JP3332782B2 - Load drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a load driving circuit using a relay circuit.

[0002]

2. Description of the Related Art A conventional power supply circuit using a DC relay for fail-safe of a switching transistor of a load will be described with reference to FIG. FIG. 1 shows an example of a load drive circuit used for electronic control of a vehicle-mounted heater element 9, for example, in which a load MOS switching transistor 4 activated by a signal from a microcomputer 7 receiving an operation signal turns on / off a load MOS transistor. When turned off, the heater element 9 is energized to perform temperature control based on a signal from a temperature sensor (not shown). Power MOS used here
If the power MOS is broken by an overvoltage or an accident such as a short circuit in the heater element 9 which is a load and an excessive current flows occurs, the inside of the power MOS becomes a short mode and a continuous overcurrent flows. In this case, the circuit current cannot be cut off by the signal of the microcomputer 7, so that a wire harness or the like connecting the circuit from the outside may generate heat and cause a fire. As a fail-safe means in consideration of the property of the switching transistor 4 of the load which is a power MOS, a DC relay 2 is inserted in series. The fail-safe operation of the DC relay 2 is as follows. When the potential signal generated by the short / open detection resistor 5 is input to the microcomputer 7 via the AD converter 6 and the microcomputer 7 determines that the signal is abnormal, the microcomputer 7 sets the DC relay 2
Is output to the transistor 3 to cut off the current.

[0003]

As described above, in the operation of this circuit so far, the microcomputer 7 uses the driving transistor 3 of the DC relay 2 and the switching transistor 4 of the load to start energizing the heater element 9. On the other hand, the control signal was output at the same time. However, since the DC relay 2 performs an electromagnetic mechanical operation after receiving the control signal, there is a slight delay until energization. When the control operation starts (before the DC relay 2 is turned on), the microcomputer 7 takes in the signal of the short / open detection resistor 5 and erroneously determines that the microcomputer 7 is open due to no power supply. Could be done.

Immediately after the DC relay 2 and the switching transistor 4 are turned on to start energization,
Since the resistance value of the heater element 9 which is a load is at room temperature and is lower than in the steady state during heating, the rush current immediately after the start of energization becomes high, and the potential of the short / open detection resistor 5 is determined as an abnormality based on the steady state. Since the voltage fluctuates higher than the potential, there is a possibility that a large current is detected and a short circuit is erroneously determined.

[0005] Further, it is known that as a customary relay, when the contact 22 is turned on and off while the circuit is energized, the contact 22 is roughened by a current spark.
As described above, at the start of energization, after the switching transistor 4 is turned on, the DC relay 2 is turned on with a delay from the control signal.
And the DC relay 2 is turned off after the switching transistor 4 is turned off at the time of current interruption, and the contact 22 of the DC relay 2 is roughened. .

SUMMARY OF THE INVENTION It is an object of the present invention to solve such a problem, to prevent erroneous determination of open / short of a load, and to eliminate rough contacts of a DC relay.

[0007]

According to the present invention, a relay circuit, a load and a switching transistor are connected in series between a power supply and a ground, and the relay circuit and the switching transistor are connected to each other. On the other hand, a first drive signal for turning on the relay circuit and a second drive signal for turning on the switching transistor.
A load control unit that outputs a drive signal of the first drive signal and an abnormality determination unit that detects a current flowing through the load and determines abnormality of the load. After the first drive signal is output, the second drive signal is output after a first predetermined time corresponding to the time from when the first drive signal is output to when the contact in the relay circuit is closed. The abnormality determining means determines an abnormality of the load after a second drive signal is output by the load control means.

[0008] The abnormality determining means may be configured to output a second drive signal from the load control means to output a second drive signal from the load control means until the temperature of the load is stabilized after the load is energized. After a lapse of a predetermined time, the abnormality of the load is determined.

A relay circuit, a load, and a switching transistor are connected in series between the power supply and the ground, and a first drive signal for turning on the relay circuit for the relay circuit and the switching transistor. And load control means for respectively outputting a second drive signal for turning on the switching transistor,
An abnormality determining unit configured to detect a current flowing in the load and determine abnormality of the load, wherein the load control unit disconnects the relay circuit with respect to the relay circuit and the switching transistor. And a second cut-off signal for turning off the switching transistor. The second cut-off signal is output after the second cut-off signal is output. After a third predetermined time corresponding to the constant delay time has elapsed, the first cutoff signal is output.

[0010]

[0011]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating an example of a load drive circuit according to the present invention, and illustrates a configuration of a circuit that controls energization of a heater element mounted on a vehicle. In this example, the operation of the microcomputer has a feature, and the hardware configuration is the same as that of the conventional technology. Therefore, the description will be made again with reference to FIG.

