IECEP FILES ELECTRONICS PROBLEM SOLVINGCompiled by : Mark Djeron C. Tumabao

Calculate the efficiency of a transformer-coupled class A amplifier for a supply of 12 V and outputs of 6V.

V CEMAX=V CEQ+V ( p )=12 V +6V=18 V

V CEMIN=V CEQ−V ( p )=12V −6V=6 V

Resulting in

%η=50( 18 V−6 V18 V +6V )

2

%=12.5 %

For a class B amplifier providing a 20-V peak to a 16-Ω load (speaker) and a power supply of Vcc = 30 V, determine the circuit efficiency.

I L ( p )=V L( p)

RL

=20V16

=1.25 A

I DC=2π

I L ( p )=2π

(1.25 A )=0.796 A

Pi (dc )=V CC I dc=(30V ) (0.796 A )=23.9 W

Po (ac )=V 2

L

2 RL

=¿¿

For resulting efficiency of

%η=Po(ac)Pi ¿¿

For a class B amplifier using a supply of Vcc = 30 V and driving a load of 16Ω, determine the maximum output power.

Maximum Pi (dc )=2V2cc

πRL=

2(30V )2

π (16)=35.81W

For a class B amplifier using a supply of Vcc = 30 V and driving a load of 16Ω, determine the transistor dissipation

Maximum

Po=maximum P2Q

2=0.5( 2V 2

cc

π 2 RL)=0.5[ 2(30 V )2

π216 ]=5.7 W

Calculate the efficiency of a class B amplifier for a supply of Vcc = 24 V with peak output voltages of VL (p) = 22 V.

%η=78.54V L (P)

V CC

%=78.54( 22V24 V )=72 %

Calculate the total harmonic distortion for the following amplitude components: fundamental amplitude of 2.5 V, second harmonic amplitude of 0.25 V, third harmonic amplitude of 0.1 V, and fourth harmonic amplitude of 0.05 V.

% D 2=|A2||A1|

×100 %=0.25 V2.5 V

× 100 %=10 %

% D 3=|A3||A1|

× 100 %=0.1 V2.5 V

× 100 %=4 %

% D 4=|A4||A1|

× 100 %=0.05V2.5 V

× 100 %=2 %

%THD=√ D22+D3

2+D42 ×100 %

IECEP FILES ELECTRONICS PROBLEM SOLVINGCompiled by : Mark Djeron C. Tumabao

¿√ (0.10 )2+(0.04 )2+ (0.02 )2× 100%=0.1095 ×100%=10.95%Determine what maximum dissipation will be allowed for an 80-W silicon transistor (rated at25) if the reading is required above 25 by a derating factor of 0.5W/ at case temperature of 125.

PD (125 )=PD (25 )−(125−25 ) (0.5 W / )

¿80 W −100 (0.5W / )=30W

A silicon power transistor is operated with a heat sink (θSA=1.5 /W ) .the transistor, rated at150 W (25 ) , hasθCS=0.5 /W , and the mounting insulation has θCS=0.6 /W . What maximum power can be dissipated if the ambient temperature is40∧T Jmax

=200?

PD=T J−T A

θJC+θCS+θSA

= 200−400.5/W +0.6/W +1.5 /W

≈ 61.5 W

A dc voltage supply provides 50 V when the output is unloaded. When connected to a load, the output drops to 56 V. Calculate the value of voltage regulation.%V . R .=

V NL−V FL

V FL

×100 %=60V −56 V56 V

× 100 %=7.1%

Calculate the ripple voltage of a full-wave rectifier with a 100-μF filter capacitor connected to a load drawing to a load drawing 50 mAV r (rms )=2.4 (50 )

100=1.2V

Calculate the filter dc Voltage of a full-wave rectifier with a 100-μF filter capacitor connected to a load drawing to a load drawing 50 mA if the peak rectifier voltage is 30 V.V dc=V m−

4.17 Idc

C=30−

4.17 (50 )100

=27.9V

Calculate the ripple of a capacitor filter for a peak rectified voltage of 30 V, capacitor C= 100μF, and a load current of 50 mA.r=

2.41 I dc

CV dc

× 100 %=2.4 (50 )

