We have the technology

Kevin Parmenter is the field applications engineering director for distribution and EDMS (electronic design manufacturing services) at Fairchild Semiconductor (Tempe, AZ). His group of engineers helps customers with their designs, often by providing test services. The group specializes in power electronics, working on devices that range in power from milliwatts to kilowatts and that go into products from guitar amplifiers to welders.

T&MW: What kind of support does your group provide to designers?

Parmenter: We recommend parts, provide paper designs, and provide reference designs that include test data based on measurements in our lab. We also provide technical support for customers who have problems with their designs. We often meet with customers and help them with measurements.

T&MW: What kind of problems does your group solve?

Parmenter: Many of our customers design power circuits for products that must operate in a standby, low-power mode to comply with Energy Star and other requirements. Most requirements call for standby power consumption of under 1 W.

Many customers try to make measurements with whatever equipment they have, which is often just a handheld DMM. But standby power generates complex, aperiodic waveforms with frequencies in the kilohertz range that DMMs can't accurately measure: Their sampling rate is too slow, and they can't synchronize voltage and current measurements. We use power analyzers from Voltech and Yokogawa that have wide dynamic range, fast sampling, and synchronization of the voltage and current measurements. It's possible to make these measurements with an oscilloscope if it has the right software, but most engineers don't have that.

Engineers designing power circuits may not have the equipment they need to properly test their designs. They usually lack electronic loads or variable AC power sources. Instead, they build home-made test loads from several resistors, or they perform tests using the power circuit's intended load circuit. We have programmable loads and AC power sources that let us test power circuits under a wide range of conditions. We often use the electronic loads to test the dynamics of a customer's power-circuit design. For stability measurements, we use an AP Instruments analyzer, which is designed for the noisy environment of power supplies. Stability problems aren't always caused by an IC; they also occur at the system level. For example, a customer may not have designed a circuit's magnetics properly or may not have measured the effective series resistance of a capacitor. Board layout can also introduce problems.

T&MW: What kind of measurement questions do you ask your customers?

Parmenter: We ask engineers, "What happens if you run this design at full load at 85°C?" We also ask if they've tested their DUT over various loads and input voltages. Many engineering labs don't have temperature chambers. I've seen engineers try to run temperature tests by placing the DUT in a shoe box with a light bulb inside. It's amazing how creative people can get when their boss won't let them have the right equipment.

T&MW: Why do so many engineers lack the test equipment they need?

Parmenter: Management tells engineers to get by with equipment they already have. And it's difficult for engineers to come up with return-on-investment numbers, which makes it difficult to get approvals for new equipment until something goes wrong—a new-product introduction is late or a product fails in the field. After that, it's easy to get approvals for more equipment.

Every other month, we will publish an interview with an electronics engineer who has test, measurement, or inspection responsibilities. If you'd like to participate in a future column, contact Martin Rowe at mrowe@tmworld.com.