GB2253101A

GB2253101A - A static electronic flasher device, particularly for controlling the direction indicators of a motor vehicle

Info

Publication number: GB2253101A
Application number: GB9203147A
Authority: GB
Inventors: Franco Balangero
Original assignee: ITALAMEC Srl
Current assignee: ITALAMEC Srl
Priority date: 1991-02-21
Filing date: 1992-02-14
Publication date: 1992-08-26
Also published as: ES2081232B1; ITTO910122A0; DE4204710A1; IT1249834B; ES2081232R; FR2673307A1; ES2081232A2; GB9203147D0; ITTO910122A1

Abstract

A flasher device includes static electronic power switch (30), preferably a FET, driven by an oscillator (10) and interposed between a first terminal (2) connected to a voltage supply (11) and a second terminal (12) connected to the load (L). A control circuit (20) is interposed between the oscillator (10) and the switch (30) in order to cut off the switch when the sensed current flowing towards the load (L) exceeds a predetermined threshold or when the voltage sensed across the switch (30) exceeds a predetermined value. <IMAGE>

Description

1 A static electronic flasher device, particularly for controlling the

direction indicators of a motor vehicle The present invention relates to a flasher device, particularly for controlling the direction indicators of a motor vehicle.

More specifically, the invention is concerned with an electronic flasher device including:

an oscillator for outputting a square-wave driving signal, and at least one static electronic power switch, preferably a FET, interposed between a first terminal which is intended to be connected to a voltage supply and a second terminal which is intended to be connected to the load, the switch having a control input which is controlled by the output of the oscillator.

At the moment, direction/hazard indicators are controlled by electronic or electromechanical flasher devices which, in any case, include electromechanical power switches, typically relays, for driving the lamps.

These devices usually operate satisfactorily but have some disadvantages connected. essentially with the presence of electromechanical switches with movable switching contacts. The useful lives of these flashers are thus generally limited by the wear of the contacts and their performance is unsatisfactory in the presence of vibrations or at high temperatures. Moreover, their ability to withstand accidental 2 overloads and to operate in hostile environments is generally poor.

Recently, the production of electronic f lasher devices which are completely static and thus include (at least) one static electronic power switch has been considered. These devices also have problems. In the first place, the voltage drop in the electronic output switch involves considerable power dissipation which is problematical in view of the fact that flashers are usually required to have very small dimensions. Moreover, the ability of electronic flashers to withstand the ef fects of excess currents is poor and the electronic power switch may be damaged as a result even of an overload lasting only for a few thousandths of a second. In the electrical systems of motor vehicles, in fact, protection against excess currents is generally entrusted to fuses, which have fairly long response times of the order of a few seconds. An overload or short-circuit condition can quite easily occur, however, in such systems.

The static electronic flashers which have been produced up to now are also quite sensitive to excess voltages due to the switching of inductive loads (for example, the radiator-fan motor, the windscreen-wiper motor, etc.) which may reach peak values, for example, of 150V or more, or to the disconnection of the battery of the motor vehicle's electrical system, as a, result of which a voltage peak of considerable durapion and energy may be generated in the system.

The object of the present invention is to provide a static electronic flasher device which is not prone to the problems indicated above.

1 3 According to the invention, this object is achieved by an electronic flasher device of the type specified above, the main characteristic of which lies in the fact that it includes:

first and second sensor means for detecting, respectively, the intensity of the current flowing through the electronic switch, and hence of the current flowing towards the load, in operation, and the voltage drop in the electronic switch, and a control circuit which is interposed between the oscillator and the electronic switch and is connected to the first and second sensor means and which is adapted to cut off the electronic switch when the current flowing towards the load exceeds a predetermined threshold or when the voltage in the switch exceeds a predetermined value, in operation.

In one embodiment, the control circuit includes a transistor with its base-emitter junction connected substantially in parallel with the electronic switch and its emitte r-col lector path connected between the output of the oscillator and earth so that, when the electronic switch conducts current, the transistor can become conductive and cut off the electronic switch when the voltage in the electronic switch exceeds the prdetermined value for a predetermined period of time and/or when the current flowing towards the load exceeds the threshold for a predetermined period of time and/or when the temperature of the electronic switch exceeds a predetermined value.

