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Biasing might only be required for small signal switching below 1V. Small input signals might not always have enough voltage to cross the 0.7V B-E potential barrier. Then a slight offset voltage (biasing) must be used to bring the signal closer to the critical decision voltage of 0.7V across the B-E junction.
Note that I would refer to the B-E junction to be 0.7V rather than just the Base since it's not actually the Base that requires the 0.7V but it's the potential across the junction. Although the Base voltage is the same as the Base-Emitter voltage when the Emitter is connected to the ground, it's not always the case.
Biasing is not necessary for switching signals larger than 1V since the amplitude is enough even with Base resistor to raise the B-E junction potential from 0V to above 0.7V if correct value for base resistor is used.
It is however very important that a Base resistor Rb is provided to limit the current flowing from the input through the B-E junction to the ground. Transistors are best protected when the control is done with the correct current and not voltage, given that the correct voltages are applied. This resistor should be determined by the forward bias current gain (B) of the transistor, supply voltage, input switching signal voltage (Vin) and the load resistance RL.
Example: If one use a NPN transistor and connect the Emitter to the ground to switch a basic load via the collector. The load resistance (RL) = 100R, Supply voltage (Vs) = 10V, transistor forward bias current gain (B) = 100, and input switching voltage (Vin) = 5V, then the following method may be used
First consider:
Collector current:
Ic=(Vs - Vce)/RL
Base current:
Ib=(Ic*10)/(B) (The factor 10 is used for deviations in hfe value, it is a safety factor)
Vin-Vbe=Rb*Ib
Thus:
Rb= [B.RL.(Vin-Vbe)]/((Vs-Vce)*10)
Rb= [100.100.(5-0.7)]/((10-0.1)*10)
Rb= 434R
N.A.V.=470R
More about using transistor as a switch for DC supplies
Switching lights or relays on by using the Collector of a NPN is okay, but the method is not advised at all for more complex circuits. Beware of using the method to turn on other electronic systems or circuit boards. In this method the circuit will float at Vs when off, which can also damage other equipment dependant on them. It will also never be properly grounded when on. That may lead to erratic response in digital equipment or increased circuit noise in analog.
For turning on circuit boards or complex devices, the alternative in a NPN to turn the circuit on via its positive supply with the Emitter. This is not a good idea either since the 0.7V drop might cause supply voltage to be to low and increase line resistance. The supply voltages will drop and not be constant for changes in supply current.
Rather use PNP transistor, supply positive voltage to the Emitter and supply the load with the Collector. Pull the Base voltage low to create a 0.7 volt drop across the Base-Emitter junction. The calculations work almost the same as above except the Vin is now with reference to the Vs and not ground since we are pulling down. But this will ensure less resistance from the transistor when on and less volt drop, approximately 0.1V. Since the load is now controlled through it's positive supply. The load remains properly grounded for all conditions. But in this method one would have to pull the Base voltage low through a Base resistor aswell. To turn the device on a second NPN transistor is often used at it's Base to perform that function if conventional Vin=On and ground = Off input states are used. This method will result in a two transistor switch.
ANSWER: yes it is not required since the transistor must be forced to saturate to be used as a switch. However the current cannot be to the extent of adding a voltage forward drop to the transistor satureted comndition. as a rule a forced beta of ten is used
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What is difference between transistor and bias?
"Biasing" applies to transistor amplifier circuits. Simple amplifier circuits can only amplify positive signals. Negative signals cause the amplifier to shut down. However, AC signals in general have both a positive and a negative part. To allow a transistor to amplify AC, we add a positive voltage to the AC signal. Then after it is amplified, we remove the positive voltage again. The voltage, ac or dc on the base, compared to the emitter to cause operation of the transistor to conduct to the collector or to the emiiter in a NPN transistor.
Why is NPN transistor a straight switch and Why is PNP transistor an inverted switch?
npn and pnp transistors have the same operation as one another, they are both switches, pnps may be known as inverted switches because they work on negative voltage supplys and not positive voltage supplies.
The base emitter junction is baised and base collector junction is baised in this circuit to work as amplifier?
Yes. DC biasing a transistor is necessary to force it to operate in its' linear region. What you have written is true. Reference this site for an example of this: http://www.tpub.com/content/neets/14179/css/14179_105.htm
Transistor work on ac or DC?
