JP2004166343A - Power supply circuit and electronic equipment - Google Patents

Abstract

Provided is a power supply circuit for preventing generation of an inrush current. A voltage control circuit for converting an input voltage to another voltage based on a voltage applied to a reference voltage input terminal and outputting the converted voltage. In the power supply circuit 10 capable of switching the voltage value output from the voltage transformation control circuit based on the switching instruction signal for switching the output voltage, the reference voltage input terminal FB of the voltage transformation control circuit 13 and the output terminal of the power supply circuit 10 A resonance circuit 14 having a plurality of resonance frequencies is connected between _Lout and the resonance frequency of the resonance circuit 14 when the output voltage is switched by the switching instruction signal.
[Selection] Fig. 2

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power supply circuit suitable for an electronic device such as an electronic organizer.
[0002]
[Prior art]
2. Description of the Related Art Various electronic devices such as electronic notebooks and electronic dictionaries operate using AA or AAA alkaline batteries or manganese batteries as power supplies. These electronic devices include, for example, a display unit including a liquid crystal display, a keyboard for inputting characters, a memory for storing input data and dictionary software, and a CPU (Central Processing) for centrally controlling the operation of the electronic devices. Unit).
2. Description of the Related Art In recent years, the data holding voltage of a memory has been reduced in order to save power. For example, a value lower than the input voltage (3 V) such as 2.1 V is often used as the data retention voltage of the memory, while the operating voltage of the CPU or the like is higher than the input DC voltage such as 3.3 V. Often it is. Therefore, a DC / DC converter is used in a power supply circuit of such an electronic device in order to obtain a rated voltage of a CPU, a memory, or the like by increasing or decreasing an input DC voltage.
[0003]
In order to increase or decrease the input DC voltage, a method of using a DC / DC converter for boosting and a DC / DC converter for stepping down (for example, see Patent Document 1), and a method of using a reference voltage of one DC / DC converter A method of switching between step-up and step-down is conceivable. Also, a multi-output DC / DC converter in which a DC / DC converter is provided with a booster circuit and a step-down circuit and a control circuit for controlling the respective circuits so as to obtain an output voltage higher and lower than the input DC voltage. A DC converter is also known (for example, see Patent Document 2).
[0004]
[Patent Document 1]
JP 2001-60569 A
[Patent Document 2]
JP-A-11-215823 (pages 3 to 4, FIG. 2)
[0005]
[Problems to be solved by the invention]
However, the above-described conventional multi-output DC / DC converter (Patent Document 2) employs substantially the same configuration as the case of using a DC / DC converter for boosting and a DC / DC converter for stepping down (Patent Document 1). ing. Providing two DC / DC converters for boosting and stepping down in an electronic device requires about twice as many components as in the case of using a single DC / DC converter, resulting in high cost. Further, since a mounting space is required, it is not possible to respond to a demand for miniaturization and thinning of electronic devices.
Therefore, when using a method in which one DC / DC converter performs step-up and step-down, when the DC / DC converter switches the reference voltage from the low voltage side to the high voltage side, the DC / DC converter sharply increases the output voltage. Therefore, the rapid step-up operation may cause an inrush current into the circuit, and may damage components in the power supply circuit.
[0006]
An object of the present invention is to provide a power supply circuit in which occurrence of an inrush current is prevented.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, an invention according to claim 1 is a transformer control circuit that transforms an input voltage to another voltage based on a voltage applied to a reference voltage input terminal and outputs the transformed voltage. A power supply circuit comprising a switching circuit capable of switching a voltage value output from the voltage transformation control circuit at a timing according to a voltage switching instruction signal, wherein a reference voltage input terminal of the voltage transformation control circuit and the voltage transformation control circuit A power supply circuit comprising: a resonance circuit having a plurality of resonance frequencies between the power supply circuit and the output terminal of the power supply; and switching a resonance frequency of the resonance circuit to another frequency when an output voltage is switched by the switching instruction signal.
[0008]
According to the first aspect of the present invention, there is provided a resonance circuit having a plurality of resonance frequencies between a reference voltage input terminal of the transformation control circuit and an output terminal of the transformation control circuit, and switching of the output voltage by a switching instruction signal. Sometimes, the resonance frequency in the resonance circuit is switched to another frequency, so that when the output voltage is switched, the response speed at which the output voltage fluctuated at the output terminal of the voltage transformation control circuit is transmitted to the reference voltage input terminal of the voltage transformation control circuit. Can be switched. This prevents the transformation control circuit from abruptly increasing the input voltage when the output voltage is switched by the switching instruction signal, thereby preventing the occurrence of an inrush current in the power supply circuit and preventing the elements constituting the power supply circuit from being damaged. can do.
