JPH0819757A - Volumetric load drive circuit - Google Patents

Abstract

PURPOSE:To provide a volumetric load drive circuit which is capable of obtaining a high drive voltage at a low power consumption without the use of a transformer. CONSTITUTION:A first coil L1 and a transistor T1 are connected in series in that order between a first power supply terminal VCC and a second power supply terminal GND, and a transistor T2 and a coil L2 are connected serially in that order between the power supply terminals. In addition, transistors T3, T4 are connected in series between contact points for these two coils and two transistors, and an EL element E as a volumetric load is connected between this contact point and the second power supply terminal GND. Further, the first coil L1 and the second coil L2 are caused to work alternately by turning the transistors T1, T4 and the transistors T2, T3 ON/OFF alternately for every specified period of time so that one coil accumulates a magnetic energy, while the other coil generates a reverse-induced voltage. Thus the EL element E is driven by applying this reverse-induced voltage as a drive voltage of mutually different polarity to an area between the terminals of the EL element E.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a capacitive load such as a piezoelectric buzzer and an EL element.

[0002]

2. Description of the Related Art Conventionally, driving a capacitive load such as a piezoelectric buzzer or an EL element requires an oscillating drive voltage of about 100 V. Such a drive voltage is an alternating current generated by a booster circuit using a transformer. It is common to use voltage,
Such a transformer system has a large device scale and is not suitable as a drive circuit for a capacitive load such as a piezoelectric buzzer or an EL element in a small device such as a watch. Therefore, as an alternative drive circuit of this kind, there is a drive circuit as shown in FIG. This is a coil L4 with one end connected to the power supply terminal
, A transistor tr4 is connected in series between the coil L4 and the ground, and a capacitive load e4 is connected in parallel to the coil L4. By supplying the pulse signal shown in FIG. 5A to the base of the transistor tr4, The capacitive load e4 is driven by the back electromotive force generated in the coil L4 at the fall of the pulse, and the drive voltage has a burst waveform as shown in FIG. 5B.

Further, Japanese Utility Model Laid-Open No. 53-162675 discloses a drive circuit as shown in FIG. In the drive circuit of FIG. 6, the same numbers as those shown in FIG. 4 indicate the same configurations, and here, a diode d6 is provided between the power supply terminal and the coil L4. Even with this drive circuit, FIG.
By supplying the pulse signal shown in to the base of the transistor tr4, the coil L4
The capacitive load e4 is driven by the back electromotive force generated in the drive voltage. At that time, since the drive voltage is rectified by the diode d6, the drive voltage becomes close to a rectangular wave as shown in FIG. 7B.

[0004]

Both the drive circuits shown in FIGS. 4 and 6 use a unipolar voltage due to the back electromotive force generated in the coil L4 as the drive voltage.
In order to obtain a high voltage like that using a booster circuit using a transformer, the current value supplied to the coil must be increased. However, in a small device such as a timepiece in which the driving circuit as described above is mainly used, it is difficult because the battery life becomes short. Therefore, when the piezoelectric buzzer is used as the capacitive load, high volume cannot be obtained, and when the EL element is used, high brightness cannot be obtained.

Therefore, it is an object of the present invention to provide a drive circuit for a capacitive load that can obtain a high drive voltage with low power consumption without using a transformer.

[0006]

A first coil having one end connected to a first power supply terminal, and a first switching element connected in series between the first coil and the second power supply terminal,
A second coil whose one end is connected to a second power supply, a second switching element connected in series between the second coil and the first power supply terminal, a first coil and a first switching element A connection point between the second switching element and the second
Third and fourth switching elements connected in series with the connection point between the coil and the coil, a connection point between the third switching element and the fourth switching element, and a second power supply. A capacitive load connected in series with the terminal and a control circuit that alternately turns on and off the first and fourth switching elements and the second and third switching elements for each specific period By configuring the drive circuit of the load,
To achieve the above objectives.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A capacitive load drive circuit according to an embodiment of the present invention will now be described.

