Understanding the 3.3V Voltage Regulator

I created these notes to help better understand the role of the components we are soldering on the MAKERbuino. They also contribute towards an understanding of the schematic. Please feel free to suggest changes.

The 3.3V Voltage Regulator

This component is very simple (on the outside). It takes in positive power of anywhere between 2.7V and 13.2V and outputs a steady 3.3V. The purpose and value of this is self-evident but it is probably worth pointing out that it’s a particularly useful way of (i) dealing with a varying voltage source (such as a battery) or (ii) changing a voltage to a required level.

Take a look at the schematic and you’ll see the LiPo battery outputs 3.7V. In fact this is an average of 3.7V and not a constant 3.7V. You can Google the discharge curve for these types of batteries and you’ll see the voltage level drops as the battery discharges. This means the battery voltage is not consistent. But, also, we already know our SD card requires 3.3V power and will be damaged by a higher voltage. So a voltage regulator is a necessity for this project and 3.3V is an appropriate voltage. Note that the output voltage (3.3V) is labelled as VCC on the schematic. This means anything on the schematic connected to VCC is connected to the output of the voltage regulator and receiving 3.3V.

The voltage regulator has a capacitor on each of its lines: positive power in and positive power out. We have already discussed the role of these capacitors as decoupling capacitors. Looking at the schematic again, we see that Switch 1, we have already soldered, disconnects the positive terminal of the battery which removes battery power from the input of the regulator. So, unless something else is supplying power to the V_BAT line or the VCC line, the circuit is unpowered and the device ‘turned off’.