JPS6243576A - Earth detection circuit for electronically applied equipment - Google Patents

Abstract

PURPOSE:To prevent possible accidents such as electric shock, by connecting capacitors in series to an AC power source line while a large-capacity capacitor is connected between these capacitors and the case of an equipment to detect whether the case of the equipment is earthed or not. CONSTITUTION:Capacitors 12 are connected separately in series to an AC power source line 7, a large-capacity capacitor done between the capacitors 12 and the case 8 of an equipment and a voltage detector 33 done to the connection midpoint between the capacitors 12 and 14 to detect the voltage level. When the case 8 is earthed securely, a fine voltage proportional to the leakage current generates between the capacitors 12 and 14, a condition which is detected with the detector 33 to confirm the earthing of the case 8. On the other hand, when the case 8 is not earthed, no leakage current flows to the capacitor 14. Hence, no fine voltage is generated between the capacitors 12 and 14, a condition which is detected with the detector 33 to confirm that the earthing of the case 8 fails.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a ground detection circuit for electronic application equipment that detects whether the outer casing of the electronic application equipment is grounded.

BACKGROUND OF THE INVENTION Generally, the outer casing of electronic equipment is grounded. This is to prevent accidents such as electric shock due to electrical leakage. In particular, in the case of electronic equipment that causes radio wave interference, such as those with built-in power switching amplifiers, in order to prevent interference to the outside due to harmful noise,
Grounding the outer casing is important. Furthermore, in medical equipment that directly treats the human body, grounding of the outer casing is even more important because a weak leakage current may cause a serious accident.

On the other hand, the outer casing is grounded, and a ground line from the internal circuit is generally connected to such an outer casing. Here, as an example of the connection of the ground line to the outer casing, there is one in which the AC power line and the outer casing are connected by the ground line via a noise filter.

The noise filter includes a bypass capacitor, and the bypass capacitor is connected in series between each of the AC power lines and the outer casing. With such a configuration, not only electric leakage in the internal circuit is prevented, but also high frequency noise is removed by the bypass capacitor and radio wave interference is prevented.

Problems to be Solved by the Invention Electronic application equipment whose safety is ensured by being grounded will no longer be guaranteed safety if it is no longer grounded due to disconnection of the ground.

However, the above-mentioned device has the disadvantage that there is no way to detect whether or not it is grounded, and if an accident such as disconnection of the ground occurs, a dangerous situation will occur. This is particularly inconvenient for medical devices that are expected to be 100% safe.

The present invention has been made in view of these points, and an object of the present invention is to provide a circuit that can detect whether or not the outer casing of an electronic application device is grounded.

Means for Solving the Problems The present invention connects capacitors in series to each AC power supply line, and connects a large-capacity capacitor with a larger capacitance than the capacitors between these capacitors and the outer casing of the electronic application equipment. A voltage detector to detect the voltage level was connected to the midpoint between the large capacitors and the capacitors.

As a result, leakage current from the AC power line flows to the outer casing through the capacitor and the large-capacity capacitor, and is grounded from the outer casing. At this time, if the outer casing is securely grounded, a small voltage proportional to the leakage current will be generated between the capacitor and the large capacitor. This minute voltage is detected by a voltage detector, confirming that the outer casing is grounded.

On the other hand, if the outer casing is not grounded, leakage current will not flow to the large capacitor, and therefore no minute voltage will be generated between the capacitor and the large capacitor, which will be detected by the voltage detector and connected to the external capacitor. It is confirmed that the casing is not grounded.

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

First, electronic application equipment (not shown) is provided.

This electronic application device is, for example, a medical ultrasound device.

The electronic application device has a pair of power input terminals 1 and a ground terminal 2. The power input terminal 1 is connected to an outlet plug 3. The outlet 4 into which the outlet plug 3 is inserted is connected to a power source 6 whose one end is connected to ground 5. On the other hand, the ground terminal 2 is connected to the ground 5. Here, the earth 5 means grounding to the earth.

In the electronic application equipment, the power input terminal 1 is connected to the AC power line 7, and the ground terminal 2 is connected to an outer casing, the shape of which is not shown. This outer casing is ground 8. Here, the AC power line 7 is connected to a circuit (not shown) of an electronic application device, and a choke coil 9 is connected to each of the middle points of the connection. Further, between these choke coils 9 and the power input terminal 1, there is a connection line from the AC power line 7.
The ground lines 10 are pulled out one by one, and these ground lines 10 are connected at a connection point 11 on the way to form one line. Capacitors 12 are connected in series between the connection point 11 and the AC power line 7, and a noise filter 13 is formed by these capacitors 12 and the choke coil 9.

Thus, the ground line 10, which has become one at the connection point 11, is connected to the ground 8 via a large capacity capacitor 14. This large capacity capacitor 1
4 has a larger capacitance than the capacitor 12.

On the other hand, an earth detection line 15 is connected to the earth line lO between the connection point 11 and the large capacity capacitor 14.
is connected. This connection portion serves as a detection point 16. The ground detection line 15 includes the detection point 16.
Safety device 17 and rectifier amplifier 18. Comparator 19
and an alarm device 20 are connected.

