Electronic circuit device for protecting electronic circuits from unwanted removal of ground terminal

Abstract: An electronic circuit device with an external ground terminal (23) used for vehicle AC regulators comprises a detection circuit (26) for detecting that the external ground terminal has been removed from a ground, and a protection circuit for protecting an electronic circuit (22) according to the detected signal of the detection circuit (26). The protection circuit includes a low voltage protection circuit (24) for stopping an operation of an output transistor (18) of the electronic circuit (22), a latch circuit (25) operated by output signals from both the detection circuit (26) and the low voltage protection circuit (24), and an input cut-off circuit (16) for cutting off input signals applied to the electronic device.

Description: The invention relates to an electronic circuit device having the features indicated in the preamble clause of claim 1, as disclosed in EP-A-0 239 862. This prior art document discloses in the single figure thereof a driver circuit for a power MOSFET T1. An electronic switch 1 comprises semiconductor components, and the driver circuit has input terminals 2 and 3. A supply voltage U B provided at a terminal 7 is supplied to a terminal 4 of the electronic switch 1, the other power supply terminal 5 thereof being connected to a ground potential M2. An output terminal 6 of the electronic switch 1 provides a voltage for switching on the power MOSFET T1. The source terminal of T1 is connected to an upper end of a load R L , the other end of which has a terminal 8 connected to ground potential M1. In a plurality of cases, for example in the internal wiring of automobiles, the ground potential connection M2 of the electronic switch 1 is not identical with the ground potential M1 to which the load R L is connected. In case an interruption or disconnection occurs between the ground potential M2 and the ground potential terminal 5 of the electronic switch 1, the output potential of the electronic switch 1 changes, resulting in that also the gate potential of the power MOSFET T1 changes such that T1 is partially switched on. The prior art circuit solves this problem (preventing a partial switch on of the power MOSFET, if a disconnection occurs between the electronic switch and ground potential), by connecting between the source and gate terminals of the power MOSFET T1 the source-drain section of a depletion MOSFET T2, and by connecting the gate terminal of the depletion MOSFET T2 with the terminal 5 of the electronic switch 1 intended to be connected to ground potential. The prior art circuit operates as follows: It is at first assumed that the electronic switch 1 is properly connected through its terminal 5 with ground potential M2, and that the power MOSFET T1 is non-conductive. If a positive voltage appears at the output terminal 6, this positive voltage is present at the drain terminal of T2 and at the gate terminal of T1. Since the source terminal of both transistors and the gate terminal of T2 is at ground potential, T2 is conductive. The depletion transistor T2 is dimensioned such that it draws at U GS = 0 Volt, less current than the electronic switch 1 provides at its output terminal 6. Therefore, current flows into the gate/source capacity of T1, such that T1 is switched on. During power up the source potentials of both transistors increase towards the battery voltage U B . This results in T2 receiving a negative gate/source bias voltage such that T2 is rendered non-conductive if the potential at the gate is lower, in an amount corresponding to the threshold voltage, than the source potential. Now the potential at terminal 6 also increases and reaches a value which is higher than the battery voltage U B . This may be achieved by a particular design of the electronic switch which includes a charge pump, as described for example, in "Siemens Components", No. 4, 1984, pages 169 - 170. If during the switched-off state of T1 the connection between terminal 5 and ground potential M2 is interrupted, the reference potential at terminal 5 of the electronic switch 1 increases, because of off-state currents of the electronic components in electronic switch 1, and increases towards the battery voltage U B . This results in that the potential at the gate terminal of T2 increases with respect to the source potential thereof, such that transistor T2 is rendered fully conductive. The current occurring at the output terminal 6 therefore flows only through transistor T2 and the load R L to the ground M1, such that the power MOSFET T1 cannot be switched on. The technical background of the present invention will be explained briefly hereinafter for facilitating to understand the basic concept thereof. As an electronic circuit generally used for vehicle AC regulators or the like, a low-side switching system circuit arrangement has been widely employed. In this circuit, one terminal of an output switching element is connected to an external power supply through