SMPS Driving Circuit Preventing Switch False Triggering
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Solution Overview
Problem
In switching mode power supplies (SMPS), false triggering of the switch occurs due to ripple in the zero-crossing detecting signal, leading to uncontrolled switching and increased current through the primary winding, as the signal can easily reach the zero-crossing threshold, causing the switch to turn on and off repeatedly.
Innovation Solution
A driving circuit comprising a peak detecting circuit, a delay circuit, and a switching control circuit that detects the peak of the input signal, times a delay period, and starts the on and off switching operations of the first switch only after the delay expires, preventing false triggering by ensuring the zero-crossing detecting signal does not reach the threshold due to ripple fluctuations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If zero-crossing detecting signal is used to control switch turning on, then switch can be turned on at appropriate timing, but false triggering occurs due to ripple causing uncontrolled switching
Solution Approach 1:
The patent applies preliminary action by detecting the peak of the input signal in advance and generating a delay signal before the switching operation begins. This delay signal is generated based on the timing relationship between the input signal peak and the expected switching moment, proactively preventing false triggering before it can occur by ensuring the switch is not turned on during periods when ripple could cause erroneous zero-crossing detection
Solution Approach 2:
The patent introduces a delay signal as an intermediary element between the input signal detection and the switch control. This delay signal acts as a mediator that filters out the harmful effect of ripple by timing the switching operation to occur only after the delay period has elapsed, thus preventing false triggering while maintaining reliable control
2Productivity
If switch is turned on when zero-crossing detecting signal reaches threshold, then power conversion can proceed, but current through primary winding increases uncontrollably due to repeated on-off cycling
Solution Approach 1:
The patent applies preliminary action by establishing the timing relationship between the input signal peak and the delay signal generation before switching operations begin. This ensures that the switch will only be turned on after the delay period has elapsed, preventing the uncontrolled current increase that would result from repeated false triggering while maintaining efficient power conversion
Solution Approach 2:
The patent uses feedback by continuously monitoring the input signal and adjusting the delay signal timing based on the detected peak position. This feedback mechanism ensures that the switching operation is synchronized with the input signal characteristics, maintaining stable current through the primary winding while preserving power conversion efficiency
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 effectively prevents false triggering of the switch, maintaining controlled switching operations and stabilizing the current through the primary winding, thereby preventing uncontrolled increases and ensuring efficient conversion of the input signal to the output signal.
Implementation Method 1
an auxiliary winding LA coupled to the primary winding LP to sense the current IL flowing through the primary winding LP and then generates a zero-crossing detecting signal VZCD based on the current IL
Data Source
AI summary
A switching mode power supply preventing a first switch from being falsely triggered. The switching mode power supply detects a peak of an input signal and starts timing a period of time since the arrival of the peak of the input signal is detected. The first switch starts performing the on and off switching operations when the period of time expires.