JP2004103561A - El drive circuit device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an EL drive circuit device without being large-sized or heavy-weighted, even for use for an EL drive of a large panel size. <P>SOLUTION: Field Effect Transistors (FET) Q1 to Q4 are connected in full bridge, between connecting center points a, b of which, a parallel circuit of a constant current circuit 3 and a diode D2 is connected. When the FET's Q1, Q4 are on and the FET's Q2, Q3 off, an electric current is passed from +V through the FET Q1, the constant current circuit 2, an EL panel 1, the diode D2, and the FET Q4 in that order to charge the EL panel 1, and when FET's Q1, Q4 are off and FET Q2, Q3 on, an electric current is passed through +V, a constant current circuit 3, the EL panel 1, a diode D1, and FET Q2 in that order, and after a charged portion of the EL panel 1 is discharged, it is charged in a reverse polarity. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an EL drive circuit device for driving an EL panel used for lighting, display, and the like.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a circuit for driving an EL lighting panel, there are many self-excited or separately-excited oscillation circuits using a transformer or an inductor. FIG. 7 shows an example of this type of drive circuit device. This circuit alternately turns on / off switching elements Q1, Q4 of a full bridge circuit in which switching elements Q1, Q2, Q3, Q4 are bridge-connected, and switching elements Q2, Q3, and converts a generated pulse signal into a transformer. This is a voltage resonance type inverter whose voltage is boosted by T and forms a resonance circuit by the choke coil L and EL (for example, see Non-Patent Document 1). There is a self-excited inverter as another EL drive circuit device.
[0003]
[Non-patent document 1]
Published by Nikkan Kogyo Shimbun, 1998, "Introduction to Switching Power Supply Design," 78P
[0004]
[Problems to be solved by the invention]
Since the above-mentioned conventional EL drive circuit device uses a transformer and an inductor, the size of the transformer and the inductor and the size of the superimposed device become large, especially when driving a large-sized EL panel. is there. Further, in order to increase the luminance, it is necessary to increase the power supply voltage.
[0005]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an EL drive circuit device which is large in size and does not overlap, even if it is used for EL drive of a large size.
[0006]
[Means for Solving the Problems]
According to a first EL drive circuit device of the present invention, a series circuit of first and second switching elements and a series circuit of third and fourth switching elements are connected in parallel. Switching element, a bridge circuit in which the second and third switching elements are alternately turned on / off, and a connection point between the connection point of the first and second switching elements and one electrode of EL. A first constant current circuit connected between the third connection point of the third and fourth switching elements and the other electrode of the EL, and charged in a direction opposite to the current of the first constant current circuit. A second constant current circuit that supplies a current to the EL.
[0007]
In the EL drive circuit device according to the present invention, when the first and fourth switching elements are on, a charging current flows through the EL through the first constant current circuit, and the EL is charged. Next, when the second and third switching elements are turned on, a current in the opposite direction flows through the EL through the second constant current circuit, so that the charged electric charge up to that point is discharged and the electric charge of the opposite polarity is further performed. The EL is driven by this repetition.
[0008]
A second EL drive circuit device according to the present invention comprises at least a series circuit of first and second switching elements and a power supply to which the series circuit is connected, and the first and second switching elements are alternately turned on. A first constant current circuit connected between a bridge circuit to turn on / off, a connection midpoint between the first and second switching elements, and one electrode of the EL, and another electrode of the EL. And a second constant current circuit connected between the first and second constant current circuits and flowing a discharge current in the opposite direction to the current of the first constant current circuit to the EL.
[0009]
In the EL drive circuit device according to the present invention, when the first switching element is on, a charging current flows through the EL through the first constant current circuit, and the EL is charged. Next, when the second switching element is turned on, a discharge current flows in the reverse direction from the second switching element through the second constant current circuit to the EL due to the charging voltage of the EL. Done. The EL is driven by this repetition.
[0010]
According to a third EL drive circuit device of the present invention, a first circuit in which first and second switching elements are connected in series, and the first and second switching elements are turned on / off alternately; A second circuit in which a second constant current circuit is connected in series and is connected in parallel with the first circuit to form a full bridge circuit; and a power supply circuit for supplying a power supply voltage to the first and second circuits. And an EL connected between the connection midpoint of the first circuit and the connection midpoint of the second circuit.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to embodiments. FIG. 1 is a circuit diagram of an EL drive circuit device according to one embodiment of the present invention. In the EL drive circuit device of this embodiment, a field-effect transistor (FET: first switching element) Q1 and a field-effect transistor (FET: second switching element) Q2 are connected in series at a connection midpoint a to form a series circuit. Make up. Further, a field effect transistor (FTE: third switching element) Q3 and a field effect transistor (FET: fourth switching element) Q4 are connected in series at a connection midpoint b to form a series circuit. These two series circuits are connected in parallel and connected between the + V power supply and 0V. Thus, the four field effect transistors Q1,..., Q4 form a full bridge circuit.
