A look at tech trends for electronic displays, including machine learning and virtual reality
By Warren Miller, contributing writer
It seems as
if all forms of consumer electronics are evolving into multimedia platforms
from phones and MP3 players to home digital assistants and smart TVs. Obviously,
electronic displays are essential to any multimedia experience. Here are five of the biggest trends in commercial technology
currently affecting the display market, according to a report by the Society for Information Display (SID).
to digital assistants for the home and/or office, AI
and machine-learning tech is one of the most rapidly growing markets in
consumer electronics. Most of the world’s biggest tech conglomerates have made
forays into this sector, with giants like Amazon and Google leading the way. Amazon’s
newest iteration of its digital assistant, the Echo Show, is capable of
streaming TV shows, making video calls via Skype or other similar applications,
and even displaying digital photos. Streaming video seems to be an integral
component of all commercial electronic devices, both now and in the future.
Image source: Pixabay.
augmented reality (VR and AR, respectively) systems are another swiftly
expanding area in consumer electronics, requiring the most detailed and vivid
displays to create a world for their users to not only see but experience. Not
just limited to gaming, VR and AR provides opportunities to take virtual tours
of potential real estate purchases or virtual test drives of automobiles.
self-service stations and kiosks are also becoming ubiquitous at airports,
shopping centers, and hotels. Video displays and touchscreens guide users
through procedures that no longer require human interaction — the proliferation
of this kind of automation seems inevitable, so much so that it doesn’t seem
far-fetched to check in and out of a hotel without ever encountering a living,
breathing employee in the near future.
being incorporated more frequently into automobiles, both of the autonomous and
more traditional variety. Family-sized vans and SUVs with video displays in the
rear sections, ostensibly for kids to zone out and watch movies/TV while their
parents enjoy some merciful downtime, have been available for years. Now
automotive manufacturers are incorporating video displays into center consoles
and dashboards, possibly acknowledging that the future of autonomous driving
will necessarily include mechanisms to divert the attention of passengers while
they sit back and let the cars do the work.
another realm in which video displays, be they on laptops, tablets, or electronic
readers, are being more commonly incorporated. China has been at the forefront
of using electronic textbooks, or eSchoolbooks, in educational environments. Although
there’s some debate over whether staring into a digital display could be
harmful to the developing eyes of young children, the “flat” backgrounds
offered by eReaders like the Amazon Kindle may provide a solution. Digital
writing surfaces are also being used more frequently to teach art and design because they provide a more portable and sustainable alternative to more traditional
take an explosion of imagination to foresee a future in which almost everything
powered by electricity, be it a home appliance, a piece of wearable technology, or even a child’s toy, will incorporate a video display. As all consumer
electronics move closer and closer to becoming immersive multimedia platforms,
digital displays will be in anything and everything.
Since 2012, Chemnitz
University of Technology in Germany has actively researched additive
manufacturing for electric motors. By layering and then sintering the
materials, researchers have successfully manufactured all required motor
components in a lab through a proprietary 3D-printing process that utilizes copper,
iron, and ceramic pastes.
Stators of the first 3D-printed electric machine. Photo: TU Chemnitz/Jacob Müller.
These include “copper electrical conductors,
which create magnetic fields in combination with iron or iron alloys, and
ceramic electrical insulation, which insulates the conductors from each other
and from the iron components,” said the researchers.
Doctor and professor Ralf Werner and research assistants
Johannes Rudolph and Fabiana Lorenz initially presented a 3D coil in 2017,
which was capable of withstanding temperatures over 300°C. “The goal of
about two-and-a-half years of work has been to shift the limit of the operating
temperature of electrical machines significantly upwards,” said Werner in a press
According to researchers, viscous pastes are
extruded through a die that builds the 3D body in layers, offset with
specialized binders (which are later expelled as the metallic and ceramic
particles fuse together) depending on the body shape of the printed material.
The researchers add that the reduction in volume must be considered when building
the CAD data and that the heat treatment results in a solid body with low
The 3D multi-material process allows for several
materials to be used simultaneously while something is being printed, which
provides for a greater variety of desirable characteristics like heat
resistance and thermal conductivity. The process also allows for
self-supporting structures, which means that it can be used to print structures
with both closed and empty cavities, which can allow for passive and active
The use of ceramic
materials, as opposed to more traditional polymer-based materials, affords a greater
temperature resistance in which the upper temperature limit — at up to 700°C
— is set by the iron.
process-related, slightly reduced electrical conductivity of the copper, it is
also possible in special applications to increase the efficiency by
significantly reducing the winding temperature,” said Lorenz in a press release.
