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Home > Industry Information > How to choose the power adapter, choose the adapter and remember these nine basic principles!

How to choose the power adapter, choose the adapter and remember these nine basic principles!

2019-03-20

How to choose the Power Adapter, choose the adapter and remember these nine basic principles! The power adapter is the adapter between the city electricity and the charged Power Supply, for example, the 5V/1A power adapter equipped with the mobile phone to be charged.

First: Power adapter can only be matched large but not small in theory.
12V 1A AU
For example, charging current needs 5V/800mA, and the best power adapter should be 5V/1000mA (5V/1A).

1. Small power adapter may lead to low voltage dragging during charging, resulting in sampling drift of charging circuit. What is sampling drift? It should be known that the charging of lithium battery must be voltage and current limiting. The basic reference values of voltage and current limiting need to be selected in the circuit.

2. The current value of charger is usually obtained by calculating the voltage at both ends of current sampling resistance. The key point of constant current is to protect the battery plate and avoid the impact of large current on the battery plate. For example, 1000 mAH battery, the normal charge is 1/10 of the capacity value, both charging current is 100 mA. Lithium batteries can be charged quickly, several times that. Summary: As long as the voltage is stable, even if the current fluctuates, the damage to lithium batteries is generally small. In short, current fluctuations in a certain range are "relatively safe" for lithium batteries.

3. But the voltage fluctuation is fatal to the value of voltage. Most charging circuit voltage sampling is based on the input voltage value. The output voltage of power adapter is dragged down, which means that the sampling terminal voltage has been in a "low" state. The key to measure whether the lithium battery is full is to test whether the voltage reaches the 4.2V limit. For the low reference value, the result is that the output is on the high side. The circuit "thinks" that the maximum voltage (4.2V limit) must be higher than the actual voltage. Although the circuit is intelligent, but you can not deny that the machine is a machine, the reference point is not accurate, how can the output be accurate? Strict charging circuit, the reference source has an independent voltage regulator circuit, where "too low" is the "ultra low" that has reached the destruction of the reference source.

Summary: Even if the current is stable and the voltage is too low, it is dangerous for the charging circuit which takes the reference value from the input terminal. Such a circuit will cause frequent overcharging of lithium batteries. For lithium batteries, the most lethal cause is overcharge. The harm caused by overcharge is swelling, permanent damage, explosion and so on.

2. Choose a good quality power adapter:

What is a good quality power adapter? For power adapters, EMC, output ripple and voltage fluctuation are very important indicators. Ordinary consumers can not know which manufacturer is good, the only thing we can trust is the manufacturer, so: refuse to Shanzhai is an eternal slogan!!

Third: Is the power adapter the better?

Strictly speaking, the adapter is only slightly larger than the requirement. Assuming that your charged circuit is very efficient and stable, the influence of high power adapter can be ignored in theory, and most of the input power will not be a problem. But you have to admit: Machines are man-made things, who can guarantee that he does not make things in case? In case the charging circuit collapses and the input end is instantly added to both ends of the lithium battery, who can predict the consequences? So: the manufacturers of Niu X dare not ignore the lithium battery protection board. In case of more protection and less protection, the principle of responsible manufacturers remains unchanged. Millet mobile power supply battery temperature detection circuit is an example, I dismantled many domestic mobile power supply, the first time in domestic goods, saw this small battery temperature detection probe (the scientific name seems to be NTC thermistor), and in foreign battery products, this thing is almost necessary.

Summary: As long as the adapter is slightly larger than the requirements, too large adapters can only be used temporarily, not for long-term use.

IV: Voltage selection of power adapter:

Strictly speaking, the voltage of power adapter should not exceed 1% error. I personally measure the power adapters of many brands. The output is usually between 5.1 and 5.2 V. Has this exceeded 1%? Not necessarily! In fact, the output voltage accuracy of most brand power adapters can be controlled below 1%. 5.2V is the real effective value of the so-called 5V. If the error is 1%, the power supply voltage should be between 4.95 and 5.05, not between 5.15 (5.1V) and 5.25V (5.2V), so the real output value of the so-called 5V power adapter is 5.1 or 5.2V.

If the voltage of the power adapter is too low, you will find it difficult to charge (which will be differentiated from charging identification, described in detail below), even unable to charge, reference offset, etc. If the voltage is too high, it will bring a high voltage drop to the charging switch tube, resulting in high temperature, which can also cause various fatal instability.

Summary: Whether the output voltage of power adapter is too high or too low, it can cause devastating consequences. Choosing the power adapter provided by the original factory is the kingdom. Every manufacturer has identification and protection measures for their lithium battery products. In fact, it can not be blamed that the manufacturer has not considered the free choice of consumers. If the manufacturer does not take strict protection measures for products with certain dangers such as lithium batteries, it is believed that the word "lithium battery explosion" will often appear in the headlines.

Five: What is charge identification?

The manufacturer requires an electric (battery) with a charge (power adapter), since my power adapter can only adapt to my lithium battery charging circuit. Consumers choose power adapters other than the original factory, and the circuit automatically closes and charges. This is to prevent ordinary consumers from abusing unqualified power adapters. The method of circuit identification is two data lines besides Mini USB power supply (USB has two wires besides + and - of power supply). Millet mobile power supply can adapt to many kinds of mobile phones because it has a circuit to switch the two wires to meet the requirements of various mobile phones. It is compatible with Millet mobile power supply.

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