an external load and the other terminal of the output switching element is grounded. Fig. 4 shows a low-side switching system electronic circuit whose output terminal is connected to an external power supply through an external load. More specifically, an input terminal 1 for receiving a signal supplied from an external circuit A is connected to an output driver circuit 2, and the output driver circuit 2 is connected to an output switching element 3. The output switching element 3 is connected to an output terminal 4 of the electronic circuit. The output driver circuit 2 is connected to an external power supply 6a through a power supply terminal 5. The output driver circuit 2 and the output switching element 3 are connected to a ground terminal 7 and grounded. One terminal of an external load 8a is connected to the output terminal 4, and the other terminal of the load 8a is connected to the external power supply 6a. In such an electronic circuit, the output switching element 3 is driven by a driving signal from the output driver circuit 2, and its output signal is fed from the output terminal 4. Fig. 5 shows a high-side switching system electronic circuit, wherein an output switching element is connected to an external power supply, and an external load is grounded. More specifically, as in Fig. 4, an input terminal 9 for receiving a signal from an external circuit A is connected to an output driver circuit 10, and the output driver circuit 10 is connected to an output switching element 11. The output switching element 11 is connected to an output terminal 12 of the electronic circuit. The output driver circuit 10 and the output switching element 11 are connected to an external power supply 6b through a power supply terminal 13. One terminal of the output driver circuit 10 is connected to a ground terminal 14 and grounded. One terminal of an external load 8b is connected to the output terminal 12, and the other terminal of the external load 8b is grounded. In such a high-side switching system electronic circuit, since the external load is grounded as compared with the conventional low-side switching system electronic circuit, it can be easily replaced so that the electronic circuit is easily handled. According to this advantage, a low-side switching system electronic circuit used for vehicle AC regulators is being replaced with a high-side switching system electronic circuit. However, in the high-side switching system electronic circuit shown in Fig. 5, when a ground terminal 14 is removed from the ground, the safety associated with controlling the electronic circuit is not considered. More specifically, when the ground terminal 14 is removed from the ground, a current from the external power supply 6b is supplied to the ground terminal 14 through the circuits constituting the electronic circuit, and the electric potential of the ground terminal is increased. The applied voltage from the external power supply 6b, which is measured from the ground terminal 14 whose electric potential is considered as a reference electric potential, is apparently decreased by an increase in the electric potential of the ground terminal 14. As a result, while the voltage of the external power supply 6b is applied to the output switching element 11, the input signal is supplied to it under such a condition that the reference voltage is changing, thereby feeding the output signal to the external load 8b through the output terminal 12. Therefore, the output of the electronic circuit will not be cut off while keeping the output control under the unstable condition. Accordingly, the output control will become impossible. It is, therefore, an object of the present invention to provide an improved electronic circuit device providing additional protection. The present invention provides an electronic circuit device having the features indicated in claim 1. Preferred embodiments of the invention are indicated in the dependent claims. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram showing a high-side switching system electronic circuit device having a protection means according to an embodiment of the present invention; Fig. 2 is a circuit diagram showing the electronic circuit device of Fig. 1; Figs. 3A to 3D are waveform charts showing output waveforms at an output terminal of the electronic circuit device shown in Fig. 2; Fig. 4 is a block diagram showing a conventional low-side switching system electronic circuit device; and Fig. 5 is a block diagram showing a conventional high-side switching system electronic circuit device. An electronic circuit device having a protection means according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 shows a block diagram of a high-side switching system (load ground system) electronic circuit device according to an embodiment of the present invention, which includes a protection means provided with a protection circuit, a detection circuit, and the like. In this case, an electronic circuit device having an input terminal 15, an output terminal 