Isolated 5V 5-10ma supply - Page 1
Forum section: electronics / projects

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 05, 2019, 08:33:53 pm
content: Hi,I need to have 16 channel, isolated 5V 5-10ma supply, what's the cheapest solution to do that?any Ideas? the input can be flexible,like 12V or 5V or 3.3V, the design should be small efficient and cheap, I was thinking about using EFD15 ferrite core with a 10 pin bobbin and generating 3-4 channel isolated voltage on each transformer, But I think maybe we have something better and smaller.

author: David Hess
author_rank: Super Contributor
timestamp: December 06, 2019, 05:04:42 pm
content: A flyback switching regulator with multiple output windings is one way. Better I think is to use a square wave inverter because then current is continuous allowing for a smaller transformer and lower noise. If the lowest noise is required, then a sine wave inverter can be used with the associated loss of efficiency.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 07, 2019, 06:17:13 am
content: Since the output current is so small, I was thinking of a simple circuit with open loop, and use low cost post LDO's to regulate the outputs. in this way maybe I could save one aux winding and add one more output.

author: TurboTom
author_rank: Super Contributor
timestamp: December 07, 2019, 07:37:24 am
content: Isolation requirements? Capacitive coupling? Depending on the application, there are many options. I once played with the idea to use the smallest available mains-rated symmetric common mode chokes with a common exciter to provide a multitude of well-isolated outputs. The sensitivity of the application required a sine drive and as little stray capacitance as possible. A few quick-and-dirty proof of concept tests showed this approach to be quite promising but since the expense of the PSU was of little importance, finally the decision was reached to use off-the-shelf DC/DC converters (which coused their own, different problems...of course).If you plan to follow this road, please be aware that the exciter has to be perfectly symmetric (capacitive coupling) to avoid core saturation (there is no air gap in the ferrite cores) and that the secondary rectifier also has to provide a symmetrical load (full bridge or voltage doubler). Otherwise, this concept works really well and requires little post-regulation since it's a pure forward converter with good output voltage stability. If a single exciter is going to be used for all channels, it's good practice to use an individual DC blocking capacitor for each transformer to minimize mutual coupling.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: December 07, 2019, 08:42:56 am
content: You can buy Isolated DC DC converters ready made:https://www.digikey.com/product-detail/en/recom-power/RFM-0505S/945-3159-ND/8550767On EBay or Aliexpress even cheaper. No need to reinvent the wheel.

author: TurboTom
author_rank: Super Contributor
timestamp: December 07, 2019, 09:28:30 am
content: Quote from: JohnnyBerg on December 07, 2019, 08:42:56 amDepends on the requirements. If you are involved in designing an electrical measurement system with multiple channels (cannot go into more detail) that's supposed to match CAT3 / 1000V or possibly higher, your choices are getting sparse and expensive. Other requirements may make spinning your own design also appear to be not such a bad choice. Just look at the isolation clearance and the data (test isolation voltage 1kV for 1s, less voltage for repeated or prolonged tests...) of the device you linked. It's also interesting to read publications on long-term behavior and deterioration of isolation barriers. All this puts designing high-reliability devices as mentioned above under a completly different light, not only regarding isolated power supplies but also the data links.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: December 07, 2019, 09:52:33 am
content: Quote from: TurboTom on December 07, 2019, 09:28:30 amOp had a DIY solution with EFD15 ferrite core with a 10 pin bobbin in mind .. Any industrial DC DC converter will beat that.

author: David Hess
author_rank: Super Contributor
timestamp: December 07, 2019, 05:29:09 pm
content: Quote from: ali_asadzadeh on December 07, 2019, 06:17:13 amWith an inverter, there is a good chance you can get away with either no regulation or only primary side regulation. If diodes are used for rectification of the secondaries, then primary side regulation can be done by including compensating diodes in the feedback loop. Alternatively with only a 5 volt output and square wave drive, bipolar transistors or MOSFETs can synchronously rectify the outputs without special drivers.For those who like to abuse parts, CMOS inverters can be wired backward to make a full wave synchronous rectifier. Drive goes to the inputs and outputs and rectified DC is pulled from the supply pins. Use several gates in parallel to decrease series resistance.The flyback configuration always requires regulation of the pulse width modulator and the outputs roughly track each other.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 08, 2019, 06:11:31 am
content: QuoteSound a good plan, is there any schematics or info that you could share?QuoteThanks david, I was thinking of driving the primary with a dirt cheap DC motor driver part, something like thishttps://lcsc.com/product-detail/Motor-Drivers_MX116_C113342.htmldo you suggest any circuit for your idea? since my product would be manufactured in volumes and each single unit is cost sensitive and should have 16 channel of isolated 5V supplies, I should design something reliable and dirt cheap( maybe with all chinese parts from lcsc)

