JPH0962385A - Current control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current control system capable of surely supplying a prescribed quantity of current without receiving the influence of temperature change. SOLUTION: A chopper part 10 is provided with a function to supply the current to coils L1-L3. A CPU 60 transfers an on/off signal to instruct whether or not the current should be permitted to flow on the coils L1-L3 to individual switch parts 20-40. The individual switch parts 20-40 control whether or not the current should be permitted to flow according to the on/off signal when the chopper part 10 supplies the current to the coils L1-L3. A current detecting part 50 detects the sum of the current on the coils L1-L3, and reports a detection result to the CPU 60. The CPU 60 calculates the duty of a chopper signal based on a current value detected by the current detecting part 50, and transmits the chopper signal to the chopper part 10. The chopper part 10 supplies the current to the coils L1-L3 according to the chopper signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for controlling a current flowing through a plurality of loads, and more particularly to a contactor driver for controlling a coil current of a contactor.

[0002]

2. Description of the Related Art A technique for controlling the state and operation of a device by opening and closing a contact (for example, a relay contact) by controlling a current flowing through a coil is widely practiced. Such a contact portion, including a coil in some cases, is called a contactor. A circuit that opens and closes the contactor by controlling the current is called a contactor driver.

FIG. 4 is a circuit diagram of a conventional contactor driver. In FIG. 1A, the coil L is a part of a contactor that opens and closes a contact (not shown) by passing a current therethrough. A flywheel diode FD is provided for the coil L. The switch SW is a MOS transistor and has a control voltage V applied to its gate terminal.
Turns on / off according to C. The control voltage VC is an output signal of the AND gate 101 and is the logical product of the ON / OFF signal and the chopper signal. Then, when the switch SW is turned on, the coil L and the switch S
An electric current flows through W, and the contacts are closed (the contactor is turned on) by the electromagnetic induction phenomenon caused by the coil current.

Next, the control of the coil current will be described. In order to pass the current through the coil L, first, as shown in FIG. 4 (b), the duty D = 1 (1
00%) signal for a predetermined time T. As a result, the switch SW is turned on for the time T. The ON / OFF signal is in the "H" state.

While the switch SW is in the ON state, the coil current increases. Then, when the coil current exceeds a predetermined value, the contacts are closed due to an electromagnetic induction phenomenon. This predetermined value is called the maximum drop-off current, and is the minimum current value required for the contact to be in the contact state (ON state) or the minimum current value for ensuring that the contact is in the contact state.

In order to keep the contacts in the ON state, it is sufficient to continue to flow a current larger than the predetermined value to the coil L. Therefore, if the coil current is kept at a value slightly larger than the above-mentioned predetermined value, it is possible to avoid wasting current.
The contact can be kept on. The contactor driver is a circuit that causes an appropriate current as described above to flow through the coil when the contacts are turned on.

The coil current is controlled by the duty of the chopper signal. That is, set the chopper signal to "H"
When the switch SW is turned on, the switch SW is turned on and the coil current is increased. On the other hand, when the chopper signal is turned "L", the switch SW is turned off and the coil current is decreased. Therefore, the duty of the chopper signal is appropriately adjusted. By setting, the coil current (average value of the coil current) can be determined. If the coil resistance is R, the chopper signal duty is D, and the power supply voltage is VDD, the coil current is I
It can be expressed as = VDD · D / R. This duty is preset according to the power supply voltage, the coil resistance of the coil L, and the like, so that the coil current becomes a value slightly larger than the predetermined value.

[0008]

The coil current is determined by the coil resistance of the coil L, but this coil resistance changes depending on the temperature. Usually, the coil resistance is
It increases with increasing temperature. The coil resistance is
Since there is an error due to the product variation of the coil L, the value may be different for each coil even at a specific temperature.

FIG. 5 is a graph showing an error due to temperature dependence of coil resistance and product variation. In the figure,
Lines 102 and 103 respectively show the values of the coil current when the coil resistance is maximum and when the maximum error of the product variation of the coil L is taken into consideration.

