Data Sheet

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358. BJT and FET
Connect points C and D with the 1kW resistor (42) in project #357.
Press the press switch (61) for a while and you will hear gun shots in
soft volume. This is because the 100W resistor (41) limits the current
through the speaker (93). Release the press switch (61) and wait
for a while. You will eventually hear the gun shots start breaking up
and fading out. There are two types of transistors: Bi-polar Junction
Transistors (BJT) like the ones discussed in project #107, and Field
Effect Transistors (FET).
359. FETs
Connect points A and B with the 4-wire (4) in project #357. Press
the press switch (61) for a while and you will hear the re siren in
soft volume. This is because the 100W resistor (41) limits the current
through the speaker (93). Release the press switch (61) and wait for
a while. You will eventually hear the re siren start breaking up and
fading out. FET is a type of transistor where the current is controlled by
electric elds. FET transistors consist of three terminals: source, drain
and gate. Holes or electrons ow from the source terminal to drain
terminal via an active channel, and the ow of holes or electrons can be
controlled by the voltage applied across the source and gate terminals.
There are two main types of FET transistors: JFET and MOSFET.
360. JFET
Connect points E and F with a 4-wire (4) in project #347. Press the
press switch (61) for a while and you will hear space battle sounds in
soft volume. This is because the 100W resistor (41) limits the current
through the speaker (93). Release the press switch (61) and wait for a
while. You will eventually hear the space battle sounds start breaking up
and fading out. The makeup of a Junction Field Effect Transistor (JFET) is
shown in the gure below. Unlike BJTs, JFETs
are exclusively voltage-controlled. They do
not need a biasing current. Electric charge
nominally ows through a semiconducting
channel between source and drain terminals.
Then, applying a reverse bias voltage to
the gate terminal, the channel is squeezed
so that the electric current is reduced or
blocked completely.
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