JP4983735B2 - Semiconductor integrated circuit for power control - Google Patents

Description

  The present invention relates to a DC power supply device that generates an LED drive power supply, for example, a power supply control semiconductor integrated circuit constituting a switching power supply device that generates a drive current of a WLED (white light emitting diode) used for a backlight of a liquid crystal monitor. It is related to effective technology.

In portable electronic devices such as cellular phones, WLEDs are used as backlights for display liquid crystal panels. In general, a DC-DC converter including a step-up switching regulator is used for a power supply device that generates a drive power supply for a WLED. In such an LED drive power supply device, a drive current flowing through the LED is converted into a voltage, fed back to the control circuit, and compared with a reference voltage by an error amplifier to generate a drive pulse having a pulse width corresponding to the potential difference, Feedback control is performed in which a switching element that allows current to flow intermittently through an inductor (coil) is driven to keep the driving current constant.
JP 2003-332623 A

  A WLED drive power supply device (WLED driver) is usually configured to output a drive current at a voltage capable of driving three to eight LEDs in series. However, in recent years, portable electronic devices are increasingly having two screens or large liquid crystal panels. In these electronic devices, it is necessary to provide 10 or more LEDs in order to guarantee a predetermined brightness. There is. On the other hand, considering the withstand voltage of the WLED driver IC, the current limit is about 8 lamps per row. Therefore, when it is desired to provide 10 or more LEDs, two or more WLED drivers are prepared, and a configuration in which 3 to 8 LEDs in series are connected to each driver to be lit.

  Therefore, there is a problem that the number of parts constituting the system increases. Specifically, when two WLED drivers are used, it is necessary to provide a coil as an inductor, a diode as a rectifier, and a capacitor as a smoothing capacitor corresponding to each driver. There is a problem that this causes an increase in the size of the power supply device (enlargement of the power supply device).

  Further, as an invention in which a plurality of LED rows are driven to be lit by a single switching power supply device, there is an invention described in Patent Document 1, for example. However, the invention of Patent Document 1 does not consider the case where the forward voltage of the LED varies. Moreover, in the switching power supply device of the invention of Patent Document 1, it becomes easy for a current to flow through the LED array in which the forward voltage of the LED is the smallest, thereby increasing the variation in brightness. Therefore, a large-screen liquid crystal panel has a problem that the brightness of the backlight is uneven and the appearance of the display is deteriorated.

  The present invention has been made paying attention to the problems as described above, and the object of the present invention is to provide an LED drive power supply device that can suppress an increase in the number of components and mounting area due to the multiple lighting of LEDs. An object of the present invention is to provide a semiconductor integrated circuit for power control.

  Another object of the present invention is to provide a semiconductor integrated circuit for power control of an LED drive power supply device capable of avoiding the occurrence of unevenness in screen brightness in an electronic device including a liquid crystal panel having an LED as a backlight. There is.

A plurality of LED units in a power source driving semiconductor integrated circuit constituting an LED driving power source device that drives a switching element for passing current intermittently through an inductor and rectifies the current flowing through the inductor to generate a driving current for the LED. A plurality of external terminals that draw current from each of the plurality of external terminals, a plurality of current sources respectively connected to the plurality of external terminals, and a voltage corresponding to a potential difference between a voltage of the plurality of external terminals and a predetermined reference voltage. comprising an error amplifier, and on the switching element based on the output of the error amplifier circuit corresponding to the lowest ones of the previous SL voltages of a plurality of external terminals, configured to generate a control pulse for turning off It is a thing.

More specifically, a power source driving semiconductor integrated circuit that constitutes an LED driving power source device that drives a switching element that causes current to flow intermittently through the inductor and rectifies the current flowing through the inductor to generate a driving current for the LED. A plurality of external terminals that draw current from each of the plurality of LED units, a plurality of current sources respectively connected to the plurality of external terminals, and a potential difference between a voltage of the plurality of external terminals and a predetermined reference voltage. an error amplifier circuit for outputting a voltage according compares the pulse control circuit for generating control pulses for controlling said switching element in response to the output of the error amplifier circuit, the voltage before Symbol plurality of external terminals a voltage comparison circuit which most voltage to detect low external terminal, and a switching circuit for selecting a voltage in accordance with the output of the voltage comparator circuit, said Pal Control circuitry configured to generate the control pulse based on the output of the error amplifier circuit corresponding to the lowest ones of the previous SL voltages of a plurality of external terminals.

