Flyback Clamping Switch Control for Low-Input Full-Load Efficiency
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Solution Overview
Problem
In flyback circuits using non-complementary active clamping, the efficiency at full load with low input voltage is reduced due to the additional negative current caused by frequent turn-on of the clamping switch, leading to increased magnetic core loss and conduction loss.
Innovation Solution
The flyback circuit and control method reduce the total turn-on time of the clamping switch by limiting its turn-on frequency, thereby reducing additional negative current, magnetic core loss, and conduction loss, and improving efficiency under low input voltage conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the clamping switch is turned on frequently to release energy in the clamping capacitor, then the overvoltage problem is solved, but the additional negative current increases causing higher magnetic core loss and conduction loss
Solution Approach 1:
The clamping switch is controlled to turn on periodically at specific intervals rather than in every switching cycle. The control unit enables the clamping switch only in switching cycles where the primary current is decreasing and the drain-source voltage of the main switch is below a threshold, creating a periodic action pattern that releases clamping capacitor energy only when necessary, thereby reducing unnecessary negative current and energy losses.
Solution Approach 2:
The invention changes the operational parameters of the clamping switch by introducing conditional control based on primary current slope and drain-source voltage threshold. Instead of fixed periodic operation, the clamping switch operation parameters (turn-on timing, frequency) are dynamically adjusted based on real-time circuit state, optimizing the balance between energy release and loss reduction.
2Reliability
If the clamping switch turn-on time is extended to ensure complete energy release, then the energy accumulation problem is solved, but the efficiency at full load with low input voltage deteriorates
Solution Approach 1:
The invention applies partial action by enabling the clamping switch only in specific switching cycles rather than continuously. The control unit determines selective turn-on based on whether the primary current is decreasing and voltage conditions are met, providing just enough energy release action to prevent overvoltage without the excessive continuous operation that would cause efficiency deterioration.
Solution Approach 2:
The clamping switch operation is made self-regulating through automatic detection of circuit conditions. The control unit monitors primary current slope and drain-source voltage automatically, enabling the clamping switch only when the circuit naturally indicates energy needs release, making the system self-service rather than requiring continuous external control.
Data Source
AI summary
A flyback circuit and a control method of a clamping switch of the flyback circuit are provided. The flyback circuit includes a transformer, a main switch, a clamping capacitor, a clamping switch, and a secondary rectifier unit. The transformer includes primary and secondary windings with a turns ratio of K. The main switch and the primary winding are connected in series to receive an input voltage. The clamping switch and the clamping capacitor are connected in series and then connected to the primary winding in parallel. The secondary rectifier unit and the secondary winding are connected in series to provide an output voltage to a load. The control method includes: when a product of K and the output voltage is greater than or equal to the input voltage, controlling the clamping switch to turn on M times during N consecutive switching cycles of the main switch, where I≤M<N.