Capacitor Start-Up Apparatus with Current-Limiting Control
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Solution Overview
Problem
High capacitance capacitors, such as double-layer capacitors, cause excessive current draw during start-up, potentially disabling power supplies and leading to catastrophic failures, while also causing start-up delays and safety hazards due to their high current requirements.
Innovation Solution
A current-sensing resistor and switch circuit with a differential high-gain device, such as a comparator or operational amplifier, is used to control the charging current of high capacitance capacitors, limiting the current draw and preventing excessive charging by comparing a control voltage to a feedback voltage generated by the charging current, ensuring the capacitor is only fully charged once the power supply reaches a stable nominal level.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high capacitance capacitors are connected across power supply output to improve AC noise suppression and ride-through capability, then noise suppression and ride-through performance are improved, but excessive current draw occurs during start-up
Solution Approach 1:
The circuit performs preliminary detection of power supply voltage stability before enabling capacitor charging. The controller monitors whether the power supply output voltage has reached a stable nominal level, and only after this preliminary condition is satisfied does the controller enable the charging current to flow to the capacitor, preventing excessive current draw during unstable start-up conditions
Solution Approach 2:
The circuit implements feedback control by continuously monitoring the power supply output voltage and using this information to control the charging current to the capacitor. The controller adjusts the charging current based on feedback about whether the power supply has stabilized, ensuring that capacitor charging only occurs when it is safe to do so, thus resolving the contradiction between providing large capacitance and limiting current draw
2Duration of action of stationary object
If high capacitance capacitors are used to extend power supply ride-through duration, then ride-through time is extended, but start-up delays increase
Solution Approach 1:
The system performs preliminary detection to determine when the power supply has reached a stable nominal voltage level before initiating capacitor charging. This preliminary check prevents premature charging that would cause start-up delays, while still enabling the capacitor to charge fully once stability is confirmed, thus extending ride-through duration without excessive start-up delays
Solution Approach 2:
The circuit dynamically adjusts the capacitor charging process based on real-time power supply voltage conditions. The controller enables or disables charging current based on whether the power supply has stabilized, creating a dynamic charging profile that minimizes start-up delays while maximizing ride-through duration through optimal capacitor utilization
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
The solution effectively limits charging currents, preventing start-up delays and power supply failures, ensuring stable operation and safety by controlling the charging process to match the power supply's capabilities, thereby enhancing ride-through performance and reducing the risk of capacitor failures.
Implementation Method 1
a current-sensing resistor... An inverting input of the differential high-gain device receives a feedback voltage generated by the charging current flowing through the current-sensing resistor
Data Source
AI summary
Electronic circuits couple energy storage devices, such as double layer capacitors or rechargeable battery cells, to a power supply output, thereby improving noise suppression and extending ride-through capability of the power supply. In a typical circuit, an energy storage device is coupled in series with a switch that controls the charging current into the energy storage device. The switch is controlled by a comparator that receives a signal related to the voltage level of the power supply. In some embodiments, the comparator also receives a feedback signal related to a charging current flowing into the energy storage device. The circuit is configured so that the switch limits the charging current to a predetermined current level, or does not allow the charging current to flow until the output voltage of the power supply reaches a predetermined voltage level.