![]() ![]() This process of diffusion occurs until diffused electrons and holes oppose further movement of charge carriers to other sides as shown in the above figure. When electrons move from emitter this leaves an empty place, this will be occupied by movement of holes from Base region. In base electrons from Emitter will combine with holes in Base to form electron hole pairs. When combined the electrons from Emitter ( N-type material ) will diffuse into Base ( P-type material ) since concentration of charge carries in Emitter is higher than Base. Working of transistor can be understood by understanding how charge carries behave within its three regions. The process of making a BJT transistor that is combining N-type, P-type and N-type material together will form two transistor junctions – Emitter and Base ( BE ) & Base and Collector ( BC ). However in a BJT transistor there is three regions involved but working principle remains same. Diode has two (N-type and P-type semiconductor ) material combined together. Working of transistor is very much similar to diode since there is a significant resemblance in construction of diode to transistor. This leaves more number of free electrons to move from Emitter to Base and to Collector of the BJT transistor.Ĭircuits Library - 220+ practical circuits Size of the regions in a BJT follows this: Base Base >Collector. Collector forms the largest region in a BJT. Area of Emitter is bigger than Base but smaller than Collector. Base region will be smaller comparing to Emitter and Collector. The important thing to note in the above diagram is that Area of Emitter, Base and Collector are not equal in size. These terminals need to be used by the user to operate the transistor. The terminals attached to NPN or PNP transistors are Collector, Base, Emitter. This is quite similar to the construction of a diode where two semiconductor materials such as P type and N-type joined together whereas in transistor these materials are either two P-type with one N-type in the middle or two N-type with one P-type in the middle. First one is NPN transistor where the device is put together in N-type, P-type and N-type configuration whereas in PNP transistor the device is combined in the following fashion: P-type, N-type and P-type materials as shown in the figure above. This construction of N-type, P-type, N-type semiconductor materials creates two possible transistor configurations. Must read: Resources to self learn Electronics Construction of BJT transistor:īipolar Junction Transistor is a three terminal semiconductor device constructed by joining three semiconductor materials together. Modern electronics we use today made possible because of transistors since it played a huge role in reducing the size of boards drastically. Paralleling linearly controlled MOSFETs for current sharing means having a feedback loop for each device.Transistor is a popular three terminal semiconductor device used in Switching and Amplification applications. Here is a recent example of what happens when the MOSFET is not controlled by the feedback loop. ![]() IRe1 = \$\frac\$ needs to be actively controlled by a feedback loop. With a first order model of Vbe's change with temperature, a simple equation for current in Re1 is: ![]() As the parts heat up, Vbe will reduce allowing more base drive to the transistor from the fixed value of Vc. The problem is that Vbe has a temperature coefficient (\$\gamma\$) of about -1.6mV/C. Re1 and Re2 will help balance current between BJTs. Here is a starting example circuit to show emitter resistor placement. As Olin Lathrop says, the circuit will need to have resistors in series with the BJT emitters to help balance current. For an application where you need to parallel transistors and control current in a linear fashion (not switching the transistors fully on and off), BJTs are your best bet. ![]()
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