SunFounder ESP32 Starter Kit
5.7 Transistor
Transistor is a semiconductor device that controls current by current. It functions by amplifying weak signal to larger
amplitude signal and is also used for non-contact switch.
A transistor is a three-layer structure composed of P-type and N-type semiconductors. They form the three regions
internally. The thinner in the middle is the base region; the other two are both N-type or P-type ones - the smaller
region with intense majority carriers is the emitter region, when the other one is the collector region. This composition
enables the transistor to be an amplifier. From these three regions, three poles are generated respectively, which are base
(b), emitter (e), and collector (c). They form two P-N junctions, namely, the emitter junction and collection junction.
The direction of the arrow in the transistor circuit symbol indicates that of the emitter junction.
• P-N junction - Wikipedia
Based on the semiconductor type, transistors can be divided into two groups, the NPN and PNP ones. From the
abbreviation, we can tell that the former is made of two N-type semiconductors and one P-type and that the latter is the
opposite. See the figure below.
Note: s8550 is PNP transistor and the s8050 is the NPN one, They look very similar, and we need to check carefully
to see their labels.
5.7. Transistor 699
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