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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 6.7

Thyristor Quiz

Try this quiz based on thyristors. 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 thyristors as you go.

1.

What is the value indicated by point X in Fig. 6.7.1?

• a) The holding current I_H.
• b) The break over current I_BO.
• c) The latching current I_L.
• d) The forward conducting current I_FB.

2.

What is the function of a crowbar protection circuit?

• a) To provide over voltage protection.
• b) To isolate a high voltage triac from a low voltage control circuit.
• c) To prevent thermal runaway.
• d) To prevent a power supply output short circuit.

3.

Referring to Fig. 6.7.2, what is the maximum achievable conduction angle using this circuit?

• a) 90 degrees.
• b) 180 degrees.
• c) 270 degrees.
• d) 360 degrees.

4.

Which of the following advantages and disadvantages describes a zero crossing SCR circuit?

• a) Usable with AC motors but unsuitable for heaters.
• b) Reduces low frequency flicker but increases RF interference.
• c) Suitable for incandescent lamps but not for inductive loads.
• d) Produces low frequency flicker but reduces RF interference.

5.

Which quadrants are used when triggering a triac with a negative going trigger pulse in both the positive and negative half cycles of the AC wave?

• a) I and II
• b) II and III
• c) III and IV
• d) I and IV

6.

Referring to Fig. 6.7.3, what is the purpose of diodes D1 to D4 in this circuit?

• a) A Bridge rectifier to provide a DC voltage to drive the diac.
• b) Transient pulse suppression diodes to protect the triac.
• c) Steering diodes to eliminate hysteresis.
• d) A bridge rectifier to enable the circuit to trigger during both AC half cycles.

7.

What is the function of a Metal Oxide Varistor (MOV) in the protection of thyristor power supplies?

• a) Protection against voltage spikes.
• b) Protection against high current surges.
• c) Protection against high inrush currents.
• d) Protection against thermal runaway.

8.

Under which of the following conditions will a triac cease conducting?

• a) When I_GT falls to zero.
• b) When the current between MT2 and MT1 falls below I_L
• c) When the current between MT2 and MT1 falls below I_H
• d) When V_DRM falls below V_BO

9.

Which of the following statements is untrue?

• a) Solid State Relays are likely to be safer in failure mode than Electromagnetic Relays.
• b) Solid State Relays can switch faster than Electromagnetic Relays.
• c) Solid State Relays have a higher 'ON' resistance than Electromagnetic Relays.
• d) Solid State Relays have a lower 'OFF' resistance than Electromagnetic Relays.

10.

What is the function of a TVS diode when used in a high power SSR?

• a) To trigger the power Triac.
• b) To clip interference spikes.
• c) To counteract CTR variations.
• d) To provide over current protection.

© 2007− 2023 Eric Coates MA BSc. (Hons) All rights reserved. (Revision 15.00 29th December 2020)