1. The output of cell phone chargers is usually direct current. The formula P=UI can be used, that is, maximum output power = rated output voltage x maximum output current. The unit of voltage is the volt, the unit of current is the ampere and the unit of power is the watt. If current is measured in milliamperes, power is measured in milliwatts. 1A = 1000 milliamps.
2. The charger is not a pure resistive load, and the power factor is not 1, so the formula cannot be used to calculate the input power. Input power should be P=UIcosφ.
3.200 MA input current refers to the maximum input current (generally 200 to 300 MA), not the actual input current at work, representing the input current at full load at the minimum input voltage (with a little rounded margin). p.s. The working voltage range of the power supply is generally nominal 100 ~ 240 v, and the actual design is 90 ~ 265 v.
4. For AC, 220 volts and 200 mA are valid values. Since AC input is followed by a rectifier bridge, the current is nonlinear, and the direct multiplication of voltage and current RMS is not equal to the active power (multiplied by the power factor, generally measured 0.3 to 0.5 for small power sources without power factor correction). The most convenient way to measure input power is to use a power meter.
5. The energy efficiency of mobile phone chargers is generally 70 ~ 80%, and the specific index is related to the output power. Simple calculation is as follows: for 5V1A power supply, the efficiency is greater than 73.623% in accordance with the six energy efficiency requirements of the United States; the efficiency is greater than 73.773% in accordance with the requirements of the fifth edition of the European Union CoC; the efficiency is greater than 78.704% in accordance with the six energy efficiency requirements of the United States; 5V1A Power supply: Output power :5V*1A=5W efficiency (based on the above calculation).
6. According to experience, if the active power of AC input is 5W÷0.74=6.757W and the power factor is 0.4, then the apparent power of AC input is 6.757W ÷0.4 = 16.892 volt-ampere. At the minimum input voltage, the effective value of the input current is 16.892 volt-ampere /100 volts = 168.92 MA, with a 20% margin yielding 200 mA. That is, the main problem is that the difference between input and output power is so large mainly because the input power is wrong (calculated at 100 volts) and the conversion ratio of power factor * efficiency is less calculated.
