Circuit Diagram 19-Analysis of the Principle of High-Frequency Anti-Interference Circuit of Power Supply

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Circuit Diagram 19-Analysis of the Principle of High-Frequency Anti-Interference Circuit of Power Supply [Copy link]

There are a lot of high-frequency interference components in the 220V AC city power grid. For example, the high-frequency pulses generated when the power switches of various electrical appliances will parasitize in the AC power grid, and the various electrical appliances hung in the power grid will interfere with each other. For example, when the power switch of indoor electrical appliances is turned on, a "click" sound will be emitted from the radio, which is the interference to the radio during the power switch of the electrical appliances.

When the requirements for electrical appliances to resist interference are not high, a high-frequency anti-interference circuit may not be set in the power supply circuit, otherwise it must be set to ensure the normal operation of the electrical appliances.

The high-frequency interference circuits in electronic appliances are mainly the following: high-frequency anti-interference circuit of power transformer shielding layer; high-frequency anti-interference circuit of capacitor; high-frequency anti-interference circuit of inductor; high-frequency anti-interference circuit of capacitor and inductor.

1. High-frequency anti-interference circuit of power transformer shielding layer

The figure below shows the anti-interference circuit of power transformer shielding layer. In the circuit, S1-1 and S1-2 are double-layer power switches, F1 is a fuse, and T1 is a power transformer. 3447421.1 Circuit Analysis In the circuit, a shielding layer is added between the primary winding and the secondary winding of the power transformer T1. One end of the shielding layer is grounded. This structure is equivalent to a small capacitor, which can bypass the high-frequency interference from the AC mains to the ground, and prevent the high-frequency interference from being added to the secondary winding of the transformer, thereby achieving the purpose of anti-interference. The function of this anti-interference circuit is realized by the power transformer itself, which is a magnetic shielding anti-interference method. Since the power transformer needs to add a shielding layer, the process is complicated and the cost increases, it is rarely used now. 2. Circuit fault analysis 1) When the grounding of the shielding layer is open, the power transformer step-down work is normal, and the whole circuit will work normally, but there is no high-frequency anti-interference effect. 2) When the leads at both ends of the shielding layer are grounded, the magnetic circuit of the transformer is short-circuited, and the power transformer will burn out due to heat.

2. Capacitor high-frequency anti-interference circuit

The figure below shows a capacitor high-frequency anti-interference circuit. In the circuit, T1 is a transformer, and C1 and C2 are high-frequency anti-interference capacitors connected to the primary winding.

[attach]344743 [/attach]

1. Circuit analysis

[color=rgb(34, 34, In the circuit, C1 and C2 are connected in parallel between the two primary windings of the power transformer and the ground wire. The capacity of C1 and C2 is very small. For 50Hz AC, their capacitive reactance is very large, which is equivalent to an open circuit. However, for high-frequency interference signals, the capacitive reactance of C1 and C2 is very small. In this way, the high-frequency interference signal in the primary winding of the transformer is bypassed to the ground by C1 and C2, and cannot be added to the primary winding of the power transformer, achieving the purpose of anti-interference.

The capacity of C1 and C2 is equal, and the withstand voltage is required to be relatively high, because they are connected to the 220V circuit, and the withstand voltage is generally not less than 450V.

The safety performance of this high-frequency anti-interference circuit is not very good, because the capacitors C1 and C2 leak, there is a risk of electric shock.

2. Circuit Fault Analysis

1) When one of the capacitors C1 and C2 is short-circuited, the fuse of the 220V AC power will be blown, and the power transformer T1 and the subsequent circuits will have no working voltage.

2) When the grounding wires of C1 and C2 are open, the high-frequency anti-interference effect still exists, but it only has an anti-interference effect on the higher frequency components in the high-frequency anti-interference signal, and the anti-interference ability for the components with slightly lower frequencies decreases. Because after the grounding wires of C1 and C2 are open, C1 and C2 are connected in series, and the total capacity after series connection decreases by half, and the capacitive reactance to the high-frequency interference signal doubles, so the shunt attenuation ability to the high-frequency interference signal decreases by half.

3. Inductor high-frequency anti-interference circuit

The figure below shows an inductor high-frequency anti-interference circuit. In the circuit, L1 and L2 are inductors, T1 is a power transformer, and L1 and L2 are connected in series in the primary winding incoming line loop of the power transformer T1.

[attach]344744 [/attach]

1. Circuit analysis

It can be seen from the circuit that L1 and L2 are connected in series in the two incoming line loops of the primary winding of the power transformer T1. Due to the high frequency of the high-frequency interference signal, the inductor has a large inductive reactance to the high-frequency signal, so the high-frequency interference signal cannot enter the primary winding of the power transformer T1, achieving the purpose of high-frequency anti-interference. The working principle of the inductor high frequency anti-interference circuit is: 1) For 50Hz AC mains, because the frequency is very low, the inductive reactance of L1 and L2 to AC is very small and forms a path, so that 220V AC mains can be added to the primary winding of the power transformer T1.34)]2) This anti-interference circuit is connected in series in the AC circuit. The anti-interference components L1 and L2 do not need a grounding wire, so the safety performance is relatively good.

2. Circuit fault analysis

1) When one of L1 and L2 is open, the 220V AC voltage cannot be added to both ends of the primary winding of the power transformer T1. At this time, the whole circuit does not work.

2) The main fault of this high-frequency anti-interference circuit is the open circuit fault of L1 and L2.

4. Capacitor and inductor mixed high-frequency anti-interference circuit

The figure below shows a capacitor and inductor mixed high-frequency anti-interference circuit. In the circuit, L1 and L2 are inductors, T1 is a power transformer, and C1 and C2 are high-frequency anti-interference capacitors.

1. Circuit Analysis

This circuit is composed of adding high-frequency anti-interference capacitors C1 and C2 to the inductor high-frequency anti-interference circuit. L1 and L2 have large inductive reactance to high-frequency interference components, which can prevent high-frequency interference components from being added to both ends of the primary winding of the power transformer.

The working principle of the capacitor and inductor mixed high-frequency anti-interference circuit is:

1) The capacitance of capacitors C1 and C2 is very small, and their inductance to 50Hz AC is very large, resulting in an open circuit characteristic, but their capacitive reactance to high-frequency interference signals is very small, so the high-frequency interference signals are bypassed, that is, the high-frequency interference signals on the 220V AC ignition line directly reach the neutral line through capacitors C1 and C2, and no high-frequency interference signal current flows through the power transformer, thus achieving the purpose of anti-interference.

2) This circuit is a dual anti-interference circuit, that is, the capacitor and inductor play the role of high-frequency anti-interference at the same time. This circuit has stronger anti-interference ability than the previous circuits.

2. Circuit Fault Analysis

1) When one of the inductors L1 and L2 is open-circuited, the 220V AC voltage cannot be added to both ends of the primary winding of the power transformer T1, and the entire circuit does not work.

2) When one of the capacitors C1 and C2 is short-circuited, the 220V AC fuse will be blown, and the power transformer T1 and subsequent circuits will have no working voltage, and the entire circuit will not work.

3) Since there are many anti-interference components in this circuit, the circuit failure rate is relatively high.