A diode is a simple electronic component that acts like a one-way valve for electricity, letting it flow in one direction but not the other. Many useful circuit designs have diodes and one or two other parts. By building a variety of small projects with diodes, you can quickly gain useful, hands-on experience.
A rectifier converts alternating current (AC) to direct current (DC) for powering electronic devices from a standard household outlet. It consists of four diodes connected together in a diamond pattern. The diodes control current flow so that, during the positive half of an AC cycle, one pair of diodes conducts in the forward direction and the other pair blocks current flow. During the negative half of the cycle, the two pairs switch roles, reversing the current's direction. The rectifier produces a positive output regardless of the input.
A voltage doubler circuit is another simple diode arrangement that works with AC. A doubler uses a pair of diodes to charge a pair of capacitors. When the AC cycle swings positive, one capacitor stores the peak voltage. When it swings negative, the other diode reverses the current direction, making the voltage positive again. The two cycle halves add together, producing a peak DC voltage output that doubles the peak value of the incoming AC wave.
You can build simple AND and OR computer logic gates using two diodes and a resistor. In both cases, the resistor acts to limit current through the diodes and the circuit you use to drive the inputs. The OR gate simply sums two input currents together, so it outputs a logic "high" value if either input goes "high." The AND gate sends current back into the driving circuits unless both of them have a "high" value. When this happens, current flows to the output, driving it "high."
A single diode and switch can serve as a lamp dimmer circuit. The switch connects to both sides of the diode, so when you close it, it routes all the current through it, avoiding the diode and driving a lamp to full brightness. When you open the switch, it puts the diode in the circuit. The diode conducts during one-half of the AC cycle but blocks the other half, which effectively dims the lamp by 50 percent. To build this circuit, you'll need to select a diode rated to at least 150 volts and to the lamp's maximum current.
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