Need Help...I have (2) 25volt 3 amp Transformers and Need 1 40-50volt 3amp Trans

[kylefrink]

Need Help...I have (2) 25volt 3 amp Transformers and Need 1 40-50volt 3amp Transformer,....Is it possible to just connect the Output of two 25 volt 3 amp tranf in series, and would it have one input?

[kylefrink]

I am Building a Lm3886 Audio Amp and I will run it on 8 ohm Speakers and Want to run it at 60 watts, my circuitry needs a center tapped transfer of between +28-0-28-,  through +50-0-50-, How could i go about getting this power? can i use (2) 25volt Center tapped Transformers in series?

[Hero999]

The LM3886 requires +/- raills ranging from 28VDC to 35VDC.

Transformer voltage ratings are specified in RMS.

The peak voltage is √2 times the RMS voltage.

The DC voltage from a rectifier is equal to the peak voltage minus the rectifier losses.

So why not use a single 25-0V-25V transformer to get a supply of +/-35VDC?

[Alex Tsekenis]

kylefrink

You can use your original 25V transformers connected in series like this:



for a supply of +/-35VDC as Hero pointed out.

[audioguru]

The LM3886 needs a supply of plus and minus 35VDC. The spec is written as 50W but the graphs show 60W into 8 ohms.
Your transformers are (2) 25VAC. The peak voltage of 35.4V is dropped to 33.0V by the rectifiers and filter capacitors. So the output of the amplifier will be about 53W into 8 ohms.

One amplifier will use 53W for the speaker and produce 30W of heat so its total from the power supply is 83W. Your transformer is 25V x 2 x 3A= 150VA so it can almost power two amplifiers at full blast continuously. Your transformer will power two amplifiers perfectly with music or speech as their inputs.   

[audioguru]

I answered in the forum.
Audioguru