CHAPTER 4. DIODE CIRCUITS71SGFigure 4.8: Full-wave rectiﬁer and its output waveform.4.3.3Power Supply FilteringThe rectiﬁed waveforms still have a lot of ripple that has to be smoothed out in order togenerate a genuine DC voltage. This we do by tacking on a low-pass ﬁlter. The capacitorvalue is chosen in order to ensure small ripple, by making the time constant for dischargingmuch longer than the time between re-charging.4.3.4Split Power SupplyOften a circuit requires a power supply that provides negative voltage as well as positivevoltage. By reversing the direction of the diode and the capacitor (if it is polarized), thehalf-wave rectiﬁcation circuit with low-pass ﬁlter provides a negative voltage.Similarly,reversing the direction of the diodes and capacitor in the full-wave rectiﬁed supply producesa negative voltage supply. A split power supply is shown in ﬁgure 4.9.GROUND-V+VSGFigure 4.9: Split power supplies.