Integrated LED Driver Circuit with Auto-Zero Offset Compensation
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Solution Overview
Problem
Current LED driver technologies fail to accurately control LED output current due to system offsets, process variations, and parasitic effects, requiring external components like resistors and not supporting the LDO mode in boost regulator topologies.
Innovation Solution
A fully integrated current controlling circuit using an auto zero method with switched capacitor circuits to eliminate offsets, allowing for accurate current control without external components and supporting true PWM dimming and LDO mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If traditional external resistor-based current control method is used, then current control is simpler, but current accuracy deteriorates due to ground voltage offset and parasitic effects
Solution Approach 1:
The patent merges the current sensing function and the offset compensation function into a single integrated circuit. The sensing resistor is integrated on-chip with the LED driver, and the auto-zero circuit is combined with the current control loop, eliminating the need for external resistors and separate compensation circuits. This integration resolves the contradiction by achieving both simplicity and accuracy.
Solution Approach 2:
The auto-zero circuit performs preliminary offset measurement and compensation before the actual current control operation. By pre-characterizing and storing the offset values in lookup tables, the system eliminates ground voltage offset and parasitic effects before they affect current accuracy, thereby achieving high precision without increasing overall system complexity.
2Adaptability or versatility
If fully integrated LED driver is used, then device integration is improved, but current control accuracy deteriorates due to system offsets and process variations
Solution Approach 1:
The patent implements a feedback mechanism where the actual LED current is sensed through the integrated sensing resistor, compared with the reference current, and the error signal is used to adjust the PWM duty cycle. This closed-loop feedback compensates for system offsets and process variations, enabling fully integrated drivers to achieve high current accuracy.
Solution Approach 2:
The patent uses parameter storage in lookup tables to compensate for process variations. By pre-characterizing the relationship between process variations and offset values, and storing compensation parameters in memory, the system dynamically adjusts for process variations, maintaining high accuracy in fully integrated drivers.
3Power
If traditional boost regulator topology is used, then voltage boosting is achieved, but LDO mode operation becomes unavailable
Solution Approach 1:
The patent implements a dynamic operating mode selection mechanism that can switch between boost mode and LDO mode based on the input voltage and load conditions. The control circuit dynamically adjusts its operation: when input voltage is higher than LED forward voltage, it operates in boost mode; when input voltage is close to or lower than LED forward voltage, it operates in LDO mode. This dynamic adaptability resolves the contradiction by supporting both operating modes.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides high accuracy in LED current control, eliminates the need for external components, stabilizes feedback ratios, and supports LDO mode, enhancing system efficiency and loop stability.
Implementation Method 1
a first switched capacitor circuit configured to sample a reference voltage at the first terminal of said reference resistor when a switching signal is at a first level and to transfer the sampled reference voltage to the first terminal of said sensing resistor when the switching signal is at a second level
Implementation Method 2
a current sensing circuit comprising a reference resistor whose first terminal is connected to said reference current source unit, a sensing resistor whose resistance is in a first proportion to the resistance of said reference resistor
Data Source
AI summary
The present disclosure proposes a fully integrated accurate LED output current controlling circuit and method, which can be seamlessly combined with true PWM dimming. The current controlling circuit has an auto zero function in the light-emitting diode driver to eliminate offsets caused by the system, process variations, parasitic effects, dimming and so on in an LED driver application, and thus is capable of controlling the LED current with high accuracy. Moreover, the driver of the present disclosure does not require the use of external components such as an external resistor to regulate current accuracy.