12 V NiCd battery charger

capacitor itself is charged to about 12 V. Diode D3 is then reverse biased, but D4conducts, so that C4 is charged to just over 20 V, which is ample for our purposes. The 78L05 in the IC2position func- tions as a current source, which tends to keep its output voltage, Uo, appearing across R3, at 5 V. The out- put current, /0, is therefore easily calculated from /0=1/0/R3=5/680=7.4 mA. The 78L05 itself also draws current: the central terminal (normally earthed) delivers about 3 mA. The total load current is, therefore, of the order of 10 mA, which is a good value for con- tinuously charging NiCd batteries. The LED has been incorporated to indicate that charging current flows. The characteristic of the charging cur- rent versus battery voltage in figure 2 shows that the circuit is not perfect: a 12 V battery will be charged with a current of only about 5 mA. There are several causes for this: 7-30 14- (mA) 13 - 12- 11 9- a- 7- 6- 5. 4- 3- 2- 1- O 4 ; 8 9 10 11 12 13 14 15 16 17 18 19...