JPH0412622A - Power supply circuit - Google Patents

Abstract

PURPOSE:To maintain safety, by providing a common capacitor and adopting a dual system. CONSTITUTION:A generation rate, at which the voltage of a power supply 1 is applied to a case 3, is denoted as P. When a failure rate lambda, at which a common capacitor 5 fails in short circuit mode, is 1 (FIT), a failure rate lambdat, at which a capacitor C1 and the common capacitor 5 fail simultaneously in short circuit mode, comes into lambdat 2Xlambda1XlambdaXt, where t denotes an operating time. When the operating time t is 10 years, i.e., about 10<5> hour, P comes into P=1/10X1/10X2X1/10<9>X1/10<9>X10<5>=2X10<-15> (FIT). Therefore, even if the capacitor C1, C2 for absorbing noises fail in short circuit mode, unless the added common capacitor 5 fails simultaneously in short circuit mode, it is not caused that the voltage of the power supply 1 is applied to the case 3. Thereby, safety can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device for improving the safety of a noise absorption circuit such as a power supply circuit.

[Conventional technology]

In the power supply circuit of conventional products, a noise canceling circuit as shown in FIG. 2 is used to prevent noise generated by the power supply from being outputted to the outside. In Figure 2, 1 is the power supply, 2 is the ground, and 3 is connected to the product casing.

4 indicates the power supply main body. In this way, in the conventional technology, the noise generated in the power supply main body 4 is transferred to the capacitor C2 or
The capacitor C1 is used to prevent noise from appearing in the external circuit. In the same figure,
If capacitor C□ fails and the failure is in short-circuit mode, the power supply voltage will be applied to the casing. There is no problem if the casing is grounded, but it is possible that it is not grounded.

In such a case, if a human body touches the casing, electric shock may occur depending on certain conditions. In reality, there is no problem if an earth leakage breaker is attached (omitted in Fig. 2), but it is possible that no earth leakage breaker is attached. In such a case, an electric shock is expected.

As described above, the conventional technology has an unsafe potential.

In addition, for example, an example of a noise filter (or line filter) as a noise prevention method is quoted from the literature (``Electronic circuit noise & trouble countermeasures'', Mitsuru Mogi, CQ Publishing, pp. 26-28) as shown in Figure 3. In any case, as mentioned above, if the capacitor fails in short-circuit mode and the casing is not grounded, an electric shock is assumed.

[Problem to be solved by the invention]

The present invention aims to improve the unsafe potential of the prior art described above.

[Means to solve the problem]

In the present invention, as a means to improve the above-mentioned unsafe potential, a common capacitor is provided, and a dual system is adopted from the viewpoint of safety.

[Effect]

In the present invention, even if the noise absorbing capacitors Cs and Ct fail in short mode, the power supply voltage will not be applied to the casing unless the additional common capacitor fails in short mode at the same time, and safety is maintained. It will be done.

As an alternative, the method shown in Figure 4, quoted from the above-mentioned literature, can be considered, but in this case, although it is good from a safety point of view, it is difficult to remove noise, which may cause pollution such as malfunction of other equipment. .

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. Second
In the figure, 1 is the power supply (100V or 200V).

2 is grounding (one terminal on the secondary side of the pole transformer is grounded).

Reference numeral 3 indicates a connection to the casing, 4 indicates a power supply main body, and 5 indicates a common capacitor claimed in the present invention. In the present invention, even if the capacitor C□ in FIG. 1 fails in a short-circuit mode, the common capacitor C is added, so power will not be applied to the casing.

Assume the incidence of power being applied to the case (according to the prior art shown in Fig. 2). In Figure 2, the probability that the housing 3 is not grounded is 1710, and the probability that the earth leakage breaker is not attached is 17.
10, and the failure rate λ1. which causes short mode failure of capacitors c1 and c2. Let λ2 be 1, and capacitor c
1. The failures of c, have an exponential distribution over the elapsed time (
In general, it is assumed that the failure rate distribution of electronic components over time is exponentially distributed, as is well known. Let P be the occurrence rate of power being applied to the casing, let P be the occurrence rate of power being applied to the casing in the case of the present invention shown in Fig. 1, and let the short mode failure rate λ of the common capacitor C be 1 (FIT). shall be. The failure rate λt at which capacitors C□ and C fail simultaneously in the short mode is approximately the value of equation (2).

λt is 2Xλ, ×λ×t (2) where t represents the operating time.

If t is a thousand years and approximately 106 hours, then = 2 x 1
0-"' (FIT) - (3).

Therefore, the incidence of power being applied to the casing according to the prior art shown in equation (1) can be reduced by four orders of magnitude with the present invention shown in equation (3). That is, by creating a dual system by adding a common capacitor, it was possible to provide a power supply circuit with significantly higher safety than that of the conventional technology. With the simple addition of a single circuit, the safety of the conventional power supply circuit could be increased by four orders of magnitude.

The invention can be applied to any type of line filter. That is, the present invention can basically be applied to circuits that allow noise to escape into the housing, and a power supply circuit with extremely high safety can be easily provided at low cost.

[Brief explanation of drawings]

FIG. 1 is a power supply circuit diagram of an embodiment of the present invention, FIG. 2 is a power supply circuit diagram according to the prior art, FIG. 3 is a circuit diagram of a line filter according to the prior art, and FIG. 4 is a circuit diagram of a line filter according to the prior art.
It is a circuit diagram of a filter. 1... Commercial power supply 2... Grounding 3... Housing
4... Power supply body 5... Common capacitor 1 figure 2 figure 2 figure 5 figure 4 figure

Claims (1)

[Claims] 1. A noise absorption circuit for a power supply circuit, characterized in that a plurality of capacitors are connected in series to release noise generated from the power supply body to a housing.