What Is a TRIAC?

SCR (Silicon Controlled Rectifier) is short for SCR, it is a kind of high-power electrical component, also called thyristor. It has the advantages of small size, high efficiency and long life. In the automatic control system, it can be used as a high-power drive device to control high-power equipment with low-power controls. It has been widely used in AC and DC motor speed regulation system, power regulation system and follow-up system.

Everyone uses a unidirectional thyristor, which is often called an ordinary thyristor

Resistive-Capacitive Phase-Shifting Bridges

There are several classification methods for thyristors.

(1) Classification by turn-off, conduction and control methods: Thyristors can be divided into ordinary thyristors, bidirectional thyristors, reverse conduction thyristors, and gate-off by their turn-off, conduction, and control methods. Thyristor (GTO), BTG thyristor, temperature controlled thyristor and light controlled thyristor.

(Two) press

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Current

Rated on-state current (IT) is the maximum stable operating current, commonly known as current. The commonly used thyristor IT is generally from one amp to several tens of amps.

Commonly used thyristors

The most basic use of ordinary thyristors is controlled rectification. The familiar diode rectifier circuit is an uncontrollable rectifier circuit. If put

There are mainly three types of SCRs: spiral, flat and flat bottom. Spiral is widely used. Thyristor has three electrodes --- anode (A) cathode (C) and control electrode (G). It has die type P

Major manufacturers: ST, NXP / PHILIPS, NEC, ON / MOTOROLA, RENESAS / MITSUBISHI, LITTELFUSE / TECCOR, TOSHIBA, JX, SANREX, SANKEN, SEMIKRON, EUPEC, IR, JBL, etc.

IT (AV)-On-state average current

VRRM--Reverse Repetitive Peak Voltage IDRM--Off-State Repeat

1.Noise level on the grid

In an environment with electrical noise, if the noise voltage on the gate exceeds VGT and there is sufficient gate current to excite positive feedback inside the thyristor (thyristor), it will also be triggered to conduct.

When installing the application, first make the wiring outside the gate as short as possible. When the wiring cannot be short, twisted or shielded wires can be used to reduce the intrusion of interference. Add a 1K resistor between G and MT1 to reduce its sensitivity. You can also connect a 100nf capacitor in parallel to filter out high frequency noise.

2.About the conversion voltage change rate

When driving a large inductive load, there is a large phase shift between the load voltage and current. When the load current crosses zero, the triac (thyristor) starts commutation, but due to the phase shift, the voltage will not be zero. So thyristor (thyristor) is required to turn off this voltage quickly. If the change of the commutation voltage at this time exceeds the allowable value, there will not be enough time to release the charge between the junctions and force the triac (thyristor) to return to the on state.

In order to overcome the above problems, an RC network can be added between the terminals MT1 and MT2 to limit the voltage change to prevent false triggering. Generally, the resistor is 100R and the capacitor is 100nF. It is worth noting that this resistor cannot be omitted.

3.About the conversion current change rate

When the load current increases, the power supply frequency increases or the power supply is non-sinusoidal, the change rate of the conversion current becomes high. This situation is most likely to occur in the case of inductive loads, and it is easy to cause damage to the device. An air inductor of several millihenries can be connected in series in the load circuit.

4.About thyristor (thyristor) open circuit voltage change rate DVD / DT

When a bidirectional thyristor (thyristor) in a cut-off state is applied with a high-speed changing voltage smaller than its VDFM, the current of the internal capacitor will generate sufficient gate current to make the thyristor (thyristor) conductive. This is especially serious at high temperatures. In this case, an RC snubber circuit can be added between MT1 and MT2 to limit VD / DT, or a high-speed thyristor (thyristor) can be used.

5.About continuous peak open circuit voltage VDRM

When the power supply is abnormal, the voltage across the thyristor (thyristor) will exceed the maximum value of the continuous peak open-circuit voltage VDRM. At this time, the leakage current of the thyristor (thyristor) increases and breaks through. If the load can tolerate large inrush currents, the local current density on the silicon chip is high, allowing this small portion to turn on first. Causes the chip to burn out or be damaged. In addition, incandescent lamps, capacitive loads or short-circuit protection circuits will generate high surge current. At this time, filters and clamp circuits can be added to prevent spikes (burrs) from being applied to the triac (thyristor) ^[2] .