  According to the configuration described above, even if there are variations in the forward voltage of the plurality of LED units to be driven, the switching elements are driven so that the output voltage is suitable for the unit having the largest forward voltage. The LED unit can be supplied with a current required for lighting, so that there is no great difference in brightness between the units, and the inductor, switching element and rectifying element can be used in common. In addition, the number of parts can be reduced as compared with the case of separately configuring the power supply apparatus, and the apparatus can be downsized.

  Here, it is preferable that the error amplifier circuit includes a plurality of the error amplifier circuits, and the switching circuit outputs an output corresponding to the lowest voltage of the external terminal among the outputs of the plurality of error amplifier circuits by the voltage comparison circuit. Is supplied to the pulse control circuit. As a result, the output of the desired error amplifier circuit can be supplied to the pulse control circuit as soon as the switching circuit is switched.

  The switching circuit is provided before the error amplification circuit, and the voltage comparison circuit supplies the lowest voltage among the voltages of the plurality of external terminals to the error amplification circuit. The output of the circuit may be supplied to the pulse control circuit. As a result, the error amplifier circuit can be shared, power consumption can be reduced, and the chip size can be reduced.

  Further preferably, each of the plurality of current sources is a variable current source capable of changing a magnitude of a current to be supplied, and an external control for inputting control information for designating a current value to be supplied to the variable current source from the outside. And a control circuit for controlling a current value of the variable current source in accordance with the control information input to the external control terminal. As a result, the brightness of the LED can be adjusted by an external command.

  Preferably, a voltage detection circuit is provided for detecting whether or not the voltages of the plurality of external terminals are within a predetermined voltage range, and the pulse control circuit performs the control operation according to the output of the voltage detection circuit. Configure to switch. As a result, when the output voltage of the power supply apparatus becomes abnormal due to a circuit failure or LED malfunction, this can be detected and appropriate control can be performed.

  Further, preferably, a current detection circuit for detecting a magnitude of a current flowing through the inductor is provided, and the pulse control circuit is configured to generate a control pulse in accordance with an output of the current detection circuit. This makes it possible to perform either constant voltage control that keeps the output voltage constant or constant current control that keeps the output current constant, and can use different controls depending on the system and situation. It becomes possible.

  Further, an overcurrent detection circuit is provided for detecting whether or not the current flowing through the inductor is greater than a predetermined current value, and the pulse control circuit stops generating the control pulse by the output of the overcurrent detection circuit. It may be configured. Thereby, it can be avoided that an excessive current flows and the circuit is destroyed.

In another invention of the present application, a power source driving semiconductor integrated circuit that constitutes an LED driving power source device that drives a switching element that causes current to flow intermittently through an inductor and rectifies the current flowing through the inductor to generate an LED driving current. In the circuit, a plurality of external current output terminals that output currents to the plurality of LED units, a plurality of current sources respectively connected to the plurality of external current output terminals, and voltages of the plurality of external current output terminals And an error amplifier circuit that outputs a voltage corresponding to a potential difference from the reference voltage of the plurality of external current output terminals, and the switching based on the output of the error amplifier circuit corresponding to the highest potential among the voltages of the plurality of external current output terminals A control pulse for turning on and off the element is generated.

  According to the configuration described above, in the current output type power supply driving semiconductor integrated circuit, even if the forward voltages of the plurality of LED units vary, the output voltage is suitable for the unit having the largest forward voltage. Since the switching element is driven, a current necessary for lighting can be supplied to all the LED units, and a large difference in brightness between the units can be prevented.

  According to the present invention, it is possible to suppress an increase in the number of components and the mounting area accompanying the increase in the number of LEDs. In addition, in an electronic device including a liquid crystal panel having an LED as a backlight, there is an effect that it is possible to realize a power source control semiconductor integrated circuit of an LED driving power source device that can prevent unevenness in screen brightness.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment of an LED driving power supply device to which the present invention is applied.

