Arroyo Instruments 4205 Manual

Many Arroyo Instruments laser drivers feature an analog modulation input (typically 0-10V, Paks use a
lower voltage). This input is typically driven using a function generator. All well and good if you have a
function generator available. However, in some systems, the only signal available is a fixed trigger signal,
often 5V. This document explores how to use that fixed voltage signal with the modulation input to
achieve set point control.

Modulating Range and Output Current Range Defined

Modulation range refers to the difference between the maximum and minimum modulation current. For
example, if modulating between 2A and 6A, the modulation range would be 4A.
The output current range is the modulation range plus the Io Setpoint... the set point and the
modulation input sum together to form the output drive current. Note that when the source voltage is
off (0V), the diode will be driven by the amount of current as set with Io Setpoint.

Defining the Output Current Range

The first step is to determine the modulation voltage required to achieve the target output current. For
the following examples, we'll assume a +5V trigger signal is what's available, and that we are working
with a 4308 LaserSource, which has an 8A output and a 0-10V modulation input.
Your modulation range will be limited by your trigger voltage divided by 10V and multiplied by the range
of the instrument:
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For a 4308 with a 5V source, this equates into 4 Amps. If you need to achieve a higher maximum
current, adjust the Io Setpoint up as needed. If in the trigger off state operating the diode at a non-zero
current is not acceptable, you will need a higher trigger voltage which is outside the scope of this
document.
AN-019 - Modulating Output with a Fixed Voltage
APPLICATION NOTE AN-019
Modulating Output with a Fixed
Voltage
February 19, 2020, Rev B
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