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
Figure 1: pin diagram of bc547B
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