JP2003274646A - Switching power supply device and electric equipment using the same - Google Patents

Abstract

(57) [Problem] To provide a switching power supply device capable of turning on only a part or all of LEDs selected from a plurality of systems of liquid crystal backlight LEDs with constant current control at the same current value. SOLUTION: A feedback control is performed so that a feedback current flowing through a resistor 8 is constant, and a current is supplied only to a liquid crystal backlight LED 6, a current is supplied only to a liquid crystal backlight LED 6 ', or a liquid crystal. A switching power supply device that switches, by switches 18 and 19, whether to supply current to a series connection of the backlight LED 6 and the liquid crystal backlight LED 6 '.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LED (Light Emitting D) used as a backlight of a liquid crystal display device.
The present invention relates to a switching power supply device for supplying electric power to an iode) and an electric device using the same.

[0002]

2. Description of the Related Art A conventional switching power supply device for supplying power to an LED (hereinafter, referred to as a liquid crystal backlight LED) used as a backlight of a liquid crystal display device will be described. FIG. 6 shows the configuration of a conventional switching power supply device.

A power supply voltage V _CC is applied to one end of the coil 1. The other end of the coil 1 is connected to the anode of the Schottky diode 2 and the collector of the NPN type transistor 3. The emitter of the transistor 3 is grounded. The cathode of the Schottky diode 2 is at one end of the capacitor 4,
It is connected to the cathode of the Zener diode 5 and the anode side of the LCD backlight LED 6. The other end of the capacitor 4 and the anode of the Zener diode 5 are grounded.

The cathode side of the LCD backlight LED 6 is connected to one end of a switch 7. The other end of the switch 7 is connected to one end of the resistor 8 and the positive phase input side of the error amplifier 9. The other end of the resistor 8 is grounded. Further, one end of the variable resistor 10 is connected to the negative phase input side of the error amplifier 9. The other end of the variable resistor 10 is grounded.

The output side of the error amplifier 9 and the negative phase input side are connected via a resistor 11. The output side of the error amplifier 9 is connected to the control circuit 12 '. The control circuit 12 'is connected to the base of the transistor 3. Further, the enable signal EN is input to the switch 7 and the control circuit 12 '.

The transistor 3, the switch 7, the resistor 8, the error amplifier 9, the resistor 11, and the control circuit 12 '.
And are provided in the semiconductor integrated circuit device 102. The semiconductor integrated circuit device 102, the coil 1, the Schottky diode 2, the capacitor 4, the Zener diode 5, and the variable resistor 10 constitute the conventional switching power supply device 202.

Next, the operation of the conventional switching power supply device 202 having the above configuration will be described. Energy is stored in the coil 1 when the transistor 3 is on. On the other hand, when the transistor 3 is off, energy is stored in the coil 1 and energy is supplied to the liquid crystal backlight LED 6. By such an operation, the power supply voltage V _CC is boosted and the liquid crystal backlight L
Supplied to ED6.

The Schottky diode 2 prevents the current output from the DC-DC converter 202 toward the liquid crystal backlight LED 6 from flowing backward. Further, the capacitor 4 smoothes the output voltage. Further, the Zener diode 5 is an L for a liquid crystal backlight.
The DC-DC converter 202 is protected from an abnormal voltage rise state that occurs when the current of the LCD backlight LED 6 is not input to the semiconductor integrated circuit device 102 even when the switch 7 is closed due to a mounting failure of the ED 6 or the like. It is provided for.

When the switch 7 is in the closed state, the voltage corresponding to the voltage drop of the resistor 8 due to the feedback current I from the LCD backlight LED 6 is input to the positive phase input of the error amplifier 9. Here, the voltage V _O output from the error amplifier 9 is represented by the equation (1). However, the resistance value of the resistor 8 is R ₈ , the resistance value of the variable resistor 10 is R ₁₀ , and the resistance value of the resistor 11 is R ₁₁ . V _O = (1 + R ₁₁ / R ₁₀ ) × R ₈ × I ... (1)

The control circuit 12 'has a high frequency (for example, 100
A built-in oscillation circuit (not shown) that oscillates a triangular wave of (kHz). The control circuit 12 'compares the triangular wave with the voltage V _O, and if the triangular wave is larger than the voltage V _O , the control circuit 12' outputs High.
It outputs an h level signal, and outputs a low level signal if the triangular wave is not higher than the voltage V _O. As a result, the control circuit 12 ′ can output a pulse signal according to the voltage V _O , and the transistor 3 is turned on / off by the pulse signal. Therefore, the conventional switching power supply device 202 performs feedback control to make the feedback current I a constant current. The set value of the feedback current I can be adjusted by the resistance value R ₁₀ of the variable resistor 10.

The LCD backlight LED 6 has a structure in which a plurality of LEDs are connected in series. Therefore, the conventional switching power supply device 202 is used for the LE for the liquid crystal backlight.
LED for LCD backlight by applying constant current to D6
The same current flows through each of the LEDs constituting the LED 6, and the uneven brightness of each LED is reduced. Further, as described above, since the set value of the feedback current I can be adjusted by the resistance value R ₁₀ of the variable resistor 10, the liquid crystal backlight LED 6 can be set to a desired brightness.

