Mode Switching Circuit for Switching Power Supply Voltage Overshoot
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Solution Overview
Problem
Traditional switching power supplies experience overshoot of output voltage and poor dynamic response when load transitions from heavy to light, due to slow discharge of output capacitor and discontinuous inductor current.
Innovation Solution
A mode switching circuit that controls the power supply to switch between two modes based on load conditions, allowing inductor current to be negative in one mode to prevent overshoot, and using detection circuits and counters to manage switching between continuous and discontinuous conduction modes to optimize efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If traditional switching power supply operates with synchronous switch turned off when inductor current crosses zero, then the control is simple, but output voltage overshoot occurs when load transitions from heavy to light
Solution Approach 1:
The patent implements dynamic mode switching between DCM and CCM based on real-time detection of inductor current characteristics. The system transitions from static zero-crossing control to dynamic conduction mode control, adjusting the operating mode according to load conditions to prevent voltage overshoot while maintaining control effectiveness.
Solution Approach 2:
The patent introduces detection circuits that monitor inductor current and provide feedback to the control system. By detecting whether the synchronous switch body diode is conducting, the system gains real-time information about inductor current state, enabling adaptive control decisions to maintain output voltage stability during load transitions.
2Strength
If synchronous switch is turned off at zero current crossing, then device stress is reduced, but dynamic response becomes poor due to slow output capacitor discharge
Solution Approach 1:
The system dynamically adjusts the turn-off timing of the synchronous switch based on the detected conduction mode. In CCM, the switch is turned off after the body diode stops conducting, allowing inductor current to remain continuous and enabling faster energy transfer to the output capacitor, thereby improving dynamic response while managing device stress appropriately.
Solution Approach 2:
By maintaining continuous inductor current conduction in CCM mode, the system ensures continuous energy transfer to the output capacitor. This continuity of useful action prevents the discontinuous current gaps that cause slow response, while the controlled conduction mode ensures device stress remains within acceptable limits.
3Reliability
If inductor current is allowed to be negative to prevent overshoot, then output voltage stability improves, but energy loss increases
Solution Approach 1:
The system dynamically selects between DCM and CCM based on load conditions and detected current characteristics. By switching modes adaptively rather than operating continuously in CCM with negative current, the system achieves voltage stability when needed while minimizing energy loss during light load conditions through DCM operation.
Solution Approach 2:
The patent changes the fundamental operating parameter of inductor current continuity by switching between conduction modes. This parameter change allows the system to optimize the balance between voltage stability (achieved through controlled negative current in CCM) and energy efficiency (achieved by operating in DCM when appropriate), adapting to different load scenarios.
Data Source
AI summary
A mode switching circuit for a switching power supply having a power switch and a synchronous switch is configured to: control the switching power supply to switch between a first mode and a second mode in response to a transitioning of a load of the switching power supply, in order to suppress overshoot of an output voltage of the switching power supply; where an inductor current of the switching power supply is not less than zero in the first mode; and where the inductor current is allowed to be less than zero in the second mode.