JPH0786031A - Electromagnet drive circuit - Google Patents

Abstract

PURPOSE:To provide an electromagnet drive circuit of a structure, wherein a fly-back current can be absorbed in a low-cost circuit constitution. CONSTITUTION:The side of an exciting coil LM of a first series circuit, which consists of the exciting coil LM and a transistor TR1, is connected to a first power terminal GND and the side of the transistor TR1 is connected to a second power terminal V2. Moreover, a diode D1 for fly-back current absorption is connected between a terminal Va, which is located at the connection point of the coil LM with the transistor TR1, and a third power terminal V3 to form a second series circuit, which consists of the diode D1 and the coil LM, and the diode D1 is connected between the terminals GND and V3 in the opposite direction to the direction of the terminal GND. A fly-back current, which is generated in the coil LM when the transistor TR1 is turned on to make a current Ia for drive flow through the coil LM and the transistor TR1 is turned off, is made to flow through the terminal V3 via the diode D1 and is made to absorb in the diode D1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnet driving circuit.

[0002]

2. Description of the Related Art Conventionally, an electromagnet has been used to drive a printing pin or the like of an impact printer, and an electromagnet drive circuit for driving these has an opening / closing element provided in a power supply line for supplying a drive current to an exciting coil. The drive of the exciting coil is controlled by opening / closing the open / close element. In such a device, in order to improve the responsiveness of the electromagnet drive, the applied voltage is increased and the drive current value is increased in order to accelerate the rise of the drive current in the initial stage of drive.
If the drive current value is increased, the flyback current flowing through the exciting coil becomes large when the switching element is closed, and the switching element may be destroyed. In order to avoid such destruction of the switching element, a flyback current absorption circuit composed of a Zener diode or the like is connected in parallel to the exciting coil, and the flyback current flowing in the exciting coil is configured to be absorbed by the flyback current absorbing circuit. There is. Further, in order to suppress the wasteful energy consumption of the electromagnet, the drive current is set to flow a large value in the initial stage of driving and then supply a smaller value to maintain the driving state to the exciting coil. The one is disclosed in Japanese Patent Publication No. 62-26162. As shown in FIG. 5, the configuration is such that a flyback current absorption circuit f formed by connecting a diode d in series to a parallel circuit formed by connecting a zener diode zd and a transistor tr2 in parallel is used as an exciting coil l.
Are connected in parallel. This is because the driving current value is increased at the initial stage of driving, so that the transistor t is kept for a fixed time period at the initial stage of driving.
A drive current is passed through the exciting coil 1 by opening r1. After this,
In order to pass a drive current to the extent that the drive state is maintained, the transistor tr2 is closed and the transistor tr2 is opened, and the flyback current is fed back by the exciting coil l to gradually reduce the drive current. Then, the transistor tr2 is closed to absorb the flyback current by the zener diode zd, and the current flowing through the exciting coil is sharply reduced to end the driving.

[0003]

In this configuration, since the transistor tr2 is used for returning the flyback current due to the closing of the transistor tr1 to the exciting coil l, the circuit configuration becomes complicated.
This will increase the cost.

Therefore, an object of the present invention is to provide an electromagnet drive circuit capable of absorbing flyback current with an inexpensive circuit configuration.

[0005]

A first series circuit composed of an exciting coil and a switching element is connected to the exciting coil side to a first power supply terminal and to the switching element side to a second power supply terminal. A rectifying element for absorbing flyback current is connected between the connection point between the exciting coil and the switching element and the third power supply terminal to connect between the first power supply terminal and the third power supply terminal. A second series circuit including the exciting coil and the rectifying element is formed. Further, the rectifying element achieves the above object by connecting the first power supply terminal and the third power supply terminal in opposite directions.

Here, a second switching element, which is opened / closed complementarily to the opening / closing of the switching element, is connected between the connection point between the exciting coil and the switching element and the second power supply terminal. It is preferable.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is an electric circuit diagram showing the configuration of this example, in which LM is an exciting coil and RM is its internal resistance. TR1 is a transistor as a switching element, the collector of which is connected to the terminal Va of the exciting coil LM, and forms a first series circuit together with the exciting coil LM. Here, the terminal Va is a connection point.

