How does the mobile phone charger change voltage?
Jul 22, 2020
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How does the mobile phone charger change voltage?
There is also a transformer inside the mobile phone charger, but it is different from the traditional linear power supply method in the past! Although the charger does not have a traditional power frequency transformer, it still has a high frequency transformer inside.
Nowadays, mobile phone chargers are basically designed using switching power supplies. The main advantage is that switching power supplies can be small and light! Easy to carry!
1. Traditional linear power supply design
The traditional linear power supply uses a power frequency transformer, and the operating frequency is generally 50/60HZ. For example, the more common step-down transformer converts high-voltage AC power to a suitable low-voltage AC. The transformer of the linear power supply is large and bulky, and the conversion efficiency is low!
The design method of the linear power supply is: power frequency transformer transformer → → rectification → → filtering → → voltage stabilization. The following figure shows the design of a 5V DC power supply using a traditional linear power supply. The power frequency transformer is selected from 220V to 6V~8V. The power is based on Load demand selection, and then get 1.2 times of AC voltage through bridge rectification and filtering, and then get 5V voltage through 7805.
2. Switching power supply design
The mobile phone charger uses a switching power supply design method. The high-frequency transformer of the same power is much smaller than the ordinary transformer. Therefore, its design is small in size, light in weight, and high in conversion efficiency.
The basic design method of the switching power supply is: rectification→→switch tube PWM modulation→→high-frequency transformer transformer→→rectification, filtering→→feedback, the following figure is a circuit diagram using a switching power supply to output 5V, and directly pass the 220V high voltage AC through the rectifier bridge Rectification obtains about 310V high-voltage DC, and then turns on/off the switching tube by PWM pulse modulation to form a constantly changing current, outputs AC through a high-frequency transformer, then rectifies and filters to obtain the corresponding DC voltage, and feedbacks the output voltage value in real time. Adjust the PWM modulation signal.
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