A Zener diode, having breakdown voltage equal to 15 V, is used in a voltage regulator circuit shown in figure.  The current through the diode is

Voltage across Zener diode remains constant.  Zener diode and load resistance are in parallel. ∴IL=V0RL=15103=15mAAlso, voltage across series resistance= Vs= E - Vo=20-15=5 V∴Current through series resistance  = IS=VsRs=5250=20mAHence, current through diode = IZ= IS−IL=20−15=5mA