AC-DC Converter Inrush Current Suppression via Voltage Comparison
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Solution Overview
Problem
Existing AC-DC converters with inrush current suppressing circuits rely on a set value for short-circuiting the inrush current resistor, which limits flexibility and may allow inrush current when the input AC voltage is not lower than the set value, particularly near peak AC voltage levels, restricting the degree of freedom in selecting the set value.
Innovation Solution
An AC-DC converter with an inrush current suppressing circuit that includes an inrush current suppressing resistor and a resistance short-circuiting switch, controlled by a circuit that turns off the switch when the absolute value of the input AC voltage is higher than the output DC voltage, ensuring secure suppression of inrush current through a comparison between input and output voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the set value for short-circuiting the inrush current resistor is increased to securely prevent inrush current, then inrush current suppression reliability is improved, but the degree of freedom in selecting the set value is reduced and conduction loss increases
Solution Approach 1:
The patent applies dynamics by making the inrush current suppression circuit configuration changeable based on operating conditions. The control circuit dynamically selects between two different set values (first set value and second set value) depending on whether the converter is in an abnormal state (inrush current risk) or normal operating state, allowing optimal performance in each condition without compromising the other
Solution Approach 2:
The patent changes the resistance value parameter of the inrush current suppression circuit based on operating conditions. By switching between a first resistance value (higher, for better suppression) and a second resistance value (lower, for reduced loss), the system adapts the parameter to match the current operational state, resolving the contradiction between suppression reliability and conduction loss
2Reliability
If the set value is set higher than the peak value of rated maximum input AC voltage to securely prevent inrush current, then inrush current suppression is improved, but the degree of freedom in selecting the set value is considerably limited
Solution Approach 1:
The system dynamically adjusts the set value based on the detected input AC voltage level. When the input voltage is low (abnormal state), the first set value is used for secure inrush current prevention. When the input voltage is normal, the second set value is used, providing flexibility and avoiding unnecessary constraints on set value selection
Solution Approach 2:
The patent segments the operating conditions into at least two states: abnormal state (where inrush current may occur) and normal operating state. Each state has its own dedicated set value, allowing the system to optimize for inrush current prevention only when necessary, while maintaining flexibility during normal operation
3Reliability
If the inrush current suppressing resistor is always connected to prevent inrush current, then inrush current suppression is improved, but conduction loss increases
Solution Approach 1:
The control circuit periodically monitors the input AC voltage and operating state, and periodically switches the inrush current suppression circuit configuration between active (first resistance value) and inactive (second resistance value) states based on the detected conditions, optimizing both suppression and efficiency over time
Solution Approach 2:
The patent extracts the inrush current suppression function from being always active and makes it conditional. The control circuit detects whether inrush current suppression is actually needed and only activates the high-resistance configuration when necessary, removing the unnecessary resistance connection during normal operation to eliminate wasted conduction loss
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 configuration effectively suppresses inrush current regardless of input AC voltage levels and circuit configurations, ensuring reliable operation during startup and recovery from power interruptions without causing conduction loss.
Implementation Method 1
an inrush current suppressing resistor provided on a path through which a current from the input AC power supply flows to charge the output capacitor of the step-up converter
Implementation Method 2
a resistance short-circuiting switch that short-circuits the inrush current suppressing resistor
Implementation Method 3
a control circuit that generates a signal for turning off the resistance short-circuiting switch when an absolute value of the input AC voltage is higher than the output DC voltage
Data Source
AI summary
An alternating current-direct current (AC-DC) converter includes: an input AC power supply that outputs an input AC voltage; a step-up converter that converts the input AC voltage into an output DC voltage to be outputted from an output capacitor; and an inrush current suppressing circuit. The inrush current suppressing circuit includes: an inrush current suppressing resistor provided on a path through which a current from the input AC power supply flows to charge the output capacitor and returns to the input AC power supply; a resistance short-circuiting switch that short-circuits the inrush current suppressing resistor; and a control circuit that generates a signal for turning off the resistance short-circuiting switch when an absolute value of the input AC voltage is higher than the output DC voltage.