LED Current Detection Circuit With Accurate Current Mirroring
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Solution Overview
Problem
Existing LED current detection circuits suffer from deviations in mirrored current due to varying source-drain voltages and omission of abnormal information reporting, especially when power transistors age or the number of control switches changes, complicating circuit design.
Innovation Solution
A high-precision LED current detection circuit with a current sampling and comparison/determination circuit, using current mirrors and a reference transistor array to ensure mirroring precision and series connection, and a feedback loop with a comparator to accurately detect current within preset limits, adjusting threshold voltages proportionally with power transistor array states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a MOS transistor is used to mirror the output current of the LED light source, then the current detection function is achieved, but the mirroring precision deteriorates due to varying source-drain voltages
Solution Approach 1:
The patent introduces an operational amplifier as an intermediary component to compensate for the voltage drop across the sensing resistor. The operational amplifier maintains a stable voltage difference between its input terminals, thereby compensating for variations in source-drain voltage and ensuring accurate current mirroring despite voltage fluctuations in the circuit.
Solution Approach 2:
The patent implements a feedback mechanism where the operational amplifier continuously monitors the voltage across the sensing resistor and adjusts its output to maintain the desired voltage difference. This feedback loop compensates for variations in source-drain voltage, ensuring that the mirrored current accurately reflects the LED output current regardless of voltage fluctuations.
2Ease of operation
If the power transistor array is connected in parallel with the detection circuit, then the circuit can operate, but abnormal information is omitted when power transistors age
Solution Approach 1:
The operational amplifier serves as an intermediary that directly measures the current through the sensing resistor in series with the LED light source. This measurement path is independent of the power transistor array's operational state, allowing the detection circuit to accurately detect abnormal currents even when power transistors age or fail, without omitting abnormal information.
3Adaptability or versatility
If the number of control switches in the power transistor array is changed, then the LED brightness can be adjusted, but the threshold voltages need to be readjusted, increasing design complexity
Solution Approach 1:
The operational amplifier provides continuous feedback to maintain accurate current detection regardless of changes in the power transistor array configuration. This feedback mechanism automatically adapts to different numbers of control switches and power transistor configurations, eliminating the need for manual threshold voltage readjustment and reducing design complexity while maintaining adaptability.
Data Source
AI summary
A high-precision LED current detection circuit, including a current sampling circuit and a comparison and determination circuit; the current sampling circuit is configured to collect an output current of the LED light source; the comparison and determination circuit is configured to determine whether the output current of the LED light source is within a preset normal range or not.