JP2003284334A - Reference voltage generating circuit and battery charging circuit employing it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a reference voltage generating circuit in which a stabilized variable reference voltage output VOUT is obtained regardless of a variation in the signal level of a control signal PWM. <P>SOLUTION: The reference voltage generating circuit comprises a voltage level shift circuit 2 generating a voltage higher than a reference voltage VREF1 depending on the first reference voltage VREF1, and a comparator 3 for comparing the voltage of a pulse width modulated control signal PWM with the voltage of a second reference voltage VREF2 wherein a transistor TR2 turned on/off depending on the output from the comparator 3 steps down a voltage V2 generated from the voltage level shift circuit 2 to the ground level side of a power supply. A reference voltage output VOUT variable over a wide range from the voltage V2 higher than the reference voltage VREF1 to the ground level is thereby obtained and the variable reference voltage output VOUT corresponding to the duty of the control signal PWM is obtained stably regardless of a variation in the signal level of a control signal PWM. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reference voltage generating circuit, and more particularly to a reference voltage generating circuit that generates a variable reference voltage.

[0002]

2. Description of the Related Art In recent years, in a battery charger used for charging a lithium-ion battery used as a power source for a mobile phone or the like, the output voltage of a DC-DC converter for battery charging corresponds to the number of cells of the battery which differs depending on various devices. It is necessary to supply the charging voltage. In general, the battery charging control IC has a highly accurate reference voltage generation circuit, and the reference voltage generation circuit generates a reference voltage for supplying an accurate charging voltage corresponding to the battery voltage of various devices. It

FIG. 2 is a diagram showing a reference voltage generating circuit for variably outputting a reference voltage used for voltage control of an output voltage of a conventional DC-DC converter circuit for charging a lithium battery or the like. In FIG. 2, the reference voltage VR is applied to one end of the resistor RB.
EF1 is applied, and the integrating circuit 1 is connected to the other end of the resistor RB. Further, a control signal PWM whose pulse width is modulated is applied to one end of the resistor RA at the input stage of the integrating circuit 1, for example, from a microcomputer or the like. Then, the control signal P
By changing the duty of the WM, the output voltage of the reference voltage output VOUT at the point C is variably output.

More specifically, the input of the integrating circuit 1 is, for example,
When the control signal PWM of 2V amplitude is applied, the integration circuit 1
The control signal PWM is integrated by the resistor RA and the capacitor CA that constitute the control signal PWM, and a constant DC voltage corresponding to the duty of the control signal PWM is applied to the point C from 0V to 2V in proportion to the duty, as shown in FIG. The voltage is obtained.

Further, the reference voltage VR is connected to one end of the resistor RB.
EF1 is connected, and the other end of the resistor RB is connected to a connection point between the resistor RA of the integrating circuit 1 and the capacitor CA. Then, from the connection point of the resistor RB and the resistor RA, the reference voltage output V
OUT is output. As a result, a divided voltage obtained by dividing the voltage value proportional to the duty of the control signal PWM applied to the input side of the integration circuit 1 and the reference voltage VREF1 by the resistors RA and RB is output from the reference voltage output VOUT. . Here, the value of the reference voltage VREF1 is, for example,
The values of 2.5V, RA and RB are, for example, 30K
Ω, 20 KΩ. The duty of the control signal PWM is 0
In the case of%, the level of the control signal PWM is always 0V, and the reference voltage output VOUT is 1.5V which is the divided voltage divided by the resistors RB and RA. When the duty of the control signal PWM is 100%, the control signal PW
The level of M is always 2V, and the reference voltage output VOUT
Is 2.3 V which is the divided voltage divided by the resistors RB and RA. In addition, when the duty of the control signal PWM is 50%, the level of the control signal PWM is
Becomes a voltage of 1V, and the reference voltage output VOUT is
1.9 of the divided voltage divided by the resistors RB and RA
It becomes V.