[0009]
According to a second aspect of the present invention, in the power supply circuit according to the first aspect, the resonance circuit includes a constant section that controls a resonance frequency, and the resonance frequency being set to a predetermined value when the output voltage is switched by the switching instruction signal. And a switching unit for switching to another frequency only for a time.
[0010]
According to the second aspect of the present invention, when the output voltage is switched by the switching instruction signal, the switching unit switches the resonance frequency to another frequency for a predetermined time, so that the constant unit is switched only when the output voltage is switched. By shifting the resonance frequency to a lower frequency, the response speed of the transformer control circuit can be reduced, and the occurrence of inrush current can be prevented. Then, after a lapse of a predetermined time, the response speed of the transformer control circuit returns to the normal speed by returning the resonance frequency to the original value, so that the output stability of the power supply circuit can be improved.
[0011]
According to a third aspect of the present invention, in the power supply circuit according to the first aspect, the output voltage output from the output terminal of the power supply circuit is a boosted voltage obtained by increasing the input voltage or a reduced voltage obtained by decreasing the input voltage. Are output from the same output terminal of the power supply circuit.
[0012]
According to the third aspect of the present invention, it is possible to obtain a boosted voltage obtained by increasing the input voltage and a reduced voltage obtained by decreasing the input voltage from the same output terminal of the power supply circuit. Thus, the power supply voltage can be appropriately switched and supplied to each circuit unit based on the processing operation of the CPU.
[0013]
In a power supply circuit having a booster circuit and a step-down circuit, an input power supply is connected to the step-up circuit, an output of the step-up circuit is connected to an input of the step-down circuit, and an output of the step-down circuit is a power supply circuit. And an output terminal of the power supply circuit, the output voltage of the power supply circuit bypassing the step-down circuit when the input voltage is boosted and output by the booster circuit. And when outputting the output voltage of the step-down circuit from the output terminal of the power supply circuit, inputting the input voltage or the higher voltage of the output voltage of the booster circuit to the step-down circuit. Features.
[0014]
According to the fourth aspect of the present invention, when switching the output voltage, a state in which neither the output of the booster circuit nor the output of the step-down circuit is output from the output terminal of the power supply circuit does not occur. From the output terminal of the power supply circuit.
[0015]
According to a fifth aspect of the present invention, there is provided the power supply circuit according to any one of the first to fourth aspects.
[0016]
According to the fifth aspect of the present invention, the plurality of voltages generated by transforming the input voltage are output from the same output terminal of the power supply circuit, so that each of the circuit units is based on the processing operation of the CPU. The power supply voltage can be appropriately switched and supplied. In addition, it is possible to prevent an inrush current generated when the output voltage is switched, and to supply a stable and accurate voltage to each circuit unit in the electronic device.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an electronic device 1 including a power supply circuit 10 according to the present invention. The electronic device 1 is a portable electronic device such as an electronic organizer, an electronic dictionary, and a PDA (Personal Digital Assist).
[0018]
As shown in FIG. 1, the electronic device 1 includes a CPU 2, a RAM 3, a ROM 4, an external storage memory 5, an input unit 6, a display unit 7, and a communication control unit 8, which are connected to each other by a bus 9. Have been. The rated voltage (data holding voltage) of the storage device such as the RAM 3, the ROM 4, and the external storage memory 5 is, for example, 2.1 V lower than the input DC voltage 11, and the CPU 2, the input unit 6, the display unit 7, and the communication control unit The rated voltage such as 8 is set to, for example, 3.3 V higher than the input DC voltage 11.
[0019]
The electronic device 1 includes a power supply circuit 10 for generating and outputting two different levels of voltage from the input DC voltage 11 of 3 V in order to switch and supply different voltages to each unit according to the processing operation of the CPU 2. . When the CPU 2 performs a normal operation such as a display process, the output line L _out Outputs a voltage (for example, 3.3 V) higher than the input DC power supply 11, and when the CPU 2 causes the storage device to perform an operation such as data retention, the power supply circuit 10 supplies a lower voltage (for example, 3.3 V) than the input DC power supply 11. , 2.1V).
