The biggest design change in power supplies was the move to switch mode operation in the 1970’s. As a result of using switching techniques, efficiency of around 70% was achievable for 5 Volt outputs, which was over double that which could be obtained from linear devices.

The Xgen series from Excelsys offers class-leading efficiency offering very high power densities with low noise and high temperature operation.

The 1980’s saw the shift to FET devices. By the mid 90s there was a significant move towards the use of synchronous rectification to produce the DC output voltage of power supplies. Better magnetic materials, improved and cheaper FETs, cheaper multilayer boards, and more sophisticated integrated controllers have led to steady improvements since that time.

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Regulatory requirements: Safety

In the USA, lower mains voltages (and consequently higher currents) have meant that the main focus of safety regulation is fire hazard. This has primarily resulted in the need for care in choice of materials, but has little direct influence on design otherwise. In Europe, by contrast, the prime focus, because of the higher mains voltages used, has been on preventing electric shock. This has been done by mandating the quality of insulation, but also, critically, by mandating creepage (across a surface) and clearance (through air) distances which must be used when providing safety isolation from mains voltages. This has the effect of setting minimum dimensions for isolating transformers.

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Environmental concerns

It is hardly necessary to repeat the current worries about global warming. Unfortunately as long as a significant proportion of our energy needs are met by burning fossil fuels, more power used will lead to more CO₂ in the atmosphere. Also unfortunately, a significant amount of the power used in most current systems ends up as heat in the power supply itself. An efficient supply produces less heat per unit output. Many benefits flow from reducing this heat which we will address a little later, but it is clear that all responsible organisations and individuals would wish to minimise this wasted energy, and it would seem likely that in the foreseeable future regulatory authorities will take a serious interest. Initiatives like Energy Star are now becoming the de facto standards. It is clear that the effort is currently concentrated on the PC and server market, simply because that is where the biggest savings in power can be made, due to the quantity of product sold, and the relatively short life of such products, but the benefits are available to users of configurable, modular PSUs too, with the Xgen series from Excelsys. Note also, that the longer useful life of such applications, compared to PCs and servers, make it important to introduce efficiency improvements now.

Major Benefits of high efficiency power converters

Less CO₂

Less power wasted equals less fossil fuel burned.

Lower temperatures

Less heat produced implies lower temperatures and less cooling required (fans and air conditioning)

Higher reliability

Lower temperatures mean higher reliability. All currently used reliability models predict this. As an order of magnitude 10° C cooler means double the MTBF (MeanTime Between Failure).

Longer operating life

In addition to MTBF considerations electronic assemblies have parts that wear out. In particular the evaporation of the electrolyte in electrolytic capacitors and loss of lubricant in fans are inevitable. (Insert Loss Vs Efficiency Graph here). The rate of such loss goes up with temperature, and thus the working life of such components is reduced when they run.

Smaller size

With surface mount components and smaller magnetic parts the size of electronic assemblies is now primarily governed by the ability to remove heat from available surfaces. Less heat means smaller possible size.

Lower noise

Less heat needs smaller fans to remove it (or none). For machine shop environments this may not be critical; for domestic and office environments it is. Note also that although lower noise (for similar airflow) fans are available they are usually more expensive.

Less infrastructure cost

With high efficiency, and PFC, upwards of 1200 watts of regulated DC power can be made available even when the mains connection is a simple wall socket. Dedicated wiring is avoidable, at these powers, which is not possible with earlier designs.

Longer battery life

Even with mains powered equipment many applications will have an emergency battery powered Uninterruptible Power Supply (UPS) providing some temporary back-up in the event of mains failure. The less power is wasted, the longer this will last.

The design

As a standard product the Xgen series is used in an extremely wide variety of applications. Thus control and protection are critical. A range of current/power limits, overvoltage protection, over-temperature protection, and current share control mechanisms ensure that it is extremely difficult to overstress the devices.    

The efficiency of a supply will always vary somewhat with load. At low loads the basic overhead of control functions will dominate, and at the highest loads I²R loss will become increasingly significant. Particularly for a standard product the designer must attempt to ensure good performance over a reasonable range of loads.

 

The Efficiency Vs Load graph shows that tuning of the quasi-resonant switching loss characteristics has created a product with efficiency within 3% of maximum from half to full load (600W to 1000W). For the user who wishes to optimise his application efficiency, using 70% to 92% of capability will achieve that goal.

The Xgen utilises leading edge switching techniques, synchronous rectification and the use of best in class components such as silicon carbide diodes, planar magnetics. The result is a design has higher efficiency and close to double the power density of competing products, and which can be specified with high temperature, low noise or medical variants.

Summary

The Xgen series of standard product from Excelsys offers class leading efficiency which results in the ability to offer very high power densities with the options of low noise and high temperature operation. This performance is achieved with carefully optimised choices both in component selection and circuitry choice, while still permitting the use of power factor correction. Overall efficiency in energy utilisation still requires the system designer to optimise his application circuitry, and to apply common sense principals when connecting the power supply, but the use of the Xgen solution gives him a head start in producing the energy efficient systems necessary in today’s world.

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