JPH09182417A - Power supply device and electric apparatus using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form the compact and inexpensive power supply device by setting a switching element in the cut-off state until the counter-electromotive force by an inductance element becomes the current value or less for specifying the forward-direction voltage of a flywheel diode. SOLUTION: A switching element 3 and an inductance element 4 are connected in series between a voltage input terminal T1 and an output terminal T3. A monitoring circuit 6 detects the current flowing to the terminal T3 and prevents the fowling of the current higher than a specified value. The switching element 3 is turned on or off in accordance with the result of the current detection at a driving circuit 7 and the monitoring circuit 6. A flywheel diode 8 forms the path, through which the current caused by the counter-electromotive force of the inductor element 4 flows when the switching element 3 is turned off. Then, a characteristic improving circuit 9 sets the switching element in the cur-off state until the counter-electromotive force caused by the inductance element 4 becomes the current value or less for specifying the forward-direction voltage of the flywheel diode 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply device called a DC-DC converter used in electric equipment such as a multifunctional telephone, an electric vacuum cleaner, and a charging device for a secondary battery such as a lithium ion battery. Regarding circuit configuration.

[0002]

2. Description of the Related Art Conventionally, electric equipment using a semiconductor device such as a one-chip microcomputer is required to have a stable output voltage characteristic as a power source of the semiconductor device, and is highly efficient due to external restrictions of each equipment. There is a demand for a small power supply device. As satisfying this demand, FIG.
A power supply device of a system called a DC-DC converter as shown in the circuit diagram is used.

A power supply device 1b shown in FIG. 5 has an input power supply circuit 2 including a DC power supply 2a and an input capacitor 2b, a switching element 3 including a transistor 11, an inductance element 4, an output capacitor 5, resistors 21, 22 and. 24, Zener diode 23, monitoring circuit 6 including transistors 19 and 20, transistor 14, resistor 1
The drive circuit 7 is composed of 2 to 14, and a diode (hereinafter referred to as “flywheel diode”) 22.

The input power supply circuit 2 is connected to the transistor 1 via a terminal T1 (hereinafter referred to as "voltage input terminal T1").
1, the collector side of the transistor 11 (wiring L ′ in FIG. 5) is connected to the terminal T3 (hereinafter referred to as “output terminal T3”) via the inductance element 4,
The output capacitor 5 is connected between the output terminal T3 and the terminal T2 (hereinafter referred to as “reference voltage terminal T2”).
The collector output of the transistor 19 of the monitor circuit 6 is connected to the base of the transistor 14 of the drive circuit 7 and also connected to the wiring L ′ via the capacitor 16. Further, the reference voltage terminal T2 is also connected to the wiring L ′ via the diode 8.

The operation will be described. First, the power supply device 1
When a load such as a motor or a semiconductor device is connected between the output terminal T3 of b and the reference voltage terminal T2 and the DC power supply 2a is set to a predetermined voltage V1, the voltage is applied to the subsequent circuits via the voltage input terminal T1. Applied and becomes operable. By applying this voltage, when the transistor 14 becomes conductive, the transistor 1
1 is conducted, and a current (hereinafter referred to as “output current”) flows through the inductance 4 to the monitoring circuit 6 and the load. At this time, since the base current flows through the transistor 14 even through the capacitor 16, the transistor 14
The collector current of the transistor becomes large, and the transistor 11 saturates rapidly.

When the output current is large, the output current flows through the monitoring circuit 6 to generate a voltage in the resistor 22 which makes the transistor 20 conductive, and the transistor 20 becomes conductive, so that the transistor 19 becomes conductive. On the other hand, when the output current is small and the output voltage rises, the transistor 19 becomes conductive by the voltage generated in the resistor 24. In this way, the transistor 19
Is turned on, the base voltage of the transistor 14 becomes low level, so that the transistor 14 is cut off and the transistor 11 is cut off. At this time, since a counter electromotive force is generated in the inductance 4, a current due to this counter electromotive force continues to flow in the load and the diode 8.

After that, when the counter electromotive force gradually decreases and the output current decreases, the voltage drop due to the resistor 22 decreases, and the transistor 20 is cut off. Then, the transistor 19 is cut off and the base voltage of the transistor 14 is cut off. Rises, so that the transistor 11 becomes conductive again. The output current is charged in the output capacitor 5 by repeating the above-described operation cycle so that a substantially constant output current can be supplied to the load.