author: TurboTom
author_rank: Super Contributor
timestamp: December 08, 2019, 10:22:15 am
content: There isn't much of a schematic regarding this experiment -- I used an AWG to generate the drive signal, amplified it by a DIY wide-band amplifier (LT1210 based, an off-the-shelf unit would have done just as well), and through a coupling capacitor (MLCC 4.7µF) to a common mode choke (CoilCraftSBU9-2820R5L_would be a decent choice). On the secondary, a schottky bridge rectifier was used along with some RFI reduction and voltage post processing stuff (the PSU had to power a sensitive analog front end with considerable power consumption -- some 5W IIRC).In your case, you could well use the mentioned MX116 motor driver to power the system, but I would use it single-ended and utilize the capacitive coupling mentioned above. If your power requirements are really only 10mA@5V, you can use a single driver to feed all 16 transformers (8 on each output) and driving both inputs with a 70~100kHz square wave of opposite polarity. Use a voltage-doubling rectifier (2* small Schottky, 2* 1µF MLCC) and if the stability and load regulation isn't too important, you can adjust the supply voltage of your driver to provide the proper output voltage (loaded). If inrush/switching currents are a problem, you may want to place inductances in series with the diodes, but due to the very small required power, I'ld initially try without.Of course, that's just a quick-and-dirty suggestion that would probably be a reasonable starting point that will provide very good high-pot isolating characteristics.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 08, 2019, 04:45:28 pm
content: Also, maybe you could specify your isolation requirements (voltage) first (primary to secondaries and secondary to secondary...)Then of course the solution would also depend on factors like cost vs. quantity, area/volume taken, EMI, ...

author: David Hess
author_rank: Super Contributor
timestamp: December 09, 2019, 02:45:53 am
content: Quote from: ali_asadzadeh on December 08, 2019, 06:11:31 amI do not see any specifications for speed. Above 20 kHz is typical. Some gate driver ICs are suitable.QuoteThe transformer will be the difficult part. Gate drive and pulse transformers are suitable if you want to get something from Coilcraft or someone to experiment with.

author: rvalente
author_rank: Frequent Contributor
timestamp: December 10, 2019, 12:10:48 am
content: This is siemens S7 1200 RS485 board, you can see their aproach using the MAX253 to drive the trafo.You coud do something similar, with multiple winding in the secondary. Lets say 4 outputs per trafo.https://datasheets.maximintegrated.com/en/ds/MAX253.pdfQuote from: David Hess on December 09, 2019, 02:45:53 am

author: David Hess
author_rank: Super Contributor
timestamp: December 10, 2019, 12:31:36 am
content: Quote from: rvalente on December 10, 2019, 12:10:48 amA lot of standard pulse transformers are trifillar 1:1:1 and some are quadfillar 1:1:1:1.https://www.mouser.com/Power/Transformers/Pulse-Transformers/_/N-8u9sj?P=1yqdy9r

author: rvalente
author_rank: Frequent Contributor
timestamp: December 10, 2019, 01:54:26 am
content: Ethernet transformer could be pretty cheap due to the high production volumes

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 10, 2019, 06:41:38 am
content: Thanks for suggestions, The isolation from primary to secondary is about 1Kv and secondary to secondary is about 500V, the links for the transformers are useful, but they would fail the production due to the cost! who would pay 7.7$ on a single transformerwe have 0.03MUC and 0.07 DC motor driver, we should be able to find some sub 0.1$ transformer too.

author: ebclr
author_rank: Super Contributor
timestamp: December 10, 2019, 06:50:42 am
content: The easiest and cheaper way will be buying one ready to usehttps://pt.aliexpress.com/item/32970698143.html?spm=a2g0o.productlist.0.0.32b2ad14r3Nb1E&algo_pvid=dcbdee7c-994d-480f-af12-58c746218f39&algo_expid=dcbdee7c-994d-480f-af12-58c746218f39-25&btsid=0727019c-b39d-44fc-b1b6-765fe6496c6a&ws_ab_test=searchweb0_0,searchweb201602_9,searchweb201603_53

author: Marco
author_rank: Super Contributor
timestamp: December 10, 2019, 08:54:17 am
content: Quote from: ali_asadzadeh on December 10, 2019, 06:41:38 amChinese UU9.8 common mode filters seem to get close to that.

author: David Hess
author_rank: Super Contributor
timestamp: December 10, 2019, 08:27:09 pm
content: Quote from: rvalente on December 10, 2019, 01:54:26 amEthernet transformers could work but I have not tried them myself. The inverter frequency would need to be higher but should still be feasible.

author: GreggD
author_rank: Regular Contributor
timestamp: December 10, 2019, 09:01:00 pm
content: B0505S-1W200mA outAbout 68% effRequires a 10% loadKeep load capacitors below 47uF10pcs for $7.20 USD, free shippinghttps://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20191210125104&SearchText=b0505sI just ordered boards today from JLCPCB that have one on it as well as the mentioned UU9.8 choke.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 11, 2019, 09:27:58 am
content: QuoteDo you have any link?

