Digital Power Supplies Offer PMBus Communication

“We believe our new N-0275 series packs more power and features into a smaller package than any other product currently on the market,” claims Tim Worley, CEO of Powerstax. “The high efficiency design also reduces overall system power consumption and cooling requirements giving our OEM customers more design flexibility and a distinct competitive edge.

“Conventional power supplies are controlled and protected by analogue circuitry that is optimised for one set of conditions, such as cold start-up. This could compromise other operational characteristics such as coping with power line drop-outs or sudden load changes where the power supply response time is compromised by stored charges in components,” continues Worley. “The N-0275 series overcomes these problems by employing a dedicated digital micro-controller to continuously supervise the unit’s operation.”

The on-board micro-controller monitors a number of the power supply’s parameters, dc voltage on the bulk capacitor (supplied by the ac mains), output voltage, output current, auxiliary 12V output voltage, transformer temperature, ambient temperature, and fan tachometer. Unlike conventional analogue control circuitry, that can provide timing accuracies in the range of +/- 10%-20%, the micro-controller can provide timing accuracies in the 1% range and does not suffer from stored charge memory. It responds to changing conditions 500 times per second with knowledge of the past but without being slowed down by the analogue “memory”.

The micro-controller is responsible for enabling the main output whenever all of the required start-up conditions are met and shutting it down on command of the system controller, at loss of input power or whenever the power supply’s reliability is threatened by excessive loads or temperatures. It always provides the host system with advanced warning of an impending shutdown so that it may perform a controlled shutdown with no loss of data or damage to other system components.

To minimize acoustic noise, the micro-controller can turn a 12V fan on or off based upon actual load conditions and the amount of cooling air available. Because it’s programmable, the micro-controller code can be customised to fit the OEM’s specific requirements.

An optional I²C digital communications interface is also available to allow up to four N-0275 power supplies to communicate over the same bus using the PMBus™ protocol. This communications interface allows routine remote control of the main outputs and the 12V fans. It can also notify the host if a fan fails (via lost tachometer pulses). The host can also interrogate the micro-controller for its output voltage and current status and ambient and transformer temperatures.

The N-0275 Series incorporates industry leading features such as active power factor correction for reduced input power, built in or’ing diodes, active inrush current protection, remote on-off, and high efficiency, up to 90% in some models. All Powerstax power supplies meet a full range of international agency approvals, including UL, DEMKO, FCC Class B and are CE Marked.