LM317/LM337 project needs help pls

Hey guys, I would like to get and use the LM317/LM337 to obtain ±15VDC. I have available a transformer which provides two 37VAC, one 24VAC and one 16VAC secondary. The question is can I use any pair of these as input (by connecting a Neutral/line as a centre tap), or I need a new 24-26VAC centre tapped as suggested for this project?

Depending on what you are trying to achieve by learning, I would suggest purchasing a plus and minus 15 volts power supply. These regulators need a DC input for regulation and you will need to rectify your AC into a decent DC voltage before having the regulator do its job.

1 Like

You could use a full wave bridge rectifier design.

There are multiple design considerations for filtering and and power dissipation depending on the current (I) needs of this kind of supply.

What are you going to use it for.

More info: Adjustable Power Supply Using LM317 (Part 7/13)

1 Like

As an alternative to a center tap, you could create dual 15V supplies and connect them to create -15V / 15V, bear in mind they must be floating so you potentially lose ground protection.

Unfortunately the 37V is probably too high for 15V output, it would be on border of power dissipation limit for LM317 (15W), but could be done with large heatsink and/or forced air circulation. The 16V is too low for 15V and LM317 which has 2.5 - 3V drop out (need minimum of 20V AC). (All depending on current and temperature, I assume you are looking for 1.5A at typical room temperatures).

So ideally you really need a 48V center tapped secondary (24-0-24), or two 24V secondaries.


Thanks a lot fellas! Much appreciate!

1 Like