JP2006211747A - Power supply device and electronic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a power supply device that can adequately set the boosting rate of a charge pump circuit. <P>SOLUTION: In the power supply device 100 that converts an input voltage Vbat to a prescribed set voltage and outputs it, a boosting rate setting part 30 sets the boosting rate XCP of the charge pump circuit 10 on the basis of the input voltage Vbat and the prescribed set voltage. A voltage adjustment part 20 is a regulator circuit, and adjusts a voltage Vx so that an output voltage Vout of the charge pump circuit 10 approximates the set voltage. An output voltage setting part 40 generates the prescribed set voltage as a digital value Dset. An A/D converter 32 analog/digital-converts the input voltage Vbat. The boosting rate setting part 30 sets the boosting rate on the basis of the comparison result of an analog/digital-converted input voltage Ddet and the set voltage Dset. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a power supply device, and more particularly to a control technology for a charge pump circuit in which a boosting rate can be switched.

  In a small information terminal such as a cellular phone or PDA (Personal Digital Assistance) in recent years, the output voltage of a battery is higher than the output voltage of a battery such as a light emitting diode (hereinafter referred to as an LED) used for a backlight of a liquid crystal. There are devices that require voltage. In these small information terminals, Li-ion batteries are often used, and the output voltage is usually about 3.5 V, and is about 4.2 V even when fully charged, but the LED has a drive voltage higher than the battery voltage. Requires high voltage. As described above, when a voltage higher than the battery voltage is required, the battery voltage is boosted by using a boost type power supply device using a charge pump circuit or the like to drive a load circuit such as an LED. Getting the required voltage.

  Patent Document 1 discloses a technique related to a charge pump circuit in which a plurality of boosting rates can be switched. By using such a charge pump circuit that can switch multiple boost rates, even if the battery voltage fluctuates due to battery consumption or charging, a more appropriate voltage can be set in the load circuit by setting an appropriate boost rate. Can be supplied.

  Consider a case where the charge pump circuit boosts the battery voltage, which is the input voltage, at a boost rate of 1.5 or 2 times. Since the charge pump circuit outputs the input voltage multiplied by the boost ratio, if it is desired to stabilize the output voltage to a predetermined value, it is necessary to provide a regulator circuit on the input side of the charge pump circuit and adjust the input voltage. is there. That is, assuming that the voltage to be applied to the load circuit is 4.5V, the input voltage of the charge pump circuit is adjusted to 3V and 2.25V by the regulator circuit when the boost rate is 1.5 times and 2 times, respectively. There is a need.

Japanese Patent Laid-Open No. 6-78527

  Here, a method for setting the boosting rate of the charge pump circuit will be considered. As a method of setting the boosting rate of the charge pump circuit, a method of monitoring the output voltage of the charge pump circuit is conceivable. In this case, the output voltage is monitored, and when the output voltage falls below a predetermined set value, the step-up rate is set one step higher.

  However, as described above, there are a plurality of combinations of the input voltage and the step-up rate with respect to the target value of the output voltage of a certain charge pump circuit. For example, when the battery voltage is 3V, the battery voltage is directly boosted at a boost rate of 1.5 times, or the battery voltage is stepped down to 2.25V by a regulator circuit and then boosted by a factor of 2. Also, an output voltage of 4.5V can be obtained. However, since the efficiency of the charge pump circuit generally decreases as the step-up rate increases, the latter deteriorates in efficiency.

Further, considering the case where the output voltage of the charge pump circuit is changed with time, for example, a high voltage and a low voltage are alternately output. When outputting a high voltage after outputting a low voltage, if the output voltage is monitored, the step-up rate may be set higher than necessary.
As described above, when the output voltage is monitored at the time of setting the step-up rate of the charge pump circuit, there is a possibility that the efficiency is unnecessarily deteriorated.

  In addition, when the output voltage of the charge pump circuit is turned on and off in time, there is a problem that the boost rate cannot be set well during the period until the output voltage of the charge pump circuit is stabilized.

  The present invention has been made in view of these problems, and an object thereof is to provide a power supply device capable of appropriately setting the boosting rate of the charge pump circuit and an electronic device using the same.

  One embodiment of the present invention relates to a power supply apparatus. This power supply device is a power supply device that converts an input voltage into a target voltage as a target value and outputs the voltage, a charge pump circuit capable of switching a plurality of boosting rates, a set voltage that defines the input voltage and the target value A boost rate setting unit that sets the boost rate of the charge pump circuit based on the voltage, and a voltage adjustment unit that adjusts the input voltage so that the output voltage of the charge pump circuit approaches a predetermined voltage and outputs the voltage to the charge pump circuit. .

