Steps For Selecting an Appropriate PLED Device for your Application

Here are the steps typically involved in selecting a Littelfuse PLED device for an LED application:

1) Define Vf (Forward voltage), If (Forward current), and the connection scheme of the LEDs.

2) Define the number of LEDs in the LED string and understand the constant current source value and compliance voltage of the power supply.

3) Determine the PLED device to fit for Vf, If and the PLED protection ratio, as follows:

• PLED switching current must be less than constant current source value
• PLED turn-on voltage must be less than power supply compliance voltage.
• Choose how many LEDs (1, 2 or 3) in a string are to be protected by each PLED. A PLED6, which triggers at 6 volts, protects one LED; a PLED9, which triggers at 9 volts, can be used with a pair of LEDs; and a PLED13 can be used with three (Note that that failure of one LED will cause two or three, respectively, to go out).

4) Determine the package of the PLED device to fit the lighting environment.

5) Define the ambient temperature of the PLED environment and provide adequate heat sinking if required.

6) Perform testing on the PLEDs by shunting with the protected LEDs.

7) Review steps 2 and 3 to see if there is any issue.