How does current flow in BJT?

Charge flow in a BJT is due to diffusion of charge carriers across a junction between two regions of different charge carrier concentration. The regions of a BJT are called emitter, base, and collector. A discrete transistor has three leads for connection to these regions.

Where does current flow in 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.

Can current flow backwards through a BJT?

Yes current can flow in both directions. An NPN transistor backwards is also an NPN. There will still be a reverse beta, however, the backwards NPN transistor won't work as well as a correctly oriented one will. It's not recommended.

Which way does the current flow in a transistor?

In an NPN transistor, current actually flows from the collector to the emitter. In a PNP transistor, it's exactly the opposite. In a PNP transistor, current flows from the emitter to the collector.

Which terminal in BJT controls the flow of electrons?

The base controls the flow of current through the transistor from the collector to the emitter in an NPN transistorn and in the opposite direction in a PNP transistor. The little arrow found on the transistor symbols emitter tells you which way the currnet flows, into or out of the emitter.

Current in a Transistor | Electronics

Does current flow from collector to emitter in transistor?

No current flows from collector to emitter. Active -- The current from collector to emitter is proportional to the current flowing into the base. Reverse-Active -- Like active mode, the current is proportional to the base current, but it flows in reverse.

Can BJT conduct in both directions?

No. The common types of NPN and PNP transistors would not maintain base emitter current flow if the polarity of the power supply was reversed.

Does current flow from collector to base?

Current also flows from base to collector. Hopefully, that is also straightforward. In both cases, current is flowing across a forward biased junction when the transistor is in saturation. Due to transistor action, current also flows from collector to emitter.

Can current flow from emitter to base?

There will always be some leakage current, even with the base tied to the emitter. However, that is "small" in practical applications to the point it is generally ignored. If you apply enough voltage to anything, current will eventually flow.

How does a BJT transistor work?

How does BJT Work? For an NPN transistor, it consists of a layer of P-doped semiconductor between two layers of N-doped material, where electrons are passed from the emitter to the collector instead. The emitter then “emits” electrons into the base, with the base controlling the no. of electrons the emitter emits.

Why BJT is a current controlled device?

A BJT is a current controlled device because its output characteristics are determined by the input current. A FET is voltage controlled device because its output characteristics are determined by the Field which depends on Voltage applied.

What is emitter in BJT?

Emitter (E):It is the region to the left end which supply free charge carriers i.e., electrons in n-p-n or holes in p-n-p transistors. These majority carriers are injected to the middle region i.e. electrons in the p region of n-p-n or holes in the n region of p-n-p transistor.

Does current flow when a transistor is off?

Every semiconductor device has some leakage current, even when the device is "off". You are getting a bit more that leakage current, because even at a base bias of 0.2v, some base current will flow, and this will cause collector current to flow.

Do transistors have polarity?

The NPN transistor always has an arrow pointing out. It is clear that the current directions and voltage polarities in PNPs and NPNs are always opposite to each other. NPN transistors require a power supply with positive polarity with respect to common terminals, but PNP transistors require a negative power supply.

Which direction does current flow in a NPN transistor?

In an NPN transistor, the flow of current runs from the collector terminal to the emitter terminal.

Why does current flow from collector to emitter?

The NPN transistor is designed to pass electrons from the emitter to the collector (so conventional current flows from collector to emitter). The emitter "emits" electrons into the base, which controls the number of electrons the emitter emits.

What causes the collector current to flow?

During the positive half-cycle of the signal, the base is positive with respect to the emitter and hence the base-emitter junction is forward biased. This causes a base current and much larger collector current to flow. The positive half-cycle of the signal is amplified in the collector.

How BJT can be used as a switch?

The transistor will operate as an amplifier or other linear circuit if the transistor is biased into the linear region. The transistor can be used as a switch if biased in the saturation and cut-off regions. This allows current to flow (or not) in other parts of a circuit.

Why BJT is called bipolar?

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.

What is the current gain of BJT is?

The current gain for a CB configuration is called Alpha, ( α ). In a BJT amplifier the emitter current is always greater than the collector current as I_E = I_B + I_C, the current gain (α) of the amplifier must therefore be less than one (unity) as I_C is always less than I_E by the value of I_B.

What is difference between BJT and MOSFET?

There are many differences between the MOSFET and BJT. The MOSFET (voltage controlled) is a metal-oxide semiconductor whereas the BJT (current controlled) is a bipolar junction transistor.

How does a transistor control current?

By turning a small input current into a large output current, the transistor acts like an amplifier. But it also acts like a switch at the same time. When there is no current to the base, little or no current flows between the collector and the emitter. Turn on the base current and a big current flows.

Why is emitter current negative?

Currents that flow into the transistor are called positive. Conversely, currents that flow out of the transistor are called negative. If the actual conventional current directions agree with the transistor convention, they are called positive. If not, they are called negative.

Can we use BJT as a diode?

However, since bipolar transistors are not designed to be used as diodes, using them as diodes might cause a problem in terms of current and other ratings. For example, transistors are generally used with a base current that is less than one-tenth the required collector current.

Why is BJT not suitable at very low temperature?

BJTs, fabricated using standard bipolar processes, have been charac- terized only down to 77 K [11], since at lower temperature BJTs are not well behaved due to a significant decrease in their current gain β and an increase in their base resistance RB [12].