Diode voltage blocking circuits are used to switch in backup power supplies. In these circuits two diodes are used. When the main power to an electronic device goes out, the main power diode turns off and the auxiliary power diode turns on. In this application, the diodes work much like switches. One diode switches off and disconnects the electronic device from the main power supply and the other diode switches on, connecting the electronic device to the auxiliary power supply.
Often designers need to limit the amount of voltage applied to the input of an electronic component. With a diode clamping circuit, this is easily accomplished. A simple clamping diode circuit includes just one diode that is connected between the input pin of the electronic component and the positive terminal of the circuit's power supply.
Because your everyday diode has a forward voltage of 0.7 volts, a diode clamp to a 5-volt power supply terminal from an input pin will limit the maximum voltage at the input to 4.3 volts, since 5 – 0.7 is 4.3.
Diodes are used in full rectifier circuits to convert alternating voltage (AC Voltage) obtained from your standard wall socket, to a constant voltage (DC voltage), such as that obtained from a battery. Electronic devices like computers, cell phones, printers and copy machines often need a constant 5-volt power supply to operate. For that reason, you will almost always find a full wave rectifier in all of today's electronic devices.
The light-emitting diode, also known as an LED, emits light when a voltage is applied across its terminals. The basic LED circuit consists of a battery in series with a resistor and an LED. The value of the resistor controls how much current will flow into the LED. Since the amount of current is proportional to the brightness of the LED, the value of the resistor also controls the brightness of the LED. For the LED diode circuit, the battery voltage must be higher than the forward voltage specification of the LED. The forward voltage of LEDs ranges from about 1.7 volts up to 6 volts. Forward voltage specifications are dependent on the color of the LED and the size of the LED.