TR2 is a transistor, P1 is an inverter, and R1 to R4 are resistors. The transistor TR2 has its emitter connected to the constant voltage source Vcc, its collector connected to the base of the transistor TR1, and its base connected to the inverter P1. Inverter P
A control signal for controlling the opening / closing operation of the transistor TR1 is input to the first terminal S1.

GND, V2, and V3 are a first power source terminal, a second power source terminal, and a third power source terminal, respectively, and have potentials of 0v, -40v, and + 40v, respectively. Here, the first power supply terminal GND is connected to the exciting coil LM side of the first series circuit, and the second power supply terminal V2
Is connected to the emitter of the transistor TR1. Further, the third power supply terminal V3 is connected to the terminal Va via a diode D1 as a rectifying element for absorbing flyback current, and is connected to the first power supply terminal GND from the exciting coil LM and the diode D1. A second series circuit is formed.

The operation of the present example configured as above will be described with reference to the timing charts shown in FIGS.

First, as shown by S1 in FIG. 2, the control signal "1" is input to the terminal S1 of the inverter P1 during the initial driving time t0. Upon receiving the inverted output of the inverter P1, the transistor TR2 is turned on and the transistor TR2 is turned on.
Turn 1 on. As a result, one terminal Va of the exciting coil LM becomes the potential -40v of the second power supply terminal V2,
As a result, the drive current Ia as shown by Ia in FIG. 2 begins to flow in the exciting coil LM. Here, the time t0 is a time until the driving current value for sufficiently exciting the exciting coil LM is reached, and is set appropriately.

Next, the control signal "0" is input to the inverter P1 for the time t1 following the time t0. Inverter P1
Transistor TR2 is turned off in response to the inverted output of
The transistor TR1 is turned off. Second power supply terminal V2
Power supply to the exciting coil LM is interrupted and the flyback current generated in the exciting coil LM passes through the diode D1
Of the drive current Ia flowing through the exciting coil LM.
Decreases sharply as shown by Ia in FIG.

Thereafter, the control signals "1" and "0" are alternately input at each time t2 to t4 following the time t1 to turn on / off the transistor TR1. As a result, the terminal Va is alternately touched by the potentials of the power supply terminals V2 and V3, as shown by Va in FIG. 2, and the average value of the drive current Ia flowing through the exciting coil LM is held at an appropriate value. Then, by fixing the control signal to "0", the flyback current generated in the exciting coil LM passes through the diode D1 and the third power supply terminal V3.
Drive current I flowing to the exciting coil LM
a rapidly decreases, and the driving of the exciting coil LM ends.

As described above, the flyback current generated in the exciting coil LM flows into the third power supply terminal V3 via the diode D1 and is absorbed. Therefore, the flyback current is made extremely simple without using a switching element. Can be sharply reduced. In other words, it is possible to control the driving power supply operation to the exciting coil LM and the flyback current absorption operation with one switching element, and the circuit can be simplified.

Further, by switching the transistor TR1, it is possible to suppress the excess current flowing in the exciting coil, and it is possible to suppress unnecessary power consumption.

Next, another embodiment of the present invention will be described. In this example, the power supply of the first series circuit is intermittently cut off when the drive current flowing in the excitation coil reaches an appropriate value required for excitation, and the flyback current generated at this time is fed back to obtain a feedback circuit. The drive current value can be held at an appropriate value with good energy efficiency. As shown in FIG. 3, the configuration is the same as that of the above-described embodiment, but a diode D2 as a second rectifying element and a second switching element are provided between the terminal Va and the first power supply terminal GND. Is connected to the transistor TR3. A buffer P2 is connected to the base of the transistor TR3.

Next, the operation of this example will be described with reference to the timing chart of FIG. As shown at S1 in FIG. 4, the control signal "1" is input to the terminal S1 of the inverter P1 during the initial driving time t0. As a result, the transistor TR1 is turned on, and the exciting coil LM is turned on as shown in FIG.
The drive current Ia flows like Ia.

