DIY Power Bank Circuit

The features of digital products are growing enormously, which triggers the frequent usage of smartphones in several applications.  Thus, the battery backup time is decreasing. It will be fun to build a Power Bank for a Mobile Phone as a spare charging source for emergency purposes, 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 the protection circuits and the quality of the batteries. But, when this comes to 18650 cells, the risk factor is less compared with pouch batteries. Good protection is offered by a few readymade modules available in the market. When working with lithium batteries, safety is paramount. While pouch batteries require extensive protection circuits, 18650 cells are inherently safer and work well with readily available power bank charging modules.

Components Required for DIY Power Bank Circuit

Building a reliable power bank circuit board requires specific components that work together to charge, protect, and deliver power safely.

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 Quick Reference

Specification	Details
Battery Type	18650 Lithium-ion Cell (3.7V)
Output Voltage	5V DC (USB Standard)
Output Current	Up to 1A
Charging Method	CC-CV (Constant Current - Constant Voltage)
Protection Features	Overcharge, Over-discharge, Overcurrent
Efficiency	Up to 92%

Power Bank Circuit Diagram and Working Principle

Below is the circuit diagram for our power bank. As we can see, it's fairly easy to make a power bank with a Li-ion battery, TP4056 module and a boost converter. The power bank circuit diagram below illustrates the complete connection scheme. This simple yet effective design combines a power bank charging module (TP4056) with a boost converter to create a functional mobile charging solution.

There are two modes of operation for the circuit:

Charging Mode Operation

• Input power is connected to the TP4056 power bank charging circuit through Micro USB
• The module uses the CC-CV charging protocol for lithium-ion batteries
• Built-in protection mechanism stops the charge at 4.2 volts
• The red LED will indicate that charging is taking place
• The blue LED will come on when the battery is fully charged

Discharge Mode (Phone charging)

• The toggle switch will activate the boost converter circuit
• The 5V power bank module will convert the 3.7 volts to standard 5 volts in a USB outlet
• Over-discharge protection will not allow the battery to discharge if the battery reaches 2.4 volts. 
• Current is limited to be short-circuit safe

18650 Lithium Cell:

The 18650 lithium cell is an important part of this power bank circuit. The term 18650 cell is due to the cell dimension, it is cylindrical in shape with a 18mm diameter and a height of 65mm. Also, these cells are available in different capacities corresponding to applications. These rechargeable cells are widely used in power bank circuit boards due to their reliability and safety features. They are rechargeable cells with 3.7V output.

The method of charging a single lithium-ion cell requires two processes.

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 the maximum limit of the cell should be applied, during which the current declines steadily to the lower threshold current (i.e., 3% of the constant current). All these operation is carried out by the TP4056 module, which is a highly reliable and affordable choice. The power bank charging module supplies a fixed current (typically 1A) while the voltage gradually increases from 3.0V to 4.2V. The TP4056 module automatically handles both stages, making it the ideal power bank charging circuit solution.

 

TP4056 Charging Module with Protection Circuit

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 make it a 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 the overall additional components. The TP4056 is a complete, cost-effective power bank charging module designed for single-cell lithium-ion batteries. It's widely used in DIY power bank circuits because it integrates charging control, protection features, and visual indicators in a compact package.

The module also has two indications: a Red colour LED (L1) to indicate the ongoing charging condition. Blue colour 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 the current can be adjusted by changing a resistor in the module. But the default current will be 1A when bought.

Built-in Protection Circuit Components

The protection circuit is critical for safe power bank circuit board operation. The protection circuit includes,

1. DW01x – Single-cell lithium-ion battery protection IC with dual MOSFET control feature. Below is an 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, overdischarge control, and Overcurrent control by controlling the MOSFET through the circuit.

 

3V to 5V Boost Converter Module

A lithium battery only provides 3.7 volts here, but we need 5v to charge the Cellphone, so we have used a 3-volt to 5v boost converter module here. This boost converter module has a high efficiency of up to 92% and integrated overcurrent protection. The topology used inside is a 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 the 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 a USB Type-A female receptacle, which is universal. Any USB power cable can be used as an interface. The operating temperature of the module is -40°C to +85°C. It also has an LED indication to indicate the presence of a supply from a battery source. The Red colour LED indicates the presence of a power supply across the terminals. This 5V power bank module efficiently steps up the voltage to meet USB power delivery standards.

Boost Converter Technical Specifications

Parameter	Specification
Input Voltage Range	2.5V - 5V
Output Voltage	5V ±5% (adjustable to 12V)
Output Current	1A maximum (at 5V output)
Maximum Power Output	5W
Conversion Efficiency	Up to 92%
Switching Frequency	1MHz
Output Ripple	20mV peak-to-peak
Operating Temperature	-40°C to +85°C

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:

Once assembled, your power bank circuit needs to be charged before first use. The TP4056 power bank charging module provides clear visual feedback throughout the charging process.