19, a power supply terminal 21, and a ground terminal 23 externally grounded, is shown by an one-dot, one-dash line, and further includes a high-side switching system electronic circuit 22 which has an output driver circuit 17 and an output switching element 18 and which is protected by a protection means. More specifically, an output terminal A of an external circuit is connected to an input cut-off circuit 16 through the input terminal 15. The input cut-off circuit 16 is connected to the output driver circuit 17, and the output driver circuit 17 is connected to the output switching element 18. The output driver circuit 17 and the output switching element 18 are connected to a power supply terminal 21 connected to an external power supply 20. The output terminal of the output switching element 18 is connected to an output terminal 19 of the electronic circuit device, to which an external load 27 is connected, and the output terminal of the output switching element 18 is connected to a detection circuit 26 for detecting that a ground terminal 23 of the electronic circuit device has been removed from the ground. A low voltage protection circuit 24 receiving an output signal of the detection circuit 26 is connected to the output driver circuit 17 and the output switching element 18, and a memory circuit 25 receiving both output signals of the low voltage protection circuit 24 and the detection circuit 26, which serves as a latch circuit, is connected to the input cut-off circuit 16. In the electronic circuit device having such an arrangement, an input signal is entered into the output driver circuit 17 through the input cut-off circuit 16 from the output terminal A of the external circuit. The output switching element 18 is driven by the driving signal of the output driver circuit 17, and the output signal of the output switching element is fed to the external load 27. When the ground terminal 23 is removed from ground, however, current from the external power supply 20 is supplied to the ground terminal 23 through the circuits constituting the electronic circuit device, thereby raising the electric potential of the ground terminal 23. Depending upon such an increase in the electric potential, a voltage applied from the external power supply, which is measured from the ground terminal 23 whose electric potential is considered as a reference electric potential, is apparently decreased. When this voltage drop occurs, the low voltage protection circuit 24 is operated to decrease the drive signal, fed from the output driver circuit 17, to the same electric potential as in the ground terminal 23, so that the output switching element 18 is not driven. In addition, as described above, when the ground terminal 23 is removed from ground, the detection circuit 26 is operated by a potential difference which is generated by a current flowing from the ground terminal 23 to the output terminal 19 through a circuit element such as a diode or a resistor included in the detection circuit 26, thereby applying a signal representing the removed condition of the ground terminal to the memory circuit 25. The memory circuit 25 sends an input cut-off signal to the input cut-off circuit 16 according to both the signal representing the removed condition of the ground terminal and a protective operation signal fed from the low voltage protection circuit 24. The input cut-off circuit 16 breaks the input signal from the external circuit according to the signal indicating the input signal cut-off condition not to drive the output driver circuit 17. As described above, even if the ground terminal is removed from ground, the output driver circuit 17 and the output switching element 18 will not be driven to protect the electronic circuit 22. In this embodiment, it is proposed to use a charge pump circuit as the output driver circuit 17. However, other circuits may be used if they can drive the switching element 18. An electronic circuit device according to the present invention, provided by practical circuit elements instead of the above described block diagram, will be described with reference to Fig. 2. The output switching element 18 is provided by an output transistor Tr1 of the MOSFET type, wherein the drain is connected to the power supply terminal 21, the source is connected to both the output terminal 19 and a diode 28 of the detection circuit 26, and the gate is connected to the output driver circuit 17, respectively. A coil 29 is connected to the output terminal 19 as the external load 27. The low voltage protection circuit 24 has a transistor Tr2, whose collector, emitter and base are connected to the power supply terminal 21, to the output driver circuit through a connection point B, and to the cathode of a Zener diode 30 whose anode is grounded, respectively. A resistor R1 is connected between the collector and the base of the transistor Tr2 to provide an internal power supply. A connection point C is connected through a resistor R2 to a drain of a transistor Tr3 whose source is grounded. One