AC-DC｜Design
Isolated Flyback Converter Basics: What are Characteristics of Flyback Converter?
2016.01.13
Points of this article
・The flyback converter should be used as appropriate based upon a solid understanding of its characteristics.
In this design example, we use a conversion method called “flyback”. The flyback is based on the following basic circuit with characteristics described below:
There are three types of flyback converters: In addition to the commonly available PWM control type, self-exciting Ringing Choke Converter (RCC), and quasi-resonant type applying resonance technology to the RCC. These converters are widely used in switching power supplies up to 100W.
The basic circuit is a simple one, as illustrated in the figure, composed of a relatively few components. The circuit chops the input voltage (DC) by using a switching transistor and transmits the energy to the secondary side via a switching transformer. The secondary side rectifies and smooths the output and converts it to a required DC voltage. The actual circuit is provided with additional feedback and control circuits that monitor the output and control the switching transistor.
Flyback converters can be configured for both step-down and step-up operations, capable of accommodating both isolation and non-isolation applications. While offering the advantage of accommodating a broad input voltage range, on the deficit side the converter, in which relatively large peak currents flow to the switching element, diode, and output capacitor, requires components capable of controlling such current flows.
For isolation configuration, the feedback from the secondary side, that is, from the output, is isolated by means of an optocoupler or a tertiary winding. Some control ICs can provide regulation without feedback from the output. The characteristics of the flyback converter may be summarized as follows:
Characteristics of the flyback converter
- Amenable to step-down and step-up configurations
- Capable of accommodating isolated and non-isolated configurations
- Simplicity of configuration with a minimum number of components
- Suitable for switching power supplies up to 100W
- Accommodating a wide input range
- Compared with the forward type, requires a large capacitor
- In situations not requiring a great deal of output precision, an approximate output voltage can be set in terms of a transformer winding ratio for use as an unregulated output power supply unit.
【Download Documents】 Design Example for PWM Flyback Converter
ROHM’s seminar materials provided at the seminar venue. Explanation how to design a flyback converter using a power supply IC.
AC-DC
Basic
- AC-DC Basics
- DC-DC Conversion (Regulated) System after Smoothing
- Design Procedure for AC-DC Conversion Circuits (Overview)
- Issues and considerations in AC-DC Conversion Circuit Design
- Summary
- Extra Plus Basic Knowledge
Design
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Overview of Design Method of PWM AC-DC Flyback Converters
- Isolated Flyback Converter Basics: Flyback Converter Operation and Snubber
- Isolated Flyback Converter Basics: What are Discontinuous Mode and Continuous Mode?
- Want are Isolated Flyhback Convertors?
- Design Procedure
- Isolated Flyback Converter Basics: What is Switching AC-DC Conversion?
- Determining Power Supply Specifications
- Designing Isolated Flyback Converter Circuits
- Isolated Flyback Converter Basics: What are Characteristics of Flyback Converter?
- Designing Isolated Flyback Converter Circuits: Transformer Design (Calculating numerical values)
- Choosing an IC for Design
- Designing Isolated Flyback Converter Circuits: Transformer Design (Structural Design) – 1
- Designing Isolated Flyback Converter Circuits: Transformer Design (Structural Design) – 2
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components ? MOSFET related – 1
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components ? MOSFET related – 2
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components ? CIN and Snubber
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components ? Output Rectifier and Cout
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components ? VCC of IC
- Designing Isolated Flyback Converter Circuits: Selecting Critical Components – IC Settings Etc.
- Designing Isolated Flyback Converter Circuits: Addressing EMI and Output Noise
- Example Board Layout
- Summary
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Overview of Design Examples of AC-DC Non-isolated Buck Converters
- What are Buck Converters? – Basic Operation and Discontinuous Mode vs. Continuous Mode
- Selection of Power Supply ICs and Design Examples
- Selecting Critical Components: Input Capacitor C1 and VCC Capacitor C2
- Selecting Critical Components: Inductor L1
- Selecting Critical Components: Current Sense Resistor R1
- Selecting Critical Components: Output Capacitor C5
- Selecting Critical Components: Output Rectifying Diode D4
- EMI Countermeasures
- Board Layout and Summary
-
Introduction
- Design Procedure
- IC Used in Design
- Power Supply Specifications and Replacement Circuit
- Synchronous Rectifying Circuit Section: Selection of Synchronous Rectifying MOSFET
- Synchronous Rectification Circuit Section: Power Supply IC Selection
- Troubleshooting ①： Case When Secondary-Side MOSFET Suddenly Turns OFF
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components－C1, R3 at MAX_TON Pin, and VCC Pin
- Troubleshooting ②： Case When Secondary-Side MOSFET Turns On Due to Resonance Under Light Loading
- Troubleshooting ③： Case When, Due to Surge, VDS2 Rises to Above Secondary-Side MOSFET VDS Voltage
- Comparison of Efficiency of Diode Rectification and Synchronous Rectification
- Points to Note Relating to PCB Layout
- Summary
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components－D1, R1, R2 at DRAIN Pin
- Shunt Regulator Circuit Section: Selection of Peripheral Circuit Components
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Introduction
- Power Supply ICs Used in Design: Optimized for SiC MOSFETs
- Design Example Circuit
- Transformer T1 Design – 1
- Transformer T1 Design – 2
- Selecting Critical Components: MOSFET Q1
- Selecting Critical Components: Input Capacitor and Balancing Resistor
- Selecting Critical Components: Switch Setting Resistors for Overload Protection Points
- Selecting Critical Components: VCC-Related Components of Power Supply ICs
- Selecting Critical Components: Components Related to Power Supply IC BO (Brownout) Pins
- Selecting Critical Components: Components Related to Snubber Circuits
- Selecting Critical Components: MOSFET Gate Drive Adjustment Circuit
- Selecting Critical Components: Output Rectifying Diode
- Selecting Critical Components: Output Capacitors, Output Setting and Control Components
- Selecting Critical Components: Current Sense Resistors and Components Related to Detection Pins
- Selecting Critical Components： Components for Dealing with EMI and Output Noise
- PCB Layout Example
- Example Circuit and Component List
- Evaluation Results: Efficiency and Switching Waveform
- Summary
Evaluation
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What are Isolated Flyback Converters Performance Evaluation and Checkpoints?
- Overview and important features of a power supply IC used in example performance evaluation
- Design goals and circuits in performance evaluation
- Performance evaluation using an evaluation board: Measurement method and results
- Critical checkpoint: Output transient response and rising output voltage waveform
- Critical checkpoint: Measuring temperature and loss
- Critical checkpoint: Aluminum electrolytic capacitors
- Summary
- Critical checkpoint: Transformer saturation
- Critical checkpoint: MOSFET VDS and IDS, and rated voltage of output rectifier diode
- Critical checkpoint: Vcc voltage
Product Information
FAQ