TYPES OF DIODES Light Emitting Diode (LED)- is a diode that produces light when there occurs a transfer of electric current between the electrodes. Schottky Diode- is a diode, also known as hot-carrier diode, which has a low forward voltage drop and its switching action is very fast. It is formed by joining a semiconductor with a metal. Zener Diode- is a diode that operates in reverse bias. When the reverse bias voltage exceeds the breakdown voltage, Zener effect takes place. Photodiode- is a diode that is used in the detection of light. It generally operates in reverse bias. Varactor Diode- is a diode that has a variable capacitance. There is no current flow because it operates in reverse bias. Shockley Diode- is a diode essentially used for switching applications. It is a semiconductor diode with four layers. It is identical to a thyristor with a disconnected gate. Constant-current Diode- is a diode that limits current to a specific value. It is also known as current-limiting diode (CLD) and current-regulating diode (CRD). This diode keeps the flow of current constant when there are changes in the voltage. Step Recovery Diode (SRD)- is a diode that is able to generate extremely short pulses. It is also called snap-off diode or charge-storage diode or memory varactor. Tunnel Diode- is a diode that has the ability to operate very fast. This is made possible by tunneling, a quantum mechanical effect. PIN Diode- is a diode that has an undoped intrinsic semiconductor region between heavily doped p-type semiconductor and n-type semiconductor regions. Vacuum Diode- is a diode consisting of two electrodes, a cathode, and an anode or plate. The cathode emits free electrons; on the other hand, the anode collects the free electrons. Laser Diode- is a diode used in DVDs and CD drives. This diode is much more expensive that LEDs and also has a partial life. RELATED EQUATIONS OF VARIOUS RECTIFIER CIRCUITSHALF- WAVE RECTIFIER A half-wave rectifier is a rectifier that changes an AC half cycle into a pulsating DC. Figure 1 shows a half-wave rectifier with an AC input waveform and a resultant output waveform.Average Value of the Half-Wave Output Voltage Figure 2 shows the average value of the half-wave output voltage.The average value of the half-wave output voltage can be determined by finding the area under the curve divided by a full cycle. Vp is the peak value of the voltage and 2 ? is the value of full cycle in radians.V_AVG=V_p/?Effect of the Barrier Potential on the Half-Wave Rectifier Output Figure 3 shows the value of input is reduced by 0.7V as an effect of the barrier potential on the half-wave rectifier output.The input voltage must overcome the barrier potential of 0.7 V before the diode becomes forward-biased during the positive half-cycle. The result is a half-wave output with a peak value 0.7 V less than the peak value of the input. V_p(out) =V_(p(in))-0.7VPeak Inverse Voltage (PIV) Figure 4 shows that PIV occurs at the peak of each half-cycle of the input voltage when the diode is reverse-biased. The peak inverse voltage is the peak value of the input voltage. PIV=V_(p(in))Root-mean-square (RMS) Voltage Figure 5 shows the derivation for the RMS voltage of a half-wave rectifier.Root-mean-square (RMS) Current Figure 6 shows the derivation for the RMS current of a half-wave rectifier.FULL-WAVE RECTIFIER A full-wave rectifier allows unidirectional current through the load during the entire 360° of the input cycle. Figure 7 shows a full-wave rectifier circuit with AC input and a resultant output waveform.Average Value of the Full-Wave Output Voltage The average value for the full-wave rectified sinusoidal voltage is twice that of the half-wave.V_AVG=(2V_p)/?Root-mean-square (RMS) Voltage Figure 8 shows the derivation for the RMS voltage of a full-wave rectifier.Root-mean-square (RMS) Current Figure 9 shows the derivation for the RMS current of a full-wave rectifier.POWER SUPPLY Figure 10 shows the block diagram of a power supply with the corresponding waveforms produced in each component.The basic building blocks of a power supply are the transformer, rectifier, filter, and regulator. With an AC voltage input, the transformer steps it down to the required voltage level. The ratio of the turns in the transformer is adjusted to acquire the required voltage value. The output of the transformer would be the input of the rectifier. The rectifier then performs the rectification process. Here, the AC voltage is converted into pulsating DC value. This serves as the input to the filter. The pulsating DC value has very high ripple content. This is what the filter is used for. It eliminates fluctuations in the rectified voltage. There are different types of filters used in power supplies such as capacitor, LC filter, and choke input filter. Lastly, the regulator maintains a constant output even when there are changes in the input.OTHER APPLICATIONS OF A DIODE Power Conversion Diodes are used to convert AC power to DC power. Single diodes can be used to transform 110V household power to DC by forming a half-way rectifier. On the other hand, four diodes can do the same by forming a full-wave rectifier. Signal Demodulation Diodes are used to remove an AC signal’s negative component for it to be used easier with electronics. Demodulation of signals is most commonly used in radios to help extract radio signal from the carrier wave. Over-Voltage Protections Diodes can also be used to protect devices for electronic components that are sensitive. Under normal operating conditions, diodes are non-conducting but they are immediately short when a high voltage spike to the ground where it cannot harm an integrated circuit. Current Steering A basic application of diodes is steering current and making sure that current flows in the proper direction.