1. FULL-WAVE RECTIFIER (FWR) Rs I p (peak value I rms t I V av Irms = 0.7 Ip Idc = 2/π Ip Idc = Iav = 0.9 Irms Form factor = 1/0.9 = 1.11

2. EX: For the circuit shown in Fig. Each diode has forward resistance of 50Ω and is assumed to have an infinite resistance in the reverse direction. Calculate the following: The value of the multiplier Rs. The ac sensitivity Sac. The dc sensitivity Sdc. RsRs I fsd = 1mA R m = 100 Ω E = 10 v

3. (a) The equivalent dc voltage Vdc = Vav = 0.9 X 10 = 9 v RT = 2RD + Rs + Rm = 9/Ifsd = 9/0.001 = 9000 Ω Rs = RT – 2 RD – Rm = 9000 – 2 X 50 – 100 =8800Ω (b) RT = Sav. V Sav = 9000/10 = 900 Ω/v (c)Sav = 0.9 Sdc = 1/ Ifsd Sdc = 900/ 0.9 = 1000 Ω/v = 1/0.001=1000 Ω/v

4. H ALF - WAVE R ECTIFIER (HWR) RsRs R VoVo VrVr IfIf IrIr R f =smal value Forward biase chs reverse biase chs Rr=αRr=α VfVf

5. D IODE VfVf VfVf + + + + - - - - P N + + + + - - - - - VrVr VrVr + + + + - - - - P N + + + + - - - - Forward bais Reverse bais

6. H ALF - WAVE R ECTIFIER (HWR)

7. H ALF - WAVE R ECTIFIER ( CONT.) Note: The AC sensitivity = 0.45 DC sensitivity EX: Compute the value of the multiplier resistance RS for a 10V rms -ac range on the voltmeter shown in Fig.1 using three methods. given: I fsd = 1mA and R m = 300Ω.

8. H ALF - WAVE R ECTIFIER ( CONT.) Method (1): Ω/v R T = R S + R m = S ac X V rms = 450 X 10 = 4500 Ω R S = R T - R m = 4500 – 300 = 4200 Ω

9. H ALF - WAVE R ECTIFIER ( CONT.) Method (2)

10. H ALF - WAVE R ECTIFIER ( CONT.) Method (3) R S = R T – R m = 4500 – 300 = 4200 Ω Note: We said before that the scale is calibrated in terms of rms value of a sinusoidal waveform but for other input forms rather than sine wave you have to multiply the reading by the corresponding form factor.

11. H ALF - WAVE R ECTIFIER Practical circuit for Half wave rectifier for voltmeter Rs R sh RmRm

12. H ALF - WAVE R ECTIFIER (HWR) ( CONT.) The addition of D 2 is to provide an alternate path for reverse-biased leakage current that would normally flow through the meter and diode D 1. The purpose of the shunt resistance R Sh­ is to increase the current flow through the +ve half cycle so that the diode is operating in a more linear portion of its characteristic curve.