JP2002272091A - Voltage doubler dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a voltage doubler DC/DC converter that can prevent the ringing of a capacitor of a power supply. SOLUTION: A resistor having a specific resistance is inserted to a second switch circuit that substantially doubles the voltage to charge a first capacitor in an ON state for transferring them to a second capacitor in series, an oscillating frequency in a variable frequency oscillation circuit exceeds the upper limit of an audio frequency when the second switch circuit is turned on while a load current is smaller than a specific value, thus keeping the changing voltage of the double voltage in the second capacitor to be low when the load current is small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a double voltage boosting type D
More specifically, a C / DC converter is a step-up DC / D 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.
In a C converter, a double voltage boost type DC / D capable of preventing the noise of the power supply capacitor
It relates to a C converter.

[0002]

2. Description of the Related Art Conventionally, in a battery-driven electronic device such as a portable telephone such as a PHS or a portable telephone, a portable electronic device, etc., a device operating at a voltage higher than the battery voltage, for example, a transmission circuit or a liquid crystal backing. A light LED element drive circuit is provided. Therefore, a DC / DC converter for boosting the battery voltage is provided therein as one of the power supply circuits. On the other hand, in this type of battery-driven electronic device, the size and weight of the device itself have been reduced, and the power supply circuit itself has been reduced in size.
In addition, a device with low power consumption is required. Therefore, in the power supply circuit of this type of device, as a driving circuit for the LED element, a charge boosting circuit corresponding to so-called voltage doubler rectification is configured by transferring charge by a switched capacitor method using a charge pump circuit or the like. Then, the boosted voltage is stabilized to a constant voltage by a regulator to generate an LED drive voltage and the like. As a result, miniaturization of the device and low power consumption are realized. Paying attention to this, the power supply circuit itself is a so-called switched capacitor type (charge pump step-up type) DC / DC converter of a voltage doubler rectification type such as a charge pump circuit.

FIG. 3 shows an example of the circuit. 3, the DC / DC converter 10 includes an oscillation circuit (OS
C) a charge pump circuit (double voltage booster circuit) 12 that switches at the oscillation frequency of 13; As a result, for example, power having a voltage of about 3.6 V (3.0 V to 4.2 V) is received from the lithium ion battery 11 and is switched at a predetermined frequency to charge the capacitor C1 (first capacitor). The charge charged in the capacitor C1 is substantially doubled by the switching which is turned on / off complementarily to the above-mentioned switching, and is transferred to the capacitor C2 (second capacitor) to be charged. By repeating the voltage rectification, a voltage of about 7.2 V is generated in the capacitor C2.

The variable frequency oscillating circuit 13 receives power from the lithium ion battery 11 and oscillates, and outputs a pulse having a predetermined frequency and a duty ratio of 50% to the charge pump circuit 12. Then, the output voltage Vo boosted by the charge pump circuit 12 is detected by the output voltage detection circuit 14 and is fed back to the variable frequency oscillation circuit 13 to output the output voltage V
The oscillation frequency of the variable frequency oscillation circuit 13 is controlled so that o becomes a constant voltage. Thereby, the output voltage Vo is stabilized. The output voltage detecting circuit 14 includes a voltage dividing resistor circuit 14a for detecting the output voltage and the error amplifier 1
4b, and the resistance R of the voltage dividing resistor circuit 14a.
The voltage Vs at the connection point N between 1 and the resistor R2 is applied to the (+) input terminal of the error amplifier 14b. That is the error amplifier 14b
Is compared with the reference voltage Vref of the (-) input terminal to generate a control voltage (or control current) so that the voltage at the connection point N matches the reference voltage Vref, and sends it to the variable frequency oscillation circuit 13. I do.

