JP2001026109A - Capacitive load driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a low power consumption and restrain heat generation of a driving element by utilizing the capasitive load. SOLUTION: In driving a capacitive load C1, capacitors C2, C3 are charged, utilizing the current change in mutual inductors TX1, TX2. By supplying the charge accumulated in the C2 to the load in a subsequent C1 charging process, the charge supply amount from a power source is reduced. Furthermore, by returning the charge to the power source by the C3 electric discharge in a subsequent C1 discharging process, the power can be saved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitive load driving circuit for driving a capacitive load such as a driving circuit for an ink jet printer head using a piezoelectric element. More specifically, the present invention relates to a technique for reducing power consumption when viewed from a power supply side in this drive circuit.

[0002]

2. Description of the Related Art In a drive circuit of an ink jet printer head using a piezoelectric element, a trapezoidal pulse voltage is applied to a piezoelectric element of an ink jet nozzle to perform suction and discharge of ink by a change in volume in an ink chamber. It is configured. Conventionally, as such a drive circuit, a current amplifier circuit in which two transistors Q1 and Q2 are push-pull connected as shown in FIG. 4 is used. In this figure,
C1 is a capacitive load, and the piezoelectric element is considered to be a capacitive load. In this current amplification circuit, a capacitive load (from a power supply via one transistor Q1) is provided based on a trapezoidal waveform pulse voltage (input) output from a trapezoidal waveform voltage generation circuit (not shown) configured in the preceding stage. Piezoelectric element) C1 is charged and the other transistor Q2 is charged.
Discharge from the capacitive load to the ground via.
FIG. 5 shows the voltage waveform and the current waveform at this time.

[0003]

However, the conventional driving circuit has a problem that the power consumption is large because all the electric charges required for charging the capacitive load are supplied from the power supply. Since most of the power is consumed by the transistors and becomes heat, there is also a problem that a large heat radiating device is required to prevent the breakdown of the transistors.

[0004] In view of the above problems, the object of the present invention is to:
It is an object of the present invention to provide a capacitive load driving circuit capable of reducing power consumption when viewed from a power supply and suppressing heat generation of a driving element by utilizing the fact that a load is capacitive.

[0005]

According to the present invention, there is provided a capacitive load driving circuit for repeatedly charging and discharging a capacitive load based on an input signal.
When the charging load drive element charges a capacitive load, a charging charge supply source that selects a power supply or a charging capacitor charged to a potential between the power supply and the ground as a charge supply source. A switching circuit, or, when the discharge load driving element discharges from the capacitive load, a discharge charge inflow destination switching circuit for selecting a ground or a discharge capacitor as a discharge destination, or
In the configuration having both the charging charge supply source switching circuit and the discharge charge inflow destination switching circuit and including the charging charge supply source switching circuit, at the time of charging, the potential of the capacitive load is:
When the potential is lower than the potential of the charging capacitor, the charge is supplied from the charging capacitor through the charging load driving element,
When the potential of the capacitive load is higher than the potential of the charging capacitor, the charge is supplied from the power supply, and in the configuration having the discharge charge inflow destination switching circuit, the potential of the capacitive load is set at the time of discharging. When the potential is higher than the discharging capacitor, the charge is discharged from the load through the discharging load driving element to the discharging capacitor. When the potential of the capacitive load is lower than the potential of the capacitor, the discharging is performed to the ground. The electric charge is discharged through the discharge load driving element.

Further, when a charging charge supply source switching circuit is provided, the primary side of the charging mutual inductance is inserted between the power supply and the charging charge supply source switching circuit, and the charging charge supply source switching circuit is provided. When a current flows from the power supply, the charging capacitor connected to the secondary side of the mutual inductance for charging is charged, a voltage is also generated on the primary side, and a voltage lower than the power supply voltage is applied to the charge charge supply source switching circuit. In addition, the heat generated in the charge charge source switching circuit is small. That is, when there is no mutual inductance for charging, part of the energy that has been converted into heat is stored as energy of the electric field, and this energy is used during the subsequent charging operation.

[0007] In this way, the energy supplied from the power supply during charging is smaller than in the past, and the heat generated by the charging load driving element is reduced. Even when a discharge charge inflow destination switching circuit is provided, the same effect as in charging can be obtained by inserting a discharge mutual inductance between the discharge charge inflow destination switching circuit and the ground.

Further, when the charge charge supply source switching circuit and the discharge charge inflow destination switching circuit are used together, the mutual inductance inserted between the charge charge supply source switching circuit and the power supply is connected to the discharge capacitor, Similar effects can be obtained by connecting the mutual inductance inserted between the charge inflow destination switching circuit and the ground to the charging capacitor.

