pfc900w - Page 1
Forum section: electronics / projects

author: mirbagheri1122
author_rank: Contributor
timestamp: January 21, 2015, 09:26:19 am
content: helloi`ve builded a power factor correction 900w 385v based on der274 from power integration design example.my problem is blowing pfs729 as i increasing load from 200w to 400w.pls guide

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 21, 2015, 12:02:40 pm
content: Can you explain more what's going on wrong?

author: mirbagheri1122
author_rank: Contributor
timestamp: January 22, 2015, 08:00:24 am
content: HelloThanks for your time,I read your reply.maybe my problem is carbon contaminants under pfs that cause arcing,although I have not connect the new replaced PFC to power yet.I have attached correct schematics PDF for your reference, please note that in der274 there is no snuber cap,But in PI expert software it showed a capacitor should be placed across boost diode in schematics, and I have added a 100pf 1K cap,is that a problem?

author: bktemp
author_rank: Super Contributor
timestamp: January 22, 2015, 08:12:09 am
content: The inductor looks quite small. Are you sure it is not going into saturation at higher current levels and overloading the mosfet?

author: mirbagheri1122
author_rank: Contributor
timestamp: January 22, 2015, 08:48:00 am
content: Thanks,Actually my heat-sink is quite huge,It has these dimensions(15cm X 5cm X 10cm) and my inductor core is sendust 125u from Magnetics inc the part number is 0077254A7, I have attached the datasheet for your reference

author: bktemp
author_rank: Super Contributor
timestamp: January 22, 2015, 09:16:15 am
content: Something is odd:The core has 168nH/T², therefore it needs 109 turns for 2mH. But I can count only around 34 in your picture. This would give around 200uH.109 turns at around 5A peak current (rough estimation for 900W) gives a NI value of 545AT. The graph in the datasheet ends at 400AT. At 545AT the core will be totally saturated.Either way, the core is too small.

author: mirbagheri1122
author_rank: Contributor
timestamp: January 22, 2015, 09:43:40 am
content: Thanks for your reply, Actually if you see the inductor picture again you will see some gray tapes on inner layers, there is 3 layers of wire and the total count is 109 turns, I have added the tape for increasing the insulation between layers

author: mirbagheri1122
author_rank: Contributor
timestamp: January 22, 2015, 09:54:17 am
content: I have cut down the inductor wires to be much lower, But I have not tested the new chip,I'm worried about blowing a new chip again,do you have any Idea?

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 24, 2015, 07:25:17 am
content: Connect your PFC device directly on your Heatsink

author: johansen
author_rank: Super Contributor
timestamp: January 24, 2015, 09:50:55 am
content: several things can be happening. first is that the inductor is probably saturating.second is that the inductance of the output capacitor and the boost diode is too high and the fet is blown by overvoltage.third is that the fet fails due to over current.. probably caused by a saturated inductor.

author: Circlotron
author_rank: Super Contributor
timestamp: January 24, 2015, 12:55:23 pm
content: How long are the earth tracks on the pcb, particularly on the mosfet source lead? Could you post a pic of the pcb layout? At these power levels layout is everything. I spend several months working on a 3.6 kW pfc about 10 years ago (someone else's design, I was just the lab hack) and at full load particularly when you wind the AC input down toward the minimum they can be scary!

author: mirbagheri1122
author_rank: Contributor
timestamp: January 25, 2015, 12:50:56 pm
content: hi thanks for your replybecause of emi i added another trace between source of ic and small low esr caps and connected floated heatsink to source.now my circuit is giving 700 w without overheating but more than 700 is overheating.my final layout is added to this post.

author: mirbagheri1122
author_rank: Contributor
timestamp: January 25, 2015, 12:52:45 pm
content: hi could you send me your 3.6kw design

author: mirbagheri1122
author_rank: Contributor
timestamp: January 26, 2015, 12:03:56 pm
content: hi thanks for your timemy reverse recovery charge is 50 nq and in attention to frequency and voltage give me about 1 w dissipation.cmos of ic is aout 200pf that is nonsignificant.and my heatsink resistant is about 0.8.and my silpad is gray.