The red colour LED indicates the battery is charging in this power bank circuit.

 

Blue colour LED indicates the charge is complete.

 

Charging the Mobile Phone with this Power Bank:

The DIY power bank for mobile phone charging is now ready to provide emergency power. The 5V power bank module delivers standard USB power compatible with all smartphones.

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

 

2. Turn the slide switch ON.

 

3. The mobile phone's battery starts to charge from the power bank

 

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

Troubleshooting Common Power Bank Circuit Issues

Problem	Possible Cause	Solution
No LED illumination	Incorrect wiring or dead charger	Check all connections, verify polarity, test with different USB charger
LED flashing	Battery deeply discharged or faulty	Leave connected for 30 minutes; if persists, replace battery
Blue LED always on	Battery not connected or bad connection	Verify battery connections to B+ and B- terminals
No output voltage	Switch off or loose connections	Verify switch position, check boost converter input connections
Low output voltage (<4.5V)	Battery depleted or boost converter issue	Recharge power bank; test boost converter with fresh battery
Intermittent charging	Loose USB cable or poor solder joints	Try different cable; re-solder all connections

Conclusion:

Creating a DIY power bank circuit is a unique way to gain experience in practical electronics and battery management systems. It is possible to use inexpensive and simple modules - the TP4056 power bank charging module and a 5V power bank module (boost converter) - together with a 18650 lithium cell to create a power bank for charging mobile phones.

The power bank circuit diagrams included in these projects depict typical protection features (such as overcharge protection, overdischarge protection and overcurrent) commonly found in commercial power banks. While power banks can be more convenient and aesthetically pleasing than designing your own circuit, they will not teach you about battery charging applications, nor are they as satisfying as your own DIY power bank circuit board. Using the above projects, a power bank circuit board can also be a valuable source of education, functionality, and appearance.

You may require a portable backup source of power, want to learn about charging circuits, or plan to alter the circuit design for special applications, such as a 12V power bank module, and you can acquire a reliable understanding of portable charging circuits from here. 

Frequently Asked Questions on the Power Bank Circuit

⇥ Q1: What is the reason for the power bank circuit? I'm using a boost converter?
A boost converter is necessary because 18650 batteries are 3.7V, and smartphones have a charging voltage of 5V as defined in USB specifications. The boost converter module increases the voltage input from 3.7V and outputs a charge of 5V with a nominal efficiency of around 92%; therefore, the phone can receive an acceptable charge.

⇥ Q2: How many times can I charge my phone with a 2500mAh Power Bank? 
A 2500mAh power bank can initially charge a 3000mAh phone battery to approximately 60-70% before depleting. The actual performance can vary since you'll lose approximately 10-15% of the accumulated energy due to conversion losses, and battery health is also important. You may want to utilise a 18650 cell capacity of 3500mAh or more to charge a phone battery completely. 

⇥ Q3: Can I safely build a DIY power bank circuit at home?
Yes, building a power bank circuit at home is completely safe, assuming you are using the correct protection circuits. The TP4056 type modules include a DW01 protection IC and a FS8205A MOSFET switch, which prevents overcharge, overdischarge, and short-circuit conditions. It's important to always use genuine 18650 batteries, check polarity prior to usage, and avoid shorting protection implemented in the protection circuits.

⇥ Q4: What do the red and blue LED lights on the TP4056 charging module mean?
The red LED indicates that the active battery is charging (constant voltage and constant current stage). The blue LED illuminates when charging is complete (battery voltage reaches 4.2V and when charge current drops below ~3% threshold), indicating the power bank is fully charged and ready to use! 

⇥ Q5: Can you make a 12V power bank with this circuit?
You do have the ability to adjust the feedback resistor for the boost converter to get 12V out, but the output current is reduced to approximately 400mA. The circuit is usable for LED strips, routers, and other devices that are low-powered and require a 12V supply, but not for high-current applications. 

⇥ Q6: How efficient is this diy power bank circuit?
The boost converter is efficient at ~92%. The total efficiency with charging losses included is approximately 85-90%. This means if you have a 2500mAh battery (3.7V = 9.25Wh), you would expect to output ~1850-2250mAh at 5V to your phone.

⇥ Q7: How can I tell when to recharge my power bank battery?
When the battery has low voltage = undervoltage (less than 2.5 - 3V), the boost converter's red LED will fade or turn off. Your phone will either slow down or cease charging altogether. To avoid over-discharge damage to a lithium battery, you should charge it when the performance drops. You can also add a battery voltage indication module to your battery pack for a more accurate indication.

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