Switching Power Supply Loop Compensation for Output Ripple
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Solution Overview
Problem
The existing loop compensation methods in switching power supplies result in large output ripples due to instability at light or idle loads, as the error amplifier cannot track changes in output voltage in real time, leading to low-frequency ripple issues.
Innovation Solution
A loop compensation device is introduced, comprising an error amplifier, switching logic gate, and delay generation circuit, where the delay generation circuit outputs a valid switching control signal after the power switch is turned off, controlling the switching logic gate to charge/discharge the loop compensation capacitor, ensuring stable loop compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a loop compensation capacitor Cea is added to the output end of the error amplifier to achieve loop compensation, then the loop stability is improved, but the output ripple becomes too large because the loop cannot be stable within a range from light load to idle load
Solution Approach 1:
The patent applies dynamics by making the connection between the error amplifier output and the loop compensation capacitor controllable rather than fixed. The switching logic gate dynamically connects or disconnects the capacitor based on operating conditions, allowing the system to adapt between light load and idle load states, thereby maintaining loop stability while reducing output ripple across different load ranges
Solution Approach 2:
The patent implements periodic action through the delay generation circuit that produces periodic switching control signals. These signals periodically activate the switching logic gate to connect the loop compensation capacitor to the error amplifier output during specific phases (when the power switch is off), creating a rhythmic compensation action that stabilizes the loop while minimizing ripple generation
2Reliability
If the error amplifier continuously tracks the output voltage to maintain loop stability, then the loop compensation is improved, but the output ripple increases due to low-frequency ripple issues at light or idle loads
Solution Approach 1:
The patent applies partial action by having the error amplifier track the output voltage only during specific periods when needed for loop stability, rather than continuously. The switching logic gate enables the error amplifier to exert its stabilizing influence partially (during the period when the power switch is off and the delay signal is active), which is sufficient to maintain loop stability while avoiding excessive tracking that would generate low-frequency ripple
Data Source
AI summary
The invention discloses a switching power supply, a primary control chip and a loop compensation device thereof. The loop compensation device comprises: an error amplifier; a switching logic gate, wherein the input end of the switching logic gate is connected with the output end of the error amplifier; a loop compensation capacitor, wherein one end of the loop compensation capacitor is connected with the output end of the switching logic gate, and the other end of the loop compensation capacitor is grounded; and a delay generation circuit, wherein the output end of the delay generation circuit is connected with the control end of the switching logic gate, and the delay generation circuit is used for outputting a valid switching control signal within a preset time after a power switch of the switching power supply is turned off to control the switching logic gate in a turn-on state, so that the loop compensation capacitor is charged/discharged by means of an error amplification signal outputted from the error amplifier. With the loop compensation device, the problem that the output ripple from the switching power supply is too large can be solved, and the loop stability is ensured.