Power Supplies Move toward System-Level Thinking

Power supplies are a critical part of any ruggedized electronic system. In its simplest form, a power supply provides critical functions such as voltage regulation, surge protection and EMI filtering. A system may not function well, if at all, when the power supply is not designed properly. The development of a military grade power supply requires expert knowledge. Development can be lengthy and expensive; therefore, many system integrators today simply reuse existing designs or purchase them off the shelf to meet time-to-market requirements. A “smart” power supply, designed with the concept of modular building blocks, enables flexible and rapid development that scales to the power requirements of a variety of electronic systems.

Conventional power supplies perform basic power conditioning functions, such as converting MIL-STD-704 or MIL-STD-1275 28V input power into VME/VPX output voltages such as 5V, 3.3V and 12V. “Smart” power supplies, on the other hand, go beyond merely generating regulated voltages and provide the system integrator with tools (Figure 1) that are tightly coupled with the functionality of the power supplies in ways that were not previously packaged into a single module. Built-in features such as self tests, current/voltage/temperature monitoring, failure reporting, controlled power-up and power-down sequencing and nuclear event circumvention can be modularized to reduce the system development.

 

“Smart” power supplies go beyond just generating regulated voltages, and bring together functions such as self tests, current/voltage/temperature monitoring, failure reporting, controlled power-up and power-down sequencing and nuclear event circumvention.

VITA 62 and Smart Power

For that same reason, the recent VITA 62 standard defines a modular packaging standard for 6U and 3U VPX power supplies, making a COTS solution possible. Figure 2 shows an example of a VITA 62 3U VPX power supply. While the basic functions of power supplies remain the same, a modular design that conforms to standard pin-out and form factor enables system designers to quickly connect the dots and build the system with confidence.
 

The VITA 62 standard defines a modular packaging standard for 6U and 3U VPX power supplies. Shown here is an example of a VITA 62 3U VPX power supply.

In the past, monitoring, fault reporting and fault handling capabilities have often been implemented outside of the boundary of the power supply, such as a combination of a custom-design single board computer and an analog-to-digital I/O board, where I/O capabilities and processing power are available. While this might make sense at the time the system is being designed, it will eventually become a problem when components go obsolete. If no off-the-shelf replacements are available, the cards need to be redesigned to match the original pin-outs and functionality, which is both costly and time-consuming.

Power Supplies Enter Digital Age 

DC-to-DC converters and micro-controllers have rapidly evolved in recent years such that it is now possible to incorporate many “bonus” features into a smart power supply module. An industrial microcontroller would typically provide Analog-to-Digtital Conversion (ADC), discrete I/Os, memory and a programmable microprocessor core for monitoring, self tests and implementing other custom logic. With the advent of these small-footprint and highly integrated software programmable microcontrollers, designers can now place these capabilities right into the power supply module itself, substantially reducing development time. Without an integrated microcontroller, a designer would have to use multiple ICs and an array of discrete components, which will occupy valuable real estate on the already crowded circuit board.

A smart module may communicate with the host processor via a serial bus, I2C, or, in the case of VITA 46.11-compliant systems, Intelligent Platform Management Bus (IPMB) for VPX. For example, the microcontroller on board a power supply can continuously monitor the functionality of the module. In the event of a power failure, the host computer will be notified of the fault via a standard protocol called Intelligent Platform Management Interface (IPMI), enabling it to react appropriately depending on the application. This is particularly useful in a large system. A self-contained smart power supply alleviates the need to put the power monitoring circuits, which require custom I/O and board area, elsewhere in the system. This approach enables the entire system to be designed using true “COTS” building blocks (such as SBCs, switches and video cards). 

Power Management and PMBus

Internal to the module itself, the Power Management Bus (or PMBus) may also be used to communicate with increasingly popular PMBus-enabled components, such as power monitors, DC-to-DC converters, trims and power distribution modules. PMBus is a 2004 standard drafted by a coalition of industrial partners. To ensure interoperability and simplicity, PMBus is based on the System Management Bus (SMB) protocol over an I2C physical layer, similar to IPMB in concept. The adoption of PMBus would further simplify power supply designs and free up board area for other features.

Due to the need for rapid system development using off-the-shelf components and to satisfy system-level self-test coverage requirements, there is an increasing demand for power supplies to be self-contained. The present integration level enables these additional features to be packaged into the same (or smaller) form factor as earlier designs. For comparison, Figure 3 shows a conventional half-ATR power supply design.

 

Today’s integration level enables system-level self-test coverage to be packaged in the same (or smaller) form factor as earlier designs. For comparison, shown here is a conventional half-ATR power supply design.

Nuclear Event Circumvention

Another modular power supply feature is the incorporation of a nuclear event detector (NED) to protect against damage to the system electronics in a nuclear event. Nuclear event circumvention is quickly becoming an important power supply capability among military customers, especially for ground vehicles.

For its part, Curtiss-Wright has developed modular, radiation-tolerant, smart power supplies with NED and crowbar technologies, which have been tested and proven at the White Sands Missile Range. These products passed military nuclear survivability requirements and are currently deployed in ground combat vehicles and other platforms. VITA 62 also has direct support for power supplies equipped with NEDs.

Aircraft and Vehicle Standards

Ruggedized military electronic systems require power supplies that typically take unregulated power input and generate multiple voltage outputs. Such MIL grade power supplies include the MIL-STD-704F standard for aircraft and MIL-STD-1275 for vehicle use. A smart power supply designed to meet the VITA 62 standard enables electronic systems to be intelligently managed by optimizing system visibility.

Power supplies that include power management and power distribution solutions enable system designers to concentrate on other aspects of their electronic systems, to achieve quicker time-to-market. The modular approach to power management and power distribution, along with custom and standard engineered system solutions, enables smart power supply vendors to optimize and scale power supply designs for the military system designer’s specific power requirements.