Products >> Power Management (PMIC) >> AC/DC converter

power management chips, an AC/DC converter is a key type of circuit. Its main function is to convert the input alternating current (AC) voltage into a stable direct current (DC) voltage output. For example, the mains electricity we use daily is 220V alternating current, while most electronic components inside electronic devices such as mobile phones and computers need stable direct current to work properly. The AC/DC converter serves as the bridge for this conversion.

Working principle
- Rectification stage:
  - This is the first step in AC/DC conversion. It uses the unidirectional conductivity of diodes to convert the input alternating current into pulsating direct current. The most common is the bridge rectifier circuit, which consists of four diodes. When the AC input voltage is in the positive half-cycle, the current flows to the load through two diodes; when it is in the negative half-cycle, the current flows to the load through the other two diodes, thereby realizing the utilization of both positive and negative half-cycles of the AC voltage. The output is pulsating direct current voltage, but this voltage still has relatively large ripple.
- Filtering stage:
  - To remove the ripple in the rectified DC voltage, filtering is required. Generally, a filtering circuit composed of capacitors and inductors is used. Capacitors have the characteristic of "blocking direct current and passing alternating current". They can store charges and release charges when the voltage changes to smooth the voltage. For example, in a simple capacitor filtering circuit, when the pulsating DC voltage rises, the capacitor charges; when the voltage drops, the capacitor discharges, thereby reducing the voltage fluctuation. Inductors filter by using their resistance to current changes. They can form a π-type filtering circuit with capacitors to further reduce the ripple factor and make the output DC voltage more smooth.
- Voltage regulation stage:
  - Although the DC voltage after filtering is already relatively smooth, it may change with the fluctuation of the input AC voltage or the change of the load. The voltage regulation stage is to maintain the stability of the output DC voltage. Linear voltage regulation and switching voltage regulation are two common voltage regulation methods. Linear voltage regulation realizes voltage regulation by adjusting the conduction degree of the adjustment tube (such as a transistor) connected in series in the load circuit. When the output voltage rises, the conduction degree of the adjustment tube decreases, thereby reducing the output voltage; vice versa. Switching voltage regulation adjusts the output voltage by controlling the conduction and shutdown time of the switching tube (such as a MOSFET). Its efficiency is usually higher than that of linear voltage regulation and it can adapt to a wide range of input voltage changes.
Main application fields
- Consumer electronics field:
  - In mobile phone chargers, the AC/DC converter converts the mains AC voltage into a stable DC voltage required for mobile phone charging, generally 5V, 9V, or 12V, etc. Similarly, the power adapter of a notebook computer is also an AC/DC conversion device. It converts 220V alternating current into direct current suitable for notebook computers, such as different voltage specifications such as 19V.
- Industrial field:
  - Many control circuits and electronic components in industrial equipment need stable DC power supplies. The AC/DC converter can convert industrial three-phase alternating current or single-phase alternating current into stable direct current to provide power support for industrial automation equipment, instruments, and meters. For example, in the PLC (programmable logic controller) equipment on an automated production line, the internal power module usually contains an AC/DC conversion circuit to provide stable DC power for the PLC's CPU, input and output interfaces, and so on.
- Communication field:
  - Communication base station equipment requires a large amount of DC power to supply power to communication equipment and signal processing modules. The AC/DC converter can convert mains electricity or other AC power sources into appropriate DC power to meet the requirements of communication equipment for power stability and reliability. At the same time, in some small communication terminal devices such as wireless routers, AC/DC converters are also used to provide DC power for the internal chips and circuits