# Diode operating point

62 views
Distributed under Creative Commons Attribution-ShareAlike - CC BY-SA.

## Your answer

 Thanks for your contribution. Feel free to answer this question. Please avoid short answer. Your answer is most welcome. Be genuine. Upload image or document: Your name to display (optional): Email me at this address if my answer is selected or commented on: Privacy: Your email address will only be used for sending these notifications. Anti-spam verification: Are you a robot ? (Y = Yes / N = No) .captcha_q{margin-right:10px;color:#00C;} #response_field{display:none;} .q2apro_captcha { margin-bottom:20px; } To avoid this verification in future, please log in or register.

## 3 Answers

0 votes
 Lecture -3: Diode Operating Point Example - 1: When a silicon diode is conducting at a temperature of 25°C, a 0.7 V drop exists across its terminals. What is the voltage, VON, across the diode at 100°C? Solution: The temperature relationship is described by  VON (TNew) – VON(Troom) = KT (TNew – Troom) or,           VON (TNew ) = VON (Troom) + KT (Tnew – Troom) Given     VON (Troom) = 0,7 V, Troom= 25° C, TNew= 100° C Therefore, VON (TNew ) = 0.7 + (-2 x 10-3 ) (100-75)  = 0.55 V Example - 2: Find the output current for the circuit shown in fig.1(a).   Fig.1- Circuit for Example 2 Solutions: Since the problem contains only a dc source, we use the diode equivalent circuit, as shown in fig. 1(b). Once we determine the state of the ideal diode in this model (i.e., either open circuit or short circuit), the problem becomes one of simple dc circuit analysis. It is reasonable to assume that the diode is forward biased. This is true since the only external source is 10 V, which clearly exceeds the turn-on voltage of the diode, even taking the voltage division into account. The equivalent circuit then becomes that of fig. 1(b).with the diode replaced by a short circuit. The Thevenin's equivalent of the circuit between A and B is given by fig. 1(c). The output voltage is given by or,          If VON= 0.7V, and Rf= 0.2 W , then Vo = 3.66V

IIT ROORKEE

0 votes
Lecture - 3: Diode Operating Point

Example - 3

The circuit of fig. 2, has a source voltage of Vs = 1.1 + 0.1 sin 1000t. Find the current, iD. Assume that

nVT = 40 mV

VON = 0.7 V

 Solution: We use KVL for dc equation to yield Vs= VON+ ID RL Fig.2

This sets the dc operating point of the diode. We need to determine the dynamic resistance so we can establish the resistance of the forward-biased junction for the ac signal.

Assuming that the contact resistance is negligible Rf= rD Now we can replace the forward-biased diode with a 10 W resistor. Again using KVL, we have,

vs= Rf id + RL id

The diode current is given by

I = 4 + 0.91 sin 1000 t mA

Since iD is always positive, the diode is always forward-biased, and the solution is complete.

IIT ROORKEE

0 votes
Lecture - 3: Diode Operating Point

Small Signal Operation of Real diode:

 Consider the diode circuit shown in fig. 3. V = VD + Id RLVD = V- IdRL This equation involves two unknowns and cannot be solved. The straight line represented  by the above equation is known as the load line. The load line passes through two points,                          I = 0, VD = V and                  VD= 0, I = V / RL. Fig. 3

The slope of this line is equal to 1/ RL. The other equation in terms of these two variables VD & Id, is given by the static characteristic. The point of intersection of straight line and diode characteristic gives the operating point as shown in fig. 4.

Fig. 4

Fig. 5

Let us consider a circuit shown in fig. 5 having dc voltage and sinusoidal ac voltage. Say V = 1V, RL=10 ohm.

The resulting input voltage is the sum of dc voltage and sinusoidal ac voltage. Therefore, as the diode voltage varies, diode current also varies, sinusoidally. The intersection of load line and diode characteristic for different input voltages gives the output voltage as shown in fig. 6.

