38 views Yuda Electronic (HK) Technology Co.,Limited. 2021-06-28
First rectify the low-frequency (50Hz) AC to DC, then use a field effect tube (equivalent to a switch in turn) to switch the DC into a high-frequency (tens of KHz) AC signal, and then transform it through a transformer, and then Rectified to direct current. The purpose of this is to reduce the size of the magnetic component, that is, the transformer. 110V AC rectification, and then use the oscillation circuit to vibrate (mostly self-excited), become a high-frequency signal of tens of kilohertz, and then transformed into a low-voltage and high-frequency of a few volts through an isolated high-frequency small transformer for filtering and stabilization Then output 5-6 volts of DC (according to the phone) to charge the phone. Similar to a small switching power supply, a power frequency transformer (heavy iron core transformer) has high efficiency and light weight.
Nowadays mobile phone chargers mostly use lithium-ion batteries. Speaking of 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 occlude and desorb lithium ions as the negative electrode active material. The ion symbol is Li-ion. Batteries are generally composed of basic elements such as positive electrode, negative electrode, separator, and electrolyte.
The charging process of lithium-ion batteries is divided into two steps: first, constant current charging, the current is constant, and the voltage continues to rise. When the voltage is charged to 4.2V, it is automatically converted to constant voltage charging. During constant voltage charging, the voltage is constant and the current is constant. It is getting smaller and smaller until the charging current is less than the preset value, so when someone uses direct charging to charge the mobile phone battery, it is obvious that the battery level is full, but it still shows that it is charging. In fact, the voltage at this time has reached 4.2V, so the battery display is full, then the constant voltage charging process is in progress.
Why is it necessary to charge with constant voltage? It is enough to charge to 4.2V directly with constant current. Actually, it is easy to explain, because every battery has a certain internal resistance. When charging to 4.2V with constant current, 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 on the internal resistance of the battery. If the current is large, the voltage consumed on the internal resistance will also be large, so that is the actual battery’s The voltage may be much smaller than 4.2V, so it is necessary to use a constant voltage charging process to slowly reduce the charging current, so that the actual voltage of the battery is very close to 4.2V.
When charging the mobile phone, the charger first converts the 110V AC power through the rectifier circuit into a high-voltage DC power, then turns it into a high-frequency high-voltage pulse through a switch tube, and then turns it into a low-voltage pulse through a transformer. The specific value of the low-voltage depends on the requirements of the charged device Voltage. Finally, the low-voltage pulse passes through the rectification and voltage-stabilizing circuit and becomes the corresponding direct current. In other words, the process from 220V alternating current to 5V direct current mainly passes through rectifier circuits, transformers, voltage stabilizing circuits, etc. The charger only changes the form of electrical energy.
The charger adopts high-frequency power supply technology and uses advanced intelligent dynamic adjustment charging technology. The industrial frequency machine is designed based on the traditional analog circuit principle. The internal electrical components of the machine (such as transformers, inductors, capacitors, etc.) are relatively large. Generally, there is less noise when the load is large. The resistance performance is stronger in the environmental conditions of the power grid, and the reliability and stability are stronger than that of the high-frequency machine.
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