AC-DC|Design
Selecting Critical Components: Inductor L1
2017.11.09
Points of this article
・The inductor should be set such that the operating mode is discontinuous mode.
・The inductance is determined from the VIN minimum condition and the maximum value of ton.
・The inductor current is determined from the VIN maximum condition and the minimum on-time.
table of contents
In this second section on “Selecting Critical Components”, we explain methods for selecting inductors, which play a vital role in switching power supplies.
Inductor L1
The inductor L1, together with the output capacitor C5, forms an LC filter, as indicated in the circuit diagram on the right. The inductance L1 is set so that the operating mode is a discontinuous mode. If the device is operated in a continuous mode, the reverse current that flows during the reverse recovery time trr of the diode causes diode losses to increase, and moreover the reverse current may reach the peak current while the MOSFET is ON, thus also increasing MOSFET losses. In order to avoid these increased losses, discontinuous mode is selected. For details please refer to the section “Basic Operation of Buck Converters and Discontinuous Mode vs. Continuous Mode”.
Inductance Calculation
First, we calculate the inductance. We use 101 V for VIN. That is, we assume 90 VAC and use 1.41 times this value as the peak voltage, and add a 20% margin.
If VIN = 90VAC×1.41×0.8 = 101V, then:
We add a 20% margin for Iomax, so that Iomax = 0.2 A×1.2 = 0.24 A.
If the critical point (peak) is Ip = Iomax×2 = 0.48 A, then:
From this calculation result, we select 470 μH as the standard value.
Calculation of Inductor Current
Next, we calculate the inductor current, and determine the allowable current in the inductor.
The inductor current is maximum when the input voltage is maximum. The maximum input voltage is 264 VAC, and under this condition, the time during which the power supply IC turns the switch (MOSFET) on is the minimum on-time of the IC. This minimum on-time is approximately 0.6 to 1.5 μs, depending on the output voltage, the inductance of the inductor, and other parameters.
Taking 1 μs to be the minimum on-time when the maximum input voltage is 264 VAC:
Hence the inductor that should be selected has an inductance of 470 μH and an inductor current of 0.8 A or greater. It should be remembered that the inductor current must always be checked in actual equipment, to confirm that the inductor does not reach saturation.
【Download Documents】Methods of Designing Non-isolated PWM Flyback Converter
Explanations how to design a non-isolated buck converter using an AC-DC converter IC, as a next trial.
List of articles related to the「Selecting Critical Components: Inductor L1」
- 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: Current Sense Resistor R1
- Selecting Critical Components: Output Capacitor C5
- Selecting Critical Components: Output Rectifying Diode D4
- EMI Countermeasures
- Board Layout and 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
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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
-
Overview of Design Method of PWM AC-DC Flyback Converters
- Evaluation
- Product Information
- FAQ