[0005]

However, in such a switched capacitor type DC / DC converter, an electrolytic capacitor or a ceramic capacitor having a large capacity is externally used as the capacitor C2. When a ceramic capacitor is connected to the capacitor C2, an abnormal sound is generated when the load current is small, such as during standby. This is because when the load current is small, the frequency of the variable frequency oscillation circuit 13 is reduced so as to enter the audible frequency range, and the output voltage is controlled to be constant. At this time, since the charging / discharging frequency of the capacitor C2 falls within the audio frequency range, the capacitor C2
Is driven and a capacitor noise is generated. Such vibration not only affects the housing of a portable small and lightweight electronic device, but also adversely affects the operation of other electronic circuits. SUMMARY OF THE INVENTION An object of the present invention is to solve such a problem of the prior art, and it is an object of the present invention to provide a double voltage boosting type D which can prevent the noise of a power supply capacitor.
It is to provide a C / DC converter.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, a double voltage boosting DC / DC converter according to the present invention is characterized by a DC power supply, a reference voltage generating circuit for generating a reference voltage, and a DC power supply. A variable frequency oscillation circuit whose frequency is controlled according to the difference between the reference voltage and the detection voltage, and an output of the DC power supply and an output of the variable frequency oscillation circuit, and the output of the DC power supply is controlled. The first switch circuit is switched at the frequency and the first
Of the capacitor and complementarily to O
The second switch circuit is switched by N / OFF switching, and in the ON state, the electric charge charged in the first capacitor is substantially doubled, transferred to the second capacitor, and charged. A booster circuit that boosts the voltage; and an output voltage detection circuit that generates a detection voltage in accordance with the output voltage of the booster circuit. When the load current value is smaller than a predetermined value, the oscillation frequency of the When the second switch circuit is turned on so as to exceed the upper limit, the second switch circuit has a predetermined resistance value, or a resistor having a predetermined resistance value is inserted in series with this. .

[0007]

As described above, according to the present invention, in the ON state, the second switch circuit transfers the charge charged in the first capacitor to the second capacitor after substantially double the voltage. When the load current value is smaller than the predetermined value, the charging voltage of the doubled voltage of the second capacitor is suppressed low. As a result, the charging voltage of the doubled voltage can be set to a value close to the target voltage, so that the oscillation frequency is frequently controlled, and the oscillation frequency of the oscillation circuit is set to the audible frequency even when the load current value is small. Can be oscillated by shifting in the direction exceeding In addition, the charging voltage of the doubled voltage can be suppressed low, so that the noise of the second power supply capacitor can be prevented. It should be noted that the second capacitor for supplying power is usually provided externally.

[0008]

FIG. 1 shows a double-voltage step-up DC / DC according to the present invention.
FIG. 2 is a block diagram of a switched-capacitor type DC / DC converter according to an embodiment to which a converter is applied, and FIG. 2 is an explanatory diagram showing a relationship between a frequency characteristic and an output current of an oscillation circuit according to the present invention. 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, 1
Is a switched capacitor type DC / DC converter driven by the power of the lithium ion battery 11, and four switch circuits of the charge pump circuit 12 are MOSF
ET transistors (hereinafter, transistors) Tr1 to Tr4 are provided, and gate voltages of the transistors Tr3 and Tr4 are supplied from the inverter 2. Moreover, here, the level of the output signal of the inverter 2 is adjusted by the output signal level adjusting circuit 3. In the figure, a p-channel transistor Tr1 and an n-channel transistor Tr2 are two switch circuits for charging the capacitor C1. The source of the transistor Tr1 is connected to the power line (voltage Vin) of the battery 11, and the source of the transistor Tr2 is
The capacitor C1 is connected to the ground GND, and is connected between the drain of the transistor Tr1 and the drain of the transistor Tr2. p-channel transistor Tr
Reference numerals 3 and 4 denote two switch circuits for transferring the voltage of the capacitor C1 to the capacitor C2 by doubling the voltage. The source of the transistor Tr3 is connected to the power supply line (voltage Vin) of the battery 11, and the drain of the transistor Tr3 is connected to the capacitor C3.
It is connected to the drain of the transistor Tr2 connected to 1. The source of the transistor Tr4 is connected to the terminal of the capacitor C2 connected to the output terminal 7, and the drain side is connected to the drain of the transistor Tr1 connected to the capacitor C1. The terminal of the capacitor C2 on the side not connected to the output terminal 7 is connected to the ground GND. Then, a regulated output voltage Vo is generated at the output terminal 7.

