Switch Control Circuit Preventing Hard-Switching in Converters
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Solution Overview
Problem
Conventional power factor correction converters experience hard-switching due to fluctuations in resonance frequency caused by changes in the inductor and parasite capacitor, leading to inefficient switching operations without additional zero current detection pins.
Innovation Solution
A switch control circuit that calculates and utilizes a rising period to determine the falling period, ensuring the power switch is turned on after the sense voltage has decreased to an on-reference voltage, preventing hard-switching without additional pins for zero current detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed delay period is used to control switch turn-on timing, then soft-switching can be achieved at a specific resonance frequency, but hard-switching occurs when resonance frequency fluctuates due to inductor or capacitor changes
Solution Approach 1:
The patent implements dynamic adjustment of the delay period based on detected resonance frequency. The control circuit measures the actual resonance frequency and automatically modifies the delay period to maintain optimal switching timing, transforming a static fixed-delay system into a dynamic adaptive system that responds to frequency variations caused by inductor or capacitor changes
Solution Approach 2:
The patent introduces a feedback mechanism where the control circuit detects the resonance frequency by monitoring voltage or current waveforms and uses this information to adjust the delay period. This closed-loop feedback ensures that the switch turn-on timing continuously adapts to maintain soft-switching conditions despite component variations
2Measurement precision
If an auxiliary wire with predetermined turn ratio is used for zero current detection, then accurate zero current detection can be achieved, but device complexity increases due to additional pins and wiring
Solution Approach 1:
The patent extracts the zero current detection function from a separate auxiliary winding and integrates it into the existing sense resistor circuit. By utilizing the voltage already present across the sense resistor, the system eliminates the need for additional auxiliary wires and pins while maintaining accurate zero current detection capability
Solution Approach 2:
The sense resistor serves multiple functions: it provides current sensing for control purposes and simultaneously enables zero current detection for soft-switching. This multi-functional approach eliminates the need for dedicated zero current detection wiring, reducing device complexity while maintaining detection precision
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 prevents hard-switching by synchronizing the power switch turn-on with the resonance start point, maintaining soft-switching even with changes in inductor and capacitor values, thus ensuring stable output voltage.
Implementation Method 1
A drain voltage of the switch is decreased due to resonance after the switch is turned off, and a resonance frequency is determined by the inductor and a parasite capacitor of the switch
Data Source
AI summary
The present invention relates to a switch control circuit, a switch control method, and a converter using the same.An input voltage rectified from an AC input in a converter is transmitted to an inductor, and output power is generated from an inductor current by the input voltage. The converter includes a power switch connected to the inductor to control the inductor current and a sense resistor having a first end connected to a ground and a second end connected to the AC input. At a time point that a sense voltage generated in the sense voltage reaches the peak point and then decreased to an on-reference voltage, the power switch is turned on. The on-reference voltage is a sense voltage at a resonance start time point between a parasite capacitor of the power switch and the inductor.