1. Past Paper Questions and Answers
DARLINGTON PAIR
Past Paper Questions and Answers

2. 2012 2EP01– Q14(a)(iv)
The illustration below is part of as logic circuit.
(a)(iv) The output current from component B is too low.
Describe one way in which this current could be increased. [2]
connect a Darlington Pair (1) to the circuit output (1)

3. – Q2(a)(iii)
A warning signal sounds when the guard of a machine is left open. The warning signal is generated by a combination of two Astables and a logic gate. A simplified block diagram of the warning signal system is shown below.
(iii) Name one appropriate transducer driver for the warning signal system. [1]
Darlington Pair (1)

4. HT – Q2(b)(i)
A designed bicycle alarm contains a combination of logic gates and a timer circuit to make it work. Shown below is a simplified block diagram of the bicycle alarm system.
(b) When the output of the AND gate was connected to the buzzer the circuit did not work.
(i) Explain the reason why a buzzer connected to an integrated circuit will not work. [2]
the IC can only supply a low current (1) which is not enough for the buzzer to work (1)

5. HT – Q2(b)(ii)
A designed bicycle alarm contains a combination of logic gates and a timer circuit to make it work. Shown below is a simplified block diagram of the bicycle alarm system.
(b) When the output of the AND gate was connected to the buzzer the circuit did not work.
(ii) Describe one way in which a named interface device may be used to drive the buzzer. [2]
connect a Darlington Pair (1) between the AND gate and the buzzer (1)

6. 2006 1974 HT – Q2(b)(i) (b) The loudspeaker circuit is shown below.
An alarm circuit is shown opposite. A 555 Astable is used to generate pulses for a loudspeaker circuit.
(b) The loudspeaker circuit is shown below.
(i) Name the transducer driver in the circuit above. [1]
Darlington Pair (1)

7. 2006 1974 HT – Q2(b)(ii) (b) The loudspeaker circuit is shown below.
An alarm circuit is shown opposite. A 555 Astable is used to generate pulses for a loudspeaker circuit.
(b) The loudspeaker circuit is shown below.
(ii) Give one advantage of using this transducer driver rather than a single NPN transistor. [1]
it can supply a larger current (1)

8. HT – Q2(e)
A logic circuit is connected to a relay interface, which switches an output circuit as shown opposite.
(e) The output of the logic circuit does not have enough power to operate the relay. It was also found that a single transistor was not powerful enough to operate the relay.
Name two devices which are powerful enough to operate the relay. [2]
Darlington Pair (1)
FET (1)