JPS5953792B2 - Direct current motor forward/reverse control circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a forward/reverse control circuit for a DC motor,
In particular, the present invention relates to a forward/reverse control circuit suitable for controlling a low-voltage, high-current DC motor with a small armature inductance and a small electrical time constant, such as a coreless DC motor.

Conventionally, the most common type of forward/reverse control circuit is a transistor bridge system as shown in FIG.

In the figure, 1 and 2 are PNP transistors, 3 and 4 are NPN transistors, and 5, 6, 7, and 8 are connected between the collectors and emitters of transistors 1, 2, 3, and 4 to prevent reverse voltage application. 9 is a DC power supply, and 10 is a DC motor serving as a load.

Here, by setting transistors 1 and 4 or 2 and 3 as a pair and turning on the transistors by flowing base current, it is possible to switch between forward and reverse rotation, and by driving with the rectangular wave base current, the transistors By performing a switching operation, pulse width modulation becomes possible.

When switching the rotation direction, the conventional method is to time the interruption time required for transistor switching, that is, the sum of the accumulation time and fall time, so that the base current of the transistor does not flow for a while after switching. It's a method. However, the disadvantage of this circuit is that the transistors are connected in a two-circuit series between the power supply and the DC motor when the DC motor is operating, so especially when the load is a low-voltage, high-current DC motor, the transistors can be connected as Darlington connections to connect the transistors to the HFE. However, since two Darlington connections are required, the saturation voltage becomes high and the power utilization rate deteriorates.

Furthermore, at present, transistors that can flow large currents are expensive, and conventional circuits that require a minimum of four transistors have drawbacks such as high cost and cost as forward/reverse control circuits. have.

The present invention has been made in view of the above-mentioned conventional drawbacks, and one embodiment of the present invention will be described below with reference to FIG. 2.

In the figure, 11 is a DC power supply, 12 and 13 are NPN transistors, and the collector is connected to the positive power supply to form an emitter follower.The base circuit includes a resistor 14, a capacitor 15, and a resistor 1, respectively.
A series circuit of 6 and a capacitor 17 is connected between the base and the negative power supply. The bases of the NPN transistors 12 and 13 are connected to the collectors of drive PNP transistors 18 and 19, respectively, and the emitters of the transistors 18 and 19 are connected to the positive power supply. 20 and 21 are thyristors, and resistors 22 and 23 are connected to the thyristors 20 and 2, respectively.
1 is connected in parallel between the anode and cathode of N
It is connected between the emitters of each of the PN transistors 12 and 13 and the negative power supply.

Here, NPN transistor 12 and thyristor 20
A DC motor 24 is connected with the connection point of the parallel circuit of the transistor 13, the thyristor 21, and the resistor 23 as P1, and the connection point of the parallel circuit of the transistor 13, the thyristor 21, and the resistor 23 as P2. Next, the operation will be explained.

Now, when a current is applied to the base of the PNP transistor 18 and the gate of the thyristor 21 to turn it on, a current flows to the DC motor 24 from P1 to P2, causing it to rotate forward, and vice versa.
When a current is applied to the gate of 0 to turn it on, DC motor 2
4, current flows from P2 to P1, causing reverse rotation. ;The turn-off of thyristors 20 and 21 here is NPN, respectively.
It depends on transistors 13 and 12, and it is possible to turn on and off the base current of the NPN transistor.Now, the base current is passed through the PNP transistor 18, turning on the rainbow, triggering the gate of the thyristor 21, and turning it on. Considering the current state, the DC motor 24
Current flows from P1 to P, causing forward rotation. In this state, the capacitor 15 is charged to approximately the DC power supply voltage through the resistor 14. The purpose of the resistor 14 here is to suppress the charging power to the capacitor 15. Next, when the base current of the PNP transistor 18 is cut off and turned off, the base current of the NPN transistor 142 is supplied by the charge charged in the capacitor 15, and its base potential is the same as that of the capacitor 1.
5 gradually decreases, and at a certain point, the NPN transistor 12 is turned off, and the operating current of the DC motor 24, that is, the anode current of the thyristor 21, is cut off.

