1 - Introduction
Component selection is an important skill to have as an EE. It can involve much research, calculation, datasheet reading, and intuition to source components effectively. In order to make the circuit required in the design challenge, you’ll need to select its components. In simpler terms, shopping is an important skill!
2 - Component Suppliers
Components for PCB projects can be sourced from supplier marketplaces where manufacturers and distributors sell their components
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Either of these sites can be used for this bootcamp but this section will cover how to use Digikey to find components, although usually the process is the same for Mouser and other sites.
How to use Digikey
When you open Digikey, you are greeted with a page like this.
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On this page, all the specifications are shown along with price and stock. Note the datasheet link on the page. This link will yield a pdf with all the detailed information about the part. The datasheet is essential to understanding how to use a component.
Components Needed
In order to make your LDO circuit, there are certain external passive components that are needed. Typically, an LDO circuit looks like the one in the schematic below. It requires a main LDO IC which stores the power FET and error amplifier required to regulate the voltage output of the LDO.
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Keep in mind, the exact components you will need will entirely depend on the LDO IC that you select so think about the order in which you need to source your components!
Selecting an LDO IC
An LDO datasheet will likely give example schematics with values which are a great starting point to selecting your passive components. A simple LDO will have the schematic shown in the photo above.
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Also ensure the IC you are selecting has enough stock, this value should be at least in the thousands to be able to reliably source it.
Selecting Resistors
When selecting resistors from Digikey, make sure to use YAGEO as a manufacturer.
Also, it is important to select standard resistor values instead of finding the closest resistance value on Digikey based on a calculation.
The following link shows See standard resistor case sizes here: Resistor Sizes and Packages
See standard resistance values .http://www.interfacebus.com/resistor_table.html here: Standard Composition Resistor Values
Typically 0603 (0.06” length by 0.03” width) is a good size for a component. 0402 is quite small and difficult to solder but can be used to be space efficient while 0805 is usually necessary for components with higher values but they are larger and as a result can usually be assembled easier.
Selecting Input and Output Capacitors
Input and output capacitors require specific capacitance values to properly filter noise on the voltage line and also supply energy in case a large transient or current rush drops the voltage line.
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Selecting LEDs
Selecting LEDs are pretty straightforward on Digikey. Most indicator LEDs on boards are chip surface mount components that look like this.
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An example datasheet is shown above where the LED characteristics are shown. Your current limiting resistor depends on the voltage of the input or output line that the LED is connected to but typically it is no more than 2kΩ. You may need to do some simple math to find the right resistor to get the target limited current you want.
Selecting Connectors
Selecting your connector is quite open, but some recommendations for connectors especially for power is to pick through hole connectors (not surface mount) and also screw terminals. Molex is usually a standard choice but manufacturers are not super important for this board. Male header pins are also another option for connectors, although they are not meant for high current applications.
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