  According to this aspect, it is possible to appropriately set the boosting rate based on the input voltage to the power supply device.

The power supply apparatus further includes an output voltage setting unit that outputs the set voltage as a digital value, and an A / D converter that converts the input voltage from analog to digital, and the step-up rate setting unit includes the analog-digital converted input voltage and a predetermined value The step-up rate may be set based on the comparison result with the above voltage.
By setting the boost rate by digital signal processing, it is possible to easily control the output voltage.

The voltage adjustment unit is an error amplifier that adjusts the voltage of the transistor provided between the terminal to which the input voltage is applied and the input terminal of the charge pump circuit, and the control terminal of the transistor based on the error voltage between the output voltage and the set voltage. And may be included.
By adjusting the voltage input to the charge pump circuit by the regulator circuit, the output voltage can be brought close to a predetermined set voltage with high accuracy. The control terminal of the transistor means a gate terminal in the case of a field effect transistor (FET) and a base terminal in the case of a bipolar transistor.

The transistor may be configured as a discrete component.
The transistor may be configured as a separate package from other circuit elements that constitute the power supply device.
By providing the transistor as a discrete component or in an integrated circuit of another package, heat generation can be dispersed.

  Another embodiment of the present invention is an electronic device. The electronic device includes a load circuit, the above-described power supply device that drives the load circuit, and a drive control unit that is provided on the drive circuit of the load circuit and that modulates the current flowing through the load circuit.

  When the current flowing in the load circuit is pulse-modulated and the drive state is controlled by the duty ratio, the boost rate is set appropriately by setting the boost rate based on the input voltage, not the output of the charge pump circuit be able to.

The load circuit is a light emitting element, and the drive control unit may control the light emission luminance.
The light emitting element refers to an LED, an organic EL (ElectroLuminescence), or the like. Even in an electronic device that adjusts luminance by pulse-modulating a current flowing through a light-emitting element, the light-emitting element can be driven by performing a boosting operation at an appropriate boosting rate.

  The load circuit may be a plurality of light emitting elements, and the drive control unit may independently control the light emission luminance of each light emitting element.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, etc. are also effective as an aspect of the present invention.

  According to the power supply device of the present invention, the boosting rate of the charge pump circuit can be set appropriately.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a power supply device 100 according to the first embodiment of the present invention.
The power supply device 100 is mounted on a small information terminal driven by a battery 500, and is necessary for driving the load circuit by boosting the battery voltage Vbat using the battery voltage Vbat output from the battery 500 as an input voltage. Generate voltage.

  The power supply apparatus 100 includes an input terminal 102 and an output terminal 104 as input / output terminals. A battery voltage Vbat output from the battery 500 is applied to the input terminal 102. A load circuit (not shown) is connected to the output terminal 104. The power supply apparatus 100 boosts the battery voltage Vbat applied to the input terminal 102 and outputs the output voltage Vout from the output terminal 104.

  The power supply device 100 includes a charge pump circuit 10, a voltage adjusting unit 20, a boost rate setting unit 30, an output voltage setting unit 40, an A / D converter 32, a D / A converter 42, and resistors R3 and R4.

The charge pump circuit 10 is configured such that by changing the number of stages of the charge pump circuit, a plurality of boosting rates can be switched and the output voltage can be changed, and the voltage Vx input to the input terminal IN is specified. The voltage is boosted at a rate and output from the output terminal OUT. The output terminal OUT of the charge pump circuit 10 is the output terminal 104 of the power supply device 100 as it is. In the present embodiment, it is assumed that the boosting rate of the charge pump circuit 10 is switched between 1 ×, 1.5 ×, and 2 ×.
The output voltage Vout = Vx × XCP is output from the output terminal 104 of the power supply apparatus 100, that is, the output terminal OUT of the charge pump circuit 10, with the step-up rate as XCP.

  The output voltage setting unit 40 generates the output voltage Vout to be supplied to the load circuit by the power supply device 100 as a digital value Dset based on data stored in a ROM (Read Only Memory) or data input from the outside. To do. The D / A converter 42 converts the digital value Dset output from the output voltage setting unit 40 from digital to analog, and outputs a set voltage Vset of the analog value to the voltage adjustment unit 20. Further, the digital value Dset generated by the output voltage setting unit 40 is input to the boost rate setting unit 30.

