GB2181895A - Variable capacitor with widened ground lead - Google Patents

Abstract

A variable capacitor suitable for reception of RF waves such as television broadcast waves has a pair of facing baseplates (1 and 2) holding a rotor shaft (3) between them on which rotor plates (4) are mounted. Two grounding leads (9 and 10) which are electrically connected with the rotor shaft (3) are attached to their respective baseplates (1 and 2). One of the leads (9) has a widened portion between the baseplates (1 and 2) which suppresses the lead reactance. <IMAGE>

Description

SPECIFICATION Variable capacitor The present invention relates to variable capacitors. In variable capacitors the capacitance is varied by changing the area of those portions of rotor plates which face their corresponding stator plates coated with a dielectric film.

Variable capacitors find extensive use in audio products, such as radio receiver and cassette tape recorder equipped with a radio receiver.

In previously proposed variable capacitors for radio receiver or the like equipped with a tuner capable of receiving the television broadcast band, the oscillator circuit strongly couples with the tuner circuit especially at higher frequencies in the band because of the reactance remaining on the rear-stage grounding lead that grounds the stage interlocking with the oscillator stage as well as the oscillator stage. As a result, when the input level is high, frequency jump or a reduction in the gain may take place.

Accordingly, it is an object of the present invention to provide an improved variable capacitor. The capacitor embodying the invention to be described hereinafter is made up of inexpensive parts, can be assembled in an economical manner, makes use of grounding lead while suppressing the reactance remaining on the lead, and is best suited for reception of RF waves such as television broadcast waves.

According to the present invention there is provided a variable capacitor having a pair of opposed baseplates, a rotor shaft rotatably mounted between the baseplates, grounding leads attached to their respective baseplates and electrically connected to the rotor shaft, rotor plates each made of a thin metal plate and rigidly fixed to the rotor shaft, poles mounted to the baseplates, and stator plates each made of a thin metal plate and coated with a dielectric, the stator plates being held by the poles so as to be disposed between their respective rotor plates in a closely spaced relation therefrom, the capacitor being characterised in that a portion of one of the grounding leads is wider than the other portions.

Because the grounding lead electrically connected with the rotor shaft is widened as mentioned previously, the lead conducts highfrequency current well. Consequently, the lead which grounds both the oscillator stage for the television broadcast band and the interlocking stage has a reduced amount of reactance remaining on it.

Variable capacitors embodying the present invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings in which: Figure 1 is a perspective view of a variable capacitor embodying the present invention; Figure 2 is a cross-sectional view of the capacitor shown in Fig. 1; Figure 3 is a perspective view of a previously proposed variable capacitor; Figure 4 is a cross-sectional view of the capacitor shown in Fig. 3; and Figure 5 is a perspective view of another variable capacitor embodying the invention.

A conventional variable capacitor is shown in Figs. 3 and 4, where a front baseplate 1 has a central hole 1a and a plurality of surrounding holes 1b. A rotor shaft 3 is inserted in the hole 1a. Poles 1c are inserted in the holes 1b. A rear baseplate 2 has trimmer holes 2a and a plurality of holes 2b. Poles 2c are inserted in the holes 2b. A metal, frontstage grounding lead 10 is attached to the front baseplate 1. The lead 10 is soldered to an audio set (not shown) at 10a. Similarly, a metal rear-stage grounding lead 13 is attached to the rear baseplate 2. The lead 13 is soldered to the audio set at 13a. Trimmer shafts 7, trimmer rotor shafts 8, and trimmer stator plates 1 7 are mounted to the rear baseplate 2 to form trimmers.The soldered portion 13a of the rear-stage lead 13 takes a substantially Vshaped form so as to snap into the audio set, for temporary attachment to the set. Each trimmer shaft 7 has a groove 7a so that it may be operated externally. A substantially semicircular trimmer rotor shaft 8 is mounted on each shaft 7 so as to be rotatable with the shaft 7. The trimmer shafts 7 extend through their respective trimmer rotor shafts 8 and trimmer stator plates 17 and through their respective holes 2a in the rear baseplate 2, and are rotatably inserted in their reapective rtimmer holes 13b formed in the rear lead 13.

