The principle of mobile phone charger
Sep 16, 2019| The principle of mobile phone charger:
First, rectify the low frequency (50Hz) AC to DC, and then use the FET (equivalent to the switch of the turn switch) to turn the DC switch into a high frequency (tens of KHz) AC signal, and then transform it through the transformer. Rectified to DC. The purpose of this is to reduce the size of the magnetic component, ie the transformer. 220 AC rectification, then start with an oscillating circuit (mostly self-excited), become a high-frequency signal of several tens of kilohertz, and then transform it into a low-voltage high-frequency of several volts through an isolated high-frequency small transformer to filter and stabilize Press and then output 5-6 volts DC (by phone) to charge the phone. Similar to a small switching power supply, the power frequency transformer (a heavy core transformer) is efficient and lightweight.
Today's mobile phone chargers mostly use lithium-ion batteries. When it comes to this lithium-ion battery, let's briefly introduce it. The so-called lithium-ion battery is a battery that uses a carbon material that can absorb and remove lithium ions as a negative electrode active material. The ion symbol is Li-ion. The battery is generally composed of basic elements such as a positive electrode, a negative electrode, a separator, and an electrolyte.
The charging process of a lithium-ion battery is divided into two steps: first, constant current charging, its current is constant, and the voltage is continuously increased. When the voltage is charged to 4.2V, it is automatically converted to constant voltage charging, and the voltage is constant during constant voltage charging. It is getting smaller and smaller until the charging current is less than the preset value. Therefore, when someone uses the direct charge to charge the battery of the mobile phone, it is clear that the power display is full, but the display is still charging. In fact, the voltage has reached this time. 4.2V so the power is displayed as full, then it is in the process of constant voltage charging.
Why do you need constant voltage charging? It is not enough to charge directly to 4.2V with constant current. In fact, it is easy to explain, because each battery has a certain internal resistance. When charging with constant current to 4.2V, this 4.2V is actually not the actual voltage of the battery, but the sum of the voltage of the battery plus the voltage consumed by the internal resistance of the battery. If the current is large, the voltage consumed on the internal resistance is also large, so that is the actual battery. The voltage may be much smaller than 4.2V, so use the constant voltage charging process to slowly reduce the charging current, so the actual voltage of the battery is very close to 4.2V.
When the mobile phone is charging, the charger first converts 220V AC into a high-voltage DC through the rectifier circuit, and then turns into a high-frequency high-voltage pulse through the switch tube, and then becomes a low-voltage pulse through the transformer. The specific value of the low voltage depends on the required equipment to be charged. Voltage. Finally, the low voltage pulse passes through the rectification and voltage stabilization circuit and becomes the corresponding direct current. That is to say, the process from 220V AC to 5V DC will mainly pass through rectifier circuit, transformer, voltage regulator circuit, etc. The charger only changes the form of electric energy.
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