Projects‎ > ‎Electronic Projects‎ > ‎

Power Supply for 5V and 3.3V


Concept


I normally use a USB port as power supply for my projects. Some ICs need 3.3V instead of 5V as Vcc. Therefore I decided to build a small power supply. 
It uses a range of 7-14V (I use 7V for less power loss) as input voltage and supplies 5V and 3.3V with 1A each. Both supplies can be switched individually.

Design


The schematic and the board design are done with eagle cad.

Schematic


Figure 1: Schematic

Board


I've tried to keep the board as small as possible. The problem is, that I don't have the possibility to etch PCBs (not yet xD). The board is designed to be soldered by hand and routed with wires. Using etching methods and conductor paths would make the board even smaller, but I think it's pretty handy.

Figure 2: Layout


Measurement


The quality of the output voltage is shown below.
The 3.3V output has a small noise of +/-10mV with no load.

Figure 3: 3.3V output, no load

The noise stays the same with a load of 330mA, but the total output voltage is slightly decreased by 20mV. 

Figure 4: 3.3V output, 330mA load

Now I switch between a 3.3mA load and a 330mA load using a function generator and a MOSFET. The jump causes a slightly decrease of the output voltage - noise stays the same.

Figure 5: 3.3V output, load jump from 3.3mA to 330mA.

Pictures


I miss some major parts in the Eagled3D library, that's why a render picture is missing.

Figure 6: Bread board test


I finally used other switches.

Figure 7: Soldered board

Comments



Sources