Table of Contents
What are BJTs used for?
As with all transistors, the basic function of a BJT is typically to function as a switch or to amplify, filter, and rectify power. Bipolar transistors are current-controlled and operated devices, meaning that a much smaller base current causes a larger current to flow from emitter to collector.
What have you learned about BJTs?
Bipolar junction transistors can increase both analogue and digital signals, as well as having the ability to switch DC power or to function as an oscillator. While BJTs are designed primarily to amplify (analogue) current, they can also function as an electronic (digital) switch in circuitry.
Can BJT be used as a switch?
A bipolar junction transistor (BJT) can be used in many circuit configurations such as an amplifier, oscillator, filter, rectifier or just used as an on-off switch.
Why BJT is better than FET?
It is more suitable for input stages of low level amplifiers. FET provides greater thermal stability compare to BJT. FET is a unipolar device….FET.
| BJT | FET |
|---|---|
| Low current gain | High current gain |
| Low input impedance | Very high input impedance |
| Low output impedance | High output impedance |
| Medium Noise Generation | Low Noise generation |
Are BJTs still used?
Yes, BJTs are still used. BJTs have higher transconductance, which gives them higher gain. They are ideal for amplifiers, where you want to maximize the gain. There is actually considerable amount of research going on in how to replicate the BJT performance in CMOS technology, especially for satellite applications.
How can BJT be used as an amplifier?
A transistor acts as an amplifier by raising the strength of a weak signal. The DC bias voltage applied to the emitter base junction, makes it remain in forward biased condition. Thus a small input voltage results in a large output voltage, which shows that the transistor works as an amplifier.
What are the properties of a BJT?
A bipolar junction transistor (BJT) has three terminals, called base, collector, and emitter. The BJT exhibits a tremendously useful property: a small current flowing into the base causes a much larger current to flow into the collector.
Why BJT is called bipolar device?
Bipolar transistors are a type of transistor composed of pn junctions, which are also called bipolar junction transistors (BJTs). Whereas a field-effect transistor is a unipolar device, a bipolar transistor is so named because its operation involves two kinds of charge carriers, holes and electrons.
Why BJT consume more power?
BJT will consume more power because it’s wasting current when it’s switch on. Also the BJT generally has a 0.3v voltage drop in the input pin, and it takes a lot of base current to do that. In a battery-powered device where you have limited power and the load is variable and often low, using BJT is a bad idea.
How do careers flow through BJT transistors?
B layer is usually thin, but characterised with high resistivity, so majority of careers will flow through into the C layer (due to different doping levels of these materials). Currents in BJT transistor can be found with Kirchhoff’s Law: I E = I C + I B.
When does a BJT become a switch?
The BJT becomes a switch as soon as the base is sourced by the AC signal, so it will work in the conducting regime to the blocking regime. The dynamic switching characteristics here are also very important, because the high-frequency velocity makes a huge impact on the losses of the device.
What are the output characteristics of BJT?
The output characteristics of BJT can be divided into three areas – cut-off, saturation and active region. In the cut-off region both collector-base and emitter-base pn-junctions are reverse-biased – transistor is off.
How does a BJT work in the saturation region?
Figure 8. An npn BJT operating in the saturation region acts like a closed switch. For a BJT to operate in the saturation region, the base-emitter junction and base-collector junction should be forward-biased, and there should be a sufficient base current to produce the collector saturation current, I C (sat).