LDX-400386 Newport Main Board

Model LDX-3412 delivers a low cost solution for general purpose driving of laser diodes and LEDs. This precision 0-200 mA current source delivers stable, low-noise output in both constant current and constant light operating modes. Easy-to-use operation is assured via an intuitive front panel with a highly-visible LED display featuring 0.1 mA resolution. The innovative Voltage Source/Constant Current output stage design makes operation dependable. Laser diode protection circuits also are included, along with user-adjustable photodiode feedback capability.

The LDX-3412 features three operating/display modes: (1) Constant Current, which delivers a stable, precision current of 0-200 mA at up to 6 V; (2) Constant Power, in which a photodiode feedback signal can be used to control the current output to ensure a constant light output level (despite varying temperature); and (3) Limit Display, in which the current limit setpoint level is conveniently displayed.

The LDX-3412 employs a unique, safe output, off/on switch technology, in which the output terminals of the unit are shunted by an innovative semiconductor switch. When the output switch is enabled, the output is turned on safely by slowly switching the shunt to a high impedance state. When the output switch is turned off, the output of the source is disabled by quickly returning the semiconductor shunting device to a low impedance state, thereby shorting the output terminals while suppressing potentially damaging current transients. The unit also employs a double-shielded transformer. This shielding reduces AC line noise and suppresses damaging line transients. Easy Connection to Any Laser/LED Package Style The output terminals of the LDX-3412 are fully floating, allowing either side to be grounded if necessary. For constant power operation, an instrumentation amplifier is used at the unit's input from the external monitor photodiode. This allows connection to any laser/LED package pin configuration.

The LDX-3412 also employs a proven current limit circuit. This circuit is fully redundant to the main precision current control of the instrument. This approach allows the current limit to be set safely, even while the unit is actively driving a laser at a lower current level. Additionally, the current limit is independent of the output compliance voltage, providing stable control over a range of load conditions.

The LDX-3412 offers low noise and high stability. Output broadband noise is less than 0.01% (1mA) rms, and temperature co-efficient stability is better than 100 ppm/°C. With a resulting output current drift of less than 20 ppm over a 30 minute period (typical), the LDX-3412 out-performs typical low cost power supplies. Additionally, the current limit is independent of the output compliance voltage, providing stable control over a range of load conditions.