Generation of high voltages 11 V-(t) RL(load) h.t. transformer (a) F2.8V v(t) (t a.T v_(t) T=1/f ( Figure 2.1 Single-phase half-wave rectifier with reservoir capacitance C. (a)Circuit.(b)Voltages and currents with load RL impedance of the diodes during conduction-and this will be done throughout unless otherwise stated-the reservoir or smoothing capacitor C is charged to the maximum voltage +Vmax of the a.c.voltage V~(t)of the h.t.transformer, when D conducts.This is the case as long as V<V~(t)for the polarity of D assumed.If I=0,i.e.the output load being zero (R=oo),the d.c.voltage across C remains constant (+Vmax),whereas V~(t)oscillates between +Vmax. The diode D must be dimensioned,therefore,to withstand a peak reverse voltage of 2Vmax. The output voltage V does not remain any more constant if the circuit is loaded.During one period,T=1/f of the a.c.voltage a charge o is transferred to the load RL,which is represented as e=/aou=元人o=r=子 (2.3)Generation of high voltages 11 (a) (b) V~(t) V~(t) V (t) t a.T V max V min D C h.t. transformer V c 2.d V a i L (t) RL i (t) (load) i (t) T = 1/f Figure 2.1 Single-phase half-wave rectifier with reservoir capacitance C. (a) Circuit. (b) Voltages and currents with load RL impedance of the diodes during conduction – and this will be done throughout unless otherwise stated – the reservoir or smoothing capacitor C is charged to the maximum voltage CVmax of the a.c. voltage V¾
t of the h.t. transformer, when D conducts. This is the case as long as V<V¾
t for the polarity of D assumed. If I D 0, i.e. the output load being zero
RL D 1, the d.c. voltage across C remains constant
CVmax, whereas V¾
t oscillates between šVmax. The diode D must be dimensioned, therefore, to withstand a peak reverse voltage of 2Vmax. The output voltage V does not remain any more constant if the circuit is loaded. During one period, T D 1/f of the a.c. voltage a charge Q is transferred to the load RL, which is represented as Q D
T iL
t dt D 1 RL
T V
t dt D IT D I f.
2.3