[0006]

However, the above-mentioned reference voltage generating circuit has a drawback in that it cannot generate the reference voltage output VOUT having a voltage higher than the reference voltage VREF1. Further, even if the duty of the control signal PWM is 0% and the L level is always 0V, the reference voltage output VOUT can be reduced only to the voltage divided by the resistors RA and RB. As a result, the reference voltage output V
There is a problem that the variable range of the voltage of OUT is narrow, and there is a problem that the voltage of the reference voltage output VOUT cannot be sufficiently changed with respect to the charging voltage corresponding to the number of cells of the rechargeable battery used in various devices. In order to deal with this problem, conventionally, an output reference voltage boost circuit for compensating the reference voltage level is required at the output stage of the reference voltage generation circuit. Further, when the signal level of the control signal PWM fluctuates, the reference voltage output VOUT also fluctuates, so that an interface circuit such as a level fixing circuit for compensating the signal level of the control signal PWM is required. As described above, in order to obtain a stable output voltage with a wide variable range, a separate circuit is required, which causes a problem that the circuit scale becomes very large.

Therefore, the object of the present invention is to provide the reference voltage VR.
It is an object of the present invention to provide a reference voltage generation circuit capable of generating a voltage higher than the voltage of EF1 and varying the voltage variable range of the reference voltage output VOUT from a voltage higher than VREF1 to a low voltage close to the ground level of the power supply.

Another object of the present invention is to provide a reference voltage generating circuit which can obtain a stable reference voltage output VOUT even if the signal level of the control signal PWM fluctuates.

[0009]

The present invention has been made in view of the above problems, and is characterized in that the first reference voltage is set to a power supply voltage higher than the first reference voltage. A level shift circuit for converting the voltage to a predetermined voltage, a comparison means for comparing the second reference voltage with a control signal, and a switch element for conducting or blocking the output voltage of the level shift circuit according to the output of the comparison means. And smoothing means for smoothing the output of the level shift controlled and output by the switch element.

Further, the control signal is a pulse width modulation signal.

Further, the battery charging circuit is characterized in that the battery is charged using the reference voltage generating circuit.

As described above, according to the present invention, the reference voltage V
Since the level shift circuit for generating a voltage higher than the reference voltage is provided according to REF1, the reference voltage VREF1
A reference voltage output VOUT higher than the voltage of is obtained.

Further, since the comparison circuit for comparing the control signal PWM and the second reference voltage VREF2 is provided, a stable reference voltage output VOUT can be obtained even if the signal level of the control signal PWM changes.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a diagram showing a configuration of a reference voltage generating circuit of the present invention. In FIG. 1, 2 is a level shift circuit, which is composed of an amplifier AMP, a transistor TR1, and resistors R1 and R2. The reference voltage VREF1 is applied to the non-inverting input of the amplifier AMP. Amplifier A
The output of MP is connected to the base of the transistor TR1. A power supply voltage Vcc higher than the reference voltage VREF1 is applied to the collector of the transistor TR1. The emitter of the transistor TR1 is
It is connected to the ground of the power supply via the resistors R1 and R2. The connection point between the resistors R1 and R2 is connected to the inverting input of the amplifier AMP. Where resistance R
1 and the voltage at the connection point between the resistor R2 and the comparison voltage V1, the amplifier AMP has the transistor TR1 so that the reference voltage VREF1 and the comparison voltage V1 are equal to each other.
To control. For example, if the comparison voltage V1 is lower than the reference voltage VREF1, the output voltage of the amplifier AMP rises, and a current corresponding to the output voltage of the amplifier AMP is supplied from the emitter of the transistor TR1 to the resistors R1 and R2. . When the comparison voltage V1 is higher than the reference voltage VREF1, the output voltage of the amplifier AMP drops, and a current corresponding to the output voltage of the amplifier AMP is supplied from the emitter of the transistor TR1 to the resistors R1 and R2. . Then, when the comparison voltage V1 of the same level as the reference voltage VREF1 is generated from the connection point of the resistors R1 and R2, the point A voltage V2 obtained by converting the voltage of the reference voltage VREF1 into a predetermined voltage is output. To be done. Transistor TR
The connection point between the emitter of 1 and the resistor R1 is the resistors R3 and R3.
It is connected via 4 to the ground of the power supply. And
An integrating circuit 1 including a resistor RA and a capacitor CA is connected to a connection point between the resistors R3 and R4.

