DIY Portable Power Supply

Whenever I am travelling from one place to another, I used to keep my electronics with me. And sometimes to test even the simplest circuits made of few components multiple voltage levels, wires and USB voltages are required. I can not carry my bench power supply with me, that’s why previously I designed a modular portable power supply which is good to go with and has some voltage testing points. But as the circuit complexities increase it can not deliver that much power and overall I need a rigid easy to use power supply unit.

This is the newly designed portable power supply, I followed the 5v boosting approach in this design. So that I can charge the power supply anytime with a standard USB C/A charger. Overall the design is minimalist, looks good and carries 2S 18650 battery for the power backup. This project is sponsored by PCBWAY, China based PCB manufacturer having 10 years of experience in working with PCB related products. PCBWAY is a one stop solution to all your prototyping requirements including SMT assembly, Stencil, 3d printing and metal CNC.

Features:

5V input battery charging feature

Multiple output voltages 12V, 8.4V, 5V, 3.3V and USB

Boost Conversion at high frequency

Low noise and good PSRR

Switches for selecting output voltages

Onboard 8.4V two cell battery charger

Components Required:

• TP5100 2S battery charger
• MT3608 voltage booster
• AMS1117 3.3/5V regulator
• 10k Potentiometer for voltage select
• Some 0603 resistor (shown in schematics)
• 1nf, 10nf, 100nf, 1uf, 10uf, 22uf ceramic capacitors
• SMD LED 0603 white
• 22uH Inductor
• Push and slide switches
• USB type A/C Female, Screw terminals, Pin headers for I/O
• 18650 battery holder
• Circuit PCB from PCBWAY

Circuit Diagram and Design Approach:

The full circuit diagram can be seen below, the circuit is divided into small sections based on applications. I follow the top to down/ left to right approach, the input is placed on the top left and output at bottom right side.

First section is the main type C input section which is used to charge the onboard 2s 18650 battery. The charging IC is placed in the middle (TP5100), 2S batteries need a max of 8.7V for battery charging. For this the voltage from the TYPE C USB is first boosted to 8.7 and then given to the battery charging unit. I used a 2S battery, two 4.2 batteries in series to get the stable 5V and 3.3V without any drop. In this way the full potential of the voltage regulators can be utilized. A 12V output voltage source is also required for other high voltage applications which is boosted from 8.7V from a second voltage booster section.

PCB Design Considerations:

Because it is a power supply board, it does not carry any differential pair or very high speed tracks across the PCB. Only a few boost conversion frequency generator small tracks which can be traced over a 2 layer stack-up easily keeping ground pour and returning paths in mind. I keep the input and output section away from each other. The 18650 2S battery is mounted on the bottom layer with battery holders.

All the SMD parts are mounted on the top layer of the PCB. The booster section produces unwanted noise frequency, so keep this section away from the voltage regulator and battery charger section. High speed tracks are kept smaller and not overlapped with any other track. Avoid using via while routing for High speed frequency tracks. Ground pour is used on both sides, stitched together via through holes on the PCB. On the silkscreen you can find some test points to see the required voltages availability.

Assembly Process of PCB:

I used the PCBWAY SMT assembly process to get the soldering and part placement done easily. All the components are mounted on the top layer which lower down the overall cost. Some of the general parts are kept as DO NOT PLACE, and soldered by me after receiving the board.

To lower down the cost you can solder the available parts yourself. Because the PCB has a lot of small components like resistor, ceramic capacitor, I opt to go with the assembly process. All the required assembly files can be downloaded from here.

First Power on and Working:

First time power on is not that simple, you can’t just plug the batteries in and use this supply. The PCB has onboard two potentiometers which need some adjustment while first time power on. Any wrong adjustments in these potentiometers may cause failure of IC and burn damages. Set the battery charger booster potentiometer to output a 8.5-8.7V. And 2nd 12V booster potentiometer to that voltage. This setting can be done by powering the portable battery supply with a low power input (max current 100mA) and this is only one time procedure.

After adjustments the batteries can be plugged into the holders, the onboard battery charger is working very fine, set to charge the batteries at a max of 1100mA. 5V, 3.3V has indicator led’s which can be controlled with a push button switch. An onboard slide switch is for 12V output and turns on the respective Led.

Further Design Improvements:

I want to keep the system minimal, but on the other hand I also want to monitor the real time voltages and current across each output port. Which can be displayed on a small OLED. But I don’t want such complexities in this hardware, so in the next update I will add a ESP8266 microcontroller which sends the current and voltage data on a server.

I am finding a solution to get the current values, for example hall effect sensor or maybe a simple shunt based one with a current amplifier. Try the best PCB services now and turn your dream projects into real world applications with PCBWAY. Explore the new PCB DESIGN CONTEST launched by PCBWAY recently.