Parallel LED Drive Circuit Using Chopper Amplifier Offset Cancellation
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Solution Overview
Problem
Existing parallel LED drive circuits face challenges in achieving consistent and uniform light and brightness due to variations in drive currents, primarily caused by mismatched forward voltages and manufacturing process variations in LEDs connected in parallel.
Innovation Solution
A parallel LED drive circuit is designed using a chopper operational amplifier and sampling resistors, where the drive current is determined by a reference voltage and the resistance value of the sampling resistor, with a switching control signal reversing the polarity of the input offset voltage to eliminate its effect, ensuring accurate matching of drive currents across LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple LEDs are connected in parallel, then the circuit can drive more LEDs with lower supply voltage, but the drive currents become inconsistent due to variations in forward voltages and manufacturing process
Solution Approach 1:
The patent divides the parallel LED array into multiple independent drive circuits, each controlling a subset of LEDs. Each drive circuit has its own current control mechanism, allowing independent adjustment and compensation for variations in forward voltage, thereby maintaining consistent drive currents across all LEDs while driving a large total number of LEDs.
Solution Approach 2:
The patent implements feedback control in each drive circuit by monitoring the actual drive current and adjusting the control signal to maintain the desired current level. This feedback mechanism compensates for variations in LED forward voltages and manufacturing tolerances, ensuring consistent brightness and current distribution across all parallel-connected LEDs.
2Manufacturing precision
If LEDs are connected in series, then the drive current consistency is improved, but the required supply voltage increases and power efficiency decreases
Solution Approach 1:
Instead of using a single high-voltage series connection, the patent segments the LED array into multiple parallel groups, each driven by its own dedicated drive circuit operating at lower voltage. This segmentation allows the system to achieve current consistency through individual circuit control while avoiding the high voltage and power loss associated with long series strings.
Solution Approach 2:
The patent changes the operating parameters of each drive circuit to optimize performance. By adjusting the control voltage and current parameters independently in each parallel drive circuit, the system achieves consistent LED brightness and current distribution without requiring the high supply voltages necessary for series connections, thereby improving overall power efficiency.
3Device complexity
If standard operational amplifiers are used in parallel LED drive circuits, then the circuit complexity is reduced, but the drive current matching accuracy deteriorates due to input offset voltage
Solution Approach 1:
The patent introduces chopper operational amplifiers as intermediary components between the control signal and the LED drive circuits. These specialized op-amps use chopping technology to modulate the input signal, effectively eliminating input offset voltage and drift errors. This intermediary mechanism enables highly accurate drive current matching across multiple parallel LEDs without significantly increasing overall circuit complexity.
Solution Approach 2:
The chopper operational amplifier employs periodic switching action to modulate the input signal at a high frequency. This periodic action allows the circuit to average out offset voltage errors over time, achieving high precision drive current matching. The periodic chopping and filtering process effectively removes DC offset errors while maintaining the desired control signal, improving current matching accuracy without complex additional circuitry.
Data Source
AI summary
The present invention relates to a parallel light emitting diode (“LED”) drive circuit and provides a drive circuit configured to drive a parallel array of LEDs. The drive circuit comprises: a plurality of switches, a plurality of sampling resistors, and a plurality of chopper amplifiers. Each switch is coupled to a respective LED in the LED array. Each chopper operational amplifier configured to receive a reference voltage and a switching control signal and generate an input offset voltage. Each chopper operational amplifier includes a differential amplifier including an input transistor pair and a current mirror transistor pair, of which the electrical positions can be reserved when the switching control signal is switched between a first state and a second state, wherein the offset voltage, which causes the lightness mismatching in a parallel LED circuit, can be cancelled.