Understanding power supply compensation... - Page 1
Forum section: electronics / projects

author: Hiemal
author_rank: Regular Contributor
timestamp: September 15, 2022, 03:15:58 am
content: Hi All;So, a project of mine has been to try and figure out how to make/design a regulated HV supply. Current thoughts/specs areVIN 30V to 40VVOUT 10kV, fed to a CW to multiply up to 50kV. Adjustable from 30 to 50kV out.50W max output.Since the output is HV, any supply type relying on an output inductor is kind of disqualified.I'm leaning towards a current fed push pull converter. But, the main problem I'm running into is figuring out how to compensate the darn thing.Having a HV divider, composed of a 5G ohm resistor(multiple smaller ones in series) and a 330K lower. So, @ 50kV, divider outputs 3.3V.The controller handling all this will be a LM5041, a cascaded PWM controller. They don't really discuss compensation in the datasheet, nor can I locate/find any literature on how compensation works for this topology... on top of, trying to figure out how putting a CW in the path of everything affects compensation as well. I imagine it'll make it a lot slower, but I haven't the slightest idea how to or where to look for help on this.Anyone have anything that might help me understand better? I appreciate it.

author: strawberry
author_rank: Super Contributor
timestamp: September 15, 2022, 07:12:29 am
content: HV divider to get ~0.1% precisionadditional sense windingor sense primary winding. 2 diode rectifier (red dots)

author: Marco
author_rank: Super Contributor
timestamp: September 15, 2022, 07:32:43 am
content: Simple, no compensation. You use a TL431 as a comparator with or without an optocoupler depending on isolation. Feedback is high or low, problem solved.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 15, 2022, 04:59:30 pm
content: I'm guessing that you want critical damping for your compensation. No wild over or undershoot.Check out these papers from TI, slup340.pdf and ADs an149a.pdf . Check out LTpowerCAD it has the comepsation tools built in.Overshoot can be a very (very) dangerous thing in an HV design. Dead components, burning DUT, wrecked dilithium crystals or worse.Hopefully, you wont have enough ouput current to drive an opto direct. Off the shelf optos only keep your LV side safe up to 5kV or so. You can brew your own of course, The required clearance is going to be 100mm or more so. A straight fibre coupling is ideal. An LED, a phototransistor some fibre a bit of heatshrink. Can you get iso power from the HV side for a fb buffer, an extra winding?Maybe its better to just add a battery. Me, I'd run the whole shebang from batteries. Put it inside a thick plastic box with an insulating divide between LV and HV compartments and equip the beast with IR control .I'm sure you know already that 50kV @ 1mA DC is fatal fist time around. If the bottom of your divider chain fails and the fb is not isolated you might be up shit creak unless all encolsures, panel switches, knobs etc can protect you from the HV. Use plastic extension control rods etc. HV connectors? Corona any one?

author: David Hess
author_rank: Super Contributor
timestamp: September 16, 2022, 03:45:17 am
content: Jim Williams discusses frequency compensation of similar circuits under the section "Feedback Loop Stability Issues" on page 55 ofLinear Technology application note 65 - A Fourth Generation of LCD Backlight Technology.