JP2002204567A - Step-down dc-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a step-down DC-DC converter that is efficient, produces less noise, and occupies a smaller area. SOLUTION: The step-down DC-DC converter is provided with a switch circuit, comprising a plurality of switches that perform switching on output signals from an oscillation circuit for generating signals of a specific frequency, and thereby alternately connect a first and a second capacitors in series and in parallel. Power of voltage divided in series connection is extracted, and power of voltage divided and charged in parallel connection is extracted from the individual capacitors. As a result, a step-down conversion is efficiently implemented, and when the voltage exceeds a target reference output voltage, a control is carried out merely by stopping the oscillation circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-down DC / DC
For the converter, specifically, a step-down DC used as a power supply circuit of a portable electronic device such as a PHS, a portable telephone such as a portable telephone, an electronic book, and a PDA (portable terminal device).
The present invention relates to a step-down DC / DC converter that is highly efficient, generates less noise, and occupies a small area.

[0002]

2. Description of the Related Art Conventionally, in a battery-driven electronic device such as a PHS, a portable telephone such as a portable telephone, and a portable electronic device, the operating voltage has been reduced in order to reduce power consumption. Recently, LSIs operated from a 3V power supply specification have been operating with a 1.8V power supply specification.
Further, an LSI with a 1.5V power supply specification has begun to be developed. On the other hand, a lithium ion battery or the like used as a power source for this type of device usually has a voltage of about 3.6 V (3.0 V to 4.2 V). Therefore, the operating power of the LSI is obtained by stepping down the voltage of the battery. In a conventional series regulator that steps down by a transistor, the efficiency is 50%.
Degree and low.

[0003] On the other hand, a voltage step-down circuit using a charge pump circuit and a step-down transistor can obtain a high efficiency of 50% or more. Therefore, this circuit has recently been used as a power supply circuit of a battery-driven electronic device. As this kind of conventional step-down switched capacitor type DC / DC converter, JP-A-8-205524 “Voltage Converter” can be mentioned. FIG. 3 shows an example of the circuit 11. The voltage converter 9 has two capacitors C1 and C2, three switches SWa, SWb and SWc for switching the connection state of these capacitors, and a switch control circuit 8. are doing. This voltage converter 9 has two capacitors C
1, C2 are connected in series by turning on / off the switches SWa and SWb, and these capacitors are charged with the power of the input voltage Vin. After the charging, the switches SWa, SWb,
By switching ON / OFF of SWc, capacitors C1, C2
Are switched in parallel, the voltages of the capacitors C1 and C2 are substantially reduced to half, and the charges of the capacitors C1 and C2 are transferred to the capacitor C3 for charging. 9A to the outside. Reference numeral 8 denotes a switch control circuit that controls ON / OFF of each of the switches SWa, SWb, and SWc.
The capacitances of the capacitors C1 and C2 are assumed to be substantially equal. 9B is an input terminal to which the power of the voltage Vin is input, and the capacitor C3 is a power capacitor for charging the power of the voltage of Vin / 2.

The output terminal 9 output by the voltage converter 9
The power of A is stepped down by the MOSFET transistor Q, and the power of the voltage Vout is output to the output terminal 11A.
The gate of the transistor Q is connected to the output terminal of the differential amplifier 7, and the output controls the output voltage Vout. The differential amplifier 7 has a reference voltage generation circuit 6
Receives the voltage from the output terminal 11A at its-input terminal, and receives the voltage Vou at the output terminal 11A.
Control is performed so that t becomes the reference voltage Vref. In this case, the voltage Vout at the output terminal 11A is directly used as the detection voltage. The voltage may be obtained as the detection voltage.

