simple symmetrical supply

80 Normally, a centre-tapped trans- former and a bridge rectifier is used to construct a symmetrical power supply. This seems such a natural solution, that people forget it can be done in a much simpler way. The accompanying circuit diagram shows the simpler version. A disadvantage is the single-sided rectification which makes it necessary to use a larger smoothing capacitor to prevent mains hum. With the values shown, a maximum of 10 mA can be supplied at a ripple voltage of about 0.2 Vp_p. By using simple symmetrical supply 80614 1N4001 —16 V max. 10 mA 1N4001 16 V max. 10 mA the formula below, values for other currents and ripple voltages can be calculated. elektor july/august 1980 7-75 20 I c (Uripple in volts (peak-to-peak), derived current I in mA and C in pF) H Uripple