[0012]

When the conventional switching power supply device 202 is used in an electric device equipped with two liquid crystal display devices, it has been conventionally required to independently control ON / OFF of the two liquid crystal display devices. Two switching power supply devices 202 must be used. this is,
This is a big problem in terms of circuit scale and cost.

For this reason, the switching power supply device having the configuration shown in FIG. 7 is sometimes used in an electric device having two liquid crystal display devices. Here, the configuration of the conventional switching power supply device shown in FIG. 7 will be described. Note that FIG.
6, the same parts as those in FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted.

The switching power supply device 203 of FIG. 7 is similar to the switching power supply device 202 of FIG.
FET (Metal Oxide Semiconductor Field Effect Tra
nsistor) 13, an n-channel MOSFET 14,
This is a configuration in which a NOT circuit 15 is newly added. LED6 for LCD backlight and LED6 'for LCD backlight
Are connected in parallel to the switching power supply device 203. The anode side of the LCD backlight LED 6 and the anode side of the LCD backlight LED 6 ′ are connected to the cathode of the Schottky diode 2. In addition, the cathode side of the LCD backlight LED 6 is connected to one end of the switch 7 via the MOSFET 13, and the LCD backlight LED 6 is connected.
The cathode side of 6'is connected to one end of the switch 7 via the MOSFET 14. The selection signal SEL is M
It is input to the gate of the OSFET 14 and also to the gate of the MOSFET 13 via the NOT circuit 15.

The switching power supply device 2 having such a configuration
03 is an L for the liquid crystal backlight according to the selection signal SEL
The ED 6 and the LCD backlight LED 6'are controlled to be turned on / off. When the selection signal SEL is at the high level, the switching power supply device 203 operates as a liquid crystal backlight LED.
6'is turned on, and the LCD backlight LED 6 is turned off. On the other hand, when the selection signal SEL is at the low level, the switching power supply device 203 causes the liquid crystal backlight LED
6 is turned on, and the LCD backlight LED 6'is turned off. As described above, the switching power supply device 203 independently turns on / off the two liquid crystal backlight LEDs.
It can be controlled off.

However, the switching power supply unit 20
No. 3 has a problem that when the two liquid crystal backlight LEDs are turned on at the same time, the two liquid crystal backlight LEDs cannot be subjected to constant current control with the same current value. The switching power supply device 203 controls the constant current by the feedback current of the LED for the liquid crystal backlight. However, since the switching power supply device 203 has the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6 ′ connected in parallel,
LED6 for LCD backlight and LE for LCD backlight
When D6 'and both are turned on at the same time, the current flowing through the LCD backlight LED 6 and the LCD backlight LED
The currents flowing through 6'were not equal.

In view of the above problems, the present invention is a switching power supply capable of constant-current-controlling only a part or all of LEDs selected from a plurality of LEDs for liquid crystal backlights with the same current value to turn them on. An object is to provide a device and an electric device using the device.

[0018]

In order to achieve the above object, in the switching power supply device according to the present invention, n (n) are used as backlights of liquid crystal display devices, respectively.
Is a natural number greater than or equal to 2) system, the ratio of the ON / OFF period of the switching means is varied, the input voltage supplied from the outside is transformed to generate the output voltage, and the output voltage is output from the output end. The ratio of the ON / OFF period of the switching means is controlled by the pulse signal created based on the feedback current so that the feedback current input from the output DC-DC converter and the feedback current input terminal becomes a constant current. An LED for supplying power is selected from the control means and the LED of the n system according to an external control signal, and when the LED for supplying power is one system, it is selected according to the external control signal. The anode side of the LED of one system is connected to the output terminal, and the cathode side of the LED of the one system selected according to the external control signal is connected to the feedback current input terminal. When the LEDs for supplying the electric power are plural systems, the plural systems of LEDs selected according to the external control signal are connected in series, and the connection state for the LEDs of the n systems is switched according to the external control signal. An anode side of a series connection body composed of a plurality of selected LEDs is connected to the output terminal, and a cathode side of a series connection body composed of a plurality of systems of LEDs selected according to the external control signal is the feedback current input end. To be connected to
And a switching unit for switching the connection state for the LEDs of the n systems.

Further, the control means includes a constant current adjusting means for adjusting the setting of the constant current value of the feedback current, and the switching means, the switching means, and the control means other than the constant current adjusting means. May be provided in the semiconductor integrated circuit device.

Further, the semiconductor integrated circuit includes voltage detection means for detecting the output voltage of the DC-DC converter and for stopping the ON / OFF operation of the switching means when the output voltage of the DC-DC converter is equal to or higher than a predetermined value. It may be provided in the circuit device.

Further, the control means detects the selection state of the switching means, and the switching means supplies an electric power from among the n-system LEDs in accordance with the external control signal.
When none of the above is selected, the on / off operation of the switching means may be stopped.

The control means may stop the on / off operation of the switching means in response to the external control signal.