[0012]
A constant current circuit 2 is connected between the connection midpoint a and one electrode 1a of the EL panel 1, and a diode (high-speed diode) D1 is connected in parallel with the constant current circuit 2. The diode D1 has an anode connected to the electrode 1a of the EL panel 1 and a cathode connected to the connection midpoint a.
[0013]
Further, a constant current circuit 3 is connected between the connection middle point b and the other electrode 1b of the EL panel 1, and a diode (high-speed diode) D2 is connected in parallel with the constant current circuit 3. The diode D2 has an anode connected to the electrode 1b of the EL panel 1 and a cathode connected to the connection midpoint b.
[0014]
The field effect transistors Q1, Q4 and the field effect transistors Q2, Q3 are turned on / off alternately by a signal from a control unit (not shown).
[0015]
In the EL drive circuit of this embodiment, when the field effect transistors Q1 and Q4 are turned on and the field effect transistors Q2 and Q3 are turned off, the power supply + V → the field effect transistor Q1 → the constant current circuit 2 → the EL panel 1 → the diode D2 → the electric field A current flows through the path of the effect transistor Q4 → 0V. At this time, the constant current circuit 2 supplies a constant current to the EL panel 1 to charge it. Since the current is constant, an excessive charging current does not flow through the EL panel 1. Until the EL panel 1 is charged to a required voltage, the field effect transistors Q1 and Q4 are turned on. The EL panel 1 is charged to the polarity of (+) on the side of the constant current circuit 2 and to the polarity of (-) on the side of the constant current circuit 3 (see (1) in FIG. 2).
[0016]
Next, the field effect transistors Q1 and Q4 are turned off, and the field effect transistors Q2 and Q3 are turned on. This time, a current flows through a path of power supply + V → field transistor Q3 → constant current circuit 3 → EL panel 1 → diode D1 → field effect transistor Q2 → 0V. A constant current flows in the opposite direction to that in the case of the constant current circuit 2, the previously charged electric charge is discharged, and the EL panel 1 is further charged to the opposite polarity [see (2) in FIG. 2].
[0017]
Subsequently, the field-effect transistors Q1 and Q4 are turned on again, the field-effect transistors Q2 and Q3 are turned off, and the state returns to the state indicated by (1) in FIG. Thereafter, (1) and (2) in FIG. 2 are repeated alternately. In this embodiment, as shown by (1) and (2) in FIG. 2, since the charging voltage in both the positive and negative directions can be used, the power supply + V can be reduced.
[0018]
FIG. 3 is a circuit diagram of an EL drive circuit device showing another embodiment of the present invention. In this embodiment, the EL drive circuit device is one in which the field effect transistors Q3 and Q4 of FIG. 1 are removed, OPEN is provided between + V and point b, and point b is connected to 0V.
[0019]
In this embodiment, the field effect transistors Q1 and Q2 are turned on / off alternately. When the field effect transistor Q1 is on and Q2 is off, a current flows through a path of power supply + V → field effect transistor Q1 → constant current circuit 2 → EL panel 1 → diode D2 → 0V. At this time, the constant current circuit 2 supplies a constant current to the EL panel 1 to charge it. The EL panel 1 is charged to the polarity of (+) on the electrode 1a side and to the (−) polarity on the electrode 1b side.
[0020]
Next, when the field effect transistor Q1 is turned off and Q2 is turned on, a discharge current flows through the diode D1 → the field effect transistor Q2 → 0V → the constant current circuit 3 by the charged voltage of the EL panel 1.
[0021]
Since this embodiment is half-charged, it requires twice the voltage as compared to the circuit of FIG. 1. However, since the circuit is simple and a transformer and an inductor are not required, the device can be reduced in size and weight.
[0022]
FIG. 4 is a circuit diagram of an EL drive circuit device showing still another embodiment of the present invention. The EL drive circuit device of this embodiment includes constant current circuits TD1 and TD2 instead of the field effect transistors Q3 and Q4 of FIG. The constant current circuit TD1 includes a bipolar transistor Q3, resistors RE1 and RB1, and a constant voltage diode ZD1. The constant current circuit TD2 includes a bipolar transistor Q4, resistors RE2 and RB2, and a constant voltage diode. ZD2. The diode D3 is connected between the collector of the transistor Q3 and the collector of the transistor Q4.
