As a simple example, let’s say the load is just a 150 Ω resistor with a 5 V supply. This means we can effectively ignore the transistor in our load current calculations and the GPIO pin current (I B) is about a tenth of the load current (I C). When a typical BJT transistor is operating as a switch in this mode, certain assumptions are usually made to make the calculations easier. This involves operating the transistor in saturation mode, i.e., V E V C for NPN and V E > V B < V C for PNP transistors. Schematic Diagram Of Transistor Switch Circuit For instance, the maximum current ratings of the GPIO pins for the Arduino Uno is 20 mA and the Raspberry Pi is 16 mA. Sometimes a BJT transistor is used as a switch to drive higher loads (current) than is typically capable from a microcontroller’s GPIO output pins.

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The resources created for this tutorial are available on GitHub for your reference. I will instead concentrate on how to set up and run simulations in KiCad because that material is not as readily available. There are already quite a few tutorials and resources on the internet to help you with creating schematics, including the KiCad Eeschema manual.

The focus of this article will be on running circuit simulations within KiCad, not on how to create a schematic. A basic understanding of electronics is expected along with knowing how to create schematic diagrams in KiCad. This tutorial will teach you how to run a circuit simulation in KiCad. Skill Level: Intermediate Table Of Contents

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