Zener Diode ratings
The maximum zener current (iZM) is the maximum reverse current that can flow in a zener diode without exceeding the power dissipation rating specified by the manufacturer. The reverse current (ir) represents the leakage current before breakdown and is specified at a certain reverse voltage (er). The reverse voltage is approximately 80% of the zener voltage (EZ).
Zener diodes that have a breakdown voltage of 5 V or more have a positive zener voltage temperature coefficient, which means that the breakdown voltage increases as the temperature increases. Zener diodes that have a breakdown voltage of less than 4 V have a negative zener voltage-temperature coefficient, which means that the breakdown voltage decreases with an increase in temperature. Z ener diodes with a breakdown voltage between 4 and 5 volts may have a positive or negative voltage-temperature coefficient.
Connecting a zener diode in series with a P–N – junction diode, with the P–N junction diode forward I biased and the zener diode reverse biased, forms a temperature-compensated zener diode. By careful selection of the diodes, temperature coefficients can be selected that are equal and opposite. More than one P–N junction diode may be needed for proper compensation.
Questions
1. What determines the maximum zener current of a zener diode?
2. What is the difference between the maximum zener current and the reverse current for a zener diode?
3. What does a positive zener voltage temperature coefficient signify?
4. What does a negative zener voltage temperature coefficient signify?
5. How can a zener diode be temperature compensated?