JPH0236798A - Overcurrent protecting circuit for dc motor - Google Patents

Abstract

PURPOSE:To easily protect the overcorrects of a plurality of DC motors by selecting the set value of an overcurrent detection limiter in response to the number of the driving motors. CONSTITUTION:Light emitting elements C1A-CnA of photocouplers are attached in parallel with DC motors M1-Mn. A driving motor number detector 5 receives the lights of the elements C1A-CnA, operates photodetectors C1A-CnA, and the number of connected resistors R1-Rn is varied in response to the number of the driving motors. Then, voltages input to comparators 6, 7 are varied, light emitting elements PAA, PBA, PCA emit lights in response to the number of the motors, the photodetectors PAB, PBB, PCB in an overcurrent detection limiter 4 are operated, and the set value of the overcurrent limit is varied.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overcurrent protection circuit for a DC motor when one of the motors is locked in a circuit using a plurality of DC (direct current) motors.

[Conventional technology]

As this type of overcurrent protection circuit, the one shown in FIG. 2 is known. In the figure, 1 is a drive circuit that drives a DC motor M1, 2 is a drive circuit that drives a DC motor M2, and 3 is a drive circuit that drives a DC motor M. Ql is a transistor that limits the current flowing to motors 1 to 3, and resistor R3C
The resistance value is the pace emitter voltage V of transistor Q2.
l! It is determined to be the value obtained by dividing □ by the short circuit setting current isc. That is, the drive circuit 1 detects an overcurrent when any of the DC motors 1 to 3 is locked using one setting value Lc that determines the current at which the overcurrent protection operation starts.
~3 are now protected.

Qt is conductive when overcurrent protection is activated, and the transistor Q is conductive.

is shut off or current limited. What is shown in FIG. 3 is a current boost circuit of the output short circuit protection circuit material.

[Problem to be solved by the invention]

However, in the conventional overcurrent protection circuit, the operating setting value is only one point, which causes a problem when the number of DC motors serving as a load changes. In other words, the DC motor is DC24V
The load current is 0.2A, and when locked, it is 1. OA or higher flow. This 1. When protecting a current higher than OA, if there is only one motor, use 1. The protection circuit can be activated by the OA, but when the number of loads increases to 3 to 4, even in normal conditions when 4 loads are ON, 0.8A flows and 1. OA
With the setting value, the circuit is cut off as an abnormality regardless of normality when the current increases at startup or due to variations. On the other hand, when there are 4 pieces, the setting value should be set to 0.8+ to prevent this kind of abnormal operation.
If 1.0 = 1.8A, then 1. OA no longer protects. Therefore, 4 motors cannot be operated, and the lock current of 1 motor is determined by 2~
Only three motors can be connected as loads.

As mentioned above, there is a drawback that the protection circuit cannot be operated when the number of motors changes if the set value is set at one point.

SUMMARY OF THE INVENTION An object of the present invention is to provide an overcurrent protection circuit for a DC motor that eliminates the above drawbacks and operates accurately even when the number of motors changes.

[Means to solve the problem]

The present invention includes a power supply circuit having a semiconductor element that supplies direct current from a power supply to a load, and a signal circuit that outputs a cutoff signal to the power supply circuit when a detected value reaches a selectable set value of the direct current. an overcurrent detection and restriction circuit; a drive motor number detection circuit that detects the number of DC motors being driven as the load; and a set value selection circuit that outputs a selection signal for selecting a set value to the signal circuit; The set value is selected based on the number detected by the drive motor number detection circuit, and when any of the drive motors is locked and the detected value reaches the set value, the current in the power supply circuit is limited.

[Effect]

According to this invention, a plurality of DC current setting values are provided and can be selected, and the setting value can be selected depending on the number of motors being driven, and when the detected current value reaches this setting value, the DC motor is Cut off or limit the power supply. In other words, in order to be able to protect with one simple protection circuit even when multiple motors are turned on or off, motor protection can be achieved completely by making the setting value follow the number of motors being driven. .

〔Example〕

FIG. 1 is a circuit diagram showing an embodiment of the present invention, in which the same reference numerals as in FIG. 2 indicate the same members.

4 is an overcurrent limiting circuit that detects and limits overcurrent, and T1
is a power transistor that supplies current to the first driver l and the nth driver n. A resistor R3, a resistor R52, and a resistor R are connected between the input power supply V in and the power transistor.
S3 is connected in series, and the series connection of transistor T2 and photocoupler photodetector PCB is
, and between the connection portion of resistor R2 and the human-powered RV h-. The series connection between the transistor T and the light receiving element PBB and the series connection between the transistor T4 and the light receiving element PAB are connected in parallel to the series connection between the transistor T7 and the light receiving element PCB.

