How is the switching circuit kept from interfering with others?
The commonly used thermoelectric part of switch mode power supplies has a dedicated anti-interference filtering circuit, which is generally not noticeable due to its obscurity. As for the specific location, it is in the circuit behind the fuse and varistor. This combination is not easy to break, but it is essential. Today, let's talk about some common sense here.
This part of the circuit is not complicated and is generally composed of capacitors and inductors. Speaking of which, it is necessary to mention some basic knowledge - filter circuits. Those with a slight weak current foundation know that capacitors and inductors can form LC structure or π structure filter circuits. Lc circuits can be composed of one inductor and one capacitor, while π filter circuits are composed of two capacitors and one inductor. Because the architecture is similar to a π shape, it is vividly called a π filter circuit.
The anti-interference circuit feature of the switching power supply, which is composed of inductance and capacitance, is very obvious. It is generally composed of an inductance that looks like a small transformer and two square safety capacitors. It is basically not broken here, especially the inductance rarely experiences open circuit faults because it is connected in series in the circuit, so there is no short circuit in the inductance. Unless the mains power is particularly stable, the safety capacitors are rarely burned out or short circuited.
The main function of this filtering circuit is to filter out interference pulses from the power grid, prevent the impact of interference pulses on the components of the switching power supply, and also prevent the oscillation pulses generated by the switching power supply during operation from being sent back to the power grid, causing interference to other electrical appliances using the power grid.
At this point, we understand why the capacitor here is called a safety capacitor. In order to ensure the safety of the power grid and power supply, it is stipulated that switch mode power supplies must be equipped with this filtering circuit, just like compensating capacitors in electrical cabinets. Capacitors and inductors together form a protective wall, which not only protects the switching power supply itself from harm, but also prevents it from interfering with the power grid in reverse
