You may wonder what lets the electronic devices in your household use electricity in their own ways. Electricians that create these appliances as well as other tools used in industry need to know how to connect diodes for these purposes.
When connecting a diode in an electric circuit, make sure the anode and cathode are connected in the circuit such that charge flows from the positively charged anode to the negatively charged cathode.
You can remember this by remembering that, in the diode circuit diagram, the vertical line next to the triangle looks like a negative sign, indicating that end of the diode is negatively charged. You can imagine this means that charges flow from the positive end to the negative one. This lets you remember how electrons flow in the junction of a diode.
Keep in mind the potential and current of the circuit and how that affects the diode's placement. You can imagine the diode as a switch that opens or closes to complete the circuit. If there's enough potential to let charge flow through the diode, the switch closes such that the current flows through. This means the diode is forward biased.
You can then use Ohm's Law
to calculate voltage V, current I and resistance R to measure the difference in voltage between the voltage source and the diode itself.
If you connected a diode in the other direction, this would reverse bias the diode as current would flow from cathode to anode. In this scenario, you would increase the depletion region of the diode, the area on one side of the diode junction that has neither electrons nor holes (areas of no electrons).
The movement of electrons in the negatively charged region would fill the holes in the positively charged region. When creating diode connections, pay attention to how the diode would change depending on the direction it's connected.
The Diode Circuit
When used in electrical circuits, diodes ensure current flows through a single direction. They're constructed using two electrodes, an anode and a cathode, separated by a material.
Electrons flow from the anode, where oxidation or electron loss occurs, to the cathode, where reduction or electron gain occurs. Usually diodes are made with semiconductors that let charge flow through in the presence of an electric current or by controlling their resistance using a process known as doping.
Doping is a method of adding impurities to a semiconductor to create holes and make the semiconductor either n-type (as in "negative charge") or p-type (as in "positive charge").
An n-type semiconductor contains an excess of electrons arranged such that charge can flow freely through while still remaining controllable. They're generally produced from arsenic, phosphorous, antimony, bismuth and other elements that have five valence electrons. A p-type semiconductor, on the other hand, has a positive charge due to holes, and are made from gallium, boron, indium and other elements.
The distribution of electrons and holes lets charge flow between p-type and n-type semiconductors, and, when connected together, the two create a P-N junction. Electrons from the n-type semiconductor rush over to the p-type one in diodes that let current flow in a single direction.
Diodes can typically be made from silicon, germanium or selenium. Engineers who create diodes can use metal electrodes in a chamber without any other gas or with a gas at low pressure.
Features of diodes
These features of diodes transporting electrons in a single direction make them ideal for rectifiers, signal limiters, voltage regulators, switches, signal modulators, signal mixers and oscillators. Rectifiers convert alternating current to direct current. Signal limits allow certain powers of signals to pass.
Voltage regulators maintain constant voltages in circuits. Signal modulators change the phase angle of an input signal. Signal mixers change frequency that passes through and oscillators produce signal themselves.
Diode Installation for Protection
You can also use diodes to protect sensitive or important components of electronic devices. You can use a diode that doesn't conduct under normal circumstances that, when there is a sudden spike in voltage, known as transient voltage, or some other drastic change in signal that may cause harm, the diode will suppress the voltage from harming the rest of the circuit. These electric shocks due to spikes would otherwise damage circuit by applying too much voltage without letting the circuit appropriately adapt to it.
These diodes are transient voltage suppressor diodes (TVSs), and you can use them to either reduce the transient voltage or direct it somewhere else away from the circuit. The silicon-based P-N junction can handle the transient voltage and, after that, return to normal after the voltage spike has passed. Some TVSs use heat sinks that can handle spikes in voltage over long periods of time.
Types of Diode Circuits
Circuits that convert power from alternating current (AC) to direct current (DC) can use either a single diode or a group of four of them. While DC devices use charge that flows in a single direction, AC power shifts between forward and reverse directions at regular intervals.
This is essential for converting DC electricity from power plants to the AC power, which takes the form of a sine wave, used in most household appliances. Rectifiers that do this do so by either using a single diode that only lets one half of the wave pass through or taking the approach of a full-wave rectifier that uses both halves of the AC waveform.
The diode circuit demonstrates how these behavior occur. When a demodulator removes half of the AC signal from a power source, it uses two main components. The first is the diode itself, or rectifier, that increases the signal of one half of the AC cycle.
The second is a low pass filter that gets rid of high frequency components of the power source. It uses a resistor and capacitor, a device that stores electric charge over time, and uses the frequency response of the circuitry itself to determine which frequencies to let through.
These diode circuit designs generally remove the negative component of an AC signal. It has applications in radios that use a filter system to detect specific radio signals from general carrier waves.
Other Types of Diode Applications
Diodes are also used in charging electronic devices like cell phones or laptops by switching from the power supplied by the electronic device's battery to the power of the external power supply. These methods steer the current away from the source and also ensure that, if the battery of the device died, you can take other measures to charge your devices.
This technique holds true for cars as well. If the battery of your car were to go out, you can use jumper cables to change the distribution of red and black cables to use diodes to prevent current from flowing in the wrong direction.
Computers that use binary information in the form of zeros and ones also use diodes to work through binary decision trees. These take the form of logic gates, the basic units of digital circuits that let information pass through based on comparing two different values. These are built using either types of diode pieces that are much more minuscule than diodes in other applications.
- Diodes are very delicate. Never exceed the manufacturer's recommended currents in the forward- or reverse-biased directions. Always exercise caution when building electrical circuits to avoid burning yourself or damaging your equipment.
About the Author
S. Hussain Ather is a Master's student in Science Communications the University of California, Santa Cruz. After studying physics and philosophy as an undergraduate at Indiana University-Bloomington, he worked as a scientist at the National Institutes of Health for two years. He primarily performs research in and write about neuroscience and philosophy, however, his interests span ethics, policy, and other areas relevant to science.