The forward resistance of a diode is, by Ohm's law, the voltage across the diode divided by the current through the diode. Note that, since diodes are non linear, the effective resistance is not constant over all possible voltages and currents.
Pretend you are standing over a wire with current in it. The electrons can travel away from you or toward you. In 60 Hz current they travel away for 1/120 of a second and reverse toward you for 1/120th of a second. Put a rectifier with the arrow pointing TOWARDS you in the line. In this position the electrons can travel away from you ( your forward ). The arrows pointing toward you is the forward direction (for the electrons). The electrons go INTO the arrow point. The arrow pointing away from you is the reverse direction. Blame this on Ben Franklin, he didn't know about electrons and took a 50/50 guess. OOPS.
Bulk resistance of diode depends on how it is biased. The bulk resistance of a diode is the approximate resistance of the diode when it is forward biased.
Forward Resistance:def: It is resistance offered by diode to the forward bias is known as forward resistance.This resistance is not the same for the flow of DC as for the changing current. Accordingly this resistance is of two types :1. DC FORWARD RESISTANCE.2. AC FORWARD RESISTANCE.1. DC forward resistance: It is the opposition by diode to the DC. It is measured by the ratio of DC voltages across the diode to the resulting DC current through it.2. AC forward resistance: It is the opposition offered by the diode to the changing current. It is measured by the ratio of change in voltage across diodes to the resulting change in current through diode. The AC forward resistance is more significant as the diodes are generally used with alternating voltage.Reverse Resistance:def: The resistance offered by the diode to the reverse bias is known as Reverse Resistance. It can be DC reverse resistance or AC reverse resistance depending upon whether the reverse bias is direct or changing voltage. Idealy the reverse resistance of a diode is infinte however in practice the reverse resistance is not infinite because for any value of reverse bias, there does exist a small leakage current. It may be emphasized their that reverse resistance is very large compared to the forward resistance.These Definitions are from PRINCIPLES OF ELECTRONICS by V.K MEHTA and ROHIT MEHTA
Consider ideal diode to be connected in series with resistor of 6kSilicon diode forward bias voltage = 0.7 voltsCurrent across 6k resistor = (5-0.7)/6000 amperesVoltage across {resistor + diode}=4.3 + 0.7=5vIf silicon internal resistance is 6k then voltage across diode=5vIf external resistance is 6k and diode resistance is negligible then voltage across diode=0.7v
The resistance of a forward biased pn junction is zero.
If you are talking about reverse biasing a diode, then you are talking about a zener diode. A zener diode, like a normal diode, has a forward bias around 0.7 volts (depending on current and temperature). Using Ohm's law, you can calculate the effective resistance of the diode in forward bias. (Example: 0.7 volts, 100 milliamps, 7 ohms) In reverse bias, however, a zener diode conducts at a different voltage. This is what zener diodes do. Using Ohm's law, you will get a different effective resistance of the diode in reverse bias, because it is dropping a different voltage. (Example: 5.6 volts, 100 milliamps, 56 ohms) It should be noted that attempting to measure the resistance of a diode does not make sense, because it is a non linear device. You should instead consider the current to voltage curve to understand the diode, be it regular or be it zener.
Bulk resistance of diode depends on how it is biased. The bulk resistance of a diode is the approximate resistance of the diode when it is forward biased.
Forward Resistance:def: It is resistance offered by diode to the forward bias is known as forward resistance.This resistance is not the same for the flow of DC as for the changing current. Accordingly this resistance is of two types :1. DC FORWARD RESISTANCE.2. AC FORWARD RESISTANCE.1. DC forward resistance: It is the opposition by diode to the DC. It is measured by the ratio of DC voltages across the diode to the resulting DC current through it.2. AC forward resistance: It is the opposition offered by the diode to the changing current. It is measured by the ratio of change in voltage across diodes to the resulting change in current through diode. The AC forward resistance is more significant as the diodes are generally used with alternating voltage.Reverse Resistance:def: The resistance offered by the diode to the reverse bias is known as Reverse Resistance. It can be DC reverse resistance or AC reverse resistance depending upon whether the reverse bias is direct or changing voltage. Idealy the reverse resistance of a diode is infinte however in practice the reverse resistance is not infinite because for any value of reverse bias, there does exist a small leakage current. It may be emphasized their that reverse resistance is very large compared to the forward resistance.These Definitions are from PRINCIPLES OF ELECTRONICS by V.K MEHTA and ROHIT MEHTA
The dynamic resistance of a diode, be it zener or otherwise, will be different from its static resistance because a diode is not a resistor, and resistance is not a function of current flow. It is a diode, and a diode has its own characteristic voltage to current curve, forward and, in the case of a zener, reverse.
Consider ideal diode to be connected in series with resistor of 6kSilicon diode forward bias voltage = 0.7 voltsCurrent across 6k resistor = (5-0.7)/6000 amperesVoltage across {resistor + diode}=4.3 + 0.7=5vIf silicon internal resistance is 6k then voltage across diode=5vIf external resistance is 6k and diode resistance is negligible then voltage across diode=0.7v
A thin junction diode which exhibits negative resistance under low forward bias condition is known as tunnel diode.
A thin junction diode which exhibits negative resistance under low forward bias condition is known as tunnel diode.
to determine the comparison of resistance value of both forward and reverse diode . The more the resistance the lower the current , the lower the resistance the higher the current . When reverse bias , the resistance is high and it acts in open circuit and the reverse current is very small that can be neglected . When forward bias , the resistance is low and it acts as short circuit and the forward current is increasing as the voltage supply is higher .
zener resistance of a zener diode is the resistance of the zener diode but which is the resistance of a diode
When it is forward biased and, in the case of a zener diode, when it is reverse biased as well. It just is not a linear resistance type of device, and the apparent resistance changes as a function of the applied voltage or current.
ln reverse biase high resistance and in forward biase very low resistance
What happens depends on the temperature coefficient of the diode. If that diode has a positive temperature coefficient, it resistance increases with increased temperature. A diode with a negative temperature coefficient does the opposite.
That's to avoid the diode from burning out. When it is forward biased, the resistance is extremely low; so even a small voltage can produce a large current, and that can quickly damage it.