DC-DC Converter Current Sensing Using High-Side Duty Cycle
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Solution Overview
Problem
Existing switching regulators inaccurately measure output current due to the adverse effect of switching dead time on low-side current sensing, leading to an inaccurate summation of high-side and low-side currents.
Innovation Solution
A switching regulator circuit with a current sensing circuit to measure the high-side transistor current during its on-time and a duty cycle detect and divide circuit to calculate the output current by dividing the sensed current by the real duty cycle, effectively determining the output current flowing through the inductor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If low-side current sensing is used to measure output current, then current measurement can be implemented, but switching dead time causes measurement inaccuracy
Solution Approach 1:
The patent extracts the harmful effect of dead time by separating the current measurement from the problematic low-side switching node. Instead of measuring current at the low-side switch where dead time creates gaps, the invention measures current at the high-side switch where continuous conduction occurs, thereby extracting the measurement function from the unreliable low-side region during dead time intervals
Solution Approach 2:
The patent introduces an intermediary approach by using the high-side current as a proxy measurement. Rather than directly measuring the problematic low-side current during dead time, the system uses the high-side current (which flows continuously) as an intermediary variable, combined with duty cycle information, to infer the output current without directly encountering the dead time measurement gap
2Measurement precision
If both high-side and low-side currents are summed to determine output current, then complete current measurement is achieved, but measurement accuracy deteriorates due to dead time effects
Solution Approach 1:
The patent extracts only the necessary current measurement component (high-side current) rather than requiring both high-side and low-side current measurements. By taking out just the high-side current measurement and combining it with duty cycle data, the system achieves accurate output current measurement without the complexity of dual current sensing circuits
Solution Approach 2:
The patent changes the measurement parameters from direct low-side current measurement to a combination of high-side current measurement and duty cycle measurement. This parameter substitution allows the system to achieve the same measurement goal (output current) while avoiding the dead time problem that plagues direct low-side measurement
Data Source
AI summary
A switching regulator circuit has a high side (HS) transistor actuated during on time (TON) of a duty cycle. The output current of the switching regulator circuit is determined from sensing a transistor current flowing through the HS transistor during HS transistor on time (TON) and dividing the sensed transistor current by the duty cycle to generate an output signal indicative of the output current of the switching regulator circuit. The duty cycle is determined from a ratio of the on time (TON) and off time (TOFF) of the switching regulator circuit.