JP3617442B2 - Ground connection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ground connection system, and more particularly to a ground connection system for a printed circuit board that connects a frame ground and a signal ground separated from the frame ground.
[0002]
[Prior art]
FIG. 3 is a perspective view of an example of a conventional ground connection method. In the figure, a PCB signal ground (SG) 2 is provided on an insulator 1 of a printed circuit board (PCB: Print Circuit Board). A PCB frame ground (FG) 3 is provided on the insulator 1 separately from G2. In the conventional ground connection system, this S.I. G2 and F.R. G3 is connected by soldering with a chip 0Ω resistor 4. The chip 0Ω resistor 4 may be a jumper wire.
[0003]
Also, conventionally, a pad made of a conductor is provided in a mechanical hole for screwing a PCB to the casing, so that the ground (SG) on the PCB is connected to the casing S.D. Sometimes connected to G. By these methods, S.P. G to housing F. By connecting to G, common mode noise (noise generated between FG and the output terminal of the circuit on the PCB) generated on the PCB can be removed, and radiation noise from the PCB can be reduced.
[0004]
[Problems to be solved by the invention]
However, the conventional multipoint grounding PCB has the following problems. The first problem is that S.I. G2 and F.R. Since the chip 0Ω resistor 4 or the jumper wire is used for connection to G3, once it is connected, it cannot be easily separated. Employing multi-point grounding is G line and F.R. Since a loop is formed by the G line, when noise linked to the size of the loop exists on the apparatus, the radiation noise is increased.
[0005]
Noise present on the device is usually difficult to predict and also depends on device operation. Therefore, it is necessary to optimize the grounding / separation part after the apparatus has been normally operated. However, in the conventional connection method, the connection / separation cannot be easily changed.
[0006]
The second problem is that, when multipoint grounding is adopted, the circuit on the PCB is directly connected to the housing, so that the circuit is exposed to external noise from outside the housing. In particular, when a circuit on the PCB is exposed to high-voltage noise such as ESD (Electrostatic Discharge), the device may malfunction.
[0007]
That is, S. on the PCB. G and F.M. When single-point grounding that is separated from G is used, radiation noise increases due to increased common mode noise, and when connected (when multi-point grounding is used), the possibility of malfunctioning against external noise such as ESD increases. Will do. However, in the conventional ground connection system, it is difficult to flexibly cope with them.
[0008]
The present invention has been made in view of the above points. G to F. An object of the present invention is to provide a ground connection system that can flexibly cope with an increase in radiation noise and external noise by automatically connecting to G.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a ground connection method for connecting between a signal ground and a frame ground separately provided on a printed circuit board, and a predetermined first predetermined potential and the potential of the signal ground. When a comparison result is obtained that the comparison means for comparing the set voltage and the signal ground potential is equal to or higher than the first set voltage by the comparison means, it is turned on by the output of the comparison means, and the signal ground potential is A switching element having one end connected to the signal ground, the other end of the switching element and the frame ground, which are turned off by the output of the comparison means when a comparison result indicating that the voltage is smaller than the first set voltage is obtained; And a clip circuit for clipping an input signal equal to or higher than a predetermined second set voltage to the second set voltage. Element a period of ON through the switching element and the clipping circuit, is obtained by the configuration of connecting the signal ground and frame ground.
[0010]
In order to achieve the above object, according to the present invention, in a ground connection method for connecting a signal ground and a frame ground separately provided on a printed circuit board, the potential of the signal ground and a predetermined predetermined value are set. The comparison means for comparing with the first set voltage, and when the comparison means obtains a comparison result that the potential of the signal ground is equal to or higher than the first set voltage, it is turned on by the output of the comparison means, and the signal ground A switching element whose one end is connected to the frame ground, which is turned off by the output of the comparing means when a comparison result is obtained that the potential of the switching element is lower than the first set voltage, and the other end of the switching element A clip circuit that is connected to the signal ground and clips an input signal equal to or higher than a predetermined second set voltage to the second set voltage. Switching element a period of ON through the switching element and the clipping circuit, it is obtained by the configuration of connecting the signal ground and frame ground.