author: Marco
author_rank: Super Contributor
timestamp: December 11, 2019, 12:56:03 pm
content: On phone now and not too going to look for it, but yesterday I saw an ebay offer for 100 pcs for 13$.These should be able to work at relatively low frequencies.

author: Gyro
author_rank: Super Contributor
timestamp: December 11, 2019, 01:16:11 pm
content: Quote from: rvalente on December 10, 2019, 12:10:48 amThe MAX253isa very handy little chip for such applications. It's also that rarest of beasts, a Maxim chip that has been around for at least 20 years!

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 11, 2019, 03:15:20 pm
content: I have done it! and it's working better than expected for the first try! the efficiency is around 50-60%, the output with no load is around 12V and with a 7ma load, it would drop to 7V, so Now I should find a cheap SOT23-6 LDO that would generate 5V and could accept input up to 20V, and a working temp of -40~85CThe whole thing cost is under 0.5USD in single unit QTYThe bonus point for this circuit is, that I have another none isolated boosted output too! so I have 4 separate isolated outputs and a single none-isolated output

author: Marco
author_rank: Super Contributor
timestamp: December 11, 2019, 07:54:46 pm
content: Here'sthe ebay listing for the common mode chokes.

author: SiliconWizard
author_rank: Super Contributor
timestamp: December 11, 2019, 08:27:55 pm
content: Quote from: ali_asadzadeh on December 11, 2019, 03:15:20 pmSo, what are you using to drive the primary? A MAX253 or something else?

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: December 12, 2019, 10:12:10 pm
content: QuoteThe best and cheapest of all Boost converters! it's only 0.07USD (MT3608)

author: Yansi
author_rank: Super Contributor
timestamp: December 12, 2019, 10:17:00 pm
content: Use ethernet transformers (or any 1:1 ones) with suitable isolation rating, connect all primaries together in parallel and stick them to a ~1MHz oscillator (whatever source of approx 50% duty cycle square), feed to a beefy gate driver (MCP1407 or whatver similar fast enough) and don]t forget to stick a cap in series with the output, to decouple the DC component from the xformers.Also, if you have access to Tex-F (tripple insulated wire), you can very very easily make yourself some very low capacitance transformers with small cheap ferrite toroids, rated for 4kVac safety (double) insulation. Same primary excitation circuit (beefy gatedriver, AC source).

author: rvalente
author_rank: Frequent Contributor
timestamp: December 16, 2019, 08:58:47 pm
content: Got some span mail from wurth today, maybe this can help you.http://www.ti.com/lit/ds/sllsep9h/sllsep9h.pdf?utm_campaign=Product%20%2B%20Service%20Information&utm_source=hs_email&utm_medium=email&utm_content=80848634&_hsenc=p2ANqtz--3GsPMGZEhBJUFdjvLlHe_6S_FOV3ZYuViVI95mfnChQdCjo64yAMXnFhzvkRXe-Ved5gLu5AHZzO0tUv9rItBUNH81A&_hsmi=80848634http://www.ti.com/lit/an/slla436/slla436.pdf?utm_campaign=Product%20%2B%20Service%20Information&utm_source=hs_email&utm_medium=email&utm_content=80848634&_hsenc=p2ANqtz--3GsPMGZEhBJUFdjvLlHe_6S_FOV3ZYuViVI95mfnChQdCjo64yAMXnFhzvkRXe-Ved5gLu5AHZzO0tUv9rItBUNH81A&_hsmi=80848634https://cdn2.hubspot.net/hubfs/255537/TI%20SN6501-6505%20MID-PPT%20OPM.pdf?utm_campaign=Product%20%2B%20Service%20Information&utm_medium=email&_hsenc=p2ANqtz--3GsPMGZEhBJUFdjvLlHe_6S_FOV3ZYuViVI95mfnChQdCjo64yAMXnFhzvkRXe-Ved5gLu5AHZzO0tUv9rItBUNH81A&_hsmi=80848634&utm_content=80848634&utm_source=hs_email&hsCtaTracking=b7cdc182-813f-4814-90be-08dedde1d246%7C0b0e480a-2871-4101-bb73-482fa721945bhttps://www.we-online.com/catalog/en/ctm/MID-PPTI?utm_campaign=Product%20%2B%20Service%20Information&utm_source=hs_email&utm_medium=email&utm_content=80848634&_hsenc=p2ANqtz--3GsPMGZEhBJUFdjvLlHe_6S_FOV3ZYuViVI95mfnChQdCjo64yAMXnFhzvkRXe-Ved5gLu5AHZzO0tUv9rItBUNH81A&_hsmi=80848634