Self-immune protection of switching power supplies
Switching power supply as long as a power failure, even the countryside did not go to school the old lady know to see if the fuse is blown, about the fuse of this matter like nine years of compulsory education. This on the one hand shows that the fuse protection role is very powerful, another point also shows that the switching power supply fuse is very common, today we will talk about the opening of the switching power supply. Switching power supply into the line first in series with a fuse, which do not have to say much we all know, focusing on an important component behind it, is connected in series in the fuse. After the inlet line between the two lines of varistor, the first contact will have an illusion, single fuse can be overcurrent protection, but also to get a redundant varistor, this The protection mechanism of the power supply, say a few words about the things hidden behind the fuse.
On the varistor, I briefly talk about a few characteristics: First, the characteristics of the voltage range it is allowed to withstand, it is infinite resistance, once it exceeds the range of the voltage it withstands, it is almost no resistance, equivalent to a short-circuit, the use of this feature is just to judge it good or bad, under normal circumstances, it is a very large value of the resistance, close to infinity, if the measurement to the value of the resistance is very small, indicating that the varistor is damaged. Secondly, the varistor response speed is very fast, from infinity to conduction time is very short, so you can quickly protect the circuit in time. Third, its selection, because the peak AC voltage and the actual effective voltage value of the relationship between the value is not absolutely the same, so the choice of the rated voltage of the varistor for the need to protect the voltage 2.4 times or so, using this point, you can predict the current of the circuit it is working in the overhaul.
In the end, it is not a blind man wearing glasses, redundant, here to discuss this issue?
Combined with a few points of the varistor, it is easy to understand why the fuse should be used together with the varistor, the fuse is connected in series in the circuit, varistor The fuse is connected in series in the circuit, the varistor is connected in parallel in the circuit, they have different division of labour, one protects the overcurrent, one protects the overvoltage, when the overvoltage, the varistor instantly shorts out, resulting in a high current, burning the fuse, the power failure protection. When overvoltage, the varistor instantly short-circuit, resulting in a high current, burned out the fuse, power failure to protect the circuit, they are both independent of each other, but also work together.
Speaking of here have to mention a phenomenon, some switching power supply fuse blown, change a fuse and normal use, obviously no fault but the fuse is blown. Let a person feel no reason and inexplicable, in fact, it may be the instant voltage instability, varistors play a protective role in the fuse, and its own electrical Circuit is not a problem, this is the circuit of self-immune protection.