As described above, in the present invention, by using mutual inductance, a part of the energy that would otherwise be turned into heat is stored in the capacitor as the energy of the electric field and is used later to reduce the current flowing from the power supply. It saves power and reduces heat generation.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a circuit diagram of a first embodiment of a capacitive load driving circuit according to the first aspect of the present invention.

C1 is a capacitive load. The emitter of the transistor Q1 is connected to C1 in order to flow a current for charging C1, and the emitter of the transistor Q2 is connected to C1 in order to flow a current for discharging from C1. Have been. To the bases of the transistors Q1 and Q2, a trapezoidal pulse voltage output from a trapezoidal wave voltage generating circuit (not shown) configured in the preceding stage is applied. C2 and C3 are capacitors, and part of the current charging the load C1 is supplied from the capacitor C2, and part of the current discharged from the load C1 flows into the capacitor C3. C2 and C3 are sufficiently larger than the capacitance of the load, for example, five times or more the load.

[0013] Zener diode D3, capacitor C
4, the resistor R1, the transistor Q5, the diode D5, the transistor Q3, and the diode D1 constitute a charge charge supply source switching circuit. The Zener diode D4, the capacitor C5, the resistor R2, the transistor Q6, the diode D6, the transistor Q4, and the diode D2 constitute a discharge charge inflow destination switching circuit.

TX1 is a mutual inductor. The primary side is connected to the power supply and the collector of Q3, and the secondary side is connected to the capacitor C2 through the ground and the diode D3. The power supply is, for example, about 40V. TX2 is a mutual inductor having a primary side connected to the ground and the collector of Q4, and a secondary side connected to a capacitor C3 through a power supply and a diode D4.

FIG. 2 is a diagram showing an output voltage and an output current in the drive circuit of the present embodiment. FIG. 2 shows a process of charging the load. In FIG. 2, the load driving potential is an output potential for driving the load C1, and indicates the potential of the emitter of Q1 and the emitter of Q2. The load drive potential is substantially the same as the input terminal in FIG. In FIG. 2, the potential of C2 is the potential of the terminal of C2 that is not connected to the ground, that is, the potential of the anode of D1 and the potential of the cathode of D3. In FIG. 2, i1 is the current i1 shown in FIG. I2 in FIG.
This is the current i2 indicated by.

In FIG. 2, charging starts at T1.
The reason why the current does not immediately rise between T1 and T2 is that there is resistance or inductance in the connection between the loads C1 and Q1. Here, it is assumed that C2 is already charged and has a certain potential (see FIG.
This state occurs when there are several similar pulses before the pulse of (1). During the period from T1 to T4, the output potential is lower than the potential of C2. Q1 causes an emitter current and thus a collector current to flow as the base potential rises, and most of the charge at this time is supplied from C2 through D1. This is controlled by the charge-supply-source switching circuit, but the behavior of the charge-supply-source switching circuit will be described.

The base potential of Q5 is determined by R1 and D3.
The voltage is higher than the input potential by the amount of the three intrinsic zener voltages. The Zener voltage is about 4V.

Since the emitter potential of Q5 is lower than the base potential by the base-emitter voltage (about 0.6 V), the potential of the emitter of Q5 and thus the anode of D5 is about 3.4 V higher than the input potential ( 4V-0.6V). If the potential of the emitter of Q3 is about 1.2 V lower than the anode potential of D5 (the forward voltage of D5 and the base voltage of Q3)
(The sum of the voltages between the emitters) is low, that is, "the potential of the emitter of Q3 is about 2.2 V (3.4 V-1.2 V) from the input.
If "high" (state 1), a forward current flows through D5 and a base current flows through Q3.

By the way, the state 1 is not set between the times T1 and T3 (the time T3 is a time when the input potential becomes about 2.2 V lower than the potential of C2). Because, between T1 and T3, if the potential of the input is low and in state 1, the potential of the emitter of Q3 is only 2.2V higher than the input, so that the potential of C2 is
Low potential, so the diode D1 is ON
This is because the potential of the emitter of Q3 is lower than the potential of C2 by the forward voltage of D1. That is, during the period from T1 to T3, the emitter potential of Q3, that is, the collector potential of Q1 is lower than the potential of C2 by the forward voltage of D1. Therefore, since the state 1 does not occur, Q3 is OFF, and the current i2 flowing through Q3 does not flow, and only i1 flowing through D1 flows.