5 is a drive motor number detection circuit for detecting the number of driven DC motors. A first driver 1, a second driver 2, and an nth driver n are provided as loads for the power transistor T1, and a DC motor M and a photocoupler light emitting element C+A are connected to the first driver 1. There is. Similarly, a DC motor M2 and a photocoupler light emitting element CzA are connected to the second driver 2, and a DC motor Mn and a photocoupler light emitting element CnA are connected to the first driver 1. Here, the n-th driver n indicates the n-th driver.

5 is a drive motor number detection circuit for detecting the number of driven DC motors. A light receiving element CIB that receives light from the photocoupler light emitting element CIA, a light receiving element C2B for the light emitting element C2A, a light receiving element CnB for the light emitting element CnA are connected in series, and a resistor RI+resistor Rz and an nth resistor Rn are connected in series.
and a resistor Rk are connected in series. Resistance R or resistance Rn
The resistors Rk and Rk have the same resistance value X, and the resistance value of the resistor Rx is nxx. Next, 6 and 7 are comparators consisting of operational amplifiers, and furthermore, PAA, PB
A and PCA are photocoupler light emitting elements, and resistance Rc=
A set value selection circuit is composed of Rj and diodes D and -C3.

In such a configuration, the human power source ■,,1 is DC.
When 24V is supplied, power is supplied from the first driver 1 to the first driver 1, and the DC motors M to Mn are driven. On the other hand, the photocoupler's light emitting elements CIA, C2A, Cn
A works. The above light emitting elements CIA, C2A,...
...The light receiving elements C1B, C2B,
...CnB operates. Input voltage of comparator 6■
1 changes depending on the number of DC motors that are turned on, and is the same when there is only one motor. 1=3 (71" x '1") = ゞ...
8, and when i=4, V l = V i.

So, i=5 When all are ON, VI=Vin becomes.

As above, the DC motor is ONL, depending on the number v
Since the value of l changes, only the light emitting element PAA operates when the number in the comparators 6 and 7 is 1 or 2, and the light emitting element PBA operates when the number is 3. Furthermore, when there are 4 to 5 pieces, the light emitting element PCA operates. On the other hand, resistance R3I, R3
2, R33 is determined as follows. That is, when one or two DC motors are turned on, SI. However, Is+ is the current value when one of the motors is locked.

When three DC motors are turned on, I and 3 are the current values when one of the three motors is locked.

When 4 to 5 DC motors are turned on, 5s Iss is the current value when one of the five motors is locked.

Resistor R5I according to equations (1), (2), and (3) above.

The values of R32 and R33 are determined.

When the light emitting element PCA is currently operating, that is, DC
When one of the motors locks and the current reaches the value of Iss when there are 4 or 5 motors, the transistor T2
is ONL, and the power transistor T is turned OFF.
Current is limited.

Also, when the light emitting element PBA is operating, the current is 131
When the current is reached, the transistor T3 is turned on, the power transistor T is turned off, and the current is limited.

Furthermore, when the light emitting element PAA is operating, the current I3
When the voltage reaches 1, the transistor T is turned on, the power transistor T1 is turned off, and the current is limited.

Note■8. ．． is the current when one motor is locked when there are n motors, I SN = I avX n + I pathIAV
is the load current of one motor, and I paak is the lock current of one motor.

In the above example I AV = 0.2A I , -*=
1. For OA, l5I=1.2A l53=1.6
A l5S=2. It is OA. As described above, regardless of the number of DC motors serving as a load, when one of the motors is locked, the current can be cut off or limited.

〔Effect of the invention〕

According to this invention, it is possible to select a current setting value suitable for the number of driven DC motors, and when one of the DC motors locks regardless of the number of driven motors, the detected value reaches the set value. As a result, the power supply circuit can be immediately restricted to protect the DC motor from overcurrent.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIGS. 2 and 3 are circuit diagrams showing conventional circuits. ■...First driver, 4...Overcurrent detection and restriction circuit, 5
... Drive motor number detection circuit, 6.7... Comparator,
8... Setting value selection circuit, CIA, C2A, CnA. PAA, PBA, PCA...photocoupler light emitting elements,
CIB, C2B, CnB, PAB, PBB, PCB
...Photocoupler light receiving element.

Claims (1)

[Claims] 1) A power supply circuit having a semiconductor element that supplies direct current from a power supply to a load, and a signal circuit that outputs a cutoff signal to the power supply circuit when a detected value reaches a selectable set value of the direct current. an overcurrent detection and restriction circuit; a drive motor number detection circuit that detects the number of DC motors being driven as the load; and a set value selection circuit that outputs a selection signal for selecting a set value to the signal circuit; The set value is selected based on the number detected by the drive motor number detection circuit, and when any of the drive motors is locked and the detected value reaches the set value, the current in the power supply circuit is limited. DC motor overcurrent protection circuit.