Researchers said that with the addition of additional support
structures, they’ll be able to print almost any 3D shape with high material
efficiency. And, while the team presented additional details at Hannover Messe in
April, they’re now developing the motor for series production for use in
engineering, automotive, and aviation industries.
A step up transformer basically increases the magnitude of primary applied voltage that is increases the amplitude of voltage wave form. A voltage amplifier does exactly the same.
Than a very strange but thinkable question comes what is the difference between the two and can we use a small step up transformer in place of voltage amplifier and vice-versa?
Transformers are unable to amplify (step up) an ac input Voltage without reducing (stepping down) it`s current capability.
Amplifier can amplify both current and Voltage at the same time. We can have 1V at 1uA to drive the input but might also get many volts at many Amps at the output.
Transformer`s coil windings never requires a dc Voltage to operate. Sometimes a dc Voltage might be present in a transformer winding for auxiliaries but the dc is not required for the operation of the transformer.
Amplifier almost always requires a dc working supply Voltage to operate.
Transformer has more winding added to its secondary winding to obtain Voltage amplification.
An Amplifier actually modulates a fixed dc source Voltage in response to an ac input Voltage to obtain output Voltage amplification.
A transformer`s input current is proportional to its load current.
Amplifier’s input current is normally almost independent of its load current.
A transformer is like a gearbox, whereas an amplifier is like an engine. The gearbox converts energy like a transformer.
Amplifier is like an engine, which consumes fuel to give output. Similarly amplifier consumed DC supply to give output.
A step up transformer can amplify a specified type of input which is the sinusoidal input or time varying input and add to that the range of input the transformer is very flexible in range.
Amplifier can amplify any signal and while the amplifier would have a limited range then in the saturation state.
In an ideal transformer output impedance is equal to the source impedance times the square of the turns ratio.
An amplifier can have output impedance that is independent of the source impedance.
Transformer is not an amplifier, because:
The output and input powers are same and there is not any another source other than the signal (that is incoming AC voltage), Amplifier can amplify the signal voltage without reducing the output current.
Transformer follows the principle of induction where as Amplifier follows the principle of boosting the signal (voltage or current). Actually, the amplifier generates a completely new output signal based on the input signal. We can understand these signals as two separate circuits.
The output circuit is generated by the amplifier’s power supply, which draws energy from a battery or power outlet.
LED lamps, or Light Emitting Diodes, are becoming more and more common. Having been used for some time in products such as digital watches, remote controls and brake lights, they are now being seen in many more applications such as HD TVs, and as replacements for standard incandescent bulbs in offices and houses.
LEDs do not have filaments, and so do not get as hot as incandescent bulbs; as there is no filament to burn out, they also last much longer. Because they are very small, they fit nicely into electronic circuits. But how do they work?
How does a diode work?
A diode is a semiconductor, which is a material capable of conducting electricity. The conductor material generally used for creating LEDs is called aluminium-galium-arsenide. This has additional atoms added to it (doping), thus making it more conductive.
If extra electrons are added to the semiconductor it is called N-type material; this gives it extra negatively charged particles. The free electrons then move from a negatively to a positively charged area.
If extra holes are added to a semiconductor it is known as P-type material, as it has extra positively charged particles. Electrons move between the holes, from a negatively to a positively charged area, meaning that the holes themselves seem to move from a positively charged to a negatively charged area.
When P-type and N-type materials are put together, with electrodes at each end, a diode is created, in which electricity can flow in only one direction. If you do not apply any voltage to the diode, the electrons in the N-type material fill the holes in the P-type material, which creates a “depletion zone” at the joining point of the 2 layers.
In the depletion zone a charge cannot flow, as all the holes are filled with electrons, and there are both no holes for free electrons to move to, and no free electrons to move.
If you apply enough voltage to the diode, by connecting the N-type side to the negative end of a circuit (cathode), and the P-type to the positive end (anode), the free electrons move from the N-type to the P-type material, and the holes move from the P-type to the N-type material.
This makes the depletion zone disappear and charge moves across the diode, creating light.
Light is made up of photon particles, which are released when electrons move. In a diode, when a free electron from the N-type material drops into a hole from the P-type material, energy is released as a photon; the greater the drop, the higher the frequency of energy released by the photon.
When making infared remote controls for instance, the drop is very small, meaning that the photon frequency is very low, and the light created cannot be seen.
So to create visible light, the drop needs to be greater, creating a higher frequency. The frequency of the photon decides the colour of the light produced.
Advantages of LEDs
All of this means that LEDs create light very cheaply, and across the entire visible spectrum.
