This 12 Volts transformerless power supply take advantage of the fact that a Zener diode is also a normal diode that conducts current in the forward direction. During one half wave, the current flows ...

This transformerless power supply circuit is designed for medium current applications. During the negative half period, the capacitor C5 is charged to peak voltage network. Transformerless Power ...

In the former (AN954), the transformerless power supply’s circuit ground has high voltages with reference to neutral, and connecting it to earth would cause a dangerous situation.

But for circuits where weight, volume, or cost are a major concern, a transformer may be omitted in the circuit design in favor of some sort of transformerless power supply.