Current-Mode Switching Supply Control With Low-Side Current Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current mode control type switching power supply devices face issues with delayed current feedback and noise interference due to the delay in transmitting current information from the current sensing circuit to the slope circuit, especially when the pulse width of the switched voltage is reduced, leading to unstable control systems.
Innovation Solution
A current mode control type switching power supply device that includes a controller to independently control switches based on the ratio of output voltage to input voltage, using a current sensing portion to sense current in a second switch and control the switches accordingly, reducing delay and noise interference by accumulating current information as a charge voltage before transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If current sensing is performed on the upper MOS transistor Q1 to achieve current mode control, then fast response and simplification of phase compensation are improved, but delay time occurs in current feedback transmission
Solution Approach 1:
The patent applies preliminary action by performing current sensing on the lower MOS transistor Q2 instead of the upper MOS transistor Q1. This changes the timing of current information acquisition to occur before the upper transistor switches, eliminating the delay that occurs when sensing after the fact. The current information is obtained in advance during the period when the lower transistor is conducting, allowing immediate feedback without waiting for the upper transistor's switching event.
2Device complexity
If current information is transmitted directly from current sensing circuit to slope circuit, then device complexity is reduced, but noise from switched voltage VSW is transmitted and reflected on slope voltage VSLP
Solution Approach 1:
The patent introduces an intermediary element - a capacitor - between the current sensing circuit and the slope circuit. This capacitor accumulates the current information as charge voltage, serving as a buffer that isolates the noise from the switched voltage VSW from being directly transmitted to the slope voltage VSLP. The capacitor integrates the current signal over time, filtering out high-frequency noise while preserving the essential current information needed for control.
3Productivity
If pulse width of switched voltage VSW is decreased to improve switching frequency, then productivity is improved, but delay time and noise become dominant causing current feedback failure
Solution Approach 1:
By sensing current on the lower transistor Q2, the patent obtains current information in advance before the upper transistor switches, ensuring that even with very short pulse widths, the current feedback is established before the switching event occurs. This preliminary sensing action guarantees feedback reliability regardless of how brief the subsequent voltage pulse becomes.
Solution Approach 2:
The capacitor intermediary accumulates current information over the entire period when the lower transistor conducts, integrating the signal over time. This time integration effect ensures that even if the subsequent upper transistor pulse width is very short, sufficient current information has been accumulated in the capacitor to maintain reliable feedback, making the system robust against high-frequency switching with minimal pulse widths.
Data Source
AI summary
A current mode control type switching power supply device includes a first switch having a first terminal connected to a first application terminal to which an input voltage is applied, and a second switch having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied. A current sensor is configured to sense current flowing in the second switch. A controller configured to control the first switch and the second switch, wherein the controller is configured to control the first switch and the second switch independently of a difference between the input voltage and an output voltage and in addition in accordance with the current sensed by the current sensor.