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  • DC to AC Converters
    • How to Get AC Output From DC Input Supply?
    • What If The Load Is Not Resistive?
    • General Structure of Voltage Source Inverters
    • Need For Isolated Gate-Control Signals For The Switches
    • Classification of Voltage Source Inverters
    • Harmonic Analysis of The Load Voltage And Load Current Waveforms
    • Time Domain Analysis
    • Frequency Domain Analysis
    • Analysis Of The Single-Phase Full Bridge Inverter
    • Voltage And Current Ratings Of Inverter Switches & Applications Of Square Wave Inverter
    • Three-phase square wave VSI
    • Determination Of Load Phase-Voltages
    • Uses & Limitation of 3-Phase Square Wave Inverter
    • Nature Of Pole Voltage Waveforms Output By PWM Inverters
    • Harmonic Analysis Of Pole Voltage Waveform
    • Trade Off Between Low Order And High Order Harmonics
    • Brief Description Of Some Popular PWM Techniques
    • Two-Level Versus Three-Level PWM Inverters
    • Considerations On Switch Voltage And Current Ratings
    • Introduction to sine PWM
    • Analysis Of The Pole Voltage Waveform With A Dc Modulating Signal
    • Pole Voltage Waveform With Sinusoidal Modulating Signal
    • Modulation Index & Over-Modulation
    • A 1-Phase Sine-PWM Inverter Of H-Bridge Topology
    • Generation Of 3-Phase Sine-PWM Waveform
    • A Typical Circuit For Generation Of PWM Waveforms
    • More Output Voltage From The Same DC Bus Voltage
    • Sine + 3rd Harmonic PWM Technique
    • Space Vector PWM (SV-PWM) Technique
    • Smoothly Rotating Space Voltage Vector From Inverter
    • Algorithm For Producing Sinusoidal Output Voltages Using SV-PWM
    • Some Other Popular PWM Techniques
    • Single-phase Current Source Inverter
    • Mode I operation of Single-phase Current Source Inverter
    • Mode II operation of Single-phase Current Source Inverter
    • Three-phase Current Source Inverter
    • Commutation phases of Three Phase CSI
    • Advantages and Disadvantages of CSI
    • Load-Commutated CSI
    • Equivalent circuit of Load commutated CSI
    • Characteristics of Load commutated CSI and Output

