JPH055458U - Piezoelectric element drive circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] In a transistor to which a large voltage for controlling the electric charge of a piezoelectric element is applied, when the collector-base is short-circuited, I connected to the base side.
It is prevented that the above-mentioned large voltage is applied to C to destroy it. [Structure] When the collector-base of the transistor TR4 is short-circuited, the voltage originally applied to the transistor TR4 appears at its base. When IC1 is directly connected to the base as in the conventional case, since a high voltage E is applied to this collector through the resistor 9, that voltage is IC.
It will be applied to the output terminal of 1. Then the above IC
1 is destroyed. Therefore, in this device, a diode D5 is interposed between the IC1 and the transistor TR4, and
Current is allowed to flow only from the C1 side to the base side. Therefore, even if a high voltage appears at the base of the transistor TR4, that voltage is not applied to the terminal of IC1.

Description

[Detailed description of the device]

[0001]

[Industrial application]

 The present invention relates to a drive circuit for a piezoelectric element incorporated in, for example, a piezoelectric dot printing apparatus, and more particularly to a technology for blocking and protecting the flow of electricity to the control circuit when the charge / discharge circuit for the piezoelectric element is damaged. It is a thing.

[0002]

[Prior Art]

 Conventionally, for example, a drive circuit for a piezoelectric element is known as disclosed in JP-A-2-131953. This circuit is an example applied to a dot printing device equipped with a piezoelectric print head. The piezoelectric print head has m print wires and m actuators each driving one print wire. In addition, m printing wires are arranged so as to be arranged close to each other on a straight line that intersects the printing direction. Each actuator has a laminated piezoelectric element formed by laminating a large number of piezoelectric elements as a driving source. And As shown in FIG. 3, the piezoelectric element driving circuit includes a large number of piezoelectric elements P constituting the laminated piezoelectric element of each of the above-mentioned m actuators, which are connected in parallel with each other. In the figure, one piezoelectric element P is shown as a representative, but the DC power source E, the transistor TR1, the coil L, and the piezoelectric element P are arranged in this order. The forward direction of the transistor TR1 is the same as the direction from the positive electrode side of the DC power source E toward the electrode side of the piezoelectric element P that should be the positive electrode. A diode D1 for bypassing the transistor TR1 in the reverse direction is connected to the transistor TR1. A transistor TR2 is connected between the DC power source E and the piezoelectric element P in parallel with the transistor TR1 and the coil L. The forward direction of the transistor TR2 is the same as the direction toward the electrode side of the DC power source E which should be the positive electrode, like TR1. Also connected to the transistor TR2 is a diode D2 which bypasses it in the opposite direction.

On the other hand, the terminal side of the coil L corresponding to the positive electrode of the DC power source E is grounded through the transistor TR3. The forward direction of the transistor TR3 is the same as the direction from the coil L to the ground. A diode D3 that bypasses the transistor TR3 in the reverse direction is connected to the transistor TR3. The piezoelectric element P is also connected to a diode D4 that bypasses it. The forward direction of the diode D4 is the same as the direction from the electrode side of the piezoelectric element P to be the negative electrode side to the electrode side to be the positive electrode side.

Each of the transistors TR1, TR2 and TR3 is controlled by a transistor controller 62. One controller 62 is provided for each of the m piezoelectric element drive circuits 60. The m control devices 62 are connected to a common main control device 64. Based on the print data output from the external host computer, the main controller 64 selects a print wire from which to print dots from m print wires each time the print head is moved in one pitch print direction. , And outputs a dot print command to each of the control devices 62 corresponding to the selected print wire.

The piezoelectric element drive circuit 60 that has received the dot printing command operates as follows. In the initial state, the transistors TR1, TR2 and TR3 are all in the OFF state, and the control device 62 switches the transistor TR1 to the ON state in response to the input of the dot print command. As a result, the electric charge of the DC power source E moves to the piezoelectric element P via the transistor TR1 and the coil L, the piezoelectric element P is charged, and its voltage VP rises. As the voltage rises, the print wire advances from the inoperative position toward the print sheet.

Shortly before the voltage VP of the piezoelectric element P becomes equal to the voltage of the DC power source E (hereinafter referred to as the power source voltage VE), the tip of the printing wire is pressed against the printing paper, and the printing paper is printed. Dots are printed. After the voltage VP of the piezoelectric element P becomes equal to the power source voltage VE, the potential of the diode D2 on the piezoelectric element P side becomes higher than the potential on the DC power source E side, so that the coil L moves toward the piezoelectric element P. A current returns to the coil L via the diode D2 and the transistor TR1, and electric energy is stored in the coil L. This extra electric energy is not stored in the piezoelectric element P, and the voltage VP of the piezoelectric element P does not become larger than the power source voltage VE. In this state, the electric energy of the piezoelectric element P is consumed by pressing the printing wire against the printing paper. When the voltage Vr of the piezoelectric element P decreases, the electric charge of the DC power source E moves to the piezoelectric element P through the transistor TR1 and the coil L. As a result, the voltage decrease is compensated for, and the voltage VP of the piezoelectric element P 2 becomes the power supply voltage VE. Kept in.

