JPS5937887B2 - filter - Google Patents

Description

[Detailed description of the invention] The present invention relates to a filter.

Conventionally, for example, as a noise filter, two filters as shown in Fig. 1 were used.
one capacitor C1, C2 and two coils L03L
A combination of 2 is often used.

20 However, according to this, the current capacity of the coils L0 and L2 is required to be larger than the current flowing through the load, that is, the windings are required to be thick and large, which is not desirable in terms of structure and cost.

Therefore, in order to eliminate the above-mentioned drawbacks, the present invention provides a filter that only requires the use of one coil with a small current capacity, that is, one small coil.

An embodiment of the present invention will be described below based on the drawings.

In FIG. 2, C3 and C4 are first and second capacitors, Tr4 and Tr2 are transistors, and L3 is a small coil with a small current capacity. In the above configuration, the input terminals P,,P. When normal DC power is supplied between them, a current flows from the emitter base of the transformer Trl to the base-emitter of the transistor Tr2 via the coil L3, turning on the transistor Trl7Tr2 and producing an output between the terminals P3 and P4. . In the above case, the base current flowing through the transistors Tr0 and Tr2 is determined by the DC resistance of the coil L3.

Since the above base current only needs to be small, the coil L3 should be one with a small current capacity, that is, load current x l/refe(
It suffices to have a current capacity of fe (current amplification factor of transistors Trl, Tr2). Therefore, a thin and small winding can be used. Next, when noise mixes between terminals P1 and P2, the impedance of coil L3 ZL■2πf
Since L (f=human power frequency, L inductance of coil L3) increases, the base currents of transistors Trl and Tr2 decrease, transistors Tr4 and Tr2 are turned off, and the passage of the noise is blocked.

As described above, according to the present invention, only one coil is required, and the coil can be a coil with a small current capacity, that is, a small coil, which can be extremely miniaturized and inexpensive compared to conventional coils. The effect is very large.

[Brief explanation of drawings]

FIG. 1 is an electrical circuit diagram showing an example of a conventional filter, and FIG. 2 is an electrical circuit diagram showing an embodiment of the present invention. C3...First capacitor, C4...
-Second capacitor, Trl, Tr2...transistor, L3...coil.

Claims (1)

[Claims] 1 A first capacitor that receives input, transistors with different polarities whose emitters are connected to both poles of the first capacitor, a coil connected between the bases of both transistors, and a coil connected between the collectors of both transistors. A filter consisting of a second capacitor.