BC547 is an
npn bi-polar junction transistor. a
transistor stands for transfer of resistance, mainly used for amplification and
switching purposes. it has a maximum current gain of 800. The transistor
terminals require a
fixed dc voltage
to operate in
the desired region of its characteristic curves. bc547 is used
in common emitter configuration for amplifiers.
the voltage divider
is the commonly
used biasing mode. for
switching applications,
transistor is biased so that it remains fully on if there is a signal at its base.
in the absence of base signal, it gets completely off. its equivalent
transistors are bc548 and bc549. together with other electronic components,
such as resistors, coils, and capacitors, it can be used as the active
component for switches and amplifiers.
Figure 1: pin diagram of bc547B
- VCE=.7 t0 30v
- Imax=100mA
- gain 200 to 450
- VBE on =0.7
- Vinput max =5V
- maximum frequency nearly 1MHz (750ns)
Sample application
Figure 2: TRANSISTOR AS RELAY DRIVER
BASE RESISTOR DESIGN
From data
sheet,
Maximum Collector
current Ic = 100 mA
Current gain
β = 200 – 450
take β=200 and Ic = 100 mA
β = Ic/Ib
Ib = Ic/ β
=
100/200 = 0.5mA
There will
be a drop of 0.7V across base emitter
junction of transistor
Ie,.. VBE =
0.7V;
Voltage across
the resistor Rb ,Vb =input base voltage
control signal - VBE
= 5-0.7 = 4.3V
R = Vb/Ib
=4.3/(0.5*10-3)
= 8.6 KΩ
Select the
value less than above value
Rb=7.2K
