SMPS Control Circuit for Light-Load Frequency Switching
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Solution Overview
Problem
Isolated switching mode power supplies face inefficiencies during light load working modes due to imprecision in feedback voltage feedback and difficulty in loop compensation, leading to delayed entry into light load mode and unwanted audible noise.
Innovation Solution
A control circuit for switching mode power supplies that includes a feedback pulse circuit, load determining circuit, light load pulse circuit, and selecting circuit to generate feedback, load determining, and light load pulse signals, which control the power switch's on operation, allowing smooth mode switching and frequency regulation to avoid audible noise and simplify loop compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is decreased to a very low level to achieve low power dissipation during light load working mode, then power dissipation is reduced, but loop compensation becomes difficult and audible noise is introduced
Solution Approach 1:
The patent dynamically changes the switching frequency parameter based on load conditions. During light load working mode, the switching frequency is maintained at a normal level rather than decreased to very low levels, thereby avoiding audible noise while still achieving low power dissipation through other control mechanisms such as discontinuous conduction mode operation
2Loss of energy
If the switching frequency is decreased to a very low level to achieve low power dissipation during light load working mode, then power dissipation is reduced, but loop compensation becomes difficult
Solution Approach 1:
The patent maintains the switching frequency at a normal level during light load mode, which simplifies the loop compensation design compared to very low frequency operation. This parameter choice avoids the complexity of designing compensation networks for extremely low frequency while still achieving energy efficiency through alternative control strategies
3Reliability
If indirect feedback voltage is obtained by removing isolators to save cost, then cost is reduced, but feedback precision deteriorates causing delayed entry into light load mode
Solution Approach 1:
The patent implements a feedback mechanism that monitors output voltage and load conditions to determine when to enter light load working mode. By using feedback control based on voltage comparison and load detection, the system can accurately identify light load conditions even without precise isolated feedback, enabling timely mode transition and avoiding the need for expensive isolators
Data Source
AI summary
A circuit for controlling a switching mode power supply having a power switch, having: a feedback pulse circuit, configured to receive a feedback signal, and to provide a feedback pulse signal; a load determining circuit, configured to receive the feedback signal, and to provide a load determining signal; a light load pulse circuit, configured to receive the load determining signal and a frequency regulating signal, and to provide a light load pulse signal; a frequency regulating circuit, configured to receive the load determining signal, the light load pulse signal and a normal load pulse signal, and to provide the frequency regulating signal; and a selecting circuit, configured to receive the load determining signal, the feedback pulse signal and the light load pulse signal, and to provide an on control signal and the normal load pulse signal; wherein the on control signal controls an on operation of the power switch.