JP4011312B2 - Static electricity countermeasure circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a static electricity countermeasure circuit for removing static electricity.
[0002]
[Prior art]
Conventionally, an electrostatic countermeasure circuit for removing static electricity flowing into an integrated circuit and an electronic component constituting an electronic device has been devised. For example, an electrostatic countermeasure circuit which is a surface mount type protective circuit component disclosed in Japanese Patent No. 2595491 is disclosed. is there.
[0003]
A conventional static electricity countermeasure circuit will be described with reference to FIGS. FIG. 3 is a schematic block diagram of a circuit including a conventional static electricity countermeasure circuit D. FIG. 4 is a diagram showing a circuit configuration inside the conventional static electricity countermeasure circuit D in FIG.
[0004]
The main circuit B, which is an integrated circuit such as a CMOS, is connected to the circuit C as an external unit connected by a line that divides and connects an I / O connector and the like via an electrostatic countermeasure circuit D. The circuit B is configured to be supplied with a DC power supply current from the power supply E. The circuit C and the main circuit B are connected by a signal line F that transmits a signal input to the circuit C to the main circuit B via the static electricity countermeasure circuit D. The main circuit B and the static electricity countermeasure circuit D are connected to a ground (GND) G, and the circuit C and the power source E are connected to GNDH and I, respectively.
[0005]
In addition, the electronic circuit unit J is configured by combining the main circuit B and the static electricity countermeasure circuit D with respect to the circuit C which is an external unit. In most cases, the main circuit B and the static electricity countermeasure circuit D configure the GNDG of the electronic device unit J as a common GND.
[0006]
The electrostatic discharge countermeasure circuit D in FIG. 4 has one end of the coil 24 connected to the terminal 23, the other end of the coil 24 connected to the terminal 25, and a zener diode 26 at a point d on the line between the coil 24 and the terminal 25. Are connected in parallel, the anode of the Zener diode 26 is connected to GNDG, and a capacitor 27 is connected in parallel with the Zener diode 26. The main circuit B is connected to a point c between the Zener diode 26 and GNDG, and the GND of the main circuit B is taken.
[0007]
The signal line F includes a transmission line Fa that is a signal transmission line and a GND side line Fb that is a signal transmission GND line. The terminal 23 is connected to the GND side line Fb of the signal line F connected to the circuit C. The terminal 25 is connected to the GND side line Fb of the signal line F connected to the main circuit B.
[0008]
During normal operation, a signal input from the circuit C is output to the main circuit B via the signal line F. Here, when static electricity is applied to the circuit C or the signal line F, the electrostatic current flows into the electronic device unit J from the GND side line Fb. The peak of the electrostatic current is suppressed by the coil 24, and when the electrostatic voltage exceeds a certain value, it is discharged to GNDG through the Zener diode 26 and further absorbed by the capacitor 27, thereby removing the static electricity. The
[0009]
[Problems to be solved by the invention]
However, if the GNDG is disconnected from the electronic device unit J in the use of the electronic device unit J, the connection between the electronic device unit J and the GNDG is released, and the power supply E is turned on with the GND floating in the electronic device unit J. It becomes.
[0010]
On the main circuit B, a capacitor for removing noise of the power source current from the power source E is installed, and when GND floating occurs in the electronic device unit J, the capacitor for removing noise is charged. A DC charge current due to the release of the charge flows to GNDH through the point c, the Zener diode 26, the point d, the coil 24, the GND side line Fb, and the circuit C in this order as an abnormal current line. At this time, due to conduction of an excessive DC charge current, heat generation or burning (disconnection) of the circuit board pattern of the circuit between the point d and the terminal 23 and heat generation of the GND side line Fb may occur.
[0011]
An object of the present invention is to prevent an excessive direct current from flowing to a part on an abnormal current line in which heat generation or burning occurs due to current conduction when a GND connection is abnormal.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is the static electricity that is connected to an electronic device, is connected to an in- vehicle electronic device, and flows into the electronic device from the outside through a ground line of a signal line. An anti-static circuit that is connected in series to an abnormal current line through which a DC current is conducted when a grounding connection is abnormal, and a DC interrupting unit that interrupts the DC current when the connection is abnormal; and Two Zener diodes or diodes connected in series and having anodes connected in series in opposite directions, and a static electricity removing unit that conducts the static electricity to the ground unit, the DC blocking unit connected in series, and The static electricity removing unit is connected in parallel to the ground side line .