Also, when n is 2, the switching means is
LE used as a backlight of the first liquid crystal display device
Either the terminal connected to the anode side of D or the cathode side of the LED used as the backlight of the first liquid crystal display device and the terminal connected to the anode side of the LED used as the backlight of the second liquid crystal display device. The first liquid crystal display device, a first switch that connects one of the output terminals to the output terminal according to the external control signal, a terminal connected to the cathode side of an LED used as a backlight of the second liquid crystal display device, and the first liquid crystal display device. Of the LED used as the backlight of the second liquid crystal display device and the terminal connected to the anode side of the LED used as the backlight of the second liquid crystal display device, and the feedback current input end to the external control signal. And a second switch connected accordingly.

Further, in order to achieve the above object, in the electric device according to the present invention, n (n is a natural number of 2 or more)
Liquid crystal display devices, and n (n is a natural number of 2 or more) LEs used as a backlight of the liquid crystal display device
And a switching power supply device of any one of the above configurations connected to D. As the electric device according to the present invention, for example, a mobile phone device can be cited.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of the switching power supply device according to the present invention. In addition, in FIG.
The same parts as those in FIG.

A power supply voltage V _CC is applied to one end of the coil 1. The other end of the coil 1 is connected to the anode of the Schottky diode 2 and the collector of the NPN type transistor 3. The emitter of the transistor 3 is grounded. The cathode of the Schottky diode 2 is at one end of the capacitor 4,
It is connected to the input side of the voltage detection circuit 16 and one end of the switch 17. The other end of the capacitor 4 is grounded, and the output side of the voltage detection circuit 16 is connected to the control circuit 12.
The control circuit 12 stops the on / off control of the transistor 3 when there is an output signal from the voltage detection circuit 16, except that the conventional switching power supply device 2 shown in FIG.
This is a circuit that operates in the same manner as the control circuit 12 'included in 02.

The other end of the switch 17 is connected to the A of the switch 18.
Connected to the end. The H end of the switch 18 is connected to the anode side of the LCD backlight LED 6. Switch 18
L end of switch and L end of switch 19 are L for LCD backlight
LED 6'for cathode side of ED6 and liquid crystal backlight
Connected to the anode side of. The H end of the switch 19 is connected to the cathode side of the LCD backlight LED 6 '.

The A terminal of the switch 19 is connected to one terminal of the resistor 8 and the positive phase input side of the error amplifier 9. The other end of the resistor 8 is grounded. Further, one end of the variable resistor 10 is connected to the error amplifier 9
It is connected to the negative phase input side of. The other end of the variable resistor 10 is grounded.

The output side of the error amplifier 9 and the negative phase input side are connected via a resistor 11. The output side of the error amplifier 9 is connected to the control circuit 12. The control circuit 12 is connected to the base of the transistor 3. Then, the output signal of the OR circuit 20 is sent to the control circuit 12 and the switch 17.

Further, the first enable signal EN1 is ORed.
The second enable signal EN2 is input to the circuit 20 and the switch 18, and the second enable signal EN2 is input to the OR circuit 20 and the switch 19.
The switch 18 connects the A terminal and the H terminal when the enable signal EN1 is at the high level, and enables the enable signal EN.
When 1 is at Low level, the A end and the L end are connected. Further, the switch 19 has the enable signal EN2 set to High.
When the level is level, the A terminal and the H terminal are connected, and when the enable signal EN2 is at the low level, the A terminal and the L terminal are connected.

The transistor 3, the resistor 8, the error amplifier 9, the resistor 11, the control circuit 12, and the voltage detection circuit 16
The switches 17 to 19 and the OR circuit 20 are provided in the semiconductor integrated circuit device 100. The semiconductor integrated circuit device 100, the coil 1, the Schottky diode 2, the capacitor 4, and the variable resistor 10 constitute the switching power supply device 200 according to the present invention.

Next, the operation of the switching power supply device 200 will be described focusing on the difference from the conventional switching power supply device 202 shown in FIG.

First, the operation when the enable signals EN1 and EN2 are both at the high level will be described. Since the enable signal EN1 is at the high level, the A terminal and the H terminal of the switch 18 are connected. Further, since the enable signal EN2 is at the high level, the switch 1
The A end and the H end of 9 are connected. Therefore, the switch 17 is connected to the LED for the liquid crystal backlight through the switch 18.
LED for LCD backlight connected to the anode side of 6
The cathode side of 6 is connected to the anode side of the LCD backlight LED 6 ′, and the cathode side of the LCD backlight LED 6 ′ is connected to one end of the resistor R 8 and the positive phase input side of the error amplifier 9 via the switch 19. That is, the LCD backlight LED 6 and the LCD backlight LED 6 '
Will be connected in series to the switching power supply device 200. As a result, the same constant current flows in both the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6 ′, and both the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6 ′ are turned on.

Then, the enable signal EN1 is changed to High.
The operation when the level and the enable signal EN2 are at the Low level will be described. Enable signal EN1 is High
Since it is at the h level, the A terminal and the H terminal of the switch 18 are connected. Further, since the enable signal EN2 is at the Low level, the A terminal and the L terminal of the switch 19 are connected. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 via the switch 18,
The cathode side of the LCD backlight LED 6 is the switch 1
One end of the resistor R8 is connected via 9 to the positive phase input side of the error amplifier 9. That is, the LCD backlight LED 6
A constant current is supplied only from the switching power supply device 200. As a result, LE for LCD backlight
D6 is turned on, LED6 'for LCD backlight
Turns off.