terminal of a resistor R3 is connected to the connection point C, while the other terminal of the resistor R3, one terminal of a resistor R4 and one terminal of a resistor R5 are connected to a connection point D and the other terminal of the resistor R5 is connected to a drain of a transistor Tr4. The source of the transistor Tr4 is grounded, and its gate and the gate of the transistor Tr3 are connected to a connection point E in common. These transistors Tr3 and Tr4 provide a mirror circuit. A resistor R6 is connected between the power supply terminal 21 and a drain of a transistor Tr5, whose source is grounded. The gate of the transistor Tr5 is connected to the connection point D. The drain of the transistor Tr5 is connected to both the connection point E and a gate of a transistor Tr6. The drain of the transistor Tr6 is connected to the output terminal of the output driver circuit 17, and the source of the transistor Tr6 is grounded. The detection circuit 26 includes an npn transistor Tr7 whose base is grounded. The collector of the transistor Tr7 is connected to the connection point C through a resistor R7, and its emitter is connected to the cathode of the diode 28 connected between the source of the transistor Tr1 and the ground. For providing the input cut-off circuit 16 to cut off the input signal from the input terminal 15, an inverter circuit element 31 and a NOR circuit 32 are connected in series between the input terminal 15 and the input terminal of the output driver circuit 17. The other input terminal of the NOR circuit 32 is connected to the output terminal of the memory circuit 25. The memory circuit 25 serves as a latch circuit provided by three NOR circuits 33, 34 and 35. The input terminal of the latch circuit is connected to both the drain of the transistor Tr3 and the collector of the transistor Tr7, and the output terminal of the latch circuit is connected to one input terminal of the NOR circuit 32. The electronic circuit device described above will operate as follows. That is, when the ground terminal 23 is removed from ground, the electric potential of the ground terminal is increased. The electric potential of the ground terminal becomes a sum of the voltage of the output terminal 19 and the voltage generated by the diode 28 in the forward direction, and is increased to of the order of the applied voltage level of the external power supply. When the electric potential is increased, the transistor Tr7 is turned on according to a potential difference caused by the diode 28, thereby decreasing the electric potential of the collector of the transistor Tr7. The applied voltage from the external power supply 20 is apparently decreased in accordance with the increase in the electric potential, so that the low voltage protection circuit 24 is operated. Depending upon the apparent decrease in the applied voltage, the output voltage of the internal power supply is decreased. Then, the transistor Tr5 operated by the output voltage from the internal power supply is turned off, and the transistor Tr6 is turned on. Since the transistor Tr6 is turned on, the gate voltage of the output switching element 18 is decreased to turn off the transistor Tr1. At this time, the signal entered from the collector of the transistor Tr7 to the NOR circuit 33 of the memory circuit 25 is inverted from a high (H) signal to a low (L) signal, and the signal entered from the drain of the transistor Tr3 of the low voltage protection circuit 24 is also inverted from an H signal to an L signal. Subsequently, the output signal applied from the memory circuit 25 to the NOR circuit 32 is inverted from an L signal to an H signal. Therefore, since the one input terminal of the NOR circuit 32 becomes the H signal, the NOR circuit 32 does not feed the output signal even if the input signal from the external input terminal is entered into the other input terminal of the NOR circuit 32. As a result, the output driver circuit 17 is not driven. Though the signal recognizing the removal of the ground terminal is fed from the memory circuit 25 to the NOR circuit 32, in the embodiment the output switching element 18 may be directly turned off. Moreover, a MOSFET is used as the switching element 18, but other elements capable of ON/OFF operation in the high-side switching system may be used. Similarly, though the detection circuit 26 is provided by the diode 28, the transistor Tr7 and the resistor R7, it may be provided by a resistor or a diode for detecting a current therethrough when the ground terminal 23 is removed from ground, a voltage divider circuit, and a comparator. It will be apparent that all of the ground terminals of the circuit elements are connected to the ground terminal 23 within the electronic circuit device, and that the electric potential of the ground terminal 23 becomes the ground potential when it is grounded. Figs. 3A to 3D show output waveforms fed from the output terminal 19 when the ground terminal of the electronic circuit device shown in Fig. 2 has been removed from the