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 and 2 of the accompanying drawings. In the present embodiment, a static electricity countermeasure circuit when a car audio vehicle-mounted power amplifier is used as an electronic device will be described. FIG. 1 is a schematic perspective view of a vehicle in which an in-vehicle audio system α including an anti-static circuit according to the present embodiment is installed.
[0014]
In a vehicle A such as an automobile, an in-vehicle audio system α is installed as an in-vehicle audio system α, an in-vehicle power amplifier 1 that is an electronic device that amplifies an audio signal, and a CD tuner that outputs an audio signal to the in-vehicle power amplifier 1 H / U (head unit) 2, an audio signal line 3 through which an audio signal is transmitted from H / U 2 to the in-vehicle power amplifier 1, a battery 4 that outputs a DC power supply current, and a battery 4 connected to the battery 4 A B (battery) line 5 and a Bu (Buck up) 6 which are lines for supplying the power source current from 4 to the in-vehicle power amplifier 1 and the H / U 2 are mounted.
[0015]
Here, the in-vehicle audio system α will be described with reference to FIG. FIG. 2 is a configuration diagram of the in-vehicle audio system α in FIG.
[0016]
The in-vehicle power amplifier system α mounted on the vehicle A includes an in-vehicle power amplifier 1, an H / U 2, an audio signal line 3, a battery 4, a B line 5, Bu 6, an in-vehicle power amplifier 1, H / U2 and GND7, 8, and 9, which are grounding portions of the vehicle body of the vehicle A connected to the battery 4, respectively. The audio signal line 3 includes a transmission side line 3a which is a line on the audio signal transmission side, and a GND side line 3b which is a line on the audio signal transmission GND side.
[0017]
The in-vehicle power amplifier 1 is connected to the transmission side line 3a and the GND side line 3b of the audio signal line 3 and separates the noise of the audio signal received from the transmission side line 3a, the isolation circuit 10 and the GND 7 Are connected in series to an amplifier unit 11 for amplifying an audio signal separated from noise from the isolation circuit 10, an output line 12 for outputting an amplified audio signal from the amplifier unit 11, and a B line 5. A noise removing circuit 13 for removing noise from the power supply current from the B line 5 and a DC / DC converter 14 connected in series to the noise removing circuit 13 and changing the voltage of the power supply current from which noise has been removed by the noise removing circuit 13. It comprises.
[0018]
The DC / DC converter 14 is connected to the isolation circuit 10 and the amplifier unit 11, and supplies a power supply current whose voltage is changed to the isolation circuit 10 and the amplifier unit 11. The noise elimination circuit 13 is connected in parallel with the coil 15 having one connected in series with the B line 5 and the other connected to the DC / DC converter 14 and one on the line between the coil 15 and the DC / DC converter 14. And a capacitor 16 connected to GND 7 and the other, and a capacitor 17 connected in parallel to the capacitor 16. When noise is applied to the power supply current from the power supply E or B line, the peak of the noise current is suppressed by the coil 15 and the noise current is absorbed by the capacitors 16 and 17.
[0019]
The in-vehicle power amplifier 1 is further connected in series to the GND side line 3b and connected to the input side 18 via the connection between the GND side line 3b and the isolation circuit 10, and is isolated from the input unit 18 on the GND side line 3b. One of them is connected in parallel to a point a between the ground circuit 10 and GND 7, and the other is connected to GND 7 and an anti-static circuit 19 that conducts static electricity to GND 7. It is assumed that each circuit and component on the in-vehicle power amplifier 1 are formed on a printed board.
[0020]
The in-vehicle power amplifier 1 and the H / U 2 are connected to the GND 7 and 8 of the vehicle body of the vehicle A, respectively, but when the audio signal is transmitted from the H / U 2 to the in-vehicle power amplifier 1, the vehicle body of the vehicle A By preventing the GND current due to the GND potential difference from flowing through the GND-side line 3b, mixing of noise from the GND current into the audio signal is prevented. That is, the GND current flows on the GND side line 3b between the GND 7 and the GND 8, and the GND side line 3b is connected to the input unit 13 on the in-vehicle power amplifier 1 side in order to remove noise from the GND current to the audio signal. It is not directly connected to GND 7 but is connected to GND 8 on the H / U 2 side.