Reference numeral 3 is a comparator having a positive input terminal to which the second reference voltage VREF2 is connected and a negative input terminal to which a pulse width modulated control signal PWM is applied. The output of the comparator 3 is connected to the base of the transistor TR2. The signal level of the control signal PWM is the reference voltage VR
When the voltage is higher than EF2, the comparator 3 outputs an L level voltage that can sufficiently turn off the transistor TR2. Further, when the signal level of the control signal PWM is lower than the reference voltage VREF2, the comparator 3 outputs an H level voltage that can sufficiently turn on the transistor TR2.

Further, the connection point of the resistors R3 and R4 is connected to the ground of the power source through the transistor TR2. Then, the point A voltage V2 generated in the level shift circuit 2 is divided by the resistors R3 and R4, and the divided point B voltage V3 is turned on / off by the transistor TR2 so that the duty of the control signal PWM of a predetermined cycle is obtained. The voltage drops accordingly to the ground level. And
In the integrating circuit 1 to which the B point voltage is applied, the fluctuation of the B point voltage is smoothed and a constant reference voltage output VOUT is output.

Next, the operation of the reference voltage generating circuit of FIG. 1 will be specifically described. First, for example, 12V of in-vehicle battery
When the power supply voltage Vcc of the amplifier AMP is applied to the level shift circuit 2 and the reference voltage VREF1 of 2.5V is applied to the non-inverting input of the amplifier AMP of the level shift circuit 2, The voltage applied to the base of the transistor TR1 is adjusted and output so that the voltage V1 at the connection point with R2 and the voltage of the reference voltage VREF1 become equal. Here, for example, the value of the resistor R1 is set to 13K.
If the value of Ω and the resistance R2 is 5 KΩ, the transistor TR
Point A voltage V2, which is the emitter voltage of 1, is (R2 + R
1) * VREF1 / R2 = 9V. The 9V point A voltage V2 is divided by the resistors R3 and R4. Then, the values of the resistors R3 and R4 are set to, for example, 14K.
Assuming Ω and 4 KΩ, the divided voltage divided by the resistors R3 and R4 is a DC voltage of 2V.

On the other hand, the collector of the transistor TR2 is connected to the connection point of the resistors R3 and R4. Since the output of the comparator 3 is connected to the base of the transistor TR2, when the control signal PWM is lower than the reference voltage VREF2, the output of the comparator 3 becomes H level and the transistor TR2 is turned on. Then, the point B voltage V3 at the connection point of the resistors R3 and R4 is dropped to the ground level via the transistor TR2. When the control signal WPM is higher than the reference voltage VREF2, the output of the comparator 3 becomes L level and the transistor TR2 is turned off. As a result, B
The point voltage V3 is a divided voltage of 2V obtained by dividing the voltage V2 of 9V by the resistors R3 and R4. Then, the B point voltage V3 is smoothed by the integrating circuit 1, and a voltage varied in the range of 0V to 2V, which is the ground level, is output as the reference voltage output VOUT in proportion to the duty of the control signal PWM. Specifically, if the duty of the control signal PWM is 0% and the level of the control signal PWM is L level which is always lower than the reference voltage VREF2, in the comparator 3, the H level sufficient to turn on the transistor TR2 is set. Is output. Then, the transistor TR2
Is always on, and the voltage V3 at point B drops to the ground level of 0V. Then, the B point voltage V of 0V
3 is a reference voltage output VOUT of 0V via the integrating circuit 1.
Is output as.

The duty of the control signal PWM is 10
When the level of the control signal PWM is 0% and is always higher than the reference voltage VREF2 at the H level, the comparator 3 outputs the L level at which the transistor TR2 is turned off. Then, the transistor TR2 is always turned off, and the voltage V3 is fixed to the divided voltage of 2V obtained by dividing the voltage V2 of 9V by the resistors R3 and R4. Then, the 2V point B voltage V3 is output as the 2V reference voltage output VOUT via the integrating circuit 1.

Further, the duty of the control signal PWM is 50.
%, And the level of the control signal PWM is the reference voltage VRE.
When the pulse widths of the H level higher than F2 and the L level lower than the reference voltage VREF2 are the same, the comparator 3 turns on / off the transistor TR2.
The level and the H level are output in the same cycle. Then,
The transistor TR2 is repeatedly turned on and off alternately in the same cycle. When the transistor TR2 is turned on, the 0V point B voltage V3 is divided by the resistors R3 and R4, and the 9V A point voltage V2 is divided by the resistors R3 and R4. The voltage is varied according to the control signal PWM. And
A point B voltage V3 in which 2V and 0V change in the same cycle is flattened by the integrating circuit 1, and a DC voltage of 1V is output as a reference voltage output V.
It is output as OUT.

