Underestimating Complexity of SMPS Design(1 of 5)

Problem

These disastrous results include schedule slips, cost overruns, and excessive field failures, with associated warranty costs. The root of the problem is usually underestimating the complexity of power supply design, especially switching-mode power supplies.

The perception that power supply design is trivial dates from the era when power supplies were usually a transformer-rectifier set and a dissipative series or shunt regulator. The perception was probably not true then and is certainly not true now -- now that most power supplies are of the switching-mode variety.

Because this perception led to inexperienced designers being assigned to the power supply, power supply related problems became severe in the 1970-80 decade. The Navy claimed that if power supplies just met their specifications there would be a 20% improvement in fleet readiness. They dictated that the procurement agency had to investigate if less than 10% of a project development budget was devoted to the power supply development -- an unprecedented action. Projects on an 18 month schedule sat on the shipping dock for another 18 months waiting for a working power supply.

Switching-mode power supplies are:

• non-linear circuits
• difficult to stabilize, often having real and complex poles in the right-half plane
• subject to chaos
• magnetically complex -- requiring consideration of proximity and eddy current effects and often requiring planar construction
• analog, digital, and power circuits, requiring knowledge of each discipline
• sources of electromagnetic interference
• etc.

They are not a trivial design task.

Do not use this information for design without independent verification of the information.

Editor: Jerrold Foutz