Transistors are typically operated in one of two (well, four) regions: saturation/cutoff or linear (forward or reverse). When used as amplifiers, transistors are operated in the linear region. If you look at a transistor's V-I (voltage - current) characteristic, you'll see the linear region is somewhere "in the middle", where there is sufficient voltage applied (so current flows), but not to much (so the transistor is not saturated). To get transistors to operate in this middle region, DC circuits are used to bias the transistor to the center of the linear region. So the transistor is working on both AC (the signal applied to the input that is amplified at the output) and DC (the biasing network to allow the transistor to operate as a linear amplifier). When used in saturation/cutoff, the transistor is being used as a switch (on/off). this is common in logic devices (gates, arrays, CPUs, etc.). The input to these devices is typically an irregular AC wave (a square wave of information). A power source is needed that is DC, however, to provide the power to drive the output to one state or the other. So proper transistor operation requires both AC (as the signal) and DC (as the biasing network, or power source).
What is a cmos gate?
A CMOS gate is a logical switch used in electronics. CMOS stands for Complimentary Metal Oxide Silicon. These types of semiconductors have a very high input impedance, are very sensitive use low current and work over a larger range of voltage. The alternative is TTL(Transistor to Transistor Logic) which work at 5volts only and draw higher currents. A gate, is a switch that changes state (on/off) depending on the logic voltage levels applied to it's inputs.
What are modes of biasing a transistor?
Transistor works as amplifier,oscillators,switch only when it is biased properly.biasing can be defined as how much amount of voltage that has to be supplied to each junction of the transistor in order to make it work as any one of the above given types.biasing voltage can be decided by seeing the V to I graph of a transistor
What is difference between transistor and bias?
"Biasing" applies to transistor amplifier circuits. Simple amplifier circuits can only amplify positive signals. Negative signals cause the amplifier to shut down. However, AC signals in general have both a positive and a negative part. To allow a transistor to amplify AC, we add a positive voltage to the AC signal. Then after it is amplified, we remove the positive voltage again. The voltage, ac or dc on the base, compared to the emitter to cause operation of the transistor to conduct to the collector or to the emiiter in a NPN transistor.
How transistor works in ac?
work like on off switch!!
Why biasing is needed at all?
Biasing is used in a transistor amplifier circuit in order to place the transistor as nearly as possible in the center of its linear region. Transistors have cutoff, linear, and saturation regions. Too little bias current, and you enter cutoff - Too much, and you saturate. Both conditions cause distortion when you attempt to use the transistor as an amplifier, as opposed to a switch.
What is mining of transistor?
A transistor is a device used to switch power between electrical components. Transistors work to amplify existing signals as well as open and close circuits.
How does a npn transistor switch work to switch a load on and off?
let's insert a transistor in place of the switch to show how it can control the flow of electrons through the lamp. Remember that the controlled current through a transistor must go between collector and emitter. Since it is the current through the lamp that we want to control, we must position the collector and emitter of our transistor where the two contacts of the switch were. We must also make sure that the lamp's current will move against the direction of the emitter arrow symbol to ensure that the transistor's junction bias will be correct as in Figure below(b).
Why is NPN transistor a straight switch and Why is PNP transistor an inverted switch?
npn and pnp transistors have the same operation as one another, they are both switches, pnps may be known as inverted switches because they work on negative voltage supplys and not positive voltage supplies.
What is a transistor and how does it work?
The transistor is an example of semiconductor equipment that can be used to switch and amplify electric power. It is said to be the most important part of the digital revolution because if there are no transistor, digital equipment like cellular phone, computers and other devices would not exist.
What is the work of transistor?
The work of a transistor is to amplify the input signal to get high output value.
What are the operating regions of transistors?
operating region of the transistor is the area of the voltage and an electronic configuration in which a transistor can work with its full efficiency. In that operating region transistor can be used easily what above said by harsh is correct...the following may help u further... Based on application the transistor is decided where to lie. for example transistors are made to lie in active region to make it as amplifier. when transistors are used as switch it is made to lie in saturation region(when switch is made as ON) and cut-off region(when switch is made as OFF).....
SL100 transistor's pin diagram?
transistor sl 100n has 3 pins and it is work like a switch. there is metal lead in the above metal surface the nearest pin is emeter and last pin is collector and center pin is base
What is photo transistor?
Photo transistor always work with solar power