In standard incandescent bulbs, up to 90% of the energy created is lost to heat, and in compact fluorescents that figure is 80%, but in LEDs, as there is no filament to heat up, nearly all of the energy created goes into producing light. It also means that LEDs can be used in situations where giving off heat would be detrimental to the application.
LEDs are also far more durable than incandescent bulbs as they are manufactured within epoxy resin, and as they are solid state devices, with no moving parts, they are much less likely to malfunction. As they have such long lives, use very little energy, and can be very small, they are proving more and more popular.
The MCT is type of power semiconductor device that combines the capabilities of thyristor voltage and current with MOS gated turn-on and turn-off. It is a high power, high frequency, low conduction drop and a rugged device, which is more likely to be used in the future for medium and high power applications.
A cross-sectional structure of a p-type MCT with its circuit schematic is shown in Fig. 1.
The MCT has a thyristor type structure with three junctions and PNPN layers between the anode and cathode. In a practical MCT, about 100,000 cells similar to the one shown are paralleled to achieve the desired current rating.
MCT is turned on by a negative voltage pulse at the gate with respect to the anode, and is turned off by a positive voltage pulse.
The MCT was announced by the General Electric R & D Center on November 30, 1988.
Harris Semiconductor Corporation has developed two generations of p-MCTs. Gen-1 p-MCTs are available at 65 A/1000 V and 75A/600 V with peak controllable current of 120 A. Gen-2 p-MCTs are being developed at similar current and voltage ratings, with much improved turn-on capability and switching speed.
The reason for developing a p-MCT is the fact that the current density that can be turned off is 2 or 3 times higher than that of an n-MCT; but n-MCTs are the ones needed for many practical applications.
The advantage of an MCT over IGBT is its low forward voltage drop. N-type MCTs will be expected to have a similar forward voltage drop, but with an improved reverse bias safe operating area and switching speed. MCTs have relatively low switching times and storage time. The MCT is capable of high current densities and blocking voltages in both directions.
Since the power gain of an MCT is extremely high, it could be driven directly from logic gates. An MCT has high di/dt (of the order of 2500 A/μs) and high dv/dt (of the order of 20,000 V/μs) capability.
The MCT, because of its superior characteristics, shows a tremendous possibility for applications such as motor drives, uninterrupted power supplies, static VAR compensators, and high power active power line conditioners.
The current and future power semiconductor devices developmental direction is shown in Figure 2. High-temperature operation capability and low forward voltage drop operation can be obtained if silicon is replaced by silicon carbide material for producing power devices.
The silicon carbide has a higher band gap than silicon. Hence, higher breakdown voltage devices could be developed.
Silicon carbide devices have excellent switching characteristics and stable blocking voltages at higher temperatures. But the silicon carbide devices are still in the very early stages of development.
Capacitors store electric charge. Because the charge is stored physically, with no chemical or phase changes taking place, the process is highly reversible and the discharge-charge cycle can be repeated over and over again, virtually without limit.
Electrochemical capacitors (ECs) variously referred to by manufacturers in promotional literature as Super capacitors also called ultra capacitors and Electric double layer capacitors (EDLC) are capacitors with capacitance values greater than any other capacitor type available today.
Capacitance values reaching up to 400 Farads in a single standard case size are available.
Super capacitors have the highest capacitive density available today with densities so high that these capacitors can be used to applications normally reserved for batteries. Super capacitors are not as volumetrically efficient and are more expensive than batteries but they do have other advantages over batteries making the preferred choice in applications requiring a large amount of energy storage to be stored and delivered in bursts repeatedly.
The most significant advantage super capacitors have over batteries is their ability to be charged and discharged continuously without degrading like batteries do. This is why batteries and super capacitors are used in conjunction with each other.
The super capacitors will supply power to the system when there are surges or energy bursts since super capacitors can be charged and discharged quickly while the batteries can supply the bulk energy since they can store and deliver larger amount energy over a longer slower period of time.
Construction of Super Capacitors
What makes’ super capacitors different from other capacitors types are the electrodes used in these capacitors. Super capacitors are based on a carbon (nano tube) technology. The carbon technology used in these capacitors creates a very large surface area with an extremely small separation distance.
Capacitors consist of 2 metal electrodes separated by a dielectric material. The dielectric not only separates the electrodes, but also has electrical properties that affect the performance of a capacitor.
Super capacitors do not have a traditional dielectric material like ceramic, polymer films or aluminum oxide to separate the electrodes, but instead have a physical barrier made from activated carbon that when an electrical charge is applied to the material a double electric field is generated which acts like a dielectric.
The thickness of the electric double layer is as thin as a molecule.
The surface area of the activated carbon layer is extremely large yielding several thousands of square meters per gram. This large surface area allows for the absorption of a large amount of ions.