100 (27.9 )× 100 %=4.3 %

IECEP FILES ELECTRONICS PROBLEM SOLVINGCompiled by : Mark Djeron C. Tumabao

Calculate the input bias currents at the non-inverting and inverting terminal respectively of an op=amp having specified values of IIO = 5nA and IIB = 30 nA.Determine the cutoff frequency of an op-amp having specified values B1 = 1 MHz and AVD = 200 V/mV.For an op-amp having a slew rate of SR = 2V/µs, what is the maximum closed loop voltage gain that can be used when the input signal varies by 0.5 V in 10 µs?Determine the output voltage of an op-amp for input voltages of Vi1 = 150 µV and Vi2 = 140 µV. The amplifier has a differential gain of Ad =4000 and the value of CMRR is 100.If an amplifier with gain of -1000 and feedback of β=-0.1 has a gain change of 20% due to temperature; calculate the change in gain of the feedback amplifier

|dA f

A f|≅| 1

βA||dAA |=| 1

−0.1 (−1000 )|(20%) = 0.2%

A transistor has a collector current of 10mA and a base current of 40uA. What is the current gain of the transistorβ=10mA/40uA=50

A 2N3904 has VCE=10V and IC=20mA. What is the power dissipation?PD=10V(20mA)=200mW

A zener regulator has an input voltage that may vary from 22 to 30V. If the regulated output voltage is 12V and the load resistance varies from 140Ω to 10kΩ, what is the maximum allowable series resistance?

R=( 2212

−1)140 Ω=117 Ω

IECEP FILES ELECTRONICS PROBLEM SOLVINGCompiled by : Mark Djeron C. Tumabao

A zener regulator has an input voltage ranging from 15 to 20V and a load current ranging from 5 to 20mA. If the zener voltage is 6.8V, what is the maximum allowable series resistance?R=( 15−6.8

20 mA )=410 Ω

Determine the thermal voltage of a diode at 27°C (common temperatures for components in an enclosed operating system)Vt =kT/q=(1.38x10-23J/K)(273+17)/1.6x10-19C = 26mV

What is the knee voltage of a silicon diode at 75°C? (75-25)°C*2.5mV/°C = 0.125VNew Vknee = 0.7-0.125 = 0.575V

At 20°C, the reverse saturation current of a silicon diode is 10nA, what is its value when the temperature increases to 100°C?100 °C / 20°C = 5New Ireverse = 25(10nA)= 0.32uA

A silicon diode is in series with 1kΩ resistor and a forward biasing voltage supply of 10V. If r’d is 10Ω, what is the anode to cathode current and voltage?IF=(10-0.7)/(10+1k)=9.21mAVF=0.7+10(9.21mA=0.79V

What is the wavelength of the light produced by an LED with an energy gap level of 1.43 eV?λ=hc/Eg =(6.626x10-34Js*3x108m/s) /(1.43eV*1.6x10-19J/eV) = 869nm

Calculate the power dissipation of a diode having ID = 40 mA. PD = VD x ID = 0.7V x 40 mA = 28 mWDetermine the nominal voltage for the Zener diode at a temperature of 120° C if the nominal voltage is 5.1 volts at 25° C and the temperature coefficient is 0.05%/° C.

V120C = V25C + V25C (120C – 25C) ( .0005/C) = 5.34 V

Determine the Noise Gain for the Inverting Amplifier circuit of the figure below.Kn = 1 + Rf / Ri = 1 + 4kohms/2 k ohms = 3Ans: 3

IECEP FILES ELECTRONICS PROBLEM SOLVINGCompiled by : Mark Djeron C. Tumabao

Express the Boolean function F= xy + x’z in a product of maxterm form.F = xy + x’z = (xy + x)(xy+z)F = (x+x’)(y+x’)(x+z)(y+z)F= (x’ + y)( x + z) ( y + z)

It is desired to design a phase-shift oscillator using an FET having gm= 5000μS, rd= 40kΩ and a feedback circuit whose resistance value R= 10kΩ. Select the value of the capacitor appropriate for oscillator operation of 1 kHz.

f = 1

2 π √6 RC

C= 12 π √6 (10 k )(1 k )

=6.497 x10−9 F=6.5 nF

The total dB gain of a three stage system is 120dB. Determine the dB gain of the third stage if the second stage is twice the dB gain of the first stage and the third is 2.7 times the dB gain of the first.

A1+ A2+ A3=120A2=2 A1

A3=2.7 A1

A1+2 A1+2.7 A1=120A1=21.052dB

A3=56.842dB ≈ 57 dB(nearest answer)