The present invention will now be more particularly described, purely by way of example, with reference to 4 the accompanying drawings, in which:

Figure 1 is a detailed electrical diagram of a static electronic flasher device according to the invention, and Figure 2 is a diagram of a variant of the f lasher according to the invention, shown partially in block form.

With reference to Figure 1, a static electronic flasher according to the invention includes an oscillator, generally indicated 10, for outputting a square-wave driving signal A.

The output of the oscillator 10 is connected to the input of a control circuit, generally indicated 20. The output of this circuit is connected to the gate of a solid-state electronic switch which, in the embodiment of Figure 1, is constituted by a Sense-FET 30.

The oscillator 10 has a supply terminal 11 which is intended to be connected to a direct-current voltage supply, for example, the positive pole of the battery of the motor vehicle. The control circuit 20 and the drain of the electronic switch 30 are also connected to this terminal. The source of the switch is connected to an output terminal 12. In use, the load of the flasher which, typically, is constituted by one or more direction /hazard indicator lamps of the motor vehicle is connected between that terminal and earth. One such lamp is indicated L in Figures 1 and 2.

In known manner, the oscillator 10 includes an integrated device IC (for example, the UAA1041 device made and sold by Motorola) connected to a resistor R1 and a capacitor Cl which define the frequency of the signal A. A calibrated resistor Rs, through which the current f lows in operation for supply to the load L by means of the control circuit 20 and the electronic switch 30, is also connected to the integrated device IC.

Two further resistors R2 and R3 are connected between respective inputs of the integrated device IC and earth and the output terminal 12, respectively.

The oscillator 10 comes into operation, in known manner, as a result of the connection of a load to the output terminal 12 of the flasher. The oscillator also detects the size of the load, by means of the resistor Rs, and generates a fault-indicating frequency when the load is below a predetermined value.

The control circuit 20 includes a voltage amplifier, generally indicated 21, including a capacitor C2 with one plate is connected to the output of the oscillator 10 and its other plate connected to the cathode of a diode D2, the anode of which is connected to the supply terminal 11 by means of the resistor Rs of the oscillator 10. The output of the voltage amplifier 21 is connected to the emitter of a bipolar pnp transistor Tl by means of two resistors R10 and R8. The collector of the transistor T1 is connected to earth by means of a resistor R4 and its base is connected to the output terminal 12 by means of two resistors R9 and RS. A capacitor C3 is connected between the base and the emitter of T1. The anode of a diode D3 is connected 6 to the emitter of Tl and its cathode is connected to the supply terminal 2 of the control circuit 20.

The anode of a diode D4 is connected to the emitter of Tl and its cathode is connected to the output of the oscillator 10. This diode blocks the control circuit 20 when the waveform A is at a "low" level.

The anode of a Zener diode Z1 is connected to the collector of Tl and its cathode is connected to that of D3. In operation, the Zener diode acts as a voltage stabiliser and protects the control circuit 20 should the polarity of the supply voltage be reversed.

The control circuit 20 includes a second, bipolar npn transistor T2, the collector of which is connected to the gate of the electronic switch 30 and to the output of the voltage amplifier 21 by means of the resistor Rio. The base of T2 is connected to the mirror terminal of the switch 30 by means of a resistor R7. The emitter of this transistor is connected to the junction between the resistors R9 and R5.

The main terminals of the control circuit 20 have been indicated by the reference numerals 1 to 6; the terminal 1 represents the input of the square-wave signal A emitted by the oscillator 10, the terminal 2 is the supply input, the terminal 3 is connected to the gate of the switch 30 and represents the output of the control circuit 20, the terminals 4 and 5 represent sensing inputs and are connected to the resistors R7 and R5 respectively, and, finally, the terminal 6 is connected to earth by means of the resistor R4.

In the embodiment shown by way of example in Figure 1, 7 a further resistor R6 is disposed between the mirror terminal of the switch 30 and the output terminal 12 of the flasher.