  • Power Semiconductor Devices
    • Introduction to Power Electronics
    • Difference between Power Electronics and Linear Electronics
    • Varieties of Power semiconductor Devices
    • Classification of Power Diodes
    • Silicon Controlled Rectifier (SCR)
    • Introduction to MOSFET
    • Introduction to the IGBT
    • Base/Gate drive circuit
    • Introduction to the GTO
    • Power converter Topologies
    • Protection of Power devices and converters
    • Introduction to power semiconductor devices
    • Review of P-N diode characteristics
    • Volt-Ampere ( i-v ) characteristics of a p-n junction diode
    • Construction and characteristics of Power Diodes
    • Power Diode under Reverse Bias conditions
    • Power Diode under Forward Bias Conditions
    • Specifications related to forward bias operation of power diodes
    • Switching characteristics of Power diodes
    • Parameters defining the turn off characteristics of a Power diode
    • Introduction to power BJT
    • Basic Operating Principle of a Bipolar Junction Transistor
    • Input and Output characteristics of NPN transistor
    • Constructional Features of a Power BJT
    • Output I-V characteristics of a Power Transistor
    • Safe operating areas of a Power Transistor
    • Switching characteristics of a Power Transistor
    • Turn On characteristics of a Power Transistor
    • Turn Off Characteristics of a Power Transistor
    • Switching Trajectory and Switching Losses in a Power Transistor
    • Base Drive Design of power transistor
    • Power Darlington Transistor
    • Introduction to Thyristors and Triacs
    • Constructional Features of a Thyristor
    • Basic operating principle of a thyristor
    • Static output i-v characteristics of a thyristor
    • Thyristor Gate Characteristics
    • Thyristor ratings & Voltage ratings of a thyristor
    • Current ratings of a thyristor
    • Gate Specifications of a thyristor
    • Switching Characteristics of a Thyristor
    • Turn on Switching Characteristics of thyristor
    • Turn off Switching Characteristics of Thyristor
    • Introduction to The Triac
    • Construction and operating principle of Triac
    • Steady State Output Characteristics and Ratings of a Triac
    • Triac Switching and gate trigger circuit
    • Features of GTO
    • Constructional Features of GTO
    • Operating principle of GTO
    • Steady state output and gate characteristics of a GTO
    • Dynamic characteristics of a GTO
    • GTO gate drive circuit
    • GTO Ratings - Steady state voltage and current rating
    • GTO Ratings - Gate specification & Specifications related to the switching performance
    • Features of MOSFET
    • Constructional Features of a Power MOSFET
    • Operating principle of a MOSFET
    • Steady state output i-v characteristics of a MOSFET
    • Safe operating area of a MOSFET
    • Circuit models of a MOSFET cell
    • Switching waveforms of MOSFET
    • MOSFET Gate Drive
    • MOSFET Ratings
    • Features of IGBT
    • Constructional Features of an IGBT
    • Operating principle of an IGBT
    • Steady state characteristics of an IGBT
    • Switching characteristics of IGBT
    • Gate Drive Circuit of an IGBT
    • IGBT ratings and safe operating area
    • Soft and Hard Switching & Losses of semiconductors
    • Conduction,Blocking & Switching Losses of Semiconductors
    • Diode as semiconductor device
    • Soft switching of diode

  • AC to DC Converters
    • Introduction to Rectifiers
    • Terminologies used in Single Phase Uncontrolled Rectifier
    • Single phase uncontrolled half wave rectifier with resistive Load - Circuit Diagram & Waveforms
    • Single phase uncontrolled half wave rectifier with inductive load- Circuit Diagram & Waveforms
    • Single phase uncontrolled half wave rectifier with capacitive Load - Circuit Diagram & Wave forms
    • Split supply Single Phase Uncontrolled Full wave rectifier supplying R-L Load - Circuit Diagram & Waveforms
    • Split supply Single phase uncontrolled full wave rectifier supplying a Capacitive Load- Circuit Diagram &Waveforms
    • Single phase uncontrolled full bridge rectifier supplying R-L-E Load - circuit diagram &Waveforms
    • Single phase uncontrolled full bridge rectifier supplying R-L-E Load -Input Current waveform
    • Continuous Conduction Mode and Discontinuous conduction mode
    • Single phase fully controlled halfwave rectifier with resistive Load -Circuit Diagram & Waveforms
    • Single phase fully controlled halfwave rectifier with R-L Load - circuit Diagram & waveforms
    • Single phase fully controlled bridge converter supplying an R-L-E load- Circuit Diagram & Conduction Table
    • Operation of single phase fully controlled bridge converter in the continuous conduction mode
    • Input current and its fundamental component of a fully controlled bridge rectifier
    • Operation of a single phase fully controlled bridge rectifier in DCM
    • Inverter Mode of operation in single phase fully controlled converter
    • Operating principle of a single phase half controlled bridge converter
    • Single phase half controlled converter in the continuous conduction mode
    • Variation of average output voltageas a functionof firing angle
    • Input current waveform of half controlled converters
    • Single phase half controlled converter in the discontinuous conduction mode
    • Introduction to Three Phase Uncontrolled rectifier
    • Operating principle of three phase half wave uncontrolled rectifier
    • Operation of a 3 phase full wave uncontrolled bridge rectifier supplying an RLE load Waveforms
    • Operation of a 3 phase full wave uncontrolled bridge rectifier supplying an RLE load Circuit diagram & conduction table
    • Operation of a three phase uncontrolled bridge rectifier supplying a capacitive load Circuit diagram & Waveforms
    • Introduction to Three Phase controlled bridge converter
    • Operating principle of 3 phase fully controlled bridge converter
    • Analysis of the 3 phase fully controlled bridge converter in the rectifier mode
    • Analysis of the 3 phase fully controlled bridge converter in the inverting mode
    • Higher pulse number converters
    • Dual converters
    • Gate Drive circuit for three phase fully controlled converter
    • Operating principle of three phase half controlled converter
    • Analysis of three phase half controlled converters
    • Operation of single phase fully controlled converter with source inductance- circuit diagram & waveforms
    • Three Phase Fully Controlled Converter With Source Inductance
    • Power Factor Improvement & Extinction Angle Control
    • Symmetrical Angle Control & Pulse Width Modulation Control
    • Sinusoidal Pulse Width Modulation (SPWM) Control
    • Filters
    • Low pass (L-C) filter & Two stage Filter
    • Harmonic Reductin,Low pass (L-C) filter circuit on ac side & Active Shaping of Input (line) Current

