The New Economics of On-Board Power

• more reliable, efficient solutions

• costs significantly reduced

The latest advancement in distributed power — on-board 12V busses dispensing power to numerous non-isolated, step-down, buck regulators — is not the consequence of exotic electrical-performance demands. The driving force is simpler and more potent — it’s money.

Showing little regard for the cost of power as they pursued higher performance, the developers of today’s complex IC’s have bequeathed us a dozen different “standard” supply voltages (0.8V, 1V, 1.2V, 1.5V, 1.8V, 2.5V, 3.3V, etc.) to operate chips guzzling huge amounts of current. Today’s system boards often require six to seven voltages at individual currents ranging from 2 to 60A.

The cost of such straightforward power delivery is too high. Parallel, isolated power paths from backplanes onto system boards are redundant and no longer affordable. It is impractical to pay for multiple isolation barriers, multiple sets of “stand-up” capacitors and multiple inlet filters. One economic solution is true on-board distributed power. Not a new concept, it is rapidly becoming compellingly affordable. There are three basic elements:

• A single, high-power isolated DC/DC converter coming from the backplane (typically 48V for telecom/IT) onto the board.
• An on-board “low-voltage” bus/plane (12V appears to be most popular, but 5V and 7.5V are being evaluated).
• Multiple, non-isolated, step-down converters tapping into the 12V plane.

Non-isolated DC/DC converters are less expensive. They don’t require transformers, optocouplers or isolated drive circuits controlling power FET’s in the secondary timed to events in the primary. They are inherently more reliable, more efficient and less expensive than their isolated brethren, and at similar voltage/current levels, they typically run 4-5% more efficiently at half the cost.

Configuring today’s power-distribution scheme is uncomplicated. The point-of-load power processors (POLPP’s) are designed to be true low-cost, plug-and-play components. For example, the LSN D12 Series 10A single-in-line DC/DC’s from DATEL Inc are up to 96% efficient, and they need no input/output capacitors to meet their specified noise levels. They do not require EMI filtering, as both their radiated and conducted emissions are below FCC Part 15 and EN55022 Class B levels, and they present no exotic load impedances to the bus converters. In addition, they are inexpensive in high volumes, fulfilling the need for affordability.