Boost Converter Inrush Current Control via PWM Dynamics
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Solution Overview
Problem
Conventional boost converters experience high inrush currents during start-up, leading to increased inductor sizes and manufacturing costs, as well as larger printed circuit boards (PCBs), due to the need for higher saturation currents and additional components like off-chip capacitors to manage these currents.
Innovation Solution
A system incorporating a start-up controller and pulse width modulation (PWM) circuit that generates a PWM signal with a fixed on-time and dynamic off-time, based on comparisons between the inductor current and a reference current, to control the inductor current during start-up, reducing peak inrush currents without the need for off-chip capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the saturation current of the inductor is increased to handle inrush current, then the inductor can withstand higher currents, but the size and manufacturing cost of the inductor and boost converter increase
Solution Approach 1:
The system performs preliminary action by detecting the start-up condition before the inrush current fully develops, and activates a controlled current ramping sequence through the PWM controller. This gradual current increase prevents the sudden inrush that would otherwise require oversized inductors, while still ensuring reliable current handling capability during normal operation
Solution Approach 2:
The system implements dynamic current control during start-up by varying the PWM duty cycle over time. The PWM controller dynamically adjusts the inductor current from zero to the target operating current through controlled switching cycles, transforming the static inrush current problem into a dynamic, controllable process that eliminates the need for oversized components
2Object-generated harmful factors
If off-chip capacitors are added to reduce inrush current, then the inrush current is controlled, but the system size and manufacturing cost increase
Solution Approach 1:
The system extracts and eliminates the need for external off-chip capacitors by integrating the inrush current control functionality directly into the PWM controller chip. The controller internally generates the necessary control signals and implements current limiting algorithms, removing the requirement for additional discrete components while maintaining effective inrush current suppression
Solution Approach 2:
The PWM controller serves multiple functions simultaneously: it performs standard PWM modulation for converter operation, implements start-up detection, controls current ramping, and limits inrush current. This multi-functionality consolidates what would otherwise require separate components into a single integrated controller, reducing overall system complexity
3Productivity
If the inductor charging rate is high during start-up, then the converter starts up quickly, but magnetic charge builds up causing significant inductor current increase
Solution Approach 1:
The system employs periodic action by using pulsed current ramping during start-up. The PWM controller applies a series of controlled switching cycles that gradually build inductor current in discrete steps rather than continuous charging. This periodic current application achieves quick start-up while preventing excessive magnetic charge accumulation that would cause harmful inrush current
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution maintains a constant peak inductor current during start-up, reducing the saturation current and size of the inductor, and subsequently the size and cost of the boost converter and PCB, while optimizing switch and metallization design, and eliminating the need for off-chip capacitors, resulting in a more efficient and cost-effective design.
Implementation Method 1
A start-up controller and pulse width modulation (PWM) circuit generate a PWM signal with a fixed on-time and dynamic off-time
Implementation Method 2
A boost converter is a direct current (DC) to DC converter that converts a DC input voltage to a DC output voltage... The DC output voltage is generated based on an inductor current of an inductor of the boost converter
Data Source
AI summary
A system for controlling an inductor current of a boost converter includes a start-up controller that is configured to generate a control signal that has a fixed on-time duration and a dynamic off-time duration that decreases with each cycle of the control signal, and a pulse width modulation (PWM) circuit that is configured to generate a PWM signal. During a start-up of the boost converter, the PWM signal transitions from a deactivated state to an activated state when the control signal is activated, and from an activated state to a deactivated state when the inductor current is equal to a reference current. The reference current corresponds to a peak value of the inductor current during the start-up. Thus, during the start-up, the duty cycle of the PWM signal increases with each cycle of the PWM signal. The PWM signal is provided to the boost converter for controlling the inductor current.