LED Bypass Circuit Using MOSFET Switch for Open-Loop Detection
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Solution Overview
Problem
Conventional bypass circuits for LED strings, which use Zener diodes to bypass open-circuited LEDs, suffer from high power consumption and inability to recover from temporary false triggers without rebooting the entire string.
Innovation Solution
A circuit comprising a monitoring circuit and a switch that selectively bypasses an open-circuited LED by monitoring differential voltage across the LED and activating the switch when an open circuit is detected, with periodic deactivation to check for LED recovery, using a MOSFET with a low on-voltage drop to minimize power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Zener diode bypass circuit is used to bypass open-circuited LEDs, then the LED string can continue operation, but power consumption increases significantly
Solution Approach 1:
The patent uses a MOSFET switch with very low on-resistance (Rds(on)) as a temporary bypass solution. The MOSFET acts as a low-impedance path only when the LED fails open, allowing current to continue flowing through the string. When the LED is healthy, the MOSFET remains off and consumes negligible power. This disposable-like approach accepts that the bypass element will be activated only in failure conditions, minimizing normal operation power consumption while maintaining string continuity.
Solution Approach 2:
The patent changes the electrical parameters of the bypass path by using a MOSFET whose resistance can be dynamically controlled. In normal operation, the MOSFET presents very high resistance (off state), consuming minimal power. When an LED fails, the MOSFET switches to low resistance (on state), providing a low-impedance bypass path. This parameter change allows the system to adapt its power consumption based on the operational state of the LED string.
2Reliability
If Zener diode bypass circuit is used, then open-circuited LEDs can be bypassed, but the circuit cannot recover from temporary false triggers without rebooting
Solution Approach 1:
The patent implements periodic monitoring of the LED string status through the control circuit, which continuously or periodically checks for open-circuit conditions. This periodic action allows the system to detect when a failed LED has recovered and automatically switch the MOSFET bypass off, enabling automatic recovery without manual intervention or system reboot. The periodic monitoring creates opportunities for the system to reassess the LED status and adjust the bypass state accordingly.
Solution Approach 2:
The control circuit provides feedback by continuously monitoring the voltage across each LED and controlling the MOSFET switch based on the detected status. When an open-circuit condition is detected, the control circuit activates the MOSFET bypass. When the LED recovers (voltage returns to normal range), the feedback mechanism detects this change and deactivates the bypass, enabling automatic recovery. This closed-loop feedback system eliminates the need for manual rebooting that characterized the Zener diode approach.
3Reliability
If monitoring circuit continuously checks LED status, then false triggers can be detected, but power consumption increases
Solution Approach 1:
The control circuit performs periodic status checks of the LED string rather than continuous monitoring. The monitoring occurs at intervals sufficient to detect failures and recoveries, but not so frequent as to create excessive power consumption. This periodic sampling approach balances the need for reliable fault detection with the constraint of minimizing monitoring power consumption in the LED string system.
Solution Approach 2:
The monitoring circuit is designed to be self-powered from the LED string itself, drawing minimal current during status checks. The control circuit uses the existing voltage present across the LED string during normal operation to power its monitoring function, eliminating the need for separate power supply circuitry. This self-service approach allows continuous or periodic monitoring while keeping additional power consumption to an absolute minimum.
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
This solution reduces power consumption and allows for periodic checking of the open LED's status, enabling efficient operation of the LED string without rebooting, thus improving reliability and reducing false triggering issues.
Implementation Method 1
the monitoring circuit being configured to monitor a differential voltage across the target circuit
Implementation Method 2
using a MOSFET with a low on-voltage drop to minimize power consumption
Data Source
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AI summary
The present technology is generally related to LED bypass circuits and associated methods of operation. In one embodiment, an LED bypass circuit includes a monitoring circuit and a switch. The monitoring circuit is coupled to the LED to monitor the differential voltage across the LED. The switch is coupled to the LED in parallel. When an open status is detected by the monitoring circuit, the switch is turned on to bypass the LED.