Fig. 6

In certain applications only ac equivalent circuit is required. Since only ac response of the circuit is considered DC Source is not shown in the equivalent circuit of fig. 7. The resistance rf represents the dynamic resistance or ac resistance of the diode. It is obtained by taking the ratio of Δ VD/ Δ ID at operating point.

Dynamic Resistance Δ rD = Δ VD / Δ ID

Fig. 7

IIT ROORKEE

## Related questions

3 answers 81 views

Distributed under Creative Commons Attribution-ShareAlike - CC BY-SA.

2 answers 44 views

Distributed under Creative Commons Attribution-ShareAlike - CC BY-SA.

1 answer 37 views

Distributed under Creative Commons Attribution-ShareAlike - CC BY-SA.

1 answer 12 views

In class-A amplifier conduction extends over 360° because the operating point.  1. Located near saturation point 2. Located at or near cut-off point 3. Located on load line 4. Located in the centre of load line

1 answer 22 views

The operating point of a protective current transformer is near the

0 answers 13 views

In a transistor biasing circuit with voltage divider bias circuit, if the operating point is on the left on the load line. (a) peak of the input voltage is clipped. (b) one side peak of the output voltage is clipped. (c) both positive and negative peaks are clipped. (d) there will be a distortion in the middle.

1 answer 36 views

In which region is the operating point stable in tunnel diodes?  (1) Negative-resistance (2) Positive-resistance (3) Both negative- and positive-resistance (4) Neither negative- nor positive-resistance

0 answers 15 views

When current dramatically increases, the voltage point on the diode forward V-I characteristic curve is called the  A) Breakdown voltage B) Knee voltage C) Barrier voltage D) Both B) and C) are true

1 answer 59 views
1 answer 22 views

Explain the operating principle of LASER and list applications of LASER diode.

1 answer 15 views

A charge of 0.1 C moves past a given point every 0.01 s. How much is the current?

0 answers 11 views

A charge of 6 C moves past a given point every 0.3 s. How much is the current?

0 answers 19 views

A charge of 0.05 C moves past a given point every 0.1 s. How much is the current?

0 answers 29 views

A charge of 1 C moves past a given point every 0.1 s. How much is the current?

0 answers 24 views

A charge of 2 C moves past a given point every 0.5 s. How much is the current?

1 answer 31 views

What is energy flow diagram? State its significance from Energy Audit point of view.

1 answer 12 views

Dew point temperature is constant as long as there is : (A) no change in moisture content of the air (B) no change in volume of air (C) no change in dry bulb and wet bulb temperature (D) no change in relative and specific humidity of air

1 answer 12 views

The melting point of carbon is: A) 1800 degree Centigrade B) 2200 degree Centigrade C) 3500 degree Centigrade D) 5500 degree Centigrade

0 answers 14 views

The point of intersection of two asymptotes in a plot is called (A) corner frequency in uniform scale (B) corner frequency in logarithmic scale (C) phase cross-over frequency in uniform scale (D) phase cross-over frequency in logarithmic scale

0 answers 20 views

A charge of 0.1 coulomb moves through a given point in every 0.05 seconds. The current flowing through the point is (a) 2 mA (b) 5 mA (c) 2 A (d) 5 A

0 answers 56 views

A power system network with a capacity of 100 MVA has a source impedance of 10% at a point. The fault level at that point is (a) 1500 MVA (b) 1000 MVA (c) 500 MVA (d) 100 MVA

1 answer 14 views

In root locus plot, a point on the real axis lies on the locus, if the number of open loop poles plus zeros on real axis to the a) left of the point is odd b) left of the point is even . c) right of the pointis odd d) right of the point is even

1 answer 18 views

A 4—point starter is used to start and control the speed of a  A) DC shunt motor with armature resistance control B) DC shunt motor with field weakening control C) DC series motor D) Thyristor controlled d.c. motor

1 answer 9 views

In a full wave rectifier the negative point in a circuit is   (A) cathode (B) anode (C) The central tap on the high voltage secondary (D) plate.

