AC-DC|Design
Power Supply Specifications and Replacement Circuit
2019.10.23
Points of this article
・In this design example, a diode-rectification AC-DC converter is modified for synchronous rectification.
・There are low-side and high-side types of modification for synchronous rectification.
・There is a slight increase in the number of external components, but efficiency improvement, and in particular high efficiency when in standby, is a goal of AC-DC converters, and so synchronous rectification is advantageous.
In the previous article, the BM1R001xxF series IC that will be used in the design was summarized. From this article we embark on the actual design process.
To reiterate, the purpose of this design is to use the BM1R001xxF series of secondary-side synchronous rectifying controller ICs to perform synchronous rectification in an AC-DC converter that uses diode rectification. Hence we start with the circuit and specifications of a diode-rectification AC-DC converter, and assume that these specs are inherited when modifying the design for synchronous rectification.
Example of Power Supply Specifications and Replacement Circuit
In this example, the rectifying diode and the shunt regulator section in the secondary-side diode rectification circuit of the AC-DC converter below are replaced with a BM1R001xxF series IC.
<AC-DC Converter Power Supply Specifications>
- ・Input voltage(VIN): 400 Vdc
- ・Output voltage(VOUT): 5 V
- ・Output current(IOUT): 10 A
- ・Power supply type: Isolated PWM flyback converter
- ・Switching frequency: 130 kHz
The circuit diagram for the AC-DC converter is shown below.
The area highlighted in orange is the part to be replaced; here DOUT is the rectifying diode, and U1 and the resistors are the shunt regulator section. PC1 is an opto-coupler (photocoupler), an isolating element to feed back the output voltage to the primary side with isolation. It is not replaced, since it is also necessary even in the circuit with the BM1R001xxF series IC substituted.
Next, we present the substituted circuit. The shaded areas indicate substituted circuit sections.
There are two substitution methods. On the left is the low-side type of substitution in which the switch (MOSFET) is positioned on the low side (GND line) of the transformer; on the right is the high-side type, in which the switch (MOSFET) is located on the high side (VOUT line) of the transformer. Both types will be explained, and ultimately the designs of both types of circuits will be completed and evaluated.
In the above circuits, rectifying diodes are replaced with MOSFETs, and shunt regulators are replaced with the shunt regulator within an IC. However, it must be said that there is a slight increase in the number of external components. Hence when using general secondary-side synchronous rectifying ICs, the standby power consumption is always worsened by the amount of the IC circuit current. However, these ICs incorporate shunt regulators that reduce the IC current consumption, so that efficiency can be greatly improved without worsening standby power consumption, and in addition the components of the shunt regulator section can be eliminated.
List of articles related to the「Power Supply Specifications and Replacement Circuit」
- Introduction
- Design Procedure
- IC Used in Design
- 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
-
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