electronic circuits for mechatronics elct 609 lecture 3...

Electronic Circuits for

Mechatronics ELCT 609

Lecture 3: PN Junctions (2)Dr. Eman Azab

Assistant Professor

Office: C3.315

E-mail: eman.azab@guc.edu.eg

Electronics Dept., Faculty of IET

The German University in Cairo

1

PN-Junction ApplicationsPractical Circuits

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

2

Power Supply Circuit using Diodes

DC Power supply is implemented using diodes

Rectifiers are used to convert AC signal to DC signal

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

3

DC Power Supply Circuit Components

Figure from Sedra/Smith, Copyright © 2010 by Oxford University Press, Inc.

Rectifiers

Half-wave Rectifier

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

4

𝑉𝑖𝑛𝐴𝑣𝑔. = 0 𝑉𝑜𝑢𝑡𝐴𝑣𝑔. =𝑉𝑃𝑒𝑎𝑘𝜋

Rectifiers

Full-wave Rectifier

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

5

𝑉𝑖𝑛𝐴𝑣𝑔. = 0

𝑉𝑜𝑢𝑡𝐴𝑣𝑔. =2𝑉𝑃𝑒𝑎𝑘𝜋

Figures from Sedra/Smith, Copyright © 2010 by Oxford University Press, Inc.

Rectifiers

Full-wave Rectifier

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

6

Figure from Sedra/Smith, Copyright © 2010 by Oxford University Press, Inc.

Limiters (Clippers)

Limiters (Clippers)

It is a Linear Circuit used for signal conditioning

The circuit limits the output voltage to a predefined value

Any connections with diodes can be employed (parallel!)

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

7

General Transfer Function of a Limiter

𝑉𝑜𝑢𝑡 = 𝐾𝑉𝑖𝑛𝐿−𝐾

< 𝑉𝑖𝑛<𝐿+𝐾

K is the proportionality Constant

𝑉𝑜𝑢𝑡 = 𝐿+ 𝑉𝑖𝑛 >𝐿+𝐾

𝑉𝑜𝑢𝑡 = 𝐿− 𝑉𝑖𝑛 <𝐿−𝐾

Figure from Sedra/Smith, Copyright © 2010 by Oxford University Press, Inc.

Limiters (Clippers)

Limiters Example 1:

Assume that the Diodes have Vth=0.7V

Draw ‘Vout’, if ‘Vin’ is a sinusoidal signal with 10kHz and 10Vpp

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

8

𝑉𝑜𝑢𝑡 = 𝐾𝑉𝑖𝑛𝐹𝑜𝑟 𝑉𝑖𝑛 > −𝑉𝐷𝐾

𝐾 =𝑅𝐿

𝑅𝑆 + 𝑅𝐿𝑉𝑜𝑢𝑡 = −𝑉𝐷𝐹𝑜𝑟 𝑉𝑖𝑛 < −

𝑉𝐷𝐾

Limiters (Clippers)

Limiter Example 2:

Assume that the Diodes are ideal, Draw ‘Vout’ vs. ‘Vin’

Draw ‘Vout’, if ‘Vin’ is a sinusoidal signal with 10kHz and

10Vpp

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

9

Zener Diodes

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

10

Zener Diode

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

11

Breakdown Phenomena (Breakdown Biased)

Reverse biasing can cause the diodes to conduct in opposite

direction under large reverse voltage value

Zener Effect

Avalanche Effect

Breakdown is non-destructive

Applications:

Shunt Regulator

Limiters

Zener Diode

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

12

I-V Characteristics modeling for Zener Diode

Forward

BiasedReverse Biased

Breakdown

Biased

Assume

𝑉𝐷 = 𝑉𝑇ℎ

Verify

𝐼𝐷 > 0

Assume

𝐼𝐷 = 0

Verify

−𝑉𝑍< 𝑉𝐷 < 𝑉𝑇ℎ

Assume

𝑉𝐷 = −𝑉𝑍 − 𝐼𝐷𝑅𝐵

Verify

𝐼𝐷 < 0

Zener Diode

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

13

I-V Characteristics modeling for Zener Diodes

Note: You can reverse the diode polarity in Breakdown

Breakdown Biased

Assume

𝑉𝐷 = 𝑉𝑍 + 𝐼𝐷𝑅𝐵 ≅ 𝑉𝑍

Verify

𝐼𝐷 > 0

Zener Diode Application

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

14

Voltage Regulator

Zener Diode Example

Dr. Eman Azab

Electronics Dept., Faculty of IET

The German University in Cairo

15

Draw the output voltage vs. the input voltage

Voltage limiter using Zener