[0020]
Next, each component of the electronic device 1 will be described.
The CPU 2 reads out a specified program from the system program and various application programs stored in the ROM 4 or the external storage memory 5 and expands the program into a work area in the RAM 3 to execute various processes according to the program. A control signal is sent to each unit to control the overall operation of the electronic device 1.
[0021]
Further, the CPU 2 controls the control line L to set the output level of the power supply circuit 10. _cnt To send a switching instruction signal to the power supply circuit 10. The power supply circuit 10 boosts the input DC voltage 11 based on the switching instruction signal to a boosted voltage V of 3.3 V. _outH Or a step-down voltage V of 2.1 V obtained by stepping down the input DC voltage 11 _outL And an output line L _out And output the generated voltage.
[0022]
A RAM (Random Access Memory) 3 has a work area in which various programs, input data, and various data such as processing results are stored in a random access manner, and temporarily stores various information.
[0023]
The ROM (Read Only Memory) 4 stores a system program, various application programs, and the like necessary for executing the operation of the electronic device 1.
[0024]
The external storage memory 5 includes a recording medium (not shown) in which various programs, various data, and the like are stored or writable in advance, and the recording medium is a non-volatile memory such as a magnetic or optical recording medium or a semiconductor. And the like. The recording medium may be a fixed medium such as a fixed hard disk, or may be a portable medium such as a memory card which is removably mounted.
[0025]
The input unit 6 includes a keyboard having cursor keys, numeric input keys, various function keys, and the like, a pointing device such as a touch pen, and the like, and outputs to the CPU 2 a pressing signal pressed by the operator on the keyboard and a position signal of the pointing device. I do.
[0026]
The display unit 7 includes an LCD (Liquid Crystal Display) or the like, and performs various displays according to a control signal input from the CPU 2.
[0027]
The communication control unit 8 is composed of a modem (MODEM: Modulator / DEModulator) or the like, and is an interface connectable to a transmission medium connected to various communication lines such as a LAN (Local Area Network), a WAN (Wide Area Network), or the Internet. It is.
[0028]
As shown in FIG. 2, the power supply circuit 10 is connected to an input DC power supply 11 composed of a dry battery such as an alkaline battery or a manganese battery. _out And control line L _cnt , A booster circuit including the DC / DC converter 13, and the DC / DC converter 13 outputs an output line L to the reference voltage detection point 12. _out , A voltage dividing switch circuit 18 for switching the voltage dividing ratio at the reference voltage detecting point 12, a three-terminal regulator 19 as a voltage step-down circuit, a bypass circuit 20 for bypassing the three-terminal regulator 19, and a resonance circuit. 14 is provided with a constant unit 15 and a switching unit 17 for controlling the resonance frequency. The configuration of each circuit such as the booster circuit will be described later.
[0029]
The power supply circuit 10 is connected to the control line L _cnt (See FIG. 2), an "H" level switching instruction signal instructing a boosting operation is supplied to control line L. _cnt Is input to the transistor Q via the inverter I. ₂ Signal of "L" level is applied to the gate terminal of ₂ Is turned on, the input and output of the three-terminal regulator 19 are short-circuited by the bypass circuit 20, and the output voltage output from the booster circuit is connected to the output line L of the power supply circuit 10. _out Output to On the contrary, the control line L _cnt A "L" level switching instruction signal instructing a step-down operation via control line L _cnt Is input to the transistor Q via the inverter I. ₂ Signal of “H” level is applied to the gate terminal of ₂ Is turned off, the bypass circuit 20 is cut off, the three-terminal regulator 19 is enabled, and the output voltage output from the three-terminal regulator 19 is applied to the output line L of the power supply circuit 10. _out Output to
[0030]
When boosting, output line L _out Has a boosted voltage V of 3.3 V _outH Is obtained. Also, at the time of step-down, the output line L _out 2.1V step-down voltage V _outL Is obtained. The switching instruction signal (control line L _cnt The signal level of () is “H” level when instructing the boosting operation and “L” level when instructing the step-down operation. However, the signal level is “L” when the circuit configuration is changed to instruct the boosting operation. It is also possible to set the level to the “L” level and set the “H” level when instructing the step-down operation.
