A mobile power supply usually consists of a housing, batteries and a circuit board. The shell is mainly used for product packaging, as well as to achieve beautiful appearance and protection. It is usually plastic and metal. Some well-known products often use plastic as a fireproof material. The circuit board is mainly used to realize voltage, current control, input and output control, and other functions. The battery cell is the most costly component of the mobile power supply. The 18650 battery cell and the polymer battery cell are the two most common types.
In addition to the battery cells, 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 a safe discharge cut-off voltage, and have a nominal rated maximum operating current. The design of the mobile power supply must first charge the polymer battery safely, because the battery cost is relatively high, and for the safe and reliable operation of the system, there must be a charging management system. When the portable device needs to be charged, the polymer battery discharges to the outside. Because the portable device generally has an input voltage of 5V, there is a system for boosting 5V. Whether it is a charge management system or a boost system, it needs a circuit board to provide, so the design of the internal circuit board of the mobile power determines whether the product is intelligent or not.
After a large number of security accidents have been exposed by the media, the safety performance of mobile power has become an important factor for people to consider. Therefore, engineers should spend more effort on protecting modules when designing mobile power products. Specific to the interior of the product, what protection modules does it include?
1. Overcharge protection
Lithium battery overcharge protection is achieved by the power management chip to detect the voltage, the chip is in the reference setting state (mobile phone lithium battery is generally 3.5V). When the reference rises slowly, when it rises to the design value of VSS-VDD, the voltage at this time is the protection overcharge shutdown voltage, and the low or high level is output through the logic relationship to control the external control circuit to achieve overcharge protection. When the voltage drops slowly, set the VSS-VDD voltage value to take the reference value. When the reference is detected to be below the setting, this is a logical relationship to release the overcharge protection.
2. Over discharge protection
The over-discharge protection voltage refers to the lowest voltage to protect the battery during the discharge transition. When the discharge reaches this voltage point, the protection circuit cuts off the circuit to achieve the purpose of protecting the battery. According to the relationship between the battery life and the depth of discharge and the relationship between the battery voltage and the discharge rate and depth of discharge, combined with the actual load of the equipment, the battery discharge end voltage is determined, and the battery discharge protection circuit is designed.
3. Short circuit protection
The loop current caused by a short circuit is generally more than 10 times the rated operating current, and overcurrent protection requires a delay of about tens of milliseconds. The tens of times of rated current caused by a direct short circuit will also affect the performance of the battery pack in tens of milliseconds. The existing protection method includes the PPTC method, which cuts off the circuit by the heat generated by the current, and also requires a millisecond response time, while increasing the impedance in the circuit. There is also a short-circuit integrated chip dedicated to the battery pack, which has a narrow application range and high cost.
4. PTC introduction
PTC positive temperature coefficient thermistor, also known as polyswitch, polymer resettable fuse (polymer resettable fuse) polymer resettable fuse consists of polymer matrix and carbon black particles to make it conductive. Since the polymer resettable fuse is a conductor, current will flow through it. When an overcurrent passes through the polymer resettable fuse, the generated heat (I2R) will cause it to expand. As a result, the carbon black particles will separate and the resistance of the polymer resettable fuse will increase. This will cause the polymer resettable fuse to generate heat faster and expand more, further increasing the resistance. When the temperature reaches 125 ° C, the resistance changes significantly, which significantly reduces the current. At this time, a small current flowing through the polymer resettable fuse is enough to keep it at this temperature and in a high resistance state. When the fault is cleared, the polymer reset fuse shrinks to its original shape and reconnects the carbon black particles, thereby reducing the resistance to the level with the specified holding current.
Experts teach you how to choose mobile power
one look
Look at the brand. Generally, the quality control of big brands is better. Choosing a good brand is the first step to ensure the safety and quality of mobile power.
Look at the label: capacity, input voltage / current, output voltage / current, number of output ports. This article finally explains the relevant parameters and basic common sense of mobile power.
Note: Be careful about gift power banks. After all, it is a gift, and it will not be of good quality. There is no place to claim if you burn the phone or the battery explodes.
Second, touch
If the surface of the mobile power supply is hot during charging and discharging, be careful, it is best not to use it again, or ask the manufacturer to return it.
