High-Side LED Controller Using Vertical N-Channel Transistor
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Solution Overview
Problem
The semiconductor industry faces challenges in designing LED controllers that are cost-effective and do not use P-channel transistors in high-side configurations, which can lead to increased die sizes and potential damage from shorted currents in low-side configurations.
Innovation Solution
A high-side switch configuration using a vertical N-channel MOS transistor without a P-channel transistor, coupled with a stacked configuration of lateral transistors to distribute the control voltage and eliminate the need for a charge pump circuit, allowing for efficient and cost-effective control of LED current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a P-channel MOS transistor is used in a high-side configuration to control the LED, then the LED current can be regulated, but the die size increases and costs increase
Solution Approach 1:
The patent inverts the conventional approach by using an N-channel MOS transistor in a high-side configuration instead of a P-channel transistor. This is achieved by implementing a specialized driver circuit that can provide the necessary gate drive voltage to turn on the N-channel transistor while it operates in the high-side position, thereby achieving current regulation without requiring a P-channel device and its associated larger die area
Solution Approach 2:
The patent changes the electrical parameters by using an N-channel transistor with different voltage characteristics compared to a P-channel transistor. The driver circuit is designed to provide gate voltages that are higher than the source voltage by a sufficient margin to ensure proper turn-on and linear operation of the N-channel device, thereby enabling parameter-based substitution
2Area of stationary object
If an N-channel MOS transistor is used in a low-side configuration to control the LED, then the die size is reduced, but large currents can flow through the load and damage the load if the output becomes shorted
Solution Approach 1:
The patent inverts the conventional low-side configuration by placing the N-channel MOS transistor in a high-side configuration. This allows the transistor to control current flow from the power supply to the LED, and when properly designed with appropriate current limiting in the driver circuit, prevents excessive current flow that could damage the LED in the event of a short or fault condition
Solution Approach 2:
The driver circuit acts as an intermediary between the power supply and the LED load. It provides intelligent control of the N-channel transistor to ensure safe operation, including current limiting and protection functions that prevent damage from shorted connections while maintaining the benefits of using an N-channel device
3Ease of operation
If a charge pump circuit is used to drive the gate of a high-side N-channel MOS transistor, then the transistor can be controlled, but the device complexity and cost increase
Solution Approach 1:
The patent extracts or removes the charge pump circuit from the design by implementing an alternative gate drive mechanism. The driver circuit is designed to directly provide the necessary gate drive voltage through innovative circuit topology that eliminates the need for a separate charge pump, thereby reducing device complexity and cost while maintaining the ability to control the high-side N-channel transistor
Data Source
AI summary
In one embodiment, a vertical N-channel transistor is coupled in a high side configuration to control a current through an LED. A control circuit operates the vertical N-channel transistor to control a value of the current.