Next, the operation when the enable signal EN1 is at low level and the enable signal EN2 is at high level will be described. Enable signal EN1 is Low
Since it is a level, the A terminal and the L terminal of the switch 18 are connected. Further, since the enable signal EN2 is at the high level, the A terminal and the H terminal of the switch 19 are connected. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 ′ via the switch 18, and the cathode side of the LCD backlight LED 6 ′ is connected via the switch 19 to one end of the resistor R 8 and the positive phase input side of the error amplifier 9. Connected to. That is, L for LCD backlight
A constant current is supplied from the switching power supply device 200 only to the ED 6 '. As a result, the LCD backlight LED 6 is turned off, and the LCD backlight L
ED6 'is turned on.

Finally, the operation when the enable signals EN1 and EN2 are both at the low level will be described. Since the enable signal EN1 is at the Low level, the A terminal and the L terminal of the switch 18 are connected. Further, since the enable signal EN2 is at the Low level, the A terminal and the L terminal of the switch 19 are connected. Therefore, the switch 17
Is connected to one end of the resistor R8 and the positive phase input side of the error amplifier 9 via the switch 18 and the switch 19. That is, a constant current is not supplied from the switching power supply device 200 to the liquid crystal backlight LED 6 and the liquid crystal backlight 6 '. As a result, both the LCD backlight LED 6 and the LCD backlight LED 6'are turned off.

Since the switching power supply device 200 operates as described above, the liquid crystal backlight LED to be turned on is determined by the enable signals EN1 and EN2.

When both the enable signals EN1 and EN2 are at low level, the output signal of the OR circuit 20 becomes low level. The output signal of the OR circuit 20 is Low
When the level is reached, the control circuit 12 stops the switching control and the switch 17 is opened. Thereby, the reactive current flowing through the coil 1, the Schottky diode 2, the switch 17, the switch 18, the switch 19 and the resistor 8 can be eliminated.

As described above, the enable signal EN1,
EN2 is a signal for selecting the liquid crystal backlight LED to be turned on, and is also a signal for stopping / non-stopping the switching control of the control circuit 12, that is, switching the valid / invalid of the switching power supply device. As described above, since the enable signals EN1 and EN2 have two roles, the number of external signals input to the switching power supply device 200 is small. As a result, the number of external signal input terminals of the switching power supply device 200 is reduced, and the size can be reduced.

Further, the switching power supply device 200 has the voltage detection circuit 16 built in the semiconductor integrated circuit 100.
When the voltage detection circuit 16 detects an abnormal boost, the control circuit 12 stops the on / off control of the transistor 3. Therefore, the circuit due to the abnormal boost that occurs in an open loop state such as a mounting defect of the liquid crystal backlight LEDs 6 and 6 ′. It is possible to prevent destruction. In the conventional switching power supply device 202 shown in FIG. 6, abnormal boosting is prevented by the Zener diode externally attached to the semiconductor integrated circuit device. However, in the present invention, the voltage detection circuit 16 is provided inside the semiconductor integrated circuit device 100. Therefore, miniaturization can be achieved.

The switching power supply device 200 described above can be applied to electric equipment having a plurality of liquid crystal display devices. Here, a mobile phone device will be described as an example.
FIG. 3 shows a perspective view of a mobile phone device including the switching power supply device 200.

The mobile phone device of FIG. 3 is a mobile phone device having a folding structure in which a housing 301 and a housing 302 can be folded together by a hinge 303. The housing 301 includes an antenna 304, a speaker 305, and a liquid crystal display device 30.
6 is provided. The housing 2 includes a key operation unit 307 and a microphone 308.

FIG. 4 shows a perspective view of the portable telephone device of FIG. 3 in a folded state. In FIG. 4, the same parts as those in FIG. 3 are designated by the same reference numerals. The housing 301 includes a liquid crystal display device 309 at a position that can be visually recognized by the user in the folded state.

Next, FIG. 5 shows an electrical configuration of the portable telephone device of FIG. In addition, in FIG. 5, FIG. 1, FIG. 3, and FIG.
The same parts as those in FIG. Housing 301 (Fig. 3
The transmission / reception circuit 310 built in (see) performs transmission / reception according to a signal transmitted from the key operation unit 307. At the time of transmission, an audio signal transmitted from the microphone 308 is modulated by the signal processing circuit 311 incorporated in the housing 301 (or the housing 302) (see FIG. 3) and frequency-converted by the transmission / reception circuit 310. And becomes a transmission high frequency signal, which is output from the antenna 304. On the other hand, at the time of reception, the reception high frequency signal signal input by the antenna 304 is frequency-converted by the transmission / reception circuit 310,
It is demodulated by the signal processing circuit 311 to be an audio signal and input to the speaker 305.

Housing 302 (or housing 301 may be used)
The control circuit 312 built in (see FIG. 3) receives the received electric field strength and the incoming call information from the transmission / reception circuit 310, receives the control signal from the key operation unit 307, and folds the mobile phone device from the reed switch 313. Information on whether or not it is in a state is received, and information on the battery voltage is received from a battery (not shown).

The reed switch 313 is a housing 301 (see FIG.
(See) is provided inside. Further, the housing 302 (see FIG.
A magnet is provided at a position facing the reed switch 313 in the folded state of the mobile phone device. Thereby, the reed switch 313 can recognize whether or not the mobile phone device is in a folded state.

