Isolated Switching Converter Secondary Control Circuit for Light Load Efficiency
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Solution Overview
Problem
Traditional isolated switching converters experience power loss and inefficiency during light and no load conditions due to increased currents through the optocoupler components, which negatively impact efficiency.
Innovation Solution
A control method and secondary control circuit that detect light load conditions, set the current through the optocoupler components to zero, and adjust the switching frequency or duty cycle based on the current flowing through the photo-sensitive device to regulate output voltage, thereby improving efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the current through the light emitting device and photo-sensitive device increases to regulate output voltage, then the output voltage regulation is improved, but the power loss increases and efficiency deteriorates under light load conditions
Solution Approach 1:
The patent implements burst mode operation where the switching converter operates in periodic cycles of active switching followed by idle periods. During light load conditions, the converter performs brief switching bursts to maintain output voltage, then enters idle periods where the optocoupler current is reduced to zero, eliminating continuous power loss while still providing voltage regulation through periodic correction
Solution Approach 2:
The patent dynamically changes the operating parameters of the optocoupler based on load conditions. By detecting light load conditions and adjusting the optocoupler current from its normal regulation level down to zero, the system adapts its parameters to match operating conditions, reducing power loss when full regulation capability is not needed
2Reliability
If the switching converter operates continuously to maintain output voltage regulation, then the voltage regulation is improved, but the light load efficiency and no load efficiency deteriorate
Solution Approach 1:
The system transitions from continuous operation to periodic burst mode operation under light load conditions. The converter operates in short active bursts followed by idle periods, maintaining voltage regulation capability while significantly reducing average power consumption and improving light load efficiency
Solution Approach 2:
The patent introduces dynamic operation modes that adapt to load conditions. The switching converter can switch between continuous conduction mode and burst mode based on detected load levels, making the system dynamic rather than static, thereby optimizing efficiency across different operating conditions
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 method significantly enhances light load and no load efficiency by minimizing power loss and maintaining optimal output voltage regulation.
Implementation Method 1
The light emitting device in the optocoupler OP_CO has one terminal coupled to the output voltage Vout through the resistor R2
Implementation Method 2
The photo-sensitive device in the optocoupler OP_CO has one terminal coupled to a voltage Vr (e.g. 2V), and another terminal coupled to the primary reference ground
Data Source
AI summary
An isolated switching converter includes a transformer, a primary circuit, a rectifying circuit and an optocoupler with a photo-sensitive device and a light emitting device, wherein the light emitting device has a first terminal coupled to an output voltage of the switching converter. A method for controlling the switching converter includes: sensing the output voltage and generating a voltage feedback signal; generating an error amplifying signal based on a reference signal and the voltage feedback signal, and providing the error amplifying signal to a second terminal of the light emitting device; disconnecting the error amplifying signal from the second terminal of the light emitting device if the error amplifying signal becomes lower than a first threshold voltage; and reconnecting the error amplifying signal to the second terminal of the light emitting device when the voltage reference signal becomes lower than a second threshold voltage.