Three phase AC input to 5V/500mA transformerless - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 10, 2020, 03:24:51 pm
content: A) Input is 3 phase acB) Output required is 5Vdc/500mAC) Should be trasnformless, inductor can be usedI checked VIPER318HD, (https://eds.st.com/console/#/app/acdc/ic_acdc_catalogs/filter/%5B%22buck%22%5D/selected/viper318hd:buck) & designed using ST edsign suite, but max voltage it support is 300Vac with single phaseAnother link i found here:https://www.st.com/resource/en/application_note/cd00074286-threephase-smps-for-low-power-applications-with-viper12a-stmicroelectronics.pdfit makes three phase to single dc output, but still uses transformer.Any workable solution any one know

author: Benta
author_rank: Super Contributor
timestamp: September 10, 2020, 05:30:39 pm
content: Too little information.is neutral available?What's the AC voltage?

author: bdunham7
author_rank: Super Contributor
timestamp: September 10, 2020, 06:02:11 pm
content: Quote from: Vindhyachal.takniki on September 10, 2020, 03:24:51 pmWhat is the deal with 'transformerless'. Why is that a requirement?Is it a requirement that this miniscule amount of power is drawn from all three phases? Does it have to stop producing power if any of the phases fail, or, does it need to produce power if any of the phases are live?Is there any requirement for isolation or efficiency?

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 11, 2020, 04:36:51 am
content: 1. Neutral is available.2. Trans-formless since space is constraint and very low cost3. isolation/efficiency not a concern at the moment4. Each phase 85Vac to 265Vac , freq 50 or 60Hz , since its universal 3 phase ac input.5. power to be drawn from three phase as in page 8 of this :https://www.st.com/resource/en/application_note/cd00074286-threephase-smps-for-low-power-applications-with-viper12a-stmicroelectronics.pdfwhere from 3 phase, single high voltage dc is made.

author: Jeroen3
author_rank: Super Contributor
timestamp: September 11, 2020, 06:36:28 am
content: Using a transformer is a lot easier. They don't have to be big.If isolation is not a requirement, you can skip the opto feedback and wire fb directly.With three phases you are going to need the ratio in the transformer to increase the duty cycle.Like this viper16 board.https://www.st.com/resource/en/data_brief/steval-isa118v1.pdf

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 24, 2020, 02:31:13 pm
content: 1. Have 3 phase ac input with neutral, where each phase voltage goes from, 85V-600Vacrms2. Need output at 5V/500mA3. I was checking it:https://www.st.com/resource/en/application_note/cd00074286-threephase-smps-for-low-power-applications-with-viper12a-stmicroelectronics.pdf%C2%A0its page 8 has this, that is to make dc from 3 phaseI checked ST/s VIPER267K, which has BVDSS of 1050Vdc .But at full 600V each phase, the output dc after diode, can go upto 1100V (simulated on mulltim)4.https://training.ti.com/sites/default/files/docs/Very_high_Voltage_bias_BK_13-Sept_complete.pdfpage 22 shows external fet operation, but again limited to 1200V, very close, so cant use5. Anyone have experience in this low power application where size/size constraints? Any reference design?ST Viper could have used without transformer(its sealed application). but again breakdown voltage too close.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 25, 2020, 05:49:47 am
content: 1. Yes if its single phase 85V-600Vac, I can use VIPER267K from ST (1050V BVDSS).2. If I use like this to make dc from all three phase with neutral what would be peak dc at out? Multisim simulation shows would go to 1100Vdc when each phase at max 600Vac?I think it would be less, no peak dc should remain no?

author: Berni
author_rank: Super Contributor
timestamp: September 25, 2020, 07:30:23 am
content: Good luck getting a 5V/500mA transformerless supply that is actually smaller/lighter than a switchmode transformer based one.For lower power say 5V at 10mA a simple capacitive dropper transformerless supply works great, but making one for 500mA would require a ridiculously large capacitor.Also why 3 phase? Is there a reason why you can't simply connect a single phase supply between L1 and N?

author: Kjelt
author_rank: Super Contributor
timestamp: September 25, 2020, 08:07:18 am
content: Power electronics is not my strong suit but I wonder if your schematic is correct?The Voltage after D1 bridge will be much higher (380VAc rectified) than the D2 bridge (230VAC rectified) still you just connect them?Shouldn't you use a three phase bridge instead ?

author: Berni
author_rank: Super Contributor
timestamp: September 25, 2020, 08:13:31 am
content: Quote from: Kjelt on September 25, 2020, 08:07:18 amThat bridge is the same thing as the schematic in Vindhyachal.taknikis post. Except that neutral also is treated as a "4th phase" so even if you only have 1 phase the output still has power. Tho the output falls to the equivalent of 230VAC rectified(about 320VDC) instead of 400VAC rectified (about 560VDC)

author: Kjelt
author_rank: Super Contributor
timestamp: September 25, 2020, 08:16:48 am
content: Ah yes I now see it , thanks

author: geggi1
author_rank: Frequent Contributor
timestamp: September 25, 2020, 08:37:03 am
content: I think you are overcomplicating things!1. As recomended earlier use phase and nutral. That will give you a lower maximum voltage (voltage divided on the root of 3. Calculate with 1,73). Your voltages will be between 49V-346V.2. Go looking for a embedded 2,5W SMPS with the voltage rating within the range found in pt 1.3. If you dont find something that fits, its time to design something or contact companies like TDK that make embedded powersupplies and ask what they can supply.By the way the peak voltage of a rectified AC voltage is the same as the peak voltage on the DC ( RMS multiplied by the root of two. (1,41))

author: drussell
author_rank: Super Contributor
timestamp: September 25, 2020, 10:20:09 am
content: Why would you take power from all three phases for something that only needs to do 2.5 watts?!If you're not trying to monitor for protection that all three phases are present (which would be a different application than just a small power supply,) why would you not just use any one L-L (or one L-N when a neutral is available?)If it were 5V, 500A, I could understand...