The control circuit 312 is the switching power supply unit 2.
The enable signals EN1 and EN2 are output to 00. The switching power supply device 200 includes the LED 6 used as a backlight of the liquid crystal display device 306 and the liquid crystal display device 3.
This is a power source for the LED 6'used as the backlight for the 09. Further, the control circuit 312 controls the liquid crystal display device 30.
6, a driving signal is output to the liquid crystal display device 3 and necessary information (information such as received electric field strength, battery voltage, and incoming call) is displayed.
It is displayed on 06 and 309. Further, the control circuit 312 is
The liquid crystal display device 306 also displays a setting change screen and the like.

When the main power source of the portable telephone device is off,
The control circuit 12 sets the enable signals EN1 and EN2 to Lo.
Set to w level. Thereby, the liquid crystal display devices 306, 3
No backlight for both 09 (off state)
Becomes

When the main power source of the portable telephone device is on and the portable telephone device is not folded, the control circuit 12
Sets the enable signal EN1 to high level and the enable signal EN2 to low level. As a result, the liquid crystal display device 306 is in a state in which the backlight is on (on state), and the liquid crystal display device 309 is in a state in which the backlight is off (off state). Since the liquid crystal display device 309 that is not normally used by the user is in the off state when the mobile phone device is not in the folded state, power saving can be achieved.

However, even when the main power source of the mobile phone device is on and the mobile phone device is not in the folded state, when the display contents of the liquid crystal display device 309 are set by the key operation unit 307. The control circuit 12 sets the enable signal EN1 to high level and the enable signal EN2 to high level. As a result, both the liquid crystal display devices 306 and 309 are in a state in which the backlight is turned on (on state). Accordingly, the liquid crystal display device 309
It is not necessary to appropriately switch the liquid crystal display device in which the backlight is turned on when setting the display contents of, etc., and convenience is improved.

When the main power source of the portable telephone device is on and the portable telephone device is in the folded state, the control circuit 12
Sets the enable signal EN1 to low level and the enable signal EN2 to high level. As a result, the liquid crystal display device 306 is in a state where the backlight is not lit (off state), and the liquid crystal display device 309 is in a state where the backlight is lit (on state). When the mobile phone device is in the folded state, the liquid crystal display device 306 that cannot be visually recognized by the user is in the off state, so that power saving can be achieved. Further, when there is no operation for a certain period of time in the folded state, the liquid crystal display device 309 displays, but by turning off the backlight, further power saving can be achieved.

Although the liquid crystal backlight LED has two systems in the above-described embodiment, the present invention is not limited to this and may have three or more systems. Here, a switching power supply device that can be applied to three-system LCD backlight LEDs will be described. FIG. 2 shows an example of the configuration of a switching power supply device that can be applied to liquid crystal backlight LEDs of three systems. In addition,
2, the same parts as those in FIG. 1 are designated by the same reference numerals,
Detailed description is omitted.

The switching power supply device of FIG. 2 has a configuration in which a switch 21 is added to the switching power supply device of FIG. 1 and the NOT circuit 20 is replaced with a NOT circuit 20 '. Therefore, the semiconductor integrated circuit device 101 included in the switching power supply device of FIG. 4 has the NOT circuit 20 in the semiconductor integrated circuit 100 included in the switching power supply device of FIG.
It has a configuration in which the T circuit 20 'is replaced with a switch 21.

The third enable signal EN3 is the NOT circuit 2
1'and the switch 21 are input. Also, switch 18
And the L end of the switch 19 are connected via the switch 21. The switch 21 has a third enable signal EN.
When 3 is at the high level, it is in the open state, and when the third enable signal EN3 is at the low level, it is in the open state.

The liquid crystal backlight LED 6 and the liquid crystal backlight LED 6'are L for the liquid crystal backlight.
Connected via ED6 ''. That is, the LCD backlight LED 6 is attached to the cathode side of the LCD backlight LED 6.
The anode side of the ED 6 ″ is connected, and the LCD backlight LED is connected to the anode side of the LCD backlight LED 6 ′.
The cathode side of 6 ″ is connected.

The cathode side of the liquid crystal backlight LED 6 and the anode side of the liquid crystal backlight LED 6 ″ are connected to the connection node between the L end of the switch 18 and the switch 21, and the connection node between the L end of the switch 19 and the switch 21. The anode side of the liquid crystal backlight LED 6'and the cathode side of the liquid crystal backlight LED 6 '' are connected to each other.

Next, the operation of the switching power supply device 201 will be described. First, enable signals EN1 and E
The operation when N2 and EN3 are all at the high level will be described. Since the enable signal EN1 is at the high level, the A terminal and the H terminal of the switch 18 are connected.
Further, since the enable signal EN2 is at the high level, the A terminal and the H terminal of the switch 19 are connected. Also,
Since the enable signal EN3 is at the high level, the switch 21 is in the open state. Therefore, switch 1
7 is an LED 6 for a liquid crystal backlight via a switch 18.
LED6 for LCD backlight connected to the anode side of
Is connected to the anode side of the LCD backlight LED 6 ″, the cathode side of the LCD backlight LED 6 ″ is connected to the anode side of the LCD backlight LED 6 ′, and the cathode side of the LCD backlight LED 6 ′ is a switch. One end of the resistor R8 is connected via 19 to the positive phase input side of the error amplifier 9. That is, the liquid crystal backlight LED 6, the liquid crystal backlight LED 6 ″, and the liquid crystal backlight LED 6 ′ are connected in series to the switching power supply device 201. As a result, the LCD backlight LED 6 and the LCD backlight LED
6 "and the LED 6'for the LCD backlight, the same constant current flows, and the LED 6 for the LCD backlight, the LED 6" for the LCD backlight, and the LED 6'for the LCD backlight.
And are turned on.

