Feasibility of a small custom 1W SMT DCDC transformer for qty 1000 - Page 1
Forum section: electronics / projects

author: Psi
author_rank: Super Contributor
timestamp: March 25, 2024, 10:32:44 pm
content: I'm looking at the feasibility of replacing 4x isolated SIP package DCDC bricks with a small custom SMT DCDC transformer.It would have 5 isolated windings, 1 in 4 out.Just wondering how feasibility a custom transformer would be for a low volume product. We sell like 300 a year. but could maybe purchase 1000 transformers at a time. I know places like coilcraft can make custom transformers to order, but is that cost effective for this volume?What sort of price would you expect for a small SMT mount 5 winding 1W (total) power transformer. If I ordered say 1000?The current DCDC bricks cost $1.5 each so we're spending $6 on them.Making the design simpler and more SMT less TH is an advantage, so having just one transformer instead of 4 SIP modules is an advantage even if it costs the same. Probably not worth it if it costs more.Thanks

author: thm_w
author_rank: Super Contributor
timestamp: March 25, 2024, 11:40:36 pm
content: Get your rough specs together and ask for a few quotes on alibaba.https://www.alibaba.com/product-detail/ee10-smd-inductor-flyback-transformer-smps_1600529170703.htmlhttps://www.coilcraft.com/de-de/products/transformers/dc-dc-transformer-worksheet/I'm guessing coilcraft would be in the $3-8 range.China <$2.What is isolation voltage between secondaries?Are you ok with possibly more losses if loads are imbalanced?4 out means 8 wires which might require a larger core or maybe multiple small units?

author: jbb
author_rank: Super Contributor
timestamp: March 25, 2024, 11:42:05 pm
content: Haven’t used them in a long time, but I thinkhttps://www.marquemagnetics.com/is OK with moderate order quantities.Magnetics manufacturers often have access to quite a large catalog of components like cores and bobbins and triple insulated wire that aren’t easily available in small quantities or from the usual distributors.So I suggest you give them a briefing of what you want to accomplish (volume, operating freq, mag inductance, turns ratios, required isolation etc.) and see what they come back with instead of ‘please fabricate this exact design.’

author: Psi
author_rank: Super Contributor
timestamp: March 25, 2024, 11:52:47 pm
content: Quote from: jbb on March 25, 2024, 11:42:05 pm

author: tszaboo
author_rank: Super Contributor
timestamp: March 26, 2024, 12:51:29 am
content: https://www.we-online.com/en/components/products/pbs/cm/pcdI haven't used them for transformers yet and I don't know how good is the support outside the EU. Here its really good.

author: temperance
author_rank: Super Contributor
timestamp: March 26, 2024, 03:10:46 am
content: A Pulse P0585NL might work.

author: Psi
author_rank: Super Contributor
timestamp: March 26, 2024, 11:37:57 am
content: Quote from: temperance on March 26, 2024, 03:10:46 amYeah, that's the sort of thing I need, but could probably be lower power. Also would need 1:2:2:2:2 winding ratio so i can do 5V to 12/12/12/12

author: temperance
author_rank: Super Contributor
timestamp: March 26, 2024, 10:51:29 pm
content: A planar transformer will be a low cost solution. A small multi layer PCB will do the job.Cores with the required size: less than €0.25 per piece, two required. Cores without air gaps are easy to obtain.Core clamp: around the same price tag.25 x 25 mm PCB, 6 layers: €0.55.Or the same size with 8 layers : €0.7Some pin headers (see next comment) to mount the transformer: €0.3Mounting costs: unknown. But less work in comparison to the original solution if you ignore the driver and rectifiers. If you really want, you can make the transformer PCB into a surface mount component if it can fit onto a standard tray for TQFP's or something. (like a stamp with castellated sides)Last but not least: some fun to implement.It would have been nice if you stated the input/output voltage requirement. I think must people here where under the assumption that Vin=Vout.

author: jbb
author_rank: Super Contributor
timestamp: March 26, 2024, 11:04:57 pm
content: If you’re making supplies for isolated gate drivers, then you’ll need to carefully consider winding-to-winding capacitance.

