AC-DC｜Evaluation
Summary
2017.07.06
In this series, with the title of “Evaluation Series: Isolated Flyback Converters Performance Evaluation and Check Points” for AC-DC converters, we have explained measurement methods and actual measurement data for evaluation of the performance of isolated flyback AC-DC converter circuits, and have also described important check points for confirming whether a device is operating normally as well as for evaluating performance aspects.
Where performance evaluation is concerned, it is important that the features and characteristics of the power supply IC be fully understood in order to configure a circuit to be evaluated. As we have mentioned a number of times before, in recent power supply designs, generally a power supply IC is used, and consequently design is not possible without an understanding of the power supply IC. Moreover, in essence the datasheet for the power supply IC is used in design, and the characteristics and performance are checked to confirm that they are as expected; the importance of this process was probably well understood. It was also noted that, as a reference for evaluations, use of an evaluation board provided by the power IC manufacturer is extremely effective.
Where actual evaluations are concerned, we have explained check points and measurement methods to determine whether or not a designed circuit is operating normally. As the procedure to be used, characteristic graphs presented in the datasheet for the power supply IC and evaluation board characteristics are compared with the characteristics of the circuit you have designed yourself; but if operating margins and potential issues are not examined, mass production and shipment are not possible. The check points and judgment criteria are precisely the knowhow needed for power supply design. It is important that latent problems be discovered promptly and without error on the basis of in-house legacy technical information, personal experience and past results, and that reliable design and manufacturing be executed.
Of course, in order to make such knowhow one’s own, one must above all repeat the cycle of design and evaluation. In particular, AC-DC converters handle high voltages, and so with respect to measurements, the knowledge and experience to ensure safety are above all important.
The following is a summary of the topics and key points explained in this series. Please have a look at them once again.
＜Isolated Flyback Converters Performance Evaluation and Check Points＞
- Overview and important features of a power supply IC used in example performance evaluation
Key Points
・Evaluating performance involves a verification as to whether given design goals are successfully attained.
In other words, an evaluation is possible only if clearly defined design goals are established.・An evaluation is possible only if the datasheet for a power supply IC is well understood.
- Design goald and circuits in performance evaluation
Key Points
・In the actual design process, evaluate the created PCB to confirm whether the design goals are satisfied.
- Critical check point: Measurement method and results
Key Points
・With basic instruments, power parameters can be measured with relative ease.
・The measurement process involves the handling of high voltages. Learn the steps necessary to ensure safety, and work in strict adherence to the safety precautions.
- Critical check point: MOSFET VDS and IDS, and rated voltage of output rectifier diode
Key Points
・Check whether the MOSFET VDS and IDS values are within the rated values, and whether there are abnormal spikes or ringing.
・The reverse voltage Vr applied to a rectifier diode is checked to ensure it is within the rated voltage for the device, and the waveform is also checked.
・Comparison with an evaluation board supplied by the manufacturer is a practical and useful way to evaluate one’s own circuit.
- Critical check point: Transformer saturation
Key Points
・A transformer must not be allowed to reach saturation.
・Use an oscilloscope, current probe, etc. to observe the primary-side current waveform.
・If a transformer reaches saturation, an excessive current flows, possibly causing destruction of a MOSFET or other device.
- Critical check point: Vcc voltage
Key Points
・The Vcc voltage should be checked to confirm an appropriate range given fluctuations in the input and load.
・The Vcc voltage should be checked to confirm an appropriate range given fluctuations in the input and load.
・Understand the operation of Vcc generation circuits using third windings, diodes and capacitors.
- Critical check point: Output transient response and rising output voltage waveform
Key Points
・The load transient response of the output is optimized by adjusting the phase compensation circuit of the feedback circuit.
・The same is true of optimization of the output rising waveform.
・These evaluations and adjustments are mutually related, and so constitute a series of tasks.
- Critical check point: Measuring temperature and loss
Key Points
・Confirming that the junction temperature (Tj) of a device (chip) is within the absolute rated value is essential, for safe operation as well as to ensure reliability.
・Temperatures are determined by actual measurements and utilizing the concept of thermal resistance.
・Losses are determined by observing switching waveforms and using equations.
・Allowed losses are determined by consulting a graph on the datasheet, but ultimately are based on the value of Tj.
- Critical check point: Alminum electrolytic capacitors
Key Points
・Aluminum electrolytic capacitors should be selected with particular attention paid to the lifetime.
・The lifetime of an aluminum electrolytic capacitor is shortened dramatically at higher temperatures; in general, the “10-degree rule” for halving of the lifetime applies.
・Capacitance loss due to degradation is highly likely to cause malfunctions in circuit operation.
With this, we conclude the “AC-DC Evaluation Series: Performance Evaluation and Check Points for Isolated Flyback Converters”.
【Download Documents】 Isolated Flyback Converters: Performance Evaluation and Checkpoints
This handbook explains how to evaluate the performance of isolated flyback type AC-DC converters using power supply ICs, with examples of actual measurement data. Important checkpoints are also explained.
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
-
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
-
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
-
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
-
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