Check out this post for more information on low-side vs. Like the NPN, it has the same max voltage and current ratings: 40V and 200mA. Its emitter connects to the “high voltage.” Since I recommended a 2N3904 for the NPN, I will suggest its complement: the 2n3906. A high-side circuit is where the load sits between the transistor’s collector and the circuit’s ground.
Its current rating is only 200mA, but that is enough for most relays.įor high-side switch circuits, you need a PNP style BJT. You can easily switch big, like great than 12 volt loads with this transistor’s max 40 volt rating. high-side switches.Ī common transistor I use is the 2N3904.
This configuration means whatever you want to control is connected between the “high” voltage and the collector of the transistor. You can find most often NPN Transistors in low-side switch circuits. You’ll commonly find through-hole parts in the 3-pin TO-92 style package. These little guys are the workhorses of most control circuits, for small current applications. Here are some more details on each of these.īipolar transistors come in small packages, can be driven by I/O pins directly, and are VERY cheap. For NPN Check out the BC547, for PNP the BC557. Jan (comment below) points out that there are European Equivalents that may be more available for those located in that part of the world.
For most circuits either a BJT or MOSFET can be used, depending on the load current you need to switch. For most projects, they are used to turn on a load that would kill the I/O pin of a microcontroller or microprocessor. In digital circuits, they switch on and off while in analog circuits they are used to amplify signals. Transistors are one of the most versatile discrete components in electronics. Every electronics enginerd’s toolbox should have a few of each. Fear not, before wading through spec sheet after spec sheet, consider one of these four general purpose transistors. Which makes answering the question “Which transistor should I use or buy?” a daunting task. When your project needs a transistor, there are tons of choices.
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