Compensation Circuit Type(s) Trend In Today's Server PSUs? - Page 1
Forum section: electronics / projects

author: Trurl
author_rank: Regular Contributor
timestamp: June 30, 2024, 05:40:09 am
content: About a month ago, I'd posted my observations of a HP server PSU (HSTNS-PD43 1400W Gen9), including my own probed schematic of its auxiliary PCB.https://www.eevblog.com/forum/projects/hp-hstns-pd43-psu-hack-feedback-circuit-(partial)/msg5520835/#msg5520835As the post above has been buried in the forum, I post my questions again below;1. What type of feedback compensator is used in this PSU's feedback circuit and where are its core traces/components on the schematic? Perhaps a "type 3" mutant not in textbooks?2. How is the OVP being controlled and where are its core traces/components on the schematic?3. What are the roles of the 2 switching regulators marked "SF7B" (Texas Instruments LMR12010) - 1 on the primary side and 1 on the secondary side?...Thanks...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 30, 2024, 06:35:00 am
content: I don't see an error amp section offhand.It looks like the schematics were captured from PCB layout? So no very readable. I could sit and stare a while, but you might prefer showing what part of the circuit you're actually asking about, what components are involved, and to redraw the section for better readability. (You may even answer your own question in the process!)I will say something general about these sorts of modern supplies; where there's an error amp into an opto, and the opto is more or less direct-driving the primary-side controller, and the controller input is a cascode type pin, and it's probably LLC resonant topology; then, the RC at the error amp probably compensates the opto's dominant pole (which is rather low because of low bias current and the already low bandwidth of the phototransistor) and the controller transfer function is basically type 1; regulation (especially transient response) is still good because the "plant" itself responds quickly (say, within a cycle). This actually makes the output capacitance determined by opto pole, since the controller/plant can't respond any faster than that, and the capacitance takes over at shorter time scales (< ~1ms).Tim

author: Trurl
author_rank: Regular Contributor
timestamp: June 30, 2024, 03:58:02 pm
content: Tim, thank you for your comments.I realize the schematic is quite a "load" (perhaps a bit gross) at first glance. Pardon me. I intentionally made my schematic to be as similar to the actual PCB layout so those that want to check the actual hardware & layout would have an easier time doing so, especially with so many vias/hidden traces.I've attached my entire schematic again below but with "traces of interest" marked inredandblue(red related to voltage feedback, andblue related to OVP feedback). The links branch out but I've tried to keep my markings on the immediate connections that are more obvious.The dotted lines connect vias/hidden traceswhich are not obvious though marked with my own short-hand grid notation.I'd gladly redraw a more "readable" schematic as you'd suggested, if I thought I could, but I'd best not so as to prevent further complications.I'd appreciate any insights based on the initial "traces of interest" I've marked in the attached schematic.Thanks...*Attachment Note: To view schematic in full size and in your preferred image viewer,Click on the link BELOW the small image(thumbnail) of the schematic, and download the full sized schematic - be sure to zoom in for detailed views.(If you just click the small thumbnail image of the schematic below, you won't be able to see any details of the schematic.)