Internal analysis of mobile power supply

A mobile power source usually consists of a housing, a battery core, and a circuit board. Shell is mainly a product package, and to achieve a beautiful appearance, protection and other functions, common for plastic and metal, some good products are often used in plastic fire protection materials. The circuit board is mainly used for voltage and current control, input and output control, and other functions. The battery core 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 cells, the circuit board in the mobile power supply is also very important. For rechargeable batteries, the specification has a safe charge cut-off voltage and safe discharge cut-off voltage with a calibrated rated maximum operating current. The design of the mobile power supply must firstly safely charge the polymer battery, because the battery cost is relatively high, and for the safe and reliable operation of the system, there must be a charge management system. When it is necessary to charge a portable device, the polymer battery is discharged to the outside. Since the portable device generally has a 5V input voltage, there is a system that boosts the voltage by 5V. Whether it is a charging management system or a booster system, it needs a circuit board to provide, so the internal circuit board design of the mobile power supply determines the intelligence of the product.

After a large number of security incidents were 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 the protection module when designing mobile power products. That is specific to the product. Which protection module does it include?

Overcharge protection

Lithium battery overcharge protection is achieved by using the power management chip to detect the voltage, and the chip is internally set to the reference state (the cell phone lithium battery is generally 3.5V). When the reference rises slowly, when it rises to the VSS-VDD design value, the voltage at this time is the protection over-charge shutdown voltage, and the external control circuit is controlled by the logic output low or high level to achieve overcharge protection. When the voltage slowly drops, set the VSS-VDD voltage value to take the reference value. When the reference detects that it is below the setting, this is the logical relationship cancellation of overcharge protection.

2. Over-discharge protection

Over-discharge protection voltage refers to the lowest voltage of the protection battery during discharge transition. When the voltage is discharged to this point, the protection circuit cuts off the circuit to protect the battery. According to the relationship between the battery life and depth of discharge and the relationship between the battery voltage and discharge rate and depth of discharge, combined with the actual load of the device, determine the battery discharge termination voltage, design the battery discharge protection circuit.

3. Short circuit protection

The loop current caused by the short circuit is generally more than 10 times of the rated operating current, and the overcurrent protection needs to delay about tens of milliseconds. The dozens of times of the rated current caused by the direct short circuit will also affect the performance of the battery pack within tens of milliseconds. The existing protection methods include the PPTC method, which is a thermal cut-off circuit generated by current, and also requires a millisecond response time, while increasing the impedance in the loop. There are also short-circuit integrated chips dedicated to battery packs, which have a narrow range of application and high cost.

4.PTC introduction

PTC positive temperature coefficient thermistor, also known as polyswitch, polymer resettable fuse polymer resettable fuse from the polymer matrix and carbon black particles that make it conductive. Since the polymer self-resetting fuse is a conductor, there will be current through it. When there is over-current through the polymer self-resetting fuse, the heat (I2R) will cause it to expand. So that the carbon black particles will separate, the resistance of the polymer self-resetting fuse will rise. This will cause the polymer self-healing fuse to generate heat more quickly, expand more, and further increase the resistance. When the temperature reaches 125 °C, the resistance changes significantly, so that the current is significantly reduced. The small current flowing through the polymer resettable fuse at this point is sufficient to keep it at this temperature and in a high-impedance state. When the fault is removed, the polymer shrinks to its original shape from the recombination fuse 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. The quality control of big brands is generally good. Selecting a good brand is the first step in ensuring the safety and quality of mobile power.

Look at the indicators: capacity, input voltage/current, output voltage/current, number of output ports. This article finally explains the parameters and basic common sense of mobile power.

Note: Gift mobile power must be careful, after all, is to send things, not a good quality, burned cell phone or battery explosion is no place to claim.

Second, touch

If the mobile power source is hot at the time of charge and discharge, be careful not to use it again or ask the manufacturer to return it.

Third, listen

Take the mobile power to your ear. If you hear a buzzing sound, it is best not to use it again, or ask the manufacturer to return it. Otherwise, the phone may be damaged.