Coil current is minimized in high temperature conditions where coil resistance increases. Therefore, in order to surely turn on the contact at an arbitrary temperature within the operating temperature range, the coil current has a predetermined value (here, the maximum detachment current: 0. 185
It should be larger than A). That is, when the coil L is placed in a high temperature state, it is necessary to determine the duty of the chopper signal so that the coil current becomes larger than the predetermined value.

However, when the coil current is set in the high temperature state, the coil resistance becomes small in the room temperature state and the low temperature state, so that the coil current becomes larger than necessary. In the example shown in the figure, when the product variation of the coil L is taken into consideration, the coil current is 0.329 A at 20 ° C.
It is 0.483 A, which is considerably higher than the maximum drop current. As described above, passing a current larger than necessary not only increases power consumption, but also leads to a vicious cycle in which the temperature of the coil L is further increased.

In order to solve the above problem, a method has been devised in which a temperature sensor is provided near the coil L and the duty of the chopper signal is changed according to the temperature detected by the temperature sensor. However, this method cannot directly detect the temperature of the coil L itself.
When the duty of the chopper signal is determined according to the detected temperature, it is necessary to have a margin, and an unnecessarily large current will flow.

An object of the present invention is to solve the above problems, and an object thereof is to provide a current control system capable of reliably supplying a current of a predetermined magnitude without being affected by temperature changes.

[0014]

FIG. 1 is a diagram illustrating the principle of the present invention. The current control circuit of the present invention is configured to supply current to a plurality of loads and has the following means.

The current supply means 1 supplies a current based on the current control signal generated by the control means 5 to each of the loads 3-1 and 3-.
2,. . . , 3-n. The current control signal is, for example, a chopper signal.

Switching means 2-1 and 2-
2,. . . , 2-n are loads 3-1 and 3-, respectively.
2,. . . , 3-n. Then, the control means 5 causes the switching means 2-1, 2-2 ,. . . , 2
Receiving an on / off control signal generated every −n, if the on / off control signal is in the first state (for example, “H” level), the current is passed through the load, and the second state (for example, “”) If the L level), the operation is performed so that no current flows through the load.

The current detecting means 4 includes loads 3-1 and 3-
2,. . . , 3-n is detected. The control means 5 sets the ON / OFF control signal transferred to the switching means provided for the load through which the current should flow to the first state, and controls the current based on the current value detected by the current detection means 4. Generate a signal. The current control signal is, for example, a chopper signal, and the control means 5
The duty is changed according to the current value detected by the current detection means 4. Further, the control means 5 sets a target current in advance for each load, and the sum of the target currents set for the current-carrying load and the current value detected by the current detection means 4. Alternatively, the current control signal may be generated based on the comparison result.

[0018]

In the current control circuit of the present invention, the control means 5
Generates a current control signal based on the load current detected by the current detection means 4, and the current supply means 1 determines the current value supplied to each load according to the current control signal. That is, feedback control using the load current is performed. Therefore, even when the resistance of the load changes due to a temperature change or the like, the current can be maintained at a constant value (target current).

The current supply means 1 supplies a current to a plurality of loads, the current detection means 4 detects the value of a current flowing through the plurality of loads, and the control means 5 controls the current flowing through the plurality of loads.
Therefore, each of these means may be provided in common for each of the plurality of loads.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is a configuration diagram of a contactor driver taken as one embodiment of the current control circuit of the present invention. This contactor driver is configured to supply current to three coils, and causes a current to flow through a predetermined coil to close a contactor (contact) (not shown) by utilizing an electromagnetic induction phenomenon generated at that time. Closing the contactor means bringing the contact into a contact state, and this state is called an on state. In the following, the three coils will be described as having the same characteristics (inductance, coil resistance, etc.).

The contactor driver of this embodiment comprises a chopper section 10, individual switch sections 20, 30, 40, a current detection section 50, and a CPU 60. The chopper unit 10 has a function of supplying a current to the coils L1 to L3. Since the coils L1 to L3 have the same characteristics as each other, when the individual switch units 20, 30, and 40 are turned on, the coils L1 to L3 are supplied with the same magnitude of current, respectively. The magnitude of the current supplied to each of the coils L1 to L3 is controlled by the duty of the chopper signal from the CPU 60.

