DE3727498A1 - Device for controlling the power of an electrical load - Google Patents

Abstract

In the case of a device for controlling the power of an electrical load, especially in motor vehicles having an electrical power source, having a clock generator, having an output stage which receives the clock pulses from the clock generator and has a switch in series with the electrical load, and having a short-circuit monitor which measures the voltage at the junction point of the electrical load and opens the switch if the voltage exceeds a predetermined threshold value, the short-circuit monitor can be controlled by the clock generator and becomes effective during the clock-pulse generation in order to identify reliably a short circuit on the electrical load.

Description

The invention relates to a device for controlling the Performance of an electrical consumer, especially in Motor vehicles, with a power source, with a Clock generator, with an output stage, which the clock pulses of Clock generator receives and the one switch in series with has the electrical consumer and with a Short circuit monitoring, the voltage at the connection point of the electrical consumer with the switch and the the switch opens when the voltage is a predetermined Threshold exceeded.

Such a device is from DE-OS 34 36 456 previously known. Short-circuit monitoring is provided there, that is always effective.

However, the known device has disadvantages. Thereby that the short-circuit monitoring is always effective can when switching on and off the one that acts as a switch Field effect transistor possibly occurring Voltage peaks the voltage at the connection point so high drive that the short circuit monitoring erroneously as Short circuit detects. The consequence would be an unwanted opening the switch and thus switching off the electrical Consumer, although there is actually no short circuit is. Such voltage peaks occur in particular Motor vehicles frequently.

A short-circuit monitoring in the clock pulse breaks is often unnecessary because of a risk to components in the Clock pulse pauses, i.e. not possible when the switch is open is.  

Finally, especially if an electric motor is used as an electrical consumer when starting the Electric motor the voltage at the connection point exceed the predetermined threshold. The previously known Device would then also incorrectly unite Register short circuit.

The invention has for its object to provide a device which then a short circuit at the electrical consumer possible detects if the short circuit to a Of components would result.

This object is achieved in that the Short-circuit monitoring can be controlled by the clock generator, and that the short-circuit monitoring during the Clock pulse duration is effective.

The fact that the short-circuit monitoring by Clock generator is controllable, it is possible to function the short-circuit monitoring depending on the clock frequency of the To influence clock pulses. Influencing the function the short-circuit monitoring is carried out depending on the Clock frequency that the short-circuit monitoring only during the Clock pulse duration is effective. That is, only if the Switch is closed and therefore current through the switch can flow through the electrical consumer, the Voltage at the connection point compared with the threshold. Only if the voltage at the connection point during the Clock pulse duration exceeds the threshold, the Switch opened and the consumer through the Short-circuit monitoring switched off.

The invention has the advantage that a malfunction of the function the device according to the invention by voltage peaks is not possible when switching the switch on and off. This makes it wrong to open the switch detected short circuit not possible, because different from the  The voltage spikes were not known as a short circuit can be recognized.

On the other hand, damage to the electrical Consumer or switch by an actual one Short circuit excluded because the invention Short circuit monitoring is only effective if the Switch is closed and if there is a current flow through it the switch and the consumer is even possible.

Further advantageous refinements and developments of Subject of the invention emerge from the subclaims.

It is particularly advantageous if the clock generator is through a setpoint generator is controllable because such a continuous control of electrical power consumption of the consumer and thus the performance of the Consumer is possible. A comes as a setpoint generator Potentiometer in question, whose slider position is a measure of the clock frequency or the pulse width of the clock generator can. An electronic setpoint generator can also be used Use circuit that is part of a particular Interior temperature control for motor vehicles is, and the controls the air flow through the vehicle interior.

It is also particularly advantageous if the clock generator a fixed predetermined frequency and one depending on Setpoint generator has variable clock pulse duration. This ensures that the period in which the Short-circuit monitoring is effective, long enough to be chosen can cause a short circuit in the electrical consumer detect.

One can take advantage of the threshold of the Depending on the nominal power consumption of the electrical consumer choose to allow so-called creeping Short circuits to open the switch. As creeping short circuits are called states in  which the electrical consumer does not completely, but is only partially bridged.

