MPSA42 BJT NPN – Transistor 300v 500mA (0.5A)

A BJT MPSA42 NPN can be quite a useful component when designing circuits. First we will start off with a some background information. BJT stands for bipolar junction transistor. If you are not sure what a transistor is then we can somewhat think of it as a relay or switch that is controlled by a very small amount of current, although there are many many other uses for them as well. Amplification and rectification are a couple more common uses as well. What sets this apart from your typical relays is that it you can use an extremely small amount of current to control it, it will control a relatively large amount of current to the control, it is very quick, does not mechanically switch like your traditional relay that you can hear clicking when it turns on and off. They are usually a bit smaller as well and most times in circuits a simple transistor will get the job done in these types of applications. You simply can't go wrong with the MPSA42 BJT NPN.

To touch on the very basics of transistors we will give a very quick explanation. There are two common types of BJT transistors. There are NPN and PNP. While not entirely correct, you can think of the NPN as negative-positive-negative. This means you would use a small amount of positive voltage to control the negative/ground aspect or continuity. The PNP is the exact opposite. While this is a very rudimentary explanation at best, it hopefully will guide you in the right direction of what and how to use a transistor. There is a plethora of information out there on transistors.