Flyback Converter Delay Device Synchronous Rectification
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Solution Overview
Problem
Existing synchronous rectification control circuits in flyback converters, such as those using voltage and current sensing, face inefficiencies in Continuous Current Mode (CCM) devices due to fast transients that prevent timely turn-off of the rectifier switch, resulting in significant reverse currents.
Innovation Solution
A flyback converter circuit with a delay device on the primary side that introduces a transient before the primary switch turns on, allowing the secondary switch to turn off completely before the primary switch activates, minimizing reverse currents through the rectifier switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage and current sensing control circuits are used for synchronous rectification, then the control is effective in DCM and CrCM devices, but the rectifier switch cannot turn off quickly enough in CCM devices due to fast transients
Solution Approach 1:
The patent applies preliminary action by introducing a delay circuit that generates a transient signal before the primary switch turns on. This preliminary transient action on the primary side causes the rectifier switch to turn off in advance, before the fast transient from primary switch turn-on occurs, thereby resolving the timing conflict in CCM operation
2Power
If the primary switch is hard switched into the ON position, then power conversion is achieved, but fast transients are generated that prevent timely rectifier switch turn-off
Solution Approach 1:
The patent applies preliminary anti-action by using the delay circuit to generate a counteracting transient signal before the harmful fast transient occurs. The preliminary transient from the delay circuit causes the rectifier switch to turn off, which counteracts and prevents the harmful reverse currents that would otherwise be generated by the subsequent fast transient from primary switch turn-on
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
The solution effectively reduces reverse currents in the rectifier switch by ensuring the rectifier switch is fully turned off before the primary switch activates, improving synchronous rectification in CCM flyback converters.
Implementation Method 1
turning OFF a rectification switch connected to a secondary coil of the transformer when the transient on the primary coil is transferred to the secondary coil via the transformer
Data Source
AI summary
A flyback converter circuit in accordance with an embodiment of the present application includes a DC input operable to receive a DC voltage from a DC voltage source, a transformer including a primary coil and a secondary coil, a primary switch operable to selectively connect the primary coil to the DC input, a controller operable to provide a control signal to turn the primary switch ON and OFF, wherein the primary coil is connected to the DC input when the primary switch is ON, a delay device operable to delay an ON pulse of the control signal provided to the primary switch such that the primary switch is turned on after a delay of a predetermined period of time and a secondary switch connected in series with a capacitor and controlled by the control signal from the controller, wherein the secondary switch and the capacitor are connected in parallel with the primary switch. The control signal from the controller turns the secondary switch ON during the delay, such that a transient is induced in the primary coil before the primary switch is turned ON.