[0023]
The collector of the transistor Q3 of the constant current circuit TD1 is connected to the collector of the transistor Q4 through the diode D3 and to one electrode 1b of the EL panel 1. The emitter of the transistor Q3 is connected to the power supply + V via the resistor RE1. The base of the transistor Q3 is connected to a power supply + V via a constant voltage diode ZD1, and is connected to a connection midpoint a (electrode 1a side of the EL panel 1) via a resistor RB1.
[0024]
The emitter of the transistor Q4 of the constant current circuit TD2 is connected to the power supply 0V via the resistor RE2. The base of the transistor Q4 is connected to a connection midpoint a via a resistor RB2, and to the power supply 0V via a constant voltage diode ZD2. The circuit of this embodiment does not include the constant current circuits 2, 3 and the diodes D1, D2 provided in FIG.
[0025]
In the circuit of this embodiment, the field effect transistor Q1 is now ON (Q2: OFF), a voltage is applied to the source S of the field effect transistor Q1, the electrode 1a of the EL panel 1, and the connection midpoint a, and the resistance RB2, the constant voltage A current flows through the diode ZD2. At this time, a constant current of I = (Vzd2-Vbe) / RE2 flows through the emitter of the transistor Q4 (where Vzd2 is the zener voltage of ZD2, and Vbe is the BE voltage between the BEs of the transistor Q4). Then, the charging current (i1) flows to the EL panel 1 in the direction of power supply + V → field-effect transistor Q1 → EL panel 1 → diode D3 → transistor Q4 → 0V. When the EL panel 1 is sufficiently charged and reaches a certain voltage determined by the power supply voltage and the voltage necessary for the charging circuit, the EL panel 1 is saturated and the current becomes zero.
[0026]
Next, when the field effect transistor Q2 is turned ON (Q1: OFF), a constant current (i2) flows in the direction of power supply + V → resistor RE1 → transistor Q3 → EL panel 1 → field effect transistor Q2 → 0V, The electric charge charged in the EL panel 1 by the above operation is discharged, and the EL panel 1 is further charged in the reverse direction. When the voltage between the terminals of the EL panel 1 reaches a certain voltage, the EL panel 1 saturates and the current becomes 0. .
[0027]
Next, the field effect transistor Q1 is turned on, and the same operation as the first operation is repeated, and the EL panel 1 is charged and discharged to both electrodes. Note that the constant voltage diodes ZD1 and ZD2 may be constant voltage elements, and a constant voltage element or a constant voltage circuit other than a zener diode may be used.
[0028]
FIG. 6 is a circuit diagram of an EL drive circuit device showing still another embodiment of the present invention. The EL drive circuit device according to this embodiment uses field effect transistors Q3 and Q4 instead of the bipolar transistors Q3 and Q4 in FIG. 4. The source S of the field effect transistor Q3 is connected to a power supply + V, The source S of the effect transistor Q4 is connected to 0V, and the drains D of the field effect transistors Q3 and Q4 are connected via a diode D3. The drain D of the field effect transistor Q3 is connected to the electrode 1b of the EL panel 1. Further, the gate G of the field effect transistor Q3 is connected to the connection point a via the resistor RC1, and is connected to the power supply + V via the parallel circuit of the resistor RG1 and the constant voltage diode ZD1. Similarly, the gate G of the field effect transistor Q4 is connected to the connection midpoint a via the resistor RC2, and is also connected to the power supply 0V via a parallel circuit of the resistor RG2 and the constant voltage diode ZD2.
[0029]
The basic operation is the same as that of the circuit of FIG. 4, but the conditions for determining the value of the constant current in this circuit are the bias voltages (Vgs1, Vgs2) between the G and S of the field effect transistors Q3, Q4, respectively. Is a value determined by the characteristic of the field-effect transistor. The resistors RG1 and RG2 are operation stabilizing resistors to be inserted in the GS of the respective field effect transistors Q3 and Q4, and are not essential in the operation principle.
[0030]
Further, here, the P-type MOS is used for the field-effect transistor Q3 and the N-type MOS is used for the field-effect transistor Q4. However, this is merely an example of a circuit. For example, an N-type MOS may be used for Q3 and its driving circuit may be used. Equivalent operation can be realized.
[0031]
In the above embodiment, a field effect transistor is used as a switching element, but another switching element such as a bipolar transistor may be used instead.