The load 6 receiving the output power from the DC / DC converter 1 includes, for example, a load current detecting circuit 4 including a current mirror circuit connected to the load 6 by a current mirror.
Is provided, and the detected load current is applied as a voltage signal to the output signal level adjustment circuit 3 via the current / voltage conversion circuit (I / V) 5. Inverter 2
Is composed of CMOS transistors Tr5 and Tr6,
The source of the p-channel transistor Tr5 is the battery 11
And the source of the n-channel transistor Tr6 is grounded (connected to the ground GND) via the output signal level adjusting circuit 3.
The output signal level adjustment circuit 3 is, for example, a voltage follower or an n-channel MOS transistor, and is a voltage variable circuit that sets the voltage level of the source of the transistor Tr6. Or the gate of the n-channel transistor receives from I / V5. Thus, the output signal of the inverter 2 to which the drains of the transistors Tr5 and Tr6 are connected is adjusted to a low level (hereinafter “L”) by controlling the output signal level adjusting circuit 3.

In this level adjustment, when the load current Io is lower than the current value I in the normal use state, such as in a standby state, the output of the inverter 2 is set to the original "L" (ground GND).
The voltage is adjusted to a predetermined voltage higher than D), thereby setting the internal impedance of the transistors Tr3 and Tr4 to a predetermined value. When the load current Io exceeds the current value I in the steady use state, the voltage of the I / V5 increases, and the transistor on the sink side of the voltage follower of the output signal level adjustment circuit 3 or the n-channel MOS transistor turns on, and the inverter 2 is substantially at ground G
It becomes ND potential.

Here, the transistors Tr3 and Tr4 are controlled by adjusting the level of the output of the inverter 2 to "L".
Changes the resistance value between the source and the drain. When the load current Io is less than the current value I in the steady use state, the "L" output of the inverter 2 is adjusted to a predetermined voltage higher than the ground GND, so that the transistors Tr3 and Tr4 are turned on.
, A predetermined resistance value, for example, about 10Ω to 20Ω is in series. Therefore, when the voltage of the capacitor C1 is doubled and transferred to the capacitor C2, the resistance components of the two transistors are added in series to the switch circuit, and the voltage of the capacitor C2 is reduced accordingly. As a result, when the load current Io is less than the current value I in the steady use state, the boosted voltage can be set at a position higher than the target voltage and close to the target voltage. As a result, when the load current Io is a small current value, the voltage of the capacitor C2 immediately drops from the charge voltage higher than the target voltage and close to the target voltage to the target control voltage or less. As a result, the charge pump circuit 12 starts the switching operation of the next power supply, and the control frequency shifts to the higher one. In addition, the maximum driving voltage of the capacitor C2 at this time is lower than the doubled voltage, and the load voltage applied to the capacitor C2 is also low. At this time, the resistance values of the transistors T3 and Tr4 when ON are selected so that the oscillation frequency of the variable frequency variable frequency oscillation circuit 13 is equal to or higher than the upper limit of the audible frequency. By these actions, the noise of the external power supply capacitor C2 is prevented. As a result, as shown in FIG. 2, the oscillation frequency characteristic of the variable frequency oscillation circuit 13 becomes 20 kHz or more even when the load current Io is a small current value as in the standby state. Also, like that,
The output “L” of the inverter 2 is adjusted. In the figure,
The vertical axis is the oscillation frequency of the variable frequency oscillation circuit 13,
The horizontal axis represents the value of the output current Io for the load 6.

As described above, in the above embodiment,
The output signal level adjusting circuit 3 is constituted by a voltage follower or an n-channel MOS transistor, and when the load current Io is a current lower than the current value I in the steady use state,
The internal impedance of the transistors Tr3 and Tr4 is changed in accordance with the detection voltage, and the oscillation frequency of the variable frequency variable frequency oscillation circuit 13 is changed accordingly. Alternatively, the internal impedance of the transistors Tr3 and Tr4 may be set to a value such that the oscillation frequency of the variable frequency variable frequency oscillation circuit 13 is set to a specific impedance so as to be 20 kHz or more. This is because, for example, the output signal level adjustment circuit 3 controls the transistor Tr in accordance with the voltage of the I / V5.
6 can be easily realized by performing either one of the switching operation of setting the source to a constant voltage or the ground GND potential. Further, instead of using the internal impedance of the transistors Tr3 and Tr4 as a resistor, a resistor is inserted in series with one of the transistors Tr3 and Tr4, and a switch circuit is connected in parallel with this resistor to turn on / off the switch circuit. Of course, it may be turned off. When the logic of the inverter output in the embodiment is driven as negative logic, the above “H” changes to a LOW level (“L”). In addition, the switching operation of the inverter output whose level is adjusted includes transistors Tr3 and T3.
Only one of r4 may be used. Further, the output signal level adjustment circuit described in the embodiment is an example,
The present invention is not limited to this, and the external capacitor is not limited to a ceramic capacitor. Further, in the embodiment, an example using a lithium battery is given, but the power source is not limited to the lithium battery, and even if the power source is a ferroelectric capacitor,
It may be a power source that is converted from AC commercial power to DC.
The present invention is applicable to any DC power supply. Note that the voltage doubler used in the specification and the claims is not limited to twice, and n
It includes a double voltage (n is an integer of 2 or more).

