Power Supply Circuit for MCUs

Introduction

Part 1: 5V and 3.3V 1A Power Supply

Here is the power supply module that the 1A circuit is based off of. We have used this module frequently in other classes and it is capable of plugging into a breadboard directly. A major goal with our power supply design is to be able to plug it directly into a breadboard and use it similarily to this power supply module. Jumper headers on either side of the board allow us to choose between 5V and 3.3V output.


Figure 1. 1 Amp Power Supply Module.

This is the schematic of this power supply module. The important bits are the AMS1117 regulators and their associated components. We don't need to incorporate the USB-A port into our design since it is not used often.


Figure 2. 1 Amp Power Supply Module Schematic.

After taking notes on the available components' footprints (capacitors, resistors, and diodes), I recreated the schematic in Eagle PCB. The main modification made was moving the LED and resistor to indicate when the power supply is receiving power through the DC barrel jack rather than when 5V is being outputted from the first AMS1117 regulator. I also created a custom symbol and footprint for the switch availble in our lab which will function as a ON/OFF switch for the board. After the first AMS1117 a 5V_1A_OUT net label is created for later use. This also happens with the second AMS1117 which has a 3.3V_1A_OUT net label.


Figure 3. 1A power supply circuit schematic in Eagle PCB.

Now that the 1A power supply circuit schematic was finished I moved onto the 3A power supply circuit.

Part 2: 5V and 3.3V 3A Power Supply

The 3A power supply circuit is based off the following power supply module, which is able to provide up to a 3A 5V and 3.3V output. It utilizes a LM2596S voltage regulator instead of an AMS1117 as well. The circuit schematic was also generated via Texas Instrument's online app which provides what inductor and capacitor values should be used based on your inputted parameters (voltage range, temperature, current output, and voltage output).


Figure 4. 3A Power supply module.

The follow schematic was implemented in Eagle PCB based off of TI's online app's schematic. The PWR_IN net label connects this part of the schematic to the DC barrel jack input which can be seen above in Figure 3. Net labels for the 3A 5V and 3.3V are also created for later use.


Figure 5. 3A power supply circuit schematic in Eagle PCB.

Now that the main part of the power supply schematic was complete, I needed to decide how to implement the breadboard compatibility into the design. I originally wanted to use the 3-pin switches to control the outputs but I was concerned about accidentally putting two different voltage sources in parallel. In order to just avoid this issue completely I decided it was simpler to use jumper headers to control the output (like with the power supply module in Figure 1). On the right side of the schematic I set up header pins for the jumper. While the jumper is not connecting the pins an open circuit prevents any voltage from appearing at the outpin pins (OUTPUT_L and OUTPUT_R). Once connected a jumper will short the output choice to the pins that connect to the breadboard.


Figure 6. Entire power supply module schematic.

Once the schematic was completed I began designing the board layout. The first thing I did was measure a breadboard I had available so that the power supply PCB would have similar dimensions. The width of my breadboard was about 5.5 cm or 55 mm. I measured the distance between the header pins on the 1A power supply module, which turned out to be about 5 cm. Using these measurements I then placed the header pins near the bottom (with the header pins controlling outputs above them). I then placed the various other components trying to conserve space and minimize distances between components that need to be connected together. After I was happy with the layout I then edited the default trace width to be 40 mil and autorouted the design as was specified in the tutorial. I did need to edit some of the traces due to overlap errors after running a DRC check but for the most part the autorouter functioned well. After this a copper pour was done on both the top and bottom layers which were connected to GND. The board layout can be seen below in Figure 7. Figure 8 also displays a look at what the PCB will look like after manufacturing.


Figure 7. Power supply PCB board layout.


Figure 8. A render of what the power supply PCB will look like once manufactured.

Once the boards have been manufactured the design will be verified after the necessary soldering is completed. The soldermask was also verified using Online Gerber Viewer after generating the CAM Outputs and Gerber Files. The drill file was zipped together with the gerber files and submitted to PCBway for review as well. The schematic also passed the necessary ERC check (the only messages were that the header pins didn't have a value) and the board design passed the necessary DRC check.

Part 3: PCB Manufacturing and Verification

After a few weeks the manufactured PCBs were finally received. The power supply components then needed to be soldered on successfully using surface mount device components and the design should have its functionality verified. The completely soldered PCB can be seen below in.


Figure 9. Completely soldered power supply PCB.

After soldering the components onto the PCB, all of the outputs were tested to verify the voltage was correct. This was done using a simple circuit consisting of an LED and resistor so that everything could be seen visually. All of the outputs worked correctly but only a few images will be included to show it functioning. Figure 10 shows that the right side output is able to provide 3.3V using the 3.3V 3A output.


Figure 10. Testing 3.3V 3A voltage output on the right side.

Figure 11 below shows that the current output on the right side is 3.12 mA (using the 5V 1A output). The current outputs were pretty similar to one another when using the same voltage output. For example, the 5V outputs consistently had current measurements near 3.1 mA. The 3.3V outputs had current measurements near 1.48 mA. This is due to the circuit not needing to draw very much current from the power supply. The LED doesn't need to have 1A or 3A current running through it since it would likely burn out which is why the 1k ohm resistoris neeeded.


Figure 11. Testing 5V 1A current output on the right side.

Figure 12 below just shows the 5V 3A output providing 5V across the LED and resistor.


Figure 12. Testing 5V 3A voltage output on the left side.

Conclusion