In operation, when a load L is connected to the output of the flasher, the oscillator comes into operation and outputs the square-wave signal A which, when its amplitude has been increased by the circuit 21, is applied to the gate of the electronic switch 30. The switch is made conductive and cut off alternately and, during the stages when it is conductive, the current which passes through its drain-source path flows towards the load through the output terminal 12.

During normal operation, the transistor Tl is cut off.

If, in operation, the load L is short-circuited, the potential of the terminal 5 of the control circuit drops (naturally during the stages in which the electronic switch 30 is conductive). The potential difference between the terminals 2 and 5 of the control circuit increases correspondingly. The potential difference between the emitter and the base of Tl also increases correspondingly, with a certain delay due to the time constant defined by the resistance of the resistor R9 and the capacitance of C3, until Tl becomes conductive, opening a current path between the output of the voltage amplifier 21 and earth. The driving signal is therefore diverted from the gate of the electronic switch 30 which is thus cut off. If the increase in the current flowing through the output terminal 12 towards the load lasts for a period of time shorter than the delay defined by R9 and C3, however, the transistor T1 remains cut off and hence does not block-the electronic switch 30.

8 Conveniently, the delay introduced by R9 and C3 is related to the typical time taken f or the lamps L to warm up. As is known, filament lamps absorb a much larger current when they are cold than when they are hot. This greater current absorption takes place, however, for a very short period of time after the lamps are switched on. The time constant introduced by R9 and C3 thus prevents the transistor Tl from becoming conductive as a result of the greater than normal absorption of current by the cold lamps during the switching-on stage.

If, in operation, the voltage between the drain and the source of the electronic switch 30 increases, there is a corresponding increase in the potential difference between the terminals 2 and 5 of the control circuit. If the drain-source voltage of the switch exceeds a predetermined value for a predetermined time, which is also related to the time constant defined by R9 and C3, the transistor T1 also changes from the cut-off condition to the conducting condition, diverting the driving signal from the gate of the electronic switch 30.

Since the emitter-base junction of Tl is connected substantially in parallel with the drain-source path of the electronic switch 30, the transistor T1 can also become conductive if -there is an excessive increase in the temperature of the electronic switch 30 in operation, causing a corresponding change in the emitter-base voltage of T1.

In operation, the voltage produced across the resistor R6 is, indicative of the current flowing in the load L. In fact, as is known, a fraction of the total current 9 flowing through the Sense-FET flows through its mirror terminal and reaches the load L through R6. The voltage drop across R6 is read by the control circuit 20 by means of the resistors RS and R7. If the voltage between the terminals 4 and 5 of the control circuit 20 starts to increase in operation, the transistor T2 becomes more conductive and reduces the driving current flowing towards the gate of the electronic switch 30, thus effectively limiting the current supplied to the load L.

The static electronic flasher device described above has many advantages.

In the first place, the voltage drop in the electronic switch during conducting stages is low. Power dissipation is therefore very low and the device as a whole can have very small dimensions, particularly as regards any heat dissipators.

The maximum current supplied to the lamps is effectively limited by a timed control. As has been seen, this limits the initial "current surge" which normally takes place with filament lamps in operation. The useful life of the lamps is thus increased.

The device is blocked in the event either of an excess current output or of an excess voltage drop across the electronic power switch.

The device is also protected against reversals of the polarity of the supply voltage and against overheating of the electronic switch.

The flasher as a whole emits very low levels of radio interference since the typical sparking between the contacts of electromechanical devices of conventional flashers does not occur.

In practice, the flasher as a whole is therefore protected from all possible functional problems and has a longer useful life than conventional devices.

Since the flasher described above is completely static, it can be enclosed in an insulating material such as a resin or the like, so as to render it immune to attack by external environmental agents and insensitive to mechanical stress.

Figure 2 shows a variant in which the oscillator 10 and the control circuit 20 nonetheless have the same structure as that described with reference to the embodiment of Figure 1.

