BC547 is an NPN Bipolar Junction Transistor. A transistor is a semiconductor device used for amplifying or switching an electronic signal.
Like all other transistors, BC547 has three pins called the emitter, collector, and base. The transistor acts like a switch between the collector and emitter. And if the base of the transistor is given enough current, this switch closes and the current flows from the collector to the emitter. So a small current to the base pin of the transistor switches the large current between the collector and the emitter.
BC547 is also used for the amplification of the input signals. A small amount of current at the base is used to control a large amount of current between the collector and emitter. So basic applications of BC547 are switching and amplification.
Pinouts of BC547:
|Pin Number||Pin Name||Description|
|1||Collector||This pin act as an inlet as current enters the transistor from here. The collector is denoted by ‘C’.|
|2||Base||This pin controls the transistor biasing. The base is denoted by ‘B’.|
|3||Emitter||This pin act as an outlet and current comes out of the transistor from here. The emitter is denoted by ‘ E’.|
BC547 comes in two packages SMD package and TO-92 package.
Click this link to view the entire DATASHEET of BC547
You can find detailed information on BC547 in the datasheet given above. Specifications and characteristics like Absolute maximum ratings, Block diagram, biasing methods, and package dimensions can be found in the datasheet.
Features / technical specifications:
- Package-Type: TO-92
- Transistor Type: NPN
- Max Collector Current (IC): 100mA
- Max Collector-Emitter Voltage (VCE): 45V
- Max Collector-Base Voltage (VCB): 50V
- Max Emitter-Base Voltage (VEBO): 6V
- Max Collector Dissipation (Pc): 500 milliwatt
- Max Transition Frequency (fT): 300 MHz
- Minimum & Maximum DC Current Gain (hFE): 110 – 800
- Max Storage & Operating temperature Should Be: -65 to +150 Centigrade
- Low Noise: 2-10 dB
Circuit applications of BC547 transistor:
- BC547 transistor can be used as an alternative to many transistors (BC549, BC636, BC639, 2N2222 TO-92, 2N2222 TO-18, 2N2369, 2N3055, 2N3904) in the electrical circuit
- The highest transition frequency of BC547 is 300MHz. Thus, it can also be used in RF circuits.
- Amplification of current
- Audio Amplifiers
- Switching Loads < 100mA
- Transistor Darlington Pairs
- Amplifiers like Audio, signal, etc.
- Darlington pair
- Quick switching
- PWM (Pulse Width Modulation)
Working States OR Modes of Operation of BC547:
Like every other transistor BC547 transistor works in three regions:
- Active Region.
- Saturation Region.
- Cut off Region
(a) Active region
The active region lies between the cut-off and saturation regions. In the active region, the transistor emitter junction is forward biased and the collector junction is reverse biased. In the active region, the collector current is β times the base current, i.e.,
here, IC = collector current
Β = current amplification factor
IB = base current
So the collector current increases in proportional to the base current.
(b) Saturation region
In this region, transistor works like a short circuit. The collector and Emitter currents are maximum in this region. In the saturation region, both the emitter and collector junctions are forward biased. In other words, the transistor operates as a closed switch or short circuit carrying maximum current which implies:
here IC = collector current and IE = emitter current.
(c) Cut-off region
In this region, transistor works as an open switch or open circuit. The collector, emitter, and base currents are all zero in this region. In the cut-off region, both the emitter and collector junctions are reverse biased. As in the cut-off region, the collector, emitter, and base current are zero, which gives
here IC = collector current, IE = emitter current, and IB = base current.
BC547 TRANSISTOR AS A SWITCH
The region responsible for a transistor to work as a switch are Saturation Region and the Cut-off Region. When we apply high enough current at the base of the transistor, it makes a path for the collector current to go through the base towards the emitter.
In order to use the transistor as a switch, it must be driven into the saturation region with enough base current. And a transistor operates as a closed switch under the saturation region.
As soon as a positive signal (in form of voltage and current) is removed across the base of the transistor, the flow of electric current between the collector and emitter becomes zero. And the transistor behaves like an open switch under the cut-off region.
This simply implies if we apply signal (voltage/current) across the collector and emitter but not across the base, the transistor will not work. But a small signal across the base is enough to make it work.
BC547 TRANSISTOR AS AN AMPLIFIER
A transistor acts as an amplifier by increasing the strength of a weak signal applied at its base. Transistors work as an amplifier in the active region or linear region. The figure given below shows how to use a transistor as an emitter amplifier.
**Image Source: instrumentationtools
In this region, with the increase in the base current, the collector current also increases proportionally according to the formula:
Here, IC = collector current
Β = current amplification factor
IB = base current
Thus, a small input signal results in a large output, which implies that the transistor works as an amplifier.
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