AC-to-DC Converter Inrush Current Control via Microcontroller Pre-Charging
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Solution Overview
Problem
Existing power supplies face issues with large inrush currents during startup, which can cause component strain, shorten lifespan, trigger circuit breakers, and generate EMI/EMC noise, and current control methods using NTC components or relays are costly and inefficient.
Innovation Solution
A Power Factor Corrected AC-to-DC converter circuit that employs a microcontroller to determine AC supply voltage periodicity and magnitude, using pre-calculated switch turn-on times to control charging pulses into a storage capacitor, minimizing inrush current while efficiently charging it to the desired voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If NTC component is used to limit inrush current, then inrush current is reduced, but power loss increases and efficiency decreases
Solution Approach 1:
The patent applies preliminary action by pre-charging the storage capacitor through controlled current pulses before full power operation begins. The microcontroller initiates a pre-charge sequence that gradually charges the capacitor using current limiting resistors and controlled switching, preventing the need for continuous NTC resistance and eliminating ongoing power losses.
Solution Approach 2:
The patent uses periodic action by implementing a time-delayed switching technique where power switches are turned on and off in cycles to allow controlled charging current to flow into the storage capacitor. This periodic switching continues until the capacitor reaches its target voltage, replacing the continuous current limiting approach with intermittent controlled charging.
2Loss of energy
If relay is used to short current around NTC component, then power loss is reduced, but cost increases and reliability decreases
Solution Approach 1:
The patent replaces the mechanical relay system with an electronic control system using a microcontroller and solid-state power switches. This substitution eliminates the mechanical contacts that degrade over time, improving reliability while maintaining the ability to redirect current away from the NTC component during steady-state operation through software-controlled switching.
Solution Approach 2:
The system implements self-service by using the microcontroller to automatically manage the pre-charge sequence and switching operations without requiring external mechanical components. The microcontroller monitors capacitor voltage and autonomously controls the power switches to complete the pre-charge process and transition to normal operation.
3Object-affected harmful factors
If powerful microcontroller is used for time-delayed switching, then inrush current control is effective, but cost increases
Solution Approach 1:
The patent applies partial action by implementing only the essential functions needed for inrush current control using a simple microcontroller. Rather than requiring a powerful microcontroller with extensive processing capabilities, the system uses basic timing and voltage monitoring functions that can be performed by a low-cost, simple microcontroller, reducing overall system cost while maintaining effective inrush current control.
4Object-affected harmful factors
If multiple power devices are used for inrush current control, then inrush current is limited, but device complexity and cost increase
Solution Approach 1:
The patent merges multiple functions into a single integrated control approach. The microcontroller consolidates the timing, voltage monitoring, and switching control functions that would otherwise require multiple separate components. The power switches are controlled through a unified software routine that manages the entire pre-charge sequence, reducing circuit complexity while maintaining effective inrush current control.
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 method effectively reduces inrush currents, prolongs component lifespan, minimizes EMI/EMC noise, and reduces costs by using a less expensive microcontroller, while ensuring efficient charging and stable operation.
Implementation Method 1
Many schemes involve the use of an NTC (Negative Temperature Coefficient) component in the inrush current path to limit inrush current. When the power supply initially powers up, the NTC component is not hot, so its resistance is higher.
Implementation Method 2
after a period of current flow through the NTC component, the NTC component has heated up and its resistance has decreased
Data Source
AI summary
An AC-to-DC converter involves a rectifier, an inductor, a storage capacitor, a switch, and a microcontroller. In a capacitor pre-charge operation, the periodicity and voltage amplitude of an AC supply voltage are determined. Based on this, the microcontroller identifies one of a plurality of stored sequences. Each sequence is a list of values. The microcontroller turns off the switch on AC supply voltage zero crossings and turns on the switch in accordance with the values. As a result, a sequence of identical pulses of charging current flows into the storage capacitor. Each pulse passes in a current path from the rectifier, through the inductor, through the capacitor, through the switch, and back to the rectifier. During the pre-charge operation, the microcontroller does not measure the capacitor voltage and use that to calculate when to the turn the switch on next, but rather the sequence of precalculated stored values is used.