TECH NOTES

Controlled-Voltage vs. Controlled-Current Modes of Operation

Voltage Controlled Voltage Source (VCVS)
and Voltage Controlled Current Source (VCCS) Comparison

AE Techron 7000 Series amplifiers can be field-configured to operate as Voltage Amplifiers (Voltage Controlled Voltage Source) or as Transconductance Amplifiers (Voltage Controlled Current Source). The mode selection is made via a jumper setting located on the amplifier main board. For complete instructions including jumper location, please consult your product manual.

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 impedance 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 voltage wavefore to be like the input waveform.

Conversely, when configured as a Controlled Current source (transconductance amplifier), the amplifier will provide an output current that is constant and proportional to the control (input) voltage. 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 current waveform to be like the input waveform.

 

CV vs CC comparison

Figure 1: Controlled Voltage vs. Controlled Current Operation
(graphic courtesy of Brews Ohare,"Electronic Amplifier," Wikipedia)

 

Safety and Operation Considerations 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 increase 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 amplifier and for any user who might come in contact with the amplifier output terminals. 

When operating in Controlled Current (CC) mode, a compensation circuit is required to ensure accurate 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 the factory-default compensation setting will be sufficient for some applications, the compensation setting may also be adjusted in the field. See Compensating the Amplifier to the Load for CC Operation for more information.

Controlled Voltage Mode waveforms     Controlled-current mode waveforms