modified 9 years ago

LAoE 3L.3.2 Choose C for accaptable ripple

00:57:42

Calculate Rout and Cfilter for
Iout ≃ 20mA
Vripple≤1V

Mains AC is 110V RMS 
Transformer's output is 6.3Vac RMS
Peak transformer output is 6.3*√2=8.9V
1N914 Diode drop @3.35mA ≃ 0.75V
Vmax on load = 7.36V (8.9-2*0.75)

Rload=Umax/Iout=7.36/20mA=368Ω, standard value=330Ω
Iout for 330Ω=22mA

ripple: Vr=(I*dt)/C
I=22mA (max output current)
dt=capacitor discharge time (1/120ms)
22mA=C*1V/8ms
C=158uF (150uF standard value)

Iout_max=21.6mA
Cfilter=150uF
Vriple=0.86V
Rout = 330Ω

published 9 years ago

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