Rotor plates 4 take a substantially sectorial shape. The rotor shaft 3 extends through the rotor plates 4, which are mounted alternately with washers 15. The rotor plates 4 and the washers 15 are firmly fixed to the shaft 3 by nuts 18. Rotation of the shaft 3 is restricted by a stop 14 fixedly mounted on the shaft 3.

Stator plates 6 are mounted alternately with washers 16. Each stator plate 6 and a plurality of washers 16 are stacked to form one stator lamination 18. Each plate 6 is made of a thin substantially sectorial metal plate coated with a dielectric. Stator laminations 19, 20, 21 are similar in structure to the stator lamination 18. The rotor shaft 3 is held by the front baseplate 1 and the rear baseplate 2 such that its main portion is disposed between the baseplates. The grounding leads 10 and 13 are attached on the inside surfaces of the baseplates 1 and 2, respectively. The lead 13 has a pivot support portion 13c which cooperates with the bearing portion 1a of the front baseplate 1 to rotatably hold the shaft 3. The stator laminations 18-21 are supported by the poles 1 c and 2c extending between the baseplates 1 and 2.Metal terminals 5 are firmly fixed to the poles Ic and 2c.

When mounted, each terminal 5 is inserted by force from the side of the rear baseplate 2 through the pole 2c, the stator laminetions 18-21, and the pole 1 c in the recited order.

The rear-stage grounding lead 13 is bent through an angle of about 90" near one fringe of the rear baseplate 2 towards the front baseplate 1 and terminates in a portion that extends parallel with the end portion of the front-stage grounding lead 10. This end portion of the lead 13 is also so shaped as to snap into the audio set, for temporary attachment to it. The portion of the lead 13 which begins at the curve 13d and ends at the soldered portion 13a has a width of roughly 2 to 3mm to standardize the sizes of the holes that are used for installation to the audio set.

In the variable capacitor shown in Figs. 1 and 2 parts similar to the capacitor of Figs. 3 and 4 are similarly referenced. As shown the capacitor shown in Figs. 1 and 2 has a front baseplate 1 and a rear baseplate 2. The baseplate 1 is provided with a hole 1a into which a rotor shaft 3 is inserted. Also, the baseplates 1 and 2 are formed with holes 1 b and 2b, respectively, in which poles 1 c and 2c are respectively inserted. The rear baseplate 2 further has holes 2a through which their respective trimmer shafts 7 extend. A metal, frontstage grounding lead 10 is attached to the front baseplate 1. The lead 10 is soldered to an audio set (not shown) at location 10a.Similarly, a metal, rear-stage grounding lead 9 that is soldered to the audio set at location 9a is attached to the rear baseplate 2, which has trimmer rotor plates 8 and trimmer stator plates 17 mounted thereon as well as the trimmer shafts 7 to form trimmers. The soldered portion 9a of the rear-stage lead 9 takes a substantially V-shaped form so as to snap into the audio set, for temporary attachment to it. Each trimmer shaft 7 is provided with a groove 7a to allow the shaft to be operated externally. The trimmer rotor plates 8 which are substantially semicircular in shape are mounted on their respective trimmer shafts 7 so as to be rotatable with them. The shafts 7 extend through the trimmer stator plates 17, which are coated with a dielectric and disposed opposite to the rotor plates 8.

The shafts 7 also extend through the trimmer holes 2a formed in the rear baseplate 2, and are rotatably inserted in holes 9b formed in the rear-stage lead 9.

The capacitor further has rotor plates 4 that take a substantially sectorial form, and are disposed alternately with washers 15. The rotor shaft 3 extends through the rotor plates 4.

The rotor plates 4 and the washers 15 are firmly fixed to the rotor shaft 3 by nuts 18.