  The LED drive power supply device of this embodiment includes a switching transistor SW1 including a coil (inductor) L1 and an N-channel MOSFET (insulated gate field effect transistor) connected in series between a DC voltage terminal VDD and a ground point. The rectifying diode D1 connected between the connection node of the coil L1 and SW1 and the output terminal, the smoothing capacitor C1 connected between the output terminal and the ground point, and the switching transistor SW1 are controlled on and off. The switching control circuit 10 is configured as a step-up type switching regulator.

  Although not particularly limited, in this embodiment, the switching control circuit 10 is formed as a semiconductor integrated circuit (hereinafter referred to as a white LED driver IC) on one semiconductor chip, and includes the switching transistor SW1 and the coil. L1, the diode D1, and the smoothing capacitor C1 are formed of discrete components and are connected to the white LED driver IC 10 as external elements. Moreover, in this specification, what connected several LED in series is called an LED unit for convenience. That is, the unit does not mean a special form.

  The white LED driver IC includes two current drawing terminals PI1 and PI2 so that two LED units 20 composed of 3 to 8 WLED arrays in series can be driven to light. Then, constant current sources CS1 and CS2 that are connected to the current drawing terminals PI1 and PI2 and flow a driving current to the LED units 20A and 20B, respectively, are provided inside the chip.

  Further, in the white LED driver IC 10, the voltages of the current drawing terminals PI1 and PI2 are applied to the inverting input terminal, the reference voltages Vref1 and Vref2 are applied to the non-inverting input terminal, and the voltages of PI1 and PI2 and the reference voltage Vref1 are applied. , Vref2, error amplifiers 11a and 11b that output a voltage corresponding to the potential difference, a control circuit 12 that generates a control pulse for the switching transistor SW1, and the switching transistor SW1 based on the control pulse output from the control circuit 12 A driver 13 for generating a driving pulse for driving the gate terminal is provided.

  The control circuit 12 includes a PWM comparator that receives, for example, the output of the error amplifier and a triangular wave having a predetermined frequency, and when the voltage is low according to the fed back voltage, the control pulse to be output is widened to perform switching. The transistor SW1 causes more current to flow through the coil L1, and when the feedback voltage is high, the control pulse is narrowed to reduce the current flowing through the coil L1.

  Further, the white LED driver IC 10 includes a comparator 14 that compares the voltages of the current drawing terminals PI1 and PI2, and a control circuit that selectively controls the output of the error amplifier 11a or 11b according to the output of the comparator 14. And a changeover switch 15 for supplying to the power supply 12. In this embodiment, of the error amplifiers 11a and 11b, the output of the error amplifier to which the lower one of the voltages of the current drawing terminals PI1 and PI2 is input is selected and supplied to the control circuit 12. It is configured.

  If the LED forward voltages of the two LED units 20A and 20B connected to the white LED driver IC 10 vary, this appears as a difference in voltage between the current drawing terminals PI1 and PI2. Specifically, the potential of a terminal to which a unit having a large forward voltage is connected is lower than the potential of a terminal to which a unit having a small forward voltage is connected. Therefore, if the higher one of the voltages PI1 and PI2 is fed back to the control circuit 12, the output voltage can be kept low. Therefore, for a unit having a large forward voltage, the voltage is insufficient and the current source has a desired current. Cannot be drawn in and the brightness is insufficient. Therefore, the difference in brightness between the two LED units 20A and 20B increases.

  On the other hand, as in the present embodiment, if the lower voltage of PI1 and PI2 is fed back to the control circuit 12, the output voltage is set higher, so for a unit with a large forward voltage, For a unit with a suitable voltage and a small forward voltage, there is a margin in voltage, but the current source acts to draw a desired current, so that a large amount of drive current does not flow. That is, the difference in brightness between the two LED units 20A and 20B is reduced.

  FIG. 2 shows a first modification of the first embodiment. In this modification, the changeover switch 15 is provided in the preceding stage instead of being provided in the subsequent stage of the error amplifier 11, and the terminals to which the constant current sources CS 1 and CS 2 are connected to the inverting input terminal side of the error amplifier 11 by the changeover switch 15. One of the voltage at PI1 and the voltage at terminal PI2 is selected and input according to the output of the comparator 14 that determines the magnitude of the voltage. According to this modification, there is an advantage that the circuit scale and thus the chip size can be reduced by reducing one error amplifier as compared with the driver IC of FIG.