3. Listen
Hold the power bank to your ear. If you hear the buzzing sound, it is best not to use it again, or ask the manufacturer to return it, otherwise it may damage the phone.
Four, try
Press the key, and then insert the coin or small key into the phone charging port 20 times. If the power bank is broken, it means there is a problem with the quality of the power bank and it must not be used. You can ask the manufacturer to return it.
Insert the adapter and the mobile phone at the same time. If the mobile phone cannot be charged normally, it means that the power bank is defective. It is recommended not to use it.
Five, use
When using it, do the following tests to see if you have bought a power bank with a virtual capacity or current.
1 Number of mobile phone charging = (65% * nominal capacity of mobile power (mAh)) / (mobile phone capacity (mAh))
For example, if you buy a mobile power supply of 10400mAh and a mobile phone capacity of 2000mAh, then you can charge 3.38 times.
If it has not been charged so many times, it is likely that the capacity of the purchased power bank is not 10400mAh, and you can ask the manufacturer to return it.
2 Mobile power charging time = mobile power nominal capacity (mAh) / (nominal charging current (A) * 1000)
For example, if you buy a mobile power supply with a charging current of 1A and the nominal capacity of the mobile power supply is 10400mAh, it will take 10.4 hours to fully charge the mobile power supply.
If the charging time is too long, either the current of the selected adapter is too small, or the charging current of the mobile power supply is imaginary. The judgment method is also very simple. Using the standard adapter of the mobile phone to test the charging time can eliminate the possibility that the adapter current is too small.
3 Look at the power indicator or LCD power display. Insert the adapter, unplug the adapter, and plug it into the phone. If the power indicator flashes or the LCD power changes suddenly during this process, it indicates that there is a problem with the power display, and it is recommended to use it with caution.
4Whether the mobile phone can be automatically powered off after it is fully charged. If it is found that the mobile power supply has been charging the mobile phone, it is recommended not to use it. You can ask the manufacturer to return it.
Mobile power tips
1 nominal capacity
There will be a battery capacity logo on the mobile power shell, such as 10400mAh. This represents the battery capacity. The larger the capacity, the more times you can charge the phone. At present, the mainstream mobile power supply has achieved 10400mAh. But some illegal businesses will fill the cement block, or use inferior batteries. Consumers can use the previous method to identify whether there is a false battery capacity standard.
2 Charging current
The larger the charging current, the shorter the time to charge the mobile power. Generally, the charging current is between 1A and 2A. Consumers can use the previous method to identify whether the charging current is false.
3 discharge current
The larger the discharge current, the higher the current for charging the phone. This is a question often asked by many people. The charging current of the mobile phone depends on the charging current of the mobile phone itself. As long as the discharge current of the mobile power supply is greater than the rated charging current of the mobile phone, the mobile phone can be guaranteed to be charged according to the rated current. For example, Apple phones are charged at 1A, and iPads are charged at 2.1A. If the discharge current of the mobile power supply is greater than 2.1A, it can guarantee the normal charging of the ipad or Apple mobile phone.
4 input voltage
The input voltage and charging current are generally marked at the same time, indicating that the voltage output by the adapter to charge the mobile power supply, the nominal value is 5V. But the inferior adapter will cause damage to the mobile power supply, and its peak voltage may be as high as 8V.
5 output voltage
The output voltage is generally marked at the same time as the discharge current. The nominal value is 5V. The output voltage of a low-quality mobile power supply may be as low as 4V or instantaneously up to 12V, which often burns the mobile phone.
6 Efficiency
Efficiency will affect the power bank temperature and the number of times the phone is charged. The general charge and discharge efficiency requirements are higher than 90%.
7 Cell type
There are two types of batteries: polymer and 18650. The 18650 batteries that are often exploded are relatively heavy, but the price is relatively cheap. Polymer batteries are relatively safe and lightweight, but the price is higher. In the future, mobile power will gradually replace 18650 batteries with polymer batteries. Therefore, the selection of polymer batteries can greatly improve the safety factor.
8 Battery display method
There are three types of power display: LED light, digital tube and LCD screen. The LED light display is relatively intuitive, but inaccurate; the digital tube and LCD screen seem to be more accurate, but the current quality is still not enough, and the phenomenon of sudden battery power display value at the moment of insertion into the mobile phone often occurs.
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