Buck-Boost Converter Overcurrent Detection in Pulse-Skipping Mode
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Solution Overview
Problem
Existing buck-boost converters face challenges in accurately detecting overcurrents during low-power operating modes, where the voltage across the shunt resistor is very low, making traditional detection methods imprecise and power-consuming.
Innovation Solution
The control module monitors the duration of capacitor discharge periods and compares them to thresholds to detect overcurrents, implementing a pulse-skipping mode and using a monitoring circuit with timing and comparison stages to generate signals indicative of operating modes, allowing for accurate overcurrent detection with reduced power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used for overcurrent detection in low-power mode, then overcurrent detection is possible, but the voltage across the shunt resistor is very low making detection imprecise and power-consuming
Solution Approach 1:
The patent changes the detection parameter from voltage (across shunt resistor) to time duration (capacitor discharge period). By measuring how long it takes for the output capacitor to discharge to a threshold voltage, the system can detect overcurrent conditions without requiring precise low-voltage measurements, thus improving detection precision while reducing power consumption.
Solution Approach 2:
The patent introduces an output capacitor as an intermediary element between the shunt resistor and the detection circuit. The capacitor accumulates charge during normal operation and its discharge behavior serves as a mediator to indicate overcurrent conditions, allowing indirect detection that avoids the limitations of direct voltage measurement across the shunt resistor.
2Reliability
If traditional shunt resistor detection is used, then overcurrent detection is implemented, but it is power-consuming and imprecise in low-power modes
Solution Approach 1:
The patent employs periodic action by utilizing the natural charge-discharge cycles of the output capacitor. Instead of continuous monitoring, the system leverages the periodic discharge behavior to detect overcurrent conditions, reducing power consumption while maintaining reliable detection through repeated measurement opportunities.
3Use of energy by moving object
If the converter operates in low-power mode, then power consumption is reduced, but overcurrent detection accuracy deteriorates due to very low voltage across shunt resistor
Solution Approach 1:
The patent substitutes the electrical measurement system (voltage measurement across shunt resistor) with a temporal measurement system (time duration measurement). By replacing the mechanical/electrical sensing approach with a time-based measurement approach, the system achieves accurate overcurrent detection in low-power modes without being constrained by low voltage levels.
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
A control module (120) for a switching buck-boost converter (1) including an inductor (12), a capacitor (COUT), a first top switch (2) and a second top switch (4), a first bottom switch (6) and a second bottom switch (8) and a diode (24) coupled to the second top switch (4). The control module (120) controls the switching buck-boost converter (1) so as to alternate: first time periods (Tswitching), in which the second top switch (4) is open and cycles of charge (TON,T'ON) and discharge (TOFF,T'OFF) of the inductor (12) are carried out, during which the inductor (12) is traversed by a current (IL) that also passes through the diode (24) and charges the capacitor (COUT); and second time periods (TOV_MODE), in which the first and second top switches (2, 4) are open and the first and second bottom switches (6, 8) are closed so that the current (IL) in the inductor (12) recirculates, and the capacitor (COUT) is discharged by a current (ILOAD) that flows in the load (15). The control module (12) includes a circuit (60) that compares the duration (TOV_MODE) of each second time period with a limit duration (Tth_ov) and detects the occurrence of an overcurrent if the duration (TOV_MODE) of the second time period is shorter than the limit duration (Tth_ov).