Active Droop Current Sharing Circuit With Overcurrent Limiting
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Solution Overview
Problem
Conventional parallel power supplies face challenges in achieving accurate current sharing due to variations in output voltages and impedances among power converters, leading to inefficiencies and reliability issues, particularly when using synchronous rectification, and are often bulky and inflexible due to the large number of active elements in current sharing and overcurrent detection circuits.
Innovation Solution
An active droop current sharing circuit with a current limiting function is implemented, featuring a current sensor, amplifier, threshold level generator, and switching controller to adjust output voltage and limit current, using a zener diode for threshold setting and overcurrent protection, and a capacitor for control loop stabilization, thereby enabling precise current balancing and reducing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional current sharing techniques are used in parallel power supplies, then load current can be shared among converters, but current sharing accuracy degrades during abrupt changes and converters may sink current from each other
Solution Approach 1:
The patent applies preliminary anti-action by proactively limiting the output current of each converter using a current limiting circuit before current imbalance or sinking can occur. The current limiting function prevents converters from drawing excessive current or sinking current from other converters by enforcing a maximum current threshold, thereby maintaining current sharing accuracy and preventing energy loss even during abrupt load changes.
2Reliability
If current limit mode is used to protect power converters, then overcurrent protection is provided, but converters with lower output voltage idle or sink current reducing system efficiency
Solution Approach 1:
The patent implements feedback by using a current sensing amplifier to continuously monitor the output current of each converter and feed this information back to the control circuit. This feedback mechanism enables the controller to adjust the duty cycle of each converter dynamically, ensuring that all converters share the load current equally while maintaining overcurrent protection, thereby preventing idle or sinking conditions that would reduce system efficiency.
3Measurement precision
If active droop current sharing circuit is implemented, then current sharing accuracy is improved, but circuit complexity and number of active elements increase making the system bulky
Solution Approach 1:
The patent applies merging by combining multiple functions into a single integrated circuit. The current sharing circuit integrates the current sensing amplifier, voltage reference generator, and current limiting function into one unified block, eliminating the need for separate active elements for each function. This integration maintains high current sharing accuracy while significantly reducing circuit complexity and component count.
Solution Approach 2:
The patent implements universality by designing a multi-functional current sharing circuit that simultaneously performs current sensing, voltage regulation, current limiting, and droop compensation. The single integrated circuit can adapt to different operating conditions and converter configurations, providing accurate current sharing without requiring additional dedicated components for each specific function.
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 enhances current sharing accuracy, reduces circuit size and complexity, and improves efficiency by allowing flexible circuit design while preventing overcurrent conditions, thus enhancing the reliability and performance of parallel power supply systems.
Implementation Method 1
a threshold level generator for setting a threshold level equivalent to a voltage level corresponding to a maximum allowed output current of the power converter
Implementation Method 2
a current sensor placed between an output end of a power converter and a common load for generating a sensed output voltage
Data Source
AI summary
An active droop current sharing technique combined with current limiting function is employed in a parallel power supply. The parallel power supply is characterized with a current sensing amplifier that generates a current feedback signal representing a difference between a nominal output voltage and a fractional output voltage. The current sensing amplifier is coupled to a threshold level generator providing a threshold level defining a voltage level corresponding to a maximum allowed output current of the parallel power supply. If the voltage level of the current feedback signal exceeds the threshold level, the threshold level generator is turned on and the current feedback signal is coupled to a switching controller to adjust the output voltage of the power converter for properly addressing the current imbalance among plural parallel power supplies. Meanwhile, the threshold level generator induces a current to the current sense input of the switching controller, thereby limiting the output current of the power converter from exceeding the maximum allowed output current.