We all use smartphones on a daily basis, but have you ever wondered how your smartphone charger works? The process of converting AC to DC is not as simple as it seems. In fact, it involves converting AC to DC, then back to AC, and finally back to DC. In this post, we will explore how phone chargers work and why there are intermediate steps involved.
Inside a normal charger that converts 220 volts AC to 5 volts DC, there are various electronic components such as diodes, capacitors, transistors, resistors, and transformers. The charger contains a resistor, a fusible resistor, a bridge rectifier made up of four n4007 diodes, and a filter capacitor of 450 volts and 2.2 microfarad. This circuit converts AC to DC.
There is also an oscillator circuit that converts DC back to high-frequency AC of 15 to 50 kilohertz. This circuit contains components such as a transistor s8050, transistor 13001, a diode, a fast-switching diode 1n4148, and a capacitor of 50 volts 22 microfarad.
There is an AC to DC converter for the photo transistor in optocoupler, which forms a circuit. A transformer with three windings primary, secondary, and auxiliary winding wrapped around the core is used to step down the voltage. The auxiliary winding is used to run the oscillator circuit. A Schottky diode 1n5819 with a capacitor of 10 volts 470 microfarad is used to convert AC to DC and a LED for indication.
Furthermore, there is a feedback circuit that consists of an optocoupler pc817c and 4.2 volt Zener diode. The optocoupler is used for the transmission of signals without contact. There is also a capacitor of 102 nano farad used for safety purposes, which is connected between primary and secondary grounds to stop electromagnetic interference.
To understand how the charger works, let’s take a look at the circuit. Once power is supplied, it turns on and the green wires carry the positive voltage, and the blue wires carry the negative voltage or ground. The input of 220 volts 50(60) hertz AC is converted to fluctuating DC by the bridge rectifier. The fluctuating DC filters from the capacitor and becomes almost pure DC.
Now, the current passes from the 2 mega ohm resistor to the base of T1 turning it on. The transistor isn’t fully turned on because of the resistance, so it turns on partially. Due to partial turning on of the transistor, a low current passes from the primary winding of the transformer, which induces a low voltage in the auxiliary winding. The induced voltage now charges the capacitor and then the capacitor fully turns on the transistor. As the transistor is now fully on, it allows the current to flow through itself.
Now, this turns on the transistor T2, shunting the base of the T1 turning it off. As the T1 turns off, the flow of current to the T2 is cut off. Now, the current flows to the base of the T1, and the cycle repeats. This happens at 15 to 50 kilohertz, which is a thousand times faster than the rectifier circuit.
At the same time, the voltage from the auxiliary also turns the diode on and charges the capacitor and flows to the optocoupler. This diode and capacitor convert the AC from the auxiliary coil to DC for the optocoupler. The current is also induced in the secondary winding. This is converted to DC by a Schottky diode and a filter capacitor. It is indicated by the LED.
The feedback circuit comes into play when the voltage is more than 5 volts. As we reach 4.2 volts, the Zener diode turns on, allowing current to flow to the optocoupler. It also drops the voltage by 4.2 volts, hence the LED of the optocoupler doesn’t turn on. When the voltage reaches more than 5 volts, this turns on the LED of the optocoupler. The light of the LED turns on the phototransistor of the optocoupler, allowing the current to flow to the transistor T2. This turns on the transistor T2, shunting the first and stopping the flow of current in the primary winding. Also, the voltage in the secondary side of the transformer drops below 5 volts, turning off the Zener diode and optocoupler, and the circuit continues to run normally.
Now, the question arises why not directly convert AC to DC than this? This is because for the normal power supply which is at 50(60) hertz, the size of transformers and capacitors are large. They cannot be mounted in a small charger like this. Hence in the charger, the 50(60) hertz frequency is converted to 50 kilohertz. This reduces the size of the transformer and capacitor required in the circuit. So, to change the frequency of AC, first, we have to convert it to DC and then again back to AC.
In conclusion, phone chargers are not as simple as they seem. They contain various circuits and components that work together to convert AC to DC and ensure that the voltage stays within the required range. We hope that this post helps you understand how phone chargers work.