The voltage adjusting unit 20 is a regulator circuit, and steps down the battery voltage Vbat applied to the input terminal 102 as necessary, and outputs it to the input terminal IN of the charge pump circuit 10. The voltage adjusting unit 20 includes a transistor M1, an operational amplifier 22, and resistors R1 and R2.
The set voltage Vset output from the boost ratio setting unit 30 is applied to the non-inverting input terminal of the operational amplifier 22, and the output voltage Vout is divided and applied to the inverting input terminal by the resistors R1 and R2.
The transistor M1 is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), and is provided between the input terminal 102 of the power supply device 100 and the input terminal IN of the charge pump circuit 10. The output terminal of the operational amplifier 22 is connected to the gate terminal which is the control terminal of the transistor M1. The voltage adjusting unit 20 adjusts the ON resistance according to the voltage applied to the gate terminal of the transistor M1, and adjusts the voltage of the drain terminal, that is, the voltage Vx of the input terminal IN of the charge pump circuit 10.

  In the voltage adjusting unit 20, the operational amplifier 22 adjusts the voltage of the gate terminal of the transistor M1 so that the two voltages input to the inverting input terminal and the non-inverting input terminal are equal. Here, the set voltage Vset is applied to the non-inverting input terminal of the transistor M1, and the voltage Vy = Vout × R1 / (R1 + R2) is applied to the inverting input terminal. When the operational amplifier 22 performs feedback so that Vset = Vy and the on-resistance of the transistor M1 is adjusted, the output voltage is stabilized so that Vout = Vset × (R1 + R2) / R1. At this time, the voltage Vx at the input terminal IN of the charge pump circuit 10 is stabilized so as to approach Vx = Vout / XCP = Vset × (R1 + R2) / R1 / XCP.

The resistors R3 and R4 divide the battery voltage Vbat applied to the input terminal 102 of the power supply apparatus 100 and output it to the A / D converter 32. The detection voltage Vdet = Vbat × R3 / (R3 + R4) is input to the A / D converter 32.
The A / D converter 32 converts the detection voltage Vdet obtained by dividing the battery voltage Vbat from analog to digital, and outputs the digital value Ddet to the boost rate setting unit 30.

  A digital value Ddet representing the battery voltage Vbat and Dset for instructing a set value of the output voltage Vout are input to the boost rate setting unit 30. The step-up rate setting unit 30 compares two digital values Dset and Ddet to compare a set value of the battery voltage Vbat and the output voltage Vout (hereinafter referred to as an output voltage set value Vout ′), and based on the comparison result. Thus, the boosting rate XCP of the charge pump circuit 10 is set.

  The step-up rate setting unit 30 sets the step-up rate XCP by the following process, for example. The step-up rate setting unit 30 compares the battery voltage Vbat and the output voltage setting value Vout ′ by comparing the digital values Dset and Ddet. As a result, when Vbat> Vout ′, the step-up rate XCP is set to 1. Further, when Vbat> 2/3 × Vout ′, the step-up rate XCP is set to 1.5 times. Further, when Vbat> 1/2 × Vout ′, the boost rate XCP is set to double. The step-up rate setting unit 30 instructs the charge pump circuit 10 on the step-up rate XCP thus set.

  The operation of the power supply apparatus 100 configured as described above will be described. FIG. 2 is a flowchart showing a procedure for setting the boost rate XCP of the boost rate setting unit 30 in the power supply apparatus 100.

First, the A / D converter 32 performs analog-to-digital conversion on the battery voltage Vbat, and acquires the voltage value as a digital value Ddet (S100).
Next, in the output voltage setting unit 40, an output voltage setting value Vout ′ that is a setting value of the output voltage Vout is generated and output as a digital value Dset (S110). The order of the processes shown in S100 and S110 may be reversed.
The step-up rate setting unit 30 starts a comparison process between the battery voltage Vbat and the output voltage set value Vout ′ based on the digital values Ddet and Dset acquired and set in S100 and S110 (S120).

When Vbat> Vout ′ (Y in S130), the step-up rate XCP is set to 1 (S140). When Vbat <Vout ′ (N in S130), the battery voltage Vbat is compared with the voltage 2/3 × Vout ′. When Vbat> 2/3 × Vout ′ (Y in S150), the boost rate XCP is 1.5. Double is set (S160).
When Vbat <2/3 × Vout ′ (N in S150), the boost rate XCP is set to double.

For example, it is assumed that the battery voltage Vbat is 3.6V and the output voltage set value Vout ′ is 4.7V. At this time, 3.6 V> 2/3 × 4.7 V is established, and therefore the boost rate XCP is set to 1.5 by the above procedure in the boost rate setting unit 30.
When the boosting rate of the charge pump circuit 10 is set to 1.5 times and the boosting operation is started, the input voltage Vx of the charge pump circuit 10 is Vx = 4.7 / 1.5 = 3.13 V by the voltage adjusting unit 20. Feedback control is performed so that
As a result, the output voltage Vout of the power supply device 100 is stabilized at 4.7 V that is the output voltage set value Vout ′.