The charging/discharging occurs in an ion absorption layer formed on the electrodes of activated carbon.
The activated carbon fiber electrodes are impregnated with an electrolyte where positive and negative charges are formed between the electrodes and the impregnant.
The electric double layer formed becomes an insulator until a large enough voltage is applied and current begins to flow. The magnitude of voltage where charges begin to flow is where the electrolyte begins to break down.
This is called the decomposition voltage.
The double layers formed on the activated carbon surfaces can be illustrated as a series of parallel RC circuits.
As shown below the capacitor is made up of a series of RC circuits where R1, R2 …Rn are the internal resistances and C1, C2…, Cn are the electrostatic capacitances of the activated carbons.
When voltage is applied current flows through each of the RC circuits. The amount of time required to charge the capacitor is dependent on the CxR values of each RC circuit.
Obviously the larger the CxR the longer it will take to charge the capacitor.
The amount of current needed to charge the capacitor is determined by the following equation:
In= (V/Rn) exp (-t/ (Cn*Rn))
Super capacitor is a double layer capacitor; the energy is stored by charge transfer at the boundary between electrode and electrolyte. The amount of stored energy is function of the available electrode and electrolyte surface, the size of the ions, and the level of the electrolyte decomposition voltage.
Super capacitors are constituted of two electrodes, a separator and an electrolyte.
The two electrodes, made of activated carbon provide a high surface area part, defining so energy density of the component. On the electrodes, current collectors with a high conducting part assure the interface between the electrodes and the connections of the super capacitor. The two electrodes are separated by a membrane, which allows the mobility of charged ions and forbids no electronic contact.
The electrolyte supplies and conducts the ions from one electrode to the other.
Usually super capacitors are divided into two types:
Double-layer capacitors and
The former depends on the mechanism of double layers, which is result of the separation of charges at interface between the electrode surface of active carbon or carbon fiber and electrolytic solution. Its capacitance is proportional to the specific surface areas of electrode material.
The latter depends on fast faraday redox reaction.
The electrochemical capacitors include metal oxide super capacitors and conductive polymer super capacitors. They all make use of the high reversible redox reaction occurring on electrodes surface or inside them to produce the capacitance concerning with electrode potential.
Capacitance of them depends mainly on the utilization of active material of electrode.
The working voltage of electrochemical capacitor is usually lower than 3 V. Based on high working voltage of electrolytic capacitor, the hybrid super-capacitor combines the anode of electrolytic capacitor with the cathode of electrochemical capacitor, so it has the best features with the high specific capacitance and high energy density of electrochemical capacitor.
The capacitors can work at high voltage without connecting many cells in series.
The most important parameters of a super capacitor include the capacitance (C), ESR and EPR (which is also called leakage resistance).
Super capacitors can be illustrated similarly to conventional film, ceramic or aluminum electrolytic capacitors.
This equivalent circuit is only a simplified or first order model of a super capacitor. In actuality super capacitors exhibit a non ideal behavior due to the porous materials used to make the electrodes. This causes super capacitors to exhibit behavior more closely to transmission lines than capacitors.
Below is a more accurate illustration of the equivalent circuit for a super capacitor:
We group capacitors into three family types and the most basic is the electrostatic capacitor, with a dry separator.
This capacitor has a very low capacitance and is used to filter signals and tune radio frequencies.
The size ranges from a few pico-farad (pf) to low microfarad (uF).
The next member is the electrolytic capacitor, which is used for:
Rated in microfarads (μF), this capacitor has several thousand times the storage capacity of the electrostatic capacitor and uses a moist separator.
How a Capacitor Works – by Dr. Oliver Winn
Cant see this video? Click here to watch it on Youtube.
The third type is the supercapacitor, rated in farads, which is again thousands of times higher than the electrolytic capacitor. The supercapacitor is ideal for energy storage that undergoes frequent charge and discharge cycles at high current and short duration.
Farad is a unit of capacitance named after the English physicist Michael Faraday. One farad stores one coulomb of electrical charge when applying one volt. One microfarad is one million times smaller than a farad, and one pico-farad is again one million times smaller than the microfarad.
Engineers at General Electric first experimented with the electric doublelayer capacitor, which led to the development of an early type of supercapacitor in 1957. There were no known commercial applications then.
In 1966, Standard Oil rediscovered the effect of the double-layer capacitor by accident while working on experimental fuel cell designs. The company did not commercialize the invention but licensed it to NEC, which in 1978 marketed the technology as “supercapacitor” for computer memory backup.
It was not until the 1990s that advances in materials and manufacturing methods led to improved performance and lower cost.