  FIG. 3 shows a second modification of the first embodiment. In this modification, an LVP comparator CMP1 for detecting whether the voltage at the terminals PI1, PI2 to which the constant current sources CS1, CS2 are connected is lower than the lower limit voltage of the voltage allowable range, and the voltages at the PI1, PI2 Is provided with an OVP comparator CMP2 for detecting whether the voltage is higher than the upper limit voltage of the allowable voltage range. The control circuit 12 can be configured to stop the PWM control when the outputs of these comparators indicate a voltage abnormality.

  FIG. 4 shows a second embodiment of the LED driving power supply device to which the present invention is applied. In this embodiment, instead of connecting the constant current sources CS1 and CS2 to the current drawing terminals PI1 and PI2 of the white LED driver IC 10 in FIG. 1, variable current sources VC1 and VC2 are connected. The variable current source is used to make the brightness adjustable. For example, a terminal PC to which 3-bit control codes CB1 to CB3 are input and a dimming control circuit 16 including a decoder and the like are provided. The variable current sources VC1 and VC2 are configured to flow currents according to control codes CB1 to CB3 (current command values) supplied to the terminals. The control code is not limited to 3 bits, and can be an arbitrary bit. In this embodiment, there is an advantage that the brightness of the LED can be adjusted from the outside. Further, by including “0” in the current value that can be specified by the control codes CB1 to CB3, on / off switching is also possible.

  FIG. 5 shows a modification of the second embodiment. In this modification, instead of replacing the constant current sources CS1 and CS2 with the variable current sources VC1 and VC2, the constant voltage sources for generating the reference voltages Vref1 and Vref2 applied to the error amplifiers 11a and 11b are replaced with the variable voltage sources, The brightness of the LEDs is controlled by changing the reference voltages Vref1 and Vref2 in accordance with the control codes CB1 to CB3 from the outside and adjusting the currents flowing to the LED units 20A and 20B. Also in the second embodiment, a modification similar to FIG. 2 showing the first modification of the embodiment of FIG. 1 and a modification similar to FIG. 3 showing the second modification of the embodiment of FIG. 1 are possible. It is.

  FIG. 6 shows a third embodiment of an LED driving power supply device to which the present invention is applied. In this embodiment, the constant current sources CS1 and CS2 in FIG. 1 are connected not between the cathode terminals of the LED units 20A and 20B and the ground point, but between the output terminals and the anode terminals of the LED units 20A and 20B. In this way, the cathode terminal of the rectifying diode D1 is connected outside the chip, and a common current drawing external terminal PI3 to which the constant current sources CS1 and CS2 are connected is provided inside the chip.

  In this embodiment, the white LED driver IC 10 is provided with current output terminals PO1 and PO2 instead of the current drawing terminals PI1 and PI2, and the LED unit is provided between these terminals PO1 and PO2 and a ground point outside the chip. 20A and 20B are connected. In the third embodiment, the output of the error amplifier having the higher voltage among the voltages of the current output terminals PO 1 and PO 2 is selected by the changeover switch 15 and supplied to the control circuit 12. Also in the third embodiment, a modification similar to FIG. 2 showing the first modification of the embodiment of FIG. 1 and a modification similar to FIG. 3 showing the second modification of the embodiment of FIG. Furthermore, the modification similar to FIG. 5 which shows the modification of embodiment of FIG. 4 is possible.

  FIG. 7 shows a fourth embodiment of an LED driving power supply device to which the present invention is applied. In this embodiment, a current detection resistor Rs is provided in series with the switching transistor SW1 in FIG. 1, and the white LED driver IC 10 includes the resistor Rs in addition to the error amplifiers 11a and 11b for voltage control. A current detection amplifier 17 having a voltage as an input is provided, and the control circuit 12 can perform current control in addition to voltage control in a feedback loop. This voltage control and current control may be switched by an instruction from the outside, or the control circuit 12 may switch according to the situation based on its own judgment.

