CCM Flyback Current Control Using Secondary ON-Time Feedback
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Solution Overview
Problem
Achieving a constant current output in continuous conduction mode (CCM) fly-back switching power supplies is challenging due to varying initial currents in the secondary coil, making it difficult to maintain a stable current output.
Innovation Solution
A CCM-based fly-back switching power supply circuit and control method that includes a constant current control circuit, sampling circuit, and peak current control circuit, which samples the ON-time of the secondary coil, generates a duty cycle signal, and adjusts the peak current control signal to maintain a constant current output by comparing timing signals and adjusting the peak current control signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the fly-back switching power supply works under CCM, then the power supply efficiency is improved, but the current output stability deteriorates because the initial current varies in different periods
Solution Approach 1:
The patent implements a feedback mechanism by sampling the ON-time of the secondary coil to obtain duty cycle signal D_SEC, which is then fed back to the constant current control circuit. This feedback loop allows the system to dynamically adjust the peak current control signal VCST based on the actual operating conditions, thereby maintaining stable current output while operating in CCM mode.
Solution Approach 2:
The patent replaces traditional mechanical current regulation methods with electronic timing and signal processing. By converting voltage signals (CAC and VCST) into time signals and comparing them through timing modules, the system achieves precise current control without mechanical components, improving efficiency while maintaining stability.
2Stability of the object's composition
If a constant current control circuit with timing comparison is added, then the current output stability is improved, but the device complexity increases
Solution Approach 1:
The constant current control circuit performs multiple functions within a single integrated structure: it samples the secondary coil ON-time, generates the CAC voltage signal from duty cycle D_SEC and reference voltage VREF, converts both CAC and VCST signals into time signals, compares the time signals, and outputs the adjustment signal CCOUT. This multi-functionality reduces the need for separate circuits for each function, thereby limiting the increase in overall device complexity.
Data Source
AI summary
A CCM-based fly-back switching power supply circuit includes: a constant current control circuit, a sampling circuit and a peak current control circuit, wherein a sampling circuit is configured to sample the ON-time of the secondary coil to obtain its duty cycle signal D_SEC, and send the signal to a constant current control circuit; a constant current control circuit is configured to receive the duty cycle signal D_SEC, generate a voltage signal CAC from the duty cycle signal D_SEC and the preset reference voltage signal VREF, convert the voltage signal CAC and the peak current control signal VCST from the peak current control circuit into time signals, and conform a comparison on the time signals to output an adjustment signal CCOUT which is used to initiatively adjust the value of the peak current control signal VCST to cause the fly-back switching power supply circuit output a constant current.