Next, the operation when the enable signals EN1 and EN2 are at high level and the enable signal EN3 is at low level will be described. Enable signal EN1
Is at the high level, the A end of the switch 18 and the H
The ends are connected. The enable signal EN2 is Hi
Since it is at the gh level, the A terminal and the H terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the Low level, the switch 21 is in the closed state. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 via the switch 18, and the cathode side of the LCD backlight LED 6 is connected to the anode side of the LCD backlight LED 6 ′ via the switch 21. The cathode side of the light LED 6 ′ is connected to one end of the resistor R 8 and the positive phase input side of the error amplifier 9 via the switch 19. LED for LCD backlight
6 '' is short-circuited. That is, LE for liquid crystal backlight
D6 and the liquid crystal backlight LED 6'are connected in series to the switching power supply device 201. As a result, the same constant current flows through the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6 ', and the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6'are turned on, and the liquid crystal backlight LED 6'. 'Is turned off.

Next, the operation when the enable signals EN2 and EN3 are at the high level and the enable signal EN1 is at the low level will be described. Enable signal EN1
Is at the Low level, the A terminal and the L terminal of the switch 18 are connected. The enable signal EN2 is High.
Since it is at the h level, the A terminal and the H terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the high level, the switch 21 is in the open state. Therefore, the switch 17 is connected to the anode side of the liquid crystal backlight LED 6 ″ through the switch 18, and the cathode side of the liquid crystal backlight LED 6 ″ is connected to the anode side of the liquid crystal backlight LED 6 ′. The cathode side of the working LED 6 ′ is connected to one end of the resistor R 8 and the positive phase input side of the error amplifier 9 via the switch 19. That is, the liquid crystal backlight LED 6 ′ and the liquid crystal backlight LED 6 ″ are connected in series to the switching power supply device 201. As a result, the LCD backlight LED 6'and the LCD backlight LED 6 '
The same constant current flows to 6 ″, the liquid crystal backlight LED 6 ′ and the liquid crystal backlight LED 6 ″ are turned on, and the liquid crystal backlight LED 6 is turned off.

Next, the operation when the enable signals EN1 and EN3 are at high level and the enable signal EN2 is at low level will be described. Enable signal EN1
Is at the high level, the A end of the switch 18 and the H
The ends are connected. Further, the enable signal EN2 is Lo
Since it is at the w level, the A terminal and the L terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the high level, the switch 21 is in the open state. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 via the switch 18, and the cathode side of the LCD backlight LED 6 is connected to the LCD backlight L.
It is connected to the anode side of the ED 6 ″, and the cathode side of the LCD backlight LED 6 ″ is connected to one end of the resistor R 8 and the positive phase input side of the error amplifier 9 via the switch 19. That is, the liquid crystal backlight LED 6 and the liquid crystal backlight LED 6 ″ are the switching power supply device 20.
1 will be connected in series. As a result, the LCD backlight LED 6 and the LCD backlight LED 6 ″
The same constant current flows to and LED for LCD backlight
6 and the liquid crystal backlight LED 6 ″ are turned on, and the liquid crystal backlight LED 6 ′ is turned off.

Then, the enable signal EN1 becomes High.
The operation when the level and enable signals EN2 and EN3 are at the Low level will be described. Enable signal EN1
Is at the high level, the A end of the switch 18 and the H
The ends are connected. Further, the enable signal EN2 is Lo
Since it is at the w level, the A terminal and the L terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the Low level, the switch 21 is in the closed state. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 via the switch 18, and the cathode side of the LCD backlight LED 6 is connected to one end of the resistor R8 and the positive phase input of the error amplifier 9 via the switch 21 and the switch 19. Connected to the side. LED for LCD backlight
6 '' is short-circuited. That is, LE for liquid crystal backlight
A constant current is supplied from the switching power supply device 201 only to D6. As a result, the LCD backlight LED 6 is turned on, and the LCD backlight LED 6 is turned on.
6'and 6 '' are turned off.

Then, the enable signal EN2 becomes High.
The operation when the level and enable signals EN1 and EN3 are at the Low level will be described. Enable signal EN1
Is at the Low level, the A terminal and the L terminal of the switch 18 are connected. The enable signal EN2 is High.
Since it is at the h level, the A terminal and the H terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the Low level, the switch 21 is in the closed state. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 ′ via the switches 18 and 21, and the cathode side of the LCD backlight LED 6 ′ is connected via the switch 19 to one end of the resistor R 8 and the positive side of the error amplifier 9. Connected to the phase input side. LED for LCD backlight
6 '' is short-circuited. That is, LE for liquid crystal backlight
A constant current is supplied from the switching power supply device 201 only to D6 '. As a result, the LCD backlight LED 6'is turned on, and the LCD backlight L
ED6 and 6 '' are turned off.