[0011]
In the present invention, when a comparison result is obtained that the potential of the signal ground is smaller than the first set voltage, the signal ground and the frame ground are separated by the switching element, and the potential of the signal ground is the first set voltage. When the comparison result is obtained as described above, the signal ground and the frame ground can be connected through the switching element and the clip circuit.
[0012]
Here, the comparison means includes a voltage source that generates the first set voltage, and a comparator that compares the potential of the signal ground and the first set voltage from the voltage source.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration diagram of an embodiment of a ground connection system according to the present invention. In the figure, the comparator 11 has its inverting input terminal connected to the positive side terminal of the DC voltage source 18 that generates the first set voltage V1, and its non-inverting input terminal is the PCB signal ground (SG) 16. It is connected to the. The negative terminal of the DC voltage source 18 is connected to a frame ground (FG) 15 on the PCB, and the first set voltage V1 of the comparator 11 is F.V. It is set based on G15.
[0014]
Further, the output terminal of the comparator 11 is connected to the gate of the switching N-channel MOS transistor 17. One of the drain and the source of the transistor 17 is S.D. G. is connected to G16, and the other is connected to F.G via a clip circuit 14 comprising a diode 12 and a DC voltage source 13. Connected to G15. The positive side terminal of the DC voltage source 13 is connected to the cathode of the diode 12, and the negative side terminal is F.D. The second set voltage V <b> 2 is applied to the diode 12. Normally, the second set voltage V2 has the same value as the first set voltage V1, but can be set to a different value.
[0015]
The comparator 11 is F.D. G15 and substrate ground S.G. The transistor 17 for connecting to G16 is subjected to switching control. When the transistor 17 is on, the clip circuit 14 has an S.P. The G ground potential is clipped to the DC voltage of the DC voltage source 13.
[0016]
Next, the operation of the present embodiment will be described with reference to the time chart of FIG. The comparator 11 is input to the non-inverting input terminal. A comparison is made between the ground potential of G16 and a predetermined set voltage V1 indicated by II in FIG. Since the comparator 11 applies a low-level signal to the gate of the transistor 17 during the period when the ground potential I of G16 is lower than the set voltage II (V1), the transistor 17 is turned off as shown by the A region in FIG. It is said that.
[0017]
Therefore, in a period during which the transistor 17 is off (A region), S.I. G16 and F.R. G15 is not connected. Therefore, even if external noise such as ESD comes, the circuit on the PCB and the housing are connected to the S.G15. G16 and F.R. Since it is separated because G15 is not connected, malfunction of the circuit can be prevented.
[0018]
On the other hand, S.M. During the period in which the ground potential I of G16 is equal to or higher than the set voltage II (V1), the comparator 11 applies a high level signal to the gate of the transistor 17, so that the transistor 17 is indicated by the B region in FIG. Turned on.
[0019]
Therefore, during the period when the transistor 17 is on (B region), the S.P. G16 and F.R. G15 is connected via the transistor 17 and the clip circuit 14; The ground potential of G16 is clipped to the voltage IV (V2) of the DC voltage source 13, as indicated by III in FIG. That is, if the voltage V2 of the DC voltage source 13 indicated by IV is equal to the set voltage V1 of the comparator 11, S.I. When the ground potential of G16 is equal to or higher than the set voltage V1 (= V2), the diode 12 is turned on and becomes equal to the voltage V2 of the DC voltage source 13. The ground potential of G can be lowered to the set voltage V1 (= V2).
[0020]
Therefore, in this embodiment, S.I. When the ground potential of G16 is equal to or higher than the set voltage II (V1 = V2), S.I. G16 and F.R. G15 is automatically connected via the clip circuit 14, so that S.G. Of the common mode noise generated in G16, a portion equal to or higher than the set voltage II (V1 = V2) can be removed, and thereby radiation noise can be reduced.
