MOSFET Current Detection Circuit Without Sense Resistors
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Solution Overview
Problem
Existing current detection methods in switching power supply devices are inefficient due to power consumption by sense resistors, which decreases the overall efficiency and requires additional components, limiting the ability to accurately monitor and control output currents.
Innovation Solution
A current detection circuit utilizing a MOS field effect transistor configuration that generates a sense voltage without a sense resistor, using a comparator to compare this voltage with a threshold voltage, and a determiner to assess the average current flowing through the inductor, allowing for constant current control and overcurrent protection without power loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used to detect output current, then current detection is achieved, but power consumption increases and efficiency decreases
Solution Approach 1:
The patent extracts the current detection function from the traditional sense resistor approach and implements it using MOS transistors (specifically utilizing the on-resistance of high-side and low-side switches). This removes the dedicated sense resistor component that causes power loss, while maintaining the ability to detect current through voltage measurements across the transistor on-resistances during switching operations.
2Measurement precision
If a sense resistor is used for current detection, then current monitoring is enabled, but additional components are required
Solution Approach 1:
The patent makes the switching elements (high-side and low-side MOS switches) serve dual functions: they perform their primary switching function while also providing the on-resistance necessary for current detection. This eliminates the need for separate sense resistors and reduces component count, as the same transistors used for power switching also enable current measurement through their inherent on-resistances.
3Measurement precision
If sense resistors are used in the output stage, then current detection is possible, but overall system efficiency decreases
Solution Approach 1:
The patent implements self-service current detection by utilizing the inherent on-resistance of the switching elements already present in the power stage. The high-side and low-side MOS switches naturally exhibit on-resistance during their on-state, which generates measurable voltage drops proportional to the current flowing through them. This eliminates the need for additional power-dissipating sense resistors, as the switching elements serve their own detection needs.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution eliminates power consumption associated with sense resistors, enhances efficiency by using MOS transistors to generate the sense voltage, and effectively monitors and controls average currents, ensuring reliable operation and reduced energy loss.
Implementation Method 1
a first comparator COMP1 configured to compare a sense voltage, which corresponds to a current flowing through a switching element Q1 when the switching element Q1 is turned on
Data Source
AI summary
A current detection circuit includes: a first comparator configured to compare a sense voltage, which corresponds to a current flowing through a switching element when the switching element is turned on, and a threshold voltage; and a determiner configured to determine, based on an output of the first comparator, whether or not a timing at which a magnitude relationship between the sense voltage and the threshold voltage is reversed after the switching element is turned on is before a predetermined time elapses after the switching element is turned on.