In the variant of Figure 2, a normal MOSFET, indicated 300, is used instead of a Sense-PET, its gate being connected to the output terminal 3 of the control circuit 30 by means of a resistor R6, its drain being connected to the terminal 4 of the control circuit by means of a resistor R7, and its source being connected to the terminal 5 of the control circuit by means of the resistor R5. A Zener diode Z2 is connected between the gate and the source of the MOSFET 300 in order to limit the voltage applied to its gate. Unlike the solution shown in Figure 1, in the variant of Figure 2, the voltage between the drain and the source of the electronic switch 300 and the intensity of the current supplied to the load are detected jointly from a reading of the voltage between the terminals 4 and 5 of the control circuit. In effect, the voltage between 11 these terminals is related to the voltage between the drain and the source of the switch 300, this latter voltage being proportional to the current flowing through the device when the switch is conducting.

Otherwise, the version of Figure 2 operates in exactly the same manner as the version of Figure 1.

The flasher device according to the invention can be formed either as a version in which the indicators on the right-hand side and the left-hand side of the motor vehicle are controlled jointly, or as a version in which the right-hand and left-hand indicators are driVen separately with the use of several power switches.

Claims

12 CLAIMS

1. An electronic flasher device, particularly for controlling the direction indicators (L) of a motor vehicle, including:

an oscillator for outputting a square-wave driving signal, and at least one static electronic power switch interposed between a first terminal which is intended to be connected to a voltage supply and a second terminal which is intended to be connected to the load, the switch having a conrol input which is controlled by the output of the oscillator, in which it also includes:

first and second sensor means for detecting, respectively, the intensity of the current flowing through the electronic switch, and hence of the current flowing towards the load, in operation, and the voltage drop in the electronic switch, and a control circuit, which is interposed between the oscillator and the electronic switch and is connected to the first and second sensor means and which is adapted to cut off the electronic switch when the current flowing towards the load exceeds a predetermined threshold or when the voltage across the switch exceeds a predetermined value, in operation.

2. A device according to Claim 1, in which the control circuit includes a first transistor with its base-emitter junction connected substantially in 13 parallel with the electronic switch and its collector-emitter path connected between the output of the oscillator and the earth so that, when the electronic switch conducts current, the transistor can become conductive and cut off the electronic switch when the voltage in the electronic switch exceeds the predetermined value for a predetermined period of time and/or when the current flowing towards the load exceeds the threshold for a predetermined period of time and/or when the temperature of the electronic switch exceeds a predetermined value.

3. A device according to Claim 2, in which the emitter of the first transistor is connected to the supply terminal by means of a diode.

4. A device according to Claim 2, in which delay means are associated with the first transistor for delaying its change from the cut-off condition to the conducting condition.

5. A device according to Claim 4, in which the delay means include a capacitor in parallel with the emittor-base junction of the first transistor.

6. A device according to any one of Claims 2 to 5, in which the control circuit includes means for regulating the current flowing towards the load in operation.

7. A device according to Claim 6, in which the current-regulating means include a second transistor with its collector-emitter path connected between the control input of the electronic switch and the second terminal and its base connected to the second sensor means.

14 8. A device according to any one of Claims 2 to 7, in which the control circuit has a f irst Zener diode for stabilising the supply voltage and for protection against a reversal of the polarity of the supply voltage, and a diode for blocking the control circuit when the signal of the oscillator is at a low level.

9. A device according to Claim 8, in which a resistor is interposed between the collector of the first transistor and the earth, and in that the Zener diode is connected between the supply terminal and the collector of the first transistor.

10. A device according to any one of Claims 1 to 9, in which the electronic switch is a Sense-FET, the source and the mirror of which are connected to the second terminal which is intended to be connected to the load, a resistor being interposed between the mirror of the switch and the second terminal.

11. A device according to any one of Claims 1 to 9, in which the electronic switch is a MOSFET.

12. A device according to Claims 7 and 11, in which the second sensor means comprise a resistor connected between the drain of the MOSFET and the base of the second transistor.

13. A device according to Claim 11 or Claim 12, characterised in that a second Zener diode is disposed between the gate and the source of the MOSFET.

14. An electronic flasher device substantially as herein described with reference to, and as shown in, the accompanying drawings.