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
