Operating AC Power Supplies in Constant Current Mode

We look at a system for the testing of peak current detection circuits containing current transformers

Regulated AC power Supplies and Constant Current Mode

We refer to regulated AC power supplies as being “CFCV”, or “constant voltage, constant frequency”. Unlike most devices in their class, which operate on a fixed volts-per-hertz ratio, Kikusui’s regulated AC power supplies for device testing allow output parameters to be varied at will.

Our clients sometimes ask us if we have regulated AC power supplies that operate in constant current, or “CC”, mode. As mentioned above, the configurable parameters of our off-the-shelf regulated AC power supplies are voltage and frequency, not current. We therefore tell these clients that we do not have such a product. (Note that CC capability sometimes is added as a modification or as part of a bespoke order. Ask our sales team for details!) However, it would not be good for the reputation of the solutions engineering team if we were simply to turn these customers away. In this article, I describe some solutions for testing applications requiring current regulation that make use of Kikusui’s off-the-shelf regulated AC power supplies.

Tricks for Evaluating Current Transformers

Current transformers are an essential element of power monitoring applications, that is, AC current sensing, for which we are seeing increasing demand as a result of greater demand for devices used in environmental applications and for devices related to renewable energy. Because the current flowing through a current transformer will not necessarily be sinusoidal, in some applications there is a need to perform over-current detection simultaneously. I therefore believe that in order to properly assess current transformers, the testing circuit must allow the regulation of not only sinusoidal current but also peak current.

System Overview

I will now propose a system that comprises a PCR-LE series Kikusui regulated AC supply and a PCZ series AC electronic load for testing circuits that contain current transformers.

(1) Specifications of Device Under Test

The specifications of the test device envisaged by this testing system are as follows:

(1) Contains an AC current transformer having a standard specification of 50/60 Hz
(2) Mounted on a printed circuit board having a trace width able to withstand normal levels of effective (rms) current
(3) Equipped with a function to measure normal current and sound an alarm when abnormal peak current over a prescribed maximum is detected

(2) System Configuration

The regulated AC power supply is set to 50 or 60 Hz and alternating current is applied to the device under test by way of the AC electronic load, as per figure1.

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The PCZ1000A allows the user to select the crest factor of the output wave: when the crest factor is set to the maximum level of 4 and effective current is set to 10A, the power supply is capable of outputting a peak output current of 40A. This enables the peak current flowing through the device under test to be detected and the device’s operation verified. The system therefore allows the user to generate bursts of peak current without changing the effective current flowing through the circuit, meaning there is no need to worry about stress on PCB tracks.

By using the (Wavy PCZ1000A) sequence creation and control software to activate and deactivate the electronic load and sequence the selected constant current, it is possible to output intermittent bursts of peak current, albeit in bursts of no shorter than 500ms.

Figure 2 shows the waveform at crest factor 4 with current varied between 0 and 5A.

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In conclusion, if your choice of testing device (such as a power supply) does not have the functions you want, you can often solve the problem by combining it with other devices. I believe this is a good approach to take when considering testing systems. Kikusui’s customer support line welcomes inquiries of this nature.

Please feel free to contact us with any questions or concerns.

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