JPS5926655Y2 - line filter circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a line filter circuit used in a power supply circuit of a television receiver or the like.

Generally, a power supply circuit of a television receiver or the like is provided with a type of high frequency removal filter called a line filter in order to remove unnecessary high frequency radiation that enters the commercial AC power line from within the receiver.

In the conventional example of this line filter, as shown in FIG.
A pair of coils 4 and 5 wound in opposite phases with the same number of turns are respectively inserted in the coils, and a π-type high frequency removal filter 8 is provided by connecting a capacitor 6.7 between the two coils. Since the high frequency signals appearing on both lines are in phase, this high frequency signal is removed by the filter 8, but since the commercial alternating currents flowing through both lines are in opposite phases, this alternating current causes each of the coils to The magnetic fluxes generated in 4 and 5 cancel each other out, and as a result, the filter 8 has no effect on the alternating current.

Note that 9 is a load circuit. However, in such a conventional line filter circuit, both coils 4 and 5 of the filter 8
Since peak alternating current flows through the coils, both coils must be made of relatively thick conductor wires. Therefore, it is necessary to increase the number of turns in the coils to achieve a sufficient high frequency rejection effect for high frequencies. This requires a relatively large core, resulting in a large filter and an increase in manufacturing costs.

This was a particular problem in television receivers destined for Australia, where strict requirements were imposed on the prevention of unnecessary high-frequency radiation.

Therefore, the present invention proposes a line filter circuit that eliminates these drawbacks.

The line filter circuit of the present invention, as shown in Figure 2,
Two π-type filters 8 configured similarly to those in FIG.
．． 8' is provided, the first filter 8 is connected between the input terminal 1 of the commercial AC power source and the rectifying and smoothing circuit 2, and the second filter 8' is connected between the load circuit 9 of the rectifying and smoothing circuit 2. It's designed to connect.

In addition, in FIG. 2, corresponding parts of each filter 8, 8' with those in FIG. Make it.

According to the line filter circuit of the present invention having such a configuration, the second
The current flowing through both coils 4' and 5' of the second filter 8' is a direct current, and its magnitude is smaller than the peak value of the input AC current.
, 5' can use thinner conductors than the coils 4, 5 of the first filter 8, and therefore the filter 8 of FIG.
In order to achieve the same frequency characteristics as the filter 8 in FIG. Also, a small core and a small number of turns are sufficient.

Therefore, the line filter circuit of the present invention can be realized at a lower cost and has a higher effect of removing unnecessary high frequencies than the conventional one.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional line filter circuit, and FIG. 2 is a circuit diagram showing a line filter circuit of the present invention. 2: Rectifier and smoothing circuit, 8.8': π-type filter, 9: Load circuit, 3.3': Core, 4.4', 5.5': Coil, 6.6', 7.7': Condenser .

Claims (1)

[Scope of utility model registration request] A pair of coils wound in opposite phases to each other with the same number of turns around a first closed magnetic circuit core are inserted into a pair of lines between the AC power supply and the rectifying and smoothing circuit, and a capacitor is connected between the two coils. A filter is provided, and a pair of coils wound around a second closed magnetic circuit core in the same manner as the above two coils is inserted in a pair of lines between the rectifying and smoothing circuit and the load circuit. A line filter circuit that includes a second filter with a capacitor connected between the coils.