source:Industry News Popular:adapter release time:2021-06-17 09:48:43 Article author:sznbone
Overvoltage protection technology can be roughly divided into the following three categories
The first category: simple thyristor overvoltage protection.
The second category: Overvoltage protection based on voltage clamping technology.
The third category: Overvoltage protection based on voltage limiting technology.
The selection basis of overvoltage protection technology is: power adapter circuit structure, power adapter performance and cost.
The first category: thyristor overvoltage protection
Just like the meaning of its name, the overvoltage protection can short-circuit the output terminal of the power adapter in response to the output overvoltage of the power adapter. If the output voltage of the power adapter exceeds the preset value within the specified time, then the short-circuit device (Generally, thyristor) will act.
When the thyristor acts, it short-circuits the output of the power adapter, so the output voltage drops. Shown in the figure is a typical thyristor overvoltage protection circuit, which is connected to the output of the linear regulator. When designing a thyristor overvoltage surge protection circuit, it is very important to realize that the bypass function of the product's overvoltage surge protection does not necessarily provide a long-term load protection when the circuit fails.
In addition, the bypass device must have enough power to bear the short-circuit current. For the short-circuit current that exceeds the specified time or the external current limit, a fuse or circuit breaker must be able to function, so as to protect the thyristor from damage.
For linear regulator type DC power adapters, thyristor overvoltage protection is a common method, and the simple application circuit often used is shown in the figure. The working process of linear regulator and overvoltage protection is as follows:
After the unadjusted DC input voltage VH passes through a series transistor Q, the voltage drops, and at the same time provides a lower value but adjusted output voltage V. , The amplifier A1 and the resistors R1 and R2 provide a voltage control for the regulator, and the transistor Q2 and the current-limiting resistor R1 are used for current-limiting protection.
Most catastrophic circuit failures are caused by the short circuit of the series regulator Q1. In this case, the higher unregulated input voltage VH will appear at the output. In this fault situation, the entire circuit loses its voltage control and current limiting functions. At this time, the thyristor, which plays a role of over-voltage protection, must work and short-circuit the output terminal.
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