[0008]

However, the characteristics of the output voltage and the input current at the terminal T1 with respect to the output current flowing through the load of the conventional power supply device 1b are as shown in the waveform diagram of FIG. After exceeding the values (points B and B'in FIG. 5), both output voltage and input current gradually decrease, and the cycle of the above operation cycle becomes shorter as the output current increases. To work. Therefore, there is a problem in that power loss due to the transistor 11 and elements such as the inductance element 4 increases, and each element and the power supply device generate heat. Further, when the heat generation of each element increases, it becomes necessary to perform heat radiation processing on the package and the substrate using the same, and the external dimensions of each element increase, and the external dimensions of the entire power supply device and the equipment using the same also increase. There are also problems.

Therefore, the present invention solves these problems and adopts a circuit configuration that reduces the power loss of the power supply device, so that a small and inexpensive power supply device and electric equipment using the same can be easily formed. The purpose is to

[0010]

In order to solve the above-mentioned problems, a power supply device according to a first aspect of the present invention comprises a switching element and an inductance element connected in series between a voltage input terminal and an output terminal, A monitoring circuit for detecting a current flowing through the output terminal and preventing a current more than a certain value from flowing, a drive circuit for connecting and disconnecting the switching element according to the current detection result of the monitoring circuit, and a switching element And a flywheel diode for forming a path through which a current due to the counter electromotive force of the inductance element flows when the power is cut off, the counter electromotive force due to the inductance element defines the forward voltage of the flywheel diode. It is characterized by having a characteristic improvement circuit for shutting off the switching element until the current falls below the current. That.

With such a structure, although the circuit structure is simple, the internal loss of the circuit is reduced and the heat radiation process can be simplified, and small and inexpensive electronic parts or a part of them are integrated into one. It becomes possible to form a power supply device by using the miniaturized semiconductor device. Claim 2
The electric device according to claim 1 uses the power supply device according to claim 1, wherein a rectified voltage of a commercial power supply is connected to a voltage input terminal, and an output capacitor for smoothing an output voltage and a semiconductor device are connected to an output terminal. It is characterized by With such a configuration, it becomes possible to easily use a small-sized and inexpensive power supply device for the power supply circuit of the semiconductor application product.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. In this specification, the same or similar circuit elements are denoted by the same reference numerals throughout the drawings, and redundant description is omitted. FIG. 1 shows a circuit diagram of a power supply device called a DC-DC converter using the present invention, which has a switching element 3 for conducting or cutting off (hereinafter referred to as “switching”) a power supply voltage at a predetermined timing. And an inductance element 4 for generating a counter electromotive force when the power supply voltage is cut off by the switching element 3, and an electrolytic type for reducing the output impedance by being charged by the counter electromotive force generated by the inductance element 4. An output capacitor 5 and a monitoring circuit 6 for detecting the output current and stopping the operation of the switching element 3 when an abnormal voltage is input.
And the switching element 3 according to the signal from the monitoring circuit 6.
Drive circuit 7 for controlling and driving the diode, a diode (hereinafter referred to as a "flywheel diode") 8 that forms a path through which a current due to the generated counter electromotive force flows, and a characteristic of the output voltage with respect to the output current has a predetermined current value. The above is composed of the characteristic improving circuit 9 for making the drooping characteristic in which the output voltage sharply decreases.

The configuration of each circuit will be described in more detail. The switching element 3 is composed of a PNP type transistor 15 having an emitter connected to a terminal T1 (hereinafter referred to as "voltage input terminal T1") and a collector connected to an inductance element 4. It is composed of a coil wound around a core. Further, the monitoring circuit 6 has a resistor 22 for detecting a current flowing in the load (hereinafter referred to as “output current”), a terminal T3 (hereinafter referred to as “output terminal T3”), and a terminal T2 (hereinafter referred to as “reference voltage terminal T2”). , And a zener diode 23 and a resistor 24 connected in series between
And the base is connected to the output terminal T3 and the resistor 2
2 is connected between the inductor 2 and the inductance element 4, and the collector is connected through the resistor 21 to the Zener diode 23.
Of the PNP type transistor 20 connected to the connection point of the anode and the resistor 24 and the base of the Zener diode 23 on the anode side, and the emitter connected to the reference voltage terminal T2 to control the drive circuit 7 by the collector output. And an NPN-type transistor 19 for In the drive circuit 7, the base of the transistor 11 is connected to the collector via the resistor 13, the reference voltage terminal T2 is connected to the emitter via the resistor 15, and the voltage input terminal T1 is connected to the base via the resistor 12. And an NPN-type transistor 14. In the characteristic improving circuit 9, the cathode is a flywheel diode 8
Is connected to the cathode of the
It is composed of a diode 17 connected to the collector of the transistor 19 through.