[0031]
Next, the boosting operation will be described.
The booster circuit is composed of the input stage capacitor C ₀ , A boosting inductance L, a diode D for rectification and backflow prevention, and an NMOS transistor Q as a switching element for intermittently connecting the inductance L to the ground GND. ₀ , Transistor Q ₀ / DC converter (transformation control circuit) 13 for performing on / off control of a capacitor C for storing a back electromotive force generated in the inductance L ₄ , Output stage capacitor C ₅ It is comprised including.
[0032]
The booster circuit includes a transistor Q by the DC / DC converter 13. ₀ Of the output line L by controlling the on / off of the output line to intermittently supply a current to the inductance L and adding the back electromotive force generated thereby to the output line. _out To output a boosted voltage of 3.3 V higher than the input voltage.
[0033]
The DC / DC converter 13 has five terminals: a chip enable terminal CE, a power supply terminal VDD, a reference voltage input terminal FB, an external output terminal EXT, and a ground terminal GND. When the voltage value applied to the reference voltage input terminal FB is within a preset range, the DC / DC converter 13 detects the output voltage at the reference voltage detection point 12 applied to the reference voltage input terminal FB. Operates in response to the fluctuation of the reference voltage, so that the transistor Q is controlled so that the detection voltage at the reference voltage detection point 12 becomes constant. ₀ Is controlled by a PWM control method.
[0034]
The resonance circuit 14 includes a constant section 15 and a capacitor C for frequency switching. ₂ And a switching unit 17. The resonance circuit 14 has an output line L _out Functions as an output voltage detection circuit for transmitting a voltage (voltage at the reference voltage detection point 12) corresponding to the output voltage of the DC / DC converter 13 to the reference voltage input terminal FB of the DC / DC converter 13. The DC / DC converter 13 controls the transistor Q based on the voltage applied to the reference voltage input terminal FB. ₀ Is controlled so that the voltage at the reference voltage detection point 12 becomes constant. At this time, the response speed to the voltage fluctuation of the voltage applied to the reference voltage input terminal FB of the DC / DC converter 13 is controlled by the resonance frequency of the resonance circuit 14.
[0035]
The resonance frequency of the resonance circuit 14 is equal to the output line L _out Is switched from a voltage lower than the input voltage to a voltage higher than the input voltage, the resonance frequency f ₁ Is lower frequency f by the switching unit 17. ₂ Is switched to.
[0036]
The constant part 15 is a resistor R ₁ And this resistance R ₁ C connected in parallel to ₁ It is comprised including. Resonant frequency f of constant section 15 ₁ Is represented by the following equation (1).
(Equation 1)
f ₁ = 1/2 (2π × C ₁ × R ₁ ) ... (1)
[0037]
The switching unit 17 includes a frequency switching capacitor C. ₂ , PMOS transistor Q ₁ , Resistance R ₄ , Resistance R ₁₀ And capacitor C ₁₀ It is comprised including.
[0038]
The switching unit 17 outputs a switching instruction signal (control line L _cnt ) When the signal level switches from the “L” level to the “H” level, that is, when the operation of the power supply circuit 10 is switched from the step-down operation to the step-up operation by the switching instruction signal, as described below. Capacitor C for frequency switching only for the time ₂ Are connected in parallel to the constant part 15 so that the resonance frequency f ₁ The lower frequency f ₂ Switch to.
[0039]
First, the constant part 15 and the capacitor C for frequency switching ₂ Will be described in parallel. The "H" level switching instruction signal is supplied to the capacitor C via the inverter I. ₁₀ Of the capacitor C is applied as an "L" level signal to one end of the ₁₀ The charge that has been charged is released. This allows the transistor Q ₁ Signal of "L" level is applied to the gate terminal of ₁ Turns on. Transistor Q ₁ Is turned on, the capacitor C for frequency switching is ₂ Are connected in parallel, and the resonance frequency f of the constant ₁ Is the frequency f expressed by the following equation (2). ₂ Is switched to.
(Equation 2)
f ₂ = 1/2 (2π × (C ₁ + C ₂ ) × R ₁ ) ... (2)
[0040]
It should be noted that comparing Equations (1) and (2), Equation (2) shows that the denominator C ₁ To C ₂ Is smaller than the value of the equation (1). Therefore, the resonance frequency f of the switched constant portion 15 ₂ Is the resonance frequency f of the constant section 15. ₁ Lower frequency f ₂ Becomes (f ₁ > F ₂ ).
