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• To understand Zener diodes, let us first consider a regular diode.

• When a diode blocks current in the reverse direction, the diode can have a large voltage drop across it.

• When a diode allows current to flow in the forward direction,

• the diode has a very small voltage drop across it.

• Let's now replace the diode with a Zener diode.

• The Zener diode also allows current to flow in the forward direction,

• in which case the Zener diode behaves just like a regular diode.

• Each Zener diode has a “Reverse Breakdown Voltage”,

• and the value of thisReverse Breakdown Voltageis different for different Zener diodes.

• When a reverse voltage smaller than the breakdown voltage is applied,

• the Zener diode blocks current just like a normal diode.

• But, when a reverse voltage larger than the breakdown voltage is present,

• the Zener Diode will start to conduct in the reverse direction.

• When a Zener diode conducts in the reverse direction,

• the voltage drop across it stays approximately equal to the reverse breakdown voltage.

• Consider this circuit consisting of a resistor and a Zener diode.

• Let's now add a light bulb in parallel with the Zener diode.

• The Zener diode prevents the voltage across the light bulb from going higher than the Zener's breakdown voltage.

• The light bulb represents the output of our circuit.

• If the input voltage is fluctuating but is always higher than the breakdown voltage,

• then the Zener diode can be used as a voltage regulator

• ensuring that the output voltage stays approximately constant.

• If the intended input voltage is always lower than the breakdown voltage,

• then the Zener diode can be used to protect against transient overvoltage conditions

• that could damage the output.

• Suppose we use two Zener diodes in series pointed in opposite directions.

• We can now apply a positive or negative voltage to the output,

• while protecting the output against transient overvoltage conditions in either direction.

• When protecting against transient high voltage conditions,

• we need special Zener diodes that are able to react very quickly

• and that are able to absorb a very large amount of energy for brief periods of time.

• This combination of two transient suppressing Zener diodes is often manufactured as a single device,

• and is represented with the following symbol.

• Much more information is available in the other videos on this channel,

To understand Zener diodes, let us first consider a regular diode.

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C1 US diode voltage breakdown reverse output direction

Zener Diodes in electric circuits - Voltage Regulators & Transient Suppressors

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Amy.Lin posted on 2021/01/06
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