JPH06222851A - Power circuit - Google Patents

Abstract

PURPOSE:To normally start the operation at the time of starting, to obtain stable output currents, and to reduce input and output voltage difference by operating a power circuit as a linear regulator when output voltage is lower than a prescribed voltage. CONSTITUTION:This circuit is equipped with a voltage detector DET which detects whether or not the output voltage of a DC/DC convert IC 10 (the output voltage of a power source circuit) is lower than the preliminarily decided prescribed voltage (for example, 3.0V). Then, when the voltage detector DET detects that the output voltage is lower than the prescribed voltage, base currents are supplied to an outside transistor Q1 (including a transistor Q2), and the circuit is operated as the linear regulator. Also, the circuit is equipped with dividing resistances R1 and R2 (and a diode D2) as a bias means which impresses a bias voltage lower than the prescribed voltage to the voltage detector DET at the time of power supply.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit using a so-called C-MOS DC / DC conversion IC.

[0002]

2. Description of the Related Art In recent years, with the development of C-MOS technology, for example, a DC / DC convert IC having an internal structure as shown in FIG. 8 has been commercialized.

In FIG. 8, the DC / DC conversion IC 10 has a field effect transistor (FET) Q20 as a switching element, a crystal oscillator 1, and a constant voltage source 4 connected to one input terminal and the other input terminal. Is a comparator 3 for detecting the voltage of the Out terminal connected to the voltage dividing point of the dividing resistors R20 and R21, and the field effect transistor Q20 based on the output of the comparator 3 supplied with the clock from the crystal oscillator 1. And a control circuit 2 for driving the.

The DC / DC conversion IC shown in FIG.
As a general application example of 10, there is a step-up DC / DC converter circuit as shown in FIG.

In FIG. 9, the step-up type DC / D
The C converter circuit is the above DC / DC converter IC1.
0, a power supply battery B10, a coil L10, a diode D10, and a smoothing capacitor C are added as external elements. Common connection point between the coil L10 and the input terminal of the diode D10. W. Connected to the Lx terminal of the DC / DC converter IC10, the diode D
The common connection point between 10 and the smoothing capacitor C is the above DC / D.
It is connected to the Out terminal of the C conversion IC 10.
The voltage at the common connection point between the diode D10 and the smoothing capacitor C is taken out as the output voltage of the DC / DC converter circuit. The smoothing capacitor C is
It is provided to keep the output voltage of the C / DC conversion IC 10 at a constant value.

The configuration shown in FIG. 9 has a step-up type DC / D.
Although it is a C converter circuit, a step-down DC / DC converter circuit can be configured by adding an external transistor Q21 and the like as shown in FIG.

In FIG. 10, a battery B11 is an input power source, and is connected to the emitter of a switching PNP type power transistor Q21. The collector of the transistor Q21 is connected to one terminal of the choke coil L11, and the base is connected to the switching terminal Lx of the DC / DC converting IC 10 via the base resistor R23. Therefore, the base current of the transistor Q21 flows (switches) in synchronization with the switching of the switching terminal Lx, and supplies the power of the battery B11 to the choke coil L11. The resistor R22 is a bias resistor for the transistor Q21. Further, the diode D10 is a flywheel diode and forms a DC loop between the choke coil L11 and the load when the transistor Q21 is OFF. The voltage at the common connection point between the choke coil L11 and the smoothing capacitor C is taken out as the output voltage of the DC / DC converter circuit.

[0008]

However, in the step-down DC / DC converter circuit configured as shown in FIG. 10, the DC / DC conversion IC 10 operates using the voltage on the Out terminal side of the conversion IC 10. Since it does not operate at the time of starting, for example, the DC / DC conversion IC
A Zener diode ZD must be provided in order to supply power to 10, and there is a concern that noise will occur, and there is a problem that the range of the input voltage value is narrow. Further, in the step-down DC / DC converter circuit configured as shown in FIG. 10, when the input voltage (voltage of the battery B11) decreases, the output current decreases, and the input / output voltage difference is relatively high. There are some drawbacks.

Further, in general, the DC having the above-mentioned structure is used.
The DC / DC converter circuit is a DC / DC converter IC1.
Since the switching time of 0 cannot be 100%,
An input / output voltage difference of about 0.5 V is required.

