JPS60213109A - Low-pass filter - Google Patents

Abstract

PURPOSE:To switch characteristics simply by constituting three inductors connected in series by three windings divided into two parts, two and one, and wound around two winding grooves for a cap type core. CONSTITUTION:Three capacitors C1-C3, one switch SW and three inductors L1-L3 are connected as shown in the drawing to constitute a filter circuit. The three inductors parts are constituted by winding one winding N1 and two windings N2, N3 around the upper and lower winding grooves 5a, 5b of a drum type core 5 respectively and covering the whole surface of the core 5 with the vertically movable cap type core 4 and the condition of L12=L3 is satisfied between the total inductance L12 of the windings N1, N2 and the inductance L3 of the winding N3. Consequently, only the 1st trap of the filter can be moved by one switch.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low noise filter having two traps.

(Configuration of conventional example and its problems) Conventionally, in this type of filter, in order to obtain the filter characteristics shown in FIG.
+C2, c3, C4, and two switches SWI
+ SW2 has a circuit configuration as shown in the figure, and each inductance is set by a winding N1 forming an inductance Ll in the upper winding groove of a variable coil composed of a drum-shaped core with three brim and a cap-shaped core, and an inductance t
, 2. Generally, the winding N2JN3 forming the windings t and s was wound in the lower winding groove so as to have the polarity shown in the figure.

In this conventional example, the switch SWI is turned off,
When the first trap is switched to a higher frequency side, the second trap moves to a lower frequency.

Therefore, it is necessary to take a configuration in which the switch SW2 is turned OFF and correction is made so that the second trap frequency changes, which requires switching two switches. The purpose of this invention is to eliminate the problem of requiring two switches and to provide a low-pass filter that can selectively obtain the two characteristics shown in FIG. 2 by switching one switch.

(Structure of the Invention) In order to achieve the above object, the present invention provides a first trap and a second trap. Second and third inductance L l +
L2 1 L3 are connected in series, and first and second capacitors C, C2 are connected in series between the connection point of the first and second inductances L, L2 and the ground. 2 and 3rd inductance L2
, a third capacitor C3 between the connection point of L3 and ground.
' and further connected to first and second capacitors CI, respectively.

A circuit is constructed by connecting a switch between the connection point of C2 and the ground, and by turning the switch on and off, the first
The first inductance is connected to one of the winding grooves of a variable coil constituted by a drum-shaped core and a cap-shaped core having three brim members. a winding N, which forms an inductance L+'& of the winding N, which also forms the second and third inductance L21L3.
+N3 is wound around the other winding groove, and L12''
It satisfies the i,30 condition, which allows the number of switches to be reduced from two to one, and the number of capacitors to be reduced from four to three.

(Explanation of Examples) Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 3 shows a circuit diagram of a low/4' filter according to the present invention, which includes three capacitors C1+C2+C3, one switch SW, and three inductances Ll.
+ L2 + La are connected as shown in the figure to form a circuit. On the other hand, the three inductance parts in this circuit are arranged in the upper and lower two winding grooves 5a and 5b of the drum-shaped near 5 having three horns as shown in FIG.
N 2 + N 3 is formed by winding each coil at the bottom and covered with a vertically movable cap-type core 4, and between the total inductance L+2 of the windings N1 and N2 and the inductance L3 due to the winding N3. LI2=L3
0 In addition, in Fig. 4, 1 is a base with a terminal to which the drum-shaped core 5 is added, 2 is a cap core holding mold, 3 is a shield case, and 6 is a bottom of the base with a terminal 1. There are three built-in capacitors.

A filter circuit is constituted by the composite coil with a built-in capacitor constructed as described above and a switch (not shown). With this configuration, when the switch is turned on, the A characteristic at K in FIG. 2(a) is obtained, and when the switch is turned off, the B% characteristic is obtained.

FIG. 2(b) shows the relationship between switch states and characteristics in the case of the present invention and the conventional example. As can be seen from this figure, in the case of the present invention, a single switch switching operation is required. Characteristics can be switched.

(Effects of the Invention) As explained above, according to the present invention, what conventionally required two switch functions to obtain the filter characteristics shown in FIG. The required number can be reduced from 4 to 3,
A significant cost reduction effect can be obtained.

[Brief explanation of drawings]

Figure 1 shows a conventional filter circuit, Figure 24(a)
2(b) is a diagram showing the relationship between the state of each switch and the characteristics, FIG. 3 is a diagram showing the circuit configuration of the present invention, and FIG. 4 is a diagram showing the filter characteristics of the present invention and the conventional example. FIG. 3 is a diagram showing an example of an LC composite coil constituting the filter circuit of the present invention. 1... Base with terminal, 2... Cap core holding mold, 3... Shield case, 4... Cap type core, 5... Drum type core, 6... Capacitor. Figure 1 to) lb) Figure 3 No. 41 = I 2 3

Claims (1)

[Claims] In a rotor filter having a first trap and a second trap, the first. The second and third inductances Ll, L2 + L3 are connected in series, and
The first and second inductances L1. A first and second capacitor CI, C2 are connected in series between the connection point of L2 and ground, and a third capacitor is connected between the connection point of second and third inductance L2 11+3 and ground. C3 are connected to each other, and a switch is connected between the connection point of the first and second capacitors CI+02 and the ground to form a circuit, and by turning the switches on and off, the frequency of the first trap can be adjusted. In the low-pass filter, each of the inductances is connected to one winding groove of a variable coil constituted by a drum-shaped core having three horns and a cap-shaped core.
The inductance L! The winding N1 forming the second and third inductances L2+L+1 is wound in the other winding groove, and the winding N1 and the winding KL between the total inductance L12 due to N2 and the third inductance L3
Sururono and Sfilter are characterized by satisfying the condition of 12=L3.