JP2007180388A - Led driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an LED driver capable of preventing flickering on a display screen by apparently improving a resolution of a current change in the case of continuously applying current control or like processing to a plurality of LEDs for a backlight of a display apparatus. <P>SOLUTION: LED drive circuits 12-1 to 12-n drive LEDs 11-1 to 11-n corresponding to the LED drive circuits in a way of supplying each setting current to each of the LEDs to light them up. An LED current revision signal generating circuit 5 generates a plurality of LED current revision signals S1 to Sn each having a prescribed phase difference with each other, respectively, on the basis of an LED current revision signal Sc received in response to revision of the luminance of the display apparatus. An LED current control circuit 6 sequentially distributes and sets a received setting current Ia to the LED drive circuits 12-1 to 12-n, according to each input timing of the LED current revision signals S1 to Sn generated by the LED current revision signal generating circuit 5. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an LED driving device for driving an LED (Light Emitting Diode) used for a backlight light source such as a liquid crystal display device.

In recent years, white LEDs have been used as a backlight light source for liquid crystal display devices, etc., and these LEDs have a large forward voltage, so a booster circuit such as a charge pump circuit is required when the voltage of a DC power source such as a secondary battery is low. It becomes.
For this reason, in the conventional LED drive device, in order to light the LED, the voltage of the battery and the boosted voltage of the charge pump circuit that operates on the battery are selectively switched and used (for example, Patent Document 1).

By the way, in this kind of LED drive device, when adjusting the brightness of the liquid crystal display device, it is necessary to change the current value of the LED continuously (dynamically).
Therefore, an LED driving device that turns on a plurality of LEDs for backlight of a liquid crystal display device and that continuously changes the current values of the plurality of LEDs is as shown in FIG. Conceivable.

As shown in FIG. 10, the LED driving device includes an LED driving unit 1, an LED applied voltage generating unit 2, and an LED current value control circuit 3, which are operated by a DC power source 4 such as a secondary battery. It is like that.
As shown in the figure, the LED drive unit 1 includes n LEDs 11-1 to 11-n and n LED drive circuits 12-1 to 12-n.

The LED drive circuits 12-1 to 12-n are configured to drive the respective LEDs 11-1 to 11-n so as to be lit by passing respective setting currents.
The LED applied voltage generator 2 includes a charge pump circuit 21, a switch 22 connected in parallel to the charge pump circuit 21, and a voltage determination circuit 23.
The voltage determination circuit 23 detects the voltage of the DC power supply 4, compares the detected voltage with a reference value, and controls the charge pump circuit 21 and the switch 22 according to the comparison result.

That is, when the detected voltage is equal to or higher than the reference value, the boosting operation of the charge pump circuit 21 is stopped, and at the same time, the switch 22 is closed. For this reason, the voltage of the DC power supply 4 becomes the output voltage of the LED applied voltage generator 2.
On the other hand, when the detected voltage is lower than the reference value, the boost operation of the charge pump circuit 21 is instructed, and at the same time, the switch 22 is opened. For this reason, the boosted voltage of the charge pump circuit 21 becomes the output voltage of the LED applied voltage generator 2.

Each time the LED current change signal Sc is input, the LED current value control circuit 3 outputs the set current Ia to be set to the LED drive circuits 12-1 to 12-n, which is output from the LED drive circuits 12-1 to 12-12. -N is set simultaneously.
Next, an operation example of the LED driving device having such a configuration will be described with reference to FIGS. 10 and 11.

If the LED current change signal Sc input to the LED current value control circuit 3 is input at the timing shown in FIG. 11A, the LED drive circuit 12-1 input to the LED current value control circuit 3 The set current Ia of ˜12-n is output at each timing, and is set simultaneously to the LED drive circuits 12-1 to 12-n.
For example, when I0 is set as the set current in the LED drive circuits 12-1 to 12-n before time t1, the LEDs 11-1 to 11-n have the current as shown in FIG. A set current I0 flows. At this time, the total LED current Iout flowing through the LEDs 11-1 to 11-n becomes (I0 × n), for example, as shown in FIG.

Thereafter, as shown in FIG. 11A, when the LED current change signal Sc is input at time t1, the set current of the LED drive circuits 12-1 to 12-n is changed from I0 to I1 at this timing. This is simultaneously set in the LED drive circuits 12-1 to 12-n.
Therefore, each current flowing through the LEDs 11-1 to 11-n changes from I0 to I1, and this change is as shown in FIG. The amount of change ΔI in the current of the LEDs 11-1 to 11-n at this time is expressed by the following equation (1).
ΔI = I1-I0 (1)
Therefore, the minimum resolution of the current setting of the LED current value control circuit 3 is ΔI.