The modern supercapacitor is not a battery per se but crosses the boundary into battery technology by using special electrodes and electrolyte. Several types of electrodes have been tried and we focus on the double-layer capacitor (DLC) concept. It is carbon-based, has an organic electrolyte that is easy to manufacture and is the most common system in use today.
All capacitors have voltage limits. While the electrostatic capacitor can be made to withstand high volts, the supercapacitor is confined to 2.5–2.7V. Voltages of 2.8V and higher are possible but they would reduce the service life.
To achieve higher voltages, several supercapacitors are connected in series.
This has disadvantages.
Serial connection reduces the total capacitance, and strings of more than three capacitors require voltage balancing to prevent any cell from going into over-voltage. This is similar to the protection circuit in lithium-ion batteries.
The specific energy of the supercapacitor is low and ranges from 1 to 30Wh/kg. Although high compared to a regular capacitor, 30Wh/kg is one-fifth that of a consumer Li-ion battery. The discharge curve is another disadvantage. Whereas the electrochemical battery delivers a steady voltage in the usable power band, the voltage of the supercapacitor decreases on a linear scale from full to zero voltage.
This reduces the usable power spectrum and much of the stored energy is left behind.
Consider the following example.
Take a 6V power source that is allowed to discharge to 4.5V before the equipment cuts off. With the linear discharge, the supercapacitor reaches this voltage threshold within the first quarter of the cycle and the remaining three-quarters of the energy reserve become unusable.
A DC-to-DC converter could utilize some of the residual energy, but this would add to the cost and introduce a 10 to 15 percent energy loss. A battery with a flat discharge curve, on the other hand, would deliver 90 to 95 percent of its energy reserve before reaching the voltage threshold.
Table 1 below compares the supercapacitor with a typical Li-ion:
1 million or 30,000h
500 and higher
2.3 to 2.75V
3.6 to 3.7V
Specific energy (Wh/kg)
Specific power (W/kg)
Up to 10,000
1,000 to 3,000
Cost per Wh
$0.50-$1.00 (large system)
Service life (in vehicle)
10 to 15 years
5 to 10 years
–40 to 65°C (–40 to 149°F)
0 to 45°C (32°to 113°F)
–40 to 65°C (–40 to 149°F)
–20 to 60°C (–4 to 140°F)
Rather than operating as a stand-alone energy storage device, supercapacitors work well as low-maintenance memory backup to bridge short power interruptions. Supercapacitors have also made critical inroads into electric powertrains.
The virtue of ultra-rapid charging and delivery of high current on demand makes the supercapacitor an ideal candidate as a peak-load enhancer for hybrid vehicles, as well as fuel cell applications.
The charge time of a supercapacitor is about 10 seconds.
The charge characteristic is similar to an electrochemical battery and the charge current is, to a large extent, limited by the charger. The initial charge can be made very fast, and the topping charge will take extra time.
Provision must be made to limit the initial current inrush when charging an empty supercapacitor.
The supercapacitor cannot go into overcharge and does not require full-charge detection; the current simply stops flowing when the capacitor is full. The supercapacitor can be charged and discharged virtually an unlimited number of times. Unlike the electrochemical battery, which has a defined cycle life, there is little wear and tear by cycling a supercapacitor.
Nor does age affect the device, as it would a battery.
Under normal conditions, a supercapacitor fades from the original 100 percent capacity to 80 percent in 10 years. Applying higher voltages than specified shortens the life. The supercapacitor functions well at hot and cold temperatures.
The self-discharge of a supercapacitor is substantially higher than that of an electrostatic capacitor and somewhat higher than the electrochemical battery. The organic electrolyte contributes to this.
The stored energy of a supercapacitor decreases from 100 to 50 percent in 30 to 40 days.
A nickel-based battery self-discharges 10 to 15 percent per month. Li-ion discharges only five percent per month.
Supercapacitors are expensive in terms of cost per watt. Some design engineers argue that the money for the supercapacitor would better be spent on a larger battery.
We need to realize that the supercapacitor and chemical battery are not in competition; rather they are different products serving unique applications.
Cell voltage determined by the circuit application, not limited by the cell chemistry.
Very high cell voltages possible (but there is a trade-off with capacity)
High power available.
High power density.
Simple charging methods. No special charging or voltage detection circuits required.
Very fast charge and discharge. Can be charged and discharged in seconds. Much faster than batteries.
No chemical actions.
Can not be overcharged.
Long cycle life of more than 500,000 cycles at 100% DOD.
Long calendar life 10 to 20 years
Virtually unlimited cycle life – not subject to the wear and aging experienced by the electrochemical battery.
Low impedance – enhances pulse current handling by paralleling with an electrochemical battery.
