Inverting AC - Page 1
Forum section: electronics / beginners

author: TheDood
author_rank: Regular Contributor
timestamp: February 18, 2020, 08:25:24 pm
content: I'm curious if one could run 60Hz mains through an inverter cct before a traditional capacitive dropper, and what are the best types of switches to accomplish this considering switching speed, RDSon, and general applicability with inverting voltages? (Triac, FETs, transistors, ect?)Curious the power factor on a capacitive dropper when switched at 20kHz+? Would the inverting negate the "lead"? Switching would reduce necessary capacitor size, and if you stepped up voltage prior to inverting (optional), you could operate loads requiring higher forward voltages with less down time? Adjust inverting Hz to manage constant current?EDIT:You could correct lead with a smaller lagging inductor?

author: Zero999
author_rank: Super Contributor
timestamp: February 18, 2020, 09:58:25 pm
content: Just one question: why?There's no reason I can think of for doing that. If you're going to do that, you might as well use a transformer, which also provides isolation and will be much smaller, than a 60Hz transformer, given the same power level. In short, just use a switched mode power supply.

author: TheDood
author_rank: Regular Contributor
timestamp: February 19, 2020, 07:50:29 am
content: Quote from: Zero999 on February 18, 2020, 09:58:25 pmThis is what I was originally thinking..."If I'm boosting to correct PF, then inverting, then rectifying, then bucking, I figured I could eliminate some of the losses across components by reducing some. I figured if I started out inverting, and my series cap esr was low that my only major losses should come from switching and rectifying, this seemed like it might reduce components, reduce cost of components, provide decent PF, while essentially only having to control the switching Hz. That seemed less complicated than PFC control loops ect."Maybe I need to rethink.Dual boost bridgeless PFC + inverter + parallel capacitive droppersAdjust boost inductor PWM based on bulk capacitor voltage. Adjust inverter Hz to manage the loads' currents.^^^Will that work in theory? Should I be looking to replace (capacitive dropper + inverter) for HF step down transformer, then just switch the primary side of the step down xfmr being fed by bulk cap to manage current of the load? The bulk cap V should be pretty constant as I'm varying boost PWM to create a predefined voltage desired at bulk cap? Goal is efficiency. Any advice welcome. If I skip inverter then I don't have to worry about my top side switches, I didn't know which were best, PFETS or triacs, or transistors or what. If you want to give your opinion on what you'd prefer for an application like that, that'd be awesome. The more I can pick up the better.I know I can buy a PFC driver IC, but I'm trying to understand if I understand. I want to use arduino to monitor line V and at ZC detect bulk cap V and then adjust boost PWM to refill bulk cap based on the ZC measurement. Maybe implement a PID control for the PWM so that it incorporates previous bulk cap V measurements as well as instaneous bulk cap V measurement at ZC. I'm not too familiar with control loops and terminology. Or PID control either, but think I can implement with a little effort. <--does this sound plausible and efficient? Any tips? Tricks? I'd work some safety into it too, some sort of current limit/shutoff, resetable, amoung other things.I'm intending to run multiple loads off the bulk boost cap. So more than 1 xfmr would be drawing from the bulk boost cap. Or more than 1 capacitive dropper would be pulling off bulk boost cap.

author: Brumby
author_rank: Unknown
timestamp: February 19, 2020, 08:37:45 am
content: This is sounding like a Rube Goldberg approach to an undefined objective.As this is sounding like a power supply situation, the input would seem to be mains, but just exactly what is the target? If you're not comfortable with giving us details of the load, let us know things like: voltage, current, duty cycle, ripple or any other useful information.

author: TheDood
author_rank: Regular Contributor
timestamp: February 20, 2020, 12:42:47 am
content: Quote from: Brumby on February 19, 2020, 08:37:45 amYes exactly. I'm trying to build a very efficient, multiple parallel ouputs, PS. Trying for 97%+ efficiency through an operating range of 70W to 280W.Parallel outputs need to be capable of 100V DC and amperage of 1A. Number of parallel loads or used outputs will vary, but the power demand will never exceed 280W.

author: Brumby
author_rank: Unknown
timestamp: February 20, 2020, 04:49:15 am
content: Quote from: TheDood on February 20, 2020, 12:42:47 amA bold objective.Not something I could be particularly helpful in achieving, I'm afraid.