Further, when each current flowing through the LEDs 11-1 to 11-n changes from I0 to I1, the total LED current Iout flowing through the LEDs 11-1 to 11-n changes from (I0 × n) to (I1 × n). This change is as shown in FIG. At this time, the change amount ΔIout of the LED current Iout of the entire LEDs 11-1 to 11-n is expressed by the following equation (2).
ΔIout = (I1 × n) − (I0 × n) = n × (I1−I0) = n × ΔI (2)
Therefore, when the entire LED current Iout changes from (I0 × n) to (I1 × n), the change rate x is expressed by the following equation (3) using (2).
x = (ΔIout) / (n × I1) = (n × ΔI) / (n × I1) = ΔI (3)
When such an operation is performed, if the rate of change x exceeds 1 [%] to 2 [%], flicker may be felt on the display screen of the display device.

In order to suppress this flicker, it is necessary to reduce the minimum resolution ΔI as can be seen from the equations (3) and (1). That is, it is necessary to change the light emission amount of the LED little by little by reducing the interval of the set current generated at the timing when the LED current change signal S1 is input.
However, in this case, there may be a problem that the manufacturing cost of the LED current value control circuit 3 increases.
JP 2003-158299 A

  In view of the above points, an object of the present invention is to apparently improve the resolution of current change when continuously controlling the current of a plurality of LEDs for a backlight of a display device, and to flicker the display screen. An object of the present invention is to provide an LED drive device that can be prevented.

In order to solve the above problems and achieve the object of the present invention, each invention has the following configuration.
That is, the first invention is an LED driving device that lights a plurality of LEDs, and a plurality of LED driving circuits that drive each LED so that the plurality of LEDs are lit at a desired set current, and the plurality of LEDs A control unit that sets a new set current to each of the plurality of LED drive circuits at different timings when there is an instruction to change each set current of the LED drive circuit, and the increase / decrease amount of the new set current is the same It is characterized by being.

  A second invention is an LED driving device for lighting a plurality of LEDs for backlight of a display device, and a plurality of LED driving circuits for driving each LED so as to light the plurality of LEDs with a desired set current. And a control unit that sets a new set current to the plurality of LED drive circuits at different timings when there is an instruction to change the brightness of the display device, and the increase / decrease amount of the new set current is the same It is characterized by being.

  According to a third invention, in the first or second invention, the control unit generates an LED current change signal generation circuit that generates a plurality of LED current change signals each having a predetermined phase difference based on the LED current change signal; An LED current value control circuit that sequentially distributes a new set current to the plurality of LED drive circuits each time an LED current change signal generated by the LED current change signal generation circuit is input.

  In a fourth aspect based on the third aspect, the plurality of LED drive circuits can set a voltage according to a set current and detect a voltage according to a current flowing through the LED, and the detected voltage is the set voltage. The LED current value control circuit generates a plurality of set voltages corresponding to set currents of the plurality of LED drive circuits, and the LED Each time the LED current change signal generated by the current change signal generation circuit is input, the setting voltage corresponding to the setting current is selected from the plurality of setting voltages generated by the setting voltage generation circuit, and the selected setting is selected. A set voltage output circuit that sequentially distributes the voltage to the plurality of LED drive circuits.

  5th invention is an LED drive device which lights a some LED, Comprising: The some LED drive circuit which drives each LED so that these LEDs may be lighted with a desired setting current, and the some LED drive When there is an instruction to change each set current of the circuit, a new set current is simultaneously set in the plurality of LED drive circuits, and at this time, the new set current is gradually changed to a set value with respect to time. And a control unit for controlling.

  A sixth invention is an LED driving device for lighting a plurality of LEDs for backlight of a display device, and a plurality of LED driving circuits for driving each LED so as to light the plurality of LEDs with a desired set current. When there is an instruction to change the brightness of the display device, a new set current is simultaneously set in the plurality of LED drive circuits, and at this setting, the new set current is gradually set to a set value with respect to time. And a control unit for changing the control unit.

  According to a seventh invention, in the fifth or sixth invention, the control section outputs an LED current value control circuit that outputs a new set current each time an LED current change signal is input, and the LED current value control. A setting current output from the circuit is simultaneously set in the plurality of LED driving circuits, and at the time of setting, a current delay circuit that gradually changes the setting current to a setting value with respect to time is provided.

