Diode Projects
- Diodes conduct current in only one direction.Jupiterimages/Photos.com/Getty Images
A diode is an electronic device that acts like a one-way valve, letting electrical current flow in only one direction. It has a cathode (negative) and anode (positive) side, and its schematic symbol is arrow-shaped, pointing in the direction in which it prefers to conduct. You can use diodes in a variety of both alternating current (AC) and direct current (DC) circuits. Some simple circuits will show you how diodes work. - Circuits that change AC to DC use rectifiers. These are diode combinations that exploit the device's one-way action to alternately conduct and block the positive and negative parts of an AC waveform. A simple dimmer switch project will illustrate a diode's ability to cut AC voltage in half. You'll need a variac or step-down transformer of 6 to 24 volts, a diode rated for at least .5 amp, a light bulb with the same voltage as the transformer and a single-pole, double-throw (SPDT) switch. The light bulb connects to the transformer output and the switch center. The switch throws connect to the transformer and the diode. The other side of the diode connects to the transformer. When you plug the transformer into an AC outlet, the light bulb will glow brightly when switched directly to the transformer and dimly when switched to the diode.
- A zener diode works in the direction opposite to a normal diode. In this reverse mode, it holds the voltage across it to a fixed, factory-set value specified on the diode's package. You can build a simple voltage regulator with a 9-volt battery, a zener diode rated at between 6 and 8 volts, and a 100-ohm resistor. Wrap or solder one of the resistor's leads to the zener's cathode (striped side). Touch the resistor's free lead to the battery's positive terminal. Touch the free (anode) lead of the zener to the battery's negative terminal. Measure the voltage across the zener with a multimeter. You should read the same voltage as the zener's rated value.
- The voltage doubler circuit consists of a pair of diodes and a pair of 1000 picofarad capacitors. The first capacitor is in series with the AC source, followed by a diode in parallel, then a series diode and parallel capacitor. The cathode of the parallel diode connects to the anode of the series diode. The voltage across the second capacitor is twice the AC source's voltage. Do not use this circuit with 120 volts AC as the input, as the output's 240 volts could give you a nasty shock. Instead, you can set this up using the step-down transformer from the "Rectifer" section. Doubling a 12 volt AC input to 24 volts is safe.
