This batch of Ideas for Design (IFDs) wraps up Volume 1. It includes an inexpensive surge solution and a way to stabilize switch-mode power supplies (SMPS) with slope compensation resistance.
We also have the two best IFDs from the 2012 print editions of Electronic Design. Bill Schweber, a regular contributor to Electronic Design, provides an introduction to these IFDs.
A Zener diode and small resistor can create an inexpensive and effective voltage surge protector for sensitive devices. The tricky part is choosing the right suppressor and value for the resistor.
This idea describes how to compute the value of the slope resistor, Rsl, that will create the desired voltage pulse slope needed to maintain reliability and robustness of a current-control SMPS at pulse duty cycles above 0.5.
Best IFDs Demonstrate Engineering Elegance
by Bill Schweber
The Ideas for Design department is one of the most popular and widely followed sections of Electronic Design, and with good reason: It embodies the essence of engineering. How so? In an IFD, an engineer takes standard parts and connects them in a clever, innovative configuration to solve a specific problem simply and crisply, and usually at lower cost than alternative approaches. Furthermore, since in most cases it's a circuit alone without needing any software to function, anyone can look at the schematic and description to study, follow, and grasp the design's intent and execution.
This year's Best Idea for Design, "Simple Circuit Turns PWM Into a Digitally Adjustable Precision Reference" by Rick Mally, tackles a common design dilemma of needing a function that is both precise and adjustable, preferably via digital control.
The circuit uses just six passive components, including a common, low-cost LM431 shunt regulator, to configure a Sallen-Key filter that, in turn, transforms a digital pulse-width-modulated (PWM) output into a fully controlled dc voltage. The 0% to 100% duty cycle of the PWM signal maps to an output between −2.5 and +2.5 V (based on a 0- to +5-V PWM signal). This "small" circuit tackles a much larger challenge with clarity and directness.
Runner-up "Electronic Load Achieves 0 Ω" by Henry Santana packs a one-two punch. First, it shows how to build an electronic load, which is an increasingly common, more versatile replacement for a resistor-based load when doing test and evaluation. But it also shows you how adding just a little more circuit complexity lets you take this load down to 0 Ω.
Although that seems unnecessary—after all, you could just hard-short the load using an electromechanical relay—the author explains why being able to electronically transition down to 0 Ω smoothly actually results in more meaningful and insightful data, especially with low-voltage supplies. That's representative of true engineering insight, when incurring a small additional burden in component count avoids a potential problem and enables better results.