Tuesday, June 23, 2020

Selecting a High Voltage Programmable Power Supply

High-voltage power supplies are used in many scientific and industrial applications including research, development, process control, power conditioning, test and measurement.  Sometimes a fixed output power supply may be used, rather than one with a variable or programmable output, which lowers the initial acquisition cost.

As technology rapidly advances, new markets are identified or production levels ramp up, voltage, current and power requirements can change significantly.  This can result in a need for a new high voltage supply or one with more features or functions.  Specifying a programmable power supply is a sound alternative, ensuring flexibility both in the near and long term. 

The decision as to which attributes should be considered and how may they benefit the user is an important one.  When specifying and evaluating programmable power supplies, users should look for as many of the following features and functions as possible.

High voltage outputs

Scientific instruments can require tens of kilovolts to perform their specialized tasks.  The power supply needs to be able to provide stable, regulated voltages with a range of outputs that could be as high as 50 kV and power levels of 1kW.  Even if the current application requires less, having a higher rated adjustable power supply provides future flexibility.

Compact size

Space within a 19” rack is often at a premium and the power supply competes with other instruments for this space.  Selecting a supply that is 2U rather than 3U in height will reduce the overall rack height or allow additional system functionality to be added.  A shorter depth may mean that a shallower rack can be used, consuming less space in a laboratory or on a factory floor, and saving costs.

Input voltage, active PFC and efficiency

A power supply that operates just from a 230Vac input restricts operation in many countries that also use 115Vac.  In the Americas or Japan, 208Vac may not be readily available in the desired location, requiring an additional electrical circuit to be wired in by an electrician.  Ideally chose a power supply that has the ability to operate from a wide range 110 to 230Vac input.

The power supply should have active power factor correction (PFC). This ensures that a sinusoidal input current is drawn from the AC supply, reducing the RMS line current and increases the available output power that can be drawn from an AC outlet or breaker panel.  Active PFC also reduces the harmonic distortion of the AC current which avoids an adverse impact on any sensitive instruments on the same AC feed.

A high efficiency power supply consumes less electricity and generates less internal heat.  A supply that is 90% efficient wastes half the power of an 80% efficient model, and allows other system instruments to operate cooler.

Easy operation

Engineers should not have to spend their valuable time reading instruction manuals to be able to program a complex power supply.  Choose one that has an intuitive, easy-to-use graphical display.  Ensure that the supply has both coarse and fine adjustment for accurate output voltage and current setting.  Ideally a product should utilize encoders, rather than potentiometers, for longer field life and the ability to program the magnitude of the steps.

Figure 1: TDK-Lambda’s FLX-HV series front panel display

Quiet operation

Loud or annoying audible fan noise can cause operators and nearby personnel to become fatigued. Scientific equipment will often not be operating continuously and the high voltage power supply will not require as much airflow for cooling at light loads.  Selecting a power supply that has a variable speed fan will reduce audible noise and prolong the life of the fan.

Digital interfaces

For remote or automated operation a standard digital interface is essential.  Chose a standard interface like USB or LAN. The manufacturer may include additional features in additional to status and programming capability, like being able to see the total operating hours and fault history.  Check to see if the manufacturer offers a GUI (Graphical User Interface) which will save time and effort to get the equipment running.

Safeguards and safety agency certification

When working with high voltages, protective functions are critical.  Rackmount power supplies need to manage the internal heat generation, and must be capable of protecting the (often expensive) external load from damage due to an output overvoltage or overcurrent condition.  IEC 61010-1 is an industry wide safety standard, allowing the product to be CE marked for easy importation into the European Union.  Compliance to EN61000-6-2 for immunity and EN61000-6-3 for emissions will reduce susceptibility to external electrical noise and avoid the power supply from interfering with other equipment or instrumentation.

Load arcs

Load arc events are common in high-voltage applications, and require a power supply that responds in a controlled and predictable manner. TDK-Lambda’s FLX-HV series for example will count load arc events, and if three or more arcs are detected in a five-second period, the unit will shut down for a 10-second interval. Arc activity is shown on the front panel display and reported on the remote interface.  An integrated arc counter records load arcs and can be read back via the remote interface, and reset to zero if required.  The FLX-HV supply also includes a second non-resettable arc counter remote interface query.

The manufacturer and product series

Selecting a global manufacturer like TDK-Lambda is also recommended. If your product may be exported, technical support is likely to be more accessible than a supplier that is focused on just one region.

The correct choice of a programmable high voltage power supply will provide you with flexibility, reliability and ease of use.  If your budget allows, select a higher wattage model for expansion and use in another project.  Remember, with a programmable product, the output voltage and current limits can always be set lower.

Some manufacturers offer a range of products, like the FLX-HV series mentioned earlier which has nine models ranging from 10kV to 50kV and 200W to 1,000W.

Figure 2: FLX-HV high voltage power supply

For more information visit FLX-HV series

Power Guy

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