SMPS Soft-Start Control Circuit for In-Rush Current Management
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Solution Overview
Problem
Switched-mode power supply (SMPS) systems face challenges during start-up due to high in-rush current, which can cause voltage and current spikes, leading to potential power supply reset or failure, and require effective control to manage overvoltage and overcurrent conditions.
Innovation Solution
A method for starting up SMPS systems by determining the rate of increase of a pulse width modulated (PWM) signal based on input voltage and switching frequency, using a digital controller with a PID controller and DPWM to increment the duty cycle, transitioning from open loop to closed loop PWM mode, and handling fault conditions like overcurrent by adjusting the duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the power supply is turned on with high value output capacitors, then the output voltage can be maintained, but high voltage and current spikes occur during first turn-on
Solution Approach 1:
The patent applies preliminary action by implementing a soft-start mechanism that gradually increases the duty cycle from zero to its target value during power-up. This controlled ramping of the duty cycle prevents sudden in-rush current and voltage spikes that would otherwise occur when high value output capacitors are first charged, thereby resolving the contradiction between maintaining output voltage capability and avoiding harmful spikes.
2Productivity
If a large current is drawn from the input voltage during start-up, then the power supply can initialize quickly, but the input voltage drops significantly causing reset or failure to start
Solution Approach 1:
The patent applies dynamics by making the duty cycle dynamic during start-up rather than fixed. The duty cycle is continuously adjusted based on feedback from the output voltage and current sensing, allowing the system to optimize between fast start-up and input voltage stability. This dynamic control enables the power supply to initialize quickly while preventing harmful voltage drops that would cause reset or failure.
3Speed
If the duty cycle increases rapidly during start-up, then the power supply reaches operating voltage faster, but overcurrent conditions occur
Solution Approach 1:
The patent applies feedback by continuously monitoring the output current and voltage during start-up and using this information to adjust the duty cycle rate of increase. The feedback mechanism detects overcurrent conditions and automatically reduces the duty cycle ramp rate, preventing harmful overcurrent while still achieving relatively fast voltage rise. This closed-loop control resolves the contradiction between speed of voltage establishment and prevention of overcurrent.
Data Source
AI summary
A method of operating a switched-mode power supply (SMPS) includes starting up the switched-mode power supply by determining a rate of increase of a duty cycle of a pulse width modulated (PWM) signal based on an input voltage and a switching frequency of the SMPS; and generating the PWM signal having the duty cycle in accordance with the determined rate of increase.