[0041]
Next, the constant section 15 and the frequency switching capacitor C ₂ The release of the parallel connection with will be described. As described above, the capacitor C ₁₀ When an "L" level signal is applied to one end of the ₁₀ Is released. However, the resistance R ₁₀ Output line L via _out From capacitor C ₁₀ Is supplied to the capacitor C. ₁₀ Is charged and the transistor Q ₁ Signal of “H” level is applied to the gate terminal of ₁ Turns off. At this time, the frequency switching capacitor C ₂ One end of the resistor R ₄ , And the resonance frequency of the constant unit 15 returns to the original value.
[0042]
It should be noted that the constant part 15 and the frequency switching capacitor C ₂ Are connected in parallel with each other by the resistance R shown in the following equation (3). ₁₀ And capacitor C ₁₀ Is determined by the time constant τ [sec].
[Equation 3]
τ = C ₁₀ × R ₁₀ × ln (L _out ÷ V _th ) ... (1)
Note that V _th Indicates a cut-off voltage, and generally indicates 1.6 V in a 3 V drive product.
[0043]
The voltage dividing ratio switching circuit 18 includes a resistor R ₁ R connected in series with ₂ And the resistance R ₂ R connected in parallel with ₃ And NMOS transistor Q ₃ And is provided.
[0044]
The voltage dividing ratio switching circuit 18 includes a transistor Q ₃ The voltage division ratio at the reference voltage detection point 12 is switched by turning on and off the switch. Transistor Q ₃ Control terminal L _cnt Are turned on when the switching instruction signal is at “H” level instructing the boosting operation, and turned off when the switching instruction signal is at “L” level instructing the voltage lowering operation.
[0045]
Transistor Q ₃ Is off when resistance R ₃ Becomes invalid, and the voltage dividing ratio at the reference voltage detection point 12 becomes the resistance R ₁ Resistance value and resistance R ₂ Is determined by the resistance value. Transistor Q ₃ Is on, the resistance R ₃ Is the resistance R ₂ And the voltage dividing ratio at the reference voltage detection point 12 is the resistance R ₁ Resistance value and resistance R ₂ And resistance R ₃ Is determined by the combined resistance value of
[0046]
Next, the three-terminal regulator 19 will be described.
The three-terminal regulator 19 is an IC that includes three terminals, an input terminal, an output terminal, and a GND terminal, and converts a voltage input from the input terminal to a preset constant voltage (for example, 2.1 V) and outputs the same. The three-terminal regulator 19 is enabled only at the time of step-down, and the input terminal receives the higher voltage of the input voltage of the input power supply 11 or the boosted voltage appearing at the output terminal of the diode D.
[0047]
The bypass circuit 20 includes a PMOS transistor Q ₂ It is composed of Transistor Q ₂ Are connected to the input terminal and the output terminal of the three-terminal regulator 19, respectively, and the gate terminal is connected to the control line L via the inverter I. _cnt It is connected to the.
[0048]
The bypass circuit 20 includes the transistor Q ₂ The three-terminal regulator 19 is disabled or enabled by turning on and off the switch. Transistor Q ₂ Gate terminal is the control line L _cnt Via an inverter I. When an “L” level signal, which is an inverted signal level of a switching instruction signal indicating a boost operation, is applied to the gate terminal, the transistor Q ₂ Is turned on, the input terminal and the output terminal are short-circuited, and the three-terminal regulator 19 is bypassed.
[0049]
Next, the operation of the power supply circuit 10 according to the present embodiment will be described.
First, the step-down operation of the power supply circuit 10 will be described.
During the step-down operation, the switching instruction signal is at "L" level, so that transistor Q ₁ Inverter I, capacitor C ₁₀ ”Is applied. At this time, the transistor Q ₁ Is off and the capacitor C ₂ Is the resistance R ₄ Grounded. At this time, the resonance frequency of the constant unit 15 is represented by f ₁ It is.
[0050]
At this time, the capacitor C ₁₀ Is charged by an "H" level signal applied from the inverter I side, and the capacitor C is charged. ₂ Is the resistance R ₁ Output line L via _out Is supplied from the device and charged.
