Single-Pin LED Driver IC for Current and Brightness Control
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Solution Overview
Problem
Existing LED driver ICs require multiple pins to set the maximum current and control brightness, increasing cost and board space, while a single pin solution is desired to simplify the design and reduce pin count.
Innovation Solution
An LED driver IC uses a single pin to set the maximum current through LEDs by connecting a resistor to a control pin, where the PWM controller's duty cycle controls brightness, with a sample and hold circuit ensuring continuous maximum current and a low pass filter adjusting the current based on duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If multiple pins and external resistors are used to set maximum current and control brightness, then the LED driver can perform both functions, but the pin count and board space increase
Solution Approach 1:
The patent combines the maximum current setting function and brightness control function into a single pin. The single pin receives a PWM signal that simultaneously performs both functions: the duty cycle controls brightness while the average voltage level sets the maximum current. This merging eliminates the need for separate pins and external resistors for each function.
Solution Approach 2:
The single pin is designed to serve multiple functions: it acts as both the maximum current setting input and the brightness control input. By making the pin universal, the patent reduces the overall pin count of the LED driver while maintaining both current setting and brightness control capabilities.
2Manufacturing precision
If multiple external resistors are used to set maximum current, then the current can be accurately controlled, but the cost and board space increase
Solution Approach 1:
The patent eliminates the need for multiple external resistors by combining the current setting function with the brightness control pin. The single pin's PWM signal inherently provides both functions, removing the requirement for separate current-setting resistors and reducing the total number of external components.
Solution Approach 2:
The PWM signal itself carries the information needed for both maximum current setting and brightness control. The system uses the inherent properties of the PWM signal (duty cycle and average voltage) to perform both functions without requiring additional external components, making the system self-sufficient.
Data Source
AI summary
An LED driver IC is described that uses a single pin to both set the maximum current through one or more driven LEDs and variably control the brightness of the LEDs. A single resistor is connected to the control pin of the IC, where the value of the resistor sets the maximum current through the LEDs. A PWM source, outputting a pulse train at a particular duty cycle, is connected to the other end of the resistor, where the duty cycle controls the LED brightness level. When the PWM signal is low (e.g. ground), a sample and hold circuit connects the output of a feedback control voltage to an Imax current source to set a maximum current based on the external resistor value. An inverse of the duty cycle of the PWM controller controls a current Idim that is subtracted from the maximum current Imax set by the resistor. This difference current is used to control drivers for the LEDs.