Alternating current (AC) and direct current (DC) are two forms of voltage that are converted to each other. Alternating current is a current whose direction and magnitude vary in a periodic manner, while direct current is a current whose direction always remains the same. In practice, it is very common to find scenarios where AC power needs to be converted to DC power, such as using DC power to power electronic devices.
The process of converting AC voltage to DC voltage is generally accomplished through a rectifier. A rectifier is an electronic device that converts alternating current (AC) to direct current (DC) with the same polarity and constant direction. The main operating principle of a rectifier is to utilize the conductive nature of semiconductor materials to introduce a forward bias in the circuit to achieve a unidirectional flow of current.
Common types of rectifiers include single-phase full-wave rectifiers and three-phase full-wave rectifiers. The single-phase full-wave rectifier consists of four diodes and two neutrals, which realize two positive half-circuits of rectification in one AC cycle, and the output voltage is pure DC voltage. The three-phase full-wave rectifier, on the other hand, is suitable for three-phase AC power supplies and realizes full-wave rectification through six diodes.
Specifically, the rectifier works as follows:
Single-phase full-wave rectifier:
When the AC voltage is positive half-cycle, diodes D1 and D4 conduct to transfer the positive half-cycle AC voltage to the output, while D2 and D3 are in reverse cutoff.
When the AC voltage is negative half-cycle, diodes D2 and D3 conduct, the negative half-cycle AC voltage is transferred to the output, while D1 and D4 are in the reverse cutoff state.
After rectification, the polarity of the output signal is always positive and there will be a ripple factor, i.e. the output DC voltage contains a certain AC component.
Three-phase full-wave rectifier:
The principle of the three-phase full-wave rectifier is similar to that of the single-phase full-wave rectifier, except that a more complex circuit connection is used.
It consists of six diodes, each connected to a three-phase input signal, which converts the AC voltage of the three-phase power supply to DC voltage through rectification.
Compared with single-phase full-wave rectifiers, three-phase full-wave rectifiers have the advantages of smooth output and smaller ripple factor.
In practice, the conversion of AC to DC requires further filtering. The role of the filter is to remove the ripple component in the DC power, making the output DC voltage more stable. Filters usually consist of capacitors and inductors that introduce a low-pass filtering function at the rectified output.
It should be noted that there is a certain amount of energy loss in the conversion of AC to DC, mainly due to the internal resistance of components such as diodes and resistors in the rectification and filtering process, so that the output DC voltage will be slightly lower than the input AC voltage.
To summarize, the process of converting AC power to DC power is achieved through electronic devices such as rectifiers and filters. This process converts the changing direction and magnitude of AC power into DC power with a constant and stable direction to meet the demand of electronic devices for a stable DC power supply. In practice, depending on the voltage and power requirements, different types of rectifiers and filters can be selected to realize the function of AC to DC voltage conversion.
