SMPS Startup Duty-Cycle Control for Low Inrush Current
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Solution Overview
Problem
Switching-mode power supplies (SMPS) in battery-powered devices experience high peak inrush currents during startup, leading to voltage sags that can trigger power-on resets and slow startup times, which are exacerbated by increasing system complexity.
Innovation Solution
A method and apparatus for SMPS startup that controls inrush current and startup time through multiple stages, including a buck stage with passive charging, constant-current charging, and a boost stage with forced input pulse-width modulation to maintain charging speed while limiting inrush current, followed by a closed-loop regulation stage for smooth transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If SMPS uses traditional startup method, then startup speed is fast, but inrush current becomes excessively high causing voltage sags
Solution Approach 1:
The startup process is divided into three distinct stages: initial startup stage with slow ramp-up of PWM duty cycle to limit inrush current, intermediate stage with continued controlled ramping, and final stage with full PWM operation for fast charging. This segmentation allows the system to achieve both low inrush current during startup and fast charging once initialized.
Solution Approach 2:
Before full power operation is initiated, the PWM duty cycle is preliminarily set to a low value and gradually increased. This preliminary action prepares the system by limiting inrush current initially, then progressively enabling full power capability once the startup phase is complete.
2Reliability
If inrush current is limited during startup, then voltage stability is improved, but startup time increases
Solution Approach 1:
The PWM duty cycle is dynamically adjusted during startup based on the charging stage. The system transitions from slow ramp-up in the initial stage to faster charging in the intermediate and final stages. This dynamic adjustment maintains voltage stability during the critical startup phase while minimizing the overall startup time by accelerating charging once stability is established.
Solution Approach 2:
The startup process uses periodic PWM pulses with varying duty cycles across different stages. The duty cycle is periodically increased from a low initial value through intermediate values to full operation, creating a structured temporal pattern that balances voltage stability with acceptable startup time.
3Adaptability or versatility
If system complexity increases with more integrated functions, then device functionality is improved, but startup time control becomes more difficult
Solution Approach 1:
The power supply system is segmented into distinct operational stages (initial startup, intermediate, and final charging stages), each with specific PWM duty cycle control strategies. This segmentation allows complex multi-function devices to maintain controlled startup behavior regardless of the number of integrated functions, as each stage handles specific aspects of the startup process independently.
Data Source
AI summary
An apparatus includes a circuitry to perform a first startup stage and to vary, during a second startup stage subsequent to the first startup stage, a duty cycle of a pulse controlling one or more switches of the circuitry.