Switching Power Supply Circuit With Dynamic Slope Compensation
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Solution Overview
Problem
Conventional switching power supply circuits using current mode control face challenges with varying slope compensation ratios and PWM gain due to load variations, and they have room for improvement in line regulation and line step characteristics.
Innovation Solution
A switching power supply circuit is designed with a switching controller that includes a reference slope voltage generator, a sense voltage holder, and a voltage adder to maintain constant slope compensation ratio and PWM gain by determining the ON duty of the output transistor based on a slope voltage generated by adding a reference slope voltage and a held sense voltage, and an error amplifier to adjust the output voltage relative to a reference voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional current mode control is used in switching power supply circuits, then the control mechanism is simple, but the slope compensation ratio and PWM gain vary with load changes
Solution Approach 1:
The patent implements dynamic slope compensation by generating a slope compensation voltage that varies with the coil current. The slope compensation amount is dynamically adjusted based on the sensed coil current signal, ensuring that the slope compensation ratio remains constant across different load conditions. This dynamic adjustment mechanism resolves the contradiction by making the compensation adaptive rather than fixed.
Solution Approach 2:
The patent employs feedback control by sensing the coil current and using this information to adjust the slope compensation voltage. The sensed coil current signal is fed back to the control circuit, which then generates an appropriate slope compensation amount to maintain constant PWM gain and slope compensation ratio despite load variations.
2Reliability
If conventional switching power supply circuits are used, then the basic power conversion function is achieved, but the line regulation characteristics and line step characteristics are insufficient
Solution Approach 1:
The patent applies preliminary action by pre-calculating and applying slope compensation voltage before the PWM comparison occurs. The slope compensation voltage is generated in advance based on the expected coil current, allowing the control system to proactively compensate for variations rather than reactively adjusting after deviations occur. This improves line regulation and line step characteristics.
Solution Approach 2:
The patent changes the parameter of slope compensation voltage dynamically based on the operating conditions. By varying the slope compensation amount according to the coil current and load conditions, the system maintains optimal performance across different input voltages and load scenarios, thereby improving both line regulation and line step characteristics.
Data Source
AI summary
A switching power supply circuit has a switching output stage which generates an output voltage from an input voltage by driving a coil current by using an output transistor and a switching controller which turns ON and OFF the output transistor to keep the output voltage or a feedback voltage commensurate with it equal to a predetermined reference voltage. The switching controller includes a reference slope voltage generator which generates a reference slope voltage, a sense voltage holder which generates a held sense voltage by latching a sense voltage commensurate with the coil current with predetermined timing, and a voltage adder which generates a slope voltage by adding up the reference slope voltage and the held sense voltage. The switching controller determines the ON duty of the output transistor by using the slope voltage.