JP4080380B2 - Capacitive load drive - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a capacitive load driving device, and more particularly to a capacitive load driving device suitable for high voltage driving of a capacitive load.
[0002]
[Prior art]
A capacitive load such as an EL display element generally needs to be driven at a high voltage (for example, a peak-to-peak value of 100 to 1000 V), and a high breakdown voltage is required for the drive circuit.
[0003]
Further, since the EL display element has a polarization effect, it requires AC driving. That is, even if the display pixel is once charged with a certain voltage polarity to emit light and then discharged, polarization occurs in the display pixel in a direction that cancels the previously applied voltage polarity. For this reason, when the voltage of the same polarity is applied again to emit light, the light emission luminance is lowered. Therefore, in order to cause the display pixels that have once emitted light to emit light again, it is necessary to apply a voltage having a polarity opposite to that of the previous time.
[0004]
FIG. 3 is a diagram for explaining a conventional capacitive load driving device (see, for example, Patent Document 1). In the figure, when charging the capacitive load 10 to the positive high voltage power supply Vhp, the thyristor 7 is turned on with the external switching element S1 turned on and the external switching elements S2, S3, S4 turned off. The thyristor 7 can be turned on by controlling the NMOS transistor 61 in the buffer circuit 6 to be turned on and drawing the gate drive current from the anode gate.
[0005]
The charging current of the capacitive load 10 flows through a path from the power supply terminal 1 to the thyristor 7 to the diode 8 to the capacitive load 10.
[0006]
Next, when discharging the capacitive load 10 charged to the positive high-voltage power supply Vhp, the external switching elements S1, S2, and S4 are turned off, the external switching element S3 is turned on, and the thyristor 9 is turned on. As a result, the discharge current of the capacitive load 10 flows to the power supply terminal 2 via the thyristor 9. The thyristor 9 is turned on by controlling the PMOS transistor 62 in the buffer circuit 6 to be turned on and supplying a gate drive current to the cathode gate.
[0007]
Next, when charging the capacitive load 10 with the negative high voltage power supply Vhn, the external switching elements S1, S2, and S3 are turned off, the external switching element S4 is turned on, and the negative high voltage power supply Vhn is supplied to the power supply terminal 2. Is applied to turn on the thyristor 9. When the thyristor 9 is turned on, a charging current flows from the capacitive load 10 toward the power supply terminal 2, and the capacitive load 10 is charged to the negative high voltage power supply Vhn.
[0008]
Next, when discharging the capacitive load 10 charged to the negative high voltage power supply Vhn, the external switching elements S1, S3, S4 are turned off, the external switching element S2 is turned on, and the power supply terminal 1 is biased to 0V. To turn on the thyristor 7. As described above, the thyristor 7 can turn on the NMOS transistor 61 by turning it on by drawing the gate drive current from the anode gate.
[0009]
In this way, by setting either one of the power supply terminals 1 and 2 in a floating state, the capacitive load 10 can be driven at positive and negative high voltages. For this reason, the circuit of FIG. 3 is suitable for an EL panel scanning line driving circuit driven with the power supply line floating (see, for example, Patent Document 1).
[0010]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-82293 [0011]
[Problems to be solved by the invention]
As described above, in the conventional capacitive load driving device, when the positive high voltage power supply Vhp is sent to the output terminal 3, the positive high voltage power supply Vhp is applied to the first power supply terminal 1, and the second high voltage power supply Vhp is applied. The power supply terminal is floating and turns on the switching element 7 on the source side. The second power supply terminal 2 is kept at a low potential difference of about 5 V with respect to the first power supply terminal by the low voltage power supply Vb. Further, the on-drive current of the source side switching element 7 is caused to flow from the first power supply terminal toward the second power supply terminal, and the power consumption can be reduced.
[0012]
When the negative high voltage power supply Vhn is sent to the output terminal 3, the negative high voltage power supply Vhn is applied to the second power supply terminal, the first power supply terminal is set in a floating state, and the switching element 9 on the sink side is turned on. In this case, the on-drive current of the sink side switching element can be supplied from the first power supply terminal.
[0013]
However, in the conventional capacitive load driving device, it is necessary to make the first or second power supply terminal floating with respect to the potentials of the high-voltage power supplies S1, S2, S3, and S4. A dielectric strength greater than or equal to the sum of absolute values of voltages | Vhp | + | Vhn | is required.
[0014]
For this reason, for example, the low-voltage power supply Vb is insulatively configured with a transformer having high insulation properties. Further, when transmitting the control signal, it is necessary to insulate using a photocoupler or the like, which causes a problem in terms of cost in providing a low-priced EL drive circuit.
