Flyback Converter Switching Using Secondary Reverse Current for ZVS
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Solution Overview
Problem
Active clamp circuits in active clamp flyback power converters increase component count, cost, and complexity, while also increasing the complexity and cost of the controller, which hinders the efficient achievement of zero voltage switching (ZVS).
Innovation Solution
A method and controller for a flyback power converter that adjusts the duration of secondary switch activation based on signals indicative of negative current, allowing for reduced switching losses and increased efficiency without the need for an active clamp circuit, by enabling reverse current in the secondary winding to discharge parasitic capacitance in the primary switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an active clamp circuit is used to achieve zero voltage switching, then switching losses are reduced and efficiency is increased, but component count and cost increase
Solution Approach 1:
The invention extracts and eliminates the active clamp circuit from the conventional ACF topology, replacing it with a simplified controller that achieves ZVS by adjusting the primary switch on-time based on negative current sensing. This removes the additional components (clamp switch, clamp capacitor, clamp diode) while maintaining the ZVS benefit.
Solution Approach 2:
The invention changes the control parameter from fixed duty cycle to dynamic on-time adjustment based on negative current levels. By varying the primary switch conduction time in response to sensed negative current, the system achieves ZVS without requiring active clamp components.
2Loss of energy
If an active clamp circuit is used to achieve zero voltage switching, then switching losses are reduced and efficiency is increased, but controller complexity and cost increase
Solution Approach 1:
The invention extracts and removes the complex active clamp control logic from the controller, replacing it with a simpler control scheme that only requires sensing negative current and adjusting the primary switch on-time accordingly. This simplifies the controller while maintaining ZVS capability.
Solution Approach 2:
The system uses the naturally occurring negative current in the transformer to achieve ZVS, eliminating the need for separate active clamp control circuits. The controller simply responds to the existing negative current rather than actively creating it through additional switching elements.
3Reliability
If the duration of primary switch activation is extended to ensure sufficient negative current, then ZVS is achieved, but switching frequency decreases
Solution Approach 1:
The invention implements dynamic adjustment of the primary switch on-time based on real-time negative current sensing. Rather than using a fixed extended duration, the controller continuously adapts the conduction time to match the actual negative current available, optimizing both ZVS reliability and switching frequency.
Solution Approach 2:
The system incorporates feedback from negative current sensing to control the primary switch duration. The sensed negative current provides real-time information that the controller uses to adjust the on-time, creating a closed-loop system that maintains ZVS while maximizing switching frequency.
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 approach reduces switching losses and increases efficiency by dynamically adjusting switching frequency in response to negative current levels, achieving ZVS without the additional components and complexity of active clamp circuits.
Implementation Method 1
discharging capacitance of the primary switch by a negative current in the primary winding responsive to the negative current in the secondary winding
Data Source
AI summary
Reduced voltage switching of the primary switch. At least one example is a method comprising: activating, during a first switching period, a primary switch coupled to a primary winding of a transformer of a flyback topology, the activating induces a positive current in the primary winding; deactivating the primary switch and activating a secondary switch coupled to the secondary of the transformer, the activating the secondary switch during the first switching period and for a duration selected based on a signal indicative of negative current from a prior switching period, and the activating the secondary switch results in a positive current through the secondary winding followed by a negative current through the secondary winding; and discharging capacitance of the primary switch by a negative current in the primary winding responsive to the negative current in the secondary winding.