LED Driver Circuit Regulating Average Current
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Solution Overview
Problem
Existing LED drivers fail to maintain constant brightness due to variations in supply voltage, LED forward voltage, and inductance values, leading to undesired brightness changes, as they cannot accurately regulate the average load current due to propagation delays in switching operations.
Innovation Solution
A circuit and method that include a semiconductor switch, a freewheeling device, a current measurement circuit, and feedback circuits to adjust the duty cycle and peak value of the modulated reference signal, ensuring the average load current remains constant by compensating for variations in supply voltage and LED forward voltage, using a second feedback loop to adjust the amplitude of the reference signal based on the average load current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a switching converter is used to control LED current, then the LED brightness can be regulated, but propagation delays cause the average load current to exceed the desired maximum value
Solution Approach 1:
The patent applies preliminary action by anticipating the current overshoot caused by propagation delays and compensating for it in advance. The circuit measures the actual current during the delay period and adjusts the switching signal accordingly to prevent the overshoot from occurring, rather than reacting after the error has already happened.
Solution Approach 2:
The patent implements feedback by continuously monitoring the actual LED current during the propagation delay period and using this information to adjust the switching converter's output. The feedback loop compares the measured current with the desired current and modifies the switching signal to eliminate the discrepancy, ensuring accurate average load current control.
2Reliability
If common LED drivers are designed as current sources, then they can regulate current, but they cannot keep the average load current constant for different supply voltages and LED forward voltages
Solution Approach 1:
The patent applies dynamics by making the LED driver adaptive rather than static. The circuit dynamically adjusts its operation based on real-time measurements of supply voltage, LED forward voltage, and actual current flow. This allows the driver to maintain constant average load current across varying conditions without requiring manual reconfiguration.
Solution Approach 2:
The patent implements parameter changes by automatically adjusting switching parameters (duty cycle, frequency, timing) in response to changes in supply voltage and LED characteristics. The circuit modifies these parameters dynamically to compensate for variations and maintain stable current regulation across different operating conditions.
3Device complexity
If the switching converter operates with fixed timing, then the circuit design is simple, but the average load current varies with different inductance values and supply voltages
Solution Approach 1:
The patent uses feedback to measure the actual average load current and compare it with the desired value. Based on this comparison, the circuit automatically adjusts the switching timing and duration to compensate for variations caused by different inductance values and supply voltages, maintaining precise current control without complex manual calibration.
Data Source
AI summary
A circuit for driving light emitting diodes includes a first semiconductor switch that is responsive to a driver signal and a freewheeling device coupled between a first supply terminal that provides a supply voltage and a second supply terminal that provides a reference potential. An LED and an inductor are coupled in series between a common circuit node of the first semiconductor switch and the freewheeling device and either the first supply terminal or the second supply terminal. A current measurement circuit is coupled to the LED and provides a load current signal that represents a load current passing through the at least one LED. A first feedback circuit includes an on-off controller that receives load current signal and a reference signal, compares the load current signal with the reference signal and generates the driver signal dependent on the comparison.