In switch circuits, the load is what limits current. The BJT Collector just needs to conduct better than the load in order to be considered fully on. NPN bipolar junction transistor BJT switch circuit pictorial and schematic diagram by electronzap

PNP BJT current flows in the opposite direction of NPN.

The load sets the current through it and the collector when the BJT switch is on. The Load of a switch circuit is placed on the collector side of the transistor. Without Base current, there will also be no current flow from Collector to Emitter if using NPN BJTs.

The base to Emitter drops about 0.6V from the resistor used to set the Base to Emitter current.

And the BJT needs to not conduct at all while it is off. BJT switch circuits need to have the transistor conducting freely while it is on.Exact amount depends on the part number of the transistor. A small amount of Base current allows many times that amount of Collector current.There’s no Collector current without Base current.Switch circuits using BJTs are normally off. BJT Switch: Low side NPN BJT switch versus high side PNP BJT switch using bipolar junction transistors schematic diagrams by electronzap Includes 2N3904 NPN BJTs and 2N3906 PNP BJTs. Nice assortments of semiconductors that I use in my videos. Schematic symbols for NPN PNP BJTs N channel P channel JFETs and common MOSFET variations diagram by electronzap electronzapdotcom Hopefully there is a part number next to it.

Whereas, the FET symbols that I use are just 1 of many ways that you will see them if you look at a lot of schematic diagrams. The BJT symbols shown below are used by almost everyone, although they may not be circled. NPN PNP Bipolar Junction Transistor BJT gain or beta current flow illustrated by electronzap It helps to remember these things when looking at a schematic with BJTs. A small amount of Base (to Emitter) current allows many times that amount of current to flow from Collector to Emitter. To support this site, check out the following links:īipolar Junction Transistors ( BJTs) have a variable amount of current that is allowed to flow from Collector to Emitter.Light Dependent PNP BJT switch circuit example:.Light Dependent NPN BJT switch circuit example:.

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