author: Psi
author_rank: Super Contributor
timestamp: March 27, 2024, 12:44:27 pm
content: Quote from: temperance on March 26, 2024, 10:51:29 pmIn this case 5V in and multiple 12V out, but it is somewhat flexible. Could be 9V in and 10V out.But input has to be under 12V with some room for regulation and outputs needs to be 8-15VQuote from: jbb on March 26, 2024, 11:04:57 pmYes, but only switching DC so na,

author: Jefferson.Lee
author_rank: Newbie
timestamp: March 28, 2024, 01:43:49 am
content: Quote from: Psi on March 27, 2024, 12:44:27 pmCan you tell us about your detailed specifications, such as wire size, number of turns, core specification ER or EE and additional...I might be able to help you in China.

author: Psi
author_rank: Super Contributor
timestamp: March 28, 2024, 08:43:55 am
content: Quote from: Jefferson.Lee on March 28, 2024, 01:43:49 amThanks for the offer, I don't have any spec yet, or looked into creating one.I was just curious if it made sense to go down that path for lowish qty.

author: jonpaul
author_rank: Super Contributor
timestamp: March 28, 2024, 09:14:08 am
content: Planar cores are very fragile and costly. Long lead time.Suggest find a stock transformer (Coilcraft, Pulse Engineering, Halo, etc. ) and adapt your cktIf the app is to supply floating H br gate drivers, then both C-P-S and voltage rating between wdg are importantj

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 28, 2024, 09:53:59 am
content: Quote from: jonpaul on March 28, 2024, 09:14:08 amQuite a few in stock at Digikey

author: temperance
author_rank: Super Contributor
timestamp: March 28, 2024, 12:53:06 pm
content: QuoteI can obtain planar cores without an air gap in different sizes in >2K quantities for less than 30 cent @ Mouser. Here in the EU I can obtain the required size (oversized actually to make life easier) for less than 20 cent.Fragile: just like any other ferrite core.

author: temperance
author_rank: Super Contributor
timestamp: March 28, 2024, 03:50:49 pm
content: @ jonpaulDear Jonpaul, you often comment on various topics providing your opinion but you rarely provide useful information. If you read what has been been written, you will see that an off the shelf solution is probably not available and probably why the OP posted the question here.

author: voltsandjolts
author_rank: Unknown
timestamp: March 28, 2024, 05:36:45 pm
content: Quote from: Psi on March 27, 2024, 12:44:27 pmPhotovoltaic drive or SSR too slow?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 28, 2024, 06:09:04 pm
content: Quote from: voltsandjolts on March 28, 2024, 05:36:45 pmSkyworks SI8751 is another very neat solution for isolated gate drive - faster than a PV isolator

author: thm_w
author_rank: Super Contributor
timestamp: March 28, 2024, 10:33:32 pm
content: OP meant they are switching DC, eg DC-DC. 5V to 12V.Nothing to do with gate driving.

author: Psi
author_rank: Super Contributor
timestamp: March 30, 2024, 06:04:03 am
content: Quote from: mikeselectricstuff on March 28, 2024, 06:09:04 pmIs the Skyworks SI8751 actually useful for fast gate switching? I'm switching <200A split across 4 fets (DC load switch)Looking at the datasheet, GATE On Impedance is 162k and output voltage 10V.Am I correct in assuming that using a SI8751 is equivalent to applying 10V to a FET gate through a 162k resistor ?The price of the chip wouldn't save me much money but it would make things much simpler, which would be useful for other reasons.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 30, 2024, 08:29:45 am
content: Not super fast - I use it for mains trailing-edge dimming of SOT-223 MOSFETS in a SSR configuration, for which it works brilliantly. For slow DC switching maybe it could be combined with a capacitor & voltage detector to get faster switching at the expense of latency

author: voltsandjolts
author_rank: Unknown
timestamp: March 30, 2024, 10:32:13 am
content: Quote from: thm_w on March 28, 2024, 10:33:32 pmI think the OP is looking for isolated DC-DC converters, for the purpose of making four floating power supplies for gate driving four high-power FETs at a low frequency (switching a DC 200A load). So discussion of other methods of gate driving is valid.

