What Is a Silicon Controlled Rectifier?

Thyristor rectifier: It is a kind of power control equipment based on thyristor (power electronic power device) and intelligent digital control circuit as the core. It has many advantages such as high efficiency, no mechanical noise and wear, fast response speed, small size and light weight.

Thyristor rectifier: It is a kind of power control equipment based on thyristor (power electronic power device) and intelligent digital control circuit as the core. It has many advantages such as high efficiency, no mechanical noise and wear, fast response speed, small size and light weight.

Brief introduction of thyristor

Thyristor rectifier is a commonly used power semiconductor electronic device, which has the ability to control the switching of several kilowatts or even megawatts of electrical power. Structurally speaking, it is a reverse-cut triode-type thyristor composed of three PN The junction (PN-PN four layers) is composed. The external lead of the device has three electrodes: cathode, anode, and control electrode. The schematic cross-section of a typical high-current thyristor is shown in the figure. The reverse characteristics of the device (anode is negative) and PN The reverse characteristic of a junction diode is similar; its forward characteristic, in a certain range, the device is in an off state with high impedance (forward blocking state, that is, the solid line part under the dotted line in the volt-ampere characteristic one quadrant). When the forward direction When the instantaneous voltage is greater than the transition voltage, the device quickly transitions to a low-voltage, high-current on-state. ^[1]

Thyristor mark symbol, volt-ampere characteristics and schematic cross-section

For a device in the forward blocking state, if a low-power trigger signal is given to the control electrode (controller-cathode PN junction is turned on), the device can be quickly excited to the on state, and it is not necessary to continue to maintain the triggering current. Maintain in the on-state. At this time, if the current is reduced below the sustain current (at the dotted line of the volt-ampere characteristic), the device can return to the blocking state.

Thyristor rectifier : the main circuit adopts three-phase bridge or double inverted star band balanced reactor circuit. Thyristor components use high-power components, which saves energy significantly. The main control system adopts large board, high threshold anti-interference, large-scale integrated control board; all modules and integrated components are imported, with high reliability. With automatic voltage stabilization and current stabilization, the stability accuracy is better than 1%. With 0 ~ 60S soft start, electroplating oxidation coloring time can be arbitrarily set and automatically timed. Multi-phase rectification is adopted to reduce the output voltage ripple coefficient ru, which is especially suitable for hard chrome plating process, with good surface finish and uniform coating thickness. Cooling method: water cooling, air cooling, self cooling.

The thyristor is called a thyristor or thyristor: it is a kind of power semiconductor device. It has many advantages, such as large capacity, high efficiency, good controllability, long life, and small size. It is a bridge between weak current control and controlled strong current. From the standpoint of energy saving, power electronics technology is known as the new electrical technology. China's energy utilization rate is relatively low. According to the national energy consumption per unit of production, China is 4.98 times that of France and 4.43 times that of Japan. Therefore, the widespread use of thyristor-based electrical control devices is an important part of China's effective energy conservation. Measures.

SCR rectifier structure

A double triode is usually used to describe the four-layer structure of a thyristor as an interconnection of an NPN and a PNP transistor. If the common base current amplification factors of the two transistors are ₁ and ₂ (both functions of the operating state), The necessary condition for the pass is ₁ + _{2 1. In the} blocking state, the current amplification coefficients of both transistors are small; if a forward current is injected into the control electrode in the forward blocking state, the The current amplification factor ₁ increases rapidly and causes ₂ to increase, thereby satisfying the conduction conditions. ^[1]

Triac Rectifier Application

Thyristor is a very important power electronic device. It can control megawatts of power with very small control power. It is often used in rectification, switching, frequency conversion, inverter and other circuits. High power thyristors use a large area Silicon wafers need to be packaged in a tube case with a heat sink. ^[1]

Related technology of thyristor

In the waveform diagram of the controllable rectifier circuit, it is found that in each half cycle of the thyristor bearing the forward voltage, the timing of the first trigger pulse is the same, that is, the control angle and the conduction angle are equal. How can a junction transistor relaxation oscillator work accurately with AC power to achieve effective control?

In order to achieve the "controllable" output voltage of the rectifier circuit, it is necessary to make the thyristor withstand the forward voltage every half cycle. The trigger circuit sends out the first trigger pulse at the same time. This cooperative working method is called the trigger pulse. Synchronized with power.

Voltage regulator circuit diagram

How can we achieve synchronization? Let's look at the circuit diagram of the voltage regulator (above). Please note that the power of the single-junction transistor relaxation oscillator is a full-wave pulsed DC voltage from the output of the bridge rectifier circuit. When the thyristor is not turned on, the capacitor C of the relaxation oscillator is charged by the power supply, and when UC rises exponentially to the peak point voltage UP, the single-junction transistor VT turns on. During the VS turn-on period, there is an AC voltage and current on the load RL At the same time, the voltage drop across VS is small, forcing the relaxation oscillator to stop working. When the AC voltage crosses zero, the thyristor VS is forced to turn off, the relaxation oscillator is energized, and the capacitor C starts to charge again, and the above process is repeated. In this way, each time the AC voltage crosses zero, the timing of the first trigger pulse issued by the relaxation oscillator is the same. This timing depends on the resistance of RP and the capacitance of C. By adjusting the resistance of RP, the charging time of capacitor C can be changed, which also changes the moment when the first Ug is issued, and the control angle of the thyristor is changed accordingly, so that the average value of the output voltage on the load RL changes to achieve the adjustment Pressure purpose.

T1 and T2 of the triac are not interchangeable. Otherwise it will damage the pipe and related control circuits.