[0051]
Further, the transistor Q of the voltage division ratio switching circuit 18 ₃ The "L" level switching instruction signal is applied to the gate terminal of the switch to turn off. Thereby, the resistance R ₃ Becomes invalid, and the voltage dividing ratio at the reference voltage detection point 12 becomes the resistance R ₁ And resistance R ₂ Is determined by At this time, the voltage value at the reference voltage detection point 12 applied to the reference voltage input terminal FB deviates from the value in the range in which the DC / DC converter 13 operates, and the DC / DC converter 13 does not operate.
[0052]
The bypass circuit 20 includes a transistor Q ₂ Is turned off by applying an "H" level signal to its gate terminal, and the three-terminal regulator 19 is enabled.
Therefore, at the time of step-down, a current flows from the input power supply 11 through the path of the inductance L, the diode D, and the three-terminal regulator 19. The higher of the input voltage of the input power supply 11 or the boosted voltage output from the diode D is input to the input terminal of the three-terminal regulator 19. The three-terminal regulator 19 lowers the voltage and outputs the output line L via the output terminal. _out 2.1V step-down voltage V _outL Is output.
[0053]
Next, an operation in the case where the power supply circuit 10 switches from the step-down operation to the step-up operation will be described.
At this time, the switching instruction signal switches from the “L” level to the “H” level, and the transistor Q of the bypass circuit 20 is switched. ₂ The signal at the “L” level is applied to the gate terminal of the switch, and the gate terminal is turned on, and the three-terminal regulator 19 is bypassed and invalidated.
[0054]
Transistor Q of voltage division ratio switching circuit 18 ₃ Is turned on when an “H” level signal is applied to the gate terminal, and the resistance R ₂ And resistance R ₃ Are connected in parallel. At this time, the resistance value of the voltage division ratio switching circuit 18 decreases, and the voltage division ratio at the reference voltage detection point 12 changes. At this time, the voltage value at the reference voltage detection point 12 applied to the reference voltage input terminal FB is in a range where the DC / DC converter 13 operates.
[0055]
The capacitor C of the switching unit 17 ₁₀ The signal of the “L” level is applied to the terminal on the side of the inverter I through the inverter I. Thereby, the capacitor C ₁₀ Is released. Capacitor C ₁₀ Is released, the transistor Q ₁ The voltage applied to the gate terminal of the transistor Q ₁ Is turned on.
[0056]
Transistor Q ₁ Is turned on, as described above, the capacitor C ₁ And resistance R ₁ Frequency switching capacitor C ₂ Are connected in parallel, and the resonance frequency f of the resonance circuit 14 is ₁ Is low frequency f ₂ Switch to.
[0057]
As a result, the DC / DC converter 13 responds slowly to the voltage fluctuation at the reference voltage detection point 12 while ₀ On and off. Thus, the input voltage is boosted while intermittently flowing a current through the inductance L, and as shown in FIG. _out Is gradually switched from 2.1V to 3.3V.
[0058]
Then, the capacitor C ₁₀ Output line L _out , Resistance R ₁₀ Is supplied through the transistor Q ₁ The voltage applied to the gate terminal of the transistor Q gradually increases, and the transistor Q ₁ Turns off. Thereby, the frequency switching capacitor C ₂ Is the resistance R ₄ , And the resonance frequency of the constant unit 15 is f ₂ From high frequency f ₁ Return to As a result, the speed at which the resonance circuit 14 transmits the detection voltage of the output voltage at the reference voltage detection point 12 to the reference voltage input terminal FB of the DC / DC converter 13 increases, and the response speed of the DC / DC converter 13 increases. As a result, as shown in FIG. _outH Can be obtained.
[0059]
When switching the power supply circuit 10 from the step-up operation to the step-down operation, the switching instruction signal switches from the “H” level to the “L” level, and the capacitor C of the switching unit 17 is switched. ₁₀ A signal from the “L” level to the “H” level is applied to the terminal on the side of the inverter I through the inverter I. In this case, the capacitor C ₁₀ Have already been charged, and the transistor Q ₁ The transistor Q is connected to the gate terminal of ₁ Is turned off. In such a state, the capacitor C of the switching unit 17 ₁₀ Is applied to the terminal on the side of the inverter I of FIG. ₁₀ Of the transistor Q ₁ Does not turn on, the resonance frequency of the resonance circuit 14 does not switch.
