OEMs are demanding more from their power supplies - intelligence is the answer, says Stuart Lester
The last year has seen a great deal of discussion about the benefits and dangers of applying “intelligence” in power systems. As well as the talk, there has also been some significant actions, as manufacturers and power system designers have extended the concept of distributed power and intermediate bus architectures.
It is now not uncommon to find sophisticated digital controllers embedded within products, and digital communication between modules within power systems, via I2C or PMbus, is a routine occurrence.
Thus far these developments have been concentrated mostly in the realm of DC-DC architectures. But now there are signs that the trend is moving into the AC-DC world: Astec Power recently launched the industry’s first digitally-controlled switching AC-DC power supply, dubbed the iMP range.
But why would anyone want an intelligent power supply?
The first reason is the relative ease with which engineers can produce a configuration that will satisfy application-specific requirements. Power supply designers are familiar with the adage that no two applications are identical, and a programmable system like iMP offers something like 200 million options based on the same hardware, configurable via PC-based software.
The second reason is also related to speed. The intelligent power supply accelerates not only the “design” part of the process – defining the required configuration – but also the “production” phase. At UR Group’s facility in Swindon, the company is using the concept to offer customers turnaround times as short as 48 and 24 hours.
Whilst historically the major use for such a service would be for short-run and prototyping purposes, there are now a substantial number of manufacturers which can neither forecast their unit requirements, nor tolerate standard production lead-times, in particular the four, eight or even 12-week delays typical for large-scale offshore manufacturing.
The classic user of UR’s quick-turnaround offering is an industrial OEM which knows that it will require hundreds of units per year, but which cannot predict more than a few weeks ahead whether its need in any monthly period will be for, say, ten or 50 supplies. Such unstable demand is becoming increasingly commonplace in many sectors. UR’s customers include: manufacturers of analytical medical devices; communications test and measurement kit; semiconductor equipment; outdoor signage; and inspection or materials analysis instruments.
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An intelligent power suplply can be pre-approved to a variety of standards, including
medical standards such as those required for CT scanners
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The first step in using the service is for the customer to provide UR with a summary of the requirement – usually in terms of what voltages need to be supplied, power levels, and any special constraints such as size or overvoltage protection. That allows UR to come up with a hardware specification and the relevant base equipment can then be delivered to the customer.
At this point the strength of the programmable approach shows itself. The customer can use a PC-based configuration utility to work on the finer points of the design, adjusting parameters such as current limits, and introducing special tolerance values or extended voltage ranges. The system lends itself to an iterative approach; For instance, the designer can experiment with lower fan speeds to improve noise performance, whilst monitoring the impact of changes on the operating temperature of the working assembly.
Once the design is fixed, the configuration data is passed back to UR, which issues a corresponding part number. Future orders are built, programmed and tested at the Swindon facility as required.
The advantages of intelligent AC-DC supplies do not, however, end with fast turnaround time. Building to RoHS and WEEE standards becomes much easier when the system is based on a relatively small number of hardware components, supplied by a global manufacturer that, like Astec, is itself compliant.
The supplier’s role in ensuring RoHS compliance is well-understood but, traditionally, other type approvals have been more troublesome.
Building with compliant components does not necessarily make a compliant system, and so equipment such as medical devices have in the past needed to go through a lengthy testing and approval process. Suppliers such as UR, therefore, have in-house capabilities for testing conducted and radiated EMC emissions and immunity; thermal chambers and thermal imaging equipment for optimising PSU designs; and facilities for highly-accelerated life testing and stress screening (HALT and HASS).
However, an intelligent power supply can be pre-approved to a variety of standards. The iMP, for instance, complies with the EN 60601 medical standard for non-patient connected equipment, and meets the safety and performance requirements of UL and CE. Thus it is pre-tested for factors such as electromagnetic susceptibility, harmonic distortion and isolation; and can cope with defined levels of environmental stress such as shock and vibration. This cuts out both the time and cost of gaining additional approvals.
Increasingly, advanced applications also inherently need the level of control, monitoring and data logging that an intelligent supply can provide. Functions such as monitoring the temperature or output voltage of the supply can help both in providing real-time control and in giving early warning of potential problems. And it is increasingly important that power subsystems behave in a predictable fashion, both in sequencing at power-up and in shutting down in the event of an unexpected failure. Achieving a graceful shut-down and taking the correct actions to flag an error condition may literally be a matter of life and death.
Finally, there is the question of economics.
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Digitally controlled switching AC-DC power supplies
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Choosing between modified standard, configurable and full-custom power supply options has been a complex issue for designers for some time, but greater intelligence can only lend weight to the arguments for configurability. Partly this is due to the increased simplicity with which a configuration for an intelligent power supply can be built using a PC and the target hardware. The iterative nature of the process is also an advantage, allowing early delivery of an initial hardware platform, which can be fine-tuned along with the overall system design right up to sign-off for production.
All of these factors reduce the amount of engineering effort needed to implement a power supply design and they are in addition to the economy-of-scale aspects that reduce the costs of configurable hardware when compared to small-run custom products.
Despite all of this, the truism remains that every application is different. So for large-scale mass production, OEMs are likely to continue to tolerate lead-times measured in weeks, in return for drastically reduced unit costs.
But even in this sector, customers are demanding that suppliers offer more value-add, typically including metalwork, control PCBs, connectors and switches, thermal management components and EMC filtering. In this sense the move towards intelligence is a token of a wider trend. The tendency to “disaggregate” and focus on core value-add means that OEMs are likely to continue to demand more from their power systems, and the suppliers of those systems, for some time to come.
Stuart Lester is power solutions director for UR Group in the UK
www.ur-group.co.uk
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