JPH08248910A - El driving circuit - Google Patents

Abstract

PURPOSE: To reduce the power consumption of an electroluminescence element driving circuit. CONSTITUTION: When a switch 3 is turned on, a driving pulse having the cycle and the duty instructed by a control part 5 is outputted from a driving pulse generating part 4 to the base of a transistor TR2. During a period when the driving pulse is in a high level, a transistor TR1 oscillates and a high voltage is supplied to an EL 2. Next, when the driving pulse becomes a low level, a current is supplied from a capacitor C2 to a primary winding L1 and the transistor TR1 continues the oscillation and when the capacitor C2 discharges, the transistor stops the oscillation. Then, when the driving pulse becomes the high level again, the transistor TR1 starts the oscillation again. An EL 2 emits light because these operations are frequently repeated.

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 an electroluminescence device.

[0002]

2. Description of the Related Art Electroluminescence device (EL)
Is used as a lighting device such as a liquid crystal display device or a dial of a wristwatch. As a drive circuit for driving this EL,
A circuit that boosts the battery voltage with a transformer or the like is used.

[0003]

The EL drive circuit is composed of a transformer and a switching element, and oscillates the EL drive circuit at a predetermined frequency to generate a high voltage and supply it to the EL.

However, in order to make the EL emit light, E
If the L drive circuit is kept in an oscillating state at all times, power consumption increases, and when driven by a battery, the battery life becomes short.

An object of the present invention is to further reduce the power consumption of the EL drive circuit.

[0006]

The EL drive circuit of the first invention comprises an electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and a high voltage. An operating voltage supply means for supplying an operating voltage to the signal supply means via the switch means, and a periodic signal output means for outputting a periodic signal for turning on / off the switch means at a predetermined period.

The EL drive circuit of the second invention comprises an electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and a switch means for the high voltage signal supply means. The operating voltage supply means for supplying the operating voltage via the, the periodic signal output means for outputting the periodic signal for turning the switch means on and off at a predetermined cycle, and the duty of the periodic signal output from the periodic signal output means. And a duty control means for changing the duty.

The EL drive circuit of the third invention comprises an electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and a switch means for the high voltage signal supply means. The operating voltage supply means for supplying the operating voltage via the, the periodic signal output means for outputting the periodic signal for turning the switch means on and off at a predetermined cycle, and the cycle of the periodic signal output from the periodic signal output means. And a cycle control means for changing the cycle.

[0009]

According to the first aspect of the present invention, the switch means for supplying the operating voltage to the high-voltage signal supply means is turned on and off at a predetermined cycle to cause the electroluminescence element to emit light at an appropriate brightness, and the electroluminescence element of the EL drive circuit. Power consumption can be reduced.

In the second aspect of the invention, the power consumption can be reduced by further changing the duty of the periodic signal output from the periodic signal output means. In the third invention, by changing the period of the periodic signal, it is possible to drive the electroluminescent element with appropriate brightness and reduce the power consumption.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit configuration diagram of an electroluminescence (EL) drive circuit according to an embodiment of the present invention. This embodiment relates to an EL drive circuit for a backlight of a liquid crystal display device of a dial of an electronic wristwatch. .

In this EL drive circuit, a power supply voltage VDD is supplied from a battery 1 to each part of the circuit. Positive side of battery 1,
That is, the power supply voltage VDD is connected to one end of a switch 3 which is operated when the electroluminescence (EL) 2 is caused to emit light, and the other end of the switch 3 is connected to the drive pulse generating section 4.

When the switch 3 is turned on, the drive pulse generator 4 outputs a periodic signal of a period instructed by the controller 5 to the base of the transistor TR2 to turn the transistor TR2 on and off at a predetermined period.

The control unit 5 detects a key operation signal input from the key input unit 6, updates the current time data stored in the RAM 7, displays the measured current time on the liquid crystal display unit 8 and a drive pulse. This is a circuit that controls the cycle of the drive pulse generated by the generator 4, or the duty ratio.

The transformer comprises a primary winding L1 and a secondary winding L2, one end of which is connected to a power supply VDD.
The other end is connected to the collector of the transistor TR1. Further, one end of the secondary winding L2 of the transformer is connected to one end of EL2, and the other end of the secondary winding L2 is a transistor TR.
1 is connected to the base. The other end of EL2 is connected to the power supply voltage VDD.

The emitter of the transistor TR1 is connected to the collector of the transistor TR2, one end of the resistor R2 and one end of the capacitor C2 are connected to the base of the transistor TR1, and the other end of the resistor R2 is the power supply voltage VDD.
The other end of the capacitor C2 is connected to the emitter of the transistor TR1.

Further, the power supply voltage VDD and the transistor TR
A capacitor C2 is connected in parallel with the circuit for generating a high voltage to be supplied to EL2, that is, the first winding from the capacitor C2 when the transistor TR2 is turned off. An electric current is supplied to the line L1.

