Semiconductor laser diodes are often tested under stress conditions. When a laser fails, it can suffer catastrophic damage if the power supply does not have a failsafe to shut down power to devices in the event of a failure. This application note documents multiple tests conducted with three different types of power supplies to determine how they respond to a typical failure scenario.
This paper discusses typical multi-laser drive topologies used in burn-in or life testing applications and presents possible laser failure mechanisms that can challenge power supplies driving the lasers. A typical laser failure scenario is then proposed – a gradual increase in laser impedance followed by a sudden drop in impedance. A test circuit consisting of six lasers and a MOSFET transistor is constructed and this circuit is used to test how three laser diode power supplies respond in this scenario. Observed voltage and current spikes produced by the supplies are presented and the excess power and energy delivered to the lasers is calculated.