How does a BJT work in a bipolar junction transistor?

How does a BJT work in a bipolar junction transistor?

A BJT uses a small current at its base to control a much larger collector current. Before we go any further, it may be useful to define some important terms concerning the operation of a bipolar junction transistor.

How does a BJT work on a silicon wafer?

Instead, semiconductor manufacturers use a diffusion process which melts the base into the collector region and then melts the emitter region into the base region (for an NPN BJT). Thousands of transistors are diffused on a silicon wafer from which induvial transistors are then cut before being sealed in plastic or metal.

When did the first BJT transistors come out?

While some of the first transistors from the late 1940s and early 1950s were made this way, modern transistors are not. Figure 3 depicts the structure of a modern BJT. Figure 3: structure of a modern BJT. As we can see, the layers do not stack on top of one another.

What’s the difference between a PNP and a BJT transistor?

BJT transistor: (a) PNP schematic symbol, (b) layout (c) NPN schematic symbol, (d) layout. The functional difference between a PNP transistor and an NPN transistor is the proper biasing (polarity) of the junctions when operating. Bipolar transistors work as current-controlled current regulators.

How does the load line work in a BJT amplifier?

The load line is a very useful tool when designing bjt amplifiers. It indicates all the possible Q points in which the transistor can work in a given circuit. Once we have the load line for our circuit, we’ll pick the best available Q point. In the next picture the load line is painted in red, the x axis represents Vce and the y axis represents Ic.

How does the BJT work in saturation mode?

Saturation refers to a region of operation where maximum collector current flows and the BJT acts like a closed switch from collector to emitter. In this mode the BC junction forward biases and maximum current flows. The collector current cannot increase any more, even with an increase in base current.

How is the BJT used as a switch?

The BJT as Switch REVIEW: • Transistors may be used as switching elements to control DC power to a load. The switched (controlled) current goes between emitter and collector; the controlling current goes between emitter and base.

Can a BJT be connected to two diodes?

A PNP BJT will function like two diodes that share an N-type cathode region, and the NPN like two diodes sharing a P-type anode region. Connecting two diodes with wires will not make a transistor, since minority carriers will not be able to get from one P–N junction to the other through the wire.

Why is a BJT off when the base voltage is low?

Remember that a typical silicon diode needs about 0.7 V to turn on and conduct. So, with less than 0.7 V on the base the transistor is off because the low voltage does not forward bias the BE diode. If we were to apply a negative voltage to the NPN BJT in figure 4 the situation worsens; the p-n junction between the base and emitter widens.

How does a BJT work like a closed switch?

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).