![]() ![]() VCE – Collector voltage with respect to ground minus emitter voltage with respect to ground (VC – VE)Ĥ. VBE – Base voltage with respect to ground minus emitter voltage with respect to ground (VB – VE)ģ. ![]() VBE – Base voltage with respect to ground minus emitter voltage with respect to ground (VB – VE)Ģ. Some NPN Transistor Principles and Technicalities:ġ. VC – collector voltage with respect to ground VE – emitter voltage with respect to groundġ3. VB – Base voltage with respect to groundġ2. Emitter current (I E) – current flowing through the emitterġ1. Collector current (I C) – current flowing through the collectorĥ. Base current (I B) – current flowing through the baseĤ. Current gain – the ratio of two currentsģ. Do not be confused as both of them refer to the current gain of a transistor particularly the ratio I C to I B.Ģ. Beta or HFE – Beta and HFE are used interchangeably by manufacturers. These rely on the amount of base current. Once the NPN transistor is ON, you can set its operation mode whether amplifier or switch. The base and collector current of NPN transistor is related by the term beta (β). The amount of collector current will strongly depends on the level of the base current as long as the operation is in active region. ![]() Once VBE is overcome, being a current controlled device will take place. However, the variation on the VBE if not properly considered will jeopardize the transistor operation as the base current will change and then there will be change on the collector current as well, when operating in the active region. In usual applications the applied voltage to the base is always much higher than the VBEsat, thus the VBEsat variation may not a problem. (Some datasheet uses VBEsat to define base-emitter voltage). For instance BC817-25 of NXP semiconductors, VBEsat varies with temperature and collector current. In actual application, VBE must be based on the datasheet of the transistor used. The voltage needed to overcome the base-emitter junction (VBE in short) is same with a diode drop around 0.7V. ![]() To turn on a transistor, the base-emitter junction must overcome. With this property, it is now obvious that you need a resistor in series with the base to set the level of current flowing through the base.Īctually, there are only two general things to remember in dealing with NPN transistor principles:Īt first, you need to turn on the transistor before the current can flow to the base. It is not the level of the voltage applied to the base but the amount of current flowing to the base that makes the transistor to operate. What this means? This means, it needed a current flow to its base for it to function normally as expected. NPN Transistor Principles and Electrical Propertyīipolar junction transistor in general is a current controlled device. NPN transistors are useful in logic implementations, electronic switches, relay drivers, motor drivers and amplifier applications. For instance the popular small power, NPN transistor BC817 by NXP has several packages as below.Ĭredit to the owner of this photo Some NPN power packages are: NPN transistor nowadays comes in variety of packages. For a diode, anode is basically the positive terminal while cathode is the negative terminal and NPN transistor has two diodes with connected anodes as the P type material is sandwich by two N type materials. NPN transistor is can be viewed as two diodes with connected anodes as below figure. In the N type material, negative charge is dominant while positive charge is dominant in the P type material. There are two N type materials sandwiching the P type material. NPN transistors are using below structure to define its material composition. NPN transistors are using below schematic symbols. NPN transistor is the name given to a bipolar junction transistor with two N type materials or negative carriers while there is only one P type material or positive carrier. Universities are covering this topic very well but despite I still attempt to discuss NPN transistor principles that I think easier to understand for non technical people. ![]()
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