The function of a rectifier
Release time :
2025-07-17
First, it is to convert alternating current (AC) into direct current (DC), and then obtain stable DC after filtering to supply the load, such as providing charging voltage for the battery or for use in the inverter.
Generally, the functions of a rectifier are two:
First, it is to convert alternating current (AC) into direct current (DC), and then obtain stable DC after filtering to supply the load, such as providing charging voltage for the battery or for use in the inverter.
Second, detection. The function of rectification is sometimes not necessarily solely to generate direct current. Early mineral radios used thin metal wires called "cat whiskers" pressed onto galena crystals to form point contact rectifiers, known as mineral detectors or crystal detectors, with the aim of detecting waves.
At present, the most common type is the silicon rectifier. Here, we will take the silicon rectifier as an example to introduce its rectification principle.
Before that, let's first understand what P-type semiconductors are and what N-type semiconductors are. P-type semiconductor (P stands for positive, positively charged) : It is composed of a small amount of trivalent elements doped into pure silicon (or germanium) through a special process, which will form positively charged holes inside the semiconductor. N-type semiconductors (where N stands for negative, negatively charged) : They are composed of a small amount of pentavalent elements doped into pure silicon (or germanium) through a special process, which will form negatively charged free electrons inside the semiconductor.
By using different doping processes and through diffusion, P-type semiconductors and N-type semiconductors are fabricated on the same silicon semiconductor substrate, and a space charge region, known as a PN junction, is formed at their interface. The PN junction has unidirectional conductivity.
When a voltage is applied to the PN junction, that is, the P junction is connected to the positive terminal voltage and the N junction to the negative terminal voltage, the current flows from one side of the P junction to the other side of the N junction. Holes and electrons both move towards the interface, narrowing the space charge region and allowing the current to pass through smoothly, thus conducting the current. If one side of the N junction is connected to the positive terminal of the voltage and the other side of the P junction to the negative terminal, both holes and electrons will move away from the interface, widening the space charge region, preventing current from flowing through and causing the current to be cut off. This is the unidirectional conductivity of the PN junction. By taking advantage of this feature, the forward voltage can be conducted and the reverse voltage can be cut off, thereby achieving the rectification of alternating current.
From the function of the rectifier, it can be known that the main application of the rectifier is to convert alternating current power to direct current power. Since all electronic devices need to use direct current, but the power supply provided by power companies is alternating current, unless batteries are used, rectifiers are indispensable inside the power supplies of all electronic devices. Rectifiers are also used in the detection of amplitude modulation (AM) radio signals. The signal may be amplified (to increase the amplitude of the signal) before detection. If it is not amplified, a diode with a very low voltage drop must be used. When using a rectifier for demodulation, capacitors and load resistors must be carefully matched. If the capacitor is too small, too much high-frequency component will be transmitted; if it is too large, the signal will be suppressed.
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