  • DC to DC Converters
    • DC-DC Converters
    • Buck Converters (dc-dc)
    • Boost Converters (dc-dc)
    • Buck-Boost Converters (dc-dc)
    • Control Strategies of DC-DC conversion
    • Two mode operation of chopper ( Buck Converter DC-DC)
    • Maximum and Minimum Values of the Load Current
    • The Duty Ratio (k) for the Limit of Continuous Conduction & The Average Value of the Output Current
    • Classification of forced commutation methods
    • Class A, Self commutated by resonating the load & Class B, Self commutated by an L-C circuit
    • Class C, C or L-C switched by another load–carrying SCR & Class D, L-C or C switched by an auxiliary SCR
    • Class E - External pulse source for commutation & Class F, AC line commutated
    • Rate of rise of forward voltage, dv/dt
    • Three phase phase angle converter & Commutation in PAC
    • Input voltage waveform distortion & Three-phase converters
    • Commutation in DC - DC choppers
    • Introduction to regulated dc power supplies
    • Linear regulated power supply
    • SMPS versus linear power supply
    • Types of Power Supplies
    • Power supply specifications & some common types of SMPS circuits
    • Basic Topology of Fly-Back Converter
    • Principle of Operation of fly back converter
    • Circuit Equations Under Continuous-Flux Operation
    • Circuit Equations Under Discontinuous-Flux Mode & comparison
    • A Practical Fly-Back Converter
    • Introduction to Forward Type Switched Mode Power Supply
    • Principle of Operation of Forward converters
    • Modes of Circuit Operation - Forward Type Switched Mode Power Supply
    • Relation Between Input and Output Voltage of FTSMPS
    • Practical Topology of A Forward Converter Circuit
    • Selection of Transformer Turns Ratio, Filter Circuit Inductor and Capacitor
    • Analysis of CuK converter
    • Expression for average output voltage and inductor currents
    • Current ripple and voltage ripple calculations
    • The SEPIC Converter
    • Introduction to transformers in switched mode
    • Governing Equations for Utility Transformer
    • Transformer with Square-Wave Voltage and Bipolar Flux
    • Transformer with Unipolar Flux
    • Design of Inductor-Transformer