[0005]

However, in such a step-down type switched capacitor type DC / DC converter, a power transistor is required for the step-down transistor, and the conversion efficiency must be 90% or more. However, there is a problem that the power supply circuit generates heat and the occupied area increases. In this step-down type switched capacitor type DC / DC converter, the output voltage can be regulated by directly controlling the switch of the capacitor by the voltage converter 9 without using the step-down transistor. However, in this DC / DC converter, it is necessary to control the switch frequency or cycle of the switch control circuit 8 in order to stabilize the output voltage Vout. Is performed, the output voltage V
There is a disadvantage that noise is generated on the out output line. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and to provide a step-down DC / DC converter with high efficiency, low noise generation and small occupation area.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the step-down DC / DC converter according to the present invention is characterized by a first and a second capacitor, and an oscillation circuit for generating a signal of a specific frequency. A switch circuit comprising a plurality of switches for switching the output signal of the oscillation circuit to connect the first and second capacitors alternately in series and in parallel, and the first and second capacitors are connected in series. And a DC power source for charging these capacitors with a DC voltage when the first and second capacitors are connected in series, and power is extracted from a voltage point divided by these capacitors and connected in parallel. The output terminal that extracts the power of the terminal voltage of these capacitors when it is in operation, and the output voltage of this output terminal is detected and compared with a predetermined reference voltage. A comparator for generating a signal for stopping oscillation of the oscillation circuit when the reference voltage is exceeded, wherein the switch circuit connects the first and second capacitors in parallel when the oscillation circuit is stopped. It is assumed that.

[0007]

As described above, according to the present invention, a plurality of first and second capacitors are alternately connected in series and in parallel by switching according to an output signal of an oscillation circuit oscillating at a specific frequency. By providing a switch circuit consisting of the following switches, taking out the power of the divided voltage when connected in series and taking out the power of the charged voltage when connecting in parallel from each capacitor, efficient step-down conversion can be performed. it can. Furthermore, when the voltage rises above the target reference output voltage, control is performed only by stopping the oscillation circuit, so that a step-down transistor is not required, noise and heat generation of the power supply circuit are suppressed, and the occupied area is also reduced. Small enough. As a result, the step-down DC / DC converter to which the present invention is applied has a high efficiency, generates less noise, generates less heat, and occupies a smaller area.

[0008]

FIG. 1 shows a switched capacitor type DC to which a step-down DC / DC converter according to the present invention is applied.
2 is a block diagram of a switched capacitor type DC / DC converter according to another embodiment to which the step-down DC / DC converter of the present invention is applied. Note that the same components as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 1, 10
Is a switched capacitor type step-down DC / DC converter driven by the power of the lithium ion battery 1,
Oscillator circuit (OSC) 2, inverter 3, driver 4
A, 4B, a step-down charge pump circuit 5, a reference voltage generating circuit 6, and a comparator 7A.
The power of the output voltage Vout regulated to 0A is generated. Reference numeral 10B denotes an input terminal to which power of the voltage Vin is input from the battery 1, and each circuit from the input terminal 10B to the output terminal 10A is integrated into one IC.

Here, the step-down transistor Q in FIG. 3 is deleted, and the output of the comparator 7A is applied to the oscillation circuit 2. The comparator 7A receives a reference voltage Vref from the reference voltage generation circuit 6 at a negative input terminal, and has a + input terminal connected to the output terminal 10A and receives the output voltage Vout. As a result, when the output voltage Vout is higher than the reference voltage Vref, a HIGH-level (hereinafter “H”) signal is generated to stop the oscillation of the oscillation circuit 2. As described above, the voltage Vout of the output terminal 10A is directly used as the detection voltage. However, the DC / DC converter 10 divides the voltage Vout by using a resistor voltage dividing circuit or the like instead of the voltage Vout and keeps the constant voltage. The ratio voltage may be obtained as the detection voltage. In this case, the reference voltage Vref of the reference voltage generating circuit 6 becomes a low voltage corresponding to a certain ratio. The step-down charge pump circuit 5 is a circuit corresponding to the voltage converter 9 in FIG.
The connection is switched between parallel connection and series connection by switching ON / OFF of W1, SW2, SW3 and SW4.

