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This is a lengthy answer. I tried to cover all the bases b/c I'm not sure how much you already know about semiconductors.
Background:
A semiconductor junction, such as that in a diode, is a connection between an N-type material and an P-type material. The N-type material has extra electrons and the P-type material has extra "holes," or a lack of electrons. Where the two materials meet, an area with neutral charge called a depletion region forms.
In a forward-biased diode, electrons trying to travel from N to P have no problem because of the abundance of extra electrons in the N-type material. The same thing happens to the positive charge carriers (holes) in the P-type material. The depletion region (.7 volts wide in a silicon diode) collapses and electrons exchange with holes through the junction -> A current flows.
In a reverse-biased diode, the depletion region (an insulator) actually grows because the unlike charges presented to each side of the junction pull the charge carriers (both electrons and holes) further away from the junction in the center. This prevents most of the current from flowing through the region.
Answer:
Because semiconductor technology is not perfect, a few charge carriers exist where they shouldn't. some electrons exist in the P-type material and some holes exist in the N-type material. These "minority carriers" are able to move through the depletion region of a reverse biased diode, and allow a small current to flow.
Adding heat or exposing the junction to light will increase the number of minority carriers, and so more reverse-bias current will flow. This is actually useful information- for instance, by measuring the reverse current through a photodiode, you can determine how much light is hitting the junction and use this to create an optical receiver or light sensor.
Keep your diodes cool,
anp
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∙ 14y ago
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How the diode acts as a switch?
A diode is made up of a P-Type and an N-Type semiconductor. P-Type has "missing" electrons (in a sense); N-Type has extra electrons (in a sense). This means that if you have current going through the two semiconductors from N-type into P-type, it should be easier than normal to apply the current because there is a potential difference between the N-type and P-type because of their relative "positivity" and "negativity". ...but if you reverse the voltage, then you are going against this potential difference and hence the voltage is impeded, resulting in a 0 current (in theory). This will only happen until the reverse voltage exceeds a threshold ampage, at which point the current will shoot up (in reverse).
What if base current is zero in a transistor used as an amplifier with common emitter configuration?
output current is zero
Why does the current in a capacitor become zero or almost zero when fully charged?
because in a capacitor only charges are stored so the stored charges are gives the zero current
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.
What are characteristics of an ideal diode?
An ideal diode:Passes current in one direction only. (Under forward bias).Has no leakage current (passes no current under reverse bias).Has no forward voltage drop. (No voltage loss under forward bias - a real diode has Vd~=0.7)See links for more details.
What are the vi characteristics of ideal diodes?
Zero current flow when reverse biased, zero voltage drop when forward biased.
Why the resistance of forward bias is equals to zero nd resistance of reverse bias is infinite?
the junction is conducting when forward biased, approaching zero resistancethe junction is nonconducting when reverse biased, approaching infinite resistanceneither is exactly zero or infinite
Dc resistance of a diode?
It depends on the voltage applied it can be zero to a very finite value. by knowing current and using Boltzmann constant the impedance can be found. Answer: Typically: 700 Ohms when Forward Biased and >2000 Ohms when Reverse Biased.
What is an ideal diode?
A: That is no such a diode but if it exists it will have unlimited reverse voltage capability the forward voltage drop will be zero no matter of current flow and it will remain so regardless of temperature changes
Why is the current nearly zero at a voltage less than 0.4 v in a forward biased silicon diode?
The current is nearly zero at a voltage less than 0.4v in a forward biased silicon diode because of the small forward-bias voltage.
Operation of ttl gate with totem-pole output?
For the working of TTL nand with totempole When both inputs are LOW The emitter base junctions at A and B gets forward biased, base -collector junction gets reverse biased for Q1.So maximum current flows through forward biased junction. As base -collector junction of Q1 gets reverse-biased, base current through the Q2 is ZERO, which makes Q2 OFF. As Q2 is in OFF state, base current through Q4 is ZERO, which makes Q4 OFF.As Q2 is in OFF state the current through R2 flows through base of Q3 which makes Q3 and diode D to ON.As Q4 is in OFF state the current flows through the load, which make output to go HIGH state
Why diode conducts current in forward bias but does not conduct in reversed bias?
diode current flows only when the diode is forward biased because in reverse bias the barrier potential increases. Diode can conduct in reverse bias if applied votage is high enough to overcome the reverse bias barrier potential but it can be destructive.
List the two conditions under which a diode is operated?
A diode is a semiconductor material which has p region and n region. In order to "turn on" and conduct current in the forward direction, a diode requires a certain amount of positive voltage to be applied across it. An ideal diode conducts only when the diode is forward biased, and then the voltage drop across the diode (Vd) is zero. When the ideal diode is reverse biased, no current flows. The two conditions to operate a diode are: (a) Current flow is permitted; the diode is forward biased. (b) Current flow is prohibited; the diode is reversed biased. When the polarity of the battery is such that current is allowed to flow through the diode, the diode is said to be forward-biased.
Junction field effect transistor biasing?
When the gate is forward biased, the depletion region is lesser and so the majority carriers(electrons)move freely towards the drain from the source producing high output impedance.When the gate is reverse biased,the depletion region increases(especially near the drain forming wedge shaped depletion)and thus the free flow of the electrons is opposed.hence the output current decreases.The out current becomes zero if the voltage given to the gate is maximum.
Do zero turn mowers cut in reverse?
do zero turn mowers mow in reverse
Why emitter base junction is always forward biased for normal operation of transistor?
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
Where kirchhoff's law fails?
In semiconductors, at quantum scales, at temperatures close to absolute zero...