The individual switch units 20, 30, 40 are provided for the coils L1 to L3, respectively, and have the same configuration. Then, each individual switch unit 20, 30, 40
Controls whether or not the current flows when the chopper unit 10 tries to supply the current to the coils L1 to L3. This control follows an instruction from the CPU 60. Therefore, the CPU 60 controls the individual switch units 20, 30, 4
By controlling 0, a current can be passed through any of the coils L1 to L3.

The current detector 50 detects the sum of the currents flowing through the coils L1 to L3 and notifies the CPU 60 of the detection result. The CPU 60 is an instruction from the outside or the CPU 6
According to the program stored in 0, an on / off control signal for instructing whether or not to supply a current to the coils L1 to L3 is transferred to the individual switch units 20, 30, and 40. For example, when passing a current through the coil L1, the “on state” is transferred as the on / off control signal to the individual switch section 20. Further, the CPU 60 has a flag memory in which 1 bit is assigned to each of the coils L1 to L3. Then, "1" is set to the bit corresponding to the coil through which the current is flowing. As a result, the CPU 60 recognizes how many coils the current is flowing (the number of contactors in the ON state).

Further, the CPU 60 calculates the duty of the chopper signal on the basis of the current value detected by the current detecting section 50 and the number of coils passing the current, and transmits the chopper signal to the chopper section 10. The algorithm for calculating the duty of the chopper signal will be described later in detail.

Next, the operation of the contactor driver having the above configuration will be described. Here, a case will be described in which a current is passed through the coil L1 to turn on the contactor. In addition,
It is assumed that no current is applied to the coils L2 and L3.

First, the CPU 60 uses the on / off control signal as the contactor activation operation to operate the individual switch section 2
The MOS transistor Q21 provided in 0 is turned on. At this time, "1" is set to the bit corresponding to the coil L1 of the flag memory.

Further, the CPU 60 sets the duty of the chopper signal to 100% for a predetermined time (100 msec). As a result, the MOS transistor Q12 provided in the chopper section 10 remains on for 100 msec. When the MOS transistor Q12 is turned on, the MOS transistor Q11 is also turned on.

When the MOS transistor Q11 is turned on, the current flowing through the MOS transistor Q11 is supplied to the coils L1 to L3. At this time, since the MOS transistor Q21 of the individual switch unit 20 is in the ON state, the current supplied from the power supply reaches the ground via the MOS transistor Q11, the coil L1, the MOS transistor Q21, and the resistor R51 of the current detection unit 50. Flow on the path. As a result, the current flowing through the coil L1 directly flows through the resistor R51.

The current flowing through the coil L1 gradually increases while the MOS transistors Q11 and Q21 are in the ON state. This coil current is the MOS transistor Q
It becomes a sufficiently large value until 100 msec elapses after 11 and Q21 are turned on, and the contact is turned on.

In the current detecting section 50, the voltage corresponding to the voltage drop in the resistor R51 is amplified by using the amplifier 52,
The amplified voltage is constantly notified to the CPU 60. That is, the current detection unit 50 always notifies the CPU 60 of the value of the current flowing through the resistor R51.

The CPU 60 has a MOS transistor Q11.
When 100 msec has elapsed after turning on Q21 and Q21, the operation for maintaining the on state of the contact is started. That is, the control for setting the current flowing through the coil L1 to the target value is performed as follows. Here, the current value (target current) to be passed through the coil L1 in the holding operation state is a preset value. This target current is a value that is a little larger than the minimum current value required to turn on the contactor (or the minimum current value that guarantees that the contactor is turned on). In the example shown in FIG.
For example, this target current is set to about 0.25A.

First, the CPU 60 recognizes that the current is being supplied only to one coil (coil L1) by referring to the flag memory. Also, the CPU 60
Controls the duty of the chopper signal so that the current flowing through the resistor R51 (that is, the current flowing through the coil L1) matches the target current. However, since the current flowing through the resistor R51 is converted into a voltage and notified to the CPU 60, the comparison is actually performed using a predetermined conversion coefficient. The chopper signal is a signal for controlling the on / off state of the MOS transistor Q11.
The ratio of the on time and the off time of the S transistor Q11 changes.