  Thus, according to power supply device 100 according to the present embodiment, since the boosting rate is determined by directly referring to battery voltage Vbat, an appropriate boosting rate can be set even when battery voltage Vbat varies. Can do. As a result, the problem of setting the double boosting rate to 1.5 times is solved, and wasteful power consumption can be reduced.

  The circuit blocks constituting the power supply device 100 of FIG. 1 may be integrated as a unit except for the capacitor inside the charge pump circuit 10 and the transistor M1 of the voltage adjusting unit 20. At this time, the capacitor is externally attached. The transistor M1 is connected to the outside of the integrated circuit as a discrete element, or is formed on another integrated circuit. If the transistor M1 generates a large amount of heat when the voltage regulator 20 reduces the battery voltage Vbat to generate the voltage Vx, heat can be dispersed by providing the transistor M1 outside the integrated circuit. The circuit can be operated stably.

  Further, when the heat generation of the transistor M1 does not matter so much, it may be integrated on one semiconductor chip together with other circuit blocks. By integrating the transistor M1 integrally with the D / A converter 42, the output voltage setting unit 40, etc., it is not necessary to route the wiring to the outside, so that the number of terminals can be reduced and the circuit area can be reduced.

(Second Embodiment)
The power supply device according to the second embodiment boosts the battery voltage Vbat and drives the RGB three-color light emitting diodes. The three color light emitting diodes are alternately turned on by time division. Since the optimum voltage for driving the light emitting diode differs for each color of RGB, the power supply device changes the output voltage setting value every time the light emitting diode to be turned on is switched, and sets the boost rate of the charge pump circuit to the optimum value. To do.

  FIG. 3 is a circuit diagram illustrating a configuration of the light emitting device according to the present embodiment. In FIG. 3, the same or equivalent components as those in FIG. The light emitting device 1000 includes a battery 500, a power supply device 100, RGB three-color light emitting diodes 300R to 300B, and a drive control unit 400 that controls a driving state of the light emitting diodes 300R to 300B. Hereinafter, unless particularly required, the suffixes R, G, and B attached to the three RGB colors are omitted.

  The drive control unit 400 is provided on the drive system path of the light emitting diode 300 that is a load circuit, and adjusts the current flowing through the light emitting diode 300 by pulse width modulation. The drive controller 400 includes a light emission pattern generator 50, a brightness adjusting PWM oscillator 52, and constant current circuits 54R to 54B.

  The constant current circuits 54R to 54B adjust the light emission luminance by controlling the current flowing through the light emitting diodes 300R to 300B, respectively. The constant current circuits 54 </ b> R to 54 </ b> B generate a constant current having a current value indicated by the brightness adjusting PWM oscillator 52. The constant current generated by the constant current circuit 54 is pulse width modulated, and the luminance is adjusted according to the duty ratio. That is, the constant current circuit 54 adjusts the current flowing through the light emitting diode 300 based on both the current value and the duty ratio, thereby controlling the light emission luminance.

  The light emission pattern generator 50 generates a light emission control signal SIG10 that selects which of the light emitting diodes 300R to 300B emits light based on data stored in the ROM or data input from the outside. In the present embodiment, each of the light emitting diodes 300R to 300B is turned on in a time-division manner, for example, in order of R, G, and B with a period of 60 Hz, and mixed to generate a desired color.

  The brightness adjusting PWM oscillator 52 controls the current value and the duty ratio generated by the constant current circuits 54R to 54B. The luminance adjustment PWM oscillator 52 receives the light emission control signal SIG10 output from the light emission pattern generator 50, and generates a PWM signal PWMR when instructed to emit red light. Similarly, when green and blue light emission is instructed, PWM signals PWMG and PWMB are generated, respectively.

The forward voltage Vf of the light emitting diode 300 is different for each color. Therefore, in light emitting device 1000 according to the present embodiment, output voltage Vout is set high for light emitting diode 300B having a large Vf, and output voltage Vout is set low for light emitting diode 300R having a small Vf.
The output voltage setting unit 40 generates a different digital value Dset for each color. For example, as the set value of the output voltage Vout for each color, data stored in the ROM may be used, or externally input data may be stored in a register in advance. The output voltage setting unit 40 outputs a set value Dset corresponding to the color designated by the light emission pattern generator 50 to the D / A converter 42.