Next, the operation of the EL drive circuit having the above configuration will be described. When the switch 3 is turned on and the operating voltage is supplied to the drive pulse generator 4, the drive pulse generator 4
Is output to the base of the transistor TR2.

With this drive pulse, the transistor TR2
Is turned on, the capacitor C1 is charged with a time constant determined by the values of the resistor R1 and the capacitor C1. Then, when the voltage of the capacitor C1 becomes equal to or higher than the base bias voltage of the transistor TR1, the transistor TR2 is turned on and a current flows through the primary winding L1 of the transformer. When a current flows in the primary winding L1 of the transformer, the current induces a voltage in the secondary winding L2. This voltage biases the base of the transistor TR1 in the negative polarity, so that the transistor TR1 is turned off.

When the transistor TR1 is turned off and the current flowing through the primary winding L1 becomes zero, a positive voltage of the opposite polarity is induced in the secondary winding L2 of the transformer, and the voltage causes a positive voltage of the transistor TR1. The base is positively biased and transistor TR1 turns on again.

By repeating these operations, the transistor TR1 performs a switching operation, a high voltage is supplied to EL2 connected to the secondary side of the transformer, and EL2 emits light.

FIG. 2 is a timing chart showing the drive pulse and the voltage applied to EL2 when EL2 is in the light emitting state. When the switch 3 is turned on by the user (FIG. 2A), the drive pulse generator 4 outputs the drive pulse having the cycle T and the duty ratio instructed by the controller 5. This drive pulse is at high level (To
n) The transistor TR1 oscillates and a high voltage is supplied to EL2 ((c) in the figure).

Next, when the drive pulse becomes low level,
A current is supplied from the capacitor C2 to the primary winding L1 of the transformer, and the transistor TR1 stops oscillating after continuing oscillating for a certain period of time. These operations are repeated until E
The light emission time of L2 is frequency controlled or duty controlled.

Next, the above-mentioned EL drive circuit is integrated into one IC.
A second embodiment of the present invention realized in 1. will be described with reference to FIG. The reset circuit 11 operates the internal booster circuit 12, the internal oscillator circuit 13, and the frequency division / control circuit 14 when the enable signal input to the enable terminal ENB is active, and when the enable signal is inactive, these circuits are operated. The signal to stop the operation of is output.

The internal booster circuit 12 is a circuit for boosting the power supply voltage Vcc supplied from the power supply 15 to generate the second power supply voltage Vcp, and the generated second power supply voltage Vcp is level conversion circuits 16 and 17. Output to etc. This internal booster circuit 1
A capacitor 18 is externally attached to the second output terminal VCP, and the capacitor 18 smoothes the second power supply voltage Vcp.

The internal oscillating circuit 13 is an oscillating circuit for generating a signal having a cycle determined by the external resistor R, and outputs the generated signal to the frequency dividing / control circuit 14. The frequency division / control circuit 14 frequency-divides and controls the signal generated by the internal oscillation circuit 13 to generate a gate drive signal to be supplied to the gates of MOS transistors TR1 and TR2, which will be described later, and level the generated gate drive signal. It outputs to the conversion circuits 16 and 17.

The level conversion circuits 16 and 17 are circuits for converting a signal of the first power supply voltage Vcc level into a signal of the second power supply voltage Vcp level, and each of the converted signals is M
Output to the gates of the OS transistors TR1 and TR2.

The drain of the MOS transistor TR1 is connected to the input terminal CIL, and the source is grounded. The drain of the MOS transistor TR2 is the input terminal E
It is connected to the LD and the source is grounded. The input terminal CIL is connected to the other end of the inductance L3 whose one end is connected to the first power supply voltage Vcc and the anode of the diode D1. Further, the input terminal ELD is connected to the cathode of the diode D1 and the electroluminescence 18
One end of is connected. The other end of the electroluminescence 18 is connected to the first power supply voltage Vcc.

Here, the input terminals RT1 and RT2 of the IC
The external resistor R connected to is configured as shown in FIG. 4, for example. In FIG. 4, signals L1, L2, L3 output from a CPU (not shown) pass through inverters 21, 22, 23, respectively, and bidirectional buffers 24, 25, 2 respectively.
It is input to the control terminal of 6. Input terminals RT1 and RT2
Is connected in parallel with resistors R1, R2, R3, and R4, and a bidirectional buffer 24 is provided between the resistors R1 and R2, and a bidirectional buffer 2 is provided between the resistors R2 and R3.
5 is a bidirectional buffer 26 between the resistors R3 and R4.
Is connected.

Now, when the signals L1, L2, and L3 are at low level ("0"), the bidirectional buffers 24 to 26 become through, and when the signals L1 to L3 are at high level ("1"), the bidirectional buffer 24. It is assumed that .about.26 have high impedance (open).