Rapid charging – low-impedance supercapacitors charge in seconds.
Simple charge methods – voltage-limiting circuit compensates for selfdischarge; no full-charge detection circuit needed.
Cost-effective energy storage – lower energy density is compensated by a very high cycle count.
Almost zero maintenance and long life, with little degradation over hundreds of thousands of cycles. While most commercially available rechargeable batteries can be charged 200 to 1000 times, ultracapacitors can be charged and discharged hundreds of thousands of times with no damage.However, in reality, they can be charged and discharged virtually unlimited number of times, and will last for the entire lifetime of most devices and applications they are used in, thus making them environmentally friendly. Battery lifetime can be optimised by only charging under favorable conditions, at an ideal rate and, for some chemistries, as infrequently as possible. Ultracapacitors can help in conjunction with batteries by acting as a charge conditioner, storing energy from other sources for load balancing purposes and then using any excess energy to charge the batteries at a suitable time.
Increased safety since they can handle short circuit and reverse polarity. Also, there is no fire and explosion hazard.
Improved environmental safety since there is no corrosive electrolyte and toxicity of materials used is low. Rechargeable batteries on the other hand wear out typically over a few years, and their highly reactive chemical electrolytes present a disposal and safety hazard.
Rugged since they have Epoxy Resin Sealed Case which is non corrosive.
Voltage dips and transients are usually blamed on the supplier, but this is often unfair. There are many potential on-site causes; for example, starting of heavy loads may cause voltage dips and switching of inductive loads will generate transients.
Let’s talk about how actually voltage dips and transients are created and how they influence the power network:
Heavy loads, such as large motors, draw very high starting currents for several seconds as the rotor accelerates causing a voltage drop in the wiring feeding it. This voltage drop will be much greater if the wiring has not been carefully rated to account for the magnitude of the starting current.
If other equipment is fed from the same feeder, it will be subject to the same voltage drop, and may fail as a result.
Good installation practice is the key to reducing this problem; large loads should have dedicated feeders of adequate cross-section right back to the point of common coupling (PCC) so that the heavy load is separated from other, more sensitive, loads. Maintenance procedures should ensure that this circuit separation is not destroyed during system extension.
Modern low power electronic equipment is often specified as operating over a very wide supply voltage range – indeed many units are claimed to operate over the 100V to 250V range without adjustment. This can be misleading – Most equipment uses a switched mode power supply (SMPS) unit that draws pulses of current from the supply, once per half cycle, to charge an internal capacitor. Load power is drawn via a regulator, discharging the capacitor that is recharged by the next supply pulse.
If the charge on the capacitor is sufficiently high, then a stable output will still be available for a short period in the absence of a supply. This period is known as the hold-up time and, for a high quality unit at nominal supply voltage, is usually greater than one supply cycle at full load.
However, since the energy stored in the capacitor is proportional to the square of the supply voltage, a 10% reduction in supply voltage results in a nearly 20% drop in stored energy. Lower cost units have more limited hold-up times and may fail to supply the required load during a voltage dip.
In particular, wide supply voltage range units may have very low hold-up times at the lower end of the input range. It is important to remember that many computer peripherals, such as printers and communications modems, use this type of supply.
Where the electricity supply is the source of voltage dips it will be necessary to provide voltage regulation, either for the whole site or for selected sensitive equipment.
Ferroresonant transformers (figure above), sometimes called constant voltage transformers, operate with a saturated core and resonant circuit to maintain the output voltage as the input voltage varies, the primary current varying to compensate. The device operates satisfactorily over a narrow range of output loadings.
Older variable transformer regulators employed a servo motor driven brush tap around a toroidal autotransformer winding. Response time was slow – several seconds, control resolution poor and maintenance requirements high.
The modern equivalent uses a multi-tapped transformer and a solid state tap changer and is fast, accurate and maintenance free. The transformer may be an autotransformer, but in this case noise isolation is poor and dual-wound shielded transformers are preferred.
It is important that the control circuitry for such devices is true RMS sensing, otherwise distortion on the supply will be mis-interpreted as a change in voltage.
Transients are most frequently caused by switching of inductive or capacitive loads. Wherever possible, suppression should be applied at the source to prevent the transient propagating and coupling to other circuits. When the source of the transient is off-site, the suppression techniques outlined below should be used.
Low magnitude transients are unlikely to result in damage but will cause noise and can be reduced by the provision of line filters or isolating transformers. Typical small equipment line filters (6 Amp rating) have attenuation figures of 22dB for differential and 8dB for common mode noise at 150 kHz, rising to a maximum of 70dB at 30 MHz.
