Zener diode as a Voltage Regulator

Voltage regulator is a circuit which outputs constant voltage irrespective of the input the voltage. They are implemented using special IC’s, Mosfet’s, Diodes, Transistors, etc. Learn more about Voltage regulation using LM78xx IC’s. Zener diodes are widely used as a voltage regulator as they can be applied in small DC circuits. They are used to power microcontrollers and other digital integrated circuits. Zeners are used in reverse bias mode. It is operated in its breakdown region. When the breakdown occurs large reverse current flows and the reverse voltage remains constant. This the field of interest for the application of a Zener diode as a voltage regulator. The breakdown is also called as Zener effect.

Zener Diode as a Voltage Regulator circuit

Zener Diode as a Voltage regulator
Zener Diode as a Voltage regulator
  • V1 is the supply voltage and it should be always greater than the zener voltage.
  • 1N4733A 5.1V Zener Diode connected in reverse bias. Download datasheet: 1N4733A Datasheet.
  • R1 is a series resistor which is used for current limitation.
  • R2 is a load resistor.


When the load is not connected the current flowing through the resistor R1 will be the Zener current Iz. It causes overheating of the diode and it must be avoided. The resistor R1 should be selected properly to limit the current flow.

Maximum diode current = Watts/Zener Voltage.

The load resistor R2 is connected in parallel with the zener diode. Hence the voltage across zener will be same as the load voltage. The total current flowing will be IR1= Iz + IR2. In the reverse bias characteristics of the diode, the diode breakdowns after a particular value of input voltage.

At lowest value of Load Resistor, Maximum current will flow through R2 and lowest current will flow through zener diode, Hence the Zener Voltage will be minimum.

Zener Diode as a voltage regulator1
Zener as a voltage regulator- Zero Resistance

R2 is a variable resistor. Hence at 0%( marked in blue). There will be no load resistance hence the diode current will be approximately low.

Zener Diode as a Voltage regulator-Resitance 50%
Zener Diode as a Voltage regulator-Resitance 50%

At load resistance around 50% the breakdown has occured and the ouput voltage is 5V constant for 5V Zener.

Zener Diode as a Voltage regulator-Resitance 100%
Zener Diode as a Voltage regulator-Resitance 100%

The load is varied to 100% and the output voltage remains constant at around 5V DC. Hence after the breakdown voltage the output voltage is regulated and remains constant.


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