FEATURE POWER ELECTRONICS
ANALOGUE VS. DIGITAL– THE POWER STRUGGLE CONTINUES
If you are a power supply design engineer or an EE or ASE that selects power solutions for your end system, then no doubt you have stood at the cross roads and pondered the dilemma to go analogue or digital with your power train? Jeff Rodriguez, VP of Engineering Services, XP Powerexplores the options
T
here is no doubt that digital control can aid engineers in achieving higher
levels of flexibility within their designs. Using industry standard commands over a serial communications bus allows units to be turned on and off, output currents have limits set and key operating data be monitored and recorded. Setting the operating configuration parameters is a lot easier than the analogue method but with this flexibility comes the added costs associated with more complex hardware and DSP software. Contrast this with analogue control, which has been around for over 50 years, you will see that traditionally these have been more stable products and tend to be less prone to glitches. Some of the monitoring features that
a digital controlled unit provides can still be achieved but not perhaps with so much ease and the ability to set-up or amend configuration parameters is certainly not possible. But like many things in life, the
combination of both analogue and digital controls seems to bring out the best of each. Of course, finding a compromise can be difficult. Power supplies are making their way up the food chain as a primary consideration when designing a new system. Historically, a power applications engineer used to spend most of their time trying to figure out how to fit the system power in the ‘afterthought’ mechanical space left by the design team.
POWER SUPPLY DEMANDS Today we find system engineers depending on the power supply to do more than just provide analogue world attributes of conversion, conditioning, and protection, supplies are now expected to handle power management as well. System engineers want to be able to communicate with the power supply and get real time information as well as be able to control the power supply, entering the digital realm. Monitoring of real time information
such as voltage levels, current levels, faults, alarms, and time based logging of
18 JULY/AUGUST 2015 | ELECTRONICS
changing firmware is much more manageable than dialing in resistor values during initial system evolution. Digital management literally allows for a vendor to email you a new file for upload to the monitoring and control chip to see if your new configuration works. If not, go right back to the old configuration and create another one. No change to hardware means faster integration and lower cost of integration. Companies such as XP Power are using a combined approach of integrating an analogue PWM controller with the addition of a digital interface, to create communication flexibility.
that information gives a systems engineer the ability to maximise system run time through predictive failure analysis and minimise downtime by having more data to offer a repair engineer. Controlling supply translates to being
able to turn outputs on and off in a fixed sequence and timing, changing output parameters such as voltage and current, and optimising cooling fan speeds for noise minimisation and fan life. Although the monitoring and control can be achieved through analogue means, we find that going to our digital tool bag is often more practical in terms of design, support, implementation, and long-term management of the power system. When you start to consider signals and control in multiple domains such as level and time, and optimising those domains to meet your specific needs, you can see that
Figure 1: Power supplies from XP
DIGITAL POWER SUPPLIES The dawn of digital in power supplies initially focuses on the PWM and the main switching control of the supply. Although being able to digitally change and monitor critical core parameters of the supply seemed appealing at first, the company has found that the benefits that come with a digital “heart”, in most cases, are not justified when weighed against the complications associated with a DSP design. Analogue is still king when it comes to the core power conversion it’s tried and true, trusted in the industry, more readily available, and has shorter design cycles and “bugs” when it comes to new product releases. The company also wanted some of the benefits it discovered on its digital design journey, so has held on to those, but on a secondary level of monitoring and control. The root alarm and control circuits are analogue, but the interface to those circuits are filtered thought a digital layer that gives the best of both worlds. There may be a time where DSP becomes the norm, but for now, the way the company sees it, analogue is going to be around for a while but living in harmony with the digital benefits power management systems are begging for in today’s marketplace.
XP Power
www.xppower.com 0118 984 5515
/ ELECTRONICS
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