Bipolar Junction Transistor (BJT) - PDF

**Vent Alexis J Tamang BSEE-3B** **Bipolar Junction Transistor** A bipolar junction transistor is a three-terminal semiconductor device that consists of two p-n junctions. **Terminals of BJT** **Base-** The base is the middle terminal bjt between emitter and collector, it controls the flow of cu...

**Vent Alexis J Tamang BSEE-3B** **Bipolar Junction Transistor** A bipolar junction transistor is a three-terminal semiconductor device that consists of two p-n junctions. **Terminals of BJT** **Base-** The base is the middle terminal bjt between emitter and collector, it controls the flow of current between emitter **Emitter-** The emitter is the source of current if the semiconductor is PNP **Collector-** The collector is the source of current if the semiconductor is NPN **Types of BJT** **NPN**- If the majority charge carrier is electron then the flow of current will be Collector-Emitter  **PNP**- If the majority charge carrier is Hole then the flow of current will be Emitter-Collector **Regions of BJT** **Saturation-** The collector-base Junction and emitter-base junction are in forward bias.This region is used for the ON state of a switch. ( Ic=Isaturation) Current saturation is the maximum current flowing between emitter and collector **Cutoff-**The collector-base Junction and emitter-base junction are in reverse bias. The BJT work as a OFF state of a switch.  Ic=0 There are no external supplies connected. There's no collector current and hence no emitter current. In this mode, transistor acts as an off-state of the switch. This mode is achieved by reducing base voltage less than both emitter and collector voltage. Vbe \< 0.7 **Advantage of BJT** **Large Gain Bandwidth-** Gain bandwidth is the difference between maximum & minimum cutoff frequency. **Low Voltage Drop- 0.6v** Forward voltage drop **Long life-** Different techniques of biasing may be used to increase the life of the device. **Disadvantage of BJT** **Low Switching Frequency- I**ts switching time is very low which is another reason for rarely been using in Integrated Circuit. **Leakage Current** **Low Thermal Stability** **Application of BJT** **Converters-** Buck converter, boost converter, inverters or any **DC-DC, DC-AC, AC-AC and AC-DC** **Temperature sensor-** Finding temperature is one of the other applications of BJT. Where this can be found by two voltages at two different levels in a known ratio are subtracted **High driving capability-** It has High driving capability. For high voltage or current-handling capability, devices are connected in series and in parallel correspondingly. **High frequency operation -** The frequency of the BJT for small signal is much higher than its switching frequency, principally due to storage delay. The maximum switching frequency is about 3MHZ. **Digital switch** **Amplifier-** Audio amplifier **Detection circuits-** Can be used in detector circuit **Electronic Switch** **Automatic Switch**