Tsukure Mad Labs Over-Voltage Zener Protection Circuit

A protection circuit, like reverse polarity protection, short-circuit protection and over/under voltage protection, are used to protect any electronic appliance or circuit from any sudden mis-happening. Generally fuse or MCB is used for overvoltage protection, here in this circuit, we will build an overvoltage protection circuit without using Fuse.

Overvoltage protection is a power supply features which cutoffs the supply whenever input voltage exceeds the preset value. For protection from high voltage surge, we always use overvoltage protection or crowbar protection circuit. Crowbar protection circuit is a type of overvoltage protection which is most commonly used in electronic circuits.

There are many different ways to protect your circuit from overvoltage. The simplest way is to connect the fuse at the input supply side. But the problem is that it’s a one-time protection, because as the voltage exceeds the preset value, the wire inside the fuse will burn and break the circuit. Then you have to replace the damaged fuse with a new one to make the connections again.

Here in this circuit, Zener Diode and Bipolar Transistor are used for automatic overvoltage protection. It can be done by two methods,

1. Zener Voltage Regulator Circuit: This method regulates the input voltage and protects the circuit from over voltage by supplying a regulated voltage, but it doesn't disconnect the output part when voltage exceeds the safety limits . We will always receive an output voltage less than or equal to the rating of the Zener diode. 

2. Overvoltage Protection Circuit using Zener Diode: In the second method of overvoltage protection, whenever input voltage exceeds the preset level it disconnects the output part or load from the circuit.

A Zener Voltage Regulator protects the circuit from overvoltage and also regulates the input supply voltage. 

The preset voltage value of the circuit is the critical value over which either the supply is disconnected or it won’t allow any voltage above that value. Here the Preset voltage value is the rating of the Zener. Like, we are using 5.1V Zener diode then the voltage at output will not exceed 5.1v.

When the output voltage increases the base-emitter voltage decreases, due to this transistor Q1 conduct less. As Q1 conducts less it reduce the output voltage hence maintains the output voltage constant.

The output voltage is defined as:



VO is the output voltage

VZ is Zener breakdown voltage

VBE is base-emitter voltage

Components used in this module...

Find out more about the components used in this STEM Module.

Let's Get Started!

Below you will find a list of bits to gather before hand, followed by a detailed schematic. Using a breadboard lay out the components and connect them together as shown. Alternatively you can purchase this module from our shop and simply solder the components in the places indicated on the quality assured printed circuit boards provided.

What You Need...

1 5.1V Diode (Zener)
1 1K
[ Brown, Black, Black, Brown ]
Resistor (0.25 Watt)
1 2K2
[ Red, Red, Black, Brown ]
Resistor (0.25 Watt)
1 6K8
[ Blue, Gray, Black, Brown ]
Resistor (0.25 Watt)
2 FMMT718 Transistor (PNP)

NB: Any resistor colour codes specified relate to 5 band resistor codes, the 5th band has not been shown intentionally. The 5th band indicates the resistor tolerence, we use only the highest tolerence resistors in our products.

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