BC547 Transistor

 

BC547 Transistor - A transistor is essentially an electrically controlled switch. There's an input, output, and an impact line mentioned because the emitter, collector, and base. When the control line (base) is triggered it'll connect the emitter and therefore the collector a bit like switching a switch. Since the power between the emitter and collector are often above the bottom, transistors are often used as amplifiers.


The BC547 is a NPN transistor meaning when power is applied to the base (control pin) it will flow from the collector to the emitter. Typically NPN transistors are used to “switch ground” on a device, meaning, they are placed after the load in a circuit.

NPN transistor consists of a layer of P-doped semiconductor between two layers of N-doped material. By amplifying current the base we get the high collector and emitter current. It allows the greater current and faster operation; because of this reason most bipolar transistors used today are NPN.


BC547 Transistor Features

  •      Bi-Polar NPN Transistor
  •     DC Current Gain (hFE) is 800 maximum
  •     Continuous Collector current (IC) is 100mA
  •     Emitter Base Voltage (VBE) is 6V
  •     Base Current (IB) is 5mA maximum

BC547 has a gain value of 110 to 800, this value determines the amplification capacity of the transistor. The maximum amount of current that could flow through the Collector pin is 100mA, hence we cannot connect loads that consume more than 100mA using this transistor. To bias a transistor we have to supply current to base pin, this current (IB) should be limited to 5mA.

When this transistor is fully biased then it can allow a maximum of 100mA to flow across the collector and emitter. This stage is called Saturation Region and the typical voltage allowed across the Collector-Emitter (V­CE) or Base-Emitter (VBE) could be 200 and 900 mV respectively. When base current is removed the transistor becomes fully off, this stage is called as the Cut-off Region and the Base Emitter voltage could be around 660 mV.

Also See: BC548 CDIL Transistor

BC547 as Switch

When a transistor is used as a switch it is operated in the Saturation and Cut-Off Region as explained above. As discussed a transistor will act as an Open switch during Forward Bias and as a closed switch during Reverse Bias, this biasing can be achieved by supplying the required amount of current to the base pin. As mentioned the biasing current should maximum of 5mA. Anything more than 5mA will kill the Transistor; hence a resistor is always added in series with base pin. The value of this resistor (RB) can be calculated using below formulae.

RB = VBE / IB

Where, the value of VBE should be 5V for BC547 and the Base current (IB depends on the Collector current (IC). The value of IB should not exceed mA.

BC547 as Amplifier

A Transistors acts as an Amplifier when operating in Active Region. It can amplify power, voltage and current at different configurations.

  • Some of the configurations used in amplifier circuits are
  • Common emitter amplifier
  • Common collector amplifier
  • Common base amplifier

Of the above types common emitter type is the popular and mostly used configuration. When uses as an Amplifier the DC current gain of the Transistor can be calculated by using the below formulae
DC Current Gain = Collector Current (IC) / Base Current (IB)

Applications

·         Driver Modules like Relay Driver, LED driver etc..
·         Amplifier modules like Audio amplifiers, signal Amplifier etc..
·         Darlington pair

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