In this way, the variable reference voltage output VOUT from 0V to 2V is generated in proportion to the duty of the control signal PWM.

Further, the H level and L level voltages of the control signal PWM are supplied to the reference voltage VREF by the comparator 3.
The voltage is higher or lower than the voltage of 2 and the transistor TR2 is ON / OFF controlled according to the comparison result. Therefore, even if the signal level of the control signal PWM fluctuates, the duty ratio of the control signal PWM is surely changed. The value of the corresponding reference voltage output VOUT is obtained.

In the description of the embodiment, the voltage V2 at the point A is divided by the resistors R3 and R4, and the voltage V3 at the point B is 2V.
As described above, by changing the resistance ratio of the resistors R3 and R4, the voltage at the A-point voltage V from 0V to, for example, about 9V.
2 can occur as the reference voltage output VOUT. In addition, although the description has been made in the case of the point A voltage V2 of 9V,
The voltage is not particularly limited, and it is possible to set the voltage lower than the voltage of the reference voltage VREF1 from the voltage of the power supply voltage Vcc by changing the resistance ratio of the resistors R1 and R2.

In this way, the reference voltage generating circuit is composed of a simple circuit such as an operational amplifier and a comparator. And
Since the signal level of the control signal PWM is determined by the comparator 3 and the transistor TR2 is turned on / off according to the determination result, even if the signal level of the control signal PWM fluctuates, the reference voltage corresponding to the duty of the control signal PWM The output VOUT is stably obtained. As a result, an interface circuit such as a level fixing circuit for compensating for the signal level of the control signal PWM, which is conventionally required, is not required. Further, by using the amplifier AMP, the reference voltage VR
Since the reference voltage output VOUT higher than the EF1 is generated, the conventional voltage boost circuit for boosting the reference voltage output VOUT is not required, the application circuit design of the battery charging circuit is facilitated, and the parts such as the voltage boost circuit are provided. The number can be reduced.

Further, since the reference voltage output VOUT having a wide variable range up to the voltage higher than the reference voltage VREF1 can be generated, the reference voltage generating circuit of the present invention can charge a high voltage battery having a large number of rechargeable cells. It can be easily applied to equipment.

[0026]

As described above, according to the present invention, the level shift circuit 1 generates a voltage higher than the reference voltage, and the level-shifted voltage is supplied to the integrating circuit 1 according to the duty of the control signal PWM. As a result, the variable voltage range of the reference voltage output VOUT is higher than the reference voltage VREF1 from 0V which is the ground level of the power supply.
The advantageous effect that a wide voltage variable range of up to 2 can be obtained is obtained.

Further, since the comparator 3 for comparing the signal level of the control signal PWM with the reference voltage VREF2 is provided, the on / off operation of the transistor TR2 for controlling the voltage of the reference voltage output VOUT can be stably performed. Even if the signal level fluctuates, the advantageous effect that the stable reference voltage output VOUT is obtained can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a reference voltage generation circuit of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional reference voltage generating circuit.

FIG. 3 is a diagram illustrating voltage characteristics of a duty of a control signal PWM and an output voltage on the integrating circuit side.

[Explanation of symbols] 1 integrating circuit 2 Voltage level shift circuit 3 comparator

Claims (3)

[Claims] 1. A level shift circuit for converting a first reference voltage into a predetermined voltage by using a power supply voltage higher than the first reference voltage, and a comparison means for comparing the second reference voltage with a control signal. And a switch element that conducts or blocks the output voltage of the level shift circuit according to the output of the comparison means, and a smoothing means that smoothes an output of the level shift that is controlled and output by the switch element. A reference voltage generating circuit characterized by being formed. 2. The reference voltage generating circuit according to claim 1, wherein the control signal is a pulse width modulation signal. 3. A battery charging circuit, characterized in that a battery is charged by using the reference voltage generating circuit according to claim 1.