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8/22/2019 Flyback Converters
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Flyback Converters
RESOSO, Alvin C.
TOLENTINO, Ellis Zaldy M.
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Report Outline
1. Review: Transformers
2. Introduction to Flyback Converters
3. Difference with the Buck-Boost
4. Isolated SMPS
a. Non-Isolated SMPSb. Isolated SMPS
c. Advantages vs. Disadvantages
5. Topology
6. Assumptions for Analysis
7. CCM Operation
a. Switch Closed
b. Switch Open
8. DCM Operation
9. Applications
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Review: Transformers [1]
Basic function is for I/O isolation
Power supply applications work at a high frequency so transformershould be as small as possible
Ideal Model:
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Review: Transformers [1]
Basic I/O relationship:
Voltage:
Current:
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Review: Transformers [1]
For most power electronics application, we use the model with
magnetizing inductance at the primary side
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Introduction
Simplest and most implemented SMPS topology
Commonly used in low-power applications (a few watts to ~100W)[1]
Used when output needs to be isolated from the input (more on
this later) Can offer multiple isolated output voltages
Energy efficiency is lower than other SMPS circuits, but itssimplicity and low cost is favored
Has controllable switch (usually MOSFET) with operatingfrequency of around 100 kHz [1]
[1] Kharagpur. Version 2 EE IIT. Lesson 22: Fly-Back Type Switched Mode Power Supply. p3
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Introduction
Almost same as the Buck-Boost, except that the inductor isreplaced by a Transformer.
DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Introduction [1]
Almost same as the Buck-Boost, except that the inductor isreplaced by a Transformer.
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Introduction [1]
Model with magnetizing inductance at the primary side
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Difference with the Buck - Boost [1]
Flyback:
1. Uses Transformer to store
energy (typically step-up or
isolation Transformer - more
on this later)2. Can't operate on 2 modes.
3. Used for high power
applications (CRT screens,
etc.)
Buck - Boost:
1. Uses Inductor to store energy
2. Can operate in 2 modes:
a. Buck mode
b. Boost mode3. Used generally for low power
operations.
[1] What are differences between buck-boost and flyback smps.
Available: http://www.edaboard.com/thread141689.html
http://www.edaboard.com/thread141689.htmlhttp://www.edaboard.com/thread141689.htmlhttp://www.edaboard.com/thread141689.html8/22/2019 Flyback Converters
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Isolated SMPS
Non-Isolated SMPS:
These topologies have their inputs and output not isolatedfrom each other (electrically connected)
Examples:
Buck Converter [Step Down] Boost Converter [Step Up]
Buck-Boost Converter [Cascaded Buck and Boost]
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Isolated SMPS [1]
Isolation is the principle of coupling one circuit to another withoutconnecting them directly (no direct current flow between input
and output)
In isolated SMPS topologies (generally, in power electronics), the
most commonly used form of isolation is the TRANSFORMER Isolated SMPS Topologies:
Flyback
Foward
Bridge (Half, Full)
Push-Pull
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
Available: http://www.allaboutcircuits.com/vol_2/chpt_9/3.html
http://www.allaboutcircuits.com/vol_2/chpt_9/3.htmlhttp://www.allaboutcircuits.com/vol_2/chpt_9/3.html8/22/2019 Flyback Converters
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Isolated SMPS - Advantages [1][2]
Isolation between the ground of the input supply and the output load is
often desired to isolate the common returns from different parts of the
electronic system in order to eliminate ground loops between circuitries.
