Load Detection in Switched-Mode Power Converters
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Solution Overview
Problem
Existing power converter technologies face inefficiencies in detecting load presence and polarity due to power dissipation in resistive components and variability in on-resistance of power switches, as well as difficulties in sensing voltage differences in closed loop systems.
Innovation Solution
A load detection circuit for switched-mode power converters that monitors high-side and low-side drive signals and switching voltage during dead-time periods to determine load current polarity without requiring resistive components, using small logic devices to compare waveforms and determine load presence and polarity based on switching voltage states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a resistive component is inserted in the load current path to sense load current, then load current detection is achieved, but power dissipation increases and efficiency decreases
Solution Approach 1:
The patent extracts the detection function from the main current path by monitoring the switching voltage during dead-time periods when no current flows through the power switches. This separates the sensing function from the power-carrying function, eliminating the need for resistive components in the current path and thus eliminating power dissipation associated with current sensing.
Solution Approach 2:
The patent uses the switching voltage during dead-time periods as an intermediary signal to infer load current information. Instead of directly measuring current through resistive components, the system uses the voltage state during dead-time (when switches are off) as a mediator to determine load presence and polarity without power loss.
2Ease of manufacture
If the on-resistance of power switches is used to measure load current, then current measurement is achieved, but measurement accuracy deteriorates due to unit-to-unit variability and temperature dependence
Solution Approach 1:
The patent extracts the measurement function from the power switch on-resistance by using the switching voltage during dead-time periods. This separates the measurement function from the power switching function, eliminating the dependency on power switch characteristics and their associated variability and temperature dependence.
Solution Approach 2:
The patent creates a copy of the current information through voltage monitoring during dead-time periods. Instead of directly measuring current through the power switch resistance, the system captures voltage state information during dead-time that replicates the load current conditions without being affected by power switch parameter variations.
3Measurement precision
If voltage difference sensing is implemented in a closed loop system, then voltage measurement is achieved, but sensing difficulty increases
Solution Approach 1:
The patent uses periodic dead-time intervals in the switching cycle to measure voltage. During these periodic dead-time periods, both power switches are off, creating a natural measurement window. This periodic action transforms the continuous voltage sensing problem into discrete, easily measurable voltage states at specific moments in the switching cycle.
Solution Approach 2:
The switching voltage during dead-time periods naturally provides the measurement information needed. The system uses its own operating characteristics (the voltage state during dead-time) to provide the measurement function, eliminating the need for additional sensing circuitry or complex differential measurements.
Data Source
AI summary
In one embodiment, a method for detecting a load in a switched-mode power converter is provided. The switched-mode power converter includes high and low-side power switches which are configured to be driven respectively by high and low-side drive signals to provide a switching voltage. The high and low-side drive signals include a plurality of dead-time periods. The method includes monitoring a waveform of the switching voltage and at least one of the high and low-side drive signals. The monitored waveform of the switching voltage is compared to the monitored waveform of the at least one of the high and low-side drive signals to determine whether the switching voltage is high or low during at least one of the dead-time periods. A current measurement of the load is determined based on whether the switching voltage is high or low during the at least one of the dead-time periods.