When the signal L1 = L2 = L3 = 1, all the bidirectional buffers are open, so that the terminal RT1
The resistance between RT2 and RT2 is R1. Also, the signal L1
= 0 and L2 = L3 = 1, the bidirectional buffer 2
Since only 4 is through, the resistance value between the terminals RT1 and RT2 is that in which R1 and R2 are connected in parallel.

Further, the signal L1 = L2 = 0 and the signal L3 =
When 1, the resistance value between the terminals RT1 and RT2 is
R1, R2, and R3 are connected in parallel. Therefore, by changing the signals L1 to L3, terminals RT1 and R3
The resistance value R between T2 and T2 can be changed.

In this way, by varying the value of the resistance externally attached to the IC, the oscillation frequency of the circuit (comprising the MOS transistors TR1 and TR2 and the inductance L1) for generating the high voltage supplied to the EL 18 is varied. Therefore, the EL 18 can be made to emit light with an appropriate brightness.
In addition, the resistance R can be changed to adjust the EL 18 according to the user's preference.
It is also possible to change the emission brightness and color tone of.

Next, the circuit operation of the above-mentioned EL drive circuit IC will be described with reference to the timing chart of FIG. When the enable signal for enabling the IC becomes active, the internal oscillator circuit 13 generates a signal having a cycle corresponding to the value of the resistor R connected between the input terminals RT1 and RT2 at that time. Then, the frequency division / control circuit 14
Outputs the gate drive signal TR1VGS of the cycle T1 to the gate of the MOS transistor TR1 (FIG. 5A).
At this time, no signal is output to the gate of the MOS transistor TR2 ((b) in the figure).

As a result, the MOS transistor TR1 is repeatedly turned on and off in the cycle T1, and the energy stored in the inductance L3 while the MOS transistor TR1 is on passes through the diode D1 while the MOS transistor TR1 is off. And is output to the EL 18 (FIG. 7C). As a result, the MOS transistor TR1
Each time the switching is repeated, the voltage across the EL 18 gradually rises ((d) in the figure).

Then, at a certain time t1, the gate drive signal TR2 supplied to the gate of the MOS transistor TR2.
When VGS becomes high level ((b) in the figure), EL18
The energy stored in is released and the EL 18 emits light. Then, while the gate drive signal TR2VGS of the MOS transistor TR2 is at a high level, the pulsed voltage applied to the terminal CIL when the MOS transistor TR1 is off is the diode D1 and the MOS transistor TR.
Since it is discharged through 2, the voltage of EL 18 does not rise.

Then, at time t2, the gate drive signal TR2
When VGS becomes low level ((b) in the figure), the energy released from the inductance L3 is accumulated in the EL18 every time the MOS transistor TR1 is repeatedly turned on and off as described above, and the voltage of the EL18 gradually rises. To go. Such an operation is repeated and the EL 18 maintains the light emitting state.

It should be noted that the oscillation frequency or duty ratio of the high-voltage generating circuit for generating the high voltage supplied to the electroluminescence is gradually changed, and a plurality of patterns of the change are provided to obtain the electroluminescence emission pattern. It can be variously changed.

[0039]

According to the present invention, by controlling the high voltage signal supply means to be turned on and off, it is possible to cause the electroluminescence element to emit light at an appropriate brightness and reduce the power consumption of the drive circuit. Further, by varying the ON / OFF control cycle or the duty ratio, the power consumption of the drive circuit can be similarly reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a first embodiment of the present invention.

FIG. 2 is a timing chart of the circuit of FIG.

FIG. 3 is a circuit block diagram of a second embodiment.

FIG. 4 is a diagram showing an example of an external resistor R.

5 is a timing chart of the circuit of FIG.

[Explanation of symbols]

 2 Electroluminescence element 3 Switch L1 Primary winding L2 Secondary winding TR1, TR2 Transistor

Claims (3)

[Claims] 1. An electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and an operating voltage to the high voltage signal supply means via the switch means. An EL drive circuit comprising: an operating voltage supply means for supplying; and a periodic signal output means for outputting a periodic signal for turning on and off the switch means at a predetermined cycle. 2. An electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and an operating voltage to the high voltage signal supply means via the switch means. An operating voltage supply means for supplying, a periodic signal output means for outputting a periodic signal for turning on and off the switch means at a predetermined period, and a duty control means for changing the duty of the periodic signal output from the periodic signal output means. An EL drive circuit comprising: 3. An electroluminescent element, a high voltage signal supply means for supplying a high voltage signal to the electroluminescent element, a switch means, and an operating voltage to the high voltage signal supply means via the switch means. An operating voltage supply means for supplying, a periodic signal output means for outputting a periodic signal for turning on and off the switch means at a predetermined cycle, and a cycle control means for changing the cycle of the periodic signal output from the cyclic signal output means. And E
L drive circuit.