At a moment when the voltage VP of the piezoelectric element P becomes equal to the power supply voltage VE, the controller 62 switches the transistor TR1 to the off state and the transistor TR2 to the on state. As a result, a closed circuit including the coil L, the diode D2, the DC power source E and the diode D3 is formed, the electric energy of the coil L is returned to the DC power source E, and the electric energy of the electric energy of the coil L becomes zero. At the same time as the time when the electric energy of the coil L is completely returned to the DC power source E or at the time when the time elapses, the discharge of the piezoelectric element P is started when a predetermined time has elapsed from the input of the dot print command. That is, the control device 62 turns on the transistor TR 3. As a result, a closed circuit including the piezoelectric element P, the coil L, and the transistor TR 3 is formed, the electric energy of the piezoelectric element P moves to the coil L, and the piezoelectric element P is discharged.

[0008]

[Problems to be solved by the device]

 However, when the junction temperature inside the transistor TR3 exceeds the allowable value due to, for example, deterioration of heat dissipation, the transistor TR3 is short-circuited between the collector and the emitter. And in many cases, the transistor TR3 becomes defective. Normally, this is called "short mode", but at this time, the base-collector may occasionally become short-circuited. If the base collectors are short-circuited, the high voltage (for example, 100V) supplied from the DC power source E is applied to the collector of the transistor TR3 when the transistor TR1 or the like is turned on. This voltage is also applied to the base, and this voltage is also applied to the logic circuit of the transistor control device 62. If this happens, this logic circuit will be destroyed, making it impossible to drive the piezoelectric element, and there will be the problem that repair costs will be incurred due to damage to the logic circuit.

This invention was made in order to solve the above-mentioned problems, and even if the transistor should be in a defective state, electricity should not flow to the transistor control device, and the control device should be protected. At the same time, a piezoelectric element drive circuit that can minimize further damage is provided.

[0010]

[Means for Solving the Problems]

 In order to achieve this object, the piezoelectric element driving circuit of the present invention comprises a switching element provided in a charging / discharging circuit for supplying and removing electric energy to the piezoelectric element, and a switching element connected to the switching element. A control circuit for controlling on / off, and a rectifying element provided between the switching element and the control circuit in a direction for blocking a flow of electric energy from the switching element to the control circuit.

[0011]

[Action]

 According to the piezoelectric element drive circuit of the present invention having the above-described configuration, the piezoelectric element is driven by supplying or removing electric energy to or from the piezoelectric element via the charge / discharge circuit. Even if a switching element fails and a high voltage is applied to this switching element, its electrical energy flows to its control circuit in the reverse direction provided between the switching element and its control circuit. Is blocked by the shunt element of the. Therefore, damage to the control circuit of the switching element is avoided.

[0012]

【Example】

 An embodiment embodying the present invention will be described below with reference to the drawings. FIG. 1 shows an example in which the present invention is applied to a dot printing apparatus having the above-mentioned piezoelectric type print head. In FIG. 1, the same components as those described in the above-mentioned prior art are designated by the same reference numerals and the description thereof will be omitted.

Although the internal structure of the transistor control circuit 62 is illustrated in detail in this embodiment, open collector type inverters IC1, IC2 and IC3 connected to the base sides of the transistors TR1, TR2 and TR3 are provided. .. A resistor R1, a transistor TR4 and a diode D5 are serially connected in series from the transistor TR1 side between the transistor TR1 and the inverter IC1. The diode D5 is then connected in reverse. A resistor R2, a transistor TR5 and a diode D6 are serially connected from the transistor TR2 side between the transistor TR2 and the inverter IC2. The diode D 6 is also connected in the opposite direction. The emitters of the transistors TR4 and TR5 are both grounded, the connection line between the transistor TR4 and the diode D5 and the ground line of the transistor TR4, and the connection line between the transistor TR5 and the diode D6. Resistors R3 and R4 are provided between the transistor and the ground wire of the transistor TR5. Low voltage (about 5 V) power supplies E1 and E2 are connected between the diode D5 and the inverter IC1 and between the diode D6 and the inverter IC2 through resistors R5 and R6.