Reference numeral 1 denotes an operation switch for inputting an operation signal such as an operation switch operated by a driver for controlling energization and cutoff of a heater element, or an automatic input switch for detecting a passenger. Reference numeral 2 denotes a DC relay, which is a load connected to the power supply unit 8 (a heater element 9 described later).
And + B are connected in series to a power line, and a relay is turned on and off by controlling power supply to a built-in electromagnetic coil to control power supply to a load. Reference numeral 3 denotes a transistor for driving the DC relay 2, the collector terminal of which is connected in series with the ground side of the electromagnetic coil of the DC relay, the emitter terminal of which is grounded, and receives a signal of the microcomputer 7 described later to the base terminal. Thus, the current supply of the electromagnetic coil of the DC relay 2 is controlled. Reference numeral 4 denotes a switching transistor, which is a MOS transistor, is connected in series to the ground side of a load (heater element 9 described later) connected to the power supply unit 8, and transmits a signal of the microcomputer 7 described later to a base terminal. In response to this, the power supply to the load is turned on / off and controlled. 5
Is a low-resistance resistor, one end of which is connected in series to the ground side of the switching transistor 4 and the other end is grounded. It is configured to be proportional to the value and generates a signal to detect open / short of the load. Reference numeral 6 denotes an AD converter which converts a signal generated by the current detection resistor 5 from an analog value to a digital value and sends the signal to a microcomputer 7 described later. Reference numeral 7 denotes a microcomputer which receives a signal from the operation switch 1 and sends a control signal to the DC relay 2 and the switching transistor 4 to control connection and disconnection of each circuit. Further, the microcomputer 7 determines an abnormality based on a signal for detecting open / short by the current detection resistor 5 via the AD converter 6, and sends a signal for cutting off the power supply to the load when the abnormality is determined. In addition, in addition to these operations, the microcomputer 7 receives a signal from a thermometer (not shown) (located near the heater element) to control the temperature of the switch transistor 4 by controlling the duty ratio or the like. Is not a target function of the present invention, and a description thereof will be omitted. 8
Is a power supply unit, which constitutes a DC relay control circuit as described above, and a load (heater element 9 described later) provided outside the power supply unit 8 from an output terminal via a wire harness or the like. It is connected to the. Reference numeral 9 denotes a heater element as a load, which is mounted on, for example, a seat or the like and is controlled so as to generate a predetermined temperature.

Next, processing for preventing erroneous determination of open / short detection in DC relay control performed by the microcomputer 7 and processing for preventing the contact 22 of the DC relay 2 from becoming rough due to spark will be described. FIG. 2 is a flowchart illustrating the load drive control performed by the microcomputer 7.
(A) is a diagram showing a flow at the start of load energization, showing a process of preventing erroneous determination of open / short detection at the start of load energization.

In step a1, the microcomputer 7 which has received the load energization start signal of the operation switch 1 starts signal processing for starting energization, and a timer (not shown) of the microcomputer 7 sends a load energization start signal of the operation switch 1 to the microcomputer. Then, measurement is started, and the process proceeds to step a2. In step a2, the microcomputer 7 sends a signal for energization to the transistor 3, the transistor 3 is energized, the electromagnetic coil 21 of the DC relay 2 is energized, and the contact 22 of the DC relay 2 is energized.
ON (connecting the power supply side and load side)
Move to step a3. In step a3, the value T of the timer is set to a first predetermined time t1 sufficient to cope with the electromagnetic mechanical delay of the contact operation of the contact 22 of the DC relay 2.
Is determined at a predetermined cycle, and if it is determined that the value has been exceeded, the process proceeds to step a4. At step a4, the microcomputer 7 sends a signal to the switching transistor 4 to turn it on to start energizing the load, and then proceeds to step a5. After the contact operation of the contact 22 of the DC relay 2 is completed in this way, the switching transistor 4 is turned on to start energizing the load, so that the contact operation of the contact 22 of the DC relay 2 is not performed. The open / short detection is performed at a complete point in time, so that the risk of erroneous determination being violated is prevented, the electric energy is prevented from being concentrated on the contact 22, and the contact 22 of the DC relay 2 is prevented from being roughened by spark.

In step a5, the value T of the timer is
It is determined in a predetermined cycle whether or not a second predetermined time t2 sufficient to cope with a delay in which the load temperature is stabilized and the inrush current recovers to a stable region is determined. It is determined that it has reached, and the process proceeds to step a6. In step a6, the determination process is treated as valid, the mode at the start of energization is ended, and the process proceeds to step a7. In step a7, the mode shifts to the normal operation mode. Thus, by providing the time t2, the load is energized, and the determination process is performed after the resistance value of the load (corresponding to the temperature) is stabilized. Therefore, it is possible to prevent the erroneous short-circuit determination due to the fluctuation of the load resistance. . The processing in step a6 is performed by the AD converter 6
If the output from is zero, the energizing line is open, and if the output is higher than a predetermined value, it is determined that the power supply side and the ground side of the load are short-circuited.

