Newport LDC-3706 Series, User Manual

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December 2019 35 LDC-3706 Series Laser Controller
Safety Limits
TEC modules may be damaged by excessive current, so module manufacturers typically specify
a maximum safe operating current for their module. The temperature controller of the LDC-3706
provides a current limit feature that allows the user to set the maximum current that the
temperature controller supplies.
It is normal for the controller to operate at the current limit, especially when the load temperature
is far from the setpoint. The current limit LED will be lit in the TEC section (left) of the front panel
when the controller is in a current limited condition.
If the Hot Side heatsink is too small for the application, it eventually becomes heat-saturated,
wherein the heatsink can no longer dissipate the heat being generated. When the heatsink
becomes saturated, the TEC current increases in an attempt to cool the load. The additional
current creates more heat that cannot be dissipated and subsequently, more TEC current is
applied. This situation is referred to as
thermal runaway and can cause a laser to become
damaged.
To help avoid damage caused by thermal runaway, the LDC-3706’s temperature controller
provides a high-temperature limit setting. When the load temperature exceeds the temperature
limit, the LDC-3706’s temperature controller turns off the TEC current (and laser current source
output, if the LD TEC error link is enabled) and generates an error on the TEC display.
Additionally, setting the positive current limit to a lower value will reduce the likelihood of thermal
runaway.