[0021]
In this case, since the safety ground is usually taken, the S. G16 to F.M. Connecting to G15 results in multi-point grounding, but this results in multi-point grounding only during the necessary minimum, so the probability of problems occurring in ESD, which is a drawback when multi-point grounding is adopted, is also significantly reduced. be able to. By providing a plurality of ground connection circuits of the present embodiment that perform such operations on the PCB, common mode noise on the PCB can be finely removed.
[0022]
The present invention is not limited to the above-described embodiment. For example, the clip circuit 14 includes the transistor 17 and the S.P. The terminal (drain or source) provided between G16 and not connected to the clip circuit 14 of the transistor 17 is connected to the F.G. You may make it connect to G15. The clip circuit 14 may have a configuration using a transistor other than the diode clip circuit shown in FIG. 1, and the transistor 17 may be another switching element.
[0023]
【The invention's effect】
As described above, according to the present invention, when the comparison result that the potential of the signal ground is lower than the first set voltage is obtained, the signal ground and the frame ground are separated by the switching element. Even if the circuit on the PCB is exposed to external noise such as ESD, the circuit on the PCB and the housing are separated because the signal ground and the frame ground are not connected. Can be reduced.
[0024]
Further, according to the present invention, when a comparison result is obtained that the potential of the signal ground is equal to or higher than the first set voltage, the signal ground and the frame ground are automatically connected through the switching element and the clip circuit. Therefore, common mode noise generated on the PCB can be removed up to the second set voltage of the clip circuit, thereby reducing radiation noise.
[0025]
As described above, according to the present invention, the connection between the frame ground and the signal ground is adaptively separated according to the magnitude comparison result between the potential of the signal ground and the first set voltage with reference to the frame ground. It can be connected, and is flexible with respect to noise existing on a device that is usually difficult to predict, and can perform optimum noise reduction and circuit malfunction prevention.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an embodiment of the present invention.
FIG. 2 is a time chart for explaining the operation of FIG. 1;
FIG. 3 is a configuration diagram of a conventional example.
[Explanation of symbols]
11 Comparator 12 Diodes 13 and 18 DC voltage source 14 Clip circuit 15 Frame ground on PCB (FG)
17 PCB signal ground (SG)

Claims (4)

In the ground connection method that connects between the signal ground and the frame ground provided separately on the printed circuit board,
A comparing means for comparing the potential of the signal ground with a predetermined first set voltage;
When the comparison means obtains a comparison result that the potential of the signal ground is equal to or higher than the first set voltage, it is turned on by the output of the comparison means, and the potential of the signal ground is set to the first setting voltage. A switching element having one end connected to the signal ground, which is turned off by the output of the comparison means when a comparison result is obtained that is less than the voltage;
A clip circuit that is connected between the other end of the switching element and the frame ground and clips an input signal equal to or higher than a predetermined second set voltage to the second set voltage, and the switching element is turned on In the period, the signal ground and the frame ground are connected through the switching element and the clip circuit. The comparison means comprises a voltage source that generates the first set voltage, and a comparator that compares the potential of the signal ground with the first set voltage from the voltage source. The ground connection method according to 1. In the ground connection method that connects between the signal ground and the frame ground separately provided on the printed circuit board,
A comparison means for comparing the potential of the signal ground with a predetermined first set voltage;
When the comparison means obtains a comparison result that the potential of the signal ground is equal to or higher than the first set voltage, it is turned on by the output of the comparison means, and the potential of the signal ground is set to the first setting voltage. A switching element having one end connected to the frame ground, which is turned off by the output of the comparison means when a comparison result is obtained that is smaller than the voltage;
A clip circuit that is connected between the other end of the switching element and the signal ground and clips an input signal equal to or higher than a predetermined second set voltage to the second set voltage, and the switching element is turned on In the period, the signal ground and the frame ground are connected through the switching element and the clip circuit. The comparison means comprises a voltage source that generates the first set voltage, and a comparator that compares the potential of the signal ground with the first set voltage from the voltage source. 3. Ground connection method according to 3.

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