Then, the enable signal EN3 is High.
The operation when the level and enable signals EN1 and EN2 are at the Low level will be described. Enable signal EN1
Is at the Low level, the A terminal and the L terminal of the switch 18 are connected. In addition, the enable signal EN2 is Low
Since it is at the level, the A terminal and the L terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the high level, the switch 21 is in the open state. Therefore, the switch 17 is connected to the anode side of the LCD backlight LED 6 ″ via the switch 18, and the cathode side of the LCD backlight LED 6 ″ is connected via the switch 19 to one end of the resistor R 8 and the positive phase of the error amplifier 9. Connected to the input side. That is, LED for LCD backlight 6 "
A constant current is supplied only from the switching power supply device 201. As a result, LE for LCD backlight
LED for LCD backlight when D6 '' is turned on
6, 6'is turned off.

Finally, enable signals EN1, EN2,
The operation when both EN3 are at the low level will be described. Since the enable signal EN1 is at the Low level, the A terminal and the L terminal of the switch 18 are connected. Also,
Since the enable signal EN2 is at the Low level, the A terminal and the L terminal of the switch 19 are connected. Further, since the enable signal EN3 is at the Low level, the switch 21
Is closed. Therefore, the switch 17 is connected to one end of the resistor R8 and the positive phase input side of the error amplifier 9 via the switch 18, the switch 21, and the switch 19.
In addition, the LED 6 ″ for the liquid crystal backlight is short-circuited. That is, the LCD backlight LED 6, the LCD backlight LED 6 ″, and the LCD backlight LED 6 ′.
No constant current is supplied from the switching power supply device 201. As a result, the LCD backlight LED 6, LCD backlight LED 6 ″, and LCD backlight L
ED6 'is turned off.

The enable signals EN1, EN2,
When all EN3 are at the low level, the output signal of the OR circuit 20 'becomes the low level. When the output signal of the OR circuit 20 'becomes Low level, the control circuit 12 stops the switching control and the switch 17 is opened. Thereby, the reactive current flowing through the coil 1, the Schottky diode 2, the switch 17, the switch 18, the switch 21, the switch 19 and the resistor 8 can be eliminated.

[0066]

As described above, the switching power supply device according to the present invention is an n-type (n is a natural number of 2 or more) LED used as a backlight of a liquid crystal display device.
DC-outputs an output voltage generated by transforming an input voltage supplied from the outside by varying the on / off period ratio of the switching means and outputting the output voltage from the output terminal.
A DC converter, and a control means for controlling the ON / OFF period ratio of the switching means by a pulse signal created based on the feedback current so that the feedback current input from the feedback current input terminal becomes a constant current. L that supplies power from the n-system LED in accordance with an external control signal
When the ED is selected and the power supply LED is of one system, the anode side of the one system of LEDs selected according to the external control signal is connected to the output end, and selected according to the external control signal. The connection state for the LEDs of the n system is switched so that the cathode side of the LED of the one system is connected to the feedback current input terminal, and when the LEDs supplying the power are a plurality of systems, according to an external control signal. LEDs of a plurality of selected systems are connected in series, and an anode side of a series connection body composed of LEDs of a plurality of systems selected according to the external control signal is connected to the output end and selected according to the external control signal. Switching for switching the connection state for the LEDs of the n systems so that the cathode side of the series connection body composed of LEDs of a plurality of systems is connected to the feedback current input terminal It has a configuration comprising a stage, a.

With such a configuration, only some or all of the LEDs selected from the n-system LCD backlight LEDs according to the external control signal are turned on by constant current control with the same current value. be able to.

According to the present invention, the control means includes a constant current adjusting means for adjusting the setting of the constant current value of the feedback current, and the switching means, the switching means, and the constant means among the control means. Since the semiconductor integrated circuit device is provided with the portion other than the current adjusting means, the size can be reduced.

According to the present invention, the output voltage of the DC-DC converter is detected, and when the output voltage of the DC-DC converter is equal to or higher than a predetermined value, the voltage detection for stopping the ON / OFF operation of the switching means is detected. Means for providing power to the semiconductor integrated circuit device
It is possible to prevent circuit breakdown due to abnormal boosting that occurs in an open loop state such as a mounting defect of the ED. As a result, a highly safe switching power supply device can be realized.

According to the present invention, the control means is
The ON / OFF operation of the switching means is detected when the selection state of the switching means is detected and the switching means does not select any LED that supplies power from the LEDs of the n system according to the external control signal. Since the LEDs are stopped, it is possible to prevent the reactive current from flowing when no LED that supplies power is selected. As a result, power saving can be achieved.

According to the present invention, the control means is
Since the on / off operation of the switching means is stopped in accordance with the external control signal, the external control signal is a signal for controlling the switching means and a signal for switching between valid / invalid of the switching power supply device. Since the external control signal has two roles as described above, the number of external signals input to the switching power supply device is reduced. As a result, the number of external signal input terminals of the switching power supply device is reduced, and the size can be reduced.

