ECEN 215, Principles of Electrical EngineeringDr. Mina RahimianLecture# 22 Date: 11/13/13Chapter 10, DiodesDiode is an electronic device that has two terminals : Anode and cathode.Diode allows an electric current to flow in one direction (called the diode's forward direction), while blocking current in the opposite direction (called diode's reverse direction). Thus, the diode behaves as a check valve. It has many applications such as rectifiers and voltage regulators.By applying a small positive voltage across diode, it will conduct. If the voltage is negative, it blocks the current. If the reverse-biased voltage is sufficiently large, it will operate to reverse breakdown and conducts the current in the reverse direction.The unidirectional behavior of diode is called rectification and is used to convert alternating current (ac) to direct current (dc).Zener DiodeDiodes that are intended to operate in the breakdown region are called Zener diodes. Their breakdown voltage is lower than the conventional diodes to prevent it from overheating in the breakdown region.Zener diodes are used in the regulator circuits to produce a constant output from a variable supply voltage.Light-emitted diode (LED)LED is a semiconductor light source. They are used as indicator lamps in many devices. When LED is forward bised, electrons release energy in the form of photons and illuminates.Load-line analysis of diode circuitsVoltage-ampere characteristics of diodes are non-linear. In the circuits containing diodes and resistors, we can graphically find the operating point of the circuit, by drawing the load line. Load line is the plot of a line obtained from the KVL equation which involves voltage and current of the diode. The intersection of the load line and the v-i characteristic of the diode determines the operating point.Ex. Determine the operating point of the circuit with the following v-i characteristics for diode.Ideal diode modelAn ideal diode is a perfect conductor with zero voltage drop in the forward direction. In reverse direction it is an open circuit.Ex. Find the state of each diode using the ideal model.Ex. Assuming ideal diodes, sketch the voltage transfer characteristics ( Vo versus Vin).Ex. The v-i characteristics of the LED is shown. Determine the v and i.Half wave rectifierIn the half wave rectifier circuit, diode blocks the negative current and the output voltage will be zero when the input voltage is negative.Half wave rectifier with smoothing capacitorIn a rectifier we often need a nearly constant voltage at the output, to be used as a power supply for electronic circuits. One approach to smoothing the output voltage is to use a large capacitor across the output terminals.When the input reaches its peak value, the capacitor is charged to the peak voltage. When the voltage drops below its peak, diode is reversed biased and turns off. The capacitor continues to supply current to the load and slowly discharging until its voltage is less than the input voltage and the diode turns on