Flyback Converter ZVS Control via Secondary Sampling
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Solution Overview
Problem
Existing flyback power converters face challenges in precisely achieving zero voltage switching (ZVS) due to difficulties in determining the optimal ZVS period, which affects power conversion efficiency.
Innovation Solution
A flyback power converter system that includes a primary side switch, a synchronous rectification (SR) switch, and controller circuits to generate switching signals for precise control of the ZVS period, using sample-and-hold and level comparison circuits to determine the ZVS period based on input and output voltages, ensuring accurate zero voltage switching of the primary side switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the ZVS period is determined using conventional methods, then the circuit structure remains simple, but the power conversion efficiency cannot be optimized due to imprecise ZVS control
Solution Approach 1:
The patent introduces an intermediary mechanism (the secondary side controller sampling the SR switch voltage and generating ZVS pulse width control) to indirectly achieve precise ZVS control without requiring complex primary side measurements. This intermediary approach enables accurate energy optimization while keeping the overall system architecture manageable.
Solution Approach 2:
The patent implements feedback by having the secondary side controller sample the voltage of the SR switch during the dead time period and use this sampled voltage information to determine the appropriate ZVS pulse width. This feedback loop enables dynamic adjustment of the ZVS period to optimize power conversion efficiency across different operating conditions.
2Reliability
If the ZVS period is extended to ensure zero voltage switching, then the primary side switch achieves ZVS, but the SR switch conduction time increases causing additional energy loss
Solution Approach 1:
The patent makes the ZVS pulse width dynamic by determining it based on the sampled SR switch voltage, which varies with input voltage conditions. This dynamic adjustment allows the system to achieve the minimum necessary ZVS duration for reliability while minimizing excess conduction time and associated energy losses.
Solution Approach 2:
The patent changes the parameter of ZVS pulse width dynamically based on the sampled voltage level. By adjusting this parameter according to actual operating conditions rather than using a fixed duration, the system optimizes the balance between achieving reliable ZVS and minimizing SR switch conduction losses.
3Measurement precision
If the ZVS period is determined without sampling SR switch voltage, then the control circuit is simpler, but the ZVS control precision is insufficient
Solution Approach 1:
The patent uses the SR switch voltage as an intermediary measurement that provides precise information about the operating conditions. By sampling this voltage during the dead time period, the system achieves accurate ZVS control without requiring direct measurement of other parameters that would complicate the control circuit.
Solution Approach 2:
The patent leverages the existing SR switch and its voltage characteristics to provide the measurement information needed for ZVS control. The SR switch's own voltage waveform during the dead time period contains the necessary information, eliminating the need for separate measurement circuits and reducing overall system complexity.
Data Source
AI summary
A flyback power converter includes a primary side controller circuit for controlling a primary side switch; and a secondary side controller circuit for generating an SR (Synchronous Rectification) signal to control an SR switch. The SR signal includes an SR pulse and a ZVS (Zero Voltage Switching) pulse. The SR pulse controls the SR switch for synchronous rectification at the secondary side. The secondary side controller circuit samples and holds a voltage at a first end of the SR switch as a first voltage at a timing between the end of the ZVS pulse and the beginning of the SR pulse, and determines a length of the ZVS pulse so as to control the SR switch to be conductive for a ZVS time period, whereby the primary side switch achieves ZVS. The first voltage is proportional to an input voltage.