Isolation transformers provide good noise isolation providing that adequate electrostatic shielding is provided between the windings. Single, double and triple shielded types are available with increasing levels of noise attenuation.
Transients can reach several thousand volts and can seriously damage equipment but, fortunately, protection is achieved easily and economically by the use of transient voltage surge suppressers.
Typically metal oxide varistors (MOV) are used; these devices have very high resistance at normal voltage but above their breakdown voltage the resistance becomes very low, so clamping the transient to the breakdown voltage of the device. The clamp effect requires the voltage of the transient to be dropped in the impedance of the supply so a high transient current must flow and this often results in noise coupling to adjacent wiring, including signal and network cabling. For this reason, it is better to fit suppressers near the source of the problem rather than at every other device that may be affected.
Note that the transient is not completely removed, it is reduced to the breakdown voltage of the MOV, which, to prevent unduly frequent operation and to cater for manufacturing tolerances, is likely to be around 120% of the peak (170% of RMS) voltage.
It will often be found necessary to follow the suppressor with a filter to further attenuate the transient. MOVs can pass very large currents of short duration but, because their power handling capability is quite low, they are not suitable for clamping repetitive spikes.
The fast rise time edges of the current waveform contain high frequencies that can cause serious radio frequency interference (RFI) to other equipment in the vicinity. To prevent propagation of this interference on to the supply each SMPS incorporates a filter on the input consisting of a small series inductor in both the phase and neutral lines with a small capacitor to ‘earth’ from each.
Since the filter capacitor provides a path from phase to the protective conductor, current will flow. This current is made up of a small current (permitted by regulation to be up to 3.5 mA) at the fundamental frequency, a small fraction of each harmonic frequency present and high frequency transients caused by switching.
Because of the high population of electronic equipment in a modern office leakage currents can be significant.
Typically each desk will have at least a personal computer and monitor, each contributing to the leakage current. This amounts to a change of function for the protective conductor system; while it used to be provided only to carry current in the event of a fault it is now required to carry a continuous leakage current as well as serving as a sink for high frequency noise currents.
Now that the protective conductor has both safety and functional requirements to fulfil, the designer must take many more factors into consideration during design, and the services manager must be vigilant to ensure safe use. For example – integrity – to ensure the safety of operators and the public.
Leakage current //
Since the protective conductor is now carrying a leakage current, any break in the ‘earth’ side connection to it will mean that the isolated section will rise to a potentially lethal voltage – half of the supply voltage – as will all the exposed metalwork connected to it. The current available to flow will depend on the total leakage current of the equipment connected to that section.
In a typical modern office a final ring circuit could serve up to 16 operators (an area of 100 m2), each with at least a PC and monitor, so that the possible earth-leakage current for the ring is 112mA. This is likely to be fatal.
European wiring regulation standard IEC 7671 (and BS 7671) attempts to improve the integrity of such circuits by requiring that a final circuit in which the leakage current is expected to exceed 10 mA must meet either of the following two requirements:
1. Following one of the methods below //
A high integrity earth must be provided by one of the following methods:
A single protective conductor with a cross-sectional area of not less than 10 mm2.
Separate duplicate protective conductors with a cross-sectional area of not less than 4 mm2, independently connected.
Duplicate protective conductors incorporated in a multi-core cable with the live conductors of the circuit if the total cross sectional area of all the conductors is not less than 10 mm2. One of the conductors may be formed by metallic armour, sheath or braid incorporated in the construction of the cable.
Duplicate protective conductors formed by conduit, trunking or ducting and a conductor having a cross-sectional area of not less than 2.5 mm2 installed in the same enclosureand connected in parallel with it.
An earth monitoring device which, in the event of a discontinuity in the protective conductor, automatically disconnects the supply of the equipment.
Connection via a double wound transformer where the input and output circuits are electrically separated. The protective conductor between the equipment and the isolating device must be provided by one of the methods (point 1 to 5. above).
2. Ring connecting single sockets
The final circuit must be a ring connecting single socket-outlets with no spurs.
Each end of the protective conductor ring must be individually terminated (i.e. separate connections, individually screw clamped) to the distribution board.
These regulations are designed to ensure that the protective connection is as robust as possible so that the risk of shock to users is minimised. They apply specifically to final circuits, but the same considerations apply to the whole of the cabling from the point of common connection through to the final equipment.
One serious problem is that these regulations apply to final circuits in which the leakage current is expected to exceed 10 mA. Often, the use of the circuit is not known to the installer, and indeed changes over the lifetime of the building, so the above requirements are not implemented.
This means that many circuits do not have the required protective conductor integrity to safely supply IT and other electronic equipment.