FIG. 1 is an electric circuit diagram showing the configuration of this embodiment. In FIG. 1, L1 is a first coil, one end of which is connected to a first power supply terminal VCC.

T1 is n as a first switching element
It is a pn type transistor, and includes a first coil L1 and a second coil
Is connected in series with the power supply terminal GND. It should be noted that the first power supply terminal VCC is 1.5 V here, and the second
The power supply terminal GND of is grounded and is 0v.

D1 is a first diode, which is connected between the first coil L1 and the transistor T1 with this direction being the forward direction.

L2 is a second coil, one end of which is connected to the second power supply terminal GND.

T2 is p as a second switching element
It is an np type transistor, and includes a second coil L2 and a first coil L2.
Is connected in series with the power supply terminal Vcc.

D2 is a second diode, which is connected between the transistor T2 and the second coil L2 with this direction being the forward direction.

In the first diode D1 and the second diode D2, counter-induced currents generated in the first coil L1 and the second coil L2 are generated in the transistors T1 and T2, respectively.
It is to prevent it from flowing to.

T3 and T4 are a pnp-type transistor and an npn-type transistor as a third switching element and a fourth switching element, respectively. These transistors T3 and T4 are sequentially connected in series between a connection point between the first coil L1 and the first diode D1 and a connection point between the second diode D2 and the second coil L2. It is connected.

D3 and D4 are third diodes, respectively.
It is a fourth diode. These third and fourth diodes are sequentially connected in series between the transistors T3 and T4 with this direction as the forward direction.

In the third diode D3 and the fourth diode D4, counter-induced currents generated in the first coil L1 and the second coil L2 are generated in the transistors T3 and T4, respectively.
It is to prevent it from flowing to.

E is an EL element as a capacitive load,
It is connected in series between the connection point of the third diode D3 and the fourth diode D4 and the second power supply terminal GND. P is a pulse generation circuit, which is composed of an astable multivibrator or the like, and generates a pulse at the terminal A as shown in FIG. 2A. Pulse generation circuit P, capacitors C1 to C3,
A control circuit is composed of the resistors R1 and R2.

Next, the operation of the drive circuit for the capacitive load of the present example configured as described above will be described.

First, the switching operation of each transistor will be described with reference to FIG. The pulse generating circuit P outputs a pulse as shown in FIG. 2A. This is a pulse having a cycle of 2T and a duty of 1/2. Between timings t0 and t1 when the pulse is "H", the transistors T1 and T4 receiving this are turned on and the transistors T2 and T3 are turned off. An equivalent circuit of this example at this time is shown. And it looks like Figure 3a. Further, the timing t1 to t2 when the pulse is “L”
During this period, the transistors T2 and T3 receiving this are turned on, and the transistors T1 and T4 are turned off. An equivalent circuit at this time is shown in FIG. 3b.

Further, referring to these equivalent circuits, while the pulse is at "H", the first coil L1 is placed between the power supply terminal Vcc and the power supply terminal GND as shown in FIG. 3a. It can be seen that the second coil L2 is connected between the power supply terminal VCC and the power supply terminal GND as shown in FIG. 3b while the connection is made so that the current flows and the pulse is "L". .

With the above in mind, a series of operations will be described with reference to FIGS. Timing t0
When the pulse rises to "H", a back electromotive force is generated in the second coil L2 in the direction indicated by the arrow c1 in FIG. 3a when the transistor T2 is turned off. This back electromotive force is applied to the fourth diode and the transistor. Terminal C via T4
Applied between B and B. Thereby, the timing t0 to t
Up to 1, the EL element E has the pulse voltage p1 shown in FIG. 3a.

Next, at the timing t1, when the pulse falls, the transistor T1 is turned off, so that a counter electromotive voltage is generated in the first coil L1 in the direction shown by the arrow c2 in FIG. 3a. Is the transistor T
3, and is applied between terminals CB through the third diode D3. Thereby, from timing t1 to t2, EL
The pulse voltage p2 shown in FIG. 3b appears in the element E.