ground. More specifically, Figs. 3A to 3C show output waveforms of the electronic circuit device only having the low voltage protection circuit 24 shown in Fig. 2, (the memory circuit 25 and the detection circuit 26 are removed). In this case a load (reactance) of the external load 27 connected to the output terminal 19 is increased in order of (A) < (B) < (C) to measure the waveforms. According to these waveform charts, the drive voltage applied to the gate of the transistor Tr1 of the output switching element 18 is decreased to the reference voltage (the terminal voltage of the ground terminal 23) when the transistor Tr6 of the low voltage protection circuit 24 is turned on. Since input signals from the external terminal 15 are intermittently supplied to the output driver circuit 17, however, a pulsed drive voltage is applied to the gate of the transistor Tr1 to intermittently operate it. Therefore, an unstable output appears at the output terminal 19 as shown in the output waveforms described above. It can be understood that the unstable output is applied to the external load 27. Fig. 3D shows an output waveform fed from the output terminal 19 of the electronic circuit device according to the present invention. According to the output waveform shown in Fig. 3D, since the detection circuit 26 and the memory circuit 25 are operated in addition to the low voltage protection circuit 24, the input signal from the external terminal 15 is not entered into the output driver circuit 17, and the output switching element 18 does not operate. Therefore, it will be apparent that no output is fed from the output terminal 19. As has been described, according to the high-side switching system electronic circuit device having the protection means, when the ground terminal of the electronic circuit device is removed from the external ground, the output will be cut off, thereby attaining the protection and safety of the electronic circuit. It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made in the invention without departing from the scope thereof as defined in the appended Claims.

Claims: An electronic circuit device comprising a power supply terminal (21) to be connected to an external power supply (20), a ground terminal (23) to be connected to ground, an input terminal (15) for receiving input signals from an external circuit (A), an output terminal (19) to be connected to a grounded external load (27), an electronic circuit (22) for receiving said input signals to feed output signals to said output terminal (19); and a detection circuit (26) which detects that said ground terminal (23) has been removed from ground, as a change in an electric potential thereof, and a protection circuit (16, 24) which protects said electronic circuit (22) according to the detected signal of said detection circuit (26), characterized in that said protection circuit (16, 24) includes a low voltage protection circuit (24) for stopping operation of said electronic circuit (22), and an input cut-off circuit (16) for cutting off said input signals when said detection circuit (26) detects that said ground terminal (23) is removed from ground, and all ground points of said respective circuits (22, 24, 26) are electrically connected to said ground terminal (23). A device according to claim 1, characterized in that said input cut-off circuit (16) is driven through a memory circuit (25) according to both output signals from said detection circuit (26) and said low voltage protection circuit (24). A device according to claim 2, characterized in that said memory circuit (25) is comprised of a latch circuit using logic circuits (33 to 35). A device according to claim 1, characterized in that said detection circuit (26) includes a circuit element through which a current flows when said ground terminal (23) is removed from ground thereby raising the electric potential of the ground terminal (23). A device according to claim 4, characterized in that said circuit element is comprised of a diode (28). A device according to claim 4, characterized in that said circuit element is comprised of a resistor. A device according to claim 1, characterized in that said low voltage protection circuit (24) includes an internal power supply circuit. A device according to claim 2, characterized in that said input cut-off circuit (16) includes a logic circuit. A device according to claim 1, characterized in that said electronic circuit (22) includes an output driver circuit (17) and an output switching circuit (18) connected in series with each other. A high side switching system comprising an electronic circuit device according to claim 1. A vehicle AC regulator, comprising an electronic circuit device according to claim 1.

Inventors: SANO YOSHIYUKI C O INTELLECTUA, SANO, YOSHIYUKI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, TOSHIBA MICRO ELECTRONICS, KABUSHIKI KAISHA TOSHIBA, TOSHIBA MICRO-ELECTRONICS CORPORATION
Application year: 1990
Main classification: H02H5
IPC codes: H03K17, H01L21, H02H5, H01L27, H02H3, H02M1