LED is driven by the constant current, its forward voltage is between 2～4.5 volt, and is related to the color and current. The old design limited LED driving current depending on the simple resistor, but the design of led circuit based on the provision of the typical downstream pressure drop by the manufacturer may cause the over-heating of LED driving device. When the forward voltage of LED drops to the level that is far lower than the typical rated value, there may appear such kind of situation. In such event, the rise of the voltage that goes through LED driving device may lead to the high dissipation of the total power; therefore, it may cause the adverse effect to the performance or life.
Currently, most LED applications use power conversion and control assembly to connect all kinds of power source, such as the exchange wire, solar-cell panel or battery, in order to control the power dissipation of LED driving device. These connectors are protected to avoid the damage because of over current and over heating by using the polymer positive temperature coefficient (PPTC) component, which has the reset ability. The connection in series of power input and a PolySwith component can prevent the damage caused by the short circuit, current overload or the user error operating. Moreover, the metal oxide variable resistance on the input end is also helpful to the over voltage protection for the LED modules.
PolySwitch LVR can also be placed behind MOV. Many equipment manufacturers chose the PolySwitch package assembly with the ability to protect the circuit and reset the upstream fault security protection. In this example,R1 is the steady resistance combined with the protection circuit. LED driving device is easy to be damaged by DC voltage and incorrect polarity, the charged port is also easy to be damaged by over pressure transient, including the electrostatic discharge (ESD Simulator) pulse. Figure 1 indicates the typical circuit protection design specially for LED driving device and bulb array, the PolyZen components in the input driving device has not only provided the simplification of the traditional champing diode for the designers, but also avoids the needs for the large amount of cooling fins. This component is helpful to the single, small package of transient suppression, reverse bias protection and over current protection.
PolySwitch components in the driving output is conductive to prevent the damage because of harmful short circuit or other abnormal load, in order to make full use of the function of PolySwitch components, it can be connected to the metal core circuit board or LED cooling fin. In addition, PESD components placed together with LED can also protect the electrostatic discharge.
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