Fourth, try

Press the switch key, then insert the phone charging port 20 times with a coin or small key. If the mobile power supply is broken, there is a problem with the quality of the mobile power supply. Do not use it. You can ask the manufacturer to return it.

At the same time insert the adapter and mobile phone, if you can not charge the phone normally, indicating that the mobile power is defective, it is recommended not to use.

Fifth, use

When you use the following tests, you can see if you have purchased a mobile power source with a virtual standard or current.

1 mobile phone charging number = (65% * mobile power nominal capacity (mAh)) / (cell phone capacity (mAh))

For example, if you buy a mobile power supply that is 10400mAh and your mobile phone capacity is 2000mAh, you can charge 3.38 times.

If you do not charge so many times, it is very likely that the capacity of the mobile power supply is not 10400mAh, you can ask the manufacturer to return.

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 1A charging current and the mobile power supply has a nominal capacity of 10400mAh, then it takes 10.4 hours to fill this mobile power supply.

If the charging time is too long, either the selected adapter current is too small or the mobile power charging current is falsified. The judging method is also very simple. Testing the charging time using the adapter standard on the mobile phone can eliminate the possibility that the adapter current is too low.

3 Look at the battery indicator or LCD power indicator. Insert the adapter, pull out the adapter, and insert the phone. If the battery indicator flashes or the LCD shows a sudden change in power during this process, there is a problem with the battery display. It is recommended to use it with caution.

4 Whether the mobile phone can automatically power off after the mobile phone is full. If it is found that the mobile power supply has been charging the mobile phone, it is recommended not to use it. The manufacturer may be required to return the mobile phone.

Mobile power tips

1 nominal capacity

There will be a battery capacity identifier on the mobile power supply housing, such as 10400 mAh. This represents the battery capacity. The larger the capacity, the more times you can charge your phone. At present, the mainstream of mobile power has done 10400mAh. But some illegal businesses will be filled with cement blocks, or use inferior batteries. Consumers can use the previous method to identify whether there is a battery capacity falsification.

2 charging current

The greater the charge current, the shorter the time it takes to fill the mobile power supply. The general charging current is in 1A~2A. Consumers can use the previous method to identify whether the charging current is vacant.

3 discharge current

The greater the discharge current, the greater the current that does not represent charging the phone. This is a question that many people often ask. The charging current of the mobile phone depends on the charging current of the mobile phone itself. As long as the mobile power supply discharge current is greater than the rated charging current of the mobile phone, it can ensure that the mobile phone is charged according to the rated current. For example, Apple's mobile phone is 1A charging, ipad is 2.1A charging. If the mobile power discharge current is greater than 2.1A, it can be guaranteed to charge the ipad or Apple mobile phone normally.

4 input voltage

The input voltage is usually marked simultaneously with the charging current, indicating the voltage the adapter outputs to the mobile power supply. The nominal value is 5V. However, a bad adapter can cause the mobile power supply to be damaged. The peak voltage may be as high as 8V.

5 output voltage

The output voltage is generally identified at the same time as the discharge current. The nominal value is 5V. The output voltage of a poor mobile power supply may be as low as 4V or instantaneously as high as 12V, often causing the phone to burn.

6 Efficiency

Efficiency affects the temperature of the mobile power supply and the number of mobile phone charges. The general charge and discharge efficiency requirements are higher than 90%.

7 cell type

The battery is divided into two types of polymer and 18650. The 18650 batteries are often explosive, relatively heavy, but the price is cheaper. Polymer batteries are relatively safe and light weight, but they are expensive. Future mobile power will gradually replace 18650 batteries with polymer batteries. Therefore, choosing a polymer cell can greatly improve the safety factor.

8 battery display

The power display generally has LED lights, digital tubes and LCD screens. LED display is more intuitive, but inaccurate; digital tube and LCD seem to be more accurate, but the quality is still not off, often appear to insert the phone instantaneous battery power display value mutation phenomenon.