In this context, it is advantageous to set the threshold training dependent on the setpoint generator, because the Setpoint of the setpoint generator is a measure of the desired electrical power consumption of the electrical consumer is.

As an electrical consumer you can electromagnetic Use consumers when switching on and off have comparatively strong voltage peaks. Fan motors in motor vehicles in particular are considered electrical consumers by the invention Device controllable because in addition to the short circuit of the Fan motor also blocking such. B. by objects in the area of the fan blade or by seizing Storage particularly by the device according to the invention can be advantageously recognized.

In order to prevent the false triggering of the Short-circuit monitoring according to the invention, in particular when Start of a fan motor, u. a. through from the fan motor it is to prevent generated electromotive force advantageous if the short-circuit monitoring for a specified time after the fan motor has started is ineffective.

One can continue the short-circuit monitoring in this way train that after a short circuit occurs, in particular periodically after a predetermined second Time the switch closes. This is the It is possible to restart the electrical consumer, if the measured short circuit in the period from Switch off the electrical consumer until it is switched on was eliminated. The periodic attempt at activation is then particularly advantageous.  

Transistors can be used as electrical switches, because such electronic switches in terms of circuitry are particularly easy to control by the power amplifier. This applies in particular to Metal oxide film field effect transistors that are almost are currentless, so that there is an additional Driver circuit is unnecessary.

Finally, you can choose between the clock generator and the Arrange the setpoint generator to store the characteristic curve Clock behavior of the clock generator is often not proportional power output of the electrical consumer adapt. This can be achieved that a predefined setpoint change of a corresponding change corresponds to the power output of the electrical consumer.

An embodiment of the subject of the invention is in the Drawings are shown and will be described in more detail below explained.

It shows

Fig. 1 shows a device according to the invention in a block diagram,

Fig. 2 parts of the device according to the invention of FIG. 1 in an electrical circuit diagram and

Fig. 3 voltage-time diagrams at various points of the inventive device of FIG. 1.

In FIG. 1, the inventive device (ST) via a first terminal (KL 1) and a second terminal (KL 2) is conductively connected to the terminals of an eye formed as a potentiometer setpoint generator (S), the grinder via a third terminal ( KL 3 ) in turn is conductively connected to the device (ST) according to the invention. Furthermore, the device (ST) according to the invention via a fourth terminal (KL 4 ) with a first connection of an electrical consumer designed as a fan motor (M) and with the positive pole of a current source (B) , which can be designed as a motor vehicle battery and via an eighth Terminal (KL 8 ) with the negative pole of the motor vehicle battery (B) conductively connected. The second connection of the fan motor (M) is connected in parallel via a fifth terminal (KL 5 ) to the output stage (E) of the device according to the invention (ST) and via a seventh terminal (KL 7 ) to the short-circuit monitoring (K) of the control unit (ST) conductively connected. Finally, the output stage (E) of the device (ST) according to the invention is conductively connected to the negative supply voltage of the current source (B) via a sixth terminal (KL 6 ).

The supply voltage for supplying the setpoint generator (S) is stabilized in a known manner by a voltage stabilization (SP) arranged between the terminal (KL 1 ) and the terminal (KL 4 ). The input signal of the setpoint generator (S) or the wiper voltage of the potentiometer is fed in parallel to a characteristic curve memory ( KS) via the terminal (KL 3 ) and to a short-circuit monitor (K) via a line ( 3 ). A clock generator (T) is triggered by the output signal of the characteristic curve memory (KS) and , depending on this output signal, generates a pulse sequence which has a variable pulse width and a constant pulse frequency. This pulse sequence is fed in parallel to the output stage (E) and via a first line ( 1 ) to the short-circuit monitoring (K) as an input signal. As a further input signal, the short-circuit monitoring (K) is fed via the terminal (KL 7 ) or a fourth line ( 4 ) to the potential at the connection point of the fan motor (M) with a switch (TR) in the form of a transistor of the output stage. Depending on these three input signals, the short-circuit monitoring (K) controls the output stage (E) and thus the transistor (T) in addition to the clock generator (T) via a second line ( 2 ) .