The capacitor C of the step-down charge pump circuit 5
One terminal of 1 is connected to the positive electrode side (Vin) of the battery 1 via the switch SW1, and is connected to the output terminal 10A via the switch SW2. The other terminal of the capacitor C1 is connected to a ground line via a switch SW3, connected to the negative electrode of the battery 1 via this ground line, and connected to an output terminal 10A via a switch SW4. . These switches SW1, SW2, SW3,
SW4 is usually constituted by a MOSFET transistor, and is integrated into an IC. One terminal of the capacitor C2 of the step-down charge pump circuit 5 is connected to the output terminal 10A, and the other terminal is connected to the negative electrode side of the battery 1 via the ground line.

The switches SW1 and SW4 supply an output pulse P of substantially 50% duty from the oscillation circuit 2 to the driver 4.
ON during the period when the output pulse P received through A is “H”
Otherwise, it is turned off. Switches SW2 and SW3 are
The output pulse P of the oscillation circuit 2 is supplied to the inverter 3 and the driver 4
The output pulse P, which is received through B, turns on during the "L" period, and turns on / off the switches SW1 and SW4 complementarily. Therefore, when the output pulse P of the oscillation circuit 2 is "H", the capacitors C1 and C2
Are connected in series by turning on the switches SW1 and SW4, and when the output pulse P of the oscillation circuit 2 is "L", the capacitors C1 and C2 are connected to the switches SW2 and SW3.
Are turned on in parallel, and a voltage slightly lower than half the voltage Vin of the battery 1 is output to the output terminal 10A. At this time, the voltage of the reference voltage Vref is set to a voltage slightly lower than the voltage of Vin / 2 (= Vin / 2−α). For example, if the voltage of the battery 1 is 3.8 V, Vre
f = 1.8V (<1.9V), and the output voltage Vout is also stabilized at 1.8V. The voltage of the battery 1 is 3.8 V in the above case, but one voltage in the range of about 4.2 V to 3.0 V is usually selected. However, the voltage of the battery 1 is not limited to this range.

To explain the overall operation, the connection of the capacitor is switched by a pulse from the oscillation circuit 2, and the voltage of the output terminal 10A is changed to the voltage V of the battery 1.
The output voltage Vout (≒ Vin / 2−α) is generated at the output terminal 10A by reducing the voltage of the input signal “in” to substantially half the voltage. Here, α is a voltage for regulation, and when the voltage of the battery 1 is in the range of 4.2 V to 3.0 V,
A voltage of about 0.05 V to 0.5 V may be used. Output voltage Vou
When t becomes larger than Vin / 2-α, in other words,
When the output voltage Vout is higher than the reference voltage Vref, the output pulse SP of “H” is generated from the comparator 7A, the oscillation output of the oscillation circuit 2 is stopped, and the output pulse P of the oscillation circuit 2 becomes “L”.

When the oscillation of the oscillation circuit 2 is stopped, the output pulse P is maintained at "L".
SW3 remains ON and switches SW1 and SW4 are set to O
The FF remains as it is, and the capacitor C1 and the capacitor C2 are kept connected in parallel. As a result, the charged charge due to the parallel connection of the capacitor C1 and the capacitor C2 is output from the output terminal 10A and discharged. When the voltage at the output terminal 10A decreases due to this discharge and the output voltage Vout falls below Vin / 2-α, the comparator 7
The generation of the output pulse SP from A is stopped, and the oscillation of the oscillation circuit 2 is restarted. As a result, the capacitor C1 and the capacitor C2 are connected in series and charged, and as a result, control is performed such that the output voltage Vout is maintained at Vin / 2−α (= 1.8 V). That is, here, the target voltage to be stabilized is Vin / 2−α, which is the reference voltage Vref.
It corresponds to. In the above case, the oscillation frequency of the oscillation circuit (OSC) 2 is constant, and is set to a frequency at which the switch is switched after the charging of the capacitors C1 and C2 is completed. Therefore, the step-down charge pump circuit 5 always performs a reliable step-down operation in a state where the charging of the capacitors C1 and C2 is completed. As a result, switching noise generated in the output line of the output voltage Vout is suppressed.