  In an eighth aspect based on the seventh aspect, the plurality of LED drive circuits can set a voltage corresponding to a set current and detect a voltage corresponding to a current flowing through the LED, and the detected voltage is the set voltage. The LED current value control circuit generates a plurality of set voltages corresponding to set currents of the plurality of LED drive circuits, and the LED A setting voltage output circuit for selecting a setting voltage corresponding to a setting current from a plurality of setting voltages generated by the setting voltage generation circuit each time a current change signal is input, and outputting the selected setting voltage; The current delay circuit is configured to gradually change the set voltage output from the set voltage selection circuit to a set value with respect to time, and simultaneously to the plurality of LED drive circuits. Configured to feed.

  A ninth invention is an LED driving device for lighting a plurality of LEDs, and a plurality of LED driving circuits for driving the LEDs so as to light the plurality of LEDs at a desired set current, and the plurality of LED driving When there is an instruction to change each set current of the circuit, a control unit that outputs a new set current at different timings and a new set current that is output from the control unit are set in the plurality of LED drive circuits, respectively. A plurality of current delay circuits for gradually changing each set current related to the change to a set value with respect to time at the time of setting, and the increase / decrease amount of the new set current is the same Features.

  A tenth aspect of the invention is an LED drive device that lights a plurality of LEDs for backlight of a display device, and a plurality of LED drives that drive each of the LEDs so that the LEDs are lit at a desired set current. When there is a change in the brightness of the circuit and the display device, a control unit that outputs a new set current at different timings, and a new set current output from the control unit to the plurality of LED drive circuits, respectively A plurality of current delay circuits that gradually change each set current related to the change to a set value with respect to time, and the increase / decrease amount of the new set current is the same It is characterized by that.

  An eleventh invention is the ninth or tenth invention, wherein the control unit generates an LED current change signal generation circuit that generates a plurality of LED current change signals each having a predetermined phase difference based on the LED current change signal; An LED current value control circuit that sequentially distributes a new set current value to the plurality of current delay circuits each time an LED current change signal generated by the LED current change signal generation circuit is input.

  In a twelfth aspect based on the eleventh aspect, the plurality of LED drive circuits can set a voltage according to a set current and detect a voltage according to a current flowing through the LED, and the detected voltage is the set voltage. The LED current value control circuit generates a plurality of set voltages corresponding to set currents of the plurality of LED drive circuits, and the LED Each time the LED current change signal generated by the current change signal generation circuit is input, the setting voltage corresponding to the setting current is selected from the plurality of setting voltages generated by the setting voltage generation circuit, and the selected setting is selected. A set voltage output circuit that sequentially distributes the voltage to the plurality of current delay circuits, and the plurality of current delay circuits are distributed by the set voltage selection circuit Gradually changed to the setting the constant voltage to time be configured to supply each of the plurality of LED driving circuits.

According to the present invention having such a configuration, when the current control of a plurality of LEDs is continuously performed, the resolution of the current change can be apparently improved, and the flickering of the LED lighting change can be prevented.
In addition, when the present invention is applied to a backlight such as a liquid crystal display device, flickering of the display screen can be prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
The configuration of the first embodiment of the LED driving device of the present invention will be described with reference to the block diagram of FIG.
The LED driving device according to the first embodiment drives an LED used for a backlight of a liquid crystal display device. As shown in FIG. 1, the LED driving unit 1 and the LED applied voltage generating unit 2 are driven. And an LED current change signal generation circuit 5 and an LED current value control circuit 6, which are operated by a DC power source 4 such as a secondary battery.

  Moreover, in this 1st Embodiment, the electric current sent through LED11-1 to 11-n can be set with respect to LED drive circuit 12-1 to 12-n of LED drive part 1, respectively, and the setting current is the LED drive circuit 12 It is set to -1 to 12-n at different timings. The change amount (change amount) of the current when the set current is changed, that is, the increase / decrease amount (change amount) of the set current is the same.

As shown in the figure, the LED drive unit 1 includes n LEDs 11-1 to 11-n and n LED drive circuits 12-1 to 12-n.
The LED drive circuits 12-1 to 12-n are configured to drive the respective LEDs 11-1 to 11-n so as to be lit by passing respective setting currents.
The LED applied voltage generator 2 includes a charge pump circuit 21, a switch 22 connected in parallel to the charge pump circuit 21, and a voltage determination circuit 23.

The voltage determination circuit 23 detects the voltage of the DC power supply 4, compares the detected voltage with a reference value, and controls the charge pump circuit 21 and the switch 22 according to the comparison result. This control will be described later.
The LED current change signal generation circuit 5 has a plurality of phase differences as shown in FIGS. 2A to 2C based on the LED current change signal Sc input in accordance with a change in luminance of the display device. LED current change signals S <b> 1 to Sn are generated and supplied to the LED current value control circuit 6.

