Pin Definitions and Internal Circuitry of the Osram PLPT9 450LB_E

Page 10 of the Osram PLPT9 450LB_E datasheet provides the internal circuit diagram and pin definitions.

In the internal circuit, a Zener diode is connected in anti-parallel with the laser diode. This Zener diode serves as a built-in ESD protection device: during normal operation, it remains in a reverse-biased, non-conducting state and does not affect the laser diode. When an electrostatic discharge (ESD) pulse occurs, the Zener diode breaks down and clamps the voltage to a safe level, thereby protecting the laser chip.

Three points should be emphasized: First, when wiring, Pin 2 must be connected to the positive terminal of the drive power supply, and Pin 1 to the negative terminal; connecting them in reverse may damage the device. Second, the laser chip is electrically isolated from the metal housing, meaning the housing itself is not energized, which facilitates mounting onto a metal heatsink. Third, the Zener diode provides protection only against ESD—it is neither an overcurrent nor an overtemperature protection mechanism—and it does not limit current during normal operation (a point already addressed in the previous article).