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• 1. Semiconductors
• 2. Diodes
• 3. Bipolar Junction Transistors
• 4. Field Effect Transistors
• 5. Opto-Coupled Devices
• 6. Thyristors,Triacs & Diacs
• 7. Transistor Faults

Module 5.6

Optocoupler Quiz

Try this quiz based on optocouplers. Hopefully it'll be easy. Submit your answers but don't be disappointed if you get answers wrong. All the information you need is on this website. Find the right answer and learn about transistors as you go.

1.

What type of optocoupler output is illustrated Fig. 5.5.1?

• a) Phototransistor.
• b) Photodiode.
• c) Phototriac.
• d) PhotoSCR

2.

A phototransistor produces more current than a photodiode because - (Choose an answer to complete this sentence)

• a) - the phototransistor can be more heavily doped than the photodiode.
• b) - the photo transistor accepts a wider spectrum of light than the photodiode.
• c) - the current produced by photons is amplified by the h_fe of the transistor.
• d) - the photodiode is normally used in low light conditions.

3.

Which of the following operation modes do photo proximity detectors normally use?

• a) Linear Mode.
• b) Saturation Mode.
• c) Analogue Mode.
• d) Direct Mode.

4.

Fig. 5.5.2 illustrates an IL300 audio optocoupler, which uses one infrared LED and two photodiodes. What is the usual purpose of the second photodiode?

• a) To double the output voltage when connecting the two diodes in parallel.
• b) To provide back emf protection.
• c) To provide compensation for variations in CTR.
• d) To generate a DC bias from an AC signal.

5.

An optocoupler having a maximum input current (I_F) of 50mA is chosen to be driven by a current of 20mA. Which of the following answers would be a valid reason for this?

• a) To allow for input surge currents.
• b) To reduce input noise.
• c) To allow for LED ageing.
• d) To allow for the occurrence of voltage spikes at the input.

6.

Which of the formulae in Fig.5.5.3 correctly describes the CTR of an optocoupler?

• a) Formula a
• b) Formula b
• c) Formula c
• d) Formula d

7.

What is the purpose of RV1 in the audio optocoupler circuit shown in Fig 5.5.4?

• a) To adjust for maximum current I_CE.
• b) To adjust for minimum DC bias voltage.
• c) To adjust for maximum volume.
• d) To adjust for minimum distortion.

8.

Refer to Fig. 5.5.5. What will be the approximate voltages at the collector of the 2N3904 transistor when the LED is 'On' and 'Off'?

• a) On = 2.0V Off = 0.8V
• b) On = 0.1V Off = 4.9V
• c) On = 5.0V Off = 0.2V
• d) On = 4.5V Off = 0.3V

9.

Compared to a photo-diode, which of the listed advantages and disadvantages would be expected of a photo-transistor

• a) Faster response and greater sensitivity.
• b) Faster response and less sensitivity.
• c) Slower response and greater sensitivity.
• d) Slower response and less sensitivity.

10.

Refer to Fig. 5.5.6. With the input and output signals shown, what level of signal voltage would you expect at point A?

• a) 0Vpp to 0.1Vpp
• b) 0.1Vpp to 1Vpp
• c) 1Vpp to 10Vpp
• d) 10Vpp to 20Vpp

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