How can an AC power supply

be configured and operated in Constant Current (CC) mode?

Keywords: AC Power Supply, Constant Current (CC), Constant Power (CP), Electronic Load

In the field of test and measurement, it is well understood that DC power supplies typically provide both Constant Voltage (CV) and Constant Current (CC) modes. Consequently, when an AC current source is required, users often expect AC power supplies to offer a similar Constant Current (CC) capability. However, in practice, with the exception of the Ametek CS Series programmable AC current sources (which were discontinued in 2022), most AC power supplies do not support a true Constant Current (CC) mode. Even for AC/DC dual-mode power supplies, the DC operation mode often does not include a Constant Current (CC) function. The following outlines the basic specifications of the Ametek AC current source series and information regarding its discontinuation.

Programmable high power AC current source
CS Series specifications Voltage: 0 V to 270 V；Current: 44.44 A to 177.77 A；Power: 3 kVA to 18 kVA

* The above information is referenced from the Ametek Programmable Power website.

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Some AC power supplies claim to provide Constant Current (CC) or Constant Power (CP) modes; however, in practice, these functions are often realized through current limiters or power limiters. By dynamically adjusting the output voltage in response to load variations, the system effectively simulates CC or CP operation. This method is applicable when the device under test (DUT) is directly connected to the AC power supply. If the DUT is a current-sensing device—such as a current transformer (CT) or a clamp meter—which does not directly connect to the AC source, and an AC current source is required, then, the test must be carried out by coordinating an electronic load with the AC power supply to achieve the desired current output.

Products such as current transformers (CTs) and clamp meters (current clamps) require an AC current source for specification verification.

Current measurement can be performed using a shunt resistor (which requires breaking the circuit and connecting in series, as shown in Figure 1), or by using a current transformer (CT) or clamp meter that senses the magnetic field (without breaking the circuit). An AC power supply essentially functions as an amplifier with a built-in arbitrary waveform generator. Its primary purpose is to provide voltage and frequency corresponding to global power grids or to simulate abnormal grid conditions through customized voltage waveforms. In such systems, the output current varies with the load. As illustrated in Figure 2, an electronic load can be used to establish the required constant current condition for the device under test by setting the desired load current.

Figure 1: Illustration of Precision Current Shunts

Figure 2: System Diagram for Generating AC Constant Current, In this example, the setup consists of a GW Instek ASR-6000 Series programmable AC/DC power supply and an AEL-5000 Series AC/DC electronic load. The device under test (DUT) is represented by a GCM-400 Series clamp meter, though other current transformers (CTs) or clamp meters may also be used.

Conclusion
A DC constant current source can be easily obtained using the Constant Current (CC) mode of a DC power supply. For AC applications, an AC current source can be realized by combining a standard AC power supply with an AC electronic load.

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