HuiXin Electronic2017/9/19 16:17:49
Power Diode Rectifier
Structurally, rectifiers can take a multiple forms, which include olden day’s vacuum tube diodes, copper and other metal oxide rectifiers and mercury arc valves. With the introduction of semiconductor electronics in recent days, rectifiers are mostly constructed from semiconductor diodes, thyristors or silicon controlled rectifiers (SCRs) (a type of thyrister) and other silicon based semiconductor switches. The process of Rectification may also serve as a source of power besides generating the direct current. As a point of note, the detectors of radio signals also serve as rectifiers. Because of the flashing and varying nature of the AC sine wave, the rectification process alone itself produces a DC current which is unidirectional also consists of pulses of current. Many applications of rectifiers include power supplies for radio, television, computer and other electronic communication equipment which require a stable and constant DC current. In these electronic applications, the output of the rectifier is smoothed by an electronic smoothing filter or a capacitor to produce a constant form of current.
In the rectification from very low to high currents, various kinds of semiconductor diodes such as junction diodes and Schottky diodes, etc., are broadly used. Various types of silicon based semiconductor devices are used in high power rectifiers, such as those used in higher voltage direct current power transmission systems. The silicon based semiconductor devices include thyristors and many other controlled solid state switches effectively function as diodes to pass direct current solely in one direction.
Rectifier circuits can be classified as either single phase or multi phase based on the type of the alternating current. Most of the low to medium power rectifiers for household equipment are single phase whereas three phase rectifiers are very crucial for industrial applications and also in the process of transmission of energy as DC.
A variety of rectifier circuits are available today. They may be Half Wave, Full Wave and/or Bridge Rectifiers. Each type of these rectifier circuits can be categorized as either uncontrolled, a half-controlled or a fully controlled device.
Features of Power Rectifiers
Simplified mechanical designs and fast assembly
High surging capability
Large creepage distances
Designed and trained for industrial applications
Half Wave Rectification
Rectification may be defined as the process of converting the alternating of current into direct current. The power supply to the rectifiers may be either single phased or multi phased alternating current. Consider the simple case of Half Wave Rectifier of a single phase supply. If the AC sine wave is applied to it as input, then either the positive or negative half of the AC sine wave is passed (depending on the forward bias condition of the diode) by blocking the other half of the sine wave. As only one half of the input waveform reaches the output during the forward bias, the mean voltage across the resistor is lower than the usual.
Half wave rectification is not of much use as the output signal will be available in bursts and is discontinuous. The best application of half wave rectifier for house hold purposes is a two level lamp dimmer. Half wave rectification is not much effective in producing DC output from a 50Hz or 60Hz AC input. In addition the gap between the output pulses of diode current makes it more difficult to eliminate the AC ripple that remains after the rectification process.
Full Wave Rectification
A full wave rectifier circuit converts the whole of the input sinusoidal waveform to one of the polarity either positive or negative as its output. Full wave rectification converts both polarities of the input sine waveform to a pulsative direct current. The average output voltage at the resistive load is very high. Two power diodes with a centre tapped transformer or four power diodes in bridge type configuration without any centre tapped transformer are needed for full wave rectification. If the transformer that has a secondary winding with a centre tap is used, then the greater efficiency in full wave rectification can be achieved
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