That is, when the LED current change signal Sc is input, the LED current change signal generation circuit 5 first generates and outputs the LED current change signal S1 as shown in FIG. ) Generates and outputs an LED current change signal S2, and generates and outputs a plurality of LED current change signals S1 to Sn having different phase differences.
The LED current value control circuit 6 sends the input set current Ia to the LED drive circuits 12-1 to 12- every time the LED current change signals S1 to Sn generated by the LED current change signal generation circuit 5 are input. It is arranged to be assigned to n sequentially.

  That is, the LED current value control circuit 6 outputs and sets the set current Ia to the LED drive circuit 12-1 when the LED current change signal S1 is input, and the set current Ia when the LED current change signal S2 is input. Is output to the LED drive circuit 12-2 and set, and the set current Ia is sequentially distributed to the LED drive circuits 12-1 to 12-n at different timings.

Next, the operation of the first embodiment having such a configuration will be described with reference to FIG. 1 and FIG.
The voltage determination circuit 23 detects the voltage of the DC power supply 4 and compares this detected voltage with a reference value. If the detected voltage is equal to or higher than the reference value, the voltage pump circuit 21 stops the boosting operation. At the same time, the switch 22 is closed. For this reason, the voltage of the DC power supply 4 becomes the output voltage of the LED applied voltage generator 2.

On the other hand, when the detected voltage is equal to or lower than the reference value, the voltage determination circuit 23 instructs the boost operation of the charge pump circuit 21 and simultaneously opens the switch 22. For this reason, the boosted voltage of the charge pump circuit 21 becomes the output voltage of the LED applied voltage generator 2.
When the LED current change signal Sc is input, the LED current change signal generation circuit 5 first generates and outputs the LED current change signal S1 as shown in FIG. The LED current change signal S2 as shown is generated and output, and the LED current change signals S1 to Sn having different phase differences are sequentially generated and output.

The LED current value control circuit 6 sequentially supplies the set current Ia to the LED drive circuits 12-1 to 12-n at each timing when the LED current change signals S1 to Sn generated by the LED current change signal generation circuit 5 are input. It comes to distribute.
That is, when the LED current change signal S1 is input, the LED current value control circuit 6 outputs and sets a new set current Ia to the LED drive circuit 12-1, and when the LED current change signal S2 is input. The same set current Ia is output to the LED drive circuit 12-2 and set, and the set current Ia having the same value is sequentially distributed to the LED drive circuits 12-1 to 12-n at different timings. Set (change).

Therefore, the set currents Ia set in the LED drive circuits 12-1 to 12-n are changed from the previous set values to the current set values, and the LED drive circuits 12-1 to 12-n The LEDs 11-1 to 11-n are driven such that the set current of the set value flows to the LEDs 11-1 to 11-n.
As a result, the currents that flow through the LEDs 11-1 to 11-n sequentially change in accordance with the set currents that are sequentially set, and an example thereof is as shown in FIGS.

As can be seen from FIGS. 2D to 2F, when the set current Ia changes, the currents of the LEDs 11-1 to 11-n change at different timings. However, the LED 11 changes every time the set current Ia changes. The amount of change ΔI of each of the currents −1 to 11-n is the same.
That is, the amount of change in the set current Ia set in each of the LED drive circuits 12-1 to 12-n is the same.

Thus, when each current flowing through the LEDs 11-1 to 11-n changes, the total LED current Iout flowing through the LEDs 11-1 to 11-n also changes accordingly. This change is shown in FIG. As shown.
As described above, in the first embodiment, when the lighting currents of the LEDs 11-1 to 11-n are changed, the change amount is the same, but the change is sequentially performed at different timings. It is possible to prevent the flickering of the lighting change of the LED.

For this reason, when this 1st Embodiment is applied as a backlight of a liquid crystal display device, the flickering of a display screen can be prevented.
Next, specific configurations of the LED current value control circuit 6 and the LED drive circuits 12-1 to 12-n described above will be described with reference to FIG.
As shown in FIG. 3, the LED current value control circuit 6 includes an LED current setting reference voltage source 61, a voltage follower circuit 62, a tapped resistor 63 having a plurality of taps, and an LED current setting voltage selection circuit. 64.

