A Zener diode is named after Clarence Zener, an American theoretical physicist, this Zener diode is a type of diode that allows current to flow in a conventional manner – from its anode to its cathode i.e. when the anode is positive with respect to the cathode. When the voltage across the terminals is reversed and the potential reaches the Zener voltage, the junction will breakdown and current will flow in the reverse direction the desired characteristic.
A Zener diode is made of silicon, it has a high resistance until critical breakdown voltage reached, when the Zener diode is a breakdown, the voltage at both ends of the Zener diode is almost the same within the rated current range, widely used in the stabilized voltage power circuit.
This is a Zener diode I/V characteristic curve. When the reverse voltage reaches the breakdown voltage, the diode turns on, at this time, the current is the minimum regulated current because the dynamic resistance of the regulator is very small, so the voltage remains constant.
- Stable voltage(Vz): voltage at both ends of Zener diode under normal operation.
- Dissipation power(PM): when the reverse current through PN, power loss, the PN’s temperature rise. Dissipated power is determined by PN operating temperature.
- Steady current(IZ): reverse current at a steady voltage.
- Minimum stable current(Izmin): minimum reverse current at a steady voltage.
- Maximum stable current(Izmax): maximum reverse current allowed.
For example IN4742
Steady voltage: 12V
Dissipation Power: 1W
Steady current: 21mA
- When an input voltage less than Zener diode regulated value, input voltage the same as output voltage.
- When an input voltage great than Zener diode regulated value, the output voltage the same as the regulated value.