[SOLVED] Which terminal of transformer to use?

[ADGAN]

Hi! Recently I purchased a 12V, 300mA transformer which has three terminals (Black, yellow, Black) for its output. I have used transformers which has 2 terminals. I like to know what these terminals represents and which terminals to use when using it to obtain 12V DC.

 

[chuckey]

If there is a low resistance between the black terminals and the yellow one, it is a centre tapped transformer, you will have to put mains on its primary to see if its a 6-0-6 =12V with a bridge rectifier across the black terminals. Or its a 12-0-12, which will give you 12 V with two diodes on black terminals with the output on the common diode connection and the yellow terminal.
Frank

 

[ADGAN]

Thank you! There is a label on the transformer and it states that 12Vx2. How do I connect this to a bridge rectifier?

 

[chuckey]

If you insist on using a bridge rectifier, connect the black terminals to the AC input terminals of the bridge, use the + terminal as your + output use the yellow terminal as the - output. You are only using 1/2 of the bridge.
Frank

 

[ADGAN]

Thank you very much. Is it possible to use any of the black terminals?

 

[FvM]

Is it possible to use any of the black terminals?

That's a different solution. The two-diode fullwave rectifier suggested by chuckey will be slightly better in two regards
- symmetrical loading of transformer windings
- less rectifier voltage drop and power dissipation

 

[ADGAN]

I'm using 4 diodes, I have already made the PCB. What should I do? This is the power supply that I'm using.



Is it correct if I connect any black wire to point A and yellow wire to point B?

 

[FvM]

Yes, it's definitely possible. The two winding halves have slightly different DC resistance, use the lower resistance winding.

 

[ADGAN]

Thank you very much

 

[ADGAN]

I tried it with use of a 2200uF and its working. But I can hear a very low noise from the transformer (Kind of a humming). Is it some kind of fault or is it usual to hear it?