The reference voltage of the LED current setting reference voltage source 61 is applied to one end side of the tapped resistor 63 via the voltage follower circuit 62. The other end side of the tapped resistor 63 is grounded. In addition, each tap voltage of the resistor 63 with a tap is input to the LED current setting voltage selection circuit 64.
The LED current setting voltage selection circuit 64, every time the LED current change signals S1 to Sn are input, the voltage corresponding to the magnitude of the setting current Ia to be set in the LED drive circuits 12-1 to 12-n, The tap voltage of the resistor 63 with a tap is selected, and the selected tap voltage is sequentially set in the LED drive circuits 12-1 to 12-n as a set voltage.

As shown in FIG. 3, each of the LED drive circuits 12-1 to 12-n includes a MOS transistor Q1, a current detection resistor R1, and a differential amplifier circuit A1.
In the LED drive circuits 12-1 to 12-n having such a configuration, the differential amplifier circuit A1 performs feedback control so that the currents flowing through the LEDs 11-1 to 11-n become the set current values, respectively. That is, the differential amplifier circuit A1 controls the gate voltage of the MOS transistor Q1 so that the detection voltage due to the current flowing through the current detection resistor R1 becomes a set voltage value corresponding to the set current value.
(Second Embodiment)
The configuration of the second embodiment of the LED driving device of the present invention will be described with reference to the block diagram of FIG.

The LED driving device according to the second embodiment drives an LED used for a backlight of a liquid crystal display device. As shown in FIG. 4, the LED driving unit 1 and the LED applied voltage generating unit 2 are driven. And an LED current value control circuit 6A and a current delay circuit 7, which are operated by a DC power source 4 such as a secondary battery.
Moreover, in this 2nd Embodiment, the electric current sent through LED11-1 to 11-n can be set with respect to LED drive circuit 12-1 to 12-n of LED drive part 1, respectively, and the setting current is the LED drive circuit 12 -1 to 12-n are set at the same timing. In the setting, the set current is gradually changed to the set value with respect to time.

Further, the second embodiment is characterized in that the change amount (change amount) of the current when the set current is changed, that is, the increase / decrease amount (change amount) of the set current is the same.
The configurations of the LED drive unit 1 and the LED applied voltage generation unit 2 are the same as the configurations of the LED drive unit 1 and the LED applied voltage generation unit 2 shown in FIG. Is omitted.

The LED current value control circuit 6A outputs a new set current Ia that is input every time an LED current change signal Sc generated according to a change in luminance of the display device, etc. The circuit 7 is supplied.
The current delay circuit 7 simultaneously sets the setting current output from the LED current value control circuit 6A in the LED driving circuits 12-1 to 12-n. In this setting, the setting current is set with respect to time. The value is gradually changed to the set value.

Next, the operation of the second embodiment having such a configuration will be described with reference to FIGS.
The voltage determination circuit 23 detects the voltage of the DC power supply 4 and compares this detected voltage with a reference value. If the detected voltage is equal to or higher than the reference value, the voltage pump circuit 21 stops the boosting operation. At the same time, the switch 22 is closed. For this reason, the voltage of the DC power supply 4 becomes the output voltage of the LED applied voltage generator 2.

On the other hand, when the detected voltage is equal to or lower than the reference value, the voltage determination circuit 23 instructs the boost operation of the charge pump circuit 21 and simultaneously opens the switch 22. For this reason, the boosted voltage of the charge pump circuit 21 becomes the output voltage of the LED applied voltage generator 2.
The LED current value control circuit 6A outputs a new changed set current Ia each time an LED current change signal Sc as shown in FIG. 5A is input, and this is supplied to the current delay circuit 7. Is done.

The current delay circuit 7 simultaneously sets the setting current output from the LED current value control circuit 6A in the LED driving circuits 12-1 to 12-n. In this setting, the setting current is set with respect to time. Gradually change to the final set value.
For this reason, the LED drive circuits 12-1 to 12-n are simultaneously set with the same current value as the set current. At the time of this setting, the set current has a waveform that gradually changes by the current delay circuit 7. It becomes.

For this reason, each current flowing through the LEDs 11-1 to 11-n becomes a current according to the waveform of the set current output from the current delay circuit 7. An example of each current is shown in FIG. As shown.
As can be seen from FIG. 5B, when the set current Ia changes, the currents of the LEDs 11-1 to 11-n change at the same different timing. The amount of change ΔI of each current of 11-n is the same. That is, the amount of change in the set current Ia set in each of the LED drive circuits 12-1 to 12-n is the same.

Thus, when each current flowing through the LEDs 11-1 to 11-n changes, the total LED current Iout flowing through the LEDs 11-1 to 11-n also changes, and this change is as shown in FIG. .
Here, the total current flowing through the LEDs 11-1 to 11-n can be set to a curve a shown in FIG. 5D, but in this case, the change current is accurately controlled with respect to the change time. In addition to being difficult to do, it has the disadvantage of increasing its manufacturing cost.