When the MOS transistor Q11 is turned off, no current is supplied to the coils L1 to L3. Of course, since the coil has the property of holding the current, the current continues to flow in the coil L1. This current flows in a loop through the coil L1, the MOS transistor Q21, the resistor R51, and the diode D13, but gradually decreases with the passage of time. On the other hand, when the MOS transistor Q11 is turned on, as described above,
A current is supplied to the coil L1 from the power supply, and the current value increases.

As described above, the current value flowing through the coil L1 repeatedly increases and decreases as the chopper signal repeats "H" and "L". Therefore, the current value flowing through the coil L1 is controlled by controlling the duty of the chopper signal. The average value of the current can be set. The CPU 60 controls the duty of the chopper signal so that the average value of this coil current matches the target current.

When the current flowing through the coil L1 is stopped, the on / off control signal is used and the MOS transistor Q
21 is turned off. As a result, the current flowing through the coil L1 flows in the forward direction through the diode D22 and brings the Zener diode ZD23 into the reverse bias state. This reverse bias voltage is the Zener diode ZD2.
When the threshold voltage of 3 is exceeded, the energy stored in the coil L1 is regenerated by the power supply, and the current flowing through the coil L1 is stopped. At this time, the CPU 60 resets the bit corresponding to the coil L1 of the flag memory to "0".

As described above, the contactor driver of the present embodiment detects the current flowing through the coil L1 and performs feedback control so that the coil current matches the target current using the detected current value. The coil current can be maintained at a constant value (target current) even when changes due to temperature changes. If the target current is set to a value slightly larger than the minimum current value required for the contactor to be turned on, the contactor can be reliably turned on without wasting the current.

Next, the operation when a current is passed through a plurality of coils will be described. Here, an example in which a current is passed through the coils L1 and L2 to turn on the two contactors will be described.

CPU 60 turns on MOS transistors Q21 and Q31 using the on / off control signal. At this time, "1" is set to each of the bits corresponding to the coil L1 and the coil L2 of the flag memory.
Further, the CPU 60 uses the chopper signal to output the MOS transistor Q as in the case of passing the current only through the coil L1.
11 is turned on, and current is supplied to the coils L1 to L3.

At this time, the currents flowing through the coils L1 and L2 both flow through the resistor R51. That is, the resistance R5
The current flowing through 1 is the same as the current flowing through coil L1
It is the sum of the currents flowing through 2.

When the CPU 60 recognizes that the current is flowing through the two coils by referring to the flag memory, the CPU 60 outputs the chopper signal so that the current flowing through the resistor R51 becomes equal to twice the target current. Control the duty of. By such control, the coils L1 and L
A target current flows through each of the two.

As described above, the contactor driver according to the present embodiment does not have to be affected by temperature changes and the like.
The minimum current required to reliably turn on each contactor can be stably applied to one or more coils. Further, since the configuration is such that only one function is provided for each of the plurality of coils, the function of supplying the current to the plurality of coils, the function of detecting the current value flowing in the plurality of coils, and the function of controlling the current flowing in the plurality of coils are provided. The circuit scale can be reduced.

FIG. 3 is an operation flowchart of the CPU 60 which controls the duty of the chopper signal. CPU6
In 0, the following processing is repeated at predetermined intervals. In step S1, it is determined whether or not there is an instruction to newly turn on the contactors (increase the number of contactors to be turned on). This instruction is, for example, a user input or a software command.

If there is a new instruction to turn on the contactor, the contactor starting operation is started, and the "100 msec timer" is started in step S2.
Succeedingly, in a step S3, the duty of the chopper signal is set to 100%. This state is "100msec
It will continue until the "timer" times out. That is, the duty of the chopper signal is fixed to 100% for 100 msec after starting the contactor starting operation. Then, in step S15, the chopper signal is output to the chopper unit 10.