The safety device 17 is constructed by branching lines drawn from the middle of the earth detection line 15, and each line is connected to the ground 8 via a diode 21. The diodes 21 are connected in opposite directions.

The rectifier amplifier 18 is an amplifier 22 with various elements added thereto, and converts AC power into DC power. That is, the ground detection line 15 is connected to the negative input side of the amplifier 22 via a resistor 23. The positive input side of this amplifier 22 is connected to the ground 8. The negative input side of the amplifier 22 is also connected to the output side of the amplifier 22 via a diode 24, and a resistor 25 and a diode 26 are connected in series.
is also connected in parallel with the diode 24. The two diodes 24, 26 are connected in opposite directions. The ground 8 is connected between the resistor 25 and the diode 26 via a capacitor 27. The ground detection line 15 is drawn out between the connection point and the diode 26. The ground 8 is connected to the midpoint of the ground detection line 15 in this portion via a resistor 28. Here, rectifier amplifier 1
8 is formed.

Thus, the ground detection line 15 drawn out from the rectifying amplifier 18 is connected to the positive input side of the comparator main body 29 in the comparator 19 . Further, a reference power source 32 connected to the ground 8 via two resistors 30 and 31 is provided in the comparator 19, and a negative voltage of the comparator main body 29 is connected between the two resistors 30 and 31. Input side is connected. The comparator 19 is formed here.

The alarm device 20 is connected to the output side of the comparator 19.

Thus, the rectifying amplifier 18, the comparator 19, and the alarm 20 form a voltage detector 33.

In such a configuration, the electronic application device operates by applying the voltage of the power source 6 to the internal circuit through the AC power line 7. At this time, high frequency noise is removed by the noise filter 13 and radio wave interference is prevented. Further, leakage current from the AC power supply line 7 flows to the ground 8 via the capacitor 12 and the large capacity capacitor 14, and from the ground 8 to the earth 5. Here, since the reactance of the large-capacity capacitor 14 is extremely small compared to the capacitor's resistivity, even if the large-capacity capacitor 14 is present, a high-frequency noise pass effect is maintained, and leakage current is also grounded.

Therefore, the voltage detector 33 detects whether the ground 8 and the earth 5 are reliably connected, in other words, whether the electronic application equipment is reliably grounded.

That is, when the ground 8 and the earth 5 are connected, a small voltage proportional to the leakage current is generated at the detection point 16 due to the presence of the large-capacity capacitor 14. This minute voltage is input to the voltage detector 33 through the ground detection line 15.

At this time, before being input to the voltage detector 33, the safety device 17 confirms whether the minute voltage has become an excessive voltage.

Once safety is confirmed, the minute voltage is first transferred to the rectifier amplifier 1.
8 and output as a positive DC voltage.

Next, the minute voltage converted into a DC voltage is input to the comparator 19, and the comparator main body 29 compares whether it is higher or lower than the voltage of the reference power source 32. At this time, if ground 8 and earth 5 are connected.

The micro voltage level is higher. Then, comparator body 2
The output from 9 becomes logic 1, and no alarm signal is given to the alarm device 20.

Therefore, the alarm device 20 does not issue an alarm, and it is detected that the electronic application equipment is securely grounded.

On the other hand, when the ground 8 and the earth 5 are disconnected, the leakage current from the AC power supply line 7 does not flow to the large capacitor 14. Therefore, no minute voltage is generated at the detection point 16. As a result, the DC voltage level output from the Ill fluency amplifier 18 decreases, and the comparison voltage level at the comparator 19 becomes higher. Therefore, comparator 1
The output of 9 becomes logic 0, and an alarm signal is given to the alarm device 20. In the alarm device 20, measures such as generating an alarm sound are taken after the function stop signal of the electronic application equipment is generated.

Here, it is detected that the electronic application equipment is not grounded.

Effects of the Invention The present invention connects a large-capacity capacitor with a larger capacitance than the capacitor between each capacitor connected in series to an AC power supply line and an outer casing, and connects the large-capacity capacitor to the connection midpoint between the capacitor and the capacitor. Since a voltage detector that detects the voltage level is connected to the terminal, the voltage detector can detect whether or not the outer casing is grounded, thereby preventing electric shocks and other accidents. It has effects such as contributing to improved safety.

[Brief explanation of the drawing]

The drawing is an overall circuit diagram showing one embodiment of the present invention. 7... AC power line, 8... Ground (outer casing),
12... Capacitor, 14... Large capacity capacitor,
33...Voltage detector

Claims (1)

[Claims] Capacitors are connected in series to each AC power supply line, and a large capacity capacitor with a larger capacitance than the above capacitor is connected between these capacitors and the outer casing of the electronic application equipment, and the connection between this large capacity capacitor and the above capacitor is A ground detection circuit for electronic application equipment, characterized in that a voltage detector for detecting a voltage level is connected to a connection midpoint.