3-(08 august 2014) semiconductor electronics-additional problems

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Semiconductor Electronics: additional problems (08 August 2014)

1. PN-Junction

Example: PN-Junction (Razavi, 2014), p. 39.

Solution:

Example: PN-Junction (Razavi, 2014), p.56

How do you explain the phenomenon of drift? Solution: Drift is analogous to water flow in a river. Water flows from top of mountain to bottom because of gravitational field; electron flows from one terminal to the other because of electric field.

Drift Water flow electrons water

Electric field Gravitational field Drift/current Water flow

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2. Diode

Example: I/V Characteristics (Razavi, 2014), p. 49.

Solution:

Example: I/V Characteristics (Razavi, 2014), p. 52.

Solution:

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Example: Diode (Razavi, 2014), p. 61.

Solution:


Beginning with , 800D onV mV for each diode, determine the change in outV if inV changes from 2 .4V+ to 2.5V+ for the circuit shown in figure below.

Solution:

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(a) When inV changes from 2 .4V+ to 2.5V+ , 1D is on throughout the change. So0.8out inV V V - , i.e., outV changes from 1.6V+ to 1 .7V+ .

(b) When inV changes from 2 .4V+ to 2.5V+ , 1D and 2D are both on. So 1,out in D onV V V - , i.e., outV changes from 1.6V+ to 1 .7V+ .

(c) When inV changes from 2 .4V+ to 2.5V+ , 1D and 2D are both on. So 2,out D onV V , i.e., outV stays at 0.8V+ .

(d) When inV changes from 2 .4V+ to 2.5V+ , 2D is on. So 2,out D onV V , i.e., outV stays at 0.8V+ .

Example: Diode (Scherz & Monk, 2013), p.427.

(1) What does this circuit do? (2) Whats the final output voltage? (3) What are the individual voltage drops across each diode with plug tip-positive and plug

tip-negative? (Assume each diode has a 0.6V forward voltage drop) (4) To prevent diode meltdown, what would be the minimum load resistance, assuming

1N4002 diodes? Solution:

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Solution:

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Example: Voltage Regulator (Cathey, 2002), p.55. The circuit of figure (a) below is an inexpensive voltage regulator; all the diodes are identical and have the characteristic of figure (b) below. Find the regulation of 0v when bv increases from its nominal value of 4V to the value 6V. Take 2R k= W , and assume each diode can be modelled as a battery, 0.5FV V= , and a resistor, 500FR = W in series.

Solution: Combining the diode strings between points a and b and between points b and c gives the circuit of figure (b) above, where

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3. Ideal Diode

Example: I/V Characteristic (Razavi, 2014), p. 113. Plot the I/V characteristic of the circuit shown in figure below. Assume , 800D onV mV= for the constant voltage diode model.

Solution:

Example: Ideal Diode (Cathey, 2002), p.50. In the following circuit, D1 and D2 are ideal diodes. Find 1Di and 2Di .

Solution:

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Example: Ideal Diode (Cathey, 2002), p.31.

Solution:

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Example: Ideal Diode (Cathey, 2002), p.48. For the circuit of figure (a) below, sketch the waveform of Lv and Dv if the source voltage Sv is as given in figure (b) below. The diode is ideal, and 100LR = W .

Solution:

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Example: Ideal Diode (Cathey, 2002), p.49.

Assume D1 and D2 are ideal. 2 100LR R= = W , and Sv is a 10V square wave of period of 1 ms.

Solution:

4. Zener Diode

Example: Zener Diode

(1) In which region is a zener diode made to operate? (2) Name two mechanisms by which charges are created in zener diode? (3) At what value of electric field, at the junction, does zener breakdown take place? (4) Is the reverse saturation current a small current or a large current? (5) Large changes in diode current produce only small changes in diode voltage-this is true in

which region?

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Solution:

(1) Breakdown region as it is reverse biased (2) Avalanche multiplication and zener breakdown (3) 72 10 v m (4) Very small current (5) Breakdown region

Example: Zener Voltage Regulator (Scherz & Monk, 2013), p.427.

A 10- to 50-mA load requires a regulated 8.2V. With a 12V 10 percent power supply and 8.2V zener diode.

(1) What series resistance is required? (2) Assume from the data sheets (or experimentation) that the zener diodes minimum

regulation current is 10 mA. Determine the power ratings for the resistor and zener diode.

Solution:

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Example: Zener Diode (Cathey, 2002), p.65. The zener diode in the voltage regulator circuit of figure below has a constant reverse breakdown voltage 8.2ZV V= , for 75 1ZmA i A . If 9LR = W , size SR so that L Zv V= is regulated to (maintained at) 8.2V while bV varies by 1 0 percent from its nominal value of 12V.

Solution:

5. Diode Application

Example: Full-Wave Rectifier Circuit (Cathey, 2002), p.63. Find Lv for the full-wave rectifier circuit of figure below, treating the transformer and diodes as ideal. Assume 0SR = .

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Solution:

Example: LED (Cathey, 2002), p.66. A LED has a greater forward voltage drop than does a common signal diode. A typical LED can be modelled as a constant forward voltage drop 1.6DV V= . Its luminous intensity vI varies directly with forward current and is described by

40 millicandela (mcd)v DI i= A series circuit consists of such an LED, a current-limiting resistor R , and a 5V DC source SV .

(1) Find the value of R such that the luminous intensity as 1 mcd. (2) The reverse breakdown voltage ( RV ) of the LED is guaranteed by the manufacturer to be

no lower than 3V. Knowing that the 5V DC source may be inadvertently applied so as to reverse-bias the LED, we wish to add a zener diode to ensure that reverse breakdown of the LED can never occur. A zener diode is available with 4.2ZV V= , 30ZI mA= , and a forward drop of 0.6V. Describe the proper connection of the zener in the circuit to protect the LED, and find the value of the luminous intensity that will result if R is unchanged.

Solution: (1)

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(2)

References: Cathey, J. J. (2002). Electronic devices and circuits (2nd ed.): The McGraw-Hill Companies, Inc. Razavi, B. (2014). Fundamentals of microelectronics. River Street, Hoboken, NJ, USA: John Wiley

& Sons, Inc., ISBN 978-1-118-15632-2. Scherz, P., & Monk, S. (2013). Practical electronics for inventors. New York Chicago San

Francisco Lisbon: McGraw-Hill, ISBN 978-0-07-177134-4.

3-(08 august 2014) semiconductor electronics-additional problems

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