  In addition to current detection resistance connected in series with the switching transistor SW1, current detection uses a voltage between the source and drain of SW1, that is, an on-resistance of SW1, and a voltage between terminals of the coil L1, that is, resistance of L1. Or a current detecting resistor connected in series with the LED. The output of the current detection amplifier 17 is not used for feedback control of the output current, but is used for an overcurrent protection function that prohibits output when the output current exceeds a predetermined value. May be. Further, in the fourth embodiment, a modification similar to that described in the third embodiment is possible.

  FIG. 8 and FIG. 9 show still another modification of the first embodiment. 8 is provided with a terminal 18 for inputting an on / off control signal to the control circuit 12, and the on / off of the IC can be controlled by this terminal. In addition, it is possible to perform dimming control by inputting a predetermined PWM pulse to the terminal 18, for example, using this on / off function.

  The modification of FIG. 9 is provided with a soft start circuit 19 that controls the on-duty of the internal PWM pulse in the previous stage of the control circuit 12, and this circuit controls so that a large drive current is not suddenly output when the power supply is started. can do. Instead of providing the soft start circuit 19 for controlling the on-duty, a sweep circuit for gradually changing the reference voltages Vref1 and Vref2 of the error amplifiers 11a and 11b may be provided. Furthermore, the modified examples of FIGS. 8 and 9 and the modified examples related thereto can be applied to the second to fourth embodiments.

  Moreover, although the said 1st-4th embodiment showed the structure which driven two LED units in which 3-8 lights (equal number) LED was connected in series, LED unit was shown. The present invention can be applied to an LED driver IC that drives three or more LEDs, and can also be applied to drive a plurality of LED units having different numbers of series LEDs.

  Although the invention made by the present inventor has been specifically described based on the embodiment, the present invention is not limited to the above embodiment. For example, in the above embodiment, the switching transistor SW1 constituting the switching regulator is connected as an external element of the IC. However, the switching transistor SW1 may be configured as an on-chip element of the IC. Similarly, a rectifying diode may be configured as an on-chip element of an IC instead of an external element.

  Further, a switching transistor may be used instead of the rectifying diode, and the switching rectifier may be configured as a synchronous rectification type switching regulator that is turned on / off complementarily with SW1. Furthermore, in the embodiment, a MOSFET is used as the switching transistor SW1, but a bipolar transistor may be used.

  Furthermore, in the embodiment having the dimming control circuit 16, the power supply control IC is configured to receive a control code for giving a command value of the drive current from the outside. Alternatively, it is possible to provide a command by an analog signal.

  In the above description, an example in which the present invention is applied to an LED driving power supply device has been described. However, the present invention is not limited to the present invention, and is widely used for a power supply device that generates a boosted voltage and wants to feedback control the output current. can do.

It is a block block diagram which shows 1st Embodiment of the power supply device for LED drive to which this invention is applied. It is a block block diagram which shows the 1st modification of the power supply device for LED drive of 1st Embodiment. It is a block block diagram which shows the 2nd modification of the power supply device for LED drive of 1st Embodiment. It is a block block diagram which shows 2nd Embodiment of the power supply device for LED drive to which this invention is applied. It is a block block diagram which shows the modification of the power supply device for LED drive of 2nd Embodiment. It is a block block diagram which shows 3rd Embodiment of the power supply device for LED drive to which this invention is applied. It is a block block diagram which shows 4th Embodiment of the power supply device for LED drive to which this invention is applied. It is a block block diagram which shows the other modification of the power supply device for LED drive of 1st Embodiment. It is a block block diagram which shows the further another modification of the power supply device for LED drive of 1st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Switching control circuit 11a, 11b Error amplifier 12 Pulse control circuit 13 Drive circuit (driver)
14 Comparator 15 Changeover Switch 16 Current Control Circuit (Dimming Control Circuit)
17 Current detection circuit (current detection amplifier)
18 ON / OFF control terminal 19 Soft start circuit 20 LED unit L1 Coil (inductor)
C1 Smoothing capacity WLED White light emitting diode SW1 Coil driving switching transistor CS1, CS2 Constant current source VC1, VC2 Variable current source CMP1, CMP2 Voltage detection circuit (comparator)

Claims (9)