[0021]
The static electricity countermeasure circuit 19 includes a Zener diode 20 whose cathode is connected in series to the GND 7, a Zener diode 21 whose anode is connected in series to the anode of the Zener diode 20, and one of which is connected in series to the cathode of the Zener diode 21. , And a capacitor 22 connected in parallel to a point a on the GND side line 3b. A point b is a connection point between the GND 7 and the amplifier 11, the capacitors 16 and 17 of the noise removing circuit 13, and the cathode of the Zener diode 20 of the static electricity countermeasure circuit 19.
[0022]
A circuit including the Zener diodes 20 and 21 is called a clamp circuit. Each of the Zener diodes 20 and 21 has a property that current does not flow until a Zener voltage which is a constant voltage when a voltage is applied in the opposite direction. Therefore, in the clamp circuit using the Zener diodes 15 and 16, no current flows from the GND side line 3b to the GND7 and from the GND7 to the GND side line 3b until the voltage reaches the Zener voltage, and the Zener voltage reaches the Zener voltage. Current flows.
[0023]
First, an operation of amplifying an audio signal with the vehicle-mounted power-up 1 as a normal operation will be described. The audio signal output from the H / U 2 is transmitted to the isolation circuit 10 via the audio signal line 3.
[0024]
The isolation circuit 10 removes, from the received audio signal, common-mode noise mixed into the connection cord or the like from the outside, such as engine alternator noise, when the devices such as the in-vehicle power amplifier 1 and the H / U 2 are connected. Then, the isolation circuit 10 outputs the noise-removed audio signal to the amplifier unit 11, and the amplifier unit 11 amplifies the noise-removed audio signal and outputs it from the output line 12, and amplifies it to an in-vehicle speaker or the like (not shown). Audio signal is output.
[0025]
Here, when static electricity is applied to the H / U 2 or the audio signal line 3, the static electricity is sequentially conducted through the GND side line 3 b, the input unit 18, and the static electricity countermeasure circuit 19 to be discharged to the GND 7. The static electricity is generated, for example, during air drying due to friction between a passenger's clothes and a seat in the vehicle A, and is applied to the H / U 2 and the audio signal line 3.
[0026]
The static electricity is first absorbed by the capacitor 22 on the static electricity countermeasure circuit 19, and since the static electricity is not direct current, the capacitor 22 is conducted. When the voltage of the static electricity exceeds a certain value by the Zener diodes 20 and 21, a current flows. Therefore, when the electrostatic voltage passing through the capacitor 22 exceeds a certain value, it is discharged to the GND 7.
[0027]
Here, in the use of the in-vehicle power amplifier 1 which is an electronic device, the GND 7 may be disconnected from the in-vehicle power amplifier 1. In this case, an open connection occurs between the point b and the GND 7. That is, if it is going to operate in this state, the power of the battery 4 is turned on in a state where the GND lift is generated in the in-vehicle power amplifier 1. For example, when the power is turned on without taking the ground of the in-vehicle power amplifier 1 when the wiring is uncertain, or when the power is turned on without the GND of the in-vehicle power amplifier 1 being properly connected. is there.
[0028]
In this case, the charges charged in the capacitors 16 and 17 of the noise removal circuit 13 try to flow into the GND, and a DC charge current is generated. Even if the charge current flows into the GND 7, since the connection of the GND 7 is released, the abnormal current line includes the point b, the noise countermeasure circuit 19, the point a, the input unit 18, the GND side line 3b, H / It tries to flow to GND 8 through U2 in order.
[0029]
Here, if the static electricity countermeasure circuit 19 is a clamp circuit, that is, if it is composed only of the Zener diodes 20 and 21, the voltage of the charge current is a certain value or more, the point b, the Zener diodes 20, 21, the point a, It is discharged to the GND 8 through the GND side line 3b and H / U2. Therefore, a DC excessive current of a charge current having a voltage equal to or higher than a certain value flows through the GND side line 3b and the input unit 13, and heat generation or burning (disconnection) of the printed circuit board pattern on the input unit 18, GND side line 3b. Heat generation occurs.
[0030]
However, the static electricity countermeasure circuit 19 of the present embodiment further includes a capacitor 22 and cuts off direct current. Therefore, the charge current does not pass through the abnormal power supply line, and not only the GND 7 but also the GND 8 is disconnected from the charge current, and there is no GND to which the charge current flows.
[0031]
Therefore, even in the case of a connection abnormality in which the GND 7 is disconnected, the static electricity countermeasure circuit 19 prevents the excessive heat current of the input unit 18 from flowing through the input unit 18 and the GND side line 3b by the capacitor 22 to prevent an excessive DC current from flowing. Burnout and heat generation of the GND side line 3b can be prevented.