Continuity Test of Protective Conductors (VIDEO)
Reference // A Good Practice Guide to Electrical Design – Copper Development Association (Download guide)
General recommendation is to properly design and implement the facility’s grounding system to avoid unwanted involvement of ground loops with the operation of the equipment. This kind of approach can also eliminate the need to consider equipment modifications and to engage in costly diagnostic efforts since most trouble involving common-mode noise is avoided in the signal circuits.
It is generally not possible in complex systems with interconnected data and signal conductors to avoid all ground loops.
Some eight tips that may be used to avoid the detrimental effects of such ground loops include:
Tip #1 Where possible, cluster the interconnected electronic equipment into an area that is served by a single signal reference grid (SRG). If the interconnected equipment is located in separate, but adjacent rooms, then a common signal reference grid should serve all the rooms.
Tip #2 Effectively bond each frame/enclosure of the interconnected equipment to the SRG. In this way, the SRG acts like a uniformly shared ground reference that maintains a usefully low impedance over a very broad range of frequency. Typically, from dc to several tens of MHz, for example.
Tip #3 Where a work area exists and its PC is connected to a network, keep all of the work area’s equipment (e.g., CPU, monitor, printer, external modem, etc.) closely clustered and powered by a work area dedicated branch circuit. If it is required to use more than one branch circuit for the work area’s power, be sure that both are powered from the same panelboard.
Avoid connecting any other equipment to the branch circuit(s) used by the work area’s equipment.
Tip #4 Use fiber optical paths for data circuits. The best, but also the most expensive solution is to use fiber optical cables for all data circuits since there can be no ground loops with these kinds of circuits (or surge current problems).
However, due to increased initial cost and added complexity, the use of fiber optic cable circuits is usually (and unfortunately) viewed as a last resort. Instead, it should be viewed as an important first strategy that avoids problems that may ultimately cost more to resolve.
Tip #5 Use opto-isolators which can provide several kV of isolation for the data path that they are used on. These are available as add-on data transmission protocol converters for most popular forms of data circuits. This is a very useful retrofit option for data circuits being affected by surges and ground loops.
Surge protection devices (SPD) are also recommended to be applied to these circuits if protection from the higher voltages associated with larger currents is needed.
Tip #6 Other forms of protocol converters can be applied to standard forms of signal circuits to make them less susceptible to common-mode noise on grounding conductors associated with the signal path. For example, a conversion from RS-232 to RS-422 or RS-485, etc. should be considered in especially noisy environments.
Tip #7Improve the shielding provided for the data signal cables. Place the cables into well and frequently grounded metal conduits or similar raceways.
Tip #8 Follow the recommendations for installing signal cables in IEEE Std. 1100, Recommended Practice for Powering and Grounding Sensitive Electronic Equipment (e.g., the Emerald Book).
Equipment interconnected by data signal cables and located on different floors or that is widely separated in a building, may not be able to effectively use some or all of the above solutions, except those involving optical isolation and certain of the protocol conversion techniques. This occurs since the terminating equipment for the signal cables is likely to be powered from different branch circuits, panelboards, and even separately derived AC systems.
Therefore, the associated equipment ground references are likely to be at different potential at least some of the time.
Table // Ground noise susceptibility classes of different data cable types
Modbus RS-485 SCSI
Parallel ports RS-232 ports Proprietery backplane Video cables
While the best solution to the above situation involves either fiber optic or opto-isolation techniques, it is often possible to achieve good performance by providing each of the separate locations with an SRG, and then interconnecting the SRGs with widely spaced apart and multiple grounding/bonding conductors, solid-bottom metal cable trays, wireways, or conduits containing the data signal cables.
An example of using widely spaced grounding/bonding conductors to interconnect two SRG areas is when there is structural building steel available and when it can be used in this role. Since structural steel columns are installed on standard spacings in a given building, these columns can typically be used for the purpose. Wide spacing is necessary since the conductors involved are inductors and the mutual inductance between such conductors that are not widely spaced, is quite high.
This makes several closely spaced conductors appear as a single inductor and not as paralleled inductances, which exhibit lower overall reactance between the items they are being used to interconnect.
Also, each of the above separated equipment areas containing SRGs should be AC powered from a locally installed and SRG referenced isolation transformer as opposed to them being powered from panelboards and feeders from some remotely located power source.
Finally, since separated areas in a building are subject to large potential differences due to lightning discharge currents and some forms of ac system ground faults, the ends of the signal cables should always be equipped with surge protection devices (SPDs).
Practical Guide to Electrical Grounding by W. Keith Switzer, Senior Staff Engineer
Use of the Signal Reference Grid in Data Centers by Neil Rasmussen from APC