Flyback Converter Control Circuit With Blanking for Valley-Jump Noise
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Solution Overview
Problem
Quasi-resonant flyback converters face challenges with variable switching frequency due to changing operative conditions, leading to increased switching losses and difficulties in meeting efficiency recommendations, and they can generate audible noise through valley-jump phenomena.
Innovation Solution
A control circuit for flyback converters that includes a blanking circuit to adjust the switching frequency by delaying the switch-on signal based on a blanking time interval, preventing excessive switching frequency and reducing valley-jump occurrences, thereby maintaining efficient operation and minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If quasi-resonant flyback converters operate with variable switching frequency to maintain efficient operation, then energy efficiency is improved, but switching losses increase and audible noise is generated due to valley-jump phenomena
Solution Approach 1:
The patent implements periodic action by using a blanking circuit to introduce a fixed time interval (blanking period) between switching cycles. This periodic blanking action stabilizes the switching frequency by preventing excessive switching operations, thereby reducing switching losses and audible noise while maintaining energy efficiency through controlled periodic operation rather than uncontrolled variable frequency switching.
2Use of energy by moving object
If quasi-resonant flyback converters operate with variable switching frequency, then energy efficiency is improved, but audible noise is generated through valley-jump phenomena
Solution Approach 1:
The blanking circuit introduces a periodic time interval that regularizes the switching pattern, preventing the irregular valley-jump phenomena that cause audible noise. By enforcing a consistent blanking period, the circuit maintains energy efficiency while eliminating the harmful audible noise through periodic stabilization of the switching frequency.
3Loss of energy
If blanking time interval is increased to limit switching frequency, then switching losses are reduced, but switch-on delay increases
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the blanking time interval based on operating conditions. The blanking circuit is configured with specific time parameters (e.g., 10-100 microseconds) that are optimized to reduce switching losses while minimizing switch-on delay. This parameter optimization allows the system to achieve energy loss reduction without excessive time penalty.
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 limits the switching frequency and reduces audible noise, enhancing the efficiency and reliability of quasi-resonant flyback converters by stabilizing the switching pattern and reducing energy losses.
Implementation Method 1
a control circuit for a flyback converter... configured to generate a drive signal for the electronic switch... by setting the drive signal to a first logic level for a switch-on duration for closing the electronic switch and a second logic level for a switch-off duration for opening the electronic switch
Implementation Method 2
A control circuit for flyback converters that includes a blanking circuit to adjust the switching frequency by delaying the switch-on signal based on a blanking time interval
Implementation Method 3
A flyback converter comprises a transformer T comprising a primary winding T1 and a secondary winding T2... During the interval TON, when the switch SW is closed... the primary current Ipri and the magnetic flux in the transformer T increases, thereby storing energy in the transformer T
Implementation Method 4
the electronic switch SW has associated a parasitic capacitance CSW connected in parallel with the electronic switch SW... the current provided by the leakage inductance LS of the transformer T will charge this capacitance CSW
Implementation Method 5
a leakage inductance may be modelled via an inductance LS connected in series with the primary winding T1... the primary current Ipri continues to flow in the primary side T1 due to the leakage inductance LS
Data Source
AI summary
A control circuit for a driving an electronic switch associated with a switching node of a flyback converter includes a comparison circuit configured to generate a switch-off signal by comparing a current measurement signal with a current measurement threshold signal. A valley detection circuit is configured to generate a trigger in a trigger signal when a valley signal indicates a valley in a voltage at the switching node of the flyback converter, and a blanking circuit is configured to generate a switch-on signal by combining the trigger signal with a timer signal provide by a timer circuit. The timer signal indicates whether a blanking time-interval has elapsed.