What is a Zener diode?

・In Japanese

■Zener diode

Normal diodes do not allow current to flow even when a reverse voltage is applied, but current suddenly flows when a certain voltage is exceeded. This voltage is called the breakdown voltage. Normal diodes break down when this voltage is reached, but Zener diodes are designed so that they will not break down even if the breakdown voltage is reached, and the current characteristics for the breakdown voltage are steep.

■Application example of Zener diode

＜Constant voltage circuit＞

A constant voltage can be created by connecting a Zener diode as shown below. Breakdown voltage is 6V


In this case, the voltage across the terminal = breakdown voltage = 6V. The breakdown voltage must be overcome in order for current to flow through this circuit, and since the voltage here is 10V, the breakdown voltage can be overcome. On the other hand, it can be seen from the characteristics of the diode that no matter how much current flows, it will not exceed the value of the breakdown voltage.

This constant voltage circuit is also called a Vref(voltage reference).

＜Clamp circuit＞

The circuit is the same as above, and from a different point of view, we can set the upper limit of the voltage. This is called a clamp circuit. By doing this, the circuit can be protected even when a surge occurs.



As shown below, the voltage usage range differs between the constant voltage circuit and the clamp circuit.

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