Problem with recognizing MOSFET connection circuit

Thread Starter


Joined Jul 5, 2015
Hello everybody,

I have a little problem with two circuits, both of them consist one MOSFET

I have also post an electric scheme with two circuits which I can not understand.

I have taken one electronic board and I want to learn about power supplies from it. I decided to make an electronic scheme from it.

I think that this board has negative voltage outputs and that is what make me more problems to understand. On input it has +DC voltage and five outputs with different -DC voltages. I am searching on internet long time some explanation to understand how those circuits are working.

Those two circuits are parts from whole board, 1. circuit is connected in beginning of the circuit, and 2. one is connected to a transformer (transformer has 21 pins (connections). I checked with an Ohmmeter and 3 pins are always together. In this case 2. circuit is connected with pin 2 and pins 1 and 3 are connected with switching power MOSFETs (1, 2, 3 pins of transformer are together)).

I also don't know which parts of circuit are ground and which are positive or negative voltage.

I have drawn scheme exactly how it is connected on the board and I hope that someone can help me and explain how those circuits are working and what is their purpose in electronic circuits. Maybe I haven't drawn it exactly, can someone recognize which circuits are they.

If there are some extra questions to understand more about these circuits, I will answer with pleasure.

Thanks in advance
Best regards

Electric Scheme 1.jpg