ELG2136: Electronics I Diodes

Size: px

Start display at page:

Download "ELG2136: Electronics I Diodes"

Erik Derrick Park
5 years ago
Views:

1 ELG2136: Electronics I ioes Riah W. Y. Habash School of Electrical Engineering an Computer Science University of Ottawa Ottawa, Ontario, Canaa. Riah Habash, SITE,

2 What are ioes? ioes are semiconuctor evices which might be escribe as passing current in one irection only. ioes however are far more versatile evices than that. ioes may be use as voltage regulators, tuning evices in RF tune circuits, frequency multiplying evices in RF circuits, mixing evices in RF circuits, switching applications or can be use to make logic ecisions in igital circuits. There are also ioes which emit light, of course these are known as light-emitting-ioes or LE s. Riah W. Y. Habash, SITE,

3 Schematic Symbols for ioes Riah W. Y. Habash, SITE,

4 Common ioe The first ioe in the previous Figure is a semiconuctor ioe which coul be a small signal ioe. Notice the straight bar en has the letter k, this enotes the cathoe while the a enotes anoe. Current only flows from anoe to cathoe an not in the reverse irection, hence the arrow appearance. This is one very important property of ioes. The anoe terminal must be positive an the cathoe terminal negative for a current to flow. In an ieal ioe, there is no voltage rop across a ioe when current is flowing. Riah W. Y. Habash, SITE,

5 Physical Structure of the Junction ioe Riah W. Y. Habash, SITE,

6 The pn Junction Riah W. Y. Habash, SITE,

Forwar Biasing the Junction Electrons in the p-type material, near the positive terminal of the supply, break their electron pair bons an enter the supply, thereby proucing new holes.

7 Forwar Biasing the Junction Electrons in the p-type material, near the positive terminal of the supply, break their electron pair bons an enter the supply, thereby proucing new holes. Also electrons from the negative terminal of the supply enter the n-type material an migrate towars the junction. Free electrons from the n-type then flow across the junction an move into the holes which have migrate from the positive terminal. This current flow will continue as long as the external supply is connecte an is calle forwar current flow. Riah W. Y. Habash, SITE,

Reverse Biasing the Junction When the polarity of the supply is reverse, the potential within the evice is effectively reinforce an the epletion layer becomes wier.

8 Reverse Biasing the Junction When the polarity of the supply is reverse, the potential within the evice is effectively reinforce an the epletion layer becomes wier. This is because the free electrons in the n-type are attracte towars the positive terminal, away from the junction, while the electrons from the negative terminal of the supply enter the p-type an migrate towars the junction. Current flow is extremely small an is calle reverse current. Note that this current is prouce by minority carriers an the evice is sai to be reverse biase. Riah W. Y. Habash, SITE,

9 Anoe Cathoe i-v Characteristics of an ieal ioe OFF State ON State Voltage v MUST be NEGATIVE, i.e., voltage of ANOE is LOWER than voltage of the CATHOE Current i MUST be in this irection, i.e., FROM the ANOE TO CATHOE

10 ioes in Circuits 1 is ON because its ANOE is connecte to 0 V, while its CATHOE is connecte to a negative voltage, though via a 10 kω resistor. 2 is ON because its ANOE is connecte to 10 V, via a 10 kω resistor while its CATHOE is connecte to a negative voltage, though via a 10 kω resistor.

11 Ieas for igital Gates Fin Here are the possibilities OFF OFF OFF OFF OFF ON? OFF ON OFF OFF ON ON ON OFF OFF ON OFF ON ON ON OFF ON ON ON

12 i = V I ( e S The Forwar-Bias Region / V T I s is saturation current 1) V T is thermal voltage kt = = T, mv = q V T i I e V / = S V T v = V T 25,3mV ln i I s Riah Habash, SITE,

13 The Forwar an Reverse bias Regions Riah Habash, SITE,

14 Riah Habash, January The Small-Signal Moel T v nv I i i I i = + = V nv T S e I I / = ( ) ( ) t v V t v + = T I nv r =

15 i v v = 1 r = V = V o ( v V ) + i + i r r o Riah Habash, January

16 V v s = = i I R + V ( R + r ) v = v s r R + r Riah Habash, January

17 Operation in the Reverse Region- Zener ioe (Sera/Smith 3.6) V = r z I V = V + Z Zo r z I Z Riah Habash, January

18 Zener ioe The secon of the ioes is a zener ioe which are fairly popular for the voltage regulation of low current power supplies. While it is possible to obtain high current zener ioes, most regulation toay is one electronically with the use of eicate integrate circuits an pass transistors. Riah W. Y. Habash, SITE,

ELG3336: Diodes. Riadh Habash,

ELG3336: Diodes. Riadh Habash, ELG3336: ioes Riah Habash, 2012 1 What are ioes? ioes are semiconuctor evices which might be escribe as passing current in one irection only. ioes however are far more versatile evices than that. ioes