[0015]
The present invention has been made in view of these problems, and provides a simple and high withstand voltage capacitive load driving device.
[0016]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems.
[0017]
A first main terminal connected to a main power source, a second main terminal connected to an EL element which is a capacitive load having polarizability, and a cathode are connected to each other, and respective anodes are connected to the first main terminal and the second main terminal. A first diode and a second diode connected to each other; a diode bridge including a third diode and a fourth diode, each having an anode connected to each other and each cathode connected to the first main terminal and the second main terminal; A series circuit composed of a PNP transistor and a bias resistor and a parallel circuit composed of an NPN transistor to which a bias is supplied by the bias resistor, connected between a connection point of the diode and the second diode and a connection point of the third diode and the fourth diode. Provided with a switching circuit and a sink mode constant for supplying a base current to the PNP transistor. A source mode constant current circuit supplies a base current to flow circuit and the NPN transistor, said control sink mode constant current circuit turned on when a positive component of the mains voltage to the first main terminal is applied, the When a negative component is applied to one main terminal, the source mode constant current circuit is controlled to be turned on, and the PNP transistor and the NPN transistor can be controlled to be turned on / off regardless of the potential of the first main terminal and the second main terminal. did.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram illustrating an outline of a capacitive load driving device according to an embodiment of the present invention. In the figure, AC is a main power source, C is a capacitive load, T1 is a first main terminal of the switch SW, T2 is a second main terminal of the switch SW, and T is a control circuit for the switch SW. The capacitive load C is, for example, an EL display element, and the element can be used for a backlight of a liquid crystal display element. When a plurality of capacitive loads C are provided, the switch SW can be provided for each capacitive load.
[0019]
FIG. 2 is a diagram illustrating details of the capacitive load driving device according to the embodiment of the present invention. In the figure, D1, D2, D3 and D4 are first, second, third and fourth diodes, respectively, which constitute a diode bridge 21. Q1 and Q2 are first and second transistors, respectively, and R1 and R2 are bias resistors of the transistors Q1 and Q2, respectively. The switching circuit 22 is connected between the cathode common connection point t1 of the diodes D1 and D2 and the anode common connection point t2 of the diodes D3 and D4.
[0020]
The diode bridge 21 and the switching circuit 22 constitute a bidirectional switch 20. T1 is the first main terminal of the bidirectional switch and is connected to the main power supply AC. T2 is the second main terminal of the bidirectional switch and is connected to the capacitive load C.
[0021]
T3 is a sink side drive input terminal connected to the base of the first transistor Q1, and T4 is a source side drive input terminal connected to the base of the second transistor Q12.
[0022]
Q3 is a third transistor, R4, D7, and D8 are bias resistors and diodes for the third transistor Q3, R3 is an input resistor, and T5 is a first control input terminal. These constitute a constant current circuit 23 in a sink mode. To do.
[0023]
Q4 is a fourth transistor, R5 and D9, D10 is a resistor and a diode for biasing the fourth transistor Q4, R6 is an input resistor, and T6 is a second control input terminal. These constitute a source mode constant current circuit 24. . The sink mode constant current circuit 23 and the source mode constant current circuit 24 are connected to the sink drive input terminal T3 and the source drive input terminal T4 via diodes D5 and D6, respectively. VB is a power source for the constant current circuit 24.
[0024]
The bidirectional switch 20 is turned on by setting the potential of the control input terminal T5 in the sink mode constant current circuit 23 to a high level (the potential of the control power supply VB) and the potential of the control input terminal T6 in the source mode constant current circuit 2 Is at a low level (ground potential). As a result, the sink mode constant current circuit 23 and the source mode constant current circuit 24 supply constant current drive currents to the transistors Q1 and Q2, respectively. As a result, the switching circuit 22 is turned on, and the first main terminal T1 and the second main terminal are electrically connected.
[0025]
The bidirectional switch 20 is turned off by setting the potential of the control input terminal T5 in the sink mode constant current circuit 23 to a low level (ground potential) and the potential of the control input terminal T6 in the source mode constant current circuit 24 to a high level. (Potential of the control power supply VB). As a result, the sink mode constant current circuit 23 and the source mode constant current circuit 24 do not supply a constant current. As a result, the switching circuit 22 is turned off, and the first main terminal T1 and the second main terminal become non-conductive.