Next, FIG. 2B is a diagram showing a flow when the energization of the load is cut off, and shows a process for preventing the contact 22 of the DC relay 2 from becoming rough due to a spark when the energization of the load is cut off. In step b1, the microcomputer 7 receiving the load energization cutoff signal of the operation switch 1 starts signal processing for energization cutoff, and proceeds to step b2. In step b2, the microcomputer 7 switches the determination processing of the open / short detection to invalid, and proceeds to step b3. In step b3, the microcomputer 7 cuts off the energization signal to the switching transistor 4 to cut off the energization to the load, and starts measuring the interruption of the energization signal by a timer (not shown) of the microcomputer 7; Move to b4. In step b4, it is determined whether or not the value T of the timer has exceeded a third predetermined time t3 sufficient to cope with a time constant delay of energization cutoff to the switching transistor 4, and if it is determined that it has exceeded, the process proceeds to step b5. . In step b5,
The microcomputer 7 cuts off the energization signal to the transistor 3, opens the contact 22 of the DC relay 2, and proceeds to step b6. In this manner, the switching transistor 4
After a time lag until the power supply to the load is completed due to the disconnection, the contact operation of the contact 22 of the DC relay 2 is performed, so that the contact 22 of the DC relay 2 is prevented from being roughened due to a spark. At step b6, the standby mode is set, and the control operation ends.

According to the control flow as described above, the control timing is as shown in FIG. 3, and erroneous determination of short / open determination can be avoided as follows.
The contact 22 of the DC relay 2 is prevented from being roughened by the spark. That is, when the load energization is started, (a) the transistor 3 is turned on (the electromagnetic coil current of the DC relay 2 becomes O
After t after _one second after the N), (b) switching transistor 4 is turned ON, it is turned ON (c) the load current. Therefore, the load current flows after the contact 22 of the DC relay 2 is connected, so that the contact 22 is prevented from being sparked and roughened at the time of connection.
The erroneous determination caused by starting the short / open determination before the connection is established can be avoided. Also, (d) short / open judgment is made only after t ₂ seconds after the load current is turned on.
N (= execute). Therefore, the determination is started after the phenomenon of the large rush current immediately after the start of energization of the load stops and the current is stabilized, and erroneous determination can be avoided.

Next, when the load is cut off, (d) the short / open judgment is turned off (= stopped), and immediately (b) the switching transistor 4 is turned off (c).
After the load current is turned off and t ₃ seconds later, (a)
The transistor 3 is turned off (the electromagnetic coil current of the DC relay 2 is turned off). Therefore, when there is no load current, D
Since the contact 22 of the C relay 2 is cut off, it is possible to avoid the occurrence of sparks due to the disconnection of the contact 22 while energizing, thereby causing roughening. In particular, the embodiment is very effective for a load having an unstable resistance value in such a transition period of energization.

[0019]

As described above in detail, according to the present invention, in a load driving device having a relay circuit, erroneous determination of load abnormality detection can be prevented, and the contact of the relay circuit becomes rough. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a load driving circuit.

FIG. 2 is a diagram showing a flow of load drive control.

FIG. 3 is a diagram showing control timing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Operation switch 2 ... DC relay 3 ... Transistor 4 ... Switching transistor 5 ... Current detection resistance 6 ... AD converter 7 ... Microcomputer 8 ... Power supply unit 9 ... Heating elements

Claims (3)

(57) [Claims] A first drive signal for connecting a relay circuit, a load, and a switching transistor in series between a power supply and a ground, and causing the relay circuit to conduct to the relay circuit and the switching transistor. ,
And a load control unit that outputs a second drive signal for turning on the switching transistor, and an abnormality determination unit that detects a current flowing through the load to determine an abnormality of the load. The load control unit outputs a first drive signal, and outputs a first drive signal corresponding to a first time corresponding to a time from when the first drive signal is output to when a contact in the relay circuit is closed.
After the elapse of a predetermined time, outputs the second drive signal, and the abnormality determination means determines the abnormality of the load after the second drive signal is output by the load control means. Load drive device. 2. The apparatus according to claim 1, wherein the abnormality determining unit is configured to output a second drive signal from the load control unit to output a second drive signal, and supply a second drive signal to the load control unit. 2. The load drive device according to claim 1, wherein the abnormality of the load is determined after a predetermined time has elapsed. 3. A first drive signal for connecting a relay circuit, a load, and a switching transistor in series between a power supply and a ground, and causing the relay circuit to conduct to the relay circuit and the switching transistor. ,
And a load control unit that outputs a second drive signal for turning on the switching transistor, and an abnormality determination unit that detects a current flowing through the load to determine an abnormality of the load. The load control means outputs, to the relay circuit and the switching transistor, a first shutoff signal for turning off the relay circuit and a second shutoff signal for turning off the switching transistor, respectively. And outputting the first cutoff signal after a third predetermined time corresponding to a time constant delay time of energization cutoff to the switching transistor has elapsed after outputting the second cutoff signal. A load driving device, comprising: