direct-voltage doubler

A direct-voltage doubler is particularly useful when from an available supply voltage a higher one has to be de- rived. As the current in most such cases is pretty small, the cost of a suitable circuit can be kept down. Astable multivibrator IC1 is a rectangular-wave generator operating at about 8.5 kHz whose output drives transistors T1and T2. When the level at pin 3 of IC1is low, Ti is off and T2 conducts. As the negative terminal of C3 is then connected to earth, the capacitor charges4via diode D1. When the output of IC1is high, T2 is off and T1conducts. Capacitor C3 cannot dis- charge because of D1, b u t C 4 charges to a voltage roughly equivalent to the supply voltage of +12 V and the p.d. across C3 and D1. In our prototype, this voltage across C4 amounted to 20 V approximately. The maximum current should not exceed 70 mA: at that value, the output voltage is 18 V, at an efficiency of thirty-two per cent. DI D2 1N4001 1N4001 7-82 direct-voltage doubler We have not tested the...