DC/DC Converter ZVS Range Extension via Varactor Tuning
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Solution Overview
Problem
Existing DC/DC converters operating in quasi-resonant mode face limitations in achieving true zero-voltage switching (ZVS) across a wide range of input voltages, leading to inefficiencies due to energy loss when the secondary reflected voltage is not higher than the input voltage.
Innovation Solution
Incorporating a varactor with voltage-variable capacitance across the transformer, which passively tunes the resonant frequency of the DC/DC converter during a downswing in voltage, accelerating the drain-source voltage downswing and extending the ZVS range by creating a deeper valley for switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a quasi-resonant flyback converter is used with fixed capacitance, then the circuit structure is simple, but the zero-voltage switching range is limited and cannot be achieved for all operating conditions
Solution Approach 1:
The patent applies the dynamics principle by using a varactor diode whose capacitance dynamically changes with voltage during the switching cycle. The varactor is connected in parallel with the primary switch, and its capacitance automatically adjusts based on the voltage across the switch, enabling the resonant frequency to adapt to different operating conditions and extend the ZVS range without adding complex control circuitry
Solution Approach 2:
The patent implements parameter changes by utilizing the voltage-dependent capacitance characteristic of the varactor diode. As the voltage across the primary switch changes during the downswing, the varactor's capacitance changes accordingly, which in turn changes the resonant frequency of the circuit. This dynamic parameter adjustment allows the system to maintain ZVS across a broader input voltage range
2Use of energy by moving object
If the secondary reflected voltage is not higher than the input voltage, then the converter can operate at lower voltages, but energy is wasted as the voltage across the primary switch is re-set when the switch turns on
Solution Approach 1:
The patent converts the harmful effect of leakage inductance energy, which normally causes voltage spikes and energy loss, into a beneficial resonant oscillation. By timing the switch activation to occur during the natural resonant downswing of the voltage (created by the interaction of leakage inductance and varactor capacitance), the energy that would be wasted is instead utilized to achieve zero-voltage switching, eliminating the harmful voltage reset loss
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 increases the ZVS range by at least 30%, allowing the primary switch to be activated at a lower drain-source voltage, thereby reducing energy losses and improving efficiency.
Implementation Method 1
the component has a capacitance that varies with voltage, and wherein during a downswing in voltage across the primary switch the component is passively tuned by a change in voltage across the component that changes the capacitance of the component
Implementation Method 2
which utilizes the parasitic capacitance of the switch, or even an added capacitance, to absorb leakage inductance energy resulting from a leakage inductance of the DC/DC converter transformer
Implementation Method 3
to absorb leakage inductance energy resulting from a leakage inductance of the DC/DC converter transformer
Data Source
AI summary
Method and apparatus for extending a zero voltage switching (ZVS) range during power conversion. In one embodiment, the apparatus comprises a DC/DC converter, operated in a quasi-resonant mode, comprising a transformer; a primary switch, coupled to a primary winding of the transformer, for controlling current flow through the primary winding; and a component coupled to the transformer, wherein the component has a capacitance that varies with voltage across the component, and wherein during a downswing in voltage across the primary switch the component is passively tuned by a change in the voltage across the component that changes the capacitance of the component, and wherein the passive tuning of the component causes a resonant frequency of the DC/DC converter to change, and wherein the change in the resonant frequency causes the downswing to accelerate.