author: Psi
author_rank: Super Contributor
timestamp: March 31, 2024, 11:42:53 am
content: Quote from: voltsandjolts on March 30, 2024, 10:32:13 amI have 4 DCDC modules powering 4 opto-fet gate drivers atm. Works great, just not very compact or elegant or cheap. Also working on a discrete component non-isolated solution with one 12-24V DCDC. But always on the lookout for a new solution.

author: voltsandjolts
author_rank: Unknown
timestamp: March 31, 2024, 03:12:59 pm
content: How much do your DCDC converters cost?I see Mornsun have +15V/-9V DCDCs for IGBT gate drives at around GBP3.50https://www.digikey.co.uk/en/products/detail/mornsun-america-llc/QA153-1509R3/16643920How about reducing DCDC count from 4 to 1, by having just one 200A IGBT?https://www.digikey.co.uk/en/products/detail/infineon-technologies/IKQB200N75CP2AKSA1/17399196and a good gate driver...https://www.digikey.co.uk/en/products/detail/infineon-technologies/1ED3121MC12HXUMA1/14311597

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: March 31, 2024, 09:50:32 pm
content: Quote from: voltsandjolts on March 31, 2024, 03:12:59 pmPlenty of similar isolated DC-DCs at LCSC for under a dollar :https://www.lcsc.com/products/Power-Modules_634.html

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 31, 2024, 10:29:09 pm
content: Quote from: Psi on March 30, 2024, 06:04:03 amDepends what you mean by fastThey spec 85us typ to 90% (9.72V into 100pF)What is the gate capacitance of the FETS you use now ? Do you need 10V gate drive ?What isolation do you need from control side, and between units ?I see TI have a nifty looking UCC33420 PREVIEW 1ku $1.300 in a 5x4x1mm SMD package.5V/5V 1.5W 3kVrms isolated DC-DC module with integrated transformer- not yet spec'd in higher voltages, tho they do older/larger models in higher voltages.

author: Psi
author_rank: Super Contributor
timestamp: April 01, 2024, 04:15:51 am
content: Quote from: mikeselectricstuff on March 31, 2024, 09:50:32 pmYou raise a good point. Those are cheaper than what i'm paying.However one of the reasons I want to replace these is they're SIP modules and I'm not entirely happy about the way they mount to the PCB in a line. They can wobble from side to side if pushed a bit.

author: Psi
author_rank: Super Contributor
timestamp: April 01, 2024, 04:21:13 am
content: Quote from: PCB.Wiz on March 31, 2024, 10:29:09 pmYes, need 10V gate charge for 1mR RdsEverything is just 12V so don't need any serious isolation at all.There are 4 fets in parallel, so 28nFTPH1R204PL1Input capacitance 7200pFTotal gate charge = 74 nC (typ.)Gate-source charge = 16 nCGate-drain charge = 17 nCGate switch charge = 17 nCOutput charge =56 nC

author: voltsandjolts
author_rank: Unknown
timestamp: April 01, 2024, 09:33:59 am
content: Quote from: mikeselectricstuff on March 31, 2024, 09:50:32 pmSure, lots of jellybean DCDC for $1 but I was specifically looking for isolated with reinforced isolation, high CMTI and low coupling capacitance from one of the few cheap chinese DCDC brands that I have moderate trust in. That's not a $1 part. But seems like jellybean might be OK here, given low voltage.

author: Wolfram
author_rank: Frequent Contributor
timestamp: April 01, 2024, 06:04:02 pm
content: Quote from: mikeselectricstuff on March 31, 2024, 09:50:32 pmThey do, but not with the isolation voltage (5000 VAC), isolation capacitance (3.5 pF) or characterized CMTI behavior (200 V/ns) of the QAxx3 series. Practically, it's not going to matter much if this application doesn't switch super fast, but even plain superjunction FETs at higher voltage can make enough dV/dt to cause trouble with improperly selected DC/DCs. 200 A suggests a lower voltage application where dV/dt won't be a worry, but it's something to keep in mind.Note that LCSC list a range of converters with part numbers and specs identical to the Mornsun QA-series parts, and these are not meeting the specification at all. I tore down units from all the brands they list, and they were all done with plain magnet wire overwind and 30-ish pF isolation capacitance, compared to the double TIW and 3.5 pF of the original. Parts listed at Mornsun on LCSC should be the real deal.