[0032]
Further, a circuit shown in FIG. 5 may be used as a practical circuit instead of the circuit shown in FIG. In the circuit of FIG. 5, one end (upper end) of the resistor RB2 of the circuit shown in FIG. 4 is connected to the source S of the field effect transistor Q1, and one end (lower end) of the resistor RB1 is connected to the drain D of the field effect transistor Q2. A diode D4 is connected between the electrode 1a of the EL panel 1 and the drain D of the field effect transistor Q2.
[0033]
The circuit shown in FIG. 4 shows a basic circuit. During operation, the EL panel 1 is charged and discharged repeatedly by alternately turning on / off the field effect transistors Q1 and Q2, and the EL panel 1 is normally operated. To drive.
[0034]
However, this is not considered until the power is turned off. When the power is turned on when the power is turned off, that is, when the field effect transistors Q1 and Q2 are turned off, first, a current flows through a path of power supply + V → constant voltage diode ZD1 → resistors RB1 and RB2 → constant voltage diode ZD2 → power supply 0V. Q3 and Q4 are turned on. Next, a constant current flows through a path of power supply + V → resistor RE1 → transistor Q3 → transistor Q4 → resistor RE2 → power supply 0V, generating heat and consuming power.
[0035]
When the resistors RB1 and RB2 are connected and the diode D3 is connected as in the circuit of FIG. 5, the circuit operates in the same manner as the circuit shown in FIG. 4 at the time of operation, and from the power supply OFF state to the ON state, power supply + V → constant voltage diode ZD1 → Since the current path from the resistors RB1, RB2, the constant voltage diode ZD2, and the power supply 0V is cut off, generation of heat can be prevented. The circuit shown in FIG. 6 may be connected practically in the same manner as the circuit shown in FIG.
[0036]
【The invention's effect】
According to the first aspect, since a full bridge circuit and a constant current circuit are used, and a transformer and an inductor are not used, the device can be realized in a small size and light weight. In addition, since the positive and negative charging voltages are driven on the EL, the power supply voltage can be reduced. In addition, a constant current is applied to the EL, and an excessive charging current does not flow, thereby preventing the EL from deteriorating. Further, according to the second aspect, since the transformer and the inductor are not used, the device can be realized in a small size and light weight. Further, according to the third aspect, since the constant current circuit is used on two sides of the full bridge circuit, circuit components can be reduced.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an EL drive circuit device according to an embodiment of the present invention.
FIG. 2 is a view showing EL charge / discharge characteristics of the EL drive circuit device of the embodiment.
FIG. 3 is a circuit diagram of an EL drive circuit device according to another embodiment of the present invention.
FIG. 4 is a circuit diagram of an EL drive circuit device according to still another embodiment of the present invention.
FIG. 5 is a circuit diagram of an EL drive circuit device according to still another embodiment of the present invention.
FIG. 6 is a circuit diagram of an EL drive circuit device according to still another embodiment of the present invention.
FIG. 7 is a circuit diagram showing an example of a conventional EL drive circuit device.
[Explanation of symbols]
Reference Signs List 1 EL panel 1a, 1b Electrode 2 of EL panel 3, constant current circuit Q1,..., Q4 Field effect transistor D1, D2 Diode

Claims (3)

A series circuit of the first and second switching elements and a series circuit of the third and fourth switching elements are connected in parallel, and the first and fourth switching elements and the second and third switching elements are connected. A bridge circuit in which elements are turned on / off alternately;
A first constant current circuit connected between a connection midpoint between the first and second switching elements and one electrode of EL;
A second constant current, which is connected between the connection midpoint of the third and fourth switching elements and the other electrode of the EL, and flows a charging current to the EL in the opposite direction to the current of the first constant current circuit. A current circuit;
An EL drive circuit device comprising: A bridge circuit comprising at least a series circuit of first and second switching elements, and a power supply to which the series circuit is connected, wherein the first and second switching elements are turned on / off alternately;
A first constant current circuit connected between a connection midpoint between the first and second switching elements and one electrode of EL;
A second constant current circuit connected between the other electrode of the EL and a discharge current flowing through the EL in a direction opposite to the current of the first constant current circuit;
An EL drive circuit device comprising: A first circuit in which first and second switching elements are connected in series, and the first and second switching elements are turned on / off alternately;
A second circuit in which a first and a second constant current circuit are connected in series and connected in parallel with the first circuit to form a full bridge circuit;
A power supply circuit for supplying a power supply voltage to the first and second circuits;
An EL connected between a connection midpoint of the first circuit and a connection midpoint of the second circuit;
An EL drive circuit device comprising:

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