In FIG. 2, the same or equivalent parts as in FIG. 1 are provided with the same reference numerals. The transistor (TR) used as a switch is formed there as a metal oxide field effect transistor and supplied via a sixth resistor (R6) in series with a fifth resistor (R 5) via the line (1) from the clock generator (T) with clock pulses becomes. In addition, the clock generator (T) acts via the first line ( 1 ) and a first diode (D 1 ) on the inverting input of a comparator (V) as part of the short-circuit monitoring (K) . Furthermore, the inverting input of the comparator (V ) is fed via line ( 3 ) and a seventh resistor (R 7 ) the setpoint of the setpoint generator (S) . Finally, the potential of the terminal ( 7 ) is present at the inverting input of the comparator (V) via a third resistor (R 3 ).

A predetermined voltage threshold, with which the sum of the input potentials at the inverting input of the comparator (V) is compared, is at the non-inverting input of the comparator (V) via a voltage divider, consisting of the first resistor (R 1 ) and the second resistor (R 2 ), which is otherwise connected to the motor vehicle battery (B) .

To the lowering of the threshold voltage to delay the non-inverting input of the comparator (V), the first resistor (R1) is shunted with a first capacitor (C 1) whose time constant determines the delay time until the effect of the short-circuit monitoring of the invention.

The output of the comparator (V) is on the one hand via a fourth resistor (R 4 ) with the positive supply voltage (+ UB) and via a second diode (D 2 ) and the second line ( 2 ) with the control electrode of the transistor (T) and the cathode of a third diode (D 3 ) is conductively connected, the anode of which is conductively connected to the negative supply voltage (- UB) . As the last part, a second capacitor (C 2 ) is conductively connected on the one hand to the connection point of the fifth resistor (R 5 ) and the sixth resistor (R 6 ) and on the other hand to the terminal (KL 7 ).

The function of the device according to the invention according to FIGS. 1 and 2 will now be explained in more detail using the voltage-time diagrams in FIG.

In Fig. 3a, the voltage (U 3 ) on the third line ( 3 ), which is dependent on the slider position of the setpoint potentiometer (S) , is plotted as a function of time and is specified by actuating the setpoint generator (S) . It is assumed that the setpoint generator (S) is increased from a setpoint ( 0 ) at the start time (t 0 ) to a first time (t 1 ), then from the first time (t 1 ) to the second time (t 2 ) remains constant, then is further increased from a second point in time (t 2 ) to a third point in time (t 3 ) with a larger rate of change and finally remains constant at this set high value from the third point in time (t 3 ). Then the duty cycle or clock pulse duration of the clock generator (T) changes in the manner shown in Fig. 3b. The pulses of the clock generator (T) have a predetermined fixed frequency (T 1 ). The width of the pulses occurring is changed depending on the setpoint generator (S) and, if applicable, on the characteristic curve stored in the characteristic curve memory (KS) . In Fig. 3b it is assumed that the characteristic curve memory (KS) has a straight line of origin as the characteristic curve, so that with increasing voltage (U 3 ) there is an essentially linear extension of the pulse width between the occurrence of two pulses.

As shown in FIG. 3a, this first takes place until the first point in time (t 1 ). From the first point in time (t 1 ) to the second point in time (t 2 ), the pulse width then remains constant depending on the preset voltage (U 3 ). From the second point in time (t 2 ) to the third point in time (t 3 ), the pulse width increases further due to the increasing voltage (U 3 ) until, at point in time (t 3 ), the value corresponding to the now constant voltage (U 3 ) has reached and is held.

A voltage (U 4 ) is plotted against time (t) in FIG. 3c. The voltage (U 4 ) corresponds to the potential at the terminal (KL 7 ) or the potential on the fourth line ( 4 ). This voltage (U 4 ) is composed of the supply voltage applied to the motor when the transistor (T) is conductive or switched on by the clock generator via the first line ( 1 ) and the electromotive force generated by the rotating motor (M) .

