Two Boost PFCs in parallel - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: September 01, 2022, 07:42:55 pm
content: Hi,The attached (LTspice and jpeg schem) shows two 1kW Boost PFCs in parallel, using two standard Average current mode control chips (LT1248). [AKA close cousins, UC3854, L4981B, etc etc]One plays Master, other is slave. The slave copys the voltage on the Master’s MOUT pin, to its own MOUT pin….thats how they work in parallel.However, MOUT pin has a current source in it, so an opamp buffer cannot simply be fed into it. Instead, the attached labyrinth of circuitry must be used……the slave is “hacked” so that its MOUT current source is outputting at maximum current…..then an opamp pulls down on the MOUT pin through a protection diode…so as to make the MOUT pin voltage the same as the Masters.Can you see a lower component count solution?Do you agree an opamp buffer cannot be simply connected to the MOUT pin?LT1248 datasheethttps://www.analog.com/media/en/technical-documentation/data-sheets/1248fd.pdf(My apologies in advance....It was considered this application would be popular enough to warrant a post...whilst not being "rocket science" enough to be worth keeping secret. -Just general SMPS content...the type that most countries have already outsourced due to its triviality.)

author: temperance
author_rank: Super Contributor
timestamp: September 04, 2022, 12:22:36 am
content: Are pursuing a different route after your bad experience with the UCC...?I have a TI evaluation board with the UCC in question which works flawless.

author: Faringdon
author_rank: Super Contributor
timestamp: September 04, 2022, 12:32:25 pm
content: Thanks, good point!....yes, i am a "hobbyist"...."not a genuine company".....so when i order ESD sensitive chips like UCC28070A, i am highly likely to get the dross thats fallen out of the tube and been handled non-ESD precautionatively.......so this type of PFC paralleling that i present above is mega-important.Its like a restaurant, where the non-corporate customer gets given the steak that fell on the floor in the corridor outside the toilet....but the dross skimmed off it and then served up....with microbes and minute faecal residue upon it!I ordered 3 UCC28070A recently...one had legs broken!.....other two were ESD damaged.One was shoving its vcc out of the synch pin....the other was batting about, and you can see my post on ti.com forum where ti.com confiirm that my chip is ESD dead...(i sent them details of ESD damage test jig).Incidentally, the chips came in see-thru silvered sachets, with "made in Malaysia" written on them....does ti.com get UCC28070A's made in Malaysia?UCC28070A, the only dual boost AvCM PFC chip in the world, may have problems...so a way is needed to do it with separate "single PFC controller" chipshttps://www.eevblog.com/forum/renewable-energy/ucc28070-interleaved-dual-boost-pfc-controller/

author: langwadt
author_rank: Super Contributor
timestamp: September 04, 2022, 03:18:35 pm
content: let me guess, you buy your components from the very classy ebay store happybuylucky123 for a dollar with free shipping

author: temperance
author_rank: Super Contributor
timestamp: September 04, 2022, 05:56:09 pm
content: Can you as a hobbyist order stuff from RS because that's an RS package? For DIL IC's, RS uses some kind of ESD safe plastic holders.Just complain to RS and you will get some new ones shipped to you.And if you would care to search instead of complaining:Texas Instruments Malaysia Sdn. Bhd. manufactures semiconductor devices. The Company offers power management semiconductors, amplifiers, data converters, switches, processors, and sensors. Texas Instruments serves customers worldwide.

author: Faringdon
author_rank: Super Contributor
timestamp: October 22, 2022, 06:16:48 pm
content: Hi,Here is an improvement on the 2 paralleled Average current mode Boost PFCs.The attached (LTspice and jpeg) is 2 paralleled Boost PFCs. Each is grounded to a slightly different potential, as is often the case in adjacent high current SMPSs.Anyway, in order to be paralleled, one is Master, and the other is Slave. The Slave has its Current Error Amplifier input as being the same as that of the Master. Obviously each PFC sits on a slightly different ground, so a Diff Amp is needed to pass the Masters Current Error Amplifier input voltage to the Slave.The attached shows it being done. Can you think of a lower component count way of doing this?(As you may note, the simulation has been made “quicker-to-run” by forcing a fixed voltage into the Voltage Error Amplifier’s input. In the actual simulation, each PFC would have a feedback divider from the Vout, as normal.)

author: Faringdon
author_rank: Super Contributor
timestamp: October 30, 2022, 01:26:53 pm
content: Are there any thoughts on the attached method of paralleling 2 AvCM Boost PFCs?The attached shows the MOUT pin of the master simply being "copied over" to the slave.The method avoids directly connecting an opamp output to the slave's MOUT pin, which would damge the MOUT pin.....also, cctry is added to stop MOUT of slave ever being driven negatove w.r.t its local ground.Also, GND resistors are added to imitate strays.(The two boosters may be sat on different local gnd.)Nobody has ever disagreed with the attached method, which is somewhat encouraging , since the great thing about EEVBLOG, is that you get smashed down pretty quick if you put something stupid up.