Test: Types of Power Diodes - Electrical Engineering (EE) MCQ

When the input voltage is negative, there would be a negative voltage on the diode so it works like an open circuit. Hence no current flows through the load and Vout is zero.

Platinum & gold doping improves the performance of the devices.

Schottky diode uses a Al-Semiconductor junction.

The majority charge carriers in a Schottky diode are electrons not holes.

Due to the metal-silicon junction there are no stored charges hence, no reverse recovery time, due to which the switching is faster.

The metal has no holes hence major(almost full) current flows due to the electrons only.

Usually only n-type silicon is used because the p-type has certain limitations.

Due to the metal-silicon junction there are no stored charges, hence no reverse recovery time due to which the switching is faster.

 Ideal conduction = No losses.

 Recall the I-V curve of a diode in the 3rd quadrant.

Due to the metal used to carry the current, it is also called as a hot carrier diode.

The Al (Metal) always acts as the anode.

Higher the doping, more the number of charge carrier available to neutralize the opposite charges on the junction.

 Low reverse voltage rating is the only drawback against a p-n junction diode.

The metal acts as the anode and the semiconductor as a cathode.

 Zener diode is used as a voltage regulating device.

Input is positive, hence it is amplified by the operational amplifier which switches the diode on. Current flows through the load & because of the feedback, the output voltage is equal to the input voltage.

Zener diode has voltage regulating property. When voltage reaches above a certain value (Zener voltage), current starts to flow in the reverse direction.

Concept:- As the forward current increases, the diode current decreases because it is inversely proportional to diode resistance.

• The forward dynamic resistance (also known as differential resistance or small-signal resistance) of a junction diode is a measure of how the diode's voltage drop (V_D) changes with a change in the forward current (I_D).
• It is given by the derivative of the voltage across the diode with respect to the current through it, when the diode is forward-biased.

Mathematically, the forward dynamic resistance (r_d) can be calculated using the Shockley diode equation

Where:
I_D = Diode current,
I_S = Saturation current (the reverse bias saturation current),
V_D = Voltage across the diode,
n = Ideality factor, typically close to 1 for diodes but can vary between 1 and 2,
V_T = Thermal voltage, approximately (26mV) at room temperature (25°C or 298K),
e = The base of the natural logarithm ((≈ 2.71828)).

Barrier voltage

The minimum voltage required by a diode to conduct is known as barrier voltage.

It is also known as the cut-in voltage or knee voltage.

The barrier potential of the "Germanium" diode is 0.3 V.

The barrier potential of the "Silicon" diode is 0.7 V.

Above the knee voltage, the diode conducts and the forward current from p to n flows in the diode.