Power Converter Control Circuit Using Dual Clocks for Accurate Overpower Detection
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Solution Overview
Problem
Conventional methods for determining abnormal output power in power converters fail to accurately identify surges in light-load modes and are susceptible to interference from transient variations, leading to delayed shutdown and potential damage.
Innovation Solution
A control circuit comprising a switch circuit, a first comparator, and an overpower protecting circuit with a second comparator and timer, using a feedback signal from a capacitor to stabilize voltage and accurately count duration time, independent of the clock frequency for switching the power switch, ensuring timely shutdown even under load changes and interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the clock frequency is decreased in light-load mode to reduce switching loss, then energy efficiency is improved, but the timer cannot accurately count the duration time because it uses the same clock
Solution Approach 1:
The patent divides the clock system into two independent parts: a first clock for controlling power switch switching frequency and a second clock for timer duration counting. This segmentation allows each clock to operate independently - the first clock can be adjusted for energy efficiency while the second clock maintains accurate time measurement regardless of load conditions.
Solution Approach 2:
The patent introduces a second clock as an intermediary element that mediates between the timing function and the first clock. This second clock specifically serves the timer circuit, providing a stable time base that is not affected by the variable frequency of the first clock, thereby ensuring accurate duration measurement.
2Device complexity
If the timer counts duration time based on clock pulses, then time measurement is simplified, but the counting becomes inaccurate when clock period changes due to load variations
Solution Approach 1:
The patent segments the time measurement function from the power control function by providing a dedicated second clock for the timer. This separate time measurement mechanism maintains simplicity while ensuring accuracy, as the second clock operates independently of load-induced frequency changes in the first clock.
3Speed
If the sensing signal is used directly for duration counting, then real-time response to output power is achieved, but transient interference causes repeated counting and delayed shutdown
Solution Approach 1:
The patent applies preliminary filtering action by using a capacitor to smooth the feedback signal before it reaches the timer. This preprocessing step removes transient interference in advance, allowing the timer to accurately count only genuine abnormal conditions without being triggered by temporary fluctuations.
Solution Approach 2:
The patent implements feedback smoothing through a capacitor connected to the feedback signal. The capacitor provides negative feedback that filters out transient variations, creating a stable signal for duration counting while maintaining the ability to detect sustained abnormal conditions.
Data Source
AI summary
A feedback signal stabilized by a capacitor and related to an output voltage of a power converter is used to acquire the output power information of the power converter, and a control circuit uses a second clock not related to the switching frequency of the power converter to count a duration time of the feedback signal being higher than a threshold. When the duration time is higher than a preset time, an abnormal output power of the power converter is distinguished and the power converter will be turned off. The feedback signal will not vary severely even if the output terminal of the power converter is interfered, and the counted duration time will not be influenced when the switching frequency is changing caused by a load changing.