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Electronic Circuits for
Mechatronics ELCT 609
Lecture 3: PN Junctions (2)Dr. Eman Azab
Assistant Professor
Office: C3.315
E-mail: [email protected]
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
