Though the usual configuration of LED luminaires wherein a number of LEDs are arranged in series to make the power supply design simple, are supplied with high voltage, low current power supply that helps in improving efficiency of the power supply and have a modular design that allows easy scaling are very convenient to use because of the mentioned points, the open type of LED can affect the performance of the streetlight and cause complete darkness. There are also a lot of issues regarding their reliability, performance and maintenance. LEDs in these streetlights are highly stressed and as a result they develop an open circuit, which happens due to repeated cooling and heating stresses inside the LED package.
The solution to this problem is an LED shunt protector (LSP) device that can be added to the LED string design. The device then shunts the current around the inoperable LED, and enables the unaffected LEDs in the string to remain illuminated. The electronic shunt current bypass such as an LSP device isolates the open circuits, and enables the current to flow uninterrupted through the LED string. Since the device is inactive, no current flows through it. The device becomes active only when a circuit is open.
A LED shunt protector is especially designed to tolerate an open LED circuit failure. For lower LED power strings zener diodes can be used whereas very large and expensive zeners are required for high power LEDs.
LSP devices start working where the breakover voltage is proportional to the number of LEDs in a substring, which is high enough not to cut out the forward voltage but lower than the open circuit LED voltage when the breakover current is drawn. When the voltage across the device exceeds the rated breakover voltage, the LSP device switches to its on state, lowering the voltage to 1V. It minimizes power dissipation and the maximum threshold voltage is 1.2V, which is less than the forward voltage of the LED.
The amount of current required by the LSP device must be less than the current consumed by an operational LED. Therefore, using a switched mode constant current supply actually reduces the luminaire power dissipation if an LED fails. To reliably switch on the LSP, the breakover current is specified below the minimum LED operating current and high enough to prevent false triggering. This saves a lot of money on maintenance.
