96-8005549_3-18-21
Information subject to change
19
8508 OPERATOR’S MANUAL – SECTION 6
6 Applications
6.1 Controlled-Current Operation
6.1.1 Controlled-Voltage vs. Controlled-
Current Modes of Operation
AE Techron 8500 series amplifiers can be field-
configured to operate as
Voltage Amplifiers
(Voltage-Controlled Voltage Source) or as
Trans
-
conductance Amplifiers
(Voltage-Controlled
Current Source). The mode selection is made via
the back-panel DIP switch #4. See the
Advanced
Configuration
section for more information.
When configured as a
Controlled-Voltage
source
(voltage amplifier), the amplifier will provide an
output voltage that is constant and proportional
to the control (input) voltage. If the load’s imped-
ance changes, the amplifier will seek to maintain
this ratio of input to output voltage by increasing or
decreasing the current it produces, as long as it is
within the amplifier’s ability to create the required
current. Use this mode if you want the output volt-
age waveform to be like the input waveform (see
Figure 6.1
).
Conversely, when configured as a
Controlled-
Current
source (transconductance amplifier), the
amplifier will provide an output current that is con-
stant and proportional to the control (input) volt-
age. If the load’s impedance changes, the amplifier
will seek to maintain this transconductance (ratio
of input voltage to output current) by increasing or
decreasing the voltage it produces, as long as it is
within the amplifier’s ability to create the required
voltage. Use this mode if you want the output cur-
rent waveform to be like the input waveform (see
Figure 6.2
).
6.1.2 Safety and Operation Consider-
ations for Controlled Current Operation
When an AE Techron amplifier is configured as
a Controlled-Current source, care needs to be
exercised in its operation.
Any voltage controlled
current source should never be turned on
without a load, (with some impedance, real or
effective) connected to its output terminals.
When asked to operate in this way, any current
source (including an AE Techron amplifier) will in-
crease its output voltage in an attempt to drive the
requested current into the load. In an open-circuit
condition, creating current flow will be impossible.
The current source will increase its output voltage
until it reaches its voltage limit. This is a potentially
dangerous condition for both the AE Techron am-
plifier and for any user who might come in contact
with the amplifier output terminals.
Likewise, operation in Controlled Current mode
into a load that is completely resistive is
NOT rec
-
ommended.
The load must have some inductance
for Controlled Current mode to operate correctly.
When operating in Controlled-Current (CC) mode,
a compensation circuit is required to ensure ac-
curate output current. Since the load is a critical
circuit component in CC mode, the inductive and
resistive values of the load will determine the
required compensation values. While one of the
two compensation settings that can be enabled
Figure 6.1 – Input to Output Comparison,
Controlled-Voltage Operation
Figure 6.2 – Input to Output Comparison,
Controlled-Current Operation
Summary of Contents for 8500 Series
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