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 25, 2020, 02:57:13 pm
content: 1. Yes easy to use by single phase and neutral.2. But if I use like this? The output dc will go to max 850Vdc?Advantage is here, if one phase get missing/broken, system keeps on running.3. After that dc out, can i use VIPER26K, used ST-edesign suite, and put these inputs:a) Vin: 85V to 600Vacb) Vout: 5Vdc/0.47Amps

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 26, 2020, 02:38:37 pm
content: is the selection of varistor ok? 600Vac is absolute max in system.https://www.digikey.com/product-detail/en/tdk-electronics-inc/B72220S0381K101/495-4437-ND/651267

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 26, 2020, 03:06:14 pm
content: Hi,What is the application for this power supply?In many 3-phase installations the neutral wire is not available. It is 4 wire, 3-phases and ground. There is also 5 wire, 3 phases, neutral and ground.If you do this without a transformer the 5V will have to be referenced to something, where do you want the 5V to be referenced to?Does the power supply have to work if one or more phases are missing?Jay_Diddy_B

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 26, 2020, 03:11:20 pm
content: available are 3 phase and neutral.Here is ST eval board I am refering to.

author: madires
author_rank: Super Contributor
timestamp: September 26, 2020, 03:29:35 pm
content: If something isn't really feasible tell your customer that there's no feasible solution for the given requirements. Experience teaches us that if you botch something together it will haunt you later on. Not worth the effort.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 26, 2020, 03:46:46 pm
content: Quote from: Vindhyachal.takniki on September 25, 2020, 02:57:13 pmIf you are employing the neutral, the maximum AC input voltage will be 600 divided by sqrt(3) or 347 volts, which should considerably ease your requirements.

author: drussell
author_rank: Super Contributor
timestamp: September 26, 2020, 05:29:58 pm
content: Quote from: Jay_Diddy_B on September 26, 2020, 03:06:14 pmYeah, I wish we knew more about what the OP was trying to accomplish.He does say that the neutral is available, and for whatever reason wants it to continue to run even if one or two phases are missing, I guess.... but obviously have no idea why since we have no idea of the application...Quote from: Vindhyachal.takniki on September 25, 2020, 02:57:13 pm

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: September 28, 2020, 02:28:25 pm
content: Hi1. ST edsign software generates design for single phase only so here I selected 85V-600Vac as input which then gets converted to dc first to around 850Vdc2. My case it has 3 phase with neutral, I connected half bridge diode as in last post , it then makes 850Vdc around max also, rest of schematic I took refrence from ST edesign suite.3. I have put these specs in e-design suite from STVin: 85V-600VacVout: 5V/470mAIt generates below diagram: But I have below queries4) The arrow sign marked in red, how is digital low power ground connected here? How will i et 5V at the output then?5) Also do high power ground and low power ground need to be shorted (marked by green box) . Data-sheet of VIPER26K says it should.? (asked ST forum also let see)Attached is my schematic.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: October 18, 2020, 08:10:12 am
content: 1. I have attached schematic and BOM.2. Each phase have range of 85V-600Vacrms , Neutral is present. 600Vacrms is max considering all the worst case scenarios3. Freq: 50/60Hz , both4. Output required: 5V/500mA1. Selection of MOV is 750V ax max. What should be ideal max voltage should be selected? On some places I read 10-25% higher than maximum operating is ok. So 660V or higher should or work.But all I saw that MOV degrade over time, so better to have atleast 20% higher?2. I opened some another brand supply for this. They also placed a combination of C1& C3(two 1uF in series), across U1 also? Is it necessary?3. I want to select two series across U1 :https://www.digikey.com/en/products/detail/vishay-semiconductor-diodes-division/P6KE350A-E3-54/2145264Unidirectional will select. U1 has minimum breakdown voltage of 1050V, so have to protect it in any case.Issue is it this TVS combination have breakdown start from 666V (two in series). Clamping will be 964V.The maximum dc voltage when 600Vacrms is reached, will be 850Vdc across U1. But TVS will start conducting at 666V.But if higher conducting voltage TVS is selected then its clamping is very high, which deafeats the purpose to protect the 1050V switcher.4. Any other protection which can be added so that switcher canbe protected?5. Any other suggestions?

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: October 21, 2020, 01:06:42 pm
content: As in ckt in above,1. The output required is 5V/500mA i.e 2.5Watt2. Consider switch losses, buck convert efficiency, what should be the value of R1,R4,R7,R15 in terms of valueand wattage, I should select to be on safe side?Currently I have selected 33ohms, 4Watt, 5%

author: elekorsi
author_rank: Regular Contributor
timestamp: October 21, 2020, 06:36:47 pm
content: If you have 600V L-N, that means 1040V L-LThis puts you into medium voltage range, which means no more fooling around...I would really like to see an application when there is need for input voltage span from low voltage to medium voltage.