AC-Side Precharge Isolation Circuit for Surge-Free Relay Switching
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Solution Overview
Problem
Conventional precharge control methods using relay short circuiting at a fixed delay time result in large surge currents, impacting relays and other components, and fail to accurately match precharge times with varying input voltages.
Innovation Solution
An AC-side precharge-isolation-detection circuit comprising a step-down rectifier module, optocoupler isolation module, and voltage drop detection module, connected in parallel to the current limiting resistor, which isolates voltages, detects voltage drops, and transfers signals to an MCU for sampling to determine precharge completion, preventing surge currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If relay short circuits PTC at a fixed delay time, then precharge control is simple, but large surge current occurs impacting relay and components
Solution Approach 1:
The patent uses a detection circuit that monitors the voltage across the PTC resistor in real-time and feeds this information back to the MCU. The MCU adjusts the relay switching timing based on the actual voltage level, preventing excessive surge current while maintaining simple control operation.
Solution Approach 2:
The detection circuit is activated before the relay switches, allowing the system to prepare and determine the optimal switching moment. This preliminary detection ensures the relay closes at the right time to avoid surge current without complicating the overall control process.
2Ease of operation
If precharge time is fixed, then control is simple, but it cannot match different input voltages accurately
Solution Approach 1:
The patent transitions from a fixed precharge time to a dynamic detection-based timing mechanism. The MCU continuously monitors the voltage across the PTC and determines the exact moment when precharge is complete, allowing the system to adapt to different input voltages while maintaining simple operational control.
Solution Approach 2:
The real-time voltage detection and feedback mechanism allows the system to automatically adjust the precharge duration based on actual circuit conditions and input voltage levels, providing adaptability without requiring complex manual configuration or fixed timing parameters.
3Productivity
If PTC switches frequently, then precharge can be completed, but PTC heats up and resistance increases prolonging subsequent precharge times
Solution Approach 1:
The detection circuit continuously monitors the voltage across the PTC and provides feedback to the MCU. This allows the system to determine the exact moment when precharge is complete and stop switching, preventing excessive heating and resistance increase while still achieving rapid precharge completion.
Solution Approach 2:
The system uses preliminary voltage detection to identify the optimal switching moment before excessive current flows. This prevents the PTC from overheating and maintaining its resistance characteristics, allowing repeated precharge cycles without prolonged timing.
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 isolates operating voltages, detects voltage drops across the current limiting resistor, and prevents surge currents, ensuring accurate precharge completion without overheating or prolonged precharge times, even with varying input voltages.
Implementation Method 1
an optocoupler isolation module configured to isolate the precharge circuit and the voltage drop detection module
Implementation Method 2
a step-down rectifier module configured for step-down and rectification of the detection circuit
Implementation Method 3
a voltage drop detection module configured to detect voltage drop change of the current limiting resistor of the precharge circuit
Data Source
AI summary
An AC-side precharge-isolation-detection circuit is connected in parallel to both ends of the current limiting resistor PTC of the AC-side precharge circuit. The AC-side precharge-isolation-detection circuit includes a step-down rectifier module, an optocoupler isolation module, and a voltage drop detection module, wherein the step-down rectifier module is connected in parallel to the current limiting resistor PTC on the AC side, the input end of the optocoupler isolation module is connected to the step-down rectifier module, and the output end of the optocoupler isolation module is connected to the voltage drop detection module. The invention can realize isolation of operating voltages at the pre-stage input and the post-stage output for the AC-side precharge-isolation-detection circuit through the optocoupler, detect voltage drop change across the current limiting resistor PTC of the precharge circuit, and transfer a voltage drop output signal to the MCU.