Now, when an "L" level signal is input to the inverter IC1, nothing is output to the output side because the inverter IC1 is an open collector. Therefore, a current flows from the power source E1 through the resistor R5, the diode D5, and the transistor TR4 in this order, and the base current flows through the transistor TR4, so that the transistor TR4 is turned on. Then, a current flows from the power source E in the order of the transistor TR1, the resistor R1, and the transistor TR4, and the base current flows through the transistor TR1, so that the transistor TR4 is turned on.

On the other hand, when the "H" level signal is input to the inverter IC1, the inverter IC1 outputs the "L" level. Then, a current flows from the power source E1 in the order of the resistor R5 and the inverter IC1, and the potential at the junction between the output side of the inverter IC1 and the resistor R5 becomes zero. Then, the base current cannot be applied to the transistor TR4 from the junction via the diode D5. The minority carriers remaining inside the transistor TR4 are removed by the resistor R3, so that the transistor TR4 is turned off. When the transistor TR4 is turned off, the base current does not flow through the transistor TR1, so minority carriers remaining inside the transistor TR1 are removed by the resistor R9, and the transistor TR1 is turned off.

On the other hand, a diode D7 is also connected in reverse series between the transistor TR3 and the inverter IC3. A resistor R7 is provided between the connection line between the transistor TR3 and the diode D7 and the ground line of the transistor TR3, and a low voltage (about 5V) power supply is provided between the diode D7 and the inverter IC3. E3 is connected through resistor R8. Therefore, the potential between the transistor TR3 and the diode D7 is dropped to the ground level, and the potential of the diode D7 is also kept in the forward direction, so that the electric charge remaining on the transistor TR3 side of the diode D7 is grounded via the ground line. It is supposed to be discharged.

The inverters IC1, IC2 and IC3 are connected to the main controller 64, respectively. Resistors R9 and R10 are also provided between the base sides of the transistors TR1 and TR2 and the positive side of the direct current power source E. This is to supply a forward bias voltage to the transistors TR1 and TR2.

In the piezoelectric element drive circuit configured as described above, however, the charge / discharge driving control of the piezoelectric element is as described in the above-mentioned Japanese Patent Laid-Open No. 2-131953, so it is omitted here. For example, suppose that the transistor TR3 becomes defective in the short mode between the collector and the base for some reason. In that case, when the transistor TR1 is turned on, a power supply voltage (100V in this embodiment) is generated at the base of the transistor TR3. However, in this case, the diode D7 blocks the flow of electricity from the transistor TR3 to the inverter IC3, so that no high voltage is applied to the inverter IC3.

Similarly, suppose that the collector-base of the transistor TR4 becomes defective in the short mode, but in that case as well, the diode D5 blocks the flow of electricity from the transistor TR4 to the inverter IC1 and the inverter IC1 does not. No high voltage is applied. Even when the transistor TR5 becomes defective, the diode D6 blocks the flow of electricity from the transistor TR5 to the inverter IC2, and a high voltage is not applied to the inverter IC1.

In the above-mentioned embodiment, the example of the so-called bipolar transistor has been described, but the same can be said for the field effect transistor (FET). FIG. 2 shows a state in which an FET is used instead of the transistor TR3. In this figure, the above-mentioned inverter IC3 is connected to the gate of the FET, but the above-mentioned diode D7 is also provided in the reverse direction in the connection circuit.

However, if the drain and source of this FET are short-circuited and the gate is also in a short state, when the above-mentioned transistor TR1 (not shown) is turned on, the above-mentioned DC power source E is applied to the drain of the FET. Although a high voltage supplied from the FET is applied to the gate of the FET, the diode D7 blocks the flow of electricity from the FET to the inverter IC3, and the high voltage is not applied to the inverter IC3.

[0022]

[Effect of the device]

 As is apparent from the above description, according to the piezoelectric element drive circuit of the present invention, even if the switching element becomes defective, the damage will not spread further. Therefore, it is easy to repair due to a failure of the switching element, and it is possible to avoid the situation where the entire device is discarded. It is suitable for piezoelectric dot printing devices.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a piezoelectric element driving circuit according to an embodiment of the present invention.

FIG. 2 is a circuit diagram of a piezoelectric element driving circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram of a conventional known piezoelectric element drive circuit.

[Explanation of symbols]

 TR1 to TR5 Transistor (Switching element) D1 to D7 Diode (Rectifying element) E DC power supply L Coil P Piezoelectric element IC1 Inverter IC2 Inverter IC3 Inverter FET Field effect transistor

Claims (1)

Claims for utility model registration 1. A switching element provided in a charging / discharging circuit for supplying and removing electric energy to and from a piezoelectric element; and a switching element connected to the switching element to control ON / OFF of the switching element. And a rectifying element that is provided between the switching element and the control circuit in a direction that prevents a flow of electrical energy from the switching element to the control circuit.