What is reach through in BJT?
At a particular voltage, the depletion region penetrates through the emitter junction. It’s called the ‘Punch through’ or ‘Reach through’ effect. Once punch through happens, a very large current starts to flow. ∴ We never operate BJT at this point.
When BJT is used as a switch and switch is said to be on when?
A switch offers open circuit (infinite resistance) when it is put in ‘OFF’ position and offers short circuit (zero resistance) when it is put in ‘ON’ position.
Can a transistor be used as a switch?
A transistor can be used as a solid state switch. If the transistor is operated in the saturation region then it acts as closed switch and when it is operated in the cut off region then it behaves as an open switch. The transistor operates as a Single Pole Single Throw (SPST) solid state switch.
What is punch through effect in transistor?
[′pənch‚thrü] (electronics) An emitter-to-collector breakdown which can occur in a junction transistor with very narrow base region at sufficiently high collector voltage when the space-charge layer extends completely across the base region.
What is punch through effect in Mosfet?
Punch through is addressed to MOSFETs’ channel length modulation and occurs when the depletion regions of the drain-body and source-body junctions meet and form a single depletion region.
In which region does BJT act as the of switch in electronic circuit?
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, IC(sat).
How does a BJT amplify current?
The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. The amplified current is large enough to turn on and light the LED.
How BJT can be used as an amplifier?
An amplifier is an electronic circuit designed by using an active device like bipolar junction transistor (BJT), field effect transistor (FET), that changes, usually increases the amplitude of the input signal (usually voltage or current).
How a transistor works as switch?
With a zero signal applied to the Base of the transistor it turns “OFF” acting like an open switch and zero collector current flows. With a positive signal applied to the Base of the transistor it turns “ON” acting like a closed switch and maximum circuit current flows through the device.
What is the punch through condition in BJT?
In a BJT punch-through condition occurs when the base to collector reverse voltage causes widening of depletion region such that the entire base width is covered by depletion region.
How BJT works as a switch?
In the below figure the circuit shown explains the operation of BJT as a switch. In the first circuit, the transistor is in the cutoff region because the emitter-base junction is not forward biased condition. In this state, there is no connection between emitter and collector of a transistor as shown like an open switch.
What is a bipolar junction transistor (BJT)?
Bipolar junction transistors (Also known as BJTs) can be used as an amplifier, filter, rectifier, oscillator, or even a switch, which we cover an example in the first section.
What happens when BJT is in cutoff state?
When the BJT is in cutoff, the circuit (ideally) has the following values: This state is similar to an open switch. When the input equals + Vin, the transistor is driven into saturation and the following conditions occur: This state is similar to a closed switch connecting the bottom of R C to ground.
How does a BJT operate in the saturation region?
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).