In the diagram below, we estimate the ripple seen by the load so as to appreciat
ID: 2079326 • Letter: I
Question
In the diagram below, we estimate the ripple seen by the load so as to appreciate the regulation provided by the diodes. The diode bridge is a full-wave rectifier. The frequency f_in of at the input of diode bridge is 60Hz, C_1 = 100 mu F, R_1 = 1k ohm, and the peak voltage produced by the transformer is 5 V. Assume R_1 carries a relatively constant current and V_D, on = 0.8V, estimate the ripple amplitude across C_1. Using the small-signal model of the diodes, determine the ripple amplitude across the load.Explanation / Answer
a) When capacitor is discharged by a constant current at a certain frequency,
the ripple voltage is given by = I/2Cfin , where I is contant current
voltage drop across R1 = Vp-5VD,on
Current I = Vp-5VD,on / R1
hence Ripple voltage = I/Cfin
VR= Vp-5VD,on /2(R1*Cfin)
R1=1kohm
C1= 100microF
Fin = 60Hz
hence , VR = 166.67mV
b) The bias current through the diodes is the same as the bias current through R1, which is
Vp-5VD,on / R1
VT = 26mV
rd = VT/ID = 26ohm/1mA = 26 ohm
VR,load = 3rd*VR / (R1+3rd) = 12.06mV