AC-DC|Design
Design Procedure
2019.08.07
Points of this article
・The design procedure, in broad outline, is as follows.
1. Design of the synchronous rectifying circuit part:
Selection of MOSFETs for synchronous rectification, Controller IC selection, Selection of peripheral components
2. Design of the shunt regulator circuit part
3. Troubleshooting
4. Characteristic evaluation
In ” Design of a Secondary-Side Synchronous Rectifying Circuit to Improve the Efficiency of an AC-DC Converter”, an example of the synchronous rectification design of an AC-DC converter with diode rectification using the BM1R001xxF series of secondary-side synchronous rectifying controller ICs will be explained. We begin by describing the design procedure.
Design Procedure
An example of synchronous rectification design of an AC-DC converter with diode rectification using a BM1R001xxF series secondary-side synchronous rectifying controller IC is presented.
The essence of this design is replacement of the rectifying diodes and shunt regulator on the secondary side of the AC-DC converter with the BM1R001xxF series secondary-side synchronous rectifying controller IC, to improve the efficiency of the AC-DC converter. The design process generally follows the procedure outlined below.
- 1.Design of the synchronous rectifying circuit part
1-1. Selection of MOSFETs for synchronous rectification
1-2. Controller IC selection
1-3. Selection of peripheral components - 2.Design of the shunt regulator circuit part
- 3.Troubleshooting
- 4.Characteristic evaluation
The circuit designs in 1 and 2 are summarized. Primary-side design is not included in this design example.
1. Summary of design of the synchronous rectification circuit part
1-1. Selection of MOSFETs for synchronous rectification
- ・Initially, the MOSFETs used for synchronous rectification, which replace the rectifying diodes, are selected.
- ・Using as criteria the reverse voltage VR and forward current IF of the rectifying diodes, the maximum drain-source voltage, peak current, losses due to Ron, maximum allowable dissipation of the package, and other factors are considered to select the MOSFETs used for replacement.
- ・As matters to be checked, operation is always confirmed in a state in which it is incorporated into the product, and heat sinks and other heat dissipation methods are also studied as necessary.
1-2. Controller IC selection
- ・The BM1R001xxF series adopts compulsion OFF time control to enable use with various power sources.
- ・Using the previously verified reverse voltage VR and forward current IF occurring in the rectifying diodes and by calculating the maximum ON-time tMAX_ON of the secondary-side MOSFET, corresponding ICs are selected.
- ・The BM1R001xxF series can be used with synchronous rectifying MOSFETs on either the low side or the high side, and so both circuits are considered.
1-3. Selection of peripheral components
- ・In order to prevent erroneous detection due to the surge voltage occurring at the time of MOSFET switching, a component to use as a countermeasure at the drain pin is selected.
- ・Settings for the feed circuit to the IC power supply pin VCC
2. Summary of design of the shunt regulator circuit part
- ・The BM1R001xxF series incorporates a low-power, high-precision shunt regulator, to reduce the shunt regulator-related power consumption.
- ・The shunt regulator is completely separated from the synchronous rectifying controller within the IC, so that even in high side-type flyback applications, the possibility of GND reference use of the shunt regulator is considered.
- ・It is also possible not to use the shunt regulator within the IC, and the circuit resulting in this case is examined.
The next article will describe the design example and explain the BM1R001xxF series product used in the design.
List of articles related to the「Design Procedure」
- Introduction
- 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
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components-C1, R3 at MAX_TON Pin, and VCC Pin
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components-D1, R1, R2 at DRAIN Pin
- Shunt Regulator Circuit Section: Selection of Peripheral Circuit Components
- Troubleshooting ①: Case When Secondary-Side MOSFET Suddenly Turns OFF
- 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
Download Technical Documents
Basic of AC-DC Conversion
Basic studies to understand AC-DC converters and to go designing.
AC-DC
- Basic
-
Design
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Overview of Design Method of PWM AC-DC Flyback Converters
- Want are Isolated Flyhback Convertors?
- Isolated Flyback Converter Basics: What is Switching AC-DC Conversion?
- Isolated Flyback Converter Basics: What are Characteristics of Flyback Converter?
- Isolated Flyback Converter Basics: Flyback Converter Operation and Snubber
- Isolated Flyback Converter Basics: What are Discontinuous Mode and Continuous Mode?
- Design Procedure
- Determining Power Supply Specifications
- Choosing an IC for Design
- Designing Isolated Flyback Converter Circuits
- Designing Isolated Flyback Converter Circuits: Transformer Design (Calculating numerical values)
- 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
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components-C1, R3 at MAX_TON Pin, and VCC Pin
- Synchronous Rectification Circuit Section: Selection of Peripheral Circuit Components-D1, R1, R2 at DRAIN Pin
- Shunt Regulator Circuit Section: Selection of Peripheral Circuit Components
- Troubleshooting ①: Case When Secondary-Side MOSFET Suddenly Turns OFF
- 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
-
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
-
Overview of Design Method of PWM AC-DC Flyback Converters
- Evaluation
- Product Information
- FAQ