JPH0481549A - Earth processing circuit for automobile electronic system - Google Patents

Abstract

PURPOSE:To make such an accurate and stable operation performable irrespective of the magnitude of load by installing a semiconductor switch in space between earth of a control circuit and another earth of a drive circuit, and having the semiconductor switch conducted by a means detecting anything unusual when something goes wrong with the earth of the control circuit. CONSTITUTION:A semiconductor switch Tr2 is installed in space between earth of a control circuit 6a and another earth of a drive circuit 6b, and the semiconductor switch Tr2 is conducted by a means 6c detecting anything unusual when something goes wrong with the earth of the control circuit 6a. In brief, when an earth trouble in the control circuit 6a is detected, the semiconductor switch Tr2 is conducted, connecting the earth of the control circuit 6a and the drive circuit 6b, and it functions so as to cover an open circuit 7e.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a grounding circuit for an automotive electronic device.

[Prior Art] Fig. 4 shows a grounding circuit for a conventional automobile electronic device, in which 1 is an engine, 2 is a detector, 3 is a battery, 4 is a key switch, 5 is a load, and 6 is a circuit from 1 to transistor T. r 1
Electronic devices 7a to 7 consisting of drive circuits Nl6b represented by
f is a wiring.

In the device configured as described above, when the key switch 4 is turned on, the electronic device 6 starts control based on the signal from the detector 2 that detects the engine condition.

If the control result is a state where the switch SW is turned on, the base of the transistor Trl is grounded through the switch SW, and the transistor Trl is turned off.If the control result is a state where the switch SW is turned off, the base of the transistor Trl is grounded through the switch SW. A current is supplied to the base of the transistor Trl, and the transistor Trl is turned on to drive the load 5.

Further, in order to prevent control errors from occurring due to a large current flowing through the drive circuit 6b when driving the load, the control circuit 6a is connected to the drive circuit 6b.
It is separated from the earth point of b.

Furthermore, the diode D2 ensures a current path for the control circuit 6a when the wiring 7e is disconnected.

[Problems to be Solved by the Invention] However, in such a conventional device, when the wiring 7e is disconnected, the current in the control circuit 6a flows from the diode D2 through the wiring 7f, and the emitter potential of the transistor Trl is lowered. ■l, the forward voltage effect of diode D2 is V
O2, the ground potential of the control circuit 6a is V l-4
-V D2, resulting in an increase in control error. Furthermore, the diode D1, which is connected to prevent the transistor Trl from turning on when the switch SW is turned on, is connected to the diode D1 in order to prevent the transistor Trl from being turned on when the switch SW is turned on. Because it will be.

The cost also increases, and the mounting efficiency of the printed circuit board also deteriorates.

[Means for Solving the Problems] In order to solve such problems, the present invention includes a semiconductor switch between the ground of the control circuit and the ground of the drive circuit, and detects an abnormality when the control circuit is grounded abnormally. The semiconductor switch is made conductive by means of detection.

[Function] When a ground abnormality in the control circuit is detected, the semiconductor switch becomes conductive, connects the control circuit to the ground of the drive circuit, and acts to cover the #T line path.

[Example] FIG. 1 is a circuit diagram showing an embodiment of the present invention.

In the figure, the diode D1, which was necessary in the conventional circuit shown in FIG. . FIG. 2 shows an example of the internal circuit of the earth abnormality detection circuit 6C, in which R2-R7 are resistors, Tr3 and Tr4 are transistors, and D3 is a diode.

When the wiring is normal, the current flowing through the resistor R2 in the ground abnormality detection circuit 6C flows to the ground of the control circuit 6a, and no current is supplied to the base of the transistor Tr3, so the transistor Tr3 is turned off. As a result, the transistor Tr4 is also off, and no current is supplied to the base of the transistor Tr2. Therefore, transistor Tr2
is also off, and the ground of the control circuit 6a and the ground of the drive circuit 6b are completely separated. 6. Next, when the wiring 7e is disconnected, a resistor R2, Current is now supplied through the diode D3, and the transistor T r 3 is turned on.

When transistor T r 3 is turned on, transistor T
Since r4 is also turned on, a current is supplied to the base of the transistor Tr2 via the transistor Tr4 and the resistor R7, the transistor Tr2 is turned on, and the current path of the control circuit 6a is secured. When the transistor T r 2 is turned on, the current flowing through the resistor R2 starts to flow to the transistor T r 2, and the current is no longer supplied to the base of the transistor T r 3 through the resistor R2, but through the transistor Tr4 and the resistor R5. Since the current is supplied,
Until the key switch 4 is turned off, the transistor T r
3 continues to be on.

Therefore, the transistor Tr4 and the transistor Tr2 also continue to be turned on. That is, even if the wiring 7e is disconnected, the flow path of the control circuit 6a is secured, and the emitter potential of the transistor Trl is
VIE (Trll, transistor Tr2
If the collector-emitter saturation voltage is VCEfTr2), the ground potential of the control circuit 6a is V l +Vct
trrz, but usually ■BE+Trl l >
V CE (Since it is Tr21, when the switch SW is on, the base potential of the on-condition co-transistor T r ] of the transistor Trl ≧C] −+ V BEf
Trl + is not satisfied, and the device operates normally even without the diode D1, which was necessary in the conventional device.

Figure 3 shows another embodiment of the abnormality detection circuit, in which a diode D4 and a capacitor C1 are added.
4 prevents current from flowing into the control circuit 4a to protect the base of the transistor Tr3. In addition, the capacitor C1 is provided to delay the operation of the transistor Tr3 when the Toki power supply is turned on when the key switch is turned on.
This prevents a malfunction in which the transistor T r 3 is turned on even though no earth abnormality has occurred when the key switch is turned on. Since the operation is the same as that shown in FIG. 2, the explanation will be omitted.

[Effects of the Invention] As explained above, in the present invention, since the control circuit and the ground of the drive circuit are transistor-coupled, the control circuit that performs processing control based on a detector and the load control circuit that performs processing control based on a detector are installed in the same device. Even if the drive circuit that drives the detector coexists, the mounting of the detector allows for accurate and stable operation regardless of the state, output signal form, and load size, and also prevents disconnections that are unavoidable in automotive wiring. Even if this occurs, the load will not be driven regardless of the control result, and the control error will be much smaller than in conventional devices. Further, even if the number of loads increases, the number of parts does not increase as in conventional devices, and this has the effect of being extremely economical and improving printed circuit board mounting efficiency.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIGS. 2 and 3 are circuit diagrams showing details of the earth trip detection circuit shown in FIG. 1, and FIG. 4 is a circuit diagram showing an example of a conventional device. It is a diagram. 1...-Engine, 2--Detector, 5...-Load,
6- Electronic equipment, 6a... control circuit, 6b-m-...
Drive circuit, 6c ass Tatsumi detection circuit.

Claims (1)

[Scope of Claims] A control circuit that processes a signal from a predetermined detector and outputs a drive signal based on the processing result, and a drive circuit that drives various vehicle loads when the drive signal is input, and each In a ground processing circuit for an automotive electronic device in which a ground is separated, a semiconductor switch is provided between the ground of the control circuit and the ground of the drive circuit, and a means for detecting an abnormality when the ground of the control circuit is abnormal. A grounding circuit for an automotive electronic device characterized by making a switch conductive.