Next, the operation of the charge charge supply source switching circuit between T3 and T4 will be described. At T3, the above state 1
Holds, Q3 starts to flow current, but D1 is not reverse-biased and flows current. However, as the potential of the input rises, the potential of the emitter of Q3 rises, the voltage across the terminals of D1 decreases, the current i1 flowing through D1 decreases, and the current i2 increases to compensate for it.

Next, the operation of the charge charge supply source switching circuit from T4 to T6 will be described. At T4, the voltage between the terminals of D1 becomes 0 V, and after T3, reverse bias is applied. Therefore, D1 does not pass current, and i1 is 0. Since D1 does not conduct current, all current flowing to load C1 is supplied from power supply VCC through Q3. At T5, the rise of the input potential ends, and no current flows at T6. The reason that the current does not immediately become zero between T5 and T6 is that
This is because the connection between the load C1 and Q1 has resistance and inductance. During this time, the collector potential of Q1, ie, Q1
The emitter potential of No. 3 rises at about 2.2 V higher than the input.

Next, the effect of TX1 will be described.

The current i2 increases between T3 and T4 in FIG. This current flows on the primary side of the mutual inductor TX1, but since the time change rate of i2 is not zero, TX1
Causes a potential difference at both ends on the primary side. For this reason, the potential of the collector of Q3 becomes lower than the potential of the power supply VCC. Therefore, the voltage from the collector of Q3 to the emitter of Q1 is lower than when there is no TX1, and this voltage and i2
The loss represented by the product of
Regardless of whether TX1 is present or not, since the same i2 flows when viewed from the power supply, the same is true in terms of the power supplied by the power supply. However, when TX1 is present, heat is generated when TX1 is not present. It is temporarily converted to magnetic field energy. If the potential of the terminal with a black dot on the primary side of TX1 is lower than that of the terminal without a black dot, make sure that the terminal with a black dot on the secondary side has a lower potential than the terminal without a black dot on the secondary side. It is wound. Therefore, in the section from T3 to T4, the anode of D3 is at a potential lower than the ground, so that no current flows through D3.

Since the time change rate of i2 is 0 from T4 to T6 in FIG. 2, no voltage is generated on the primary side and the secondary side of TX1.

From T5 to T6 in FIG. 2, the current i2 decreases. For this reason, the potential on the primary side of the TX1 is higher than that of the terminal without the terminal marked with ●. Then, the potential of the terminal with ● on the secondary side is higher than that of the terminal without ● on the secondary side, and a potential difference corresponding to the winding ratio between the primary side and the secondary side also occurs on the secondary side. When this potential difference is higher than the potential of C2, D3 is turned ON, i5 flows, and C2 is charged. If the number of turns on the secondary side is sufficiently larger than the number of turns on the primary side, most of the energy of the magnetic field is C2
Is converted as electric field energy. The charge thus stored in C2 is used in the subsequent charging.

As described above, when C2 is charged, not only the power supply but also C2 is charged when the load C1 is charged.
Since power is also supplied to C1, the time during which the power supply supplies the current is shorter than in the past as shown in FIG. 2 (in the past, the power supply supplied the sum of i1 and i2). Become.

A case in which C2, which has been reserved previously, has not been charged will be described. In this case, there is no period corresponding to T1 to T4 in FIG. 2 and the current is supplied from the power supply VCC from the beginning. At this time, the energy of the magnetic field is stored in TX1 and, as described above, is later stored in C2. Electric charge is stored. Therefore, as the charge and discharge of the load C1 are repeated several times, the potential of C2 increases and eventually reaches a stable potential.

The operation at the time of charging the load C1 has been described above. The same operation is performed at the time of discharging the load C1. However,
The effect of power saving at the time of discharge is as follows.
This is due to the operation of flowing the electric charge stored in 3 having a potential lower than the power supply VCC to the power supply VCC.

As described above, in this embodiment, power saving is achieved by converting a part of energy which has conventionally been heat into electric field energy by using mutual inductance.

The power saving mechanism of the present invention may be used only on the charging side or only on the discharging side.

The TX1 and TX2 are connected to the anode of D3 on the secondary side of TX2, the other terminal is connected to the ground, and the terminal marked with ● on the secondary side of TX1. If it is connected to the power supply and the other terminal is connected to the cathode of D4, only the timing of charging C2 and C3 is different,
An effect similar to the above is obtained.