[0032]
The static electricity removal part of Claim 1 is the Zener diodes 20 and 21 shown in FIG. 2, for example. Moreover, the direct-current removal part of Claim 1 is the capacitor | condenser 22 shown in FIG. 2, for example. Further, the abnormal current line according to claim 1 is, for example, from the capacitors 16 and 17 shown in FIG. 2 to the GND 8 through the point b, the Zener diodes 20 and 21, the point a, the GND side line 3b, and the H / U2 in this order. It is a line that leads to.
[0033]
In addition, although this Embodiment demonstrated the antistatic circuit 19 when the vehicle-mounted power amplifier 1 was used as an electronic device, it can be applied also to another electronic device. It can also be realized by adding an additional capacitor in series to the abnormal power supply line at the time of GND connection abnormality in an anti-static circuit having the Zener diodes 15 and 16 in another configuration.
[0034]
For example, in the conventional static electricity countermeasure circuit D having the configuration shown in FIG. 4 as described in [Prior Art], the points e, f, and g are points in series with the Zener diode 26 between the points c and d. If a capacitor is added to any of the above, it is possible to prevent an excessive DC charge current from flowing through the Zener diode 26, damage of the component due to heat generation and burning of the component between the terminal 23 and the point d, and the GND side. Heat generation of the line Fb can be prevented.
[0035]
Therefore, an effect similar to that of the present embodiment can be realized by connecting a capacitor in series with the abnormal current line to a static electricity countermeasure circuit that conducts static electricity to GND using a Zener diode or a diode. Further, not only the capacitor but also the gap between terminals on the printed circuit board can be formed in series with the abnormal current line, and the same effect as the present embodiment can be realized.
As described above, the embodiments of the present invention have been described. However, the present invention is not necessarily limited only to the above-described means and methods, and within the scope of achieving the object of the present invention and having the effects of the present invention. It is possible to make changes as appropriate.
[0037]
【The invention's effect】
According to the present invention, it is possible to prevent an excessive direct current from flowing through a component on an abnormal current line in which heat generation or burning occurs due to current conduction when the grounding portion connection is abnormal.
[Brief description of the drawings]
FIG. 1 is a schematic perspective view of a vehicle in which an in-vehicle audio system including an anti-static circuit according to an embodiment of the present invention is installed.
FIG. 2 is a configuration diagram of the in-vehicle audio system in FIG. 1;
FIG. 3 is a schematic block diagram of a circuit including a conventional static electricity countermeasure circuit.
4 is a diagram showing a circuit configuration inside the conventional static electricity countermeasure circuit in FIG. 3. FIG.
[Explanation of symbols]
A ... Vehicle α ... In-vehicle audio system 1 ... In-vehicle power amplifier 2 ... H / U (head unit)
3 ... audio signal lines 3a, 23a ... transmission side lines 3b, 23b ... GND side line 4 ... battery 5 ... B line (battery line)
6 ... Bu (backup)
7, 8, 9, G, H, I ... GND
DESCRIPTION OF SYMBOLS 10 ... Isolation circuit 11 ... Amplifier part 12 ... Output line 13 ... Noise removal circuit 14 ... DC / DC converter 15, 24 ... Coil 16, 17, 22, 27 ... Capacitor 18 ... Input part 19, D ... Electrostatic countermeasure circuit 20 , 21, 26 ... Zener diodes 23, 25 ... Terminal B ... Main circuit C ... Circuit E ... Power supply F ... Signal line Fa ... Transmission side line Fb ... GND side line J ... Electronic device unit

Claims (2)

An anti-static circuit that is connected to an in- vehicle electronic device and removes static electricity flowing from the outside to the electronic device through the ground line of the signal line ,
A DC blocking unit that is connected in series to an abnormal current line through which a DC current is conducted when the grounding connection is abnormal, and that blocks a DC current when the connection is abnormal;
Comprising two Zener diodes or diodes connected in series to the static eliminator and having anodes connected in series in opposite directions, and comprising a static eliminator that conducts the static electricity to the grounding unit,
The series-connected DC blocking unit and static electricity removing unit are connected to the ground side line in parallel .   The electrostatic discharge protection circuit according to claim 1, wherein the DC blocking unit is a capacitor or a gap between terminals formed on a printed circuit board.

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