Alf_Melmok

I envy you. But it's not funny. By our standards in the electrical network there shall be 220V +20 % -20 %. You can calculate how much it turns out (176-264 It's normal :o). All of our electronics designed for this.

You are right, i forgot about the voltage losses. In my country mains voltage change from 200 to 240 very often (In rare cases, even is worse (phase is not uniformly loaded)). That's why i want to limit the input voltage. It's a vicious circle. In my country i can't buy op amp that you recommend. So that i can't use 28VAC transformer. And i can't find 28-30VAC transformer. I can't find another scheme similar PSU. I just want this power supply with 20V transformer. :'( Thanks for your help

Can you help me? I want to limit the input voltage. If the line voltage change. So that the output has always been a 20V. Just in this scheme, the output voltage 30VDC (U4+D13=30,2V). I decided if I'm have 20V, then i need replace the U4 and D13 (18+2,4=20,4V). I was wrong? The output voltage of 20V was enough for me. It also surprised me. I think D7 not needed. Am I right? Or, maybe, you advise me another way in my situation. I read this and some similar forum almost 2 weeks and dont know what to do. Thank you anyway.

Hi All! What do you think about this version of the scheme? But i have only 19,8VAC transformer. Can i use this scheme having replaced U4 on 7818, D13 on 2,4v zener? Will it work? Is this scheme reliable? (sorry for my english)