SMPS Controller Switching Modes for Loss Reduction
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Solution Overview
Problem
Switched mode power supplies (SMPS) face inefficiencies due to increased switching frequency when energy in the inductor is reduced, leading to higher switching losses and reduced conversion efficiency, particularly around zero crossings of the mains supply.
Innovation Solution
A controller that switches between boundary conduction mode (BCM) and discontinuous conduction mode (DCM) based on inductor current thresholds, with a switch mode selector determining the switching mode to reduce switching frequency and losses, and incorporates a primary stroke timer and delay timer to manage switching cycles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the switching frequency is increased to maintain energy transfer when inductor energy is reduced, then the power supply can operate around zero crossings, but switching losses and electromagnetic interference increase
Solution Approach 1:
The controller dynamically switches between two operating modes (first switching mode with higher frequency and second switching mode with lower frequency) based on the inductor current level. When inductor current exceeds a threshold, the controller uses the first switching mode to maintain operation during zero crossings. When inductor current falls below the threshold, it transitions to the second switching mode to reduce switching losses. This dynamic adaptation resolves the contradiction by allowing high frequency only when necessary.
Solution Approach 2:
The controller changes the switching frequency parameter based on operating conditions. By monitoring inductor current and comparing it to a threshold, the controller adjusts the switching frequency between two distinct levels. This parameter change allows the system to optimize between maintaining operation continuity and minimizing switching losses depending on the energy state of the inductor.
2Reliability
If the switching frequency is increased to maintain energy transfer, then power supply operation is maintained, but electromagnetic interference increases
Solution Approach 1:
The controller dynamically adjusts the switching frequency based on inductor current levels. During zero crossings when inductor energy is low, it temporarily increases frequency to maintain operation. When inductor current is sufficient, it reduces frequency to minimize electromagnetic interference. This dynamic behavior maintains reliability while reducing harmful emissions.
Solution Approach 2:
The controller implements periodic monitoring of inductor current and periodically switches between operating modes. This periodic action allows the system to maintain operation during critical periods (zero crossings) while reducing electromagnetic interference during normal operation periods when inductor energy is sufficient.
3Productivity
If boundary conduction mode is used to maintain continuous operation, then power transfer is maintained, but switching losses increase when inductor energy is low
Solution Approach 1:
The controller dynamically selects between boundary conduction mode (first switching mode) and discontinuous conduction mode (second switching mode) based on inductor current levels. When inductor current is high, boundary conduction mode maintains continuous power transfer. When inductor current drops below the threshold, the controller switches to discontinuous conduction mode with lower frequency to reduce switching losses while still transferring power.
Solution Approach 2:
The controller changes the conduction mode parameter based on inductor energy state. By monitoring inductor current and comparing to a threshold, the controller transitions between boundary conduction mode (higher frequency, continuous transfer) and discontinuous conduction mode (lower frequency, reduced losses). This parameter change resolves the contradiction between continuous power transfer and switching loss reduction.
Data Source
Figure 1a~1c
Figure 2a~2c
Figure 3~5
AI summary
The disclosure relates to a controller (606) for a switched mode power supply, SMPS (600), comprising: a switch toggling unit (670) having a first switching mode and a second switching mode, wherein the first switching mode is a continuous conduction mode or a boundary conduction mode and the second conduction mode is a discontinuous conduction mode; and a switch mode selector (676) configured to set the switching mode of the switch toggling unit (670) in accordance with a current in an inductor (602) of the SMPS (600).