Erica Synths EDU DIY Mixer Eurorack Module Kit - Manual (Page 30)

BIPOLAR JUNCTION TRANSISTORS
Bipolar junction transistors (or BJTs for short) come in two flavors: NPN and PNP. This
refers to how the device is built internally and how it’ll behave in a circuit. Apart from that,
they look pretty much identical: a small black half-cylinder with three legs.
Let’s take a look at the more commonly used NPN
variant first. Here’s how we distinguish between its three
legs.
There’s a collector, a base and an emitter . All 22
three serve a specific purpose, and the basic idea is
that you control the current flow between collector and
emitter by applying a small voltage to the base. The
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relation is simple: more base voltage equals more
collector current . Drop it down to 0 V and the
transistor will be completely closed o ff . Sounds simple –
but there are four important quirks to this.
First, the relation between base voltage and collector current is exponential. Second,
unlike a resistor, a BJT is not symmetrical
– so we can’t really reverse the direction of the
Please note that the pinout shown here only applies for the BC series of transistors. Others, like 22
the 2N series, allocate their pins di ff erently.
The voltage is measured between base and emitter. So „a small voltage“ e ff ectively means a 23
small voltage di ff erence between base and emitter!
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