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Mand Labs presents
Zener Diode
About Zener Diode
• A usual diode designed to conduct in reverse direction
• Conducts in reverse bias after a certain voltage, known as, Breakdown Voltage (Vz)
• Vz is imprinted on the zener diode
• Vz of zener diode in kit = 5V6 = 5.6 V
• Vz Range: 2 to 200 Volts
Zener in Forward Bias
Works as a normal diode when forward biased
Note: Minimum Forward Bias voltage required to make the zener diode (used in our kit) conducting is 0.99 V
Zener in Reverse Bias
Vcc i (reverse current)
< 5.6V 0
≥ 5.6V High Value
Let, Voltage across zener diode = Vzener
Vz = Breakdown Voltage (Vz) of our diode = 5.6 V
Vz = Vzener
Voltage Regulator
• Use a zener diode to maintain constant voltage across two points
• Zener diode will not allow the voltage to shoot above its voltage breakdown rating in reverse bias mode
• VAB = Breakdown Voltage, if Vs ≥ Breakdown Voltage
Example
• 10k Ω resistor is connected with a 9V battery
• Ideal Voltage Drop across 10k Ω resistor = 9V
Voltage drop will increase, if we increase the value of Vcc
Can we make this
voltage drop
constant ?
Example
Add Zener Diode
• Connect a zener diode in reverse bias and parallel with resistor
• Measure the voltage across the resistor
Voltage Reading
• Voltage across the zener diode = Voltage across the resistor
• Voltage across zener diode = 6.53 V = Breakdown Voltage
Characteristic Curve
• In +ve voltage region:
‣ Threshold Voltage: Minimum forward bias voltage required to open up a diode
‣ Forward current is in mA
‣ Current increases exponentially with voltage
• In -ve voltage region:
‣ Breakdown Voltage: Voltage after which reverse current flows
‣ Reverse current is minimal till Vz and increases exponentially after that
‣ Voltage across zener becomes constant after breakdown
‣ Avalanche Breakdown
Observations from curve
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