Arroyo Instruments LaserSource 4400 Series, Руководство пользователя

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4400 Series LaserSource User’s Manual · Page 45
Lowering BW or Risetime
When using cables that are not well suited for high performance modulation, the
4400 includes settings to lower the bandwidth or risetime and virtually eliminate
current overshoot or ringing but at the sacrifice of lower BW or rise time.

In Io HiBW mode, a Bandwidth setting allows for the lowering of the
bandwidth from maximum (“Max”) to 3kHz or 0.7kHz.

In pulse modes, a QCW Risetime setting allows for the reduction of
risetime from the minimum possible (“Min”) to approximately 100
μ
s or
500
μ
s.
Lowering the appropriate setting will generally tame even the worst cable
arrangement.
Dead Shorts
The
4400 is a high-performance laser diode driver and not designed to drive
very low resistance loads in pulse mode. Driving a dead short can result in very
high current oscillations and should always be avoided. An E-541 error is an
indication of oscillation problems.
Eliminating E-537 (Thermal Overload) Error
The E-537 error is always associated with a large difference between the peak
voltage and the nominal voltage. When the peak voltage is significantly above
(more than 2 volts) the nominal operating voltage, the instrument will alternate
the current measurement with the peak voltage measurement (
Vpk ) and also
display a
_ VPEAK _
icon. Higher differences indicate poorer cable interfaces and
therefore the possibility of higher current overshoots when operating in square
wave modulation or QCW modes. Equally important, it forces the instrument to
operate with a higher supply voltage, resulting in additional heat being
generated inside the
4400 . If the amount of heat being generated exceeds an
internal limit, the E-537 error is generated.
The E-537 error can be prevented in one of three ways:
1. Improve the wire harness – by switching to a twisted pair cable,
eliminating connectors, and shortening the wires, you will reduce the
capacitance and inductance that causes the higher peak voltages.
2. Lower the duty cycle – by operating with a lower duty cycle, the thermal
load is reduced by a similar amount.
3. Lower the set point – like lowering the duty cycle, lowering the current
will reduce the thermal load by a similar amount.
4. Increase risetime (if pulse modes) or lower bandwidth (if modulating)
via
QCW Risetime or Bandwidth settings, respectively.