[0060]
According to the present embodiment, when the operation of power supply circuit 10 is switched from the step-down operation to the step-up operation, capacitor C for frequency switching is used. ₂ The resistance R ₁₀ And capacitor C ₁₀ The resonance frequency f of the constant unit 15 is determined for a predetermined time by the time constant τ determined by ₁ The lower frequency f ₂ And the speed at which the voltage fluctuation at the reference voltage detection point 12 is transmitted to the reference voltage input terminal FB of the DC / DC converter 13 is reduced. Thereby, the response speed of the DC / DC converter 13 is reduced for a predetermined time, and the current I _bt As shown in the figure, the occurrence of an inrush current is prevented. Then, the transistor Q ₁ Is turned off, and the resonance frequency of the constant ₂ To f ₁ By returning to, the response speed of the DC / DC converter 13 can be increased and the output stability of the power supply circuit 10 can be maintained.
[0061]
FIG. 4 shows an output line L in the case where the resonance circuit 15 is not provided unlike the present embodiment. _out And the like, which show changes in the voltage appearing in FIG. As shown in FIG. 4, in the power supply circuit without the resonance circuit 15, when the step-down operation is switched to the step-up operation, a large inrush current I _bt Flows, and there is a possibility that elements constituting the power supply circuit may be damaged. Also, unlike the present embodiment, since the resonance frequency does not change, the response speed of the control circuit is always constant, and the output line L _out Changes sharply from 2.1V to 3.3V.
[0062]
The boosted voltage obtained by increasing the input voltage and the stepped-down voltage obtained by decreasing the input voltage are supplied to the same output terminal (output line L). _out ). Thus, the predetermined operation voltage can be supplied to each circuit unit by appropriately switching the output voltage based on the processing operation of the CPU.
[0063]
Further, the power supply circuit 10 of the present embodiment is provided with the three-terminal regulator 19 and the bypass circuit 17 so that the step-down voltage V of 2.1 V obtained by stepping down the input DC voltage of 3 V is obtained. _outL And a boosted voltage V of 3.3 V obtained by boosting the input DC voltage. _outH Can be obtained. Therefore, there is no need to provide the DC / DC converter for step-up and the DC / DC converter for step-down in the electronic device 1, and the number of components can be reduced. In addition, since the mounting space is reduced, the size and thickness of the electronic device 1 can be reduced.
[0064]
In addition, when boosting, the three-terminal regulator 19 is bypassed by the bypass circuit 20, so that a stable boosted voltage can be obtained. Further, at the time of step-down, the voltage value at the reference voltage detection point is changed by the voltage division switching circuit, thereby turning off the DC / DC converter, so that a stable step-down voltage can be obtained.
[0065]
It should be noted that the power supply circuit and the electronic device of the present invention are not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.
[0066]
For example, in the above embodiment, the voltage levels output from the power supply circuit 10 have been described as being 2.1 V and 3.3 V. However, the present invention is not limited to this. What is necessary is just to generate a predetermined voltage level. Also, the input DC voltage has been described as 3 V, but is not limited to this.
[0067]
The configuration of the resonance circuit 15 is not limited to the above-described embodiment, and may be any configuration that allows the resonance frequency of the resonance circuit to be switched to another frequency when the output voltage is switched by the switching instruction signal. Anything may be used.
[0068]
【The invention's effect】
According to the first aspect of the present invention, there is provided a resonance circuit having a plurality of resonance frequencies between a reference voltage input terminal of the transformation control circuit and an output terminal of the transformation control circuit, and switching of the output voltage by a switching instruction signal. Sometimes, the resonance frequency in the resonance circuit is switched to another frequency, so that when the output voltage is switched, the response speed at which the output voltage fluctuated at the output terminal of the voltage transformation control circuit is transmitted to the reference voltage input terminal of the voltage transformation control circuit. Can be switched. This prevents the transformation control circuit from abruptly increasing the input voltage when the output voltage is switched by the switching instruction signal, thereby preventing the occurrence of an inrush current in the power supply circuit and preventing the elements constituting the power supply circuit from being damaged. can do.
[0069]
According to the second aspect of the present invention, when the output voltage is switched by the switching instruction signal, the switching unit switches the resonance frequency to another frequency for a predetermined time, so that the constant unit is switched only when the output voltage is switched. By switching the resonance frequency to a lower frequency, the response speed of the transformer control circuit can be reduced, and the occurrence of inrush current can be prevented. Then, after a lapse of a predetermined time, the response speed of the transformer control circuit returns to the normal speed by returning the resonance frequency to the original value, so that the output stability of the power supply circuit can be improved.
