Alternating current rectification

The process of converting alternating current into direct current is called "alternating current rectification". Rectification can be divided into half-wave rectification, full-wave rectification and bridge rectification. The usual rectifying devices are rectified by the unilateral conductivity of electron tubes and crystal diodes. For example, rectifiers made of semiconductor materials such as germanium and silicon have been widely used in many aspects. In order to adapt to the rectification of higher voltage, many individual rectifiers can be connected in series and sealed in an insulating material called "silicon stack". Rectifier can eliminate the negative half-cycle waveform of alternating current and make alternating current become pulsating DC. Therefore, the rectified output waveform only contains the positive half-cycle waveform of sine wave. The ideal rectifier can be regarded as a switch. When the AC input is a positive half cycle, there is a voltage output, just like a switch is turned on. On the other hand, if the AC input is negative for half a cycle, there is no voltage output, which is equivalent to turning off. Therefore, when the AC input is positive half cycle, the effective resistance of the switch is zero; However, under negative half-cycle AC input, the effective resistance is infinite. The actual rectifier can't be so ideal, but the difference is not far. When the tube rectifier is not conductive, its resistance is extremely large, and the resistance at this time is called reverse resistance; When the rectifier conducts electricity, its resistance is very small, and the resistance at this time is forward (forward) resistance. In any case, all rectifiers are only allowed to conduct electricity in one direction. This characteristic is called unidirectional conduction or unidirectional characteristic, and diodes (including transistors) have this unidirectional characteristic. Any electronic component containing emitter or cathode and collector or anode is called diode (including electronic diode and crystal diode). Because the electrons in the diode can only flow in one direction. Therefore, all diodes have rectification characteristics. The bridge rectifier is a full-wave rectifier, and the variable AC voltage is a higher DC voltage, so there is no need for the transformer to have a center tap. Four crystal diodes are connected as shown in Figure 3-65 to form a bridge rectifier circuit. Four rectifiers (transistors) connect the input alternating current and the load. When the AC input voltage is positive, the current flows from one side of the input through a rectifier and a load, and then through another rectifier to the other side of the input. When the AC input voltage is negative for half a cycle, the current flows through another pair of rectifiers and loads. During the positive and negative half cycles of the input voltage, the current flowing through the load has the same direction. A pulsed DC voltage can be generated on the load. In the actual bridge rectifier circuit, four rectifiers are connected into a whole, and a bridge circuit is formed from the outside (that is, as long as there are four external connection points, two of which are connected to the power supply and two to the load). Bridge rectifier overcomes the shortcomings of low utilization ratio of half-wave rectifier and full-wave rectifier. Bridge rectifier circuit is widely used in radio technology and electrical engineering.