(Embodiment 2) FIG. 3 is a circuit diagram of a second embodiment of the present invention. Compared with FIG. 1, capacitors C6 and C7 are added as components. C6 and C7
Are connected in series between the power supply VCC and the ground.
In FIG. 1, one of the terminals of C2 is connected to the ground, but in the present embodiment, one of the terminals of C2 is connected to a connection Node1 where C6 and C7 are connected. In FIG. 1, one of the terminals of C3 is connected to the power supply VCC, but in the present embodiment, the terminal of C3 is also connected to Node1. It is desirable that C6 and C7 have a larger capacity than C2 and C3.

FIG. 2 shows the output voltage and the output current in the drive circuit according to the present embodiment, as in the first embodiment.

The operation of the circuit shown in FIG. 3 will be described. As described later, connection Nod connecting C6 and C7
e1 is at a substantially constant potential between power supply VCC and ground during operation. During operation, C2 and C3 are charged as in the first embodiment, and the terminals connected to D1 of C2 are:
The terminal connected to D2 of C3 at a higher potential than Node1 has a lower potential than Node1.

In this embodiment, as in the first embodiment,
Between T5 and T6, C2 is charged. One terminal of C2 is connected to Node1, and the potential of the anode of D1 is set to the same level as that of the first embodiment. The potential difference may be smaller than in the first embodiment. Therefore, the secondary side of TX1 does not need to generate a large voltage as in the first embodiment. In particular, in the first embodiment, TX1 is 1
Although a larger voltage is generated on the secondary side than on the secondary side, a large voltage is generated on the primary side of TX1 during the periods T3 and T4, and no current flows on the secondary side (although no current flows). Attention must be paid to a high voltage such as a withstand voltage against a reverse voltage of D3. In this embodiment,
The reverse voltage applied to D3 may be lower than in the first embodiment.

Connection Node to which C6 and C7 are Connected
1 has been described above to be at a substantially constant potential between the power supply VCC and ground during operation, which will now be described. If no
Assuming that the voltage of de1 is near ground, for example,
During charging of C1, the potential of the anode of D1 is also low, and there is no or short period during which i1 flows. When i1 flows, C2 is discharged. Therefore, in Node1, C2 is discharged from C6 and C7.
Current flows in the direction toward. Therefore, C6 is charged, C7 is discharged, and as a result, the potential of Node1 decreases. However, in this case, since i1 does not flow or hardly flows, the potential of Node1 does not decrease or hardly decreases between T1 and T2.

On the other hand, during the discharge of C1, Node
When the potential of 1 is low, the potential of the cathode of D2 is also low.
i3 can be longer than i1. At this time, since C3 is discharged, C6 and C7 are replaced by C3.
Current flows to increase the potential of Node1.

As described above, when the potential of Node 1 is low, the potential of Node 1 becomes high before and after the charge / discharge cycle. With the same concept, when the potential of Node 1 is higher, the potential of Node 1 becomes lower before and after charging and discharging.
In this manner, the potential of Node 1 approaches the vicinity of the center of the amplitude of the drive waveform by repeating charging and discharging.

As described above, in this embodiment, a voltage having a high mutual inductance is prevented from being generated by using a capacitor to generate an intermediate potential between VCC and ground.

In this embodiment, two capacitors C6 and C7 are used, but only one of them may be used.

Further, TX1 and TX2 are connected on the secondary side of TX2 with the terminal marked with ● to the anode of D3, the other terminal is connected to Node1, and the terminal marked with ● on the secondary side of TX1. If connected to Node1 and the other terminal is connected to the cathode of D4, the same effect as described above can be obtained except that the timing for charging C2 and C3 is different.

[0042]

As described above, in the capacitive load driving circuit according to the present invention, the current flowing from the power supply or the current flowing to the ground is transferred to the primary side of the mutual inductor by the magnetic field energy. Store as energy for later use. As a result, electric power flowing from the power supply is reduced, thereby saving power. Since the power thus saved is conventionally used as heat of the driving element, it becomes easy in terms of thermal design of the driving element.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a capacitive load driving circuit according to a first embodiment of the present invention.

FIG. 2 shows a voltage waveform and a current waveform according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a capacitive load drive circuit according to a second embodiment of the present invention.

FIG. 4 is a circuit diagram of a capacitive load driving circuit according to a conventional example.

FIG. 5 shows a voltage waveform and a current waveform according to a conventional example.

