What are input characteristics of BJT?

Input characteristics of BJT

BJT stands for Bipolar Junction Transistor, which is a type of transistor used in electronic circuits. The input characteristics of a BJT refer to the behavior of the transistor with respect to the input signal applied to its base terminal. The input characteristics of a BJT are:

• Base-emitter voltage (Vbe): This is the voltage difference between the base and emitter terminals of the transistor. It is the main input signal that controls the BJT's operation.
• Base current (Ib): This is the current flowing into the base terminal of the transistor. It controls the amount of current flowing through the transistor from the collector to the emitter.
• Collector current (Ic): This is the current flowing through the collector terminal of the transistor. It is controlled by the base current and the voltage applied to the base.
• Transistor gain (hfe): This is the ratio of the collector current to the base current, and it determines the amplification capability of the transistor.

The input characteristics of a BJT are usually plotted on a graph called the transfer characteristic curve or simply the transistor characteristic curve. This graph shows the relationship between the input signal and the output signal of the transistor.

A graph between base current Ib, and base-emitter voltage Vbe gives input characteristics. As the base-emitter junction of a transistor is like a diode, Ib versus Vbe graph resembles a diode curve. When collector-emitter voltage VCE2 is more than VCE1 base current decreases as shown in Fig.

frequently asked questions

Q1.What are the input characteristics of a BJT?

The input characteristics of a BJT are the graphs of the base current versus the base-emitter voltage, and the collector current versus the base-emitter voltage.

Q2.Why are the input characteristics of a BJT important?

The input characteristics of a BJT provide important information about the behavior of the transistor in different operating conditions. They are used to determine the biasing of the transistor and to calculate the parameters of the transistor such as the current gain and the cutoff frequency.

Q3.What is the purpose of the base-emitter voltage in the input characteristics of a BJT?

The base-emitter voltage is the voltage applied between the base and emitter of the transistor. It controls the amount of current flowing through the transistor and is an important parameter for determining the operating point of the transistor.

Q4.What is the role of the base current in the input characteristics of a BJT?

The base current is the current flowing into the base of the transistor. It controls the amount of current flowing through the collector of the transistor and is an important parameter for determining the current gain of the transistor.

Q5.How do changes in temperature affect the input characteristics of a BJT?

Changes in temperature can affect the input characteristics of a BJT by changing the value of the thermal voltage, which in turn changes the forward bias voltage across the base-emitter junction. This can cause changes in the current gain and the cutoff frequency of the transistor.

Q6.What are the input output characteristics of the common emitter configuration of BJT?

The input-output characteristics of a common emitter (CE) configuration of a bipolar junction transistor (BJT) can be described as follows:

Input Characteristics:

• Input Voltage: The base-emitter junction of the transistor is forward biased, and a small change in the base current causes a large change in the collector current.
• Input Current: The input current is the base current (IB) and it is measured in milliamperes (mA).
• Input Resistance: The input resistance (ri) is the ratio of the change in input voltage (ΔVBE) to the change in input current (ΔIB). In the CE configuration, the input resistance is relatively low, typically a few kilohms.

Output Characteristics:

• Output Voltage: The output voltage is the voltage across the collector and emitter (VC), and it is measured in volts (V). The voltage gain of the CE configuration is relatively high, typically in the range of 20-200.
• Output Current: The output current is the collector current (IC), and it is measured in milliamperes (mA).
• Output Resistance: The output resistance (ro) is the ratio of the change in output voltage (ΔVC) to the change in output current (ΔIC). In the CE configuration, the output resistance is relatively high, typically in the range of tens of kilohms to a few megohms.

Overall, the common emitter configuration provides voltage amplification and current amplification with medium input impedance and relatively high output impedance. It is a widely used amplifier configuration due to its versatility and ease of use.