Further, according to the present invention, in the case of two systems, since the switching means is realized by two switches, the switching means can have a simple structure.

Further, according to the present invention, the electric device is n
(N is a natural number of 2 or more) liquid crystal display devices and n (n is a natural number of 2 or more) systems used as a backlight of the liquid crystal display device are connected to the n-system liquid crystal backlight LEDs. And a switching power supply device capable of turning on only a part or all of the LEDs selected from among the LEDs by constant current control with the same current value. Therefore, only a liquid crystal display device that needs to be turned on in various usage situations Can be turned on. As a result, power saving can be achieved. Further, even if there are a plurality of liquid crystal display devices that need to be turned on, the liquid crystal display devices can be turned on with the same constant current, so that the number of use situations that can be set increases and convenience is improved. Further, even when there are a plurality of liquid crystal display devices that need to be turned on, it is not necessary to provide a plurality of switching power supply devices, so that it is possible to reduce the size and cost of the electric device. Therefore, the present invention is suitable for a mobile phone device in which there is a strong demand for power saving and miniaturization.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a switching power supply device according to the present invention.

FIG. 2 is a diagram showing another configuration of the switching power supply device according to the present invention.

3 is a perspective view of a mobile phone device including the switching power supply device of FIG. 1. FIG.

FIG. 4 is a perspective view of a mobile phone device including the switching power supply device of FIG. 1 in a folded state.

5 is a diagram showing an electrical configuration of the mobile phone device of FIG.

FIG. 6 is a diagram showing a configuration of a conventional switching power supply device.

FIG. 7 is a diagram showing another configuration of a conventional switching power supply device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 coil 2 Schottky diode 3 transistor 4 capacitors 6, 6 ', 6''LED used as a backlight of a liquid crystal display device 8 and 11 resistor 9 error amplifier 10 variable resistor 12 control circuit 16 voltage detection circuits 17, 18 and 19 Switch 20, 20 'NOT circuit 100, 101 Semiconductor integrated circuit device 200, 201 Switching power supply device 306, 309 Liquid crystal display device

Claims (8)

[Claims] 1. A switching power supply device connected to n (n is a natural number of 2 or more) LEDs which are each used as a backlight of a liquid crystal display device, wherein a ratio of ON / OFF periods of switching means is variable. DC-DC converter that transforms the input voltage supplied from the outside to generate the output voltage and outputs the output voltage from the output terminal, and the feedback current input from the feedback current input terminal so that the feedback current becomes a constant current. , A control means for controlling an ON / OFF period ratio of the switching means by a pulse signal generated based on the feedback current, and an LED for supplying power from the LEDs of the n system according to an external control signal LED that supplies the power
Is one system, the anode side of the one system LED selected according to the external control signal is connected to the output end, and the one system LE selected according to the external control signal is connected.
The connection state for the LEDs of the n systems is switched so that the cathode side of D is connected to the feedback current input terminal, and when the LEDs supplying the power are the multiple systems, the plurality of systems selected according to the external control signal. LEDs are connected in series, and a plurality of lines of L selected according to the external control signal are connected.
An anode side of a series connection body made of ED is connected to the output terminal, and a cathode side of a series connection body made of LEDs of a plurality of systems selected according to the external control signal is connected to the feedback current input terminal. A switching power supply device comprising: a switching unit that switches a connection state with respect to the LEDs of the n systems. 2. The control means comprises constant current adjusting means for adjusting the setting of the constant current value of the feedback current, and the switching means, the switching means, and the control means other than the constant current adjusting means. The switching power supply device according to claim 1, wherein the portion is provided in the semiconductor integrated circuit device. 3. The semiconductor integrated circuit includes voltage detecting means for detecting an output voltage of the DC-DC converter, and stopping the ON / OFF operation of the switching means when the output voltage of the DC-DC converter is a predetermined value or more. The switching power supply device according to claim 2, which is provided in a circuit device. 4. The control means detects the selection state of the switching means, and the switching means does not select any LED supplying power from the LEDs of the n system according to the external control signal. The switching power supply device according to claim 1, wherein the switching means stops the on / off operation of the switching means. 5. The switching power supply device according to claim 4, wherein the control means stops the on / off operation of the switching means in response to the external control signal. 6. The LE, wherein n is 2, and the switching means is used as a backlight of the first liquid crystal display device.
Either the terminal connected to the anode side of D or the cathode side of the LED used as the backlight of the first liquid crystal display device and the terminal connected to the anode side of the LED used as the backlight of the second liquid crystal display device. The first liquid crystal display device, a first switch that connects one of the two and the output end in accordance with the external control signal, a terminal that is connected to the cathode side of an LED used as a backlight of the second liquid crystal display device, Of the LED used as the backlight of the second liquid crystal display device and the terminal connected to the anode side of the LED used as the backlight of the second liquid crystal display device, and the feedback current input end to the external control signal. The 2nd switch connected according to it, The switching power supply device in any one of Claims 1-5. 7. An n (n is a natural number of 2 or more) liquid crystal display device, and n used as a backlight of the liquid crystal display device.
An electrical device comprising: the switching power supply device according to any one of claims 1 to 6, which is connected to an LED (n is a natural number of 2 or more) system. 8. The electric device according to claim 7, which is a mobile phone device.