Current-Mode Switching Power Supply Feedback Without Sensing Delay
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Solution Overview
Problem
Current mode control type switching power supply devices face challenges in performing current feedback when the ratio of output voltage to input voltage is small, leading to issues with noise transmission and delay in current sensing.
Innovation Solution
The proposed solution involves a current mode control type switching power supply device with a controller that accumulates current information during a predetermined period while the first switch is off and reflects this information on the slope voltage before the first switch is turned on, ensuring effective current feedback even at small voltage ratios.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If current sensing is performed using the difference between input voltage and switched voltage, then current mode control can be implemented, but delay time occurs after the upper MOS transistor is turned on until current information is transmitted to the slope voltage
Solution Approach 1:
The patent applies preliminary action by accumulating current information during the period when the first switch is off, before the actual current feedback is needed. The accumulating portion stores current information in advance, and the reflecting portion transmits this pre-accumulated information to the slope voltage before the first switch is turned on, thereby eliminating the delay time that would otherwise occur in conventional current sensing methods.
2Reliability
If current sensing is performed using the difference between input voltage and switched voltage, then current mode control can be implemented, but noise on the leading edge of switched voltage is transmitted and reflected on the slope voltage
Solution Approach 1:
The patent applies the taking out principle by extracting the harmful noise component from the current sensing process. Instead of using the switched voltage that contains noise on its leading edge, the invention senses current flowing through the second switch, which provides a clean current signal free from the noise that would otherwise be transmitted to the slope voltage.
3Adaptability or versatility
If the pulse width of switched voltage is decreased, then output voltage to input voltage ratio can be reduced, but current feedback cannot be performed due to dominant delay time and noise
Solution Approach 1:
By accumulating current information in advance during the period when the first switch is off, the patent enables reliable current feedback even when the pulse width of the switched voltage is decreased. The pre-accumulated current information is transmitted to the slope voltage before the first switch is turned on, ensuring that current feedback remains effective across a wider range of voltage ratios including small ratios.
Data Source
AI summary
A switching power supply device includes a first switch, a second switch, a current sensing portion configured to sense current flowing in the second switch, and a controller configured to control the first and second switches in accordance with the current sensed by the current sensing portion. The controller includes an accumulating portion configured to accumulate information of the current sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state, and reflecting portion configured to start the transmission of the current information accumulated by the accumulating portion before the first switch is changed from the off state to the on state so as to reflect the current information accumulated by the accumulating portion on the slope voltage, and controls the first and second switches in accordance with the slope voltage.