As shown in the scheme that the circuit consists of three stages. The first (which is formed by a transformer, bridge rectifier and an electrolytic capacitor 10000μF) is responsible for isolating and reduce the voltage, improve and filter. The second phase (consisting of, BC327 transistor integrated circuits and components attached) is responsible for providing a reference voltage which is used to determine, together with the potentiometer and top resistor, voltage applied to the driver transistor and power. It should be noted that they made a resistive and non-switched control (switching) so the voltage at the emitter is pulsed. Then we have a small output filter formed by the electrolytic capacitor and terminals.
