Secondary-Side Controller for USB-PD AC-DC Converters
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Solution Overview
Problem
Existing AC-DC converters with secondary-side control and SR-sense architecture face challenges in reducing cost and complexity while maintaining efficiency, particularly in accurately detecting valley voltages, leading to increased size, complexity, and cost due to the need for high-voltage FETs and external clamping circuits.
Innovation Solution
The implementation of a secondary-side controller with a single SR-sense terminal and a voltage divider circuit, including an active diode and internal resistive element, enables undivided sensing signals and reduces power loss by disabling the internal resistive element during negative-sensing and zero-crossing detection, allowing accurate valley detection and improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If external clamping circuits are used to clip the input to the secondary-side controller, then high-voltage protection is achieved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the voltage clipping function from external discrete components and integrates it directly into the secondary-side controller IC. The internal resistive element and active diode are built into the controller, eliminating the need for external clamping circuits and reducing overall device complexity while maintaining high-voltage protection capability.
Solution Approach 2:
The patent combines multiple functions into the secondary-side controller IC: voltage sensing, voltage clipping/protection, and synchronous rectifier control. By merging the clamping circuit functionality into the controller itself, the design reduces external components and simplifies the overall system architecture.
2Strength
If high-voltage FETs are used on the SR_DRAIN node, then voltage handling capability is improved, but device size and cost increase
Solution Approach 1:
The patent introduces an internal resistive element as an intermediary between the high-voltage SR_DRAIN node and the low-voltage secondary-side controller. This resistive element acts as a voltage divider and protection mechanism, allowing the use of standard low-voltage FETs and ICs while still handling high input voltages up to 230V AC.
3Ease of operation
If the internal resistive element is always enabled, then voltage sensing is simplified, but power loss increases during detach condition
Solution Approach 1:
The patent makes the internal resistive element dynamic by enabling it only when needed (during attach condition with USB device connected) and disabling it during detach condition. The controller monitors the presence of a USB device and adjusts the resistive element's state accordingly, optimizing the balance between sensing accuracy and power consumption.
Solution Approach 2:
The patent implements periodic or conditional activation of the internal resistive element based on USB device detection. The resistive element is enabled periodically when a device is attached and disabled when detached, creating a dynamic power management scheme that reduces energy loss during idle periods.
4Measurement precision
If voltage divider is always active, then voltage sensing accuracy is maintained, but power consumption increases
Solution Approach 1:
The patent dynamically controls the voltage divider circuit based on operational conditions. The internal resistive element is enabled only when voltage sensing is required (during attach condition) and disabled during detach condition, optimizing the trade-off between sensing accuracy and power consumption.
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 solution reduces the size and complexity of AC-DC converters, enhances efficiency by enabling accurate valley detection, and decreases the cost of manufacturing by using standard low-voltage technologies, thereby improving the utility of compact power converters.
Implementation Method 1
a voltage divider circuit coupled to the single SR-sense terminal that is configured to provide signals to a sensing circuit
Implementation Method 2
the active diode is configured to control the switch to enable or disable the internal resistive element based on a comparison result of a voltage at the single SR-SNS terminal and a reference voltage
Implementation Method 3
based on a comparison result of a voltage at the single SR-SNS terminal and a reference voltage
Data Source
AI summary
A secondary-side controller for an AC-DC converter that has a single synchronous rectifier sensing (SR_SNS) terminal, coupled to a synchronous rectifier (SR) of the AC-DC converter, and a voltage divider circuit coupled to the single SR_SNS terminal configured to provide signals to a sensing circuit. The voltage divider includes an active diode, an internal resistive element, and a switch, in which the active diode is configured to control the switch to enable or disable the internal resistive element based on a comparison result of a voltage at the single SR_SNS terminal and a reference voltage.