Functional But Frugal: Balancing the Power Budget

The origins of modern power management generally lie in markets for mobile consumer products. To satisfy demanding end users, designers must constantly deliver improved functions as well as longer battery life.

Achieving longer battery life by simply increasing the total available energy would impose an unacceptable increase in battery size. That's because battery chemistry tends to obey nature's laws rather than Moore's Law. Therefore, inventive and closely controlled power-management techniques are required to improve efficiency and minimise power consumption.

Nowadays, power management is unlocking significant enhancements throughout the spectrum of battery- and mainspowered electronic products for almost any application.

CIRCUIT BEHAVIOUR

The design and behaviour of electronic circuits, from the transistor level on upwards, are changing to deliver increased functions and performance for a given power budget. IC-core operating voltages are falling to maximise operating efficiency, while the device I/Os continue to operate at a higher level to maximise dynamic range and ensure compatibility with connected devices.

ICs within a system can require two or more supply voltages each, while the board as a whole may call for multiple power domains, including several digital rails plus single-ended or positive and negative analogue supplies. In some systems, a given low-voltage rail may be required to deliver currents from several amps to over 100A.

Since many systems are sensitive to the sequence in which the individual supply rails are brought up, startup sequencing is increasingly coming under the remit of power management, alongside supervisory duties to protect the board against transients occurring or impending failure on any one rail. Supervisory ICs in 8- or 16-pin packages are commonplace in many systems ranging from intelligent instruments up to network servers. To justify their inclusion, the latest trends among supervisory ICs include ultra-low current draw on the order of a few microamperes, as well as consolidation of sequencing functions and monitoring for several power-supply rails.

EFFICIENCY

The drive toward greater energy efficiency within electronic devices isn't confined to consumer markets or battery-powered products. However, it does prevail throughout markets for professional instruments, industrial drives and controls, communication equipment, and the most ubiquitous electrical systems.

Power management is essential in driving circuits for highbrightness LEDs. It helps limit heat generation, ensure consistent light output, and maximise reliability and longevity—as well as support flexible control modes to create lighting effects like colour mixing.

There are various ways to implement current control, based on specific properties of HBLEDs. Nonetheless, functions such as precision current sensing and high-voltage level shifting for long, series-connected strings of LEDs are migrating into controller and driver ICs to reduce external component count and overall footprint.

Most drivers also support a number of methods for brightness control. These allow for basic controls via an external voltage divider circuit or more sophisticated pulse-width-modulation schemes that may be directed by a microcontroller.

PRICE SENSITIVITY

On the flip side of the coin, extreme price sensitivity has slowed adoption of electronic ballast ICs in fluorescent lighting applications. Adding protection against filament failure, failure to strike, and automatic restarts has helped to create a more persuasive offering to lighting designers. On-chip timing functions enable easy setting of parameters to preheat, ignite, and run the lamp and enhance the performance of modern electronic ballasts compared to traditional discrete solutions.

PROTECTION

In fact, controlling startup current and voltage conditions is a fundamental element in power management among a wide variety of applications. For instance, it's become essential to hot-swap in systems such as telecom and Internet infrastructure equipment, solid-state circuit breakers, and a host of 24/48V industrial equipment to maximise availability and utilisation. Though carefully arranging power pins ensures the correct sequencing of supply voltages when inserting or removing a card from the live backplane, a hot-swap controller is vital to intelligently manage the powersupply connections and control inrush current to limit system voltage droop and transients.

Other important power techniques that depend on powermanagement ICs for optimal performance include Power over Ethernet (PoE) as defined in IEEE802.3af. PoE frees networked devices like VoIP phones or POS terminals from the form-factor constraints, cost, and complexity of a local power solution, such as a battery or mains connection.

A suitable powered device controller (PDC) will perform basic functions, including detection, classification, and undervoltage lockout (UVLO), with the latest devices providing enhanced features including adjustable inrush limiting and programmable UVLO. Legacy PoE systems have fixed UVLO thresholds, but variable thresholds have since been introduced for greater flexibility.

Detection and classification are important power-management functions of a PDC, allowing unterminated cables to be left unpowered, while the controller periodically checks for the presence of an Ethernet powered device (PD).

If a PD is detected, classification then determines the power requirement of the device, allowing the controller to intelligently allocate power between PDs and to protect the system against overload. In addition, some controllers are designed to operate with low-cost silicon rectifiers, to further reduce the cost and complexity of IEEE802.3af PDs.

GROWING REMIT

Demand for power management is intense as designers seek cost-effective solutions to intelligently manage power; protect systems against overcurrent, overvoltage, and power-fail conditions; reduce power-supply cost and complexity; and to support enhanced features and greater flexibility.

Farnell's Technology First initiative provides over 8000 of the latest products in one location, alongside access to application support and design-in assistance. The dedicated powermanagement micro-site is situated at Farnell's Web site: http://uk.farnell.com/jsp/bespoke/bespoke7.jsp?bespokepage=farnell/en/ed_world/tech_first/power/home.jsp.

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