top of page

Which transformer voltage should I choose?

Power for any need saving costs and avoiding heat.

Choosing the right transformer-voltage is important, as we try to avoid heat on one hand, need enough power in each situation on the other hand. That's why many customers choose a "custom made transformer", which we deliver with the needed secondary voltage matching your application for a very reasonable price. Especially for higher current applications it's necessary to fine-tune the transformer-voltage, so that regulators need to "waste" as less voltage as possible due to small voltage differences between the input and output voltage.

To make your decision easier, which transformer voltage can be chosen, you will find some measurements of the ALS-HPULN power supply (diode rectification) below:

Transformer secondary voltage recommendation for LT3045 based HPULN modules

The chart describes the often needed output voltages of 3,3VDC, 5VDC etc.

Using different loads (Ampere), different transformer voltage should be used. The reason is:

Let's assume a device with a real power need of 3,3VDC / 2A

Transformer 1 with secondaries of 3,6VAC:

3,6VAC x 1,414 = 5,09V (after rectification)

5,09V - 0,8V = 4,29V (diode voltage drop)

4,29V - 3,3V = 0,99V (voltage difference to "waste")

0,99V x 2A = 1,98W (of heat)

Transformer 2 with secondaries of 4,7VAC:

4,7VAC x 1,414 = 6,65V (after rectification)

6,65V - 0,8V = 5,85V (diode voltage drop)