Transformer and PFC coil design - Page 1
Forum section: electronics / general

author: Daniyal
author_rank: Contributor
timestamp: May 24, 2013, 02:31:00 pm
content: Ok, I'll have to start this with a mini rant; basically I'm working as an internship student at a big company in Germany (but I'm from Australia) and right now I'm helping the next project which is a 90W power supply which has PFC on it, so far my task started with doing the calculation for the PFC chock then after that I'll need to select a core for this chock (this chock needs to be in a transformer form because we using the secondary to sense the magnetization on the primary side). Soon as I start looking into this design process....there are so many factors needs to be considered like the core material and the core type and also need to keep an eye on the saturation level and so on.... after the PFC choke I also need to look into the transformer for the flyback part....so I'm kind of lost don't really know where to start.... maybe someone on the forum have some experience with this type of work it will be great if someone points me to the right direction, or even recommend some material that I should read to get better understanding on this electromagnetic stuff....

author: envisionelec
author_rank: Frequent Contributor
timestamp: May 25, 2013, 02:49:04 am
content: I'm surprised that they are letting you design an advanced SMPS as an intern. Are they serious to think you will be successful? I guess that fire and smoke will help you learn. Simulation tools are very good, especially the ExcellentIT tool.There is a LOT of information on the web. Here are some good ones to get you started:http://www.smps.comhttp://www.poweresim.com/http://www.diyaudio.com/forums/power-supplies/209221-smps-transformer-design-tool-ver-4000-a.htmlhttp://www.onsemi.com/pub_link/Collateral/SMPSRM-D.PDFhttp://ww1.microchip.com/downloads/en/DeviceDoc/dsPICSMPS%20AC_DC%20Users%20Guide.pdfBooks:Switching Power Supply Design by Abraham I. PressmanPractical Switching Power Supply Design by Marty Brown

author: envisionelec
author_rank: Frequent Contributor
timestamp: May 25, 2013, 02:58:51 am
content: Also, do not expect to be successful the first time. The system cannot be run open loop (unless that is your design), so you must adhere to some rules of thumb regarding control loop theory until you have familiarized yourself with the design.It will be helpful to work with a transformer manufacturer to build your magnetics. You can spend the entire project learning how to wind a working transformer, so I do not recommend DIY unless the design is very simple.I would do current sensing outside the transformer in case you want to change something. Only after it's proven would you strap the primary for current sense.

author: Daniyal
author_rank: Contributor
timestamp: May 25, 2013, 06:30:35 pm
content: Hey envisionelec, thanks for the information I'll definitely go through those material, let's hope I won't burn the building down with my power supply (I have already seen quite a lot of smoke off the board since I started working here) .. And I'll keep posting the progress I guess.

author: Daniyal
author_rank: Contributor
timestamp: May 25, 2013, 06:33:21 pm
content: And the system is not open loop, the main chip we using for the flyback part of the circuit handles the regulation loop so I think it should be ok.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 25, 2013, 07:56:32 pm
content: I managed to build a 500W grid tie inverter (part of my senior design project) without blowing a single MOSFET. It did, however, go bang when a via blew like a fuse and started arcing (thanks to the now infamous Texas A&M PCB services), but even that did no real damage. (It did scare away a team member, so I had to explain to her that it was OK.)I suggest building your design in pieces. You don't need PFC for the design to work (even though it might be part of the final requirements) so use a non PFC rectifier with current limiter or a bench power supply for testing. Once the main converter works, build up and test the PFC.

author: envisionelec
author_rank: Frequent Contributor
timestamp: May 26, 2013, 12:32:28 am
content: Quote from: NiHaoMike on May 25, 2013, 07:56:32 pmI want to know why the Aggies' PCB service isinfamous.Good stories?

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 26, 2013, 01:55:29 am
content: Let me just say that every PCB I got back from them (and all the ones my classmates got as well) needed quite a bit of work before they were anywhere near "ready to solder on". The via plating process is very flaky and it's very uncommon to get a board where all the vias work. Also, the etching is done by first painting on some sort of lacquer or paint, using a laser cutter to blast away parts of the lacquer, and then chemically etching as is usually done. Sometimes, that leaves behind wisps of copper that cause short circuits. (I checked my board very carefully for those as it's high voltage.)I already had the inverter built up at that point and I was trying to troubleshoot an instability problem. I put in a PIC that had a newer copy of the firmware and then I tried to start it up with a bench supply like I normally did. There was a bang (sounded like a firecracker) along with a flash of light before the auxiliary switcher even started. (Things were getting a little hectic when my friend Sophie ran away screaming!) I was a little confused when nothing seemed to be damaged, so I decided to try starting it up again to see what was going on. The flash seemed to come from under one of the DC bus caps (220uF, 450V each) so I discharged the caps and then proceeded to desolder them to check for conductive material underneath. When I removed one of the caps, there was a coating of vaporized copper all over the bottom. One of the vias was just barely connected, causing it blow like a fuse during the startup inrush and start arcing. (And blowing the other 3 vias in the path in the process.) I cleaned it up, put it back, and soldered jumpers to bypass the blown vias.Here's a picture of the finished unit, with a (7") tablet for size reference.BTW, I should mention that the smallest pitch Texas A&M could do was SOIC, the board is only double sided, and there is no solder mask. The power electronics engineers have it pretty easy. Those doing modern digital design with FPGAs, CPLDs, or high end microcontrollers are out of luck!