As described above, when the contactor is newly turned on, the duty of the chopper signal is set to 100% for a predetermined period and the current is continuously supplied from the power supply to the coils, and the current flowing through each coil is once sufficiently large. To As a result, each contact is turned on.

If there is no instruction to newly turn on the contactor in step S1, step S1
In step 1, it is checked whether the "100 msec timer" is in operation, and if it is in operation, the duty control process ends. On the other hand, if the "100 msec timer" is not in operation, the process proceeds to the contactor holding operation after step S12.

In step S12, the number of contactors in the ON state is recognized by referring to the flag memory. Then, the product of the number of contactors in the ON state and the target current per coil is calculated to obtain the total target current. Succeedingly, in a step S13, a duty output change amount ΔD is obtained by multiplying a difference between the total target current obtained in the step S12 and a current value notified from the current detecting section 50 by a predetermined coefficient K. Then, in step S14, a new duty is calculated by adding the duty output change amount ΔD to the current duty, and step S15
Then, the duty of the chopper signal is output as the calculated duty.

In the above embodiments, the characteristics of the coils are the same and the currents for turning on the contacts are also the same, but the present invention is not limited to this configuration. Not a thing. For example, the currents flowing through the coils L1 to L3 are 0.1 A and 0.2, respectively.
In the configuration in which the corresponding contact is turned on when A, 0.3 A or more, the ratio of the coil resistance of the coils L1 to L3 is set to 3: 2: 1, and as shown in FIG. The calculation formula for calculating the "total target current" may be changed in step S12 of the flowchart.

In the above embodiment, the method of controlling the coil current by picking up the contactor driver has been described, but the present invention is not limited to this, and other loads can be applied.

[0049]

The current flowing through the load is detected, and the detected current value is used to perform feedback control so that the load current matches the target current. Therefore, even when the resistance of the load changes due to temperature change or the like. The current can be maintained at a constant value (target current). Therefore, the waste of current can be suppressed.

Also, a function of supplying current to a plurality of loads,
Since only one function is provided for each of the plurality of loads and the function of detecting the current value flowing in the plurality of loads and the function of controlling the current flowing in the plurality of loads are provided, the circuit scale can be reduced.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a configuration diagram of a contactor driver adopted as an embodiment of a current control circuit of the present invention.

FIG. 3 is an operation flowchart of a CPU that controls the duty of a chopper signal.

FIG. 4 is a circuit diagram of a conventional contactor driver.

FIG. 5 is a graph showing an error due to temperature dependence of coil resistance and product variation.

[Explanation of symbols]

 1 Current Supply Means 2-1 to 2-n Switching Means 3-1 to 3-n Load 4 Current Detection Means 5 Control Means 10 Chopper Part 11, 12 MOS Transistor 13 Diodes 20, 30, 40, Individual Switch Part 21, 31 MOS transistor 22 Diode 23 Zener diode 50 Current detection part 51 Resistance 52 Amplifier 60 CPU L1-L3 coil

Claims (4)

[Claims] 1. In a current control circuit for supplying a current to a plurality of loads, a current supply means for supplying a current based on the current control signal to each load, and a current supply means provided for each load to receive an on / off control signal respectively. If the ON / OFF control signal is in the first state, the sum of the currents flowing in the loads and a plurality of switching means that operates so that the current flows in the load and in the second state the current does not flow in the load The current value detected by the current detecting means and the ON / OFF control signal transferred to the switching means provided for the load through which the current is caused to flow into the first state. And a control means for generating the current control signal based on the above. 2. The plurality of loads have the same characteristics as each other, and the control means generates the current control signal based on the number of loads that are supplying current and the current value detected by the current detection means. Claim 1 characterized by the above.
The current control circuit according to. 3. The current control signal is a chopper signal, and the control means changes the duty of the chopper signal according to the current value detected by the current detection means. The current control circuit described. 4. The control means sets a target current in advance for each load, and the current detection means detects the sum of the target currents set for the load that is flowing the current. The current control circuit according to claim 1, wherein the current control signal is generated based on a result of the comparison.