Zener diode as a
voltage regulator
Calculation of values for a zener diode.
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The power supply shown below uses a 20 V rated zener diode to give a regulated output of 20 V from an input voltage of 25.8 V
The zener diode must conduct at least 10 mA
The maximum power supply output current required is 49 mA

Zener diode as      
a voltage regulator

         
         
         
         
         
         
Vin = 25.8 V
Vout = 20 V
minimum current through zener diode (D1) = 10 mA
maximum power supply output current = 49 mA

Calculate: (answers to 1dp or integers as appropriate)
 * the maximum current throught resistor (R1) =  mA  
 * the voltage drop across R1 =  V  
 * the value of R1 under these conditions =  Ω  
  
The current drawn from the power supply falls to zero.

Calculate: (answers to 1dp or integers as appropriate)
 * the current now flowing through the zener diode =  mA  
 * the power now dissipated by the zener diode =  mW  
  
 
 
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