Cairn OptoLed Lite, Instruction Manual

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1 Introduction
The Cairn OptoLED Lite is capable of driving an LED over a wide range of
currents. The standard operating current range, which is set either by a front
panel control or by an external control voltage, is 0-2 amps (A). This current is
limited by components in the interchangeable LED heads, above which the
current driver will temporarily shut down in order to protect the LED from
damage. However, since LEDs can be transiently overdriven above their
continuous current limit (which is usually determined by thermal
considerations), the protection circuitry also allows a higher transient current
limit to be set. By incorporating the protection-setting components in each LED
head, they can be tailored to match the maximum safe levels for that type of
LED.
In addition, digital inputs are provided to switch the LED on and off with rise
and fall times of just a few microseconds (for faster requirements you will
need the full OptoLED). The operation of the unit will now be described, first
with reference to the front and rear panel facilities, and then with reference
to the further facilities available internally on the circuit boards.
Some more general notes on LED operation will follow after that. Finally, for
users who wish to try out alternative LEDs, the necessary information for
constructing or modifying LED heads is given in the Appendix.
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