Lots of projects use the microcontroller (uC) as the ‘brain’ – for example as an intelligent controller in the prototype of a flying machine. Although there are a number of solutions for powering a microcontroller-based system, each type has its advantages and disadvantages, and you need to choose the one that suits the project concerned. Presented here is one ‘universal’ power supply unit for today’s microcontroller projects.
The circuit is a compact power supply capable of providing +5 and +3.3V regulated outputs as VCCs (VCC1 and VCC2), and a stable +2.5V regulated output as a ‘clean’ reference voltage (VREF) for optional analog circuits linked up with the microcontroller unit. Since an input switching circuit is added for internal/external dc power supply selection, you can attach a ‘built-in’ 9V battery pack with the main power supply circuitry for implementing an ‘automatic power backup’ feature.
Major Components List
Add-On Power Distribution Switch
Advanced hobbyists may like this add-on circuit of the current limiting power distribution switch designed around MIC2009A. This add-on is a high-side power switch optimized for general purpose power distribution and control in microcontroller-based circuits. Datasheet and support documentation can be found on Micrel’s website.
The MIC2009A limits the current from the +5V dc input (VIN) to the +5V dc output (VOUT) with the help of the resistor connected at its pin 5 (ILIM). As soon as the output load start sourcing more than 150mA the +5V dc output voltage is automatically controlled by the MIC2009A to limit the load current to this pre-setted level.
The prototype was tested with MIC2009A-2YM6, available in 6-pin SOT-23 package. In this chip, an active-low at its pin 3 (EN) will enable the power switch (by default, pin 3 is low – see R2). But if you are using MIC2009A-1YM6, beware, an active-high signal is required for the purpose.