LED’s in Circuits

Audience and Scope

In this paper I will be talking about the use of Light Emitting Diodes (or LED’s) in in circuits used in today’s world and how they work in each device. I will explain the structure of an LED diode, its general circuit, how it works and its impact on today’s technology. The intended target are students interested or planning to study computer engineering. I will be introducing the topic of circuits with a specific use in LED diodes.  A lot of the processes will be simplified to help the reader understand the topic without much past information, but it will include ideas and topics that go further in depth into the subject that can grab the reader’s attention.

LEDs or Light Emitting Diodes is a light source based on a semiconductor. They rely on energy given by the power source which is what releases that energy in the form of light. LED diodes are very simple forms diodes. LEDs have been compared to other forms of light like fluorescent lights. Fluorescent lights are gas controlled, where the light is emitted by the burning of the gas inside the bulb.

Fundamentals of LED’s:

Figure 1: This image includes a more detailed description of an LED. The flat spot was not addressed as it is not

The LED itself is composed of multiple parts. (Figure 1) The anode and cathode leads are the segments that connect to the power source each with its corresponding charge. Anodes are positively charged, and cathodes are negatively charged. These cathodes are connected to the anvil and post, which are the segments inside the epoxy lens. The anvil and post are differentiable by its size and shape. The post is the smaller section while the anvil is larger at the top and is also holding the rest of the components on top of it. Within the anvil, there is the semiconductor chip, which is the main component, the part that lights up. The anvil is the larger segment which holds the semiconductor chip itself or the part that emits the light. The post connects to the anode lead and is connected to the anvil through a wire bond. The main parts of the LED consist of the semiconductor chip and the reflective cavity.

Figure 2: This diagram shows the general structure of an LED. This include the cathode, anode, reflective cavity, LED chip, epoxy lens, bond wire and the anvil and post. (Not labeled)

LED’s are composed of multiple small sections that complete a circuit starting from the anodes and cathodes. (Figure 2) Basic electron bonding will be needed, and chemical processes will need to be noted. The light LED’s emit is solely based on the heat produced as a byproduct to the electron bonding. This would include a proton and electron binding to create a neutral charge which would then emit heat as a result of the combination. However, the color will rely on the material that the anvil section is made from (in other words, the semiconductor). The color can also be changed by modifying the epoxy lens with the normal light, this will cause some imperfections in the spectrum of the yellow the consumer ends up seeing. Light color is strongly dependent on its material rather than the bulb color. This is very similar to fluorescent lights, where color is dependent on the material of the material rather than the color of the bulb itself. Each LED bulb needs to have a complete circuit to be able to light up. If the circuit or any component is damaged, then the light will not appear.

How and why it works

Figure 3: This is a diagram of a standard circuit that includes an LED bulb, a battery labeled with its positive and negative ends, and a resistor.

For LED’s, the energy emitted starts at the power source, which usually would be a battery. (Figure 3) The power will direct to the energy to a small circuit inside the lens. While the electrons go to the LED, the resistor shown will act as a monitor on the amount of energy heading to the LED to avoid any damage. This will chemically charge particles inside the anvil that will emit light as a result of heat generated from the bonded electrons. The electrical processes in the anode and cathode consists of ions bonding in the battery. As each cation and anion bond, energy is released. (Figure 4) The reflective cup would focus the light coming out of the chip. Then, that light is shown through the epoxy lens which will further enhance the strength in brightness of the light originally being emitted.

Figure 4: This is a diagram consists of a standard Lithium ion (Li-ion) battery ion transfer

Impact

LED’s can seem very simple, but their uses can be very complex. Its structure is very similar to that of a lightbulb. They are generally used on electronic devices to signal status of a device. You’ll see a lot of light indicators on multiple objects like toys and remotes. For example, the green/red light indicators on toys that tell the user whether something is ready for use. This has been used on some modern home appliances. There are multiple projects a person can create using these diodes and some code. You can create colorful patterns of light that might attract people. In fact, this has led to the creation and use of smart LED’s. You might have seen them around, especially in smart homes. They look like standard light bulbs with the ability to change colors and controllable through an application on a smartphone rather than on a switch.

This same LED technology has allowed for some to create and sell desktop computers with shiny and colorful cases. The use of RGB lighting involves the use of LED light strips that connect to your computer. Related to computer use, a lot of screens and monitors are LCD, which are LED based monitors. These are much more complicated than just a couple diodes behind a panel, but LED’s have provided a basis for future technology in much more compact items.

Works Cited

Liu, Chaofeng, et al. “Understanding Electrochemical Potentials of Cathode Materials in Rechargeable Batteries.” Materials Today, Elsevier, 14 Nov. 2015, www.sciencedirect.com/science/article/pii/S1369702115003181.

“How Do Light Emitting Diodes and LED Lights Work?” LampHQ, https://lamphq.com/functional-principle-of-leds/

“Leds.” The Soldering Station, http://thesolderingstation.com/how-to/leds/.

Light-Emitting Diodes (LEDs), https://learn.sparkfun.com/tutorials/light-emitting-diodes-leds/#leds-without-math.