[Explanation of symbols]

C1 Capacitive load C2, C3, C4, C5, C6, C7 Capacitor D1, D2, D3, D4, D5, D6 Diode i1, i2, i3, i4, i5, i6 Current flowing direction Node1 C2, C3, C6 C7, TX1, and TX2
Q1, Q2, Q3, Q4, Q5, Q6 Transistor R1, R2 Resistance TX1, TX2 Mutual inductor VCC Power supply

Claims (6)

[Claims] In a driving circuit for charging and discharging a capacitive load, there are a charging load driving element and a discharging load driving element connected to the capacitive load, and as a charge supply source for the charging load driving element. , A first capacitor and a power supply, and a charging charge supply source switching circuit interposed between the first capacitor, the power supply, and the charging load driving element. Connected to the power supply through the primary side of the first mutual inductor,
The secondary side of the first mutual inductor is connected to the first capacitor through a first rectifier, and the charge charge source switching circuit is configured to control the potential of the first capacitor when charging the capacitive load. When the potential is higher than the potential of the capacitive load, the charge is supplied from the first capacitor to the load drive element for charging. When the potential of the first capacitor is lower than the potential of the capacitive load, the charge is transferred to the charging load driving element. When the current supplied to the primary side of the first mutual inductor changes when the charging charge supply source switching circuit supplies a current from the power supply to the charging load drive element from the power supply, the first A capacitive load driving circuit for charging a capacitor. 2. A drive circuit for charging / discharging a capacitive load, comprising: a charging load driving element and a discharging load driving element connected to the capacitive load; and a charge discharge destination for the discharging load driving element. , A second capacitor and a ground, and a discharge charge inflow destination switching circuit interposed between the second capacitor, the ground, and the discharge load driving element. Connected to ground through the primary side of a second mutual inductor, the secondary side of the second mutual inductor
Connected to the second capacitor through a rectifier, the discharge charge inflow destination switching circuit, when discharging the capacitive load, when the potential of the second capacitor is lower than the potential of the capacitive load, Discharging from the discharge load driving element to a second capacitor; if the potential of the second capacitor is higher than the potential of the capacitive load, discharging the electric charge to the ground from the discharge load driving element; A capacitive load drive circuit, wherein the second capacitor is charged when a current flowing to the primary side of the second mutual inductor changes when a charge inflow destination switching circuit flows a current to ground. 3. The capacitive load drive circuit according to claim 1, further comprising: 4. A driving circuit for charging / discharging a capacitive load, comprising: a charging load driving element and a discharging load driving element connected to the capacitive load; and a charge supply source for the charging load driving element. , A third capacitor and a power supply, and a charge charge supply source switching circuit interposed between the third capacitor, the power supply, and the charging load driving element. As the emission destination, there is a fourth capacitor and ground,
A discharging charge inflow destination switching circuit interposed between the fourth capacitor, the ground, and the discharging load driving element, wherein the charging charge supply source switching circuit is connected to a primary of a third mutual inductor by the power supply. And the secondary side of the third mutual inductor is connected to the fourth capacitor through a third rectifier, and the discharge charge inflow destination switching circuit is connected to the ground on the primary side of a fourth mutual inductor. And the secondary side of the fourth mutual inductor is connected to the third capacitor through a fourth rectifier. The charging charge source switching circuit is configured to charge the capacitive load when charging the capacitive load. When the potential of the capacitor is higher than the potential of the capacitive load, electric charge is supplied from the third capacitor to the charging load drive element, and the electric charge of the third capacitor is supplied. When the potential is lower than the potential of the capacitive load, a charge is supplied from the power supply to the charging load drive element, and when the charging charge supply source switching circuit flows a current from the power supply, the charge of the third mutual inductor is reduced. When the current flowing to the primary side changes, the fourth capacitor is charged, and the discharge charge inflow destination switching circuit is configured such that, when the capacitive load is discharged, the potential of the fourth capacitor is changed to the potential of the capacitive load. If the electric potential is lower than the electric potential, the electric charge is discharged from the discharge load driving element to the fourth capacitor. If the electric potential of the fourth capacitor is higher than the electric potential of the capacitive load, the electric charge is connected to the ground. When the current flowing to the primary side of the fourth mutual inductor changes when the discharge charge inflow destination switching circuit discharges the current from the driving element and flows into the ground, the third key is used. A capacitive load driving circuit for charging a capacitor. 5. The device according to claim 3, further comprising a fifth capacitor, wherein one terminal of the fifth capacitor is connected to the power supply or the ground, and the other end is connected to the first capacitor and the third capacitor. Capacitive load drive circuit. 6. The device according to claim 4, further comprising a sixth capacitor, wherein one terminal of the sixth capacitor is connected to the power supply or the ground, and the other end is connected to the third capacitor and the fourth capacitor. Capacitive load drive circuit.