Mains DC-DC converter using NE555s. Will it work? - Page 1
Forum section: electronics / beginners

author: hanzdolo30@gmail.com
author_rank: Contributor
timestamp: April 22, 2017, 07:58:01 pm
content: I'm very new to EE and in order to learn, I took on a pretty difficult project for someone with my knowledge. I decided to use LTSpice and I've gone as far as designing a small flyback and PFC circuit. The wave forms look good I'm just wondering if it'll work if i built it?

author: Zero999
author_rank: Super Contributor
timestamp: April 22, 2017, 10:21:08 pm
content: Can you please post a schematic and or the .asc file?Oh and how did that PNG file end up so large? I converted it to 8-bit optimised palette and it's now a fifth of the size, with no noticeable degradation.

author: hanzdolo30@gmail.com
author_rank: Contributor
timestamp: April 24, 2017, 09:53:07 am
content: I made it in adobe fireworks, it was in the native format, I should have probably flattened first.This is actually a new schematic, I've changed a lot since that output. I'm a super newbee just playing around with circuits, so you'll probably see some errors in my schematic. Please point them out and assist me in any way possible. Thank you.

author: DmitryL
author_rank: Regular Contributor
timestamp: April 24, 2017, 10:29:11 am
content: Quote from: hanzdolo30@gmail.com on April 24, 2017, 09:53:07 amI think if you break your schematics further down to single components level and mix them a bit better on a picture this would help even more...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 24, 2017, 10:39:17 am
content: Your grasp of transistors, biasing, current limiting resistors and such, looks to be quite good.Your schematic drawing skills leave much to be desired! Preferably, signals travel from left to right, and power from top to bottom (+ to -).I'm curious why you're using any 555s at all, given that you seem to understand transistors and comparators well enough -- the 555 has many downsides, and while it can be used in many things, it's almost always a burden and a constraint, in any practical design.Your grasp of control loops, and signals and analysis, is not quite so developed, though. Something to work on.FYI, your "PFC" circuit isn't -- if for no other reason than C3 and C11 being present. You also have no means of sensing the input AC voltage and current, so how could it ever possibly correct its power factor?Consider the definitions of control loops, stability of simple linear systems, and the physics of converters (the state variable is the inductor current -- control that, first!).Cheers,Tim

author: hanzdolo30@gmail.com
author_rank: Contributor
timestamp: April 24, 2017, 08:08:21 pm
content: Quote from: T3sl4co1l on April 24, 2017, 10:39:17 amI chose the 555 because it was a GP oscillator with voltage controlled duty cycle. You're quite correct it's been quite a pain, but that's the fun part, right?, lol.I had been under the impression that being the NE555 and the comparator maintained a 360V output, no matter what the load or input voltage at the rectifier it was actually correcting the power factor.Why do the input caps (C3 & C11) change the PFC?I'll work on my knowledge of control loops, now that I actually know what to look up.You have no Idea how much I'll learn today because of the small amount of information you've provided.Though, I thought I had the inductor current issue solved. In that trace the supply is under >1kw load @360Vdc , so I thought the peaks weren't bad because without a load, if memory serves me the highest peak is 15A.The transformer steadily peaks at about 3.5A.I know the wave clippers consume too much current but when I decrease in input current, clip and amplify, the flyback switching gets distorted and the low end is above 1V, however it works fine with the boost converter? I'm guessing it's a sinking issue, because when I run it as you see it in the schematic it works (a little distortion but not much), however I'd like to perfect that and have as nice an output wave as goes in (inductively loaded).I'll work on neater schematics based on the guidelines you gave me to follow.Thanks again for the information, it's much appreciated.Gil.