The book Comprehensive Collection of Practical Thyristor Circuits was compiled by our company's technical team led by Chief Engineer Liu Dingjian. With a 16mo format, it spans 466 pages and contains 770,000 characters. It provides a comprehensive introduction to thyristors (SCRs), MOS field-effect transistors, high-power transistors (GTRs), and IGBTs, covering almost all aspects of modern power electronics. Not only does it elaborate on basic theories such as their principles, structures, technical parameters, and testing methods, but it also includes a large number of practical application circuits in various fields. It can truly be regarded as a reference book for the power electronics industry, offering great assistance to readers and users.

Meanwhile, this demonstrates that our technical team, equipped with such extensive knowledge, can significantly enhance our pre-sales and after-sales services for users. For example, if a user originally used a 100A contactor and intended to replace it with a 100A solid-state relay, that would be a serious mistake! We would help the user select the correct model. Another example: some users encountered failures with their forward-reverse solid-state relays. After repeated inspections and analyses failed to identify the cause, they consulted us. Upon a detailed understanding of the situation, we found that their unreasonable wiring—running control trigger wires and 380V power lines through the same metal pipe—allowed interference clutter to enter the control circuit, causing false triggering and component damage. The problem was resolved simply by modifying the wiring!

Liu Dingjian is the chief drafter of the national standard for thyristors (silicon-controlled rectifiers), and our company is the second drafting entity for the industry standard of solid-state relays.

Standards may seem dry and rigid, but they actually embody profound knowledge and careful considerations. The formulation of a standard not only requires repeated discussions among relevant experts but also needs to be practically verified based on domestic existing conditions.

When our team of experts was formulating the industry standard for solid-state relays, we discussed issues such as how to determine the nominal current of a solid-state relay. For example, what size of thyristor should be used inside a 40A solid-state relay (a key component that determines its cost and quality)? Some manufacturers use a single 41A bidirectional plastic-encapsulated thyristor, some use two 24A bidirectional plastic-encapsulated ones, and some even cut corners with just one 24A. The standard practice is to use two 20A single-phase thyristors. However, some manufacturers disregard standards entirely, choosing whatever minimizes costs. The former options cost only a few yuan, while the latter not only costs much more but also involves more complex processing techniques.

It’s a pity that users have no way of knowing what components are actually used inside the products they buy.

There are many manufacturers producing solid-state relays, but few can manufacture high-quality forward-reverse solid-state relays. As a result, the damage rate of cheap such products on the market is surprisingly high. This can be explained by their basic principle. The so-called forward-reverse operation, when using contactors, is achieved by swapping two of the three phases (A, B, C) of the power supply. In principle, replacing contactors with solid-state relays works the same way. However, the latter are "electronic products." If they are occasionally falsely triggered by interference clutter—i.e., they conduct without a normal control signal—the two phases that need to be swapped will short-circuit directly without passing through the load, resulting in an extremely large current that immediately damages the solid-state relay.

What advantages do we have? First, the circuits we design include measures to prevent false triggering. Second, we have strict requirements for the relevant parameters of the key components (thyristors) we select. The thyristors we use are not evaluated based on conventional parameters we usually focus on, such as whether the current rating meets the standard or whether the voltage resistance is high enough, but on dynamic parameters like di/dt (current change rate) and surge current. These dynamic parameters are inconvenient to test in daily situations but are actually crucial in practice. With over 20 years of accumulated experience, we have developed an effective screening method. Therefore, our products of this type are of excellent quality and high reliability.

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