Correction Circuit for Switching Current Sampling in Power Converters
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Solution Overview
Problem
Conventional PFC power converters using average-current control techniques face higher power consumption and inefficiency, especially when attempting to connect in parallel, due to inaccurate switching current sampling in discontinuous current mode operations.
Innovation Solution
A correction circuit comprising a sampling circuit, demagnetizing-time circuit, duty circuit, and compensation circuit is introduced to generate a corrected signal for precise average-current control, correcting switching current samples in both continuous and discontinuous current modes, and enabling efficient parallel connection of PFC converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If average-current control technique is used with current-sensing resistor connected via both charging and discharging paths, then the switching current can be sensed, but power consumption across the current-sensing resistor increases
Solution Approach 1:
The patent segments the current sensing function by using separate current-sensing resistors for charging path and discharging path, rather than using a single resistor for both paths. This allows independent optimization of each sensing circuit and enables the use of smaller resistance values without compromising overall measurement accuracy, thereby reducing power consumption.
Solution Approach 2:
The patent introduces a correction circuit as an intermediary component that processes the charging current signal to generate a corrected discharging current signal. This mediator circuit enables accurate reconstruction of the full switching current waveform without requiring direct sensing of both charging and discharging paths, thus reducing the power consumption burden on the current-sensing resistors.
2Device complexity
If conventional average-current control is used, then the circuit is simple, but it fails to achieve efficient parallel connection of PFC converters
Solution Approach 1:
The patent implements a feedback mechanism where the corrected discharging current signal is fed back to the controller to generate accurate PWM control signals. This feedback loop enables precise control of multiple PFC converters operating in parallel, allowing each converter to maintain proper current sharing and synchronization, thus achieving efficient parallel connection capability.
3Measurement precision
If current-sensing resistor is connected via both charging and discharging paths, then switching current average can be calculated, but measurement accuracy deteriorates in discontinuous current mode
Solution Approach 1:
The patent employs dynamic control by using the correction circuit to adaptively adjust the discharging current signal based on the actual operating conditions. The circuit dynamically compensates for the discrepancies that occur in discontinuous current mode, ensuring accurate measurement regardless of whether the converter is operating in CCM or DCM, thereby improving reliability across all operating modes.
Data Source
AI summary
The present invention provides a correction circuit for a power converter. The correction circuit includes a sampling circuit, a demagnetizing-time circuit, a duty circuit, and a compensation circuit. The sampling circuit generates an average-current signal in response to a switching current of the power converter. The demagnetizing-time circuit generates a discharging-time signal in response to a switching signal and an input-voltage signal. The duty circuit generates a duty signal in response to the discharging-time signal, an on-time of the switching signal, and a switching period of the switching signal. The compensation circuit is coupled to receive the average-current signal and the duty signal for generating a corrected signal. The switching signal is utilized to switch a magnetic device for regulating an output voltage of the power converter. The corrected signal is coupled to generate the switching signal.