Serves as protection for both the user and the equipment against
dangerous transient voltages induce Improved noise immunity
Ease of output connections without conflict with the primary ground
The introduction of a transformer provides necessary voltage scaling thus
enabling a higher output voltage (Vo/Vin does not depend solely on the duty
cycle)
Offers the advantage of having multiple outputs at different voltage levels
[1] Flyback Converter. National Semiconductor, 2010
[2] Power Switching Converters. Simon S. Ang, 1995, pp. 119-120
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Isolated SMPS - Advantages
Flyback converter with multiple output[1]
[1] Multi-Output Flyback Offline Power Supply, ON Semiconductor
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Isolated SMPS - Disadvantages [1]
Complexity (key design issue is the power transformer)
Electromagnetic Interference or EMI
disturbance that affects an electrical circuit due toelectromagnetic induction
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
Available: http://en.wikipedia.org/wiki/Electromagnetic_interference
http://en.wikipedia.org/wiki/Electromagnetic_interferencehttp://en.wikipedia.org/wiki/Electromagnetic_interference8/22/2019 Flyback Converters
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Topology
Flyback converter:
Elements:
Switching Device [usually MOSFET] Diode Capacitor Flyback Transformer [different from ordinary transformer]
DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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Topology - MOSFET
Used to switch the primary of the transformer ON or OFF
Has switching frequency in the 100 kHz range
Used with a dynamic control (feedback system) to adjust dutycycle (which in turn dictates the desired regulated output voltage)
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Topology - Flyback Transformer [1]
Used for voltage isolation
Primary and secondary windings so that they are linked by nearlythe same Magnetic Flux
Doesn't work the same way as a normal transformer
Primary and Secondary windings of a flyback transformerdoesn't conduct simultaneously.
The magnetic design of the flyback transformer is more like ofan inductor.
The flyback transformer may be more appropriately called aninductor-transformer
Can have multiple output windings for generating multiple isolatedvoltages (shown earlier).
[1] Kharagpur. Version 2 EE IIT. Lesson 22: Fly-Back Type Switched Mode Power Supply. pp. 3-4
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Assumptions for Analysis [1][2]
Magnetic circuit - > ideal
Coupling between Primary & Secondary -> ideal
No winding leakage inductances.
Voltage drops of switch (MOSFET) and diode are neglected.
Windings, transformer core, capacitor are lossless
CCM Additional Assumptions:
Very large output capacitance -> constant output voltage
Circuit operating in steady-state. All voltages and currents areperiodic, with period T
Duty ratio of the switch is D: closed for DT, and open for (1-D)T
Switch (MOSFET) and diode are ideal.
[1] Hart, Daniel W. Power Electronics. pp. 267-268
[2] Kharagpur. Version 2 EE IIT. Lesson 22: Fly-Back Type Switched Mode Power Supply. p4
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CCM Mode of Operation [1]
Switch closed (Assuming all components are ideal)
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM Mode of Operation [1]
Switch opened
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM Mode of Operation [1]
At steady-state,
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM Mode of Operation [1]
Output voltage
Similar to the I/O relationship of the buck-boost converter (exceptfor the transformer ratio factor)
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM Waveforms [1]
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM Waveforms [1]
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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DCM Mode of Operation
For DCM, the output voltage is given by
R is the load resistance
T is the switching period
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CCM-DCM Boundary [1]
Ave. Inductor current
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM-DCM Boundary [1]
Max. inductor current
Min. inductor current
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
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CCM-DCM Boundary [1][2]
This is the minimum required inductance to operate at CCM.
[1] DC to DC Converter (Chopper). Dr. Zainal Salam, UTM-JB, Power Electronics and Drives (Version 3-2003)
[2] Power Electronics. Marvin J. Fisher, 1991. pp.311-315
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Applications
Low Power Switch Mode Power Supplies (i.e. Cell phone chargers,etc)
Multiple outputs PS (i.e. Computer [Desktop] Power Supply)
High Voltage supply for CRT in TV sets.
High Voltage generation
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All References
Rashid. Power Electronics Handbook. pp. 217-218.
Dr. Salam, Zainal. Power Electronics and Drives. version 3-2003.Chapter 3: DC to DC Converter (Chopper).
Kharagpur. Module 3: DC to DC Converters. version 2 EE IIT.
Lesson 22: Fly-back Type Switched Mode Power Supply. Fisher, Marvin J. Power Electronics. pp. 310-315
Ang, Simon S. Power Switching Converters. pp. 119-146
Wikipedia. Flyback Converter. Available: http://en.wikipedia.org/wiki/Flyback_converter
Wikipedia. Flyback Transformer. Available: http://en.wikipedia.org/wiki/Flyback_transformer
http://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Flyback_converterhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Flyback_transformerhttp://en.wikipedia.org/wiki/Flyback_converterhttp://en.wikipedia.org/wiki/Flyback_converter8/22/2019 Flyback Converters
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Thank you for listening!
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Quiz [Total 10 points]