AC Detection Circuit for Immediate AC/DC Converter Shutdown
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional AC/DC converter control circuits delay shutdown of the secondary-side load system due to waiting for Xcap discharge after AC input cutoff, especially when the VH terminal voltage is high, which can lead to incomplete data saving and extended reset times.
Innovation Solution
A control circuit for AC/DC converters that includes an AC detection circuit generating a pulse-shaped AC detection signal and an enable signal conversion circuit, allowing immediate shutdown of the secondary-side load without waiting for Xcap discharge, by setting a timer for the HIGH level period of the AC detection signal and using a discharge control timer to manage X capacitor discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the conventional AC detection circuit waits for Xcap discharge after AC input cutoff, then the secondary-side shutdown process can be initiated safely, but the shutdown time is delayed especially when VH terminal voltage is high
Solution Approach 1:
The patent applies preliminary action by detecting AC input cutoff immediately through the AC detection circuit and generating an AC detection signal, then using an enable signal conversion circuit to control the secondary-side shutdown process without waiting for Xcap discharge. This allows the shutdown sequence to start immediately when AC input is detected as cutoff, rather than waiting for voltage decay.
Solution Approach 2:
The patent segments the shutdown control into two independent parts: (1) AC detection circuit that detects input cutoff and generates AC detection signal, and (2) enable signal conversion circuit that converts this signal to control secondary-side shutdown. This segmentation allows the detection and shutdown initiation to occur independently of the Xcap discharge timing.
2Difficulty of detecting and measuring
If the AC detection circuit uses a threshold comparison method, then it can detect AC voltage presence, but the detection signal remains high during voltage decay causing delayed shutdown initiation
Solution Approach 1:
The patent applies dynamics by making the AC detection signal pulse-shaped with a defined HIGH level period instead of a static threshold comparison output. The enable signal conversion circuit dynamically controls the signal transition, allowing the detection system to respond immediately to AC cutoff while providing a controlled signal duration for proper shutdown sequencing.
Data Source
AI summary
A control circuit for an AC/DC converter includes an AC detection circuit that periodically determines from a change in the AC input voltage whether AC voltage is being input and, upon determining that AC voltage is being input, outputs an AC detection signal that takes a HIGH level only for a prescribed duration; and an enable signal conversion circuit that filters the AC detection signal to generate the enable signal that is in a HIGH state when the AC detection signal is in the HIGH level and that becomes the LOW state after a prescribed time has passed since the AC detection signal becomes a LOW level unless the AC detection signal rises to the HIGH level again, thereby producing the enable signal that is more responsive.