I have looked at several past GCSE electronics papers and the given syllabus,
thyristors occur occasionally in the exam paper.
The knowledge at this level seems to be a basic understanding of
use and input levels required for the devise to function.
A thyristor is a switching device, used extensively in early power supplies
for customer electronics, still used in power electronics.
A pulse is supplied to the gate of the thyristor,
this fires the thyristor, to turn the the devise on.
Even when the pulse is removed the device remains
To turn the device off the the current flowing
through the device must be reduced to a "holding current" value OR more
likely the cathode voltage will be reduced to that below the Anode (reverse
This basic understanding together with identifying
the symbol above seems to be the required knowledge for GCSE electronics
Here is a typical question to test your knowledge of thyristors.
Button A and B are push to make (they make contact only when pushed
Answer the following
(a) Button A is closed the light is ..........
(b)Button A is open the light is ..........
(c)Button B is closed the light is ..........
(d)Button B is open the light is ..........
(a) Button A is closed the light is ..........ON
The thyristor is turned on with the pulse that is applied when the
switch is pressed
(b)Button A is open the light is ..........ON
Removing the turn on condition as not effect
(c)Button B is closed the light is ..........ON
Shorting the Anode and Cathode will turn the thyristor OFF, however
a circuit is made by passing through the switch
(d)Button B is open the light is ..........OFF
The switch is turned OFF breaking the circuit.