How npn transistor works as a switch?

The transistor is off when there’s no bias voltage or when the bias voltage is less than 0.7 V. The switch is on when the base is saturated so that collector current can flow without restriction. This is a schematic diagram for a circuit that uses an NPN transistor as a switch that turns an LED on or off.

When an npn transistor is used as a switch?

NPN Transistor as a Switch When a sufficient voltage (VIN > 0.7 V) is applied between the base and emitter, collector to emitter voltage is approximately equal to 0. Therefore, the transistor acts as a short circuit. The collector current VCC / RC flows through the transistor.

How does current flow in npn transistor?

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. The transistor is kind of like an electron valve.

In which mode the npn transistor is connected?

A npn transistor is connected in common emitter configuration in a given amplifier.

What’s the difference between a transistor and a NPN switch?

The equations for calculating the Base resistance, Collector current and voltages are exactly the same as for the previous NPN transistor switch. The difference this time is that we are switching power with a PNP transistor (sourcing current) instead of switching ground with an NPN transistor (sinking current).

Can a common emitter be applied to a PNP transistor?

Common emitter configuration can be applied on both types of transistor, PNP transistor, and NPN transistor. Here we especially talk about common emitter configuration of bjt. For common emitter configuration of NPN transistor, we take an emitter terminal is common between the input and output circuit of the transistor.

How does a Darlington transistor work as a switch?

Darlington Transistors simply contain two individual bipolar NPN or PNP type transistors connected together so that the current gain of the first transistor is multiplied with that of the current gain of the second transistor to produce a device which acts like a single transistor with a very high current gain for a much smaller Base current.

What is the saturation region of a PNP transistor?

Therefore the transistor is switched “Fully-ON”. Then we can define the “saturation region” or “ON mode” when using a bipolar transistor as a switch as being, both junctions forward biased, VB > 0.7v and IC = Maximum. For a PNP transistor, the Emitter potential must be positive with respect to the Base.

How NPN transistor works as a switch?

The transistor is off when there’s no bias voltage or when the bias voltage is less than 0.7 V. The switch is on when the base is saturated so that collector current can flow without restriction. This is a schematic diagram for a circuit that uses an NPN transistor as a switch that turns an LED on or off.

What resistor should I use for transistor?

The base resistor (RB) must allow sufficient current to flow to ensure the transistor is fully saturated when switched on and it is good to make the base current (IB) about five times the value which just saturates the transistor.

What is a voltage divider BJT?

Another configuration that can provide high bias stability is voltage divider bias. Instead of using a negative supply off of the emitter resistor, like two-supply emitter bias, this configuration returns the emitter resistor to ground and raises the base voltage. 1: Voltage divider bias.

What is the function of NPN transistor BJT?

As well as being used as a semiconductor switch to turn load currents “ON” or “OFF” by controlling the Base signal to the transistor in either its saturation or cut-off regions, Bipolar NPN Transistors can also be used in its active region to produce a circuit which will amplify any small AC signal applied to its Base …

Does a transistor need a resistor?

this reduction in the resistivity causes an increase in the current flowing through the semiconductor (the applied DC voltage remains constant). why do we need a resistor connected to the base of the transistor? For an amplifier to work properly, the DC current in the collector must remain constant.

What should be the voltage of a NPN BJT?

It’s probably safe to assume 0.7 V for most small-signal NPN BJTs. Once you know the voltage across the resistor and the current through it, Ohms law will tell you the answer. Thanks for contributing an answer to Electrical Engineering Stack Exchange!

What’s the difference between a transistor and a NPN switch?

The equations for calculating the Base resistance, Collector current and voltages are exactly the same as for the previous NPN transistor switch. The difference this time is that we are switching power with a PNP transistor (sourcing current) instead of switching ground with an NPN transistor (sinking current).

Why do you use a BJT as a switch?

There are plenty of reasons why you would use a BJT or a transistor as a switch. But for me, I think the main reason is driving a load with higher current consumption or voltage. For example, your load requires 100mA but you can only draw 20mA from your source, which is common for a GPIO pin of a microcontroller.

What should the base resistor be for a BJT?

There’s a rule of thumb that you make the base resistor such that the base current is a good multiple (5, 10?) of the minimum base current needed to put the BJT into saturation – you can get this from the data sheets. You need to know V B E ( s a t) – but that’s in the data sheets too.