What is Magnetic Amplification?

(Last edited 5/14/2026)

Magnetic amplification (also called mag-amp regulation) is an older but clever technique used on the output side of some SMPS designs to fine-tune voltage regulation.

It uses a special inductor with a magnetic core that can be driven into saturation. This inductor is placed in series with the secondary winding or output rectifier. The saturation level of the inductor is changed by a low current feedback signal. As the induction changes, the amount of voltage that reaches the output changes.

Unlike group regulation, the main transformer only has a single voltage output. This voltage is regulated using your typical rectification while the other rails use the mag-amp regulation.

In the past, this was a good solution because the voltage regulation was better than group regulation and the solution was cheaper than using DC to DC to regulate the rails not coming off the main transformer; but these days it’s actually far more expensive and takes up a lot more PCB space than what we typically use today, which would be a single +12V output with a DC to DC buck converter for the +3.3V and +5V rails.

Using DC to DC for the Minor Rails

These days, the most common means of regulating the secondary side is to have the +12V come off the main transformer, rectify that, and then regulate the +3.3V and +5V using a small DC to DC buck converter. When we create a lower voltage from a higher voltage, we call it “buck”. When we increase the voltage, we call it “boost”.

In the past, the MOSFETs and PWM controller to build these small DC to DC buck converters were too expensive and too large to make this a viable option to use in your everyday PC power supply, but the parts have become much smaller and cheaper, so now this method of regulating the +3.3V and +5V has become so common that any power supply that uses anything but is suspect.