The role of the rectifier

A rectifier (English: rectifier) is a device that converts alternating current into direct current, which can be used for power supply devices and to detect radio signals. The rectifier can be made of a vacuum tube, a squib tube, a solid tantalum semiconductor diode, a mercury arc, or the like. In contrast, a device that converts direct current into alternating current is called an "inverter."

1. The role of the rectifier

A rectifier is a rectifying device, simply a device that converts alternating current (AC) to direct current (DC). It has two main functions: first, to convert alternating current (AC) into direct current (DC), filtered to supply the load, or to the inverter; second, to provide the charging voltage to the battery. Therefore, it also acts as a charger.

The rectifier is DC after rectification by the car generator. The waveform still has irregular fluctuations, which directly affects the accuracy of the ignition of the vehicle. The output voltage cannot be kept relatively constant, resulting in a large difference in the energy of each spark plug ignition. The engine is shaken, and there are situations such as gear shifting, slow speed increase, idle speed instability, and inefficient vehicle air conditioning. Therefore, the performance and service life of the vehicle-mounted electrical equipment are greatly reduced; coupled with the aging of the circuit system of the old-age car, the influence of the high resistance of the circuit becomes more and more obvious to your car. The role of the electronic rectifier is to help the car eliminate clutter interference, stabilize the output voltage, improve the instantaneous discharge capacity of the power system, increase the torque output, speed up the throttle response, extend battery life, shorten the start-up time of the engine, improve ignition efficiency, etc. For small displacement cars, the effect is more obvious.

2. Rectifier principle

At present, the most common one is the silicon rectifier. The following is a description of the rectification principle of a silicon rectifier.

Before that, we first understand what is a P-type semiconductor, what is an N-type semiconductor; P-type semiconductor (P refers to positive, positively charged): a small amount of special process is used in pure silicon (or germanium) The composition of trivalent elements will form positively charged holes in the semiconductor; N-type semiconductors (N refers to negative, negatively charged): a small amount of pentavalent elements are incorporated into pure silicon (or germanium) by a special process. A negative electron with a negative charge is formed inside the semiconductor.

The P-type semiconductor and the N-type semiconductor are fabricated on the same silicon semiconductor substrate by diffusion, and a space charge region is called a PN junction at their interface. The PN junction has unidirectional conductivity.

A voltage is applied to the PN junction, that is, P is connected to the positive voltage, N is connected to the negative voltage, and current flows from the side of the P junction to the side of the N junction. The holes and electrons move toward the interface, narrowing the space charge region, and the current can be smoothly. Through, the current is turned on. If the N junction is connected to the positive pole of the voltage and the P junction is connected to the negative pole, the holes and electrons move in a direction away from the interface, so that the space charge region is widened, the current cannot flow, and the current is cut off. This is the unidirectional conductivity of the PN junction. With this feature, the forward voltage can be turned on and the reverse voltage can be turned off, thereby achieving rectification of the alternating current.

3. Rectifier application

The main application of the rectifier is to convert the AC power to DC power. Since all electronic devices require DC, the power company's power supply is AC, so unless the battery is used, the rectifiers are indispensable inside the power supply of all electronic devices.

It is much more complicated to convert the voltage of the DC power supply. One method of DC-DC conversion is to first convert the power supply to AC (using a device called a reverse inverter), then use a transformer to change the AC voltage and then rectify it back to DC power.

The rectifier is also used for detection of amplitude modulated (AM) radio signals. The signal may be amplified first (amplitude of the signal before amplification), and if it is not amplified, a very low voltage drop diode must be used. Capacitors and load resistors must be carefully matched when using a rectifier for demodulation. If the capacitance is too small, the high-frequency component will be transmitted too much, and if it is too large, the signal will be suppressed.

The fairing device is also used to provide a voltage of a fixed polarity required for electric welding. The output current of such a circuit sometimes needs to be controlled. In this case, the diode in the bridge rectifier is replaced by a thyristor (a thyristor), and its voltage output is adjusted in a phase control trigger manner.

Thyristors are also used in railway locomotive systems at all levels to achieve fine tuning of the traction motor. A turn-off thyristor (GTO) can be used to generate AC from a DC source, such as the one used on Eurostar trains to provide the power required for a three-phase traction motor.

4. The difference between ballast and rectifier

The rectifier, the input is AC, the output is DC, and those DC-operated appliances require a rectifier.

Ballasts, inductive coils connected in series in an AC circuit, limit the current strength in the AC circuit. In order to make the current intensity of electrical appliances working under AC power not exceed a certain value (such as metal halide lamps).