Multiple voltages from ringcore transformer blows up my circuit - Page 1
Forum section: electronics / beginners

author: Mind
author_rank: Newbie
timestamp: November 05, 2022, 07:15:45 pm
content: Hello!I am trying to get 2 different voltages onto my board, about 110 volt DC (or more is fine) and about 20 to 30 volt DC.I will be using the 20 to 30 volt to feed two voltage stabilizers, one at 5 volt and one at 12 volt.The 5 volt will power an arduino.The 12 volt will be used to control the Mosfet.So, before I do all this I need to get my power to the board and here is where the problem is.I have a ringcore transformer.One winding is giving me 110v RMSAnother is giving me 20v RMSThey share one terminal.I connect the shared terminal to 2 rectifier circuits.I connect the 110 v winding to one rectifier.I connect the 20 v winding to the other rectifier.I connect the negative terminal of the rectifiers together to get a shared common.However....If I only connect the 110 volt, everything is fine with that part, I measure it and everything is fine.If I only connect the 20 volt, everything is fine with that part, I measure it and everything is fine.I get what I expected to get out.If BOTH are connected at the same time, my capacitors on the 20v side explode. They are rated at 50 volt.I am trying to understand why this happens. I am a noob at electronics and a hobbyist, but have at least succesfully built a couple of circuits from scratch of my own design and making.Note that the picture I included is not exactly correct, I found no ringcore transformer part in my program so I just put 2 regular transformers there. I found no rectifier circuits in my program so I just made one from diodes. I hope you understand anyway.

author: Benta
author_rank: Super Contributor
timestamp: November 05, 2022, 08:06:09 pm
content: They key sentence is: "They share one terminal".

author: Mind
author_rank: Newbie
timestamp: November 05, 2022, 09:07:31 pm
content: Oh, I was under the impression that they should. As if I want the same groundpotential in the circuit later.

author: John B
author_rank: Frequent Contributor
timestamp: November 05, 2022, 09:12:54 pm
content: The 110V RMS circuit puts the rectified ~155V peak across the 50V caps.

author: Mind
author_rank: Newbie
timestamp: November 05, 2022, 09:21:07 pm
content: Ok. Hmm, but I need to connect the 2 parts later with mosfets, so I need to have a common ground for them. Would it work if I separated the terminals on the ringcore but had ground on the DC part connected?

author: John B
author_rank: Frequent Contributor
timestamp: November 05, 2022, 09:39:43 pm
content: When you say the transformer has 2 windings, are they completely separate pairs that you've connected yourself?If so, then you keep each pair of windings separate and each floating pair will connect to their respective bridge rectifier. The negative DC sides of each rectifier are connected to provide your common ground.

author: TimFox
author_rank: Super Contributor
timestamp: November 05, 2022, 09:47:27 pm
content: With the two bridge rectifiers discussed by John B, you must NOT connect any of the transformer winding leads to the other winding.The common ground connection is after the two filter capacitors from the two bridges.

author: Mind
author_rank: Newbie
timestamp: November 05, 2022, 11:37:58 pm
content: Thank you, I was clearly confused about this and this is indeed how I have done it, so I will disconnect them from each other on the transformer and just have common DC. Thank you very much for your help!Edit: Rebuilt it and it is now working. Wonderful.