Next, as in the above embodiment, the control signal "0" is input to the terminal S1 at each time t1 following the time t0,
The transistor TR1 is turned off. On the other hand, in synchronization with the input of the control signal "0" to the terminal S1, the buffer P2
The control signal "1" is input to the terminal S2 of the. As a result, the transistor TR3 is turned on and the transistor T3 is turned on.
The flyback current generated when R1 is turned off passes through the diode D2 and the transistor TR3 to the first
The drive current Ia flowing to the power supply terminal GND of the above and flowing to the exciting coil LM is slightly decreased.

Thereafter, the control signals "1" and "0" are alternately input to the terminal S1 at each time t2 to t4 following the time t1.
The transistor TR1 is turned on / off. In sync with this,
The control signals "0" and "1" are alternately input to the terminal S2 to turn on / off the transistor TR3 complementarily to the transistor TR1, and the flywheel is supplied each time the power supply from the second power supply terminal V2 is cut off. A back current is passed to the terminal GND through the diode D2 and the transistor TR3. As a result, the drive current Ia flowing through the exciting coil LM is held at an appropriate value as shown by Ia in FIG. After this,
Set the control signal input to terminals S1 and S2 to "0".
Fixed to. As a result, the flyback current flows through the diode D1 to the third power supply terminal V3. Therefore, the driving current Ia flowing through the exciting coil LM is equal to Ia in FIG.
As shown in, the coil is drastically reduced and driving of the coil is completed.

As described above, the flyback current caused by the intermittent opening and closing of the transistor TR1 is fed back to the exciting coil LM, so that the energy use efficiency is further improved.

In each of the above embodiments, the first power supply terminal GN
The potentials of D, the second power supply terminal V2, and the third power supply terminal V3 are set to 0v, -40v, and + 40v, respectively, but the present invention is not limited to this. For example, the first power supply terminal GND, the second
Of the diode D1 with the potentials of the power supply terminal V2 and the third power supply terminal V3 of 0 V, +40 V, and -40 V, respectively.
, D2 and each transistor are connected in the opposite direction to the above-mentioned respective embodiments, and the second power supply terminal V2 to the first power supply terminal G are connected.
The drive current may be passed in the direction toward ND to drive the exciting coil LM, and the flyback current may be absorbed by the third power supply terminal of -40v, which can be variously changed.

[0022]

According to the present invention, since the flyback current can be absorbed without using the switching element, it is possible to provide an electromagnet drive circuit having an inexpensive circuit configuration.

Further, the flyback current is fed back to the exciting coil by the second opening / closing element which is opened / closed complementarily to the first opening / closing element, whereby the energy utilization efficiency is improved.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a timing chart for explaining the operation of the embodiment of FIG.

FIG. 3 is an electric circuit diagram showing the configuration of another embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the embodiment of FIG.

FIG. 5 is an electric circuit diagram showing a configuration of a conventional electromagnet drive circuit.

[Explanation of symbols]

 GND 1st power supply terminal V2 2nd power supply terminal V3 3rd power supply terminal LM Excitation coil TR1 transistor (switch element) D1 diode (rectifier element) TR3 transistor (second switch element)

Claims (2)

[Claims] 1. A first series circuit comprising an exciting coil and an opening / closing element, wherein the exciting coil side is connected to a first power supply terminal and the opening / closing element side is connected to a second power supply terminal. A flyback current absorbing rectifying element is connected between a connection point between the switching element and the third power supply terminal, and the exciting coil and the third power supply terminal are connected between the first power supply terminal and the third power supply terminal. An electromagnet drive circuit, wherein a second series circuit including a rectifying element is formed, and the rectifying element is connected in a reverse direction between a first power supply terminal and a third power supply terminal. 2. A second switching element, which is opened / closed complementarily to the opening / closing of the switching element, is connected between a connection point between the excitation coil and the switching element and a second power supply terminal. The electromagnet drive circuit according to claim 1, wherein the electromagnet drive circuit is provided.