This slide is part of the material used to prepare the students for Module 4 of EASA part 66 examination for License category B1

1. Thyristors

2. Characteristics
 Hysteresis character
◦ It latches to its last position, on or off
◦ Example, physical s/w – you s/w it on, it
remains on.
 May be viewed as 2 transistors
working in pair.
 Constructed from bipolar junction
technology.

3. Examples of Thyristors
 Shockley diode
 DIAC
 SCR (silicon controlled rectifier)
 TRIAC
 Opto thyristors

4. Shockley Diode
 Not to be confused with schottky diode
 It is a four layer device
 Also known as PNPN diode.

5. The Working of the Shockley
Diode
 The four PNPN can be simplified to
two set of separate transistors, PNP
and NPN.
P N P
N P N

6. With high voltage, one of the transistor will be turned
on causing the other to be on. Once on, the
transistors latched. To turn off, the voltage must be
reduced to cause the current to drop below minimum

7. DIAC
 Shockley diode works with DC.
 For AC, 2 shockleys are joint.
 The result is shown in the lower image

8. SCR
 Silicon Controlled Rectifiers or
thyristors.
 Used to rectify AC and control the
power output.

9. TRIAC Dimmer

10. TRIAC FOR AC

11. Opto- tyristors

12. RESOURCES
My Blog CAA UK Recommended Books
Title Author
Aircraft Electricity and Eisman 0-02-801859-1
Electronics
Art of Electronics Horowitz 0-521-37095-7
Horowitz /Hill /Hill
Elements of Hickey/ 0070286957
Electronics Villines
Modern Aviation Helfrich 0-13-118803-8
Electronics
Micro Electronics in E Pallet 0-273-08612-X
Aircraft systems