The connection between the circuit configurations will be further described. The power supply voltage is connected to the emitter of the transistor 11 via the voltage input terminal T1, the collector side of the transistor 11 (wiring L in FIG. 1) is connected to the output terminal T3 via the inductance element 4, and the output terminal T3 and the reference terminal The output capacitor 5 is connected to the voltage terminal T2.
Further, the collector output of the transistor 19 of the monitoring circuit 6 is connected to the base of the transistor 14 of the driving circuit 7 and is also connected to the wiring L via the characteristic improving circuit 9. Further, the reference voltage terminal T2 is also connected to the wiring L via the diode 8.

Next, the circuit operation of the present invention will be described.
First, the output terminal T3 and the reference voltage terminal T2 of the power supply device 1a
A load device such as a motor or a semiconductor device is connected between the DC power source 2a and the electrolytic capacitor 2b provided in parallel with the DC power source 2a to reduce its impedance at the voltage input terminal T1. The input power supply circuit 2 is connected. Then, the DC power supply 2a is set to a predetermined voltage V
When set to 1, a voltage is applied to subsequent circuits via the voltage input terminal T1 to enable operation. By applying this voltage, when the transistor 14 becomes conductive, the transistor 11
Is conducted, and the monitoring circuit 6 is connected via the inductance element 4.
And the output current will flow to the load. At this time, the diode 17 acts like a capacitor on the base of the transistor 14 and positive feedback is applied via the resistor 18, so that the transistor 11 is saturated and conducted rapidly.

When the output current is large, the output current flows through the monitoring circuit 6 to generate a voltage in the resistor 22 which makes the transistor 20 conductive, and the transistor 20 becomes conductive, so that the transistor 19 becomes conductive. On the other hand, when the output voltage rises when the output current is small and the transistor 20 does not conduct, a current flows through the Zener diode 23 and a voltage is generated in the resistor 24 so that the transistor 19 conducts. Become. In this way, when the transistor 19 becomes conductive,
Since the base voltage of the transistor 14 becomes low level, the transistor 14 is cut off and the transistor 11
Is shut off. At this time, since a counter electromotive force is generated in the inductance 4, the output current continues to flow in the load and the diode 8 due to the counter electromotive force.

After that, the back electromotive force gradually decreases and the current due to the back electromotive force decreases to shut off the transistor 20, or the output voltage drops below a predetermined value and no current flows to the Zener diode 23. When the voltage of 24 drops, the transistor 19 will be cut off. At this time, the voltage of the wiring L becomes lower than the reference voltage (0 (V)) by the forward voltage (VF (V)) of the diode 8 as shown in FIG. 3A (described later). Therefore, the base voltage (VB14) of the transistor 14 is set to the voltage shown in the equation (1) through the diode 17 and the resistor 18 of the characteristic improving circuit 9. Actually, the resistance value (R12) of the resistor 12 is sufficiently larger than the resistance value (R18) of the resistor 18, so that the base voltage thereof is substantially the reference voltage. Therefore, the base voltage of the transistor 14 becomes smaller than the voltage between the base and the emitter thereof, and the transistor 14 remains cut off, so that the output current due to the counter electromotive force continues to flow. The resistor 18 may be omitted, but it is provided to protect the diode 17 from overcurrent.

[0018]

## EQU00001 ## VB14 = V1.times.R18 / (R12 + R18) (1) Then, the base voltage of the transistor 14 rises and becomes conductive again because the counter electromotive force and the output current further decrease and the diode 8 The flowing current is a forward voltage (typically 0.4
The current becomes equal to or less than the current (referred to as "forward current") defined by V to 1.7 V), and the forward voltage of the diode 17 disappears.

The output current is charged in the output capacitor 5 while repeating the above operation cycle, and a substantially constant output current and voltage are supplied to the load, so that as shown in FIG. Specified output current value (A in Fig. 2
Up to the point), a constant output voltage is output, and when the output current exceeds the specified output current value, the output voltage drops drastically, resulting in a drooping type output characteristic. The characteristic of the input current at the terminal T1 at this time is as shown in FIG. By having such electrical characteristics, it is possible to significantly reduce power loss when the output terminal T3 is short-circuited to the reference potential or an overload is connected, so that heat generation of the circuit is suppressed accordingly. As a result, the heat radiation process is facilitated, and the circuit and the device can be downsized. For example