At the same time, resistors 22 and 23 are used to apply a voltage in the opposite direction between the anode and cathode of thyristor 21 using the induced voltage of DC motor 24 even when NPN transistor 12 is turned off. This makes the turn-off easier. Here, even if the NPN transistor 12 or the PNP transistor 18 is turned off due to the discharge of the capacitor 15, the DC motor 24 is prevented from being cut off suddenly.
Surge voltage E when current is interrupted due to inductance L of
- This is to suppress Ldi/Dt so as not to exceed the maximum ratings of transistors and thyristors.

The situation described above when the PNP transistor 18 is turned from on to off is as shown in FIG. The waveforms here are a and b
The voltage waveforms other than and e are when the negative side of the power supply is viewed as a common terminal, and time is plotted on the horizontal axis. a is the base current to the PNP transistor 18, b is the gate trigger current to the thyristor 12, C is the terminal voltage of the capacitor 15, d is the base voltage of the NPN transistor 12, P1 is the emitter voltage of the NPN transistor 12, that is, the output terminal The voltage of P1, P2 is the anode voltage of the thyristor 21, that is, the voltage of the output terminal P2, and e is the anode current of the thyristor 21. As is clear from the figure, PN at point U
At the same time as the base current flows through the P transistor 18, the thyristor 21 is gate triggered, and the base current of the transistor is cut off at the V point.

Point W is the position where the charging potential of the capacitor 15 is lowered due to discharge due to the base current of the NPN transistor 12, and the emitter current of the transistor becomes zero, point X is the position where the thyristor 21 has completed turn-off, and point Y is the position. This represents the position where the DC motor, which had been rotating due to inertia, stops after the armature current is cut off by the transistor, and its induced voltage becomes zero. If the resistance values of the resistors 22 and 23 are the same, the reverse voltage applied between the anode and cathode of the thyristor 21 will be divided in half, and a voltage that is half the induced voltage of the DC motor will be applied.

Also, the time Toff from point W to point x is thyristor 2
The turn-off time is 1. The case where the DC motor 24 is rotated in the forward direction has been described above, but in the case of reverse rotation, each element, that is, the NPN transistor 12, the PNP transistor 18, the thyristor 21. The resistor 14 and capacitor 15 can be made to correspond to the NPN transistor 13, PNP transistor 19, thyristor 20, resistor 16, and capacitor 17, respectively, and the operations are exactly the same.

In addition, when switching between forward and reverse, it is necessary to set the timing in the same way as in the case of a conventional all-transistor bridge. If the base current of the PNP transistor is made into a rectangular waveform, it is possible to control a DC motor by pulse width modulation, similar to the conventional transistor bridge.

In the above configuration, it should be noted that when cutting off the current of the DC motor, in order to suppress the surge voltage and to gradually cut off the current so as not to cut it off suddenly, the control transistor is set in the active region during the cutoff operation. The operating point and type of transistor must be selected so that secondary breakdown does not occur in the transistor in this state.

As is clear from the above description, the forward/reverse control circuit of the present invention uses one transistor and a thyristor as the elements inserted between the power supply and the DC motor during operation of the DC motor, instead of two transistors in the case of a conventional transistor bridge. By reducing the number to one, a Darlington-connected transistor is required, especially when the load is a low-voltage, high-current DC motor, but since there is only one Darlington connection, the overall saturation voltage is lower than before. can be lowered,
This is advantageous in terms of the utilization rate of the power supply, and the heat generated by the control circuit can be reduced.

In addition, since the expensive large current transistor is replaced with a relatively inexpensive thyristor, excellent effects such as a significant cost reduction can be achieved.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a forward/reverse control circuit for a DC motor using a conventional transistor bridge, FIG. 2 is a circuit diagram showing an embodiment of the forward/reverse control circuit for a DC motor according to the present invention, and FIG.
3 is a current and voltage waveform diagram of each part in the circuit shown in the figure. FIG. 12, 13...Transistor 15, 17.
...Capacitor, 20,21...Thyristor 22,23...Resistor, 24...
...DC motor.

Claims (1)

[Claims] 1. A capacitor is connected to the base of the transistor connected as an emitter follower to supply the base current by discharge current even after the base drive current is cut off, and a thyristor and a resistor are connected between the emitter of the transistor and the other power supply. A forward/reverse control circuit for a direct current motor, comprising a pair of composite circuits in which parallel circuits of the above are connected, and a direct current motor is connected using the connection point between the emitter of the transistor and the thyristor as an output terminal.