[0013]

As described above, according to the present invention, in the ON state, the second switch which substantially doubles the electric charge charged in the first capacitor and transfers it to the second capacitor. A resistor having a predetermined resistance value is inserted in series with the circuit, and when the load current value is smaller than the predetermined value, the charging voltage of the doubled voltage of the second capacitor is suppressed low.
As a result, the charging voltage of the doubled voltage can be set to a value close to the target voltage, so that the oscillation frequency is frequently controlled, and the oscillation frequency of the variable frequency oscillation circuit is reduced even when the load current value is small. Oscillation can be performed by shifting to a direction exceeding the audible frequency. As a result, it is possible to prevent the noise of the second power supply capacitor.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram illustrating a relationship between a frequency characteristic and an output current of the oscillation circuit according to the present invention.

FIG. 3 shows a conventional switched capacitor type DC.
FIG. 3 is an explanatory diagram illustrating an example of a / DC converter.

[Explanation of symbols]

1, 10: switched capacitor type DC / DC converter, 2: inverter, 3: output signal level adjustment circuit,
4: load current detection circuit, 5: current / voltage conversion circuit (I /
V), 6: load, 7: output terminal, 12: charge pump circuit (double voltage booster circuit), 11: lithium ion battery,
13: oscillation circuit (OSC), 14: output voltage detection circuit,
C1, C2: capacitors, Tr1 to Tr6: transistors,
R1, R2 ... resistance.

Claims (3)

[Claims] 1. A DC power supply, a reference voltage generating circuit for generating a reference voltage, and a variable frequency oscillation circuit receiving power from the DC power supply and controlling a frequency according to a difference between the reference voltage and a detection voltage. Receiving the output of the DC power supply and the output of the variable frequency oscillating circuit, switching the output of the DC power supply at the controlled frequency to the first switch circuit, and charging the first capacitor when the first switch circuit is ON. The second switch circuit is switched by switching which is turned on / off complementarily to the switching, and the O
In the N state, the charge charged in the first capacitor is substantially doubled, transferred to the second capacitor, and boosted by charging the same; and a booster circuit is provided according to the output voltage of the booster circuit. An output voltage detection circuit for generating the detection voltage, wherein the second switch is such that when the load current value is smaller than a predetermined value, the oscillation frequency of the variable frequency oscillation circuit becomes a value exceeding the upper limit of the audible frequency. A double voltage boosting DC / DC converter characterized in that the second switch circuit has a predetermined resistance value when the circuit is turned on, or a resistor having a predetermined resistance value is inserted in series with the second switch circuit. 2. The method according to claim 1, wherein the DC power supply is a battery, the second capacitor is an external ceramic capacitor,
The booster circuit is a charge pump circuit, and the first
The second switch circuit includes two transistor switch circuits each including a MOSFET transistor, and a resistor having a predetermined resistance value inserted in series into the second switch circuit is such that the transistor switch circuit is turned on. It is provided as an internal resistance when it becomes a state,
Each transistor switch circuit of the first switch circuit receives an output signal of the variable frequency oscillation circuit, and each transistor switch circuit of the second switch circuit outputs an output signal of the variable frequency oscillation circuit via an inverter. The double voltage step-up DC / DC converter according to claim 1, which receives a signal. And a level adjusting circuit for adjusting a level of an output signal of the inverter, wherein the level adjusting circuit adjusts a level of the output signal of the inverter according to a detection signal of the load current detecting circuit. The double voltage boosting DC / DC converter according to claim 2, wherein a resistance value when the second switch circuit is turned on is controlled by adjusting an output level.