Therefore, the present invention has been proposed in view of the above-mentioned circumstances, and it is possible to normally start the operation even at the time of start-up, and to provide a stable output even if the input voltage is slightly lowered. It is an object of the present invention to provide a power supply circuit which can obtain a current and has a small difference between input and output voltages.

[0011]

The power supply circuit of the present invention has been proposed in order to achieve the above-mentioned object, and is a C-MOS DC / DC conversion IC designed for boosting.
DC / D for step-down by adding external transistor to
A power supply circuit used as a C converter, comprising:
The C / DC conversion IC has a voltage detection unit that detects whether the output voltage (output voltage of the power supply circuit) is lower than a predetermined voltage (for example, 3.0 V), and the voltage detection unit detects the voltage. When it is detected that the output voltage is lower than the predetermined voltage, a base current is supplied to the external transistor to operate as a linear regulator.

Further, the power supply circuit of the present invention is provided with bias means for applying a bias voltage lower than the predetermined voltage to the voltage detecting means when the power is turned on.

[0013]

According to the present invention, when the output voltage is lower than the predetermined voltage, the voltage detecting means detects that fact, and in accordance with the detection, the current is supplied to the base of the external transistor. The operation is switched to a linear regulator that does not use a DC / DC conversion IC.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

The power supply circuit of the first embodiment of the present invention is shown in FIG.
As shown in, DC / C of C-MOS designed for boosting
An external PNP-type transistor Q1 (and a transistor Q2) is added to the DC conversion IC 10 to use as a step-down DC / DC converter, which is an output voltage (power supply) of the DC / DC conversion IC 10. The output voltage of the circuit) has a voltage detector DET for detecting whether it is lower than a predetermined voltage (for example, 3.0 V), and the voltage detector DET is provided.
When it is detected that the output voltage is lower than the predetermined voltage by the external transistor Q,
1 (including the transistor Q2) is supplied with a base current to operate as a linear regulator.

Further, in the power supply circuit of this embodiment, when the power is turned on, the dividing resistor R as bias means for applying a bias voltage lower than the predetermined voltage to the voltage detector DET.
1, R2 (and diode D2) are also provided.

In this embodiment, the DC / DC converting IC 10 similar to that shown in FIG. 8 is used as a main component of the power supply circuit.

In FIG. 1, the battery B1 is an input power source, and the power source supplied by the battery B1 is about 3.5.
It is V to 4.5V. This battery B1 is connected to the emitter of a PNP type power transistor Q1 for switching. The collector of the transistor Q1 is connected to one terminal of the choke coil L1, and the base is connected to the emitter of a PNP type transistor Q2 via a base resistor R4 that limits the base current of the transistor Q1. The resistor R3 is a bias resistor for the transistor Q1.

The transistor Q2 is an auxiliary switching transistor for driving the base current of the transistor Q1. The base of the transistor Q2 is connected to the switching terminal Lx of the DC / DC converting IC 10 via the base resistor R6.
Therefore, the transistor Q2 is
The base current flows (switches) in synchronization with the switching of the switching terminal Lx of the conversion IC 10. The switching of the transistor Q2 causes the transistor Q1 to be switched, whereby the transistor Q1 supplies the power of the battery B1 to the choke coil L1. The resistor R5 is a bias resistor for the transistor Q2.

The other terminal of the choke coil L1 is connected to the other end of the smoothing capacitor C whose one end is grounded, and is also connected to one terminal of the resistor R7. The resistor R7 forms a dividing resistor together with the resistor R8,
The voltage dividing points of the dividing resistors R7 and R8 are connected to the Out terminal of the DC / DC converting IC 10. The voltage at the connection point between the other terminal of the choke coil L1 and the smoothing capacitor C is taken out as the output voltage of the power supply circuit of FIG. The smoothing capacitor C is a DC / D
It is provided to keep the output voltage of the C conversion IC 10 at a constant value.

Here, in the circuit of this embodiment, DC / D
The output voltage of the C conversion IC 10 is fixed at 3.0V. The division ratio of the division resistors R7 and R8 is 1:10. Therefore, the output voltage of the power supply circuit of FIG. 1 is fixed at 3.3V.

The diode D1 is a flywheel diode and forms a DC loop between the choke coil L and the load when the transistor Q1 is OFF.

By the way, in the power supply circuit of this embodiment, in order to obtain the output voltage (3.3 V in this embodiment) even when the input voltage drops or when the power is turned on (at the time of start-up), the above-mentioned respective configurations are provided. It also has the following configuration with the elements.

