Flyback Converter Active Clamp Control for Load Adaptation
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Solution Overview
Problem
Traditional active-clamp circuits for flyback power converters experience higher power loss at light loads due to high circulated current, limiting efficiency and requiring larger transformer sizes due to lower switching frequencies.
Innovation Solution
A control circuit for flyback power converters that recycles leakage inductance energy through an active-clamp mechanism, allowing for higher switching frequencies and improved efficiency by generating a switching signal and an active-clamp signal based on transformer demagnetization time, with the active-clamp signal being enabled only after the switching signal is disabled, and having fewer pulses during light loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If traditional active-clamp circuit is used for flyback power converter, then heavy load efficiency is improved, but light load efficiency deteriorates due to high circulated current
Solution Approach 1:
The patent implements dynamic control of the active-clamp circuit by adjusting the pulse number of active-clamp signals based on load conditions. The controller generates fewer active-clamp pulses during light load conditions and more pulses during heavy load conditions, allowing the circuit to adapt dynamically to varying load requirements and optimize efficiency across all operating conditions
Solution Approach 2:
The patent changes the operational parameters of the active-clamp circuit by varying the number of active-clamp pulses according to load conditions. This parameter adjustment enables the circuit to reduce circulated current during light loads while maintaining effective clamp operation during heavy loads, resolving the efficiency trade-off
2Speed
If traditional active-clamp circuit operates at lower switching frequency, then transformer size increases, but switching frequency cannot be increased due to high circulated current at light load
Solution Approach 1:
The patent enables dynamic switching frequency adjustment by controlling the number of active-clamp pulses. During light load conditions, the reduced pulse number allows the circuit to operate at higher switching frequencies without excessive circulated current, thereby reducing transformer size while maintaining efficiency
3Productivity
If active-clamp signal pulse number equals switching signal pulse number, then heavy load efficiency is optimized, but light load efficiency deteriorates
Solution Approach 1:
The patent applies partial action by generating fewer active-clamp pulses than switching pulses during light load conditions. This partial activation of the active-clamp circuit reduces circulated current and power loss during light loads, while full activation is maintained during heavy loads to optimize efficiency
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
The solution achieves high efficiency across both heavy and light loads by recycling transformer leakage inductance energy, enabling operation at higher switching frequencies and reducing transformer size, thus improving power converter performance.
Implementation Method 1
a transformer (10) having a primary winding (NP) and a secondary winding (NS)... the primary winding (NP) coupled to receive an input voltage (VIN)... the secondary winding (NS) coupled to provide an output voltage (VO)
Implementation Method 2
recycling the leakage inductance's energy of the transformer (10)... generated in response to a demagnetizing time of the transformer (10)
Data Source
AI summary
A control circuit of a flyback power converter according to the present invention comprises a low-side transistor, an active-clamper, a high-side drive circuit, and a controller. The low-side transistor is coupled to switch a transformer. The active-clamper is coupled in parallel with the transformer. The high-side drive circuit is coupled to drive the active-clamper. The controller generates a switching signal and an active-clamp signal. The switching signal is coupled to drive the low-side transistor. The switching signal is generated in accordance with a feedback signal for regulating an output of the flyback power converter. The active-clamp signal is coupled to control the high-side drive circuit and the active-clamper. The active-clamp signal is generated in response to a demagnetizing time of the transformer. The pulse number of the active-clamp signal is less than the pulse number of the switching signal in a light load condition.