The Half-Wave Rectifier With Capacitance Load

Author: E.E. Kimberly

Fig. 27-5. Voltage Characteristic of a Condenser-Loaded Half-Wave Rectifier When a Resistive Load Is Added in Parallel

If in the circuit of Fig. 27-3 (a) the battery is replaced by a condenser, the condenser will be charged to the peak plate voltage on the first half-cycle in which the plate is positive. Successive half-cycles of positive plate voltage will then have no effect on the potential of the condenser. If the condenser is used as a source of very small current, however, its charge will be drained off somewhat between positive half-cycles and will be restored successively by following half-cycles of positive voltage impulses. Fig. 27-5 shows the phenomenon of drain and recharge when the load is a high-resistance resistor. The rate of drain between charging impulses follows the exponential law of discharge of a condenser through a resistor and is therefore a function of C and R.

Fig. 27-6. Voltage Characteristic of a Condenser-Loaded Full-Wave Rectifier When a Resistive Load Is Added in Parallel

In applications where loss of condenser voltage because of current drain is within acceptable limits, the half-wave rectifier is satisfactory and is desirable because of its simplicity. If the current drain through the load is unusually heavy, it is advisable to use a full-wave rectifier, like that shown in Fig. 27-3 (b), which recharges the condenser to full voltage twice as often as does a half-wave rectifier. This voltage characteristic is shown in Fig. 27-6.