Diodes are electronic components that allows current to flow in one direction.
These diodes are manufactured by the semiconductor materials like germanium, silicon and selenium. Operation of diode can be classified in two ways, if it allows the current to flow then it is forward biased otherwise it is reverse biased. For silicon diodes the forward voltage is 0.7v and for germanium it is 0.3v.
In silicon diode the dark band indicates the cathode terminal and the other terminal is anode. Generally diodes are used as reverse polarity protector and transient protector.I. Types of Diodes1.
) Small Signal Diode• Mainly involved at high frequency and very low current devices like radios and TVs.• It is enveloped with a glass for contamination protection• Extensively used as 1N41148 also known as Glass Passivated Diode• Very small compared to a power diode• The maximum carrying capacity of 150mA and 500 mW.• Has high voltage drop ranging about 0.
6 to 0.7 Volts (Silicon) which means it has high resistance but low forward resistance.• Has low resistance due to low voltage drop ranging from 0.
2 to 0.3 Volts (Germanium)2.) Large Signal Diode• Has large PN junction layer which makes AC to DC voltages unbounded.• Not suitable for high frequency applications• Mainly used in battery charging devices like inverters.• The range of forward resistance is in Ohms while the reverse blocking resistance is in mega Ohms.• Since it has high current and voltage performance these can be used in electrical devices which are used to suppress high peak voltages.3.
) Zener Diode• Special type of diode which operates in the reverse bias region• Works under the principle of zener breakdown• First produced by Clarence Zener in 1934• Allows current in reverse direction when the applied voltage reaches the breakdown voltage• Designed to prevent other semiconductor devices from momentary voltage pulses• Mainly used as voltage regulators• < 5V - Zener Breakdown range; ? 5V - Avalanche Breakdwon range; 1.8-200V 4.) Light Emitting Diode (LED)• Converts electrical energy into light energy• Undergoes electroluminescence process in which holes and electrons are recombined to produce energy in the form of light in forward bias condition• PN junction radiates light when current passes through• Uses Gallium compound• Mostly used in traffic signals, camera flashes etc.Color Construction VRed GaAsP 1.
8Orange GaAsP 2Amber AlInGaP 2.1Yellow AlInGaP 2.1Green GaP 2.2White GaN 4.
1Blue GaN 5 5.) Constant current Diodes• Also known as current-regulating or current limiting diode• It functions by regulating the voltage at a particular current• Also functions as a two terminal current limiter 6.) Schottky Diode• The junction is formed by contacting the semiconductor material with metal• Forward voltage drop is decreased to minimum (0.3V)• 50-100V blocking voltage• The semiconductor material is an N-type silicon which acts as the anode where as the metal acts as cathode whose materials are chromium, platinum, tungsten etc.• Have high current conducting capability which reduces switching time and power loss• Mainly used in switching applications• Also used in high frequency rectifier applications 7.
) Shockley Diode• First semiconductor device with four layers• Also calles as PNPN diode• Equal to a thyristor without a gate terminal• With no trigger inputs, the only way the diode can conduct is by providing forward voltage• Has two operating stages: conducting and non-conducting• In non-conducting state, the diode conducts with less voltage 8.) Tunnel Diode• Used as high speed switch• Due to tunnelling effect, it has very fast operation in microwave frequency region• It is a two terminal device in which concentration of dopants is too high• Transient response is being limited by junction capacitance plus stray wiring capacitance• Mostly used in microwave oscillators and amplifiers• Acts as most negative conductance device• Can be tuned electrically and mechanically9.) Varactor Diode• Also known as Varicap diodes• Operations are performed mainly at reverse bias state only• Very famous due to its capability of changing the capacitance ranfes with the circuit in the presence of constant voltage flow• Can vary capacitance up to high values• Can be used as voltage controlled oscillator for cell phones, satellite pre-filters etc.10.) Laser Diode• Active region is formed by P-N junction similar to LED• Electrically laser diode is p-i-n diode• Active region is in the intrinsic region• Used in fiber optic communications, barcode readers, laser pointers, CD/DVD/Blu-ray and Laser printing11.
) Photodiode• converts light/solar energy to electric energy• Specifically designed to operate in reverse bias conditionII. RELATED EQUATIONS OF VARIOUS RECTIFIER CIRCUITS 1.) Half Wave Rectifier• A half-wave rectifier is a rectifier that changes an AC half cycle into a pulsating DC. The figure above shows the derivation of the average voltage of a half wave rectifier (Vave = VDC)2.) Full wave rectifier• A full-wave rectifier is a rectifier that changes every AC half cycle into a pulsating DC.
• Bridge type or Center-tapped transformer The Average Voltage of a full-wave rectifier is twice of that as a half-wave rectifier.III. Power Supply The basic building blocks of a power supply consists of the transformer, rectifier, filter, and regulator. The transformer steps down an AC voltage input to the required voltage level.
The ratio of the turns in the transformer is adjusted to acquire the required voltage value. The transformer’s output would then be the input of the rectifier which would perform the rectification process. In the rectifier, the AC voltage is converted into pulsating DC voltage. This pulsating DC voltage would serve as the input to the filter. The pulsating DC voltage has very high ripple content, in which the filter is used. The filter eliminates fluctuations and ripples in the pulsating DC voltage out from the rectifier.
The most commonly used filter in most power supply is the capacitor. Lastly, the regulator maintains a constant output even when there are changes in the input. Lastly, the regulator which regulates the output to a constant DC level despite the changes in the In AC input.IV. Diode Applications• Rectifier• Inverters• Signal Demodulation• High Speed switching • Amplifier and Oscillator circuits• Over-Voltage Protection