The above operation from timing t0 to t2 is repeated thereafter, and the bipolar element AC voltage as shown in FIG. 2C-B is applied to the EL element E, and high voltage driving can be realized. As described above, it is possible to obtain a drive voltage that is twice the conventional unipolar drive voltage. When an EL element is used as the capacitive load, the brightness is higher than that of the conventional one, and when a piezoelectric buzzer is used. It is possible to increase the volume. As a result, the current consumption can be suppressed because the current consumption can be obtained with a smaller current consumption than that required for the conventional drive circuit to obtain a specific volume or brightness.

Further, in this embodiment, since an AC voltage can be generated from a DC power supply voltage between a pair of power supply terminals without using a transformer, it is possible to generate a high driving voltage with a small circuit configuration. is there. Therefore, it can be used in a small device such as a timepiece whose circuit scale is limited and whose power source used is substantially limited to a battery. The brightness of can be improved compared to the conventional one.

Further, in the above embodiment, the EL element E as a capacitive load is connected between the connection point between the transistor T3 and the transistor T4 and the second power supply terminal GND, but the invention is not limited to this. T3 and transistor T
Even if it is connected between the connection point between the power supply terminal 4 and the first power supply terminal Vcc, the same action and effect as described above can be obtained. In this case, the first coil L1 in the above embodiment becomes the second coil, and the first power supply terminal Vcc becomes the second coil.
The power supply terminal, L2 which was the second coil, becomes the first coil, and GND which was the second power supply terminal becomes the first power supply terminal. Further, the transistors T1 and T2 serve as a second switching element and a first switching element, respectively, and the transistors T3 and T4 serve as a fourth switching element and a third switching element, respectively.

As described above, the capacitive load E
The case of driving the L element and the piezoelectric buzzer has been described.
The present invention is not limited to these, and can be used for various capacitive loads such as piezoelectric elements used in ultrasonic sensors and the like.

[0028]

According to the present invention, the back electromotive force is generated alternately in the first coil and the second coil connected between the first power supply terminal and the second power supply terminal, and these are induced by the capacitance. It is applied between the terminals of the sexual load as driving voltages having different polarities. Therefore, a high driving voltage can be obtained with a smaller amount of current consumption as compared with the conventional one that generates a unipolar driving voltage. Further, the circuit scale is smaller than that of the transformer system, and it can be used in a small device such as a watch without any space limitation.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a drive circuit of a capacitive load according to an embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of FIG.

FIG. 3 is an equivalent circuit diagram for explaining the operation of FIG.

FIG. 4 is an electric circuit diagram showing a conventional drive circuit for a capacitive load.

5 is a waveform chart for explaining the operation of FIG.

FIG. 6 is an electric circuit diagram showing a conventional drive circuit for a capacitive load.

7 is a waveform diagram for explaining the operation of FIG.

[Explanation of symbols]

 L1 1st coil L2 2nd coil VCC CC 1st power supply terminal GND 2nd power supply terminal T1-T4 1st transistor-4th transistor P pulse generation circuit (control circuit) C1-C3 capacitor (control circuit) R1, R2 resistance (control circuit)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G10K 9/122 H03K 17/60 17/74 Z

Claims (1)

[Claims] 1. A first coil having one end connected to a first power supply terminal, a first switching element connected in series between the first coil and a second power supply terminal, and one end being a second Between the second coil connected to the power source, the second switching element connected in series between the second coil and the first power supply terminal, and between the first coil and the first switching element. Third and fourth switching elements connected in series between the connection point and the connection point between the second switching element and the second coil, and the third switching element and the fourth switching element A capacitive load, a first and a fourth switching element, and a second and a third switching element which are connected in series between a connection point between the second power source terminal and A capacitor including a control circuit that alternately turns on and off The drive circuit of the load.