Switch Controller Detects Half-On Time Point for LED Current Stability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional LED current control methods using buck converters are prone to errors due to variations in input voltage, output voltage, and inductor ripple, leading to inconsistent LED current supply.
Innovation Solution
A switch controller that detects a half-on time point during the on-period of a power switch, generates a modulation wave based on the detected sense voltage, and controls the switching operation to reduce errors in LED current by using a feedback mechanism to adjust the reference wave.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LED current control using buck converter is used, then power supply is provided to LED string, but LED current varies due to input voltage variation, output voltage variation, and inductor ripple
Solution Approach 1:
The patent applies preliminary action by detecting the half-on time point in advance during the on-period of the power switch. At this predetermined timing, the controller samples the sense voltage to obtain the average inductor current value before the switching cycle completes. This advance detection allows the system to proactively adjust the LED current control based on the sampled average current, compensating for variations caused by input voltage, output voltage, and inductor ripple before they significantly affect LED current stability.
Solution Approach 2:
The patent implements feedback control by sampling the sense voltage at the half-on time point to obtain the average inductor current, then using this sampled value to adjust the LED current control. The controller compares the sampled average current with the target LED current and adjusts the duty cycle accordingly. This feedback mechanism continuously corrects deviations in LED current caused by input voltage variation, output voltage variation, and inductor ripple, thereby improving current stability and control precision.
2Productivity
If inductor inductance is decreased to increase power supply efficiency, then switching frequency can be increased, but inductor current ripple increases causing LED current error
Solution Approach 1:
The patent applies preliminary action by detecting the half-on time point in advance during the on-period of the power switch. At this predetermined timing, the controller samples the sense voltage to obtain the average inductor current value before the switching cycle completes. This advance detection allows the system to proactively adjust the LED current control based on the sampled average current, compensating for variations caused by input voltage, output voltage, and inductor ripple. By using the average current value sampled at the half-on time point, the system can accurately control LED current even when inductor ripple is large due to low inductance, thus resolving the contradiction between power supply efficiency and LED current accuracy.
Solution Approach 2:
The patent implements feedback control by sampling the sense voltage at the half-on time point to obtain the average inductor current, then using this sampled value to adjust the LED current control. The controller compares the sampled average current with the target LED current and adjusts the duty cycle accordingly. This feedback mechanism continuously corrects deviations in LED current caused by input voltage variation, output voltage variation, and inductor ripple, thereby improving current stability and control precision.
3Power
If input voltage is lower than output voltage in buck converter, then power cannot be supplied to output terminal, but this creates periods where LED current cannot be maintained
Solution Approach 1:
The patent applies preliminary action by detecting the half-on time point in advance during the on-period of the power switch. At this predetermined timing, the controller samples the sense voltage to obtain the average inductor current value. By using this advance detection and adjusting the duty cycle based on the sampled average current, the system can optimize power transfer during each switching cycle. This allows the buck converter to maintain better voltage conversion efficiency even when input voltage is close to or slightly below output voltage, reducing the duration and impact of power supply interruptions to the LED string.
Solution Approach 2:
The patent implements feedback control by sampling the sense voltage at the half-on time point to obtain the average inductor current, then using this sampled value to adjust the LED current control. The controller compares the sampled average current with the target LED current and adjusts the duty cycle accordingly. This feedback mechanism helps maintain stable LED current by compensating for power supply interruptions caused by input voltage being lower than output voltage, thereby improving continuous power supply reliability.
Data Source
AI summary
The present invention relates to a switch controller, a power supply including the same, and a method for driving the same. An AC input of the power supply is connected to a rectification circuit. The power supply includes a power switch to which an input current passed through the rectification circuit flows during an on-period and a switch controller, the switch controller detects a half-on time point that is the intermediate time point of the on-period, detects a sense voltage that is determined by a current flowing to the power switch during the on-period at the half-on time point, generates a modulation wave by controlling a reference wave according to the detected voltage, and controls switching operation of the power switch according to the modulation wave.