1)

For the comparator circuit showing the LM339, what voltage needs to ba applied to input VIN for the LED to light?

Choose one answer.

a. Vin < +5.0V

b. Vin > +5.0V

c. Vin < -5.0V

d. Vin > -5.0V

2) In the Transistor Motor control circuit below, the value of the variable resistor R is adjusted to allow a particular value of current to flow through the DC motor M (hence setting its speed). If the value of the variable resistor R is to be chosen so that the voltage across the motor is 8V, determine R (in ohms). Only enter the numerical value without units.

3) Which of the following values is the output voltage for the opamp circuit shown?

a. 3.3V

b. -2.8V

c. 2.8V

d. - 3.3V

4) For the circuit diagram of the transistor switching a relay coil (300 ohm), calculate the maximum resistor value R, such that with the switch SW open, the transistor is fully on (saturated, ie: Vce ~ 0V). [Do not employ any overdriving strategies.]
Ensure that the resistor value selected is from the E12 series. Ensure that your answer is in ohms and only enter the numerical answer (without units).

5) If a power transistor has a maximum power dissipation of 10W and needs to cope with worst case ambient temperatures of 50 deg C, determine the heatsink needed for the transistor to survive.
Assume the transistor in a TO-220 package has a thermal resistance Rjc of 4 deg C/W, has a maximum allowed junction temperature of 150 deg C. Ignore any thermal resistance between transistor case and heatsink (ie: Rcs = 0 deg C/W for mounting). Calculate the heatsink's required thermal resistance Rsa and give the answer in deg C/W, without including the units (numerical answer only).

6) With logic circuit below, choose the correct input logic (1's or 0's) for A, B and C to give a '0' at Q.

B ?

A ?

C ?

7) Based on the power supply circuit below, determine the DC output voltage Vo, taking into account voltage drops and averaging of ripple voltage for the specific load. The diodes are standard rectifier diodes 1N4004s and the LOAD resistance is 220 ohms. Note that the voltages on the transformer are given as AC rms values at 50Hz. Assume a lossless transformer.
Give the answer in volts, numerically only , without units.

8) For the given 741 OpAmp circuit, assuming that the power rails (not shown) of the OpAmp are +/- 15V, Calculate the output voltage Vo if the two input voltages V1 and V2 are 0.6V and -0.3V respectively.

a. +4.5V

b. +1.5V

c. -1.5V

d. -4.5V

9)In the circuit below, if the load resistance RLOAD was 3k3 (3300) ohms, to what voltage could the 9V battery's voltage fall, before the regulators output voltage of 5.1V would start to drop. Assume that the Zener diode needs at least 1mA flowing through it to hold the reverse breakover voltage of 5.1V.
Give the answer in volts without including the units (numerical answer only)

10) By analysing the 555 monostable circuit below, determine the period of the output pulse at Q once the switch SW is closed. Give the answer in seconds without including the units.