Knee Detection Circuit for Isolated Load Current Stabilization
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Solution Overview
Problem
Conventional isolated load circuits experience unstable average current due to voltage oscillating waveforms generated at the zero crossing detection end when the switch is turned off, leading to noise interference from the primary side winding.
Innovation Solution
A circuit for detecting the knee of a waveform is introduced, utilizing a filter, two comparators, a time recorder, and a knee detecting module to precisely detect the knee of the voltage oscillating waveform and total oscillating time, which are used to control the on/off signal of the switch and stabilize the average output current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the voltage oscillating waveform is detected at the ZCD end to determine the on/off time of the switch, then the average current can be controlled, but the noise from the primary side winding and switch turns off causes voltage oscillation and instability in the average current
Solution Approach 1:
The patent introduces an intermediary circuit (including a capacitor and resistor) between the ZCD end and the knee detection point. This intermediary circuit filters out the noise and voltage oscillation caused by the primary side winding and switch turns off, providing a stable voltage waveform for accurate knee detection while maintaining the ability to control average current.
Solution Approach 2:
The patent replaces the conventional mechanical switching control with an electronic knee detection mechanism. By detecting the knee point of the voltage waveform and using it to generate the on/off signal, the system eliminates the need for direct mechanical switching control, thereby reducing noise and improving current stability.
2Productivity
If the voltage oscillating waveform is used to control the switch on/off time, then the average current can be regulated, but the oscillation causes instability in the feedback voltage
Solution Approach 1:
The intermediary circuit (capacitor and resistor) acts as a mediator between the oscillating voltage waveform and the feedback voltage. It smooths out the oscillations and provides a stable feedback voltage that maintains current regulation capability while eliminating voltage instability in the feedback signal.
Solution Approach 2:
The patent applies preliminary action by pre-filtering the voltage waveform through the intermediary circuit before it reaches the feedback end. This preliminary filtering action removes the oscillations and noise that would otherwise cause feedback voltage instability, ensuring stable operation throughout the switching cycle.
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
The solution effectively stabilizes the average current flowing through the operating element by accurately calculating the total oscillating time and using it to control the switch, thereby resolving the instability issue in conventional circuits.
Implementation Method 1
The filter is electrically connected to the auxiliary winding for receiving and filtering the voltage oscillating waveform to generate a filtered voltage
Implementation Method 2
The first comparator has a first comparing input, a second comparing input, and a first comparing output. The first comparing input is electrically connected to the filter through a first switch for receiving at least a first reference voltage which is a difference between the filtered voltage and a first preset voltage
Implementation Method 3
The time recorder is electrically connected to the first comparing output of the first comparator, the second comparing output of the second comparator, the first switch, and the second switch for recording the total oscillating time
Implementation Method 4
when the switch PA22 is turned off, the energy store in the primary side winding PA211 would be transferred to the secondary side winding PA212 and the auxiliary winding PA213 of the isolated transformer PA21 making use of Faraday's law
Data Source
AI summary
A circuit for detecting a knee of waveform is disclosed in the present invention. The circuit detects the knee and a total oscillation time of a voltage waveform as a load switch of load circuit is turned off. In the circuit, a filter filters the voltage waveform to transmit a reference voltage to a first and a second comparator. When the first and the second comparator determine that the voltage waveform achieves a sum of the reference voltage and a set voltage, the first and the second comparator transmit a first and a second signal to a knee detection module. When the knee detection module receives the first signal rather than the second signal in an oscillation time, or receives the second signal rather than the first signal in the oscillation time, the knee detection module records the knee and trigger a time recorder computes the total oscillation time.