  • AC to AC Voltage Converter
    • Operation of an AC-AC converter with resistive load
    • Power Factor of an AC-AC converter with resistive load
    • Operation of an AC-AC converter with inductive load
    • PAC as a static switch & AC Chopper
    • Three-phase, Three-wire AC Regulator with Balanced Resistive Load
    • Three-phase Delta-connected AC Regulator with Balanced Resistive Load
    • Comparison of the Different Circuits used for Three-phase AC Regulators
    • Rating of the Parameters used in Three-phase AC Regulators
    • Phase Angle Controller Circuit for Triac-based Single-phase AC Regulator
    • TRIAC as PAC
    • DIAC as PAC
    • Basic Principle of Operation of cyclo-converters
    • Single-phase to Single-phase Cyclo-converter Resistive (R) Load
    • Discontinuous load current of single phase to single phase cyclo converter Inductive Load
    • Continuous load current of single phase to single phase cyclo converter Inductive Load
    • Advantages & Disadvantages of Cyclo-converter
    • DC Link Converter
    • Three-phase to Single-phase Cyclo-converter
    • Mode of Operation of a Three phase to Single Phase Cycloconverter
    • Cyclo-converter, using two three-phase half-wave converters
    • Three-phase to Three-phase Cyclo-converter
    • Analysis of the Cyclo-converter Output Waveform
    • Control Circuit & Synchronising Circuit for Cyclo-converters
    • Reference Voltage Sources
    • Logic and Triggering Circuit
    • Circuit for Converter Group Selection

Branch : Electrical and Electronics Engineering
Subject : Power Electronics
Unit : DC to DC Converters

Circuit Equations Under Continuous-Flux Operation


Fly – Back circuit waveforms under continuous magnetic flux:

Fig: Fly-back circuit waveforms under continuous magnetic flux

  • Under the continuous magnetic flux conduction, ‘tON’ denotes the time for which the fly-back switch is ON during each switching cycle. ‘T’ stands for the time period of the switching cycle. The ratio ( tON /T) is known as the duty cycle (δ) of the switch.
  •  The primary winding current rises from I0 to IP in ‘δT’ time. In terms of input supply voltage (EDC) and the primary winding inductance ( Lpri) the following relation holds :

.

  • Under the steady state the energy input to primary winding during each ON duration equals:     0.5Edc (IP I0) δT
  • And similarly the output energy in each cycle equals       V0 ILoad T,    where V0 is the output voltage magnitude and ILoad denotes the load current.
  • Equating energy input and energy output of the converter (the converter was assumed loss-less) in each supply cycle, one gets:                                 0.5Edc (IP I0) δ = V0 ILOAD
  • The mean (dc) voltage across both primary and secondary windings must be zero under every steady state. When the switch is ON, the primary winding voltage equals input supply voltage and when the switch is OFF the reflected secondary voltage appears across the primary winding. Under the assumption of ideal switch and diode,                                              Edc δ = (N1 / N2) V0 (1-δ)
  • Where, N1 and N2 are the number of turns in primary and secondary windings and (N1/N2)V0 is the reflected secondary voltage across the primary winding (dotted end of the windings at lower potential)
  • During mode-2 of circuit operation. One needs to know the required ratings for the switch and the diode used in the converter. When the switch is OFF, it has to block a voltage (Vswitch) that equals to the sum of input voltage and the reflected secondary voltage during mode-2.
  •  Thus,  Vswitch = Edc (N1 / N2) V0.    When the switch in ON, the diode has to block a voltage (Vdiode) that equals to the sum of output voltage and reflected primary voltage during mode-1, i.e.  Vdiode = V0 Edc (N2 / N1).
  • Since the intended switching frequency for SMPS circuits is generally in the range of 100kHz, the switch and the diode used in the fly-back circuit must be capable of operating at high frequency. The switch and the transformer primary winding must be rated to carry a repetitive peak current equal to IP.
  • Similarly the secondary winding and the diode put in the secondary circuit must be rated to carry a repetitive peak current equal to the maximum expected load current. The magnetic core of the high frequency inductor-transformer must be chosen properly such that the core does not saturate even when the primary winding carries the maximum expected current.
  •  Also, the transformer core (made of ferrite material) must have low hysteresis loss even at high frequency operation. Since the ferrite cores have very low conductivity, the eddy current related loss in the core is generally insignificant.

Questions of this topic


  • Explain the Fly-back circuit waveforms under continuous flux operation.

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  • What is the duty cycle of the switch of a fly back converter?

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