  The light emission control signal SIG10 output from the light emission pattern generator 50 is also output to the step-up rate setting unit 30. The boost rate setting unit 30 resets the boost rate according to the flowchart shown in FIG. 2 every time the color indicated by the light emission control signal SIG10 changes.

  According to the power supply device 100 according to the present embodiment, the output voltage Vout is changed to an optimal value every time a plurality of light-emitting diodes 300 driven in a time-sharing manner are switched. Can be driven. When the output voltage set value Vout ′ changes every time the light emitting diode 300 is switched as in the present embodiment, setting the boost rate based on the output voltage Vout requires time to set the boost rate. However, since the battery voltage Vbat is a stable value regardless of the switching of the light emitting diode 300, the boosting rate can be set to an optimum value in a short time even when the output voltage Vout is varied with time. .

  Furthermore, a non-light emission period in which none of the light emitting diodes 300 emits light may be provided at the time of switching the light emission of each light emitting diode 300, and the boosting operation of the charge pump circuit 10 may be stopped in this non-light emission period. In this case, unnecessary switching operations can be reduced, so that power consumption can be reduced. According to power supply device 100 according to the present embodiment, battery voltage Vbat is monitored to set the boost rate, so that the boost rate can be set even when the switching operation of charge pump circuit 10 is stopped.

  Those skilled in the art will understand that the above-described embodiment is an exemplification, and that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  For example, in the power supply apparatus 100 of FIG. 1, the step-up rate setting unit 30, the A / D converter 32, the output voltage setting unit 40, and the D / A converter 42 are omitted, and the externally set voltage and the detected voltage Vdet are analogized. The boosting rate may be set according to the comparison result.

  In the present embodiment, the transistor M1 to be used is an FET, but another type of transistor such as a bipolar transistor may be used. The selection of these transistors depends on the design specifications required for the power supply device and the semiconductor manufacturing process to be used. You can decide by such as.

  In the present embodiment, all the elements constituting the power supply device may be integrated, or a part thereof may be constituted by discrete parts. Which part is integrated may be determined based on the semiconductor manufacturing process to be used, cost, occupied area, and the like.

  The load circuit driven by the power supply device described in the embodiment is not limited to the light emitting diode, and may be another light emitting element, or may drive various other load circuits.

It is a circuit diagram which shows the structure of the power supply device which concerns on 1st Embodiment. It is a flowchart which shows the setting procedure of the pressure | voltage rise rate of the pressure | voltage rise rate setting part of FIG. It is a circuit diagram which shows the structure of the light-emitting device which concerns on 2nd Embodiment.

Explanation of symbols

  M1 transistor, 10 charge pump circuit, 30 step-up rate setting unit, 40 output voltage setting unit, 100 power supply device, 102 input terminal, 400 drive control unit.

Claims (8)

A power supply device that converts an input voltage to a predetermined voltage as a target value and outputs the voltage,
A charge pump circuit capable of switching a plurality of boosting rates;
A step-up rate setting unit that sets the step-up rate of the charge pump circuit based on the input voltage and a set voltage that defines the target value;
A voltage adjusting unit that adjusts the input voltage so that an output voltage of the charge pump circuit approaches the predetermined voltage, and outputs the voltage to the charge pump circuit;
A power supply apparatus comprising: An output voltage setting unit that outputs the set voltage as a digital value;
An A / D converter for analog-to-digital conversion of the input voltage;
The power supply apparatus according to claim 1, further comprising: a step-up rate setting unit that sets the step-up rate based on a comparison result between the analog-digital converted input voltage and the predetermined voltage. The voltage regulator is
A transistor provided between a terminal to which the input voltage is applied and an input terminal of the charge pump circuit;
An error amplifier that adjusts the voltage of the control terminal of the transistor based on an error voltage between the output voltage and the set voltage;
The power supply device according to claim 1, comprising:   The power supply apparatus according to claim 3, wherein the transistor is configured as a discrete component.   The power supply device according to claim 3, wherein the transistor is configured as a separate package from other circuit elements forming the power supply device. A load circuit;
The power supply device according to any one of claims 1 to 5, which drives the load circuit;
A drive control unit that is provided on the drive circuit of the load circuit and that modulates a current flowing in the load circuit;
An electronic device comprising:   The electronic device according to claim 6, wherein the load circuit is a light emitting element, and the drive control unit controls light emission luminance.   The electronic device according to claim 6, wherein the load circuit is a plurality of light emitting elements, and the drive control unit independently controls light emission luminance of each light emitting element.

Images