Electronics help! recitifier with a zener diode

badaboom

1. The problem statement, all variables and given/known data
Design a rectifier with a zener diode that satisfies the following:
Primary voltage = 120V @ 60Hz
V_DC = 12V
I_R2 = 100 mA (R2 being the load)
V_r(R2) <= .3V

2. Relevant equations
C=I_DC/(2fV_r)
I_DC=I_R3 + I_R1


3. The attempt at a solution
I tried calculating the capacitor, but how am I supposed to get I_DC if I dont have any other current?

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MATLABdude

Remember that a reversed Zener diode clamps the voltage, but must be above the zener current ([itex]i_{zk}[/itex]) in order to do so:
http://www.electronics-tutorials.ws/diode/diode_7.html