DC-DC Converter Valley Skipping for Zero-Voltage Switching
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Solution Overview
Problem
Quasi-resonant flyback converters face challenges in minimizing turn-on losses during switch operation due to limitations in achieving zero-voltage switching (ZVS) across a wide input voltage range, particularly when the reflected output voltage is lower than the DC input voltage.
Innovation Solution
A DC-DC power converter employing a valley skipping mode, where a primary control circuit operates a primary FET in valley skipping mode and transmits a drive signal to a synchronous rectifier drive circuit to turn on the synchronous rectifier during specified resonant voltage valleys, generating a negative current and facilitating ZVS switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If valley switching mode is used to eliminate turn-on losses, then turn-on loss is reduced, but ZVS operation cannot be achieved when reflected output voltage is lower than DC input voltage
Solution Approach 1:
The patent applies dynamics by making the switching strategy adaptive rather than fixed. The controller dynamically selects between valley switching and forced ZVS modes based on real-time operating conditions (input voltage, reflected output voltage). This allows the system to optimize turn-on loss reduction across the entire operating range, not just in specific conditions.
Solution Approach 2:
The patent changes the switching parameter (turn-on timing) based on operating conditions. When reflected output voltage is lower than input voltage, the system transitions from valley switching to forced ZVS, adjusting the gate drive signal timing to ensure ZVS is achieved. This parameter adaptation resolves the contradiction by maintaining loss reduction benefits across all voltage conditions.
2Adaptability or versatility
If forced ZVS is applied to ensure zero-voltage switching, then ZVS operation is achieved across wide input voltage range, but additional gate charge is required extending dead-time
Solution Approach 1:
The patent applies partial forced ZVS only when necessary (when reflected output voltage is lower than input voltage during valley switching). Instead of applying forced ZVS unconditionally, the system uses it selectively to achieve ZVS only in the specific voltage conditions where valley switching fails, thereby minimizing the extension of dead-time while still achieving wide input voltage range ZVS operation.
Solution Approach 2:
The dead-time is dynamically adjusted based on operating conditions. The controller applies forced ZVS gate drive signals only when the voltage relationship indicates valley switching cannot achieve ZVS. This dynamic application minimizes the overall dead-time extension while ensuring ZVS is achieved across the wide input voltage range.
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 effectively reduces turn-on losses and enhances efficiency by allowing zero-voltage switching of the primary FET, even at varying input voltages, by utilizing the valley skipping mode to manage resonant voltage valleys and optimize switching conditions.
Implementation Method 1
During quasi-resonant operation, energy stored in a primary MOSFET drain capacitor (i.e., an equivalent capacitance), resonates through a magnetizing inductance of a transformer
Data Source
AI summary
A DC-DC power converter includes an input, an output, a transformer, a primary field-effect transistor (FET), and a synchronous rectifier. The synchronous rectifier includes a drain that experiences multiple resonant voltage valleys during each dead-time period of the converter. The converter further includes a synchronous rectifier drive circuit configured to turn on and turn off the synchronous rectifier, and a primary control circuit. The primary control circuit is configured to operate the primary FET in a valley skipping mode, and to transmit a drive signal to the synchronous rectifier drive circuit to turn on the synchronous rectifier during a specified one of the multiple resonant voltage valleys to generate a negative current through the synchronous rectifier. Methods of operating a DC-DC power converter are also disclosed.