Switch-mode Power Supply Noise Filtering via Blanking Switch
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Solution Overview
Problem
Switch-mode power supplies face issues with switching noise coupling onto feedback signals, causing sub-harmonic oscillations and output voltage shifts due to increasing parasitic capacitance in smaller integrated circuit packages, which traditional low-pass filtering attempts to mitigate but at the cost of reduced system bandwidth and transient performance.
Innovation Solution
The implementation of a switch-mode power supply circuit that includes a feedback terminal, a comparator, and a switch, where the switch is blanked during transistor switching to prevent noise coupling, allowing the control circuit to generate a control signal that opens the switch prior to and closes it after the edge of the control signal, effectively eliminating noise-induced disturbances in the feedback signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If traditional low-pass filtering is used to mitigate switching noise, then noise reduction is achieved, but system bandwidth and transient performance are reduced
Solution Approach 1:
A blanking switch is introduced as an intermediary component between the feedback terminal and the comparator. This switch acts as a mediator that selectively blocks the feedback signal during transistor switching transitions, preventing noise coupling into the comparator without affecting the overall system bandwidth or transient response characteristics.
2Object-affected harmful factors
If traditional low-pass filtering is used to mitigate switching noise, then noise reduction is achieved, but transient performance is reduced
Solution Approach 1:
The blanking switch serves as a temporary intermediary that blocks the feedback path only during the brief switching transition periods when noise is generated. By selectively isolating the comparator from noise during these critical moments while maintaining normal feedback operation during steady-state, the system achieves noise mitigation without degrading transient performance.
3Volume of moving object
If parasitic capacitance is reduced through smaller integrated circuit packages, then device size is reduced, but switching noise coupling increases
Solution Approach 1:
The harmful noise coupling effect is extracted and isolated from the main feedback path by using the blanking switch to temporarily remove the feedback signal from the comparator during switching transitions. This extraction approach prevents the parasitic capacitance-induced noise from affecting the comparator, allowing small package sizes to be used without suffering from increased noise coupling.
4Object-affected harmful factors
If the switch is blanked during transistor switching, then noise coupling is prevented, but feedback signal transmission is blocked during switching
Solution Approach 1:
The blanking switch operates periodically, blocking the feedback signal only during the brief switching transition periods when noise is generated, while allowing normal feedback signal transmission during the steady-state periods. This periodic action ensures that noise coupling is prevented without causing significant loss of feedback information, as the blocking occurs only during transient switching moments.
Data Source
AI summary
A switch-mode power supply circuit includes a feedback terminal, a control circuit, a comparator, and a switch. The comparator includes a first input terminal coupled to a reference voltage source, and an output terminal coupled to an input terminal of the control circuit. The switch includes a first terminal coupled to the feedback terminal, a second terminal coupled to a second input terminal of the comparator, and a third terminal coupled to an output terminal of the control circuit.