As described above, the DC / DC of the embodiment is described.
The converter 10 performs a 降 step-down operation.
As shown in FIG. 2, the DC / DC converter 1 of the present invention
00 is a voltage slightly lower than 1 / n by setting the number of capacitors to n, connecting these n capacitors in series by switching, and switching and connecting these n capacitors in parallel by complementary switching. Of course, it can be regulated. In addition,
In this case, when n capacitors are connected in series, the lowest divided voltage point divided by these capacitors is connected to the output terminal, and power is taken out from this divided voltage point. . Further, the capacitor C of the embodiment
Although 1 and the capacitor C2 are substantially the same, an arbitrary step-down voltage can be output by selecting the capacitance of these capacitors. In the embodiment, a battery is used as the DC power supply. However, it is a matter of course that the battery may be a DC power supply circuit that generates a DC voltage from an AC power supply via a rectifier circuit or the like.

[0015]

As described above, according to the present invention, the first and second capacitors are alternately connected in series and in parallel by switching with an output signal of an oscillation circuit oscillating at a specific frequency. Efficient step-down conversion by providing a switch circuit consisting of a plurality of switches, extracting the power of the divided voltage when connected in series, and extracting the power of the charged voltage when connected in parallel from each capacitor Can be. Furthermore, when the voltage rises above the target reference output voltage, control is performed only by stopping the oscillation circuit, so that a step-down transistor is not required, noise and heat generation of the power supply circuit are suppressed, and the occupied area is also reduced. Small enough. As a result, the step-down DC / DC converter to which the present invention is applied has a high efficiency, generates less noise, generates less heat, and occupies a smaller area.

[Brief description of the drawings]

FIG. 1 is a switched capacitor type DC / DC converter according to an embodiment to which a step-down DC / DC converter according to the present invention is applied;
It is a block diagram of a DC converter.

FIG. 2 is a switched capacitor type DC of another embodiment to which the step-down DC / DC converter of the present invention is applied;
It is a block diagram of a / DC converter.

FIG. 3 is an explanatory view showing an example of a conventional switched capacitor type step-down DC / DC converter.

[Explanation of symbols]

1: Lithium ion battery, 2: Oscillator circuit (OSC), 3:
... Inverter, 4A, 4B ... Driver, 5 ... Step-down charge pump circuit, 6 ... Reference voltage generation circuit, 7A ... Comparator, 9 ... Voltage converter, 10, 11 ... Switched capacitor type DC / DC converter, 9A, 10A , 11A
... Output terminal.

Claims (14)