1 answer 12 views

The driving point impedance with poles at ω = 0(zero) and ω = ∞ (infinity) must have the  (a) s term in the denominator and an excess term in the numerator (b) s term in the numerator and an excess term in the denominator (c) s term in the numerator and equal number of terms in the numerator and denominator (d) s term in the denominator and equal number of terms in the numerator and denominator

1 answer 30 views

A dot matrix printer takes 3 msec to point a character, and 1 msec for a space between two consecutive characters. If it prints 100 characters per line, its printing speed specifications in characters per second (cps) and time to print a line of characters are respectively  (a) 100 cps and 400 msec (b) 2500 cps and 0.04 sec (c) 250 cps and 40 msec (d) 250 cps and 0.4 sec

1 answer 12 views

The critical point lies within the nyquist plot then the system is   (a) Marginally stable (b) Unstable (c) Stable (d) Undetermined

1 answer 21 views

Blind spot is a point in the zones of protection where

1 answer 43 views

If the % reactance upto the fault point is 20%, then the short circuit current will be

1 answer 20 views

The necessary and sufficient condition for a rational function of, T(s) to be driving point impedance of an RC network is that all poles and zeros should be

1 answer 14 views

Whether a given point in the S-plane lies on the Root Locus of a system can be determined by (A) Magnitude criterion (B) Angle Criterion (C) Both Magnitude and Angle Criteria (D) Break-in and Break-away Criteria

1 answer 29 views

If eight -tenths coulomb passes a point in 4 s, the value of current is equal to: A. 1.6 A B. 16 A C. 2 A D. 0.2 A

1 answer 9 views

Three different points are shown on a dc load line. The upper point represents the : -  a) minimum current gain b) quiescent point c) saturation point d) cutoff point

1 answer 14 views

The number of cross -points needed for 10 lines in a cross-point switch which is full duplex in nature and there are no self connection is  A) 100 B) 45 C) 50 D) 90

1 answer 19 views

Abating point number consist of -  a) A mantissa only b) Base only c) An exponent only d) all the above

0 answers 11 views

From the point of view of safety, the resistance of earthing electrode should be   (a) Low (b) High (c) Medium (d) The value of resistance of earth does not affect the safety

0 answers 21 views

A point charge of 120 mC is placed at the centre of a cube. What will be the total flux passing through one face of the cube?  A) 120 mC B) 60 mC C) 20 mC D) 30 mC

0 answers 14 views

Velocity of an electron (in km/S) starting at rest and travelling to a point 100 V above the starting potential is around  A) 3600 B) 4000 C) 5100 D) 6000

0 answers 11 views

Speed of improvement of computation of 64 point DFT by using FFT compared to direct computation is about  A) 4 B) 8 C) 16 D) 20

0 answers 16 views

According to Biot-Savart’s laws the magnetic field at a point due to incremental element of length dl carrying a current is  (A) Inversely proportional to the current carried by the element (B) Directly proportional to the current carried by the element (C) Directly proportional to the square of the distance (D) Inversely proportional to the length of the element

0 answers 11 views

In a control system, moving a summing point right side to the block yields in  (A) Multiplication of the G(s) in the feedback path (B) Multiplication of the 1/G(s) in the feedback path (C) Addition of gain block (D) Subtraction of gain block

1 answer 29 views

The algebraic sum of moments of the forces forming couple about any point in their plane is?

1 answer 349 views

The center of gravity of a triangle lies at the point of?

1 answer 23 views

A number of forces acting at a point will be in equilibrium if?

1 answer 425 views

The forces, which meet at one point, but their lines of action do not lie in a plane, are called?

1 answer 23 views
1 answer 17 views
1 answer 34 views
1 answer 329 views
1 answer 82 views