In this episode, Karen reviews pin junctions and talks about how they differ from other types of common diodes, such as schottky diodes, zener diodes, LEDs (light emitting diodes), laser diodes, and photodiodes. Connect with Karen on element14: http://bit.ly/2CD2ct4

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PN junctions are considered your typical diodes. They have a pn junction with a threshold voltage that has to be reached before current will flow through them. In silicon diodes, this is 0.7V. Once this is reached, the current will continue flowing. When hooked up backwards, in reverse bias, these diodes do not allow current to flow. If a diode is reverse bias, and it’s supplied with too much voltage, more than it’s breakdown voltage, it’ll “breakdown” and current will flow through it in the wrong direction. Schottky diodes often look like typical diodes. But unlike pn junction diodes, Schottky diodes have a metalsemiconductor junction. Silicon diodes require time for their depletion zone to grow and shrink when switching from allowing forward current to blocking reverse current. There’s a recovery time. Schottky junctions have no depletion zone. Because of their metalsemiconductor junction, Schottky diodes require virtually no recovery time and therefore have much faster switching speeds. This means they can handle switching current better and faster, which makes them useful in high frequency applications. They also have a lower forward voltage drop. Silicon diodes have a voltage drop of around 0.7V, but the voltage drop of Schottky diodes is between 0.15 V and 0.46 V. This means they lose less energy to heat, making them more efficient. Schottky diodes are not useful for all applications, as they can leak a small amount of current backwards. This could be problematic for certain circuits. While Schottky diodes can let some voltage leak through backwards, zener diodes are designed to allow current to flow in both directions. The pn junction of zener diodes is heavily doped, only a specific voltage, the Zener voltage (Vz) can pass through without damaging the diode. In reverse bias, current will not flow through until the zener voltage is reached, but the voltage will be limited to the zener voltage. For example, a 3.3V zener diode will not allow current to flow until the supply voltage reaches 3.3V. If it’s supplied with 2V, no current flows. However, this diode could be supplied with 5, 6, 9, 12 Volts and it will regulate the voltage output to 3.3V. Zeners can have zener breakdown voltages of anywhere from 1.8V all the way up to 200V. LEDs, light emitting diodes, use energy from the particles moving through the pn junction to create light. They can do this because they are made with gallium arsenide. Unlike silicon diodes, diodes made with gallium arsenide release energy in the form of light or photons. Like other diodes, they typically have 2 leads, though these can vary in length depending on the manufacturer. LEDs come in a wide variety of packages. Throughhole LEDs can be 3mm, 5mm, 10mm. They can have round and square lenses. Lenses can be clear or colored. 5mm round ones are the most common throughhole LEDs. Surface mount LEDs come in a variety of sizes as well. When choosing an LED, one of the first things you’ll look for is color, or wavelength. (ChartVO) Here’s a chart of the color spectrum. Another choice you’ll have is beam angle or viewing angle. Beam angle is the amount of degrees where the light is visible. Depending on your application, you may want a narrow beam angle, like 10deg or a wide beam angle, like 120deg.