How many connection methods are there for Y capacitors?

Everyone knows that the y capacitor is a safety capacitor, which is a capacitor that connects the l line to ground and the n line to ground. Its function is to suppress common mode interference. Nowadays, there are three levels of 1, which are Y 1, Y2, and yY4 in order. Due to safety regulations, the leakage current should not be too large. If the leakage current is too large, touching electrical equipment will give a tingling sensation. Therefore, the capacitance size of the capacitor is generally between 1. nf and 4.7 nf.

Safety level insulation category nominal voltage range allowable peak pulse voltage

Y1 double insulation or reinforced insulation Y1 ≥ 250V Y1 ＞ 8 kV

Y2 basic insulation or additional insulation Y2 ≥ 150V 250V ≥ Y2>5 kV

Y4 basic insulation or additional insulation Y4 ＜ 150V Y4 ＞ 2.5kV

Y capacitors are generally available in two colors: blue and yellow

So, what are the common connection methods for y capacitors in a circuit? There are generally four types:

Type 1: Jump between the primary and secondary grounding of the transformer

The primary ground is often referred to as the "hot ground", while the secondary ground is often referred to as the "cold ground". The most common connection method is to connect the y capacitor across the transformer's primary ground and secondary ground, and it usually appears in pairs because the foot distance is too short to achieve complete isolation. In a switching power supply, the continuous conduction and closure of the switching transistor will generate noise, as shown in the figure q 1 below. This mainly indicates the instantaneous voltage spike pulse signal, and the signal noise flows to the primary coil of the transformer, which is equivalent to one inductor. At this time, a higher reverse electromotive force is generated, and the generated high-order harmonics are coupled to the transformer primary, causing noise disturbance. Adding a Y capacitor between the primary and secondary ground can establish a discharge channel between the secondary ground of the transformer and the ground. The high-order harmonics of switch noise are discharged to the ground through this channel, thereby avoiding radiation through the power supply line and reducing the radiation disturbance of the switch power supply.

Type 2: Jump between the primary high voltage and secondary ground of the transformer

There are parasitic capacitors between each coil winding of the transformer, which generate voltage during operation and become the source of noise. By bridging the y capacitor between the initial high voltage and the secondary ground, common mode disturbances caused by primary and secondary coupling can be filtered out. This is similar to the first type, but the results may differ during EMI testing.

Type 3: Jump across the primary high voltage and secondary output positive terminal of the transformer

This connection method is relatively rare and sometimes used in low-power power supplies

Type 4: Jump between the primary ground of the transformer and the positive terminal of the secondary output