![]() ![]() If at some point you choose to pursue electronics at a university, perhaps an Electrical Engineering degree program, you will eventually (likely as a 3rd or 4th year student) reach a class named "Semiconductor Physics" or perhaps "Solid-state Physics". It's rooted in the physics of how charges work inside the structure that has been created inside the device. I presume you are just starting out in electronics and, as such, the WHY of the mechanism of a transistor's behavior can be quite intimidating. This is true, of course, also for diodes, bipolar transistors (BJTs) and FETs. A change of the voltage (of the E-field) causes a change of the current. In electronic circuits, this E-field is generated by an external voltage. In every conductor/semiconductor, a current (movement of electric charges) can exist under the influence of an electric field only. The following sentence alone cannot explain the transistor principle, but it shows that it is the VOLTAGE which plays the decisive role: It is not a problem to show and to verify that \$I_b\$ as well as \$I_c\$ are both dependent on the voltage \$V_ / V_t)-1]\$ because the emitter current \$I_e\$ is split into a very small current ( \$I_b\$) and a larger current \$I_c\$ ( \$I_e = I_b + I_c\$).įinal (summarizing) statement (with respect to the long list of comments): ![]() Nevertheless, during design and/or analysis of transistor stages we can in many cases treat the transistor as if \$I_b\$ would determine \$I_c\$ this is because the relation \$I_c=\beta I_b\$ does apply - but it is a correlation and does not reflect a causality). (It is really a pity that there are still some books and publications claiming that \$I_b\$ would determine \$I_c\$. It is true that the collector curent \$I_c\$ is proportional to the base current \$I_b\$ ( \$I_c/I_b=\beta\$), but this is a kind of correlation. I can understand your doubts - because, in reality, the transistor does NOT amplify the base current. ![]()
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