Flyback Converter Secondary-Side Controller Settling Time Compensation
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Solution Overview
Problem
Conventional secondary-side controllers for flyback converters face challenges in accurately determining the turn-on timing of the secondary-side SR power MOSFET due to settling time variations, especially at high frequencies and high input line conditions, leading to inefficient operation and errors in energy transfer.
Innovation Solution
The proposed solution involves a secondary-side controller that synchronously switches the secondary-side switch with the primary-side switch, determines the off time based on the reflected input voltage measured at the secondary-side winding, and accounts for settling time to minimize its effect on the off time, ensuring accurate energy transfer and efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional secondary-side controllers are used without high voltage technology, then device complexity is reduced, but measurement precision deteriorates due to settling time variation causing errors in reflected input voltage measurement
Solution Approach 1:
The patent applies preliminary action by measuring the reflected input voltage after a predetermined settling time delay. Instead of using the voltage immediately after switching, the controller waits for the settling time to elapse before sampling the voltage value. This preliminary waiting period ensures the measurement is taken when the voltage has stabilized, eliminating settling time variation effects without requiring complex high-voltage technology or additional circuitry.
2Device complexity
If settling time is not accounted for in off time calculation, then device complexity is reduced, but productivity deteriorates due to inefficient energy transfer and operation
Solution Approach 1:
The patent uses preliminary action by pre-determining the settling time value and incorporating it into the off-time calculation of the secondary-side switch. The controller calculates off-time as the sum of the reflected input voltage measurement time and the predetermined settling time. This ensures the secondary-side switch remains on long enough for the voltage to settle, maximizing energy transfer efficiency without requiring complex adaptive control mechanisms.
3Measurement precision
If high voltage technology is used for SR sense pin, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent applies the principle of using simpler, lower-cost components by replacing the high-voltage SR sense pin with a standard voltage divider circuit and ADC. Instead of requiring expensive high-voltage tolerant chip technology, the solution uses ordinary low-voltage components that can accurately measure the reflected input voltage after the settling time delay, significantly reducing device complexity and manufacturing cost while maintaining measurement precision.
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 compensates for settling time errors, leading to more accurate turn-on and turn-off timing of the secondary-side switch, thereby improving the efficiency and accuracy of energy transfer in flyback converters, even under high-frequency and high-input-line conditions.
Implementation Method 1
The transformer is used to store energy during ON periods of the primary switch, and provides isolation between the input voltage source and the output voltage
Implementation Method 2
determining an off time of the secondary-side switch based on a reflected input voltage measured at the secondary-side winding when the primary-side switch is on
Data Source
AI summary
A flyback converter includes a primary-side switch connected to a primary-side winding of a transformer and a secondary-side switch connected to a secondary-side winding of the transformer. The flyback converter is operated by controlling the primary-side switch to store energy in the transformer during ON periods of the primary-side switch, switching on the secondary-side switch synchronously with switching off the primary-side switch to transfer energy from the transformer to the secondary side, determining an off time of the secondary-side switch based on a reflected input voltage measured at the secondary-side winding when the primary-side switch is on, accounting for a settling time of the reflected input voltage when determining the off time of the secondary-side switch so that the settling time has little or no effect on the off time, and switching off the secondary-side switch based on the off time.