Zener diode is a silicon semiconductor with a p-n junction that is specifically designed to work in the reverse biased condition. When forward biased, it behaves like a normal signal diode, but when the reverse voltage is applied to it, the voltage remains constant for a wide range of currents.
The Zener Breakdown is observed in the Zener diodes having Vz less than 5V or between 5 to 8 volts. When a reverse voltage is applied to a Zener diode, it causes a very intense electric field to appear across a narrow depletion region.
The major difference between PN junction and the Zener diode is that the PN junction diode allows current to pass only in the forward direction, whereas the Zener diode allows the current to flow both in the forward and the reversed direction.
The 3SMAJ5927B is a 12 V Zener diode in a 3 W package. It's knee current, breakdown current, or minimum current is 0.25 mA. The maximum current is calculated by dividing the power rating by the Zener voltage: I=P/V = 3W/12V = 0.25A.
Load regulation is the measure of the ability of a power supply to maintain a constant output voltage despite changes in output current or load. The load regulation is not a fixed number but rather presented as a percentage.
This type of diode is called a Zener diode, and its symbol is shown in the figure(b) above . When forward-biased, Zener diodes behave much the same as standard rectifying diodes: they have a forward voltage drop which follows the “diode equation” and is about 0.7 volts.
The Zener breakdown can be defined as the flow of electrons across the p kind material barrier of the valence band to the evenly filled n-type material conduction band.
Formulas and Equations for Zener Diode & Zener Voltage Regulator Calculator
- Series Current.
- IS= VIN – VZ / RS….. ( Ohm's Law Again)
- Load Voltage.
- VL = VZ
- Change in Load Voltage.
- ∆VL = IZ x RZ
- Output (Regulated) Voltage.
- VOUT= VIN – IR = VIN – (IZ + IL) / RS = (VIN – IS) / RS
The Zener diode is like a general-purpose signal diode. When biased in the forward direction it behaves just like a normal signal diode, but when a reverse voltage is applied to it, the voltage remains constant for a wide range of currents. At this stage maximum current will flow through the zener diode.
Photodiodes can be operated without any voltage bias. APDs are designed to be reversed biased, so this section will be relevant to the P-N and PIN photodiodes. Without added voltage across the junction, dark current can be extremely low (near zero). This reduces the overall noise current of the system.
Zener diodes are highly doped diodes. This means their behavior in forward bias will be same as a normal diode. But while in reverse bias their junction potential is increased. So that means when the voltage crosses 6V then the diode is in Reverse breakdown and hence the current through the diode increases rapidly.
The Zener effect is distinct from avalanche breakdown. The avalanche breakdown occurs in lightly doped junctions, which produce a wider depletion region. Temperature increase in the junction increases the contribution of the Zener effect to breakdown, and decreases the contribution of the avalanche effect.
Zener diodes are mostly used for regulating voltages. However, yes, they can be used for rectifiers. Above it's threshold voltage(Zener voltage), the Zener diode allows reverse flow of current.
The breakdown which occurs because of the collision of the electrons inside the PN-junction is called avalanche breakdown, whereas the Zener breakdown occurs when the heavy electric field is applied across the PN- junction. Because the mechanism of Zener breakdown occurs in the heavily doped region.
Get a multimeter and measure the forward-biased voltage of the diode by placing the positive or red lead of the multimeter on the diode's anode part. This is the side of the zener that is unmarked. Place the negative or black lead of the multimeter on the cathode or marked side of the diode.
Zener diodes are heavily doped than ordinary diodes. They have extra thin depletion region. When we apply a voltage more than the Zener breakdown voltage (can range from 1.2 volts to 200 volts), the depletion region vanishes, and large current starts to flow through the junction.
During regulation action of a zener diode, the current through the series resistance charges and resistance offered by the zener changes. The current through the zener changes but the voltage across the zener remains constant.
