Diode Part-1 PDF

Lectures: Dr.Hesham Ibrahim Lecturer: Mariam Omer  configuration, operation  Diode equation  Breakdown region  Temperature effect & Diode resistance  Diode symbols, packaging & datasheet.  LED and Zener diode.  Load line analysis and equivalent circuits.  The diode is...

Lectures: Dr.Hesham Ibrahim Lecturer: Mariam Omer  configuration, operation  Diode equation  Breakdown region  Temperature effect & Diode resistance  Diode symbols, packaging & datasheet.  LED and Zener diode.  Load line analysis and equivalent circuits.  The diode is a 2-terminal device  A diode ideally conducts in only one direction  The semiconductor diode is created by simply joining an n- type (majority carrier of electrons ) and a p-type (majority carrier of holes ) material.  Hesham Ibrahim UofK EEED 12/13/2024  No bias  Forward bias  Reverse bias  The term bias refers to the application of an external voltage across the two terminals of the device to extract a response.  This region of uncovered positive and negative ions is called the depletion region due to the “depletion” of free carriers in the region Hesham Ibrahim UofK EEED 12/13/2024 the total potential barrier is reduced. There will be a diffusion of holes from the p region across the space charge region where they will flow into the n region. Similarly, there will be a diffusion of electrons from the n region across the space charge region where they will flow into the p region. The majority carriers of the n-type material must overcome the attractive forces of the layer of positive ions in the n-type material and the shield of negative ions in the p-type material to migrate into the area beyond the depletion region of the p-type material. However, the number of majority carriers is so large in the n-type material that there will invariably be a small number of majority carriers with sufficient kinetic energy to pass through the depletion region into the p-type material. The same type of discussion can be applied to the majority carriers (holes) of the p-type material. No external voltage is applied: VD = 0 V No current is flowing: ID = 0 A Only a modest depletion region exists Hesham Ibrahim UofK EEED 12/13/2024  External voltage is applied across the p-n junction in the same polarity as the p-and n-type materials The forward voltage causes the depletion region to narrow. The electrons and holes are pushed toward the p-n junction. The electrons and holes have sufficient energy to cross the p-n junction. Hesham Ibrahim UofK EEED 12/13/2024 The electric field Eapp induced by the applied voltage is in the opposite direction to the thermal‐equilibrium space charge electric field, so the net electric field in the space charge region is reduced below the equilibrium value. The electric field force that prevented majority carriers from crossing the space charge region is reduced; majority carrier electrons from the n side are now injected across the depletion region into the p material, and majority carrier holes from the p side are injected across the depletion region into the n material. The minority carrier concentrations can increase by many orders of magnitude when a relatively small forward‐bias voltage is applied  External voltage is applied across the p-n junction in the opposite polarity of the p- and n-type materials The reverse voltage causes the depletion region to widen. The electrons in the n-type material are attracted toward the positive terminal of the voltage source. The holes in the p-type material are attracted toward the negative terminal of the voltage source. Hesham Ibrahim UofK EEED 12/13/2024  Note the regions for no bias, reverse bias, and forward bias conditions. Carefully note the scale for each of these conditions. The reverse saturation current is seldom more than a few microamperes diode ideal characteristics. Silicon semiconductor diode characteristics. Hesham Ibrahim UofK EEED 12/13/2024 Hesham Ibrahim UofK EEED 12/13/2024  At a temperature of 27°C (common temperature for components in an enclosed operating system), determine the thermal voltage VT. Solution: Hesham Ibrahim UofK EEED 12/13/2024  In the absence of an applied bias across a semiconductor diode, the net flow of charge in one direction is zero.  The current that exists under reverse-bias conditions is called the reverse saturation current and is represented by Is.  The defined direction of conventional current for the positive voltage region matches the arrowhead in the diode symbol  When forward-biased, there is a small amount of voltage necessary to get the diode going. In silicon, this voltage is about 0.7 v. In Germanium the voltage about 0.3 v.  This voltage is needed to start the hole-electron combination process at the junction. Hesham Ibrahim UofK EEED 12/13/2024 Hesham Ibrahim UofK EEED 12/13/2024  The Zener region is in the diode’s reverse-bias region.  At some point the reverse bias voltage is so large the diode breaks down and the reverse current increases dramatically.  The maximum reverse voltage that won’t take a diode into the zener region is called the peak inverse voltage (PIV) or peak reverse voltage (PRV).  The voltage that causes a diode to enter the zener region of operation is called the Zener voltage (Vz) Hesham Ibrahim UofK EEED 12/13/2024 Hesham Ibrahim UofK EEED 12/13/2024  As temperature increases it adds energy to the diode.  It reduces the required forward bias voltage for forward-bias conduction.  It increases the amount of reverse current in the reverse-bias condition.  Germanium diodes are more sensitive to temperature variations than silicon or gallium arsenide diodes. Hesham Ibrahim UofK EEED 12/13/2024  In the forward-bias region the In the reverse-bias region the characteristics of a Si diode reverse current of a Si diode shift to the left at a rate of 2.5 doubles for every 10°C rise in mV per centigrade degree temperature. increase in temperature. The reverse breakdown voltage of a Si diode will increase or decrease with temperature. Hesham Ibrahim UofK EEED 12/13/2024  Semiconductors react differently to DC and AC currents.  There are three types of resistance: DC (static) resistance AC (dynamic) resistance Average AC resistance Hesham Ibrahim UofK EEED 12/13/2024  For a specific applied DC voltage VD, the diode has a specific current ID, and a specific resistance RD. Hesham Ibrahim UofK EEED 12/13/2024  The dynamic resistance is the resistance offered by the diode to the AC signal. Is is equal to the slope of the V-I characteristics (dV/dI or ΔV/ ΔI ) , Hesham Ibrahim UofK EEED 12/13/2024 An equivalent circuit is a combination of elements properly chosen to best represent the actual terminal characteristics of a device or system in a particular operating region Piecewise-Linear equivalent circuits Hesham Ibrahim DEEE UofK 12/13/2024 Simplified Equivalent Circuit Ideal Equivalent Circuit Hesham Ibrahim DEEE UofK 12/13/2024  Data about a diode is presented uniformly for many different diodes 1. Forward Voltage (VF) at a specified current and temperature 2. Maximum forward current (IF) at a specified temperature 3. Reverse saturation current (IR) at a specified voltage and temperature 4. Reverse voltage rating, PIV or PRV or V(BR), at a specified temperature 5. Maximum power dissipation at a specified temperature 6. Capacitance levels 7. Reverse recovery time, (is the time required for a diode to stop conducting once it is switched from forward bias to reverse bias) 8. Operating temperature range Hesham Ibrahim DEEE UofK 12/13/2024 DATA SHEET Hesham Ibrahim DEEE UofK 12/13/2024 Hesham Ibrahim DEEE UofK 12/13/2024