Rotation of the shaft 3 is restricted by a stopper 14 which is rigidly mounted on the shaft 3. Stator plates 6 are disposed alternately with washers 16. Each stator plate 6 and a plurality of washers 16 form a stator lamination 18. Each stator plate 6 is made of a substantially sector-shaped thin metal plate coated with a dielectric. Stator laminations 19, 20, 21 are similar in structure to the stator lamination 18.

The rotor shaft 3 described above is held by the front baseplate 1 and the rear baseplate 2 such that its main portion is disposed between the baseplates. The front-stage grounding lead 10 and the rear-stage grounding lead 9 are attached to the inner surfaces of the baseplates 1 and 2, respectively. The rear-stage lead 9 has a recessed portion 9c to receive the top end of the rotor shaft 3. The front baseplate 1 has a bearing 1a for supporting the shaft 3. Thus, the shaft 3 is rotatably held by the recessed portion 1 c and the bearing 1 a. The stator laminations 18-21 are supported by the poles 1c and 2c that extend between the baseplates 1 and 2. Metal terminals 5 are firmly secured to the poles 1 c and 2c.When mounted, each terminal 5 is forced from the side of the rear baseplate 2 into the pole 2c, the stator laminations 18, 19, 20, 21, and the pole 1 c in this order. The rearstage grounding lead 9 is bent through an angle of about 90 near one fringe of the rear baseplate 2 toward the front baseplate 1 and terminates in a portion that extends parallel with the end portion of the front-stage grounding lead 10. This end portion of the lead 9 is also so shaped as to snap into the audio set, for temporary attachment to it. The portion of the lead 9 which exists between the curve 9d and the soldered portion 9a is wider than the other portions.The curve 9d has a width of about 2 to 3 mm to facilitate the bending operation. Aiso, the soldered portion 9a has a width of about 2 to 3 mm to standardize the sizes of the holes that are used for installation to the audio set (not shown).

Referring next to Fig. 5, there is shown another variable capacitor according to the invention. This capacitor is similar to the capacitor already described in conjunction with Figs.

1 and 2 except for the following. The poles 5 have portions 5a protruding from the rear baseplate 2. The rear-stage grounding lead 12 is bent through an angle of about 90" near one fringe of the rear baseplate 2 toward the baseplate 2. The front end portion of the lead 12 takes a substantially V-shaped form so as to snap into the audio set, for temporary attachment to it. The front-stage lead 11 is bent through an angle of about 90" near one fringe of the front baseplate 1 toward the near baseplate 2, and terminates in a portion that extends parallel with the rear-stage grounding lead. This end portion is so shaped as to snap into the audio set, for temporary attachment to it. The portion of the lead 11 which is formed between the curve 1 1a and the soldered portion 11 b and extends be tween the baseplates has, a larger width than the other portions. The curve 1 lea has a width of about 2 to 3 mm to facilitate the bending operation. Also, the soldered portion 11 b has a width of about 2 to 3 mm to standardize the sizes of the holes that are used for installation to the audio set.

As described above, a portion of one grounding lead is wider that the other portions. This reduces the reactance remaining on the lead without decreasing the ease with which the device is assembled. It is not necessary to increase the number of components. Also, the dimensions of holes and parts are not required to be modified for installation to the audio set.

Claims (3)

1. A variable capacitor having a pair of facing baseplates, a rotor shaft rotatably mounted between the baseplates, grounding leads attached to their respective baseplates and electrically connected to the rotor shaft, a portion of one of the grounding leads being wider that the other portions, rotor plates each made of a thin metal plate and rigidly fixed to the rotor shaft, poles mounted on the baseplates, and stator plates each made of a thin metal plate and coated with a dielectric, the stator plates being held by the poles so as to be disposed between their respective rotor plates in a closely spaced relation therefrom.

2. A variable capacitor according to Claim 1, wherein said portion of the grounding lead that is wider than the other portions is formed between the baseplates.

3. A variable capacitor substantially as hereinbefore described with reference to Figs.

1 and 2, or 5 or the accompanying drawings.