[0070]
According to the third aspect of the present invention, it is possible to obtain a boosted voltage obtained by increasing the input voltage and a reduced voltage obtained by decreasing the input voltage from the same output terminal of the power supply circuit. Thus, the power supply voltage can be appropriately switched and supplied to each circuit unit based on the processing operation of the CPU.
[0071]
According to the fourth aspect of the present invention, when switching the output voltage, a state in which neither the output of the booster circuit nor the output of the step-down circuit is output from the output terminal of the power supply circuit does not occur. From the output terminal of the power supply circuit.
[0072]
According to the fifth aspect of the present invention, the plurality of voltages generated by transforming the input voltage are output from the same output terminal of the power supply circuit, so that each of the circuit units is based on the processing operation of the CPU. The power supply voltage can be appropriately switched and supplied. In addition, it is possible to prevent an inrush current generated when the output voltage is switched, and to supply a stable and accurate voltage to each circuit unit in the electronic device.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a functional configuration of an example of an electronic apparatus according to the invention.
FIG. 2 is a diagram showing a power supply circuit shown in FIG.
3 is a waveform diagram showing a switching instruction signal input to the power supply circuit shown in FIG. 1, an output voltage generated by the power supply circuit, and a waveform of a current generated according to the output voltage.
FIG. 4 is a waveform showing a switching instruction signal, an output voltage, and a waveform of a current generated according to the output voltage, which are generated when the power supply circuit shown in FIG. 1 does not have a resonance circuit, a switching circuit, and a time constant circuit. FIG.
[Explanation of symbols]
1 electronic equipment
10. Power supply circuit
11 Input DC power supply
12 Reference voltage detection point
13. DC / DC converter (step-up control circuit)
14 Resonant circuit
15 Constant part
17 Switching section
18 Voltage division ratio switching circuit
19 3-terminal regulator (step-down circuit)
20 Bypass circuit
C ₀ Input stage capacitor
C ₁ Capacitor
C ₂ Frequency switching capacitor (frequency switching unit)
C ₄ Capacitor
C ₅ Output stage capacitor
D diode
FB reference voltage input terminal
L inductance
Q ₀ NMOS transistor
Q ₁ PMOS transistor
Q ₂ PMOS transistor
Q ₃ NMOS transistor
R ₁ resistance
R ₂ resistance
R ₃ resistance
Lout output line
Lcnt control line
V _outH Boost voltage
V _outL Step-down voltage

Claims (5)

Based on the voltage applied to the reference voltage input terminal, the input voltage is converted into another voltage and output, and the voltage is output from the voltage conversion control circuit at a timing according to an output voltage switching instruction signal. A power supply circuit comprising a switching circuit capable of switching a voltage value,
A resonance circuit having a plurality of resonance frequencies between a reference voltage input terminal of the transformation control circuit and an output terminal of the transformation control circuit,
A power supply circuit, wherein a resonance frequency in the resonance circuit is switched to another frequency when the output voltage is switched by the switching instruction signal. The power supply circuit according to claim 1,
The resonance circuit includes:
A constant part for controlling the resonance frequency;
A switching unit that switches the resonance frequency to another frequency for a predetermined time when the output voltage is switched by the switching instruction signal;
A power supply circuit comprising: The power supply circuit according to claim 1,
An output voltage output from an output terminal of the power supply circuit outputs a boosted voltage obtained by increasing the input voltage or a stepped-down voltage obtained by reducing the input voltage from an output terminal of the same power supply circuit. . In a power supply circuit having a booster circuit and a step-down circuit,
An input power supply is connected to a booster circuit, an output of the booster circuit is connected to an input of a step-down circuit, an output of the step-down circuit is output from an output terminal of a power supply circuit, and the input voltage is boosted. When boosting and outputting by a circuit, the output voltage of the booster circuit is output from the output terminal of the power supply circuit, bypassing the step-down circuit,
A power supply, wherein when the output voltage of the step-down circuit is output from the output terminal of the power supply circuit, the input voltage or the higher voltage of the output voltage of the booster circuit is input to the step-down circuit. circuit. An electronic apparatus comprising the power supply circuit according to claim 1.

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