Primary-Side LLC Control Circuit Eliminates Optocouplers
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Solution Overview
Problem
Conventional LLC resonant circuits require numerous peripheral devices and optocouplers for controlling output current, leading to increased size and hindering system integration.
Innovation Solution
A control method that superimposes a bias voltage on the sampling resistor to generate a control signal based on the absolute value of its voltage and current reference signal, eliminating the need for optocouplers by controlling the switching circuit using the voltage of the sampling resistor, thereby reducing the number of peripheral devices required.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the output current is controlled based on sampling of secondary current using conventional technology, then the control is accurate, but many peripheral devices and optocouplers are required resulting in large circuit size
Solution Approach 1:
The patent extracts the current sampling function from the secondary side to the primary side by utilizing the voltage across the sampling resistor directly on the primary side. This eliminates the need for optocouplers and secondary side sampling circuits, reducing circuit size while maintaining control accuracy through direct voltage measurement and processing.
Solution Approach 2:
The patent introduces an intermediary processing stage that converts the voltage signal from the sampling resistor through absolute value processing and bias voltage addition. This intermediary processing enables the primary side control circuit to accurately represent and control the output current without requiring direct secondary side sampling, thus reducing peripheral devices while preserving measurement precision.
2Ease of operation
If many peripheral devices and optocouplers are used for controlling output current, then the control function is complete, but the LLC resonant circuit has large size and system integration is hindered
Solution Approach 1:
The patent merges the current sampling function with the existing primary side voltage detection circuitry. By using the voltage across the sampling resistor directly on the primary side and processing it through absolute value and bias voltage stages, the control function is maintained while eliminating separate optocoupler circuits and secondary sampling components, thereby improving system integration capability.
Solution Approach 2:
The primary side control circuit is designed to perform multiple functions: voltage detection, current sampling representation, absolute value processing, and control signal generation. This multi-functional approach eliminates the need for separate dedicated circuits for each function, reducing the overall number of peripheral devices while maintaining complete control functionality and enhancing system integration.
3Device complexity
If the voltage of sampling resistor is used directly for control, then the circuit is simplified, but the voltage may be negative requiring additional processing
Solution Approach 1:
The patent applies preliminary action by adding a bias voltage to the sampled voltage signal before it is used for control. This bias voltage ensures that the signal remains positive throughout the processing chain, preventing negative voltage issues while maintaining circuit simplicity. The absolute value processing stage also serves as preliminary action to ensure signal positivity.
Solution Approach 2:
The patent changes the parameter of the voltage signal by adding a bias voltage component. This parameter change transforms the potentially negative sampling voltage into a always-positive signal suitable for straightforward control processing. This simple parameter modification avoids complex circuitry while resolving the negative voltage issue.
Data Source
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AI summary
A control circuit, a control method and a power converter are provided. The control circuit is applied to a power converter. The power converter includes a switching circuit including at least one half-bridge, a transformer including a primary winding and a secondary winding, a resonant inductor and a resonant capacitor which are connected in series with the primary winding to form a resonant module, and a sampling resistor connected in series with the resonant module or connected in series in the resonant module. The control circuit generates a control signal based on an absolute value of a voltage of the sampling resistor and a current reference signal to control an operation state of the switching circuit to adjust an output current of the power converter. The current reference signal represents an expected value of the output current of the power converter.