High voltage applications
High voltage transmission is often thought of when thinking of high voltage applications, however there are many applications that require a high voltage power source to be able to operate at all. The definition for high voltage applications varies by industry and region. For example, the IEC defines high voltage as anything above 1kV for AC and above 1.5kV for DC, in automotive engineering high voltage is anything above 60V. The primary use of high voltage outside of transmission is in the industrial, scientific, medical and imaging fields.
High voltage applications within the medical field:
Electrophoresis is a technique used to separate proteins, and nucleic acids such as DNA/RNA based on their size and electrical charge. A gel with an electric field applied across it is used and the pores inside the gel allow different sized/charged molecules to move at different speeds. This technique is often used for PCR (polymerase chain reaction) tests, and DNA sequencing.
An x-ray tube requires a high voltage to be able to generate x-rays used for imaging. The tube consists of a cathode and anode, and the tube itself holds a vacuum. The cathode is heated to a high enough temperature, so that it starts to emit electrons through thermionic emission. As electrons are charged particles, they are affected by the voltage field across the anode and cathode of the tube. When a high enough voltage is applied to the tube the electrons are accelerated fast enough so that when they crash into the anode, they release x-rays. The energy and intensity of these x-rays depends on the voltage applied, and they exit the tube through a window to be used in the desired application.
Photomultiplier tubes also use a high voltage field to accelerate photoelectrons, causing them to collide with the dynodes inside the tube and release more electrons. This effectively multiplies the incoming light signal and is used for detection of weak signals. This often finds application in the medical field in blood inspection and flow cytometers, and is often used in portable radiation measurement devices, hygiene monitors, semiconductor wafer inspection and environmental emission measurements such as SOx monitors.
Applications outside the medical field:
High voltage testing of wires to determine the presence of moisture, solder flux or contamination and to ensure insulation is sufficient will require a high voltage power supply to provide the specified parameters.
Electrostatic chucks are often used in semiconductor manufacture, as it allows silicon wafers to be handled reliably in different environments. They can distribute force evenly across the chucks surface, they have also found application handling polymer/thin metal films. A bipolar high voltage is applied to the internal electrodes of the chuck, a directional field is generated and causes the objects charge to match the polarity of the chucks. Making them attract each other through the electrostatic force.
Electrostatic flocking is another process that also uses the same electric charge to orient fibres through an electric field. The fibres become aligned with the electric field lines and coat the substrate. The process is often used in the automotive industry to coat consoles and dashboards, as the process allows fibres to be packed tightly together.
The same electrostatic force is found in some air filters and requires a high voltage power source to operate, it is used to positively charge particles in the air as they pass through the filters. The particles lose their charge as they pass through, trapping the particles inside. The advantage is that these air filters do not need to be replaced, only washed every several months.
A similar principle is used in particle accelerators using multiple pulsed power stages to accelerate electrons, causing high energy collisions. The high voltage power supplies in this application would require fast rise times and be able to deliver voltages above the 100kV range.
A high voltage field can also be used to change the direction of charged particles, electron beam technology is often used in industries where the cost can be justified. Electron lithography, electron beam welding and electron beam sputtering are a few examples.
High voltage is a general term that covers a wide range of voltage levels, with some voltages being orders of magnitude higher than others. They also come with their own sets of challenges, requiring additional insulation and safety considerations due to the higher potential to cause arcing. However, it is still required for many applications and a low voltage alternative is not always possible.
Display Technology offer a range of high voltage power supplies to cover several industries. Specifically designed to drive x-ray applications, pulse generators, electron beams, insulation testing to name a few. Depending on the requirements, they can offer very fast rise times with low overshoot for capacitor charging or pulsed power. High power density supplies for where there is limited space, and modular designs to offer redundant operation. The power supplies are also available with safety features such as flashover protection, short circuit protection and are designed to have low stored energy.