Interesting SMPS design - Page 1
Forum section: electronics / general

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 27, 2014, 06:32:45 pm
content: Just found this SMPS that was in use powering a PBX console which we no longer use and of course opened it. At first I thought that there was something missing:but then realised that it used something I think I have never seen before:They integrated the transformer windings into the PCB and clamped a ferrite core around it:It looks like the primary winding is on one of the inner layers:This is the ferrite 'core':The thing uses a TOP204 SMPS controller to produce 48V at about 500 mA.

author: Bored@Work
author_rank: Super Contributor
timestamp: June 27, 2014, 07:34:58 pm
content: The thing is called a planar transformer. You get them as a separate component or you etch them on the PCB.

author: rob77
author_rank: Super Contributor
timestamp: June 27, 2014, 08:28:48 pm
content: that's crazy ! how far will the cost reduction go ?3 turns etched on PCB for primary... what is the switching frequency ? half a gigaherthz ?

author: c4757p
author_rank: Super Contributor
timestamp: June 27, 2014, 08:54:58 pm
content: Quote from: rob77 on June 27, 2014, 08:28:48 pmYou see excessive cost reduction, I see a really cool PCB trickQuote from: rob77 on June 27, 2014, 08:28:48 pmTOP204 datasheet says 100 kHz, 0.0001 GHz

author: tautech
author_rank: Super Contributor
timestamp: June 27, 2014, 09:18:31 pm
content: Quote+1It's not about frequency but switch "on time"

author: AmmoJammo
author_rank: Frequent Contributor
timestamp: June 27, 2014, 09:33:53 pm
content: I've seen them used for inductors, but never transformers... I wonder how far the limits could be pushed.... 3mm thick board with 8 layers? hmm...

author: SeanB
author_rank: Super Contributor
timestamp: June 27, 2014, 10:09:25 pm
content: 24 layer board, with buried vias and around 200W of power being transferred through the transformer. Thickest part was the mains filter capacitors, which were in slots milled in the board. If you are going to mill a slot for the ferrite more slots to take the radial capacitors lying on their sides is not much incremental cost.Not a common design, but doable if you get the right magnetics to fit the board. As well you have a very repeatable winding, and a very high standoff voltage between primary and secondary is possible with low cost.

author: lewis
author_rank: Frequent Contributor
timestamp: June 27, 2014, 11:07:38 pm
content: Quote from: AmmoJammo on June 27, 2014, 09:33:53 pmHow about 40kW in 1U rackspace?http://www.pknc.com/3phase/3phase_PSU.pdf

author: rob77
author_rank: Super Contributor
timestamp: June 27, 2014, 11:44:21 pm
content: Quote from: tautech on June 27, 2014, 09:18:31 pmactually it's about currentwith 3 turns it implies very short "on time" => short "on time" implies higher frequency (because no-one would design a smps with 1% duty cycle at nominal load , right ?)so it's a matter of point-of-view whether it's about current, "on time" or frequencybtw... the "half a gigahertz" was a joke

author: tautech
author_rank: Super Contributor
timestamp: June 28, 2014, 12:08:00 am
content: Quote from: rob77 on June 27, 2014, 11:44:21 pmI should have added "so much" as in: "It's not so much about frequency but switch "on time""Yes current, not for current's sake, but the transformer "Core Saturation" that is related to all these things.

author: Someone
author_rank: Super Contributor
timestamp: June 28, 2014, 12:17:47 am
content: Quote from: SeanB on June 27, 2014, 10:09:25 pmBuried vias are usually needed to get the extreme insulation levels (10kV becomes easy), though some simpler designs can fit on 4 layer boards with regular through vias. Either way its extremely cheap especially for low volume products, but the design process is relatively drawn out.Flyback, forward, and tapped inductor (autotransformer) boost topologies really benefit from the flexibility of winding your own transformer. Lots of the on board DC-DC convertors use these to reduce cost and volume of the product.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 28, 2014, 05:02:02 am
content: Used them before -- not the best performance in terms of footprint area, or copper cross section (the winding factor is < 0.2 even for many layers), nor is it easy to get very many turns on. That said, because the turns are few and close together, and easily interleaved, the bandwidth is pretty good. You can push the current density a bit more because of the small size and relatively large surface area. The profile is, of course, extremely low.Cores are available from usual distributors, e.g. Elna Magnetics, Adams Magnetic. Neat thing about them: the plate-and-E construction uses a flat plate, which is just a flat plate (if you get the kind without the retaining clip notches). Very handy for general purpose shielding!Tim

author: bktemp
author_rank: Super Contributor
timestamp: June 28, 2014, 05:20:38 am
content: This is the local power supply from a microwave antenna (37GHz for digital data transmission). It is powered using -48V via the single rf cable.The two larger cores seem to be the transformers the smaller ones inductors. When I first saw this I though, 2 turns for 48V input voltage? It must be operating somewhere in the MHz range. But no, it works at only 193kHz. The waveforms look like a normal power supply, no crazy short duty cycles or something lik this. I have not measured the inductance but I expect it to be much higher than initially thought.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 28, 2014, 05:28:38 am
content: The turns required aren't so many because the cross sectional area is higher. Inductance is determined by gap; standard values are usually available.Tim

author: firewalker
author_rank: Super Contributor
timestamp: June 28, 2014, 07:37:52 am
content: Any application (or a calculator) note for designing pcbs for those cores?Alexander.

author: Dave
author_rank: Super Contributor
timestamp: June 28, 2014, 03:37:54 pm
content: Quote from: firewalker on June 28, 2014, 07:37:52 amHere you go:Design of planar power transformersDesigning planar magnetics

author: firewalker
author_rank: Super Contributor
timestamp: June 28, 2014, 06:14:00 pm
content: Thanks you.Alexander.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: June 29, 2014, 02:44:15 pm
content: very common in high power high density DC/DC converter modules, less so in SMPS's