DIAC PPT

DIAC D i o d e  for  a l t er er n a t i n g c u r r e n t  

By  Upama Bose 13MPE0002

INTRODUCTION  A diac is an important member of the thyristor family. •

 A diac is a two-electrode bidirectional avalanche diode which can be switched from off-state to the on-state for  either polarity of the applied voltage. •

The main characteristics are of the DIAC are as follows: (i) Break over voltage (ii) Voltage symmetry (iii) Break-back voltage (iv) Break over current (v) Lower power dissipation Although most DIACs have symmetric switching voltages, asymmetric DIACs are also available. Typical DIACs have a power dissipations ranging from 1/2 to 1 watt.

Construction of a Diac  A

diac is a P-N-P-N structured four-layer, twoterminal semiconductor  device. MT2

and MT1 are the two main terminals of  the device. There is no control terminal in this device. is just like a triac without gate terminal. This

The

doping level at the two end P-layers is the same.

Operation of a Diac When

T1 is positive,current flow path is p-n-p-n For

positive polarity of T2,current flow path is p-n-p-n+ When

applied voltage in either  polarity is small (less than breakover  voltage)leakage current, flows through the device However,

when the magnitude of the applied voltage exeeds the avalanche breakdown voltage, breakdown takes place and the diac current rises sharply

Characteristics of a Diac Once

the diac goes into conduction, the diac maintains an almost continuous negative resistance characteristic. It

remains "in conduction" until the current through it drops below the holding current, I H. Most

DIACs have breakover voltage around 30 V

MATLAB SIMULATION MODEL(1ST QUAD. CHARACTERISTICS)

MATLAB SIMULATION MODEL(3rd QUAD. CHARACTERISTICS)

TABLE-VALUES  Vd

Id

0.1

0

0.5

0

0.8

0

0.9

0.0095

1

0.01905

1.1

0.02867

1.2

0.0381

1.3

0.04762

1.6

0.0747

1.7

0.8571 0

-0.1

0

-0.5

0

-0.8

0

-0.9

-0.0095

-1

-0.01905

-1.1

-0.02867

-1.2

-0.0381

-1.3

-0.04762

-1.6

-0.0747

PLOT of Vd vs Id 1

0.8

0.6

0.4

0.2

0 -2

-1.5

-1

-0.5

0 -0.2

-0.4

-0.6

-0.8

-1

0.5

1

1.5

2

Series1

Diac Applications The diacs are used as triggering devices in triac phase control circuits,employed for: 

lamp dimmer 



heat control

universal

motor  speed control etc.

 THANK YOU……