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Zener Diode

A zener diode is connected backward, in reverse bias, and holds a fixed voltage $V_Z$ across itself while conducting in this direction. It is often used as a simple voltage regulator: a series resistor absorbs the rest of the voltage from the source, and the current through it sets the zener current.

R_S=\dfrac{V_{in}-V_Z}{I_Z}

series resistor for a simple zener regulator

Symbols

$V_Z$	zener voltage	V
$V_{in}$	input voltage	V
$I_Z$	desired zener current	A
$R_S$	series resistor	$\Omega$

Example

$V_{in}=12$ V, $V_Z=5.6$ V, $I_Z=20$ mA:

$R_S=(12-5.6)/0.02=320$ Ω.

A zener diode is connected in reverse bias to regulate voltage – the opposite of an ordinary diode.

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