make something relatively quickly and with high confidence that it works from the start and don't feel comfortable starting to wind transformer and possibly having to tune them.For the same reason, using some (Altium) "channel" design would be also good as it would make the whole thing quite quick.Any suggestion along those lines?Thank you

author: Pawelr98
author_rank: Regular Contributor
timestamp: August 06, 2020, 12:22:28 am
content: Wounding transformers is easy for high freqency.An example of a transformer from an ATX power supply in the 300W range.Runs at ~50kHz or so.5V secondary is whole 3 turns IIRC. Times two because it's two diode rectifier.Primary which has 170V square wave going through it is 20+20 turns (split to reduce leakage inductance).So it's fairly easy to wind, even without experience.I have wound my first switching power supply transformer without any experience whatsoever.Just making photos and looking at how it was originally wound.Transformer provides the separation, allowing all the rails to be independent.Then by using the right amount of turns you get any output voltage you want.AC voltage is square wave so it's easy to calculate all the secondary voltages (LC tank required).If you insist on using only off-the-shelf parts then focus on non-isolated topologies.Pretty much only inductors are used.Look up Texas Instruments "power topologies handbook".https://www.ti.com/seclit/ug/slyu036/slyu036.pdfBoost to 15V and from there you may try buck and Inverting Buck-Boost for all the voltages.

author: ricko_uk
author_rank: Super Contributor
timestamp: August 06, 2020, 11:14:34 pm
content: Thank you Pawelr98!It looks like it is easier than I thought, sometimes we have mental blocks or preconceptions for no real reason.Having said that, you made me think that a while back I saw some standard transformers (maybe from Coilcraft) developed specifically for certain ICs (from memory some TI parts) and they were for isolated topologies.I will look into it now and try to find them out again. Just in case are you aware of any (both transformers and related ICs)?Thank youRiccardo