DIY Power Bank Circuit

The features of the digital products are growing enormously which triggers the frequent usage of smart phones in several applications.  Thus the battery backup time is getting decreased. It will be fun to build a Power Bank for Mobile Phone as spare charging source for emergency purpose which is also portable. In this article we will discover how to make a power bank with a super simple power bank circuit diagram.

The important factor to be considered while working with lithium batteries is protection circuits and quality of batteries. But, when this comes to 18650 cells the risk factor is less compared with pouch batteries. Good protection is offered by few readymade modules available in market.

Components required for Power Bank Circuit:

1. 18650 Lithium cell
2. TP4056 Module with battery protection circuit
3. 3V to 5V boost converter with 1A current control
4. Slide switch

Power Bank Circuit Diagram:

Below is the circuit diagram for our power bank. As we can see its fairly easy to make a power bank with li-ion battery, TP4056 module and a boost converter.

 

18650 Lithium Cell:

18650 lithium cell is the important part of this power bank circuit. The term 18650 cell is due to the cell dimension, it is cylindrical in shape with 18mm diameter and height of 65mm. Also these cells are available in different capacities corresponding to applications. They are rechargeable cells with 3.7v output.

The method of charging a single lithium ion cell requires two stage,

1. Constant current (CC)
2. Constant voltage (CV)

During CC the charger should supply constant current with increasing voltage till the voltage limit. Next a voltage equal to maximum limit of cell should be applied during which the current declines steadily to the lower threshold current (i.e., 3% of constant current). All these operation is carried out by the TP4056 module which is highly reliable and affordable choice.

 

TP4056A Module:

This is a low cost charging solution to charge any type of single lithium ion battery. Mobile batteries, 18650 NMC cells, Lithium pouch batteries, etc. The micro B Receptacle and easy adjustable 1A output current control makes it reliable choice to charge any low capacity batteries. It can be connected to any wall socket based mobile charger or any sort of USB to micro B cable. It is made of an integrated PMOS load switch architecture, hence reducing overall additional components.

The module also has two indications, Red color LED (L1) to indicate the ongoing charging condition. Blue color LED (L2) indicates the completion of charging. This module can operate at high ambient temperature since the thermal feedback can regulate the charge current. The charge voltage is 4.2V and current can be adjusted by changing a resistor in the module. But, the default current will be 1A when bought.

 

The protection circuit includes,

1. DW01x – Single cell lithium ion battery protection IC with dual MOSFET control feature. Below is a application test circuit provided in the datasheet.

 

2. FS8205A – Dual N-Channel enhancement MOSFET with common drain connection. Also the drain to source resistance is low. The gate of the MOSFET is controlled through the DW01A IC.

Thus, the DW01A provides Overcharge control, Over discharge control, Overcurrent control by controlling the MOSFET through the circuit.

 

Micro USB 3V to 5V Boost Converter:

Lithium battery is only providing 3.7 volt here but we need 5v to charge the Cellphone, so we have used 3v to 5v boost converter module here. This boost converter module has high efficiency of upto 92% and integrated over current protection. The topology used inside is Non-isolated step-up converter which operates at a switch frequency of 1MHz. The overall power output that can be drawn out of this module is 5W. The output voltage can be adjusted to 12V by changing a resistor in module but the maximum current will be 400mA. But by default this module is available at a rating of 5V, 1A. Under this rating the output ripple is 20mV pk-pk. The module also has USB type-A female receptacle which is universal. Any USB power cable can be used as interface. The operating temperature of the module is -40°C to +85°C. It also has an LED indication to indicate the presence of supply from battery source. The Red color Led indicates the presence of power supply across the terminals.

We previously used the same module in Solar Mobile Phone Charger Circuit.

 

The modules were connected and fixed to a plastic plate using hot glue.

 

Charging the Power Bank Circuit:

Red color LED indicates the battery charging in this power bank circuit,

 

Blue color LED indicates the charge complete,

 

Charging the Mobile Phone with this Power Bank:

1. Connect the USB to micro B cable to the output of boost converter.

 

2. Turn the slide switch ON.

 

3. The mobile phones battery starts to get charge from the power bank

 

So this is how you can easily make Power Bank Circuit for charging your Smart Phones. Below you can find the video which demonstrates how to build 18650 Lithium Cell based power bank circuit.