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Why emitter base junction is always forward biased for normal operation of transistor?
Wiki User
∙ 12y ago
The easy answer - it's not always forward biased. Both it, and the collector-base junction, must be forward biased to pass current through to the collector. Whether NPN or PNP the relative bias (voltage) on the base determines the conduction from emitter to collector. NPN: if the base is positive, relative to the collector and emmiter, the transistor conducts. PNP: if the base is negative, relative to the collector and emmitter, it conducts.
For either transistor arrangement, draw two diodes connected either by their anodes or by their cathodes. The base is the region between them. In an NPN, a positive voltage on the anode, compared the to the cathode(s), will forward bias both, allowing current to flow. The same applies to a PNP with a relative negative voltage being the 'switch', turning both on.
bob
02/07/2009
The first paragraph is incorrect. The collector-base junction will be reverse biased for normal operation. The only time an NPN base will be biased more positively than the collector is when it's operating in saturation mode.
The second paragraph is also misleading. It implies that current flows (for NPN) from the collector to the base and then from the base to the emitter. Emitter current is base current plus collector current. The collector-base junction is normally reverse biased, so little current would flow.
Here's a link with relevant info: http://www.nationmaster.com/encyclopedia/Bipolar-junction-transistors
Dennis
Wiki User
∙ 12y ago
Anonymous
Wiki User
∙ 11y agoAs the name itself indicates, emitter emits charge carriers (electrons or holes). That means, the charge carriers need to be attracted by the bias. Hence reverse biased......... as we know, opposite polarities attract each other.
Wiki User
∙ 11y agobecause reverse biased means current which is flowing is equal nearly to zero so no current is flowing...
Wiki User
∙ 13y agoA: To make a transistor amplify linearly a bias must be provided to bring the transistor into a linear region with respect to the loading
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Why a transistor can be operated in active region?
a transistor can only work in active region cox in active region collector base junction is in reverse bias and emitter base junction is in forward bias.
How must the two transistor junction be biased proper transistor amplifier operation?
A: Actually it is only one transistor required for amplification the other junction can be a diode. As current Begin to flow it causes a bias across one junction which is opposite biasing for the other, A good differential amplifier will have those junction virtually at the same point with a very good current source because any mismatched will cause and output without any input. It is called voltage offset on the other end if the feedback current is very small it will also produce an output voltage offset known as current offset or basically errors
When the forward saturation in Bipolar junction transistor occurs?
Forward saturation in a BJT occurs when the ratio of collecter-emitter current and base-emitter current reaches hFe or dc beta. A that point, the BJT is no longer operating in linear mode.
A PNP transistor is connected in a circuit so that the collector-base junction remains reverse biased and the emitter-base junction is forward biased This transistor can be used as a power amplifi?
No freaking way but it would make an excellent low level switch if forced at beta of 10
How is an transistor used as a amplifier?
Voltage is applied between the collector and emitter. A signal is applied between the base and emitter. The input signal will control how much the transistor turns on and the larger current flowing across the Collector/Emitter will be the same, but larger, than the input. Therefore amplified.To keep the transistor switched on and to prevent the input signal switching it off, the transistor has to be biased on. This is usually done with a network of resistors on the base, raising the voltage to keep it conducting.
What is the biasing technique in transistor for it to be in active region?
For a transistor to be in active region : Base Emitter junction should be forward biased and Emitter collector junction should be reverse biased.
A transistor is in active region when?
a transistor in active region when emitter junction is forward biased nd collector junction is reverse biased
How should the two transistor junctions be biased for proper transistor amplifier operation?
Emitter-Base junction should be forward biased.Collector-Base junction should be reverse biased.
How do you know if a transistor is a PNP or an NPN?
To know if a transistor is PNP or an NPN,the following should be verified:For a PNP transistor, the base-collector junction is forward biased while the base-emitter junction is reversed biased.For an NPN transistor, the base-emitter junction is forward biased while the base -collector junction is reversed biased.
A PNP transistor is connected in a circuit so that the collector-base junction remains reverse biased and the emitter-base junction is forward biased This transistor can be used as a power amplifier?
Yes1
Why a transistor can be operated in active region?
a transistor can only work in active region cox in active region collector base junction is in reverse bias and emitter base junction is in forward bias.
What bias conditions must be present for the normal operation of a transistor ampilifier?
Assuming you mean a bipolar junction transistor (BJT): 1. Reverse bias on the collector-base junction. 2. Forward bias on the base-emitter junction, that is 3. Sufficient to give the correct operating point of collector voltage/collector current.
How must the two transistor junction be biased proper transistor amplifier operation?
A: Actually it is only one transistor required for amplification the other junction can be a diode. As current Begin to flow it causes a bias across one junction which is opposite biasing for the other, A good differential amplifier will have those junction virtually at the same point with a very good current source because any mismatched will cause and output without any input. It is called voltage offset on the other end if the feedback current is very small it will also produce an output voltage offset known as current offset or basically errors
How do NPN bipolar junction transistors turn on and off?
In order to bias a bipolar junction transistor on, you need to forward bias the base-emitter junction at the same time you forward bias the collector-emitter junction, and the ratio of collector current over base current must be somewhat less than hFe, the transistor's gain. This is known as saturated, or non-linear mode, operation. In practice, we drive the base much harder than the calculated required current, so as to minimize dependency on varying hFe's for various transistors.Turning the transistor off is a simple matter of eliminating the base current.In the case of the NPN transistor, the base and collector would need to be more positive than the emitter. In the case of the PNP, they would need to be more negative.
When the forward saturation in Bipolar junction transistor occurs?
Forward saturation in a BJT occurs when the ratio of collecter-emitter current and base-emitter current reaches hFe or dc beta. A that point, the BJT is no longer operating in linear mode.
What is transistor action?
The transistor has three regions, emitter,base and collector. The base is much thinner than the emitter while the collector is wider than both. However for the sake of convenience the emitter and collector are usually shown to be of equal size. The transistor has two pn junctions that means it is like two diodes. The junction between emitter and base may be called emitter-base diode or simply the emitter diode.The junction between base and collector may be called collector-base diode or simply collector diode. The emitter diode is always forward biased and the collector diode is always reverse biased.
What is the deffbetween forward and reverse biased?
Asking about biasing of the emitter alone does not make sense. When you talk about bias, you talk about a junction, such as emitter-base or emitter-collector or base-collector. In a bipolar junction transistor (BJT) both the emitter-base and emitter-collector need to be forward biased, otherwise you are operating the BJT in cutoff mode. Certainly, if you intend to operate the BJT as a switch, then reverse bias for emitter-base (actually, zero bias) could well be one of the valid states, corresponding to a cutoff condition for emitter-collector. However, operation in linear mode, the other normal way to use a BJT, requires that both the emitter-base and the emitter-collector be forward biased. Of course, depending on the ratio of emitter-base to emitter-collector versus hFe, you could also be saturated, which is a non-linear mode, i.e. an on switch.