As long as there is no short circuit on the fan motor (M) , as should be the case up to a fourth point in time (t 4 ), the potential at the terminal (KL 7 ) is below the preset threshold value (SW) and there is no intervention by the invention Short-circuit protection (K) on the control of the transistor (TR) by the clock generator (T) . However, the voltage value at the terminal (KL 7 ), as shown at time (t 4 ) in Fig. 3c, exceeds the threshold value (SW) because the fan motor (M) is blocked or a short circuit has occurred at the fan motor (M) is, the potential at the inverting input of the comparator (V) exceeds the applied to the non-inverting input of the comparator (V) threshold, then and only then when the first line (1) comprises the clock generator positive potential, so that the transistor (TR) is turned on and no current can flow from the inverting input of the comparator (V) via the first diode (D 1 ) to the clock generator (TR) . If this is the case, the output of the comparator (V) changes its initial state from the positive potential which was previously impressed on it via the fourth resistor (R 4 ) to the negative potential. The control electrode of the transistor (TR) then changes its state from the high potential state to the low potential state because a current flow from the control electrode of the transistor (TR) via the second diode (D 2 ) to the ground potential of the output of the comparator is possible . The transistor (TR) is then blocked and the load circuit of the fan motor (M) is opened.

After a predetermined period of time (T 2 ), the output state of the output of the comparator (V) is changed at a fifth point in time (t 5 ), so that the clock generator (T) causes the next positive pulse to appear on the first line ( 1 ) Transistor (TR) is turned on again. The second time period (T 2 ) is determined by the choice of the second capacitor (C 2 ). If, at the fifth point in time (t 5 ), the short circuit still exists or the fan motor (M) is still blocked, the processes described above run again because the voltage at the terminal (KL 7 ) again reaches the threshold value (SW) exceeds.

After another second time period (T 2 ) has elapsed at a sixth time (t 6 ) and with the occurrence of the next positive control pulse of the clock generator (T) , an attempt is then made to switch the transistor (TR) on. These processes are repeated until the short circuit or the blocking of the fan motor (M) is eliminated or until the power supply is interrupted.

In Fig. 3 it is assumed that at a time (t 6 ) the blocking of the fan motor (M) or the short circuit is released, so that the fan motor (M) starts up again and thus the potential at the terminal (KL 7th ) does not exceed the threshold (S) when the transistor (TR) is switched on. This is shown accordingly in FIGS. 3c and 3d.

In Fig. 3c, only one threshold value (SW) is shown as a constant value. However, it is particularly advantageous to design the threshold value (SW) to be variable depending on the target value of the target value transmitter (S) . This is provided in Fig. 2 via the third line ( 3 ). In the exemplary embodiment of the inventive device of Figs. 1 to 3, a fan motor (M) has been used an interior temperature control of a motor vehicle when electrical loads. With the device according to the invention, however, other electrical consumers can also be advantageously monitored for short circuits or the blocking of movements.

Claims (10)

1. Device for controlling the power of an electrical consumer, in particular in motor vehicles, with a power source, with a clock generator, with an output stage which receives the clock pulses of the clock generator and which has a switch in series with the electrical consumer and with a short-circuit monitoring, the measures the voltage at the connection point of the electrical consumer and opens the switch when the voltage exceeds a predetermined threshold, characterized in that the short-circuit monitoring (K) can be controlled by the clock generator (T) and that the short-circuit monitoring (K) is effective during the clock pulse duration is. 2. Device according to claim 1, characterized in that the clock generator (T) is controllable by a setpoint generator (S) , in particular a potentiometer. 3. Apparatus according to claim 2, characterized in that the clock generator (T) has a fixed predetermined frequency and a depending on the setpoint generator (S) variable clock pulse duration (T 1 ). 4. The device according to claim 1, characterized in that the threshold of the nominal power consumption of the electrical consumer is dependent. 5. Apparatus according to claim 2 and claim 4, characterized in that the threshold value is dependent on the setpoint generator (S) . 6. The device according to claim 1, characterized in that the electrical consumer, an electromagnetic consumer, in particular the fan motor (M) of a motor vehicle. 7. The device according to claim 6, characterized in that the short-circuit monitoring (K ) is ineffective for a predetermined period when the fan motor (M) starts. 8. The device according to claim 1, characterized in that the short-circuit monitoring (K ) closes the switch (T) after the occurrence of a short circuit, in particular periodically after a predetermined second time period. 9. The device according to claim 1, characterized in that the switch is a transistor (T) , in particular a metal oxide field effect transistor. 10. The device according to claim 2, characterized in that a characteristic curve memory (K) is arranged between the clock generator (T) and the setpoint generator (S) .