[Claims] An oscillator circuit for generating a signal of a specific frequency; receiving an output signal of the oscillator circuit to switch the first and second capacitors in series and in parallel; A switch circuit composed of a plurality of switches connected alternately to a DC power supply that charges the first and second capacitors with a DC voltage when the first and second capacitors are connected in series; and a first and second capacitor. An output terminal that extracts power from the voltage point divided by these capacitors when the capacitors are connected in series and that extracts the power of the terminal voltage of these capacitors when they are connected in parallel; and an output of this output terminal A voltage detecting circuit that compares the voltage with a predetermined reference voltage and generates a signal for stopping the oscillation of the oscillation circuit when the voltage exceeds the reference voltage; And a regulator, wherein the switching circuit includes a step-down DC / DC converter, wherein said first and second capacitors to a parallel connection state when the oscillation circuit is in a stopped state. 2. The method according to claim 1, wherein the DC power supply is a battery, the specific frequency is constant, the reference voltage is a voltage smaller than 1/2 of the DC voltage, and the first and second capacitors are connected to each other. 2. The step-down DC / DC converter according to claim 1, wherein a charge pump circuit is configured by the switch circuit. 3. The step-down DC / D converter according to claim 2, wherein said first and second capacitors have substantially the same capacitance.
C converter. 4. The step-down DC / DC converter according to claim 3, wherein said reference voltage substantially corresponds to a target voltage to be stabilized. 5. The step-down DC / DC converter according to claim 3, wherein the detection of the output voltage is performed via a resistance voltage dividing circuit. 6. The plurality of switches of the switch circuit are constituted by MOS transistors, and are turned on / off complementarily.
5. The step-down DC / DC converter according to claim 4, which performs FF. 7. The switch circuit according to claim 1, wherein the plurality of switches are first, second, third, and fourth switch circuits, and one terminal of the first capacitor is connected via the first switch circuit. The first terminal connected to the positive electrode side of the battery and connected to the output terminal via a second switch circuit;
The other terminal of the capacitor is connected to the negative electrode side of the battery via a ground line via the third switch circuit, and is connected to the output terminal via the fourth switch circuit, 7. The battery according to claim 6, wherein one terminal of a second capacitor is connected to the output terminal, and another terminal of the second capacitor is connected to a negative electrode side of the battery via a ground line. Step-down DC / DC converter. 8. An oscillator circuit for generating a signal of a specific frequency, a first and a second capacitor, and an output signal of the oscillator circuit for switching the first and second capacitors in series and in parallel by switching. A switch circuit comprising a plurality of switches connected alternately to a DC power supply; and when the first and second capacitors are connected in series, take out power from a voltage point divided by these capacitors and connect them in parallel. An output terminal for extracting the power of the terminal voltage of these capacitors when connected, and detecting the output voltage of this output terminal, comparing the output voltage with a predetermined reference voltage, and when the output voltage exceeds the reference voltage, A comparator for generating a signal for stopping oscillation, wherein the first and second capacitors are connected to each other when the capacitors are connected in series. Is charged by the DC power supply, said switch circuit, a step-down DC / DC converter, wherein said first and second capacitors to a parallel connection state when the oscillation circuit is in a stopped state. 9. The step-down DC / D according to claim 8, wherein said first and second capacitors have substantially the same capacitance.
C converter. 10. An n number of capacitors (n is an integer of 3 or more), an oscillating circuit for generating a signal of a specific frequency, an output signal of the oscillating circuit is switched to switch the n number of capacitors in series. And a switch circuit including a plurality of switches connected alternately in parallel; a DC power supply for charging the n capacitors with a DC voltage when the n capacitors are connected in series; and the n capacitors. An output terminal for extracting power from the lowest divided voltage point divided by these capacitors when the capacitors are connected in series and extracting power for the terminal voltages of these capacitors when connected in parallel; A comparator that detects an output voltage of an output terminal, compares the output voltage with a predetermined reference voltage, and generates a signal for stopping oscillation of the oscillation circuit when the output voltage exceeds the reference voltage. A chromatography data, the switch circuit, the step-down DC / DC converter, characterized in that the oscillating circuit is a parallel connection state of said n capacitors when in the stopped state. 11. The DC power source is a battery, the specific frequency is constant, the reference voltage is a voltage smaller than 1 / n of the DC voltage, the n capacitors and the switch circuit. 11. The step-down DC / DC converter according to claim 10, wherein a charge pump circuit is constituted by: 12. The step-down DC / DC converter according to claim 11, wherein said n capacitors have substantially the same capacity. 13. An n-number of capacitors (n is an integer of 3 or more), an oscillating circuit for generating a signal of a specific frequency, an output signal of the oscillating circuit is switched to switch the n number of capacitors in series. And a switch circuit comprising a plurality of switches alternately connected in parallel; a DC power supply; and power from the lowest divided voltage point divided by these capacitors when the n capacitors are connected in series. An output terminal for extracting the power of the terminal voltage of these capacitors when they are connected in parallel, and an output voltage of this output terminal is detected and compared with a predetermined reference voltage. A comparator for generating a signal for stopping the oscillation of the oscillation circuit, wherein the n capacitors are connected to the DC power supply when these capacitors are connected in series. Is charged by the source, the switch circuit, the step-down DC / DC converter, characterized in that the oscillating circuit is a parallel connection state of said n capacitors when in the stopped state. 14. The step-down DC / DC converter according to claim 13, wherein said n capacitors have substantially the same capacity.