Seeking Feedback Loop Design Advice for ±50V 770W SMPS - Page 1
Forum section: electronics / beginners

author: Bonzahim
author_rank: Newbie
timestamp: January 28, 2025, 09:46:02 am
content: Hi everyone, this is my first post on this forum, so I hope I'm in the right place. If not, feel free to suggest a more appropriate forums!I'm designing a ±50V, 770W SMPS (Switch-Mode Power Supply) that will, hopefully, power a class D audio amplifier. My question is for those experienced in designing and building this type of SMPS: Is the feedback loop (Type II compensator) designed correctly?The component values were selected using TI's Power Stage Designer 5 software, and I have a good phase and gain margin. However, I’m unsure if the feedback loop is effectively stabilizing both the +50V and -50V rails.If it’s not, I’d really appreciate any guidance on how to properly design a feedback loop for a dual-rail SMPS. Also, if you have any articles, books, PDFs, papers, or other resources to recommend, I’d be very grateful!Thanks in advance!

author: mtwieg
author_rank: Frequent Contributor
timestamp: January 28, 2025, 12:46:16 pm
content: I'm not familiar with "TI's Power Manager software" but I doubt it would yield a valid design using an Infineon controller.The IRS27952 is apparently made to control LLC converters, but I don't see any resonant inductor.

author: TimNJ
author_rank: Super Contributor
timestamp: January 28, 2025, 06:38:07 pm
content: I am also not familiar with the IRS27952 controller. Looks a little "old school" as far as resonant controllers go. A controller specifically designed for LLC may be better off, easier to get working. My personal recommendation is TEA19161T, and newer TEA20xxx variants.Check your resonant capacitor arrangement. There are three(?) shown in an unusual looking arrangement. 3x2.2uF sounds way too high for a this power and input voltage and typical Lm and Lr selection. (I'd expect about 100-200nF total.)No PFC? LLC typically does not do well with a wide input voltage range. It needs to operate near a particular Vin:Vout ratio to get the benefits of the topology, and to get consistent performance across the 50/60Hz cycle. With a PFC, you might design the PFC voltage to have about ~20Vpp ripple or so. To get a similar amount of voltage ripple without PFC, you'll probably need like 1000uF/400V, never mind the horrible power factor/harmonic current.What is your knowledge of safety in AC-DC power conversion? There are lots of things to consider, transformer design and PCBA creepage/clearance probably being most important. This sounds like a big beginner project. Please be safe.

author: fourtytwo42
author_rank: Super Contributor
timestamp: January 29, 2025, 11:02:10 am
content: AND if C9 really is polarized it's going to explode the first time you power it up!!

author: jonpaul
author_rank: Super Contributor
timestamp: January 31, 2025, 12:19:53 pm
content: OP: A moment please:First, do you have any experience in design/debug/construction of off line SMPS at 770W?Or your first attempt?How do you propose to build the safety barrier transformer?How did you choose te mentimeded topology, and application for an audio amp class D PSU?Do you have the lab equipment, (eg current probes, scope probles for off line/high voltage) ?Do you have a mains setup for such work, eg mains islation trsf, Varic, etc?See exisitng OEM work on Class D amps, PSU etc ...https://www.hypex.nl/Suggest you learn to walk before you run.AmicalmentJon

author: floobydust
author_rank: Super Contributor
timestamp: January 31, 2025, 03:32:03 pm
content: Welcome to the hard ass forumsI think theTL431will not survive running from the 50V rail. When it's off, it will see more than its 36V spec.What I've seen used in commercial PSU's is a pre-regulator (simple zener and transistor) supplying the TL431/opto circuit power. Or a zener as a shunt reg for say 24V. Or a series zener to drop it down.I think the schematic is missing a GNDD at C11, D5 junction. Secondary rectifiers will need RC snubbers.