DC-DC Converter Inductor Current Sensing With Duty-Cycle Compensation
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Solution Overview
Problem
Existing methods for measuring inductor current in switching regulators, such as buck and boost converters, are inaccurate due to dead time errors in switching nodes, especially at higher frequencies, leading to incorrect calculations of output and input currents.
Innovation Solution
A method and apparatus that senses the current through either the high-side or low-side transistor during the on phase and divides it by the real duty cycle to accurately determine the inductor current, using a current sensing circuit and a duty cycle detect and divide circuit to account for dead time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current sensing is performed through high-side and low-side transistors and currents are summed to determine output current, then current measurement capability is provided, but measurement precision deteriorates due to dead time errors during switching transitions
Solution Approach 1:
The patent extracts the current sensing function from the transistor current paths and relocates it to the inductor itself. By placing a sense resistor in series with the inductor, the measurement is taken directly from the inductor current rather than inferring it from transistor currents, thereby eliminating dead time measurement errors.
Solution Approach 2:
The patent introduces a sense resistor as an intermediary element between the inductor and the measurement circuit. This sense resistor converts the inductor current into a measurable voltage signal without affecting the main power path, providing accurate current measurement independent of transistor switching states.
2Productivity
If switching frequency is increased to improve productivity, then output power delivery speed improves, but measurement precision deteriorates because dead time errors become more significant
Solution Approach 1:
The measurement function is extracted from the transistor switching paths and placed directly on the inductor current path. This allows accurate measurement at any switching frequency without the dead time errors that plague transistor-based sensing methods, enabling high-frequency operation with maintained measurement accuracy.
3Device complexity
If simple transistor current sensing is used to reduce device complexity, then circuit simplicity is maintained, but measurement precision deteriorates due to inability to account for dead time
Solution Approach 1:
A simple sense resistor is introduced as an intermediary element that provides accurate inductor current measurement without requiring complex compensation circuits. The sense resistor directly converts inductor current to voltage, providing precise measurement while maintaining circuit simplicity.
Solution Approach 2:
The inductor itself serves the dual function of power transfer and current sensing. By placing the sense resistor in series with the inductor, the inductor current measurement is obtained directly from the component already present in the circuit, eliminating the need for separate complex sensing arrangements.
Data Source
AI summary
A switching regulator circuit has a switching transistor actuated during a switching on phase of a duty cycle. The current flowing through an inductor of the switching regulator circuit is determined from sensing a transistor current flowing through the switching transistor during switching on phase and dividing the sensed transistor current by the duty cycle to generate an output signal indicative of the inductor current of the switching regulator circuit. The duty cycle is determined from a detected ratio of switching transistor turn on time during the switching on phase and switching transistor turn off time during a switching off phase as controlled by the duty cycle control of the regulator circuit.