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Issue #206 September 2007
Smart Power
An Intelligent Power Supply for Embedded Systems
by Alexander Popov & Jordan Popov
This “intelligent” power supply was designed specifically for testing embedded systems. In addition to its numerous useful features, the ATmega169-based power supply can provide any voltage from 0 to 5 V with 10-bit resolution.
Start | Hardware | Software | Calibration | Voltage Presets | Slowly Rising Voltage | Slowly Falling Voltage | Short Time Test | Periodcal Linear Voltage | Periodical Voltage Drops | Future Development | Sources & PDF
As digital integrated circuits evolve, their power supply requirements also change. When I started experimenting with digital ICs, the 74 TTL family was popular and easy to acquire. All the boards were powered by a single 5-V power supply. I made my first step into the embedded world with an i8031 microcontroller with the inevitable ’373 latch for addresses, external EPROM, SRAM, and a MAX232. The system was powered by a common 5-V power supply. The power supply was not a component that required attention—the same design was applicable for most digital designs.
As technologies evolve, transistors inside ICs become smaller and require lower voltages. The major focus for an embedded system moves from speed to lower power consumption and more battery-powered devices are developed. To efficiently use the capacity of a battery, a microcontroller must use the same voltage or about the same voltage provided by a battery. That is why there are a variety of voltage requirements for embedded microcontrollers (from below 1 V to more than 5 V). An embedded system developer can no longer rely only on the good old 5-V power supply to feed the new chips.
As an embedded systems developer, I always need a good power supply for my embedded projects. The Atmel AVR Design Contest 2006 was the perfect opportunity to shoot two rabbits with one bullet. I decided to participate in the contest, which I always enjoy, and build a useful power supply. This article gives me the chance to present the design to the embedded community.
My first idea was to build a digitally controlled power supply that could provide voltages down to 0 V to feed most single-supply embedded microcontrollers. But my thoughts changed after playing with the Atmel AVR Butterfly module that was shipped to the contestants. It offers a nice user interface and menu system, and it has enough resources to build a more complicated device. After thinking things over, I came to a few conclusions.
First, like every good power supply, I wanted mine to have short-circuit and overcurrent protection. This is essential for safety and reliability. I wanted the protection to be self-resetting because it can be annoying to replace fuses. Second, I wanted the display to be used to show the voltage and the current or power consumed. By monitoring the current drawn and power consumed, I knew I could directly measure the power efficiency of the system under test. Third, I wanted the device to be able to test the target system for sensitivity to major power supply problems, such as a brown-out, slow-rising power, periodical voltage drops, and noise on the power lines.
With the help of my father Jordan (especially with respect to the analog part of the circuit), I built an intelligent power supply. The working prototype is shown in Photo 1. You’ll find it easy to build a similar system. The system’s main components are depicted in Figure 1.
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| Photo 1—The prototype of the intelligent power supply did a great job proving the concept, testing the software, and evaluating the results. The finished product—which has a more compact PCB design, a 110/220-V PSU and cord, and a proper (grounded) case—features the Butterfly on its front panel. |
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| Figure 1—As you can see, the power supply is pretty simple thanks to the Butterfly module. |
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