6300 Series ComboSource User’s Manual · Page 33
Unlike the voltage limit, the current limit simply prevents the ComboSource from
delivering more current than the limit is set to. When the current limit engages,
the output will remain on.
The intermittent contact circuit is designed to protect against faulty connections
by detecting fast changes in voltages which can be caused by poor wiring or
faulty connectors. If false trigging of the intermittent contact circuit is frequently
occurring, it can be turned off from the menu.
The photodiode current and photodiode power limits are implemented in
software and may take up to one second to trigger when these conditions occur,
and therefore should not be relied on to provide fast protection of the laser
diode.
Analog Modulation
The analog modulation input BNC on the front of the instrument allows for
external control of the current set point using a 0 to 10V analog signal. 10V
equals the maximum operating range, which is dependent on the model and
Range setting. For example, a 6305 operating in the 500mA range will attempt
to drive 500mA when 10V is applied to the modulation input (so the “transfer
function” is 50mA/V).
In addition, the set point adds to the modulation input, so using the same 6305
example, if you were to apply 5V and the set point was 100mA, then the
resulting drive current would be 350mA (5V = 250mA plus the 100mA set point).
You must also consider that the modulation input is not a precision input, so for
accurate current control, you should calibrate the modulation input using a one
point or two point calibration and apply the calibration to your voltage input. The
instrument will display actual current flowing when the display is in large font
mode (press the knob button to change modes), so turn the output on with the
Io set point at 0mA, apply a modulation input signal, and the instrument will
indicate the actual current, which you can use to calibrate your voltage set point.
When modulating at higher frequencies (>1 kHz), it is critical that high quality,
shielded twisted pair cabling be used, and wire size suitable for the applied
current (or the equivalent if using a multi-conductor cable). See the chart below
for suggested sizes. Failure to do so may result in current oscillations that may
damage your laser. When operating in these modes, always use shielded cable
and never use individual wires to connect the instrument to your laser. If in
doubt, use a current probe attached to an oscilloscope to monitor actual
performance.
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