Nowadays, the power consumption of smart phones is increasing, most of the smart phone batteries are not detachable, a large capacity portable mobile power has become a necessary electronic products for people to travel. But recent mobile power security incidents have forced consumers and engineers to re-examine the design and development of mobile power, and how much do you know about the internal structure of mobile power?

   A mobile power source usually consists of a shell, a core and a circuit board. Shell is mainly product packaging, as well as the realization of beautiful shape, protection and other functions, commonly used for plastic and metal, some good products are often plastic is also used fire-proof materials. The circuit board is mainly used for voltage, current control, input and output control, and other functions. Core is the most expensive component of mobile power supply, 18650 and polymer cores are the two most common.

   Apart from the core, the circuit board in the mobile power supply is also very important. For rechargeable batteries, the specifications have a safe charge cut-off voltage and discharge cut-off voltage, and a rated maximum operating current. The design of mobile power supply, first of all, to safely charge the polymer battery, because the cost of the battery is relatively high, and in order to ensure the safety and reliability of the system, there must be a charging management system. When a portable device needs to be charged, the polymer battery discharges, and because the portable device typically has a 5V input voltage, there is a 5V boost system. Both charging management system and boost system need circuit board to provide, so the design of the internal circuit board of the mobile power supply determines whether the product is intelligent or not.

   After a large number of security incidents are exposed by the media, the security performance of mobile power supply has become an important factor for people to consider. So engineers should pay more attention to the protection module when designing mobile power products. What protection modules does it include inside the product?

   1. overcharge protection

   Lithium battery overcharge protection is achieved by using a power management chip to detect voltage, the chip in the benchmark state (mobile phone lithium battery is generally 3.5V). When the benchmark rises slowly, when it rises to the VSS-VDD design value, the voltage is to protect the overcharge and turn-off voltage, through the logic relationship output low or high level to control the external control circuit to achieve overcharge protection. Set the VSS-VDD voltage value when the voltage slowly drops to take the reference value. When the reference is detected below the setting, this is the logical relationship to remove overcharge protection.

   2. over discharge protection

   Over-discharge protection voltage refers to the minimum voltage to protect the battery during the discharge transition. When discharging to this voltage point, the protection circuit cuts off the circuit to protect the battery. According to the relationship between battery life and discharge depth, the relationship between battery voltage and discharge rate and discharge depth, and the actual load of the equipment, the discharge termination voltage of the battery is determined, and the discharge protection circuit of the battery is designed.

   3. short circuit protection

   Circuit current caused by short circuit is generally more than 10 times the rated working current, and overcurrent protection needs to delay about tens of milliseconds, direct short circuit caused by tens of times the rated current in tens of milliseconds will also have an impact on battery performance. The existing protection method is PPTC method, which cuts off the circuit through the heat generated by the current, and also requires millisecond reaction time, and increases the impedance in the circuit. There is also a short-circuit integrated chip dedicated to battery pack, which has a narrow application range and high cost.

   4.PTC introduction

   PTC positive temperature coefficient thermistor is also known as polyswitch. Polymer resettable fuse is composed of polymer matrix and carbon black particles which make it conductive. Since the polymer self fuse is conductor, there will be electric current passing through it. When an overcurrent passes through the polymer self restoring fuse, the heat generated (I2R) will expand it. As a result, carbon black particles will separate and the resistance of polymer self recovery fuse will rise. This will cause the polymer self-fuse to generate heat more quickly, expand more, and further increase the resistance. When the temperature reaches 125 degrees C, the resistance changes significantly, resulting in a significant decrease in current. The small current flowing through the polymer self-fuse is sufficient to keep it at this temperature and in a high resistance state. When the fault is cleared, the polymer shrank from the fuse to its original shape to reconnect the carbon black particles, thereby reducing the resistance to a specified holding current level. This article is reprinted by www.52dianchi.com, Shenzhen Electronics Co., Ltd.