NTC sensor used in switching power supply
Today, let’s talk about the power-on surge current, what is going on? Figure 1 is the most basic original drawing of a switching power supply. Is it the same as the power drawing you are currently designing? Switching power supply directly converts the conversion process of AC-220V (50Hz) AC power on the power grid into a DC voltage that we can directly use. Very convenient and fast. The disadvantage is that under the fuse, B and C will often open for no reason, and the internal coil under the transformer will be overheated, and the internal short circuit will occur. Except the components themselves are not reliable. The occurrence of the above phenomenon is mostly related to excessive surge current and excessive impact. How can there be inrush current?
In practice, it has been shown that due to the existence of C1, any switching power supply will generate inrush current at the moment of turning on. And the higher the load of the power supply, the greater the power, so the greater the surge current. Practice has also proved that the inrush current can be tens to 100 times the normal working current of the power supply!
Even if it is a short time, it is generally MS level. When such a large current is applied to B1, C1 and T, it may not be damaged after a single boot, and it seems that it does not matter if it is turned on several times. But what is certain is that every time the machine is turned on, the relevant device is damaged once. Turning on and off the machine year after year, this is prone to problems.
The slow start and delay insurance designed by the engineers for this purpose have avoided some failures, but they cannot be completely eliminated. Statistics show that more than 60% of electrical equipment problems are in the power supply system.