ESE 372 / Spring 2013 / Lecture 8
Last Time: Half Wave Rectifier
Diode IV
Simple Model
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ESE 372 / Spring 2013 / Lecture 8
Last Time: Half Wave Rectifier with filter capacitor
Discharge time
Charge time
Maximum value of the reverse bias voltage that diode should take:
Peak Inverse Voltage
Clearly, for rectifier to operate well one must have
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ESE 372 / Spring 2013 / Lecture 8
Full Wave Rectifier: Bridge Rectifier
Both positive and negative half waves are utilized but amplitude is reduced by
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ESE 372 / Spring 2013 / Lecture 8
PIV of Bridge Rectifier
Clearly, for rectifier to operate well one must have
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ESE 372 / Spring 2013 / Lecture 8
Bridge Rectifier with filter capacitor
Discharge time is
Voltage ripple
Twice lower since discharge time is twice shorter
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ESE 372 / Spring 2013 / Lecture 8
Peak Diode Current
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ESE 372 / Spring 2013 / Lecture 8
Where is ground in bridge rectifier
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ESE 372 / Spring 2013 / Lecture 8
Transformer
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ESE 372 / Spring 2013 / Lecture 8
Toroidal Solenoid
Inductance:
Magnetic flux created
by current
Cross‐
section area
Here:
Magnetic flux density
Number of turns
Total area
Ampere’s law:
Total current inside
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ESE 372 / Spring 2013 / Lecture 8
Toroidal core with two coils
Self inductances
Mutual Inductance: magnetic flux created by I1 will cut through coil 2 and vice versa.
Mutual inductance
in ideal case, i.e. all flux created by I1 cuts through 2
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ESE 372 / Spring 2013 / Lecture 8
Ideal Transformer
Primary coil
Secondary coil
Coupling coefficient
in ideal transformer
in ideal transformer
‐ Turn ratio
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ESE 372 / Spring 2013 / Lecture 8
Ideal Transformer
Primary coil
Secondary coil
For high or
Power delivery:
in ideal transformer
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ESE 372 / Spring 2013 / Lecture 8
Power delivery from source to load
Maximum power that can be generated by source
Power delivered to load:
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ESE 372 / Spring 2013 / Lecture 8
Impedance matching with the help of transformer
To maximize power delivery to load one can design coupling transformer such that:
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ESE 372 / Spring 2013 / Lecture 8
Phase shift between I and V in primary
1. Open circuit secondary:
Transformer behaves like inductance with V1 leading I1 by 2. Short circuit secondary:
Transformer behaves like resistance (small) 15
ESE 372 / Spring 2013 / Lecture 8
Full wave center tap rectifier
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ESE 372 / Spring 2013 / Lecture 8
Example 1: Bridge rectifier.
Design for 5 V load voltage with 1% ripple. Input – 120 V rms, 60 Hz
Assume
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ESE 372 / Spring 2013 / Lecture 8
Example 2: Center Tap rectifier.
Design for the same parameters as Bridge in example 1.
A bit less turns on each secondary but there are two of them – larger transformer is needed.
Twice bigger than for Bridge
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ESE 372 / Spring 2013 / Lecture 8
Center‐tab bipolar power supply
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ESE 372 / Spring 2013 / Lecture 8
Precision rectifier (super diode)
Problem:
1. The whole input goes between inputs
– need protection.
2. Output in saturation and OpAmp
needs time to recover – delay.
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ESE 372 / Spring 2013 / Lecture 8
Better Precision rectifier
100% negative feedback, hence virtual short between inputs
and
and
Negative feedback through R2
Is “catching diode”
It catches when it goes
negative and keeps at
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ESE 372 / Spring 2013 / Lecture 8
Basic AC voltmeter
Low Pass Filter
Super Diode
Can be calibrated to measure RMS of sine wave
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