Electronics Components: Diodes
SEMICONDUCTORS
ELTE 1403
Forward biased diode: cathode anode
Varactor is a silicon diode optimized for its variable capacitance when reversedbiased. Used for tuning frequencydependent equipment. Zener Diode is designed to operate in the breakdown region; used for voltage regulation.
Varactor
Zener
N
+
P
electron flow
depletion layer
An ideal diode acts like a closed switch when forward biased and an open switch when reverse biased. 1st approximation calculations assume an ideal diode. 2nd approximation calculations take into account the voltage drop across the diode. 3rd approximation calculations additionally take into account bulk resistance. Voltage Drop silicon diode .7V germanium diode .3V Bulk Resistance rB = ∆E/∆I A digital multimeter won't measure the resistance on a diode due to insufficient voltage. The diode check function of a digital multimeter reads the knee voltage. The knee voltage is the voltage at which a forward biased diode begins to conduct.
Avalanche Effect Reverse voltage exceeds the breakdown voltage and the minority carriers are given enough energy to dislodge valence electrons from their orbits. These free electrons then dislodge others. Zener Effect The electric field becomes strong enough across the junction of a heavily-doped reverse-biased diode to pull valence electrons from their shells. For breakdown voltages below 5V, the Zener effect dominates, above 6V the avalanche effect dominates. Second Approximation for a Zener Diode V − Vz I z = in Rs + Rz
Iz = zener current Vin = supply voltage Vz = zener voltage Rs = source resistance Rz = zener resistance
Zener Resistance is the small series resistance of a zener diode when it operates in the breakdown region. ∆Vout = ∆I z Rz
∆V = change in output voltage ∆Iz = change in zener current Rz = zener resistance
Diode Ratings: PIV Reverse Breakdown Voltage If Forward Current Limit IS Saturation Current - minority carrier current of a reverse-biased
ELTE 1403
Forward biased diode: cathode anode
Varactor is a silicon diode optimized for its variable capacitance when reversedbiased. Used for tuning frequencydependent equipment. Zener Diode is designed to operate in the breakdown region; used for voltage regulation.
Varactor
Zener
N
+
P
electron flow
depletion layer
An ideal diode acts like a closed switch when forward biased and an open switch when reverse biased. 1st approximation calculations assume an ideal diode. 2nd approximation calculations take into account the voltage drop across the diode. 3rd approximation calculations additionally take into account bulk resistance. Voltage Drop silicon diode .7V germanium diode .3V Bulk Resistance rB = ∆E/∆I A digital multimeter won't measure the resistance on a diode due to insufficient voltage. The diode check function of a digital multimeter reads the knee voltage. The knee voltage is the voltage at which a forward biased diode begins to conduct.
Avalanche Effect Reverse voltage exceeds the breakdown voltage and the minority carriers are given enough energy to dislodge valence electrons from their orbits. These free electrons then dislodge others. Zener Effect The electric field becomes strong enough across the junction of a heavily-doped reverse-biased diode to pull valence electrons from their shells. For breakdown voltages below 5V, the Zener effect dominates, above 6V the avalanche effect dominates. Second Approximation for a Zener Diode V − Vz I z = in Rs + Rz
Iz = zener current Vin = supply voltage Vz = zener voltage Rs = source resistance Rz = zener resistance
Zener Resistance is the small series resistance of a zener diode when it operates in the breakdown region. ∆Vout = ∆I z Rz
∆V = change in output voltage ∆Iz = change in zener current Rz = zener resistance
Diode Ratings: PIV Reverse Breakdown Voltage If Forward Current Limit IS Saturation Current - minority carrier current of a reverse-biased