As described above, in the second embodiment, when the lighting currents of the LEDs 11-1 to 11-n are changed, they are changed simultaneously, but each change is gradually changed to a set value with respect to time. Therefore, flickering due to the lighting change can be prevented.
For this reason, when this 2nd Embodiment is applied as a backlight of a liquid crystal display device, flickering of a display screen can be prevented.

Next, specific configurations of the LED current value control circuit 6A and the LED drive circuits 12-1 to 12-n described above will be described with reference to FIG.
As shown in FIG. 6, the LED current value control circuit 6A includes an LED current setting reference voltage source 61, a voltage follower circuit 62, a tapped resistor 63 having a plurality of taps, and an LED current setting voltage selection circuit. 65.

The reference voltage of the LED current setting reference voltage source 61 is applied to the tapped resistor 63 via the voltage follower circuit 62. Each tap voltage of the resistor 63 with a tap is input to the LED current setting voltage selection circuit 65.
The LED current setting voltage selection circuit 65 generates a voltage corresponding to the set current value Ia to be set in the LED drive circuits 12-1 to 12-n every time the LED current change signal Sc is input. The tap voltage is selected from 63 tap voltages, and the selected tap voltage is supplied to the current delay circuit 7 as a set voltage.

The LED drive circuits 12-1 to 12-n are configured in the same manner as the LED drive circuits 12-1 to 12-n shown in FIG.
Next, a specific configuration of the current delay circuit 7 shown in FIG. 6 will be described with reference to FIGS.
The current delay circuit shown in FIG. 7A includes a capacitor C10 as shown.

The current delay circuit in FIG. 7B is a combination of a resistor R10 and a capacitor C10 as shown.
The current delay circuit of FIG. 7C is a combination of a voltage follower circuit A2 and a capacitor C10 as shown.
The current delay circuit of FIG. 7D is a combination of a voltage follower circuit A2, a resistor R10, and a capacitor C10 as shown.

According to such a current delay circuit, the setting voltage output from the LED current setting voltage selection circuit 65 can be delayed.
(Third embodiment)
The configuration of the third embodiment of the LED drive device of the present invention will be described with reference to the block diagram of FIG.

  The LED driving device according to the third embodiment drives an LED used for a backlight of a liquid crystal display device. As shown in FIG. 8, the LED driving unit 1 and the LED applied voltage generating unit 2 are driven. An LED current change signal generation circuit 5, an LED current value control circuit 6A, and current delay circuits 7-1 to 7-n, which are operated by a DC power source 4 such as a secondary battery. Yes.

In the third embodiment, the first embodiment as shown in FIG. 1 and the second embodiment as shown in FIG. 4 are combined and the advantages of both are utilized.
The configurations of the LED drive unit 1 and the LED applied voltage generation unit 2 are the same as the configurations of the LED drive unit 1 and the LED applied voltage generation unit 2 shown in FIG. Is omitted.

The LED current change signal generation circuit 5 generates a plurality of LED current change signals S1 to Sn having a predetermined phase difference based on the LED current change signal Sc input according to a change in luminance of the display device, etc. This is supplied to the LED current value control circuit 6.
The LED current control circuit 6 applies the same set current value Ia to be input to the current delay circuits 7-1 to 7-7 at every timing when the LED current change signals S1 to Sn generated by the LED current change signal generation circuit 5 are input. -N is assigned sequentially.

The LED current control circuits 7-1 to 7-n set the setting currents Ia supplied from the LED current control circuit 6 at different timings to the corresponding LED drive circuits 12-1 to 12-n, respectively. In this case, the set current Ia is gradually changed to a set value with respect to time.
Next, the operation of the third embodiment having such a configuration will be described with reference to FIG.

The voltage determination circuit 23 detects the voltage of the DC power supply 4 and compares this detected voltage with a reference value. If the detected voltage is equal to or higher than the reference value, the voltage pump circuit 21 stops the boosting operation. At the same time, the switch 22 is closed. For this reason, the voltage of the DC power supply 4 becomes the output voltage of the LED applied voltage generator 2.
On the other hand, when the detected voltage is equal to or lower than the reference value, the voltage determination circuit 23 instructs the boost operation of the charge pump circuit 21 and simultaneously opens the switch 22. For this reason, the boosted voltage of the charge pump circuit 21 becomes the output voltage of the LED applied voltage generator 2.

