Switching Power Supply Negative Current Protection
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Solution Overview
Problem
Conventional switching power supplies face issues with power efficiency degradation and electromagnetic interference (EMI) due to negative current flowing through junction diodes and LC resonance during discontinuous conduction mode (DCM), which can damage switching elements and degrade performance, especially at light loads.
Innovation Solution
Incorporating a negative current sensor and controller to manage the switching of high and low side switches, enabling DCM and maintaining the low side switch on-state until the inductor current reaches zero, and optionally using a freewheeling switch to connect both inductor terminals, preventing negative current flow and resonance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the high side switch is turned off in DCM, then the switching power supply can operate in discontinuous conduction mode, but negative current flows to the junction diode of the high side switch causing element damage and power efficiency degradation
Solution Approach 1:
The patent introduces a freewheeling diode as an intermediary component to redirect the negative current path. When the high side switch turns off in DCM, the negative current flows through the freewheeling diode instead of the junction diode of the high side switch, preventing element damage while maintaining DCM operation capability
Solution Approach 2:
The patent segments the current path by introducing separate pathways for different current directions. The freewheeling diode creates a dedicated path for negative current, separating it from the normal forward current path through the junction diode, thus protecting the switching elements during DCM operation
2Loss of energy
If both high side switch and low side switch are turned off in DCM, then the switching power supply can reduce switching losses, but LC resonance caused by the inductor and parasitic capacitor degrades EMI property
Solution Approach 1:
The freewheeling diode acts as an intermediary to provide a controlled current path during the off-state. By maintaining a continuous current path through the freewheeling diode, the patent prevents the abrupt current interruption that causes LC resonance between the inductor and parasitic capacitor, thereby reducing EMI while still allowing both switches to be off for loss reduction
3Use of energy by moving object
If the switching power supply operates at light load, then power efficiency is maximized, but negative current flow through junction diodes becomes more problematic
Solution Approach 1:
The freewheeling diode serves as a mediator that becomes particularly important at light loads. It provides a safe path for negative current during DCM operation, enabling the switching power supply to maintain high efficiency at light loads without risking element damage from negative current flow through the junction diodes
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 protects switching elements, enhances power efficiency, and improves EMI properties by preventing negative current flow and resonance, thereby ensuring reliable operation even at light loads.
Implementation Method 1
a negative current sensor configured to sense an inductor current flowing through the first electrical path, and generate an over-current protection signal when the inductor current is sensed as a negative current equal to or more than a preset value
Implementation Method 2
an inductor connected to an input voltage terminal
Implementation Method 3
a first switch configured to form a first electrical path between the inductor and an output voltage terminal; a second switch configured to form a second electrical path between the inductor and a ground voltage terminal
Data Source
AI summary
A switching power supply may include: an inductor connected to an input voltage terminal; a first switch configured to form a first electrical path between the inductor and an output voltage terminal; a second switch configured to form a second electrical path between the inductor and a ground voltage terminal; a negative current sensor configured to sense an inductor current flowing through the first electrical path, and generate an over-current protection signal when the inductor current is sensed as a negative current equal to or more than a preset value; and a controller configured to enable a discontinuous conduction mode (DCM) when the over-current protection signal is generated, and turn off the first switch and turn on the second switch, in response to the enabled DCM.