Flyback Control Circuit Synchronizing Switches to Prevent Inrush Current
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Solution Overview
Problem
Flyback circuits used in chargers face instability in output voltage and current due to delays in feedback control, leading to concurrent turn-on states of primary-side and secondary-side switches, causing transient inrush currents and reliability issues.
Innovation Solution
A control circuit that generates a secondary-side control signal based on current ripple and DC components of output signals, controlling the turn-off of the secondary-side rectifier and the turn-on of the primary-side switch, ensuring timely and synchronized operation without simultaneous switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If an opto-coupler feedback circuit is used to sense output voltage and regulate power, then output power regulation is achieved, but feedback delay occurs causing output voltage and current instability
Solution Approach 1:
The patent introduces an auxiliary control signal as an intermediary that directly controls the primary-side switch based on secondary-side rectifier state, bypassing the delayed opto-coupler feedback path. This mediator enables real-time coordination between primary and secondary switches without waiting for the slow feedback loop to respond.
Solution Approach 2:
The auxiliary control signal performs preliminary action by preemptively turning off the primary-side switch before the secondary-side rectifier turns on. This advance action prevents the harmful concurrent conduction state from occurring in the first place, rather than reacting to it after detection.
2Adaptability or versatility
If independent control of primary-side switch and secondary-side rectifier is used, then control flexibility is achieved, but concurrent turn-on state occurs causing transient inrush current and reliability issues
Solution Approach 1:
The patent implements a feedback mechanism where the state of the secondary-side rectifier (controlled by the secondary controller) feeds back to the primary controller through the auxiliary control signal. This feedback loop ensures that the primary-side switch is turned off in response to the secondary-side rectifier's state, preventing concurrent conduction while maintaining independent control capabilities.
3Device complexity
If feedback delay is present in the control circuit, then response time to output variations is slow, but circuit complexity is reduced
Solution Approach 1:
The patent segments the control function into two independent pathways: the main feedback path through the opto-coupler for power regulation, and the auxiliary control signal path for real-time switch coordination. This segmentation allows each pathway to perform its specific function with appropriate response characteristics without compromising the other.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution enables real-time adjustment and stabilization of output voltage and current, preventing concurrent switching and reducing stress on circuit elements, thereby enhancing the reliability and stability of the flyback circuit.
Implementation Method 1
the energy stored in the primary winding Np starts to be transmitted to a secondary winding Ns of the transformer T
Data Source
AI summary
A control circuit is configured to control a flyback circuit comprising a primary-side switch, a secondary-side rectifier and a transformer. The control circuit comprises a feedback control circuit configured to generate a secondary-side control signal based on a current ripple signal of the transformer, and at least one of a direct-current component of an output voltage signal and a direct-current component of an output current signal of a secondary side of the flyback circuit, wherein the secondary-side control signal is configured to control a turn-off of the secondary-side rectifier, an isolated transmission circuit coupled to the feedback control circuit and configured to generate a first primary-side control signal based on the secondary-side control signal, and a primary control circuit coupled to the isolated transmission circuit and configured to control a turn-on of the primary-side switch in response to receiving the first primary-side control signal.