[0026]
Next, the reason why the on-control is performed regardless of the potential of the main terminals (T1 and T2) of the bidirectional switch 20 when the on-control of the bidirectional switch 20 constituting the capacitive load driving device according to the embodiment is performed. explain.
[0027]
First, when the positive component of the AC power supply AC is applied to the main terminal T1 of the bidirectional switch 20, when the bidirectional switch 20 is turned on, the sink mode constant current circuit 23 is turned on. As a result, a sink constant current I1 is passed through the resistor R1 via the diode D1. When VBE1 of the first transistor Q1 satisfies VBE1> I1 × R1, the PNP transistor Q1 becomes conductive, and the collector current ICE1 flows through the resistor R2. Furthermore, with this current, when VBE2 of the second transistor Q2 satisfies VBE2> ICE1 × R2, the second transistor Q2 conducts, and the collector current ICE2 flows through the diode D1 and the diode D4, and the first main terminal T1 and the first transistor T1 The two main terminals T2 are conducted to charge the capacitive load C to a positive potential.
[0028]
On the other hand, when the negative component of the AC power supply AC is applied to the main terminal T1 of the bidirectional switch 20, when the bidirectional switch 20 is turned on, the source mode constant current circuit 24 is turned on, thereby the diode D6. The source constant current I2 is passed through the resistor R2 via When VBE2 of the second transistor Q2 satisfies VBE2> I2 × R2, the second transistor Q2 conducts, the collector current ICE2 flows through the diode D2 and the diode D3, and the first main terminal T1 and the second main terminal T2 conduct. Then, the capacitive load C is charged to a negative potential.
[0029]
Accordingly, the bidirectional switch 20 can be controlled to be turned on / off regardless of the potentials of the main terminal T1 and the main terminal T2 of the bidirectional switch 20.
[0030]
As described above, according to the present embodiment, the AC power supply AC can be turned on / off regardless of the potential of the main terminal of the bidirectional switch 20. Thereby, the insulation performance of the power transformer required to make the main terminal of the power supply floating can be relaxed. Further, the photocoupler for insulating the input circuit of the control signal supplied to the control input terminals T5 and T6 is not necessary. The switching circuit 22 can be constituted by a switching element such as MOSFET, J (junction type) -FET, IGBT, etc. in addition to a bipolar transistor.
[0031]
【The invention's effect】
As described above, according to the present invention, a simple and high withstand voltage capacitive load driving device can be provided.
[Brief description of the drawings]
FIG. 1 is a diagram for explaining an outline of a capacitive load driving device according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating details of the capacitive load driving device according to the embodiment of the present invention.
FIG. 3 is a diagram illustrating a conventional capacitive load driving device.
[Explanation of symbols]
20 bi-directional switch 21 diode bridge 22 switching circuit 23 sink mode constant current source 24 source mode constant current source AC AC power supply T1 first main terminal T2 second main terminal T3 first drive input terminal T4 second drive input terminal T5 first Control input terminal T6 Second control input terminal D1 First diode D2 Second diode D3 Third diode D4 Fourth diode C Capacitive load Q1 First transistor Q2 Second transistor Q3 Third transistor Q4 Fourth transistors D5, D6, D7 , D8, D9, D10 Diodes R1, R2, R3, R4, R5, R6 Resistor VB Control power supply

Claims (2)

A first main terminal connected to a main power source, a second main terminal connected to an EL element which is a capacitive load having polarizability, and a cathode are connected to each other, and respective anodes are connected to the first main terminal and the second main terminal. A diode bridge comprising a first diode and a second diode connected to each other, and a third diode and a fourth diode, each having an anode connected to each other and each cathode connected to the first main terminal and the second main terminal;
A series circuit including a PNP transistor and a bias resistor connected between a connection point of the first diode and the second diode and a connection point of the third diode and the fourth diode, and an NPN transistor to which a bias is supplied by the bias resistor. A switching circuit with a parallel circuit;
A sink mode constant current circuit for supplying a base current to the PNP transistor and a source mode constant current circuit for supplying a base current to the NPN transistor;
When the positive component of the main power supply voltage is applied to the first main terminal, the sink mode constant current circuit is controlled to be turned on, and when the negative component is applied to the first main terminal, the source mode constant current circuit is turned on. A capacitive load driving device characterized in that the PNP transistor and the NPN transistor can be controlled to be turned on and off regardless of the potentials of the first main terminal and the second main terminal . 2. The capacitive load driving device according to claim 1 , wherein the diode bridge, the switching circuit, and the constant current circuit are integrated.

Images