A small base current controls a larger collector current; IC=βIB.
A BJT has emitter, base and collector. In the active region a small base current gives a larger collector current, I_C=βI_B (β 50–300), and V_BE≈0.7 V. NPN and PNP types. Used for amplification and switching.
A base current of 0.1 mA with β=100 gives 10 mA collector current.
The bipolar transistor amplifies current and switches loads, and it is still widely used in analogue and high-speed designs.
A small base current controls a larger collector current; IC=βIB.
The bipolar transistor amplifies current and switches loads, and it is still widely used in analogue and high-speed designs.
It is the ratio of collector current to base current, typically between about 50 and 300, so a small base current controls a large collector current.
It limits the base current to a safe value and sets the operating point, otherwise the transistor can be damaged by excess current.
Typical applications include using a small signal to switch a relay coil, amplifying a microphone signal before an ADC and driving a motor from a microcontroller pin with a power transistor.
Study "LEDs and photodiodes" first (topic 8 of 104 in Electronics & Embedded). It covers the groundwork this topic builds on.
I_C=I_S e^{V_BE/V_T}. Early effect. Cutoff, active and saturation regions.
A base current of 0.1 mA with β=100 gives 10 mA collector current.
The next topic is "BJT biasing", which builds directly on this one.
It is classed as Beginner in Electronics & Embedded (topic 9 of 104). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
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