That is, in FIG. 1, the connection point between the other terminal of the choke coil L1 and the smoothing capacitor C is also connected to the input terminal of the diode D3. The output end of the diode D3 is connected to the output end of the diode D2. The midpoint of connection between the diodes D3 and D2 is also connected to the voltage detection terminal of the voltage detector DET. The voltage detector DET has an output terminal that becomes a "Low" level when the voltage at the voltage detection terminal becomes lower than a predetermined voltage (3.0 V in this embodiment). The output terminal of the voltage detector DET is connected to the base of the transistor Q2 via the resistor R6.

Further, the input terminal of the diode D2 is
Dividing resistors R1 and R2 for supplying a bias voltage lower than the detection voltage (3.0 V above) to the voltage detector DET.
It is connected with the partial pressure point of. That is, the diodes D2 and D3 take the logical sum of the bias voltage of the dividing resistors R1 and R2 and the output voltage of the power supply circuit and supply the voltage to the voltage detection terminal of the voltage detector DET. It is a diode.

Here, in the circuit of this embodiment, when the output voltage is lower than 3.0 V, for example, or when the power is turned on (at the time of starting), that is, the voltage at the voltage detection terminal of the voltage detector DET is at the predetermined value. Is lower than the voltage (3.0 V) of the voltage detector DET, the output terminal of the voltage detector DET is “Lo”.
Then, the transistor Q2 whose base is connected to the output terminal of the voltage detector DET via the resistor R6 is turned on. As a result, the transistor Q1 is also turned on and the power supply of this embodiment is turned on. The circuit operates as a linear regulator, that is, the power supply circuit of the present embodiment, the voltage detector DET and the transistor Q1, when the output voltage becomes lower than a predetermined voltage (3.0V) at the time of startup. A linear regulator is constituted by Q2, and the bias voltage by the dividing resistors R1 and R2 is also a voltage necessary for operating the voltage detector DET at the time of startup.

When the power is turned on (at the time of startup), the transistor Q1 is turned on as described above, and the DC / DC conversion IC is further passed through the choke coil L1.
A voltage is applied to the Out terminal of the DC / DC converter IC 10, so that the DC / DC conversion IC 10 operates. Therefore, after this time, the power supply circuit of the present embodiment switches from the linear converter at the time of starting and starts to function as a DC / DC converter.

Next, FIG. 2 shows a power supply circuit according to a second embodiment of the present invention. In FIG. 2, the same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

The power supply circuit of the second embodiment shown in FIG. 2 is an example in which the output terminal of the voltage detector DET is directly connected to the base of the transistor Q1 via the resistor R4. Also in the second embodiment circuit, the same operation as in the first embodiment circuit is possible.

Further, FIG. 3 shows the internal construction of another concrete example of the DC / DC conversion IC of the power supply circuit shown in FIGS. The DC / DC conversion IC 2 shown in FIG.
Also in 0, the same components as those of the DC / DC conversion IC 10 (see FIG. 8) are designated by the same reference numerals, and detailed description thereof will be omitted.

The DC / DC conversion IC 20 shown in FIG.
Is a transistor in which the output-stage transistor Q20 provided inside the DC / DC converting IC 10 is omitted, and is configured for the purpose of driving a large current by externally attaching the transistor. The output of the terminal EXT of the DC / DC conversion IC 20 of FIG.
It is a logical inversion of the output from the terminal Lx of the DC / DC conversion IC 10.

FIG. 4 shows a configuration in which the DC / DC conversion IC 20 shown in FIG. 3 is applied to the above-described configuration of FIG. 10 so that the Zener diode ZD required in the configuration of FIG. 10 is deleted. Is shown.
Also in FIG. 4, the same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 4, a starting resistor R10 is provided instead of the Zener diode ZD of FIG. Furthermore, the output of the DC / DC conversion IC 20 of FIG.
Since it is logically inverted with the output of 0, in this configuration, the NPN transistor Q3 for logical inversion is
It is arranged at the position of the transistor Q2 in FIG.

Further, FIG. 5 shows the configuration of the power supply circuit of the third embodiment of the present invention. Even if the input voltage is lowered by adding the same voltage detector DET as described above to the power supply circuit of FIG. ,
The output voltage is stable. In FIG. 5 as well, the same components as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. In the case of the power supply circuit of the third embodiment shown in FIG. 5,
The resistor R5 in FIG. 1 is omitted.

