Synchronous Buck Converter Control for Stable LED Negative Current
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Solution Overview
Problem
There is a delay between the controller issuing a command to interrupt the current flow in synchronous buck converters for LED applications, leading to incorrect negative current peaks, which vary with the operation state of the LED load, causing inefficiencies.
Innovation Solution
A synchronous buck converter with a control circuitry that adapts the threshold value for switching off the low side switch based on feedback signals from the LED load, including LED voltage and current, to ensure constant negative current values, even at varying load conditions, using ICs like ASICs and microcontrollers to implement this adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed threshold value is used for switching off the low side switch, then the control circuit operation is simple, but the negative current peak becomes incorrect and varies with LED load conditions
Solution Approach 1:
The patent applies dynamics by making the threshold value adaptive rather than fixed. The control circuitry dynamically adjusts the threshold value based on feedback signals from the LED load (LED current and/or voltage) to compensate for the delay between issuing the switching-off command and the actual interruption of current flow. This ensures the negative current peak remains accurate across varying load conditions while maintaining reasonable control complexity.
Solution Approach 2:
The patent implements feedback by using LED current and/or voltage feedback signals to adapt the threshold value. The control circuitry continuously monitors the LED load conditions and adjusts the threshold value accordingly, creating a closed-loop control system that maintains accurate negative current peaks despite the inherent switching delay.
2Manufacturing precision
If the threshold value is adapted based on LED feedback signals, then the negative current peak accuracy is improved, but the device complexity increases
Solution Approach 1:
The patent applies parameter changes by adapting the threshold value parameter based on LED feedback signals. Instead of changing the physical structure of the control circuitry, the solution modifies the operational parameter (threshold value) dynamically based on LED current and/or voltage measurements, achieving accurate negative current peaks through parameter adaptation rather than structural complexity.
Data Source
Figure 1
Figure 2a~3
AI summary
A synchronous buck converter for supplying a LED load comprises: - a high side switch and a low side switch connected in series, - an inductor connected to the midpoint of these switches, and - a control circuitry controlling the alternate switching operation of the two switches, wherein the switches are controlled such that there are time periods in which a negative current is flowing through said low side switch, wherein the control circuitry is supplied with a feedback signal indicating the level of the negative current and is arranged to issue a switching-off command to the low side switch as soon as the feedback signal reaches or crosses a threshold value, wherein a least one feedback from the LED load is fed back to the control circuitry, and wherein the at least one feedback signal comprises at least one of LED voltage and LED current. The control circuitry is arranged to adapt its threshold value depending on the at least one feedback signal.