LED light circuit protection
Connect a PolySwitch device in series with the LED light power
supply circuit to provide overcurrent protection. In addition to
overcurrent protection, the PolySwitch device can provide
overtemperature protection if it is thermally bonded to the metal
core circuit board or LED heat sink.
A Tyco Electronics ROV Metal Oxide Varistor (MOV) placed across
the input helps provide overvoltage protection in the LED modules.
Placing a PolyZen device on the input of the LED driver helps
protect your driver from inadvertent exposure to overvoltage and
reverse polarity events
In the event the driver circuit does not require input protection
the driver output can still be protected from short circuit or other
load anomalies. PolySwitch devices may be used to help protect
driver outputs from inadvertent short circuits or other load
If an LED does not have built-in ESD protection, a PESD
protection device placed in parallel with the LED can help protect
against ESD damage.
Inherently limited power sources - a transformer, power supply,
or battery - may have protective devices as long as they are not
relied upon to limit the output of the Class 2 supplies. Non-inherently
limited power sources by definition, have a discrete protective
device that automatically interrupts the output when the current and
energy output reaches a prescribed limit. Tyco Electronics provides
designerswith awide range of circuit protection devices that help
ensure safe operation of Class 2 power sources for LED lighting
applications. As an example, in Figure 7, the addition of an MOV in
coordination with a PolySwitch device on an output circuit branch
enables a power supply to meet the requirements of UL 1310 paragraph
35.1 overload test on switches and controls.
Problem: Thermal Runaway If the cooling vents in a monitor become
blocked, the heat generated by the LED backlighting can increase and
lead to thermal runaway if the LED driver circuit is a constant
voltage or constant luminous flux type. Solution: PolySwitch Devices
Careful consideration must be used to determine an appropriate
location to thermally bond the PolySwitch device in the optimum
location to interrupt the current in the event the LCD is operated
when the vents are blocked in the LCD housing.
Source: 2Pro, PolySwitch, PolyZen, Raychem, SiBar, TE logo and
Tyco Electronics are trademarks.