The LED current change signal generation circuit 5 generates a plurality of LED current change signals S1 to Sn having different phase differences based on the LED current change signal Sc, and supplies the LED current change signals S1 to Sn to the LED current control circuit 6.
The LED current control circuit 6 applies the same set current value Ia to be input to the current delay circuits 7-1 to 7-7 at every timing when the LED current change signals S1 to Sn generated by the LED current change signal generation circuit 5 are input. Sort sequentially to -n.

The LED current control circuits 7-1 to 7-n set the setting currents Ia supplied from the LED current control circuit 6 at different timings to the corresponding LED drive circuits 12-1 to 12-n, respectively. In this case, the set current Ia is gradually changed to a set value with respect to time.
As described above, in the third embodiment, when the lighting currents of the LEDs 11-1 to 11-n are changed, the changes are sequentially performed at different timings, and each change is gradually set with respect to time. The flickering due to the lighting change can be prevented.

For this reason, when this 3rd Embodiment is applied as a backlight of a liquid crystal display device, the flickering of a display screen can be prevented.
Next, specific configurations of the LED current value control circuit 6 and the LED drive circuits 12-1 to 12-n described above will be described with reference to FIG.
As shown in FIG. 9, the LED current value control circuit 6 includes an LED current setting reference voltage source 61, a voltage follower circuit 62, a tapped resistor 63 having a plurality of taps, and an LED current setting voltage selection circuit. 64.

The reference voltage of the LED current setting reference voltage source 61 is applied to the tapped resistor 63 via the voltage follower circuit 62. Each tap voltage of the tapped resistor 63 is input to the LED current setting voltage selection circuit 64.
The LED current setting voltage selection circuit 64 sets the set current value Ia to be set in the LED drive circuits 12-1 to 12-n each time the LED current change signals S1 to Sn are input from the LED current change signal generation circuit 5. Is selected from the tap voltages of the resistor 63 with a tap, and the selected tap voltage is sequentially supplied to the current delay circuits 7-1 to 7-n as a set voltage.

  The LED drive circuits 12-1 to 12-n are configured in the same manner as the LED drive circuits 12-1 to 12-n shown in FIG. Moreover, each circuit shown in FIG. 7 can be used for the current delay circuits 7-1 to 7-n.

It is a block diagram which shows the structure of 1st Embodiment of this invention. It is a wave form chart of each part explaining an example of operation of a 1st embodiment. It is a figure which shows the specific structure of the LED current value control circuit and LED drive circuit of 1st Embodiment. It is a block diagram which shows the structure of 2nd Embodiment of this invention. It is a wave form chart of each part explaining an example of operation of a 2nd embodiment. It is a figure which shows the specific structure of the LED current value control circuit and LED drive circuit of 2nd Embodiment. It is a figure which shows the specific structure of the current delay circuit of FIG. It is a block diagram which shows the structure of 3rd Embodiment of this invention. It is a figure which shows the specific structure of the LED electric current value control circuit and LED drive circuit of 3rd Embodiment. It is the block of the power supply device examined prior to the present invention. It is a wave form chart of each part explaining an example of operation of the power unit.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... LED drive part, 2 ... LED applied voltage generation part, 4 ... DC power supply, 5 ... LED current change signal generation circuit, 6, 6A ... LED current value control circuit, 7, 7-1 to 7-n ... current delay circuit, 11-1 to 11-n ... LED, 12-1 to 12-n ... LED drive circuit, 21 ... charge pump circuit, 22 · ..Voltage judgment circuit.

Claims (12)

