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Zener Diode

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Zener Diode This is a diode designed with adequate power

dissipation capabilities to operate in the breakdown region.

When both sides are heavily doped, the depletion layer is very thin (100 Ǻ).

Even 4 V may give a field of 107 V/m, causing breakdown.

Whatever may be the breakdown phenomenon, it is called ‘zener diode’.

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V-I Characteristics

Ideally the breakdown curve should be a perfect vertical line and dynamic diode impedance should be zero.

In practice, however, Dynamic Zener Impedance has small values ranging from few ohms to several hundred ohms.

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Equivalent Circuits

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By controlling the thickness of the depletion layer, Zener Diode can be made to have breakdown at a specified Zener Voltage.

Generally Zener Voltage ranges from 0 volts to 200 volts.

As long as the current through the diode is limited by the external resistance in the circuit within permissible values, it does not burn out.

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Zener Diode Applications1. Voltage Stabilizer or Regulator.2. Peak Clipper.3. Switching Operation.4. Reference Element.5. Meter Protection.

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Voltage Regulator

•It has the ability to maintain a constant output even when either the input voltage or load current varies.

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A voltage regulator provides a constant voltage from a source whose voltage may vary appreciably.

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Analysis Procedure of Circuit

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Step 1 : Find the state of zener diode.(Remove diode and find voltage across open-circuit.)

Step 2 : Substitute the appropriate equivalent model and solve.

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Specifications of Zener Diode1. Zener Voltage (VZ)2. Maximum Power Dissipation (PZmax)3. Maximum Current (IZmax)4. Minimum Current (IZmin)

IZmin = 10 % of IZmax

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This voltage (82.5 V) is more than VZ (= 60 V).

Hence, diode is ‘ON’. Replace the diode by its equivalent.

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This is more than VZ. Hence diode is ‘ON’. We now calculate the minimum value of zener current.

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When V1 becomes 120 V :

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Review V-I Characteristics. Zener Diode Applications :

Voltage Regulator. Peak Clipper. Switching Operation. Reference Element. Meter Protection.

Analysis Procedure of Circuit. Specifications of Zener Diode.