Switching Power Supply Control Circuit for Constant Current in CCM and QR Modes
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Solution Overview
Problem
Traditional constant current control methods for flyback switching power supplies are ineffective in Continuous Conduction Mode (CCM) and quasi-resonant (QR) mode, leading to low efficiency, increased design costs, and precision issues due to compatibility limitations and differences in output current between modes.
Innovation Solution
A control circuit and method that includes a constant current control module, precision compensation module, sample-and-hold module, and voltage controlled oscillator to regulate the duty cycle and switching frequency, ensuring constant current output in both CCM and QR modes by detecting working modes and input conditions, and compensating for differences in output currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional constant current control method is used, then constant current output can be achieved in DCM, but the control method becomes invalid in CCM and QR mode
Solution Approach 1:
The control circuit dynamically detects the working mode (DCM or CCM/QR) and switches between different control strategies accordingly. The controller adjusts the control method based on real-time operating conditions, enabling effective constant current control across all working modes rather than being restricted to a single mode.
Solution Approach 2:
The invention changes the control parameters and control law based on the detected working mode. In DCM, one control approach is used, while in CCM and QR mode, different control parameters and methods are applied to maintain constant current output effectiveness across varying operational conditions.
2Measurement precision
If traditional constant current control method is used, then constant current output can be maintained, but the ratio of TP to TD must be strictly constant which reduces efficiency
Solution Approach 1:
The invention allows the ratio of switching period TP to demagnetization time TD to vary dynamically based on the working mode. In CCM and QR mode, the ratio is no longer strictly constant, enabling the power supply to operate more efficiently while the control circuit compensates to maintain constant current output precision.
Solution Approach 2:
The control circuit uses feedback mechanisms to monitor the actual current output and adjusts control parameters in real-time. This feedback loop compensates for variations in the TP/TD ratio, maintaining precise constant current control even when the ratio changes to improve efficiency in different working modes.
3Measurement precision
If traditional constant current control method is used, then constant current output is achieved, but the design of transformer is restricted to ensure power supply does not work in CCM
Solution Approach 1:
The control circuit dynamically adapts to different working modes including CCM, eliminating the need to restrict transformer design to prevent CCM operation. The transformer can be designed with greater flexibility, and the control system will automatically adjust its strategy based on whether the transformer operates in DCM or CCM/QR mode.
4Reliability
If different control methods are used for different working modes, then control effectiveness is improved, but the design cost and complexity increase
Solution Approach 1:
The control circuit is designed as a universal multi-functional system that can handle multiple working modes (DCM, CCM, QR) within a single integrated controller. Rather than requiring separate control circuits for each mode, the single controller detects the working mode and automatically applies the appropriate control strategy, reducing overall system complexity while maintaining control effectiveness.
Data Source
AI summary
A control circuit and a control method of a switching power supply, according to feedback signals on a pin FB and a pin CS, a constant current control module generates and outputs a control signal to control an output current of the switching power supply, thereby regulating duty cycle of a first transistor adaptively and controlling an output current Io of a power supply system to be constant; according to the feedback signals on the pin FB and on the pin CS, a constant current precision compensation module adaptively regulates circuit parameters of the constant current control module and a sample-and-hold module, preventing precision of constant current output from being influenced by change of a working mode and/or by variation of input conditions; when an output voltage changes, QR mode keeps unchanged or depth of a CCM keeps approximately constant.