Next, FIG. 6 shows the relationship between the input and output voltages of the power supply circuit of each of the embodiments described above. From this FIG.
According to the power supply circuit of the present embodiment, it is understood that the predetermined voltage is supplied even if the input voltage is reduced to near the set voltage (for example, 3.3V).

Further, in FIG. 7, the input / output voltage of the conventional power supply circuit (the conventional step-down DC / DC converter circuit described above) is compared with the relationship of the input / output voltage in the power supply circuit of the present embodiment. Shows the relationship. As shown in FIG. 7, in the conventional power supply circuit, when the input voltage falls below 4.0 V, for example, the output voltage falls below the set voltage.

As described above, according to the power supply circuits of the respective embodiments of the present invention, the voltage detector DET for detecting the decrease in the output voltage (output voltage of the power supply circuit) of the DC / DC conversion ICs 10 and 20, and the power supply. It has dividing resistors R1 and R2 and a diode D2 as bias means for supplying a bias voltage lower than the detection voltage to the voltage detector DET at the time of turning on, and when the output voltage is low, it operates as a linear regulator and the detection voltage is preset. Specified voltage value (3.0V)
When it becomes higher, it operates as a DC / DC converter, so that the input / output voltage difference is low and the power consumption is low.
A C / DC converter can be realized. Therefore, the power supply circuit of this embodiment is particularly suitable as a power supply circuit for a battery-powered portable electronic device or the like.

[0038]

In the power supply circuit of the present invention, the DC / D
The voltage detection means for detecting a decrease in the output voltage of the C conversion IC (output voltage of the power supply circuit) and the bias means for supplying a bias voltage lower than the detection voltage to the voltage detection means when the power is turned on have a low detection voltage. Sometimes it operates as a linear regulator, and when the output voltage becomes higher than a predetermined voltage value, it operates as a DC / DC converter, so the DC voltage difference between the input and output is low and the DC power consumption is low.
A / DC converter can be realized. That is, according to the power supply circuit of the present invention, it is not necessary to provide a Zener diode for start-up, the output current can be prevented from decreasing even if the input voltage is slightly decreased, and the difference between the input voltage and the output voltage can be reduced. become. The power supply circuit of the present invention is particularly suitable as a power supply circuit for battery-powered portable electronic devices and the like.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a schematic configuration of a power supply circuit according to a first embodiment.

FIG. 2 is a circuit diagram showing a schematic configuration of a power supply circuit according to a second embodiment.

FIG. 3 is a circuit diagram showing an internal configuration of another specific example of the DC / DC conversion IC.

FIG. 4 is a circuit diagram showing a configuration of a power supply circuit when the DC / DC conversion IC of FIG. 3 is used.

FIG. 5 is a circuit diagram showing a schematic configuration of a power supply circuit according to a third embodiment.

FIG. 6 is a characteristic diagram showing a relationship between input and output voltages of the power supply circuit of each example.

FIG. 7 is a characteristic diagram showing a relationship between input and output voltages of a conventional power supply circuit.

FIG. 8 is a circuit diagram showing an internal configuration of a C-MOS DC / DC conversion IC.

FIG. 9 is a circuit diagram showing a schematic configuration of a step-up DC / DC converter (power supply circuit).

FIG. 10 is a circuit diagram showing a schematic configuration of a conventional step-down DC / DC converter (power supply circuit).

[Explanation of symbols]

 10 --- DC / DC conversion IC Q1, Q2 ...- Transistor L1 ...- Choke coil D1 ...- Flywheel diode D2, D3 ... Diode B1 ... Battery DET ... Voltage detector C ... Smoothing capacitor R3, R5 ... Bias resistance R4, R6 ... Base resistance R1, R2 ・ ・ ・ ・ Division resistors R7, R8 ・ ・ ・ ・ ・ ・ Division resistors

Claims (2)

[Claims] 1. A DC / DC conversion IC for boosting,
A power supply circuit using an external transistor as a step-down DC / DC converter for detecting whether or not the output voltage of the DC / DC conversion IC is lower than a predetermined voltage. A voltage detecting unit is provided, and when the output voltage is detected to be lower than the predetermined voltage by the voltage detecting unit, a base current is supplied to the external transistor to operate as a linear regulator. And power circuit. 2. The power supply circuit according to claim 1, wherein the voltage detecting means is provided with bias means for applying a bias voltage lower than the predetermined voltage.