36 eTech - ISSUE 6 eTech - ISSUE 6 37

In our previous eTECh article we discussed how the high level power architecture in complex multi-rail power systems can have a strong infl uence on product energy use. This article builds on the initial discussion to describe a new concept in power system design - the Rapid Power System (RPS).

New Concept - Rapid Power SystemOften, provision of the power supply for a new product is considered late in the development process. The RPS allows a designer to implement a custom multi-rail power supply at the very fi rst stages of new product development which brings a number of key benefi ts:

1. The ability for a designer to rapidly confi gure a complex multi-rail power subsystem with minimal power design experience.

2. The capability to easily provide detailed power use information during product development which helps the user to minimise product energy use and form an accurate power system load profi le.

3. The fl exibility to modify the power supply very quickly if the specifi cation changes.

4. A low risk route to easily map the custom power subsystem into volume production.

RPS consists of two main products; a prototyping test system which is used during the product development phase and a generic platform onto which proven designs can then be mapped for volume production.

The RPS provides a main 12Vdc rail and four user pluggable module zones giving the capability of up to fi ve DC output rails. A total system load of 60W is possible with module output of up to +/-25Vdc and +/-6Adc. The test system will monitor the minimum, maximum and average value of each DC output voltage and current as well as measuring mains AC input power, frequency, RMS voltage, RMS current, system output power, total power loss, overall conversion effi ciency and operating temperature. Use of the host application running on a computer allows the user to chart all the system variables over time in order to provide complete power qualifi cation of a new product.

“...provides detailed real-time

knowledge required to

minimise power consumption

throughout the new product ”

Rapid power for the modern electronics system

Continued page 38>

figure 1 – Rapid Power System (RPS) Test Unit

by Dr. Iain mosely, Technical Director of Zonetechwww.zonetech.com

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Switch Eng ad 285x220mm:1 15/2/11 11:38 Page 1

38 eTech - ISSUE 6

< Continued from page 37

Example System – External hard Disk DriveAn external hard disk drive requiring +5V and +12V voltage rails was powered using the RPS system. The data captured shown in Figure 2 details four of the twenty three possible useful measurements during the course of the test:-

1. PLOT 1 - Shows the power drawn from the 230Vrms mains supply (Note the peak level measured at the start of the test)

2. PLOT 2 - Shows the voltage measured on the +12V output including minimum, maximum and average levels

3. PLOT 3 – Shows the power drawn from the +12V. Again, note the peak power consumption at the start of the test

4. PLOT 4 – Shows the power drawn from the Z1 Module (5VDC in this case).

The results of the hard disk test show that the typical total mains power draw of the product is around 10W in steady state with a five second peak of about 32W during start-up. Analysis of the output rail powers show the high peak occurs on the 12V rail and it is most likely that this is the rail used to drive the motors in the hard disk. The 5V rail power is constant until a data read or write is performed. During a data read/write, the load on the 5V rail increases from around 2W to 3.5W, probably a result of moving the hard disk heads across the disk. Thus, the power supply used to drive this disk would have a basic specification of:-

+12V/500ma with a 2.3a/5 second peak capability+5V/800ma

So, how can we use the data to save energy? The data shows that the power use when the disk is reading or writing data is around 9.6W. The power use when in idle mode is 7W. In particular, during idle mode, more than 70% of the power draw is on the 12V rail and is being used to spin the disks. Since external hard disk drives are often used for data back-up, the most straightforward way to reduce energy consumption would be to power down the motor during periods of disk inactivity.

ConclusionMeasurement of product energy use is often only performed at the end of the development cycle when the options for improvement are limited. The use of the RPS system by product designers during the first stages of the development cycle provide the detailed real-time knowledge required to minimise power consumption throughout the new product.

The simple approach used by RPS provides a low risk solution to the complex power requirements of modern products. The speed of implementation frees up design engineers to focus on the key aspects of their new product design, safe in the knowledge that the power system sitting behind it is proven and can be mapped into a volume product when they move into production.

find out more about ZoneTech at www.zonetech.com

measurements

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1.5 Gb Data Write

figure 2. Data Captured During Test of an External Computer hard Disk

figure 3. This plot shows a zoom of the first 30 seconds

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