Offline Power Converter Line Sensing Circuit
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Solution Overview
Problem
Conventional offline power converters require additional external terminals for line voltage sensing, increasing the cost and complexity of the power factor controller chip and circuit board.
Innovation Solution
Integration of a line sensing circuit within the power factor controller that uses the DRV signal to measure the duty cycle and perform line sensing without an explicit line sense signal, reducing the need for external terminals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an explicit line sense terminal is used for line voltage sensing, then line sensing accuracy is improved, but device complexity and terminal count increase
Solution Approach 1:
The patent combines the line sensing function with existing internal circuit nodes, specifically using the driver output node and current sense resistor that already exist in the power converter circuit. This merging eliminates the need for a separate external line sense terminal while maintaining sensing capability through the relationship between driver current, sense resistor voltage, and line voltage.
Solution Approach 2:
The patent makes existing circuit elements serve multiple functions: the current sense resistor is used both for current sensing and line voltage sensing; the driver output node serves both as a control output and as a sensing point for line voltage detection. This multi-functionality reduces the need for dedicated sensing terminals.
2Reliability
If an explicit line sense terminal is used for line voltage sensing, then protection functions are enabled, but ease of manufacture deteriorates due to additional external connections
Solution Approach 1:
The protection function is integrated into the existing control circuitry by using the same internal nodes (driver output and current sense resistor) for both line sensing and protection detection. This eliminates the need for separate external protection circuitry and reduces circuit board complexity while maintaining comprehensive protection capabilities.
3Device complexity
If duty cycle measurement is used for line sensing, then terminal count is reduced, but measurement precision must be maintained through alternative methods
Solution Approach 1:
The patent employs feedback through the current sense resistor to accurately determine line voltage. By measuring the voltage across the sense resistor and using the known relationship between driver current, sense resistor value, and line voltage, the system achieves precise line sensing without requiring direct external voltage measurement, thus maintaining accuracy while reducing terminal count.
Data Source
AI summary
An integrated circuit power factor controller includes a pulse width modulator and a line sensing circuit. The pulse width modulator has a first input for receiving a feedback signal, a second input for receiving a line sense signal, and an output for providing a drive signal having a duty cycle formed in response to the feedback signal and the line sense signal. The line sensing circuit has an input for receiving the drive signal, and an output coupled to the second input of the pulse width modulator for providing the line sense signal. The line sensing circuit forms the line sense signal in response to measuring a duty ratio of the drive signal. In another form, an offline converter includes an integrated circuit power factor controller that provides a line sense signal in response to a duty ratio of the drive signal without measuring a voltage on the input line.