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Electronic Circuits

VOLTAGE REGULATION

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Electronic Circuits

THE ZENER REGULATOR;

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Electronic Circuits

The zener diode is operated in its reverse bias mode (positive on its cathode) and relies on the reverse breakdown voltage occurring at a specified value.

THE REMAINDER OF THE UNREGULATED VOLTAGE DROPS ACROSS THE RESISTOR “R”

THE ZENER DIODE DROPS CONSTANT VOLTAGE

WITHIN THE DESIGN LIMITS THE LOAD RESISTOR “RL” SEES A CONSTANT VOLTAGE REGARDLESS OF CURRENT

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Electronic Circuits

When being used a voltage regulator, if the voltage across the load tries to rise then the Zener passes more current.

The increase in current through the resistor causes an increase in the voltage dropped across the resistor.

This increased in voltage across the resistor causes the voltage across the load to remain at a constant value.

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Electronic Circuits

In a similar manner, if the voltage across the load tries to fall, then the zener passes less current.

The current through the resistor drops and the voltage across the resistor both falls, maintaining the correct voltage across the load RL.

Zenering current or Izt is the minimum current that must flow through the zener to maintain a fixed voltage.

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Electronic Circuits

Also called the zener diode turn on current (Izt), it must not fall below a certain limit. At that point voltage regulation will cease.

Thus a zener diode makes is valuable in regulating the output voltage against both variations in the input voltage from an unregulated power supply or variations in the load resistance.

The current through the zener will change to keep the voltage to within the design limits.