A power supply control semiconductor integrated circuit that constitutes an LED drive power supply device that drives a switching element that causes current to flow intermittently through an inductor and rectifies the current that flows through the inductor to generate a drive current for the LED,
A plurality of external terminals that draw current from each of the plurality of LED units;
A plurality of current sources respectively connected to the plurality of external terminals;
An error amplifying circuit that outputs a voltage according to a potential difference between a voltage of the plurality of external terminals and a predetermined reference voltage;
A pulse control circuit for generating a control pulse for controlling the switching element in accordance with an output of the error amplifier circuit;
A voltage comparison circuit for comparing the voltages of the plurality of external terminals and detecting the external terminal having the lowest voltage;
According to the output of the voltage comparison circuit, a switching circuit that selects the lowest one of the voltages of the external terminals from the plurality of outputs of the error amplification circuit and supplies the selected voltage to the error amplification circuit;
A semiconductor integrated circuit for power control, comprising: A power supply control semiconductor integrated circuit that constitutes an LED drive power supply device that drives a switching element that causes current to flow intermittently through an inductor and rectifies the current that flows through the inductor to generate a drive current for the LED,
A plurality of external terminals that draw current from each of the plurality of LED units;
A plurality of current sources respectively connected to the plurality of external terminals;
A plurality of error amplifying circuits provided corresponding to each of the plurality of external terminals and outputting a voltage corresponding to a potential difference between the voltage of the external terminal and a predetermined reference voltage;
A pulse control circuit for generating a control pulse for controlling the switching element in accordance with an output of the error amplifier circuit;
A voltage comparison circuit for comparing the voltages of the plurality of external terminals and detecting the external terminal having the lowest voltage;
In accordance with the output of the voltage comparator circuit, among the outputs of said plurality of error amplifying circuit, the circuit switching to supply by selecting the output corresponding to said one voltage of the external terminal is the lowest to the pulse control circuit,
The semiconductor integrated circuit power supply control, wherein the obtaining Bei a. A current detection circuit for detecting a magnitude of a current flowing through the inductor is provided, and the pulse control circuit is configured to generate a control pulse according to an output of the current detection circuit. 3. A semiconductor integrated circuit for power supply control according to 1 or 2 . An overcurrent detection circuit that detects whether or not the current flowing through the inductor is greater than a predetermined current value, and the pulse control circuit is configured to stop generating the control pulse by the output of the overcurrent detection circuit. 4. The power integrated semiconductor integrated circuit according to claim 3, wherein Each of the plurality of current sources is a variable current source capable of changing a magnitude of a current to flow, an external control terminal for inputting control information for designating a current value to be passed to the variable current source from the outside, and the external depending on the control information input to the control terminal the variable current source power control semiconductor integrated according to any one of claims 1-4, characterized in that a control circuit for controlling the current value of circuit. 6. The power supply control semiconductor integrated circuit according to claim 5, wherein the control information includes information specifying "0" as a current value of the variable current source. A variable voltage source for generating the predetermined reference voltage, an external control terminal for inputting control information for designating a voltage value generated by the variable voltage source from the outside, and the input to the external control terminal The power supply control semiconductor integrated circuit according to claim 1, further comprising a control circuit that controls a voltage value of the variable voltage source according to control information. A voltage detection circuit for detecting whether or not the voltages of the plurality of external terminals are within a predetermined voltage range, and the pulse control circuit is configured to switch its control operation according to an output of the voltage detection circuit; 8. The semiconductor integrated circuit for power control according to claim 1 , wherein A power supply control semiconductor integrated circuit that constitutes an LED drive power supply device that drives a switching element that causes current to flow intermittently through an inductor and rectifies the current that flows through the inductor to generate a drive current for the LED,
A plurality of external current output terminals that respectively output current to a plurality of LED units;
A plurality of current sources respectively connected to the plurality of external current output terminals;
An error amplifying circuit that outputs a voltage corresponding to a potential difference between a voltage of the plurality of external current output terminals and a predetermined reference voltage; and
A control pulse for turning on and off the switching element is generated based on an output of an error amplifying circuit corresponding to the highest potential among the voltages of the plurality of external current output terminals. A semiconductor integrated circuit for power control.

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