Analog electronics, Electronic components, Hobby, Projects, Semiconductors

Meet the zener diode

The zener diode is a special type of diode. In this post, will be shown how it works and some ideas for projects.


As I explained in the post about diodes, this component allows the passage of electrical current only in one direction.

DiodeClick here

With the zener diode, the current can also flow in the reverse direction, since the voltage in the reverse mode reaches a value known as zener voltage or breakdown voltage (Vz).

The black belt side in the zener diode is the cathode, while the opposite side is the anode.

What is the structural difference between a common diode and the zener type? The zener diode is more doped with impurities than the common, creating a depletion layer thinner than 1μm (micrometer), thinner than the common diode’s layer. The breakdown voltage in the zener diode is much lower than in the normal diode. This diode will keep the breakdown voltage -Vz almost constant, since the reverse current stays between the minimum current limit (Iz_{min}) and the maximum (Iz_{max}).

Applications and projects

One of the main applications is voltage regulator. In this circuit, the LED turns on when the input voltage Vin surpass 9.2 V.

The datasheet of 1N4737A, which can be found here, shows that this component’s zener voltage is 7.5 V.

The voltage value in the output Vout will be close to 7.5 V, when Vin stays above 9.2 V until the zener current pass from 121 mA. This property allows that the zener diode to serve as protection against overvoltage. If put some diodes in series, can obtain well defined voltage levels.

In the circuit above, VDC must be above 20 V, to three outputs have these constant voltage levels. If you put LEDs, these will turn on in sequence when the VDC voltage increases.

Two diodes positioned in this way can limit the wave amplitude of alternate signal. The output signal stays almost like a square wave.


About Pedro Ney Stroski

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