I. converts electrical energy into light energy. Mostly

I. TYPES OF DIODEA diode is a two terminal device that conducts current during the forward bias of it, then blocks current if it is in reverse bias. It is not technically blocked but rather a small amount of current still flows in it, usually in mA. The most common diode that we use in present time is the Silicon diode. It is usually in charge to the rectification process in a power supply block diagram. There are many different types of diode that are available for use in electronic designs. 1. Small Signal Diode –  usually applied mainly at high frequency and low current devices. Example of the device that used this type of diodes are radios and televisions. Unlike the common diode that we see, wherein the colors are black and gray (which denotes the negative part). The small signal diode has different color markings, either black or red. 2. Large Signal Diode –  unlike the small signal diode, this type of diode can not hold high frequency applications, Example of one of the applications of it is the inverter. 3. Zener Diode – unlike the normal diode that we use, a Zener diode allows current in both direction (forward and reverse bias). It is usually used in electronic equipments of all kind.4. Light Emitting Diode (LED) – it is a diode which converts electrical energy into light energy. Mostly used in a device that involves light. The maximum voltage that it can accept is 3V. 5. Constant Current Diodes – used as a current limiter, usually have a high output impedance. It also regulates the voltage at a particular current.6. Schottky Diode – one of its important use is that it can increase or decrease the transition of the on and off time of the switch depending of what is the maximum value of the diode used. Usually used in switching applications. 7. Tunnel Diode – used in fast switching applications. Much faster than the Schottky Diode, usually the time measured in nanoseconds. Used in amplifiers. It can be tuned in either electrically or mechanically.8. Varactor Diode – acts almost the same as the variable capacitor. The capacitance can be varied with the use of this diode. Usually used for voltage controlled oscillator for cellphones and pre-satellite filter.9. Laser Diode – usually used in fiber optic communication. 10. Avalanche Diode – usually worked when the diode is in the avalanche breakdown region. It only conducts when it is in reverse bias condition. 11. Vacuum Diodes – consists of two electrodes which acts as anode and cathode. Acts like a switch. The electron will only flow from anode to cathode.  Figure 1.1 Small Signal Diode   Figure 1.2 Large Signal Diode Figure 1.3 Zener Diode Figure 1.4 Light Emitting Diode Figure 1.5 Constant Current Diode Figure 1.6 Schottky Diode Figure 1.8 Tunnel Diode Figure 1.9 Varactor Diode Figure 1.10 LASER diode Figure 1.11 Vacuum Diode II. VARIOUS RECTIFIER CIRCUITS  Half-wave Rectifier During the positive half cycle of the AC sine wave, diode becomes forward bias. Therefore the waveform below is produced. The negative half cycle becomes  reverse biased, therefore no current can flow through it. The half-wave rectifier is used most often in low-power applications. It is much better to use the full wave rectifier than the half wave because the ripple is more steady. Figure 1.12 Half Wave Rectifier Circuit Formula in getting the Average Value of Half-Wave SignalFull-wave RectifierIt allows the current to flow in a one way cycle. It is twice the input frequency and pulsate every half cycle of the input  Figure 1.13 Full Wave Rectifier CircuitFormula in Getting the average Value of a Full Wave Rectified SignalIII. BLOCK DIAGRAM OF A POWER SUPPLY  A DC power supply converts the standard 120V, 60 Hz AC voltage into a constant DC voltage. It is commonly used in appliances used in the house. The process involves the following. From 120V,60Hz AC voltage it will be stepped down into lower AC voltage with the use of a transformer. The primary and secondary turns of the transformer affects the voltage and the current. If the secondary has more turns than the primary, the output voltage in the secondary will be higher while the current will become smaller. After this, it will undergo to the rectification process. There are two types of rectifiers: half wave and full wave. The most commonly used rectifier in the power supply is the full wave rectifier. It consists of four diodes (two forward bias and two reverse bias). The rectifier will then convert the AC input voltage into a pulsating DC voltage, meaning  there is a high ripple present on it. After this, it will eliminate the fluctuations in a rectified voltage with the use of filter. It usually compose of a capacitor, which charge or discharge. After the voltage is filtered, it will maintain the constant dc voltage with the use of a regulator. IV. APPLICATIONS OF DIODE- Rectifier- Voltage Regulator- Clipper- Clamper- Logic Gates

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