Zero in on Power Analysis

Given the emphasis on "green" initiatives, in which anything and everything is touted as "energy efficient," there's been lots of chatter about low-power design. Naturally, much attention is focused on switched-mode power supplies, power devices, and power-conversion circuitry of all kinds. This is where a lot of power efficiency is either lost or gained, depending on how carefully you approach the design task. You know, a milliohm here, a milliohm there, and pretty soon you're talking about real voltage drops that are going to affect the performance of a power-distribution system.


Thus, in all corners of the design and development infrastructure, there are efforts aimed at low-power design. For one, device manufacturers are just as aware as you are of the critical nature of their products in determining overall system efficiencies. That's why Intel has spent a fortune developing 22-nm FinFET 3D transistor technology for its next-generation processors. There's tons of interest in gallium nitride (GaN) transistors for microwave power amplifiers because of their robustness at high temperatures. They'll also fit well in applications like high-voltage switching devices for the power grid. Silicon carbide (SiC) is another promising material for high-voltage, fast-switching power device applications.

Then there are the tools that design teams and technicians have to work with when facing the challenges of designing and debugging power supplies and associated circuitry. No designer or technician would dive into such a task without his or her trusty scope at the ready. Out of the box, most modern scopes will accomplish the basic tasks associated with power supply or device analysis, such as measurement of power losses, saturation voltages, high-side gate drive, dynamic on-resistance, and safe operating area. But setting up all these measurements is a time-consuming task. Better you should spend more of your time getting results than setting up measurements.

Teledyne LeCroy's Power Analysis software in action

One way to reduce the overhead of power analysis is to equip your oscilloscope with power-analysis software, which serves to automate those measurements and analyses for characterizing power devices and circuits. Shown at left is a screen capture from Teledyne LeCroy's Power Analyzer software. The image is an example of device analysis, including analysis of power losses and safe operating area for the switching FET in a switched-mode power supply.

Such software automatically sets up and displays a wide range of waveforms and parameters. In the example shown, the upper trace shows the FET's drain-to-source voltage while the center trace shows the FET's drain current waveform. The bottom trace shows the power dissipated by the FET. Meanwhile, at right is a safe operating area plot, with the horizontal axis being voltage and the vertical axis being current. The upper-right corner of the plot represents maximum power. SOA plots help determine whether the device is exceeding its maximum voltage, current, or power rating.

Likewise, control-loop analysis of such a circuit digs into variations in the parameters of a power supply's feedback loop. For example, you might want to explore how well a PWM control loop responds to load changes. You can easily display the dynamics of the width variation on a per-cycle basis, and, for that matter, duty cycle as well.

Low-power design is here to stay, and as system designs evolve to encompass more and more functionality, power analysis will be at the forefront of the battle to keep power consumption under control. If your testbench is on the front lines, then you probably ought to look into equipping your oscilloscope with power analysis software.