An LED driving device for lighting a plurality of LEDs,
A plurality of LED drive circuits for driving each LED so as to light the plurality of LEDs with a desired set current;
A control unit that sets a new set current to the plurality of LED drive circuits at different timings when there is an instruction to change each set current of the plurality of LED drive circuits,
The LED drive device, wherein the new set current increases and decreases are the same. An LED driving device for lighting a plurality of LEDs for backlight of a display device,
A plurality of LED drive circuits for driving each LED so as to light the plurality of LEDs with a desired set current;
A control unit configured to set a new set current to each of the plurality of LED drive circuits at different timings when there is an instruction to change the brightness of the display device;
The LED drive device, wherein the new set current increases and decreases are the same. The controller is
An LED current change signal generating circuit for generating a plurality of LED current change signals each having a predetermined phase difference based on the LED current change signal;
An LED current value control circuit that sequentially distributes a new set current to the plurality of LED drive circuits each time an LED current change signal generated by the LED current change signal generation circuit is input;
The LED driving device according to claim 1, further comprising: The plurality of LED drive circuits can set a voltage according to a set current, detect a voltage according to a current flowing through the LED, and turn on the LED so that the detected voltage matches the set voltage And
The LED current value control circuit is:
A set voltage generation circuit for generating a plurality of set voltages respectively corresponding to set currents of the plurality of LED drive circuits;
Each time an LED current change signal generated by the LED current change signal generation circuit is input, a setting voltage corresponding to a setting current is selected from a plurality of setting voltages generated by the setting voltage generation circuit. A set voltage output circuit that sequentially distributes the set voltage to the plurality of LED drive circuits;
The LED driving device according to claim 3, comprising: An LED driving device for lighting a plurality of LEDs,
A plurality of LED drive circuits for driving each LED so as to light the plurality of LEDs with a desired set current;
When there is an instruction to change each set current of the plurality of LED drive circuits, a new set current is simultaneously set in the plurality of LED drive circuits, and in this setting, a new set current is set with respect to time. A control unit that gradually changes to a value,
An LED driving device comprising: An LED driving device for lighting a plurality of LEDs for backlight of a display device,
A plurality of LED drive circuits for driving each LED so as to light the plurality of LEDs with a desired set current;
When there is an instruction to change the luminance of the display device, a new set current is simultaneously set in the plurality of LED drive circuits, and at this time, the new set current is gradually changed to a set value with respect to time. A control unit,
An LED driving device comprising: The controller is
An LED current value control circuit that outputs a new set current each time an LED current change signal is input;
A current delay circuit that simultaneously sets a set current output by the LED current value control circuit in the plurality of LED drive circuits, and gradually changes the set current to a set value with respect to time at the time of setting;
The LED driving device according to claim 5, further comprising: The plurality of LED drive circuits can set a voltage according to a set current, detect a voltage according to a current flowing through the LED, and turn on the LED so that the detected voltage matches the set voltage And
The LED current value control circuit is:
A set voltage generation circuit for generating a plurality of set voltages respectively corresponding to set currents of the plurality of LED drive circuits;
A setting voltage output circuit that selects a setting voltage corresponding to a setting current from a plurality of setting voltages generated by the setting voltage generation circuit and outputs the selected setting voltage every time the LED current change signal is input And comprising
The current delay circuit is configured to gradually change a set voltage output from the set voltage selection circuit to a set value with respect to time and supply the set voltage to the plurality of LED drive circuits simultaneously. Item 8. The LED drive device according to Item 7. An LED driving device for lighting a plurality of LEDs,
A plurality of LED drive circuits for driving each LED so as to light the plurality of LEDs with a desired set current;
A control unit that outputs a new set current at different timings when there is an instruction to change each set current of the plurality of LED drive circuits;
A new set current output from the control unit is set in each of the plurality of LED drive circuits, and in this setting, a plurality of set currents related to the change are gradually changed to a set value with respect to time. A current delay circuit,
The LED drive device, wherein the new set current increases and decreases are the same. An LED driving device for lighting a plurality of LEDs for backlight of a display device,
A plurality of LED driving circuits for driving each of the plurality of LEDs so as to light up at a desired set current;
When there is a change in the brightness of the display device, a control unit that outputs a new set current at different timings, and
A new set current output from the control unit is set in each of the plurality of LED drive circuits, and in this setting, a plurality of set currents related to the change are gradually changed to a set value with respect to time. A current delay circuit,
The LED drive device, wherein the new set current increases and decreases are the same. The controller is
An LED current change signal generating circuit for generating a plurality of LED current change signals each having a predetermined phase difference based on the LED current change signal;
An LED current value control circuit that sequentially distributes a new set current value to the plurality of current delay circuits each time an LED current change signal generated by the LED current change signal generation circuit is input;
The LED driving device according to claim 9, further comprising: The plurality of LED drive circuits can set a voltage according to a set current, detect a voltage according to a current flowing through the LED, and turn on the LED so that the detected voltage matches the set voltage And
The LED current value control circuit is:
A set voltage generation circuit for generating a plurality of set voltages respectively corresponding to set currents of the plurality of LED drive circuits;
Each time an LED current change signal generated by the LED current change signal generation circuit is input, a setting voltage corresponding to a setting current is selected from a plurality of setting voltages generated by the setting voltage generation circuit, and this selection is performed. A set voltage output circuit that sequentially distributes the set voltage to the plurality of current delay circuits,
The plurality of current delay circuits are configured to gradually change the set voltage distributed by the set voltage selection circuit to a set value with respect to time and supply the set voltage to the plurality of LED drive circuits, respectively. The LED driving device according to claim 11.

Images