Primary Side Feedback for Isolated Resonant Converters
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Solution Overview
Problem
Conventional isolated resonant converters using secondary side feedback control face issues with high standby power loss and cost due to the use of opto-couplers, which are affected by operating conditions, and lack current control methods applicable to various application situations.
Innovation Solution
A primary side feedback control method is introduced, omitting the opto-coupler feedback circuit, which estimates output current or voltage by integrating cross voltages through an integrator or voltage boosting circuit, and calculates output current or voltage using specific formulas based on switching periods and inductor currents, applicable to both series resonant converter (SRC) and LLC resonant converter regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If secondary side feedback control using opto-coupler is used, then output voltage feedback can be achieved, but standby power loss increases and cost increases
Solution Approach 1:
The patent extracts and removes the opto-coupler component from the feedback circuit. By using primary side feedback control that monitors current and voltage directly on the primary side, the invention eliminates the need for secondary side feedback through opto-coupler, thereby reducing standby power loss while maintaining feedback functionality
Solution Approach 2:
The patent creates a feedback mechanism that copies the essential feedback function without using the traditional opto-coupler path. By measuring primary side current and voltage and calculating equivalent secondary side parameters, the system replicates the feedback effect without the power-consuming optical coupling component
2Measurement precision
If secondary side feedback control using opto-coupler is used, then output voltage feedback can be achieved, but device cost and volume increase
Solution Approach 1:
The patent removes the opto-coupler and associated secondary side feedback components from the circuit. By implementing primary side feedback control with direct measurement of primary current and voltage, the invention significantly reduces device volume and complexity while eliminating costly optical coupling components
Solution Approach 2:
The patent replicates the feedback function by calculating equivalent secondary side parameters from primary side measurements. This copying approach achieves the same control objective without requiring the physical opto-coupler infrastructure, thereby reducing cost and volume
3Stability of the object's composition
If voltage control method is used to decrease time difference between peak currents, then control stability improves, but inductance value must be increased
Solution Approach 1:
The patent changes the control parameter from voltage-based control to current-based feedback control. By directly measuring and controlling primary side current and using this information to regulate output, the invention achieves control stability without relying on increased inductance values, thereby avoiding the weight penalty
4Device complexity
If primary side feedback control method is used, then feedback circuit cost and volume decrease, but output current and voltage estimation accuracy must be maintained
Solution Approach 1:
The patent creates accurate estimates of secondary side output current and voltage by copying the feedback function through primary side measurements. By measuring primary current and voltage and using transformer ratio relationships, the system calculates equivalent secondary parameters with sufficient accuracy for control purposes
Solution Approach 2:
The patent replaces the physical opto-coupler measurement system with an electrical calculation system. By substituting direct optical feedback with mathematical estimation based on primary side measurements and transformer parameters, the invention achieves the same control function with reduced hardware complexity
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 reduces the cost and volume of isolated resonant converters while enabling accurate estimation of output current and voltage, improving efficiency and adaptability to different application scenarios by eliminating the need for opto-couplers and incorporating voltage and current control methods.
Implementation Method 1
integrating a cross voltage of the current sampling resistor via the integrator to obtain the output current
Implementation Method 2
boosting a cross voltage of the current sampling resistor to have an added level via the voltage boosting circuit
Data Source
AI summary
A method for estimating an output voltage of an isolated resonant converter is disclosed. The proposed method, wherein the isolated resonant converter includes a transformer having an auxiliary winding and a secondary winding, a first output diode electrically connected to the secondary winding in series and a voltage holder coupled to the auxiliary winding, includes: obtaining the output voltageVo=[vaux_dh(t)+VF]·NsNaux-VF,where vaux_dh(t) is an output voltage of the voltage holder, VF is a forward voltage drop of the first output diode, NS is a number of turns of the secondary winding and Naux is a number of turns of the auxiliary winding.