JPS6015402Y2 - Electronics - Google Patents

Description

[Detailed description of the invention] This invention relates to electronic equipment that uses commercial power.
The present invention relates to an electronic device in which a commercial power supply line is grounded to the casing via a capacitor, so that noise superimposed on the commercial power supply is bypassed to the casing by the capacitor.

Normally, AC 100 (V) commercial power line 1000 [V
] It is not uncommon for noise pulses of more than 100 volts to be superimposed, and in the case of lightning, etc., voltages of several thousand volts may be generated.

In order to protect necessary circuits within the electronic device from such abnormal noise voltages, electronic devices having a protection function as shown in FIG. 1 are well known.

In FIG. 1, lines 2 and 3 from a commercial power source 1 are connected to a primary side T1 of a transformer T in an electronic device.

Further, the secondary side T2 of the transformer is connected to a load circuit 4 for operating the functions of the electronic device.

Next, at least one line 2 of the primary side T1 has a capacitance C
It is grounded to the casing 5 of the electronic device via.

Therefore, for example, the common mode external noise generated by the common mode noise source 6 and superimposed on the commercial power line 2 is bypassed to the casing 5 via the capacitor C, so that there is no adverse effect on the secondary side T2. do not have.

However, if the value of capacitance C is increased to increase the noise path effect, if a human body touches a non-live part such as the housing 5 of an electronic device, part of the commercial power supply current will be transferred to the human body through this capacitance C. Because the current flows through the capacitance, you may receive a considerable electric shock depending on its capacitance.

For this reason, the value of the capacitance C is set to o, so that the maximum current when the case 5 is directly grounded (-
ot cμF] or less.

In addition, for people with particularly sensitive idiosyncratic constitutions, the value of capacitance C must be further reduced to 1 degree or less.

In the case of such a small value of capacitance C, if the case 5 is not directly grounded, but is grounded with a stray stray capacitance C1 of 1000 (pF) or more, most of the external noise voltage will be caused by the transformer T. Coupling capacitance C2 between the primary and secondary sides of
This means that the load circuit 4 is not adversely affected.

In view of these problems, the present invention connects a varistor in addition to a capacitor between the commercial power line and the casing.
The present invention provides an electronic device that aims to improve the noise path effect and prevent electric shock.

FIG. 2 shows an embodiment of the present invention.

In particular, the differences from the conventional example shown in FIG. 1 will be described.

At least one line 2 of the commercial power lines 2 and 3 is connected to the casing 5 via a series circuit of a capacitor C and a varistor 7.

It is assumed that the varistor 7 has a characteristic that the impedance suddenly becomes low at a voltage higher than a certain value exceeding the commercial power supply voltage, for example, at about twice ACloo (V).

Further, at the commercial power supply voltage, the varistor 7 has a very high resistance value, for example, 10 [MΩ] or more.

Next, the value of capacitance C is a relatively large value, for example 0.1 [μ
F].

According to such an embodiment, as mentioned above, the varistor 7 usually has a resistance value of 10 [MΩ] or more, so even if a human body touches the housing, the current is small and the varistor 7 is protected from electric shock. protected.

On the other hand, if a voltage more than twice the commercial power supply voltage is applied as external noise, this noise has a relatively short period and the value of capacitance C is large compared to the noise frequency, so there is almost no voltage across capacitance C. No noise voltage is generated.

Therefore, the noise voltage becomes a suppression voltage determined by the varistor 7, and is limited to about 200 (V), for example.

For this reason, the load circuit 4 only needs to have a noise tolerance of about twice the commercial power supply voltage, but it is usually designed to have this level of noise tolerance.

Therefore, even if an external noise voltage is induced in the load circuit 4 by the coupling capacitance C2, no adverse effect will occur because the external noise voltage is suppressed by the varistor 7.

As mentioned above, the present invention connects the commercial power line and the housing of the electronic device using a capacitor with a relatively large value and a varistor that has low impedance at a certain voltage higher than the commercial power supply voltage. Although it is a very simple configuration,
This can be expected to prevent electric shocks and improve the noise path effect.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional example, and FIG. 2 is a diagram showing an embodiment of the present invention. In the figure, 1 is a commercial power supply, 4 is a load circuit, 5 is a housing, and 6 is a noise source.

Claims (1)

[Scope of utility model registration request] An electronic device in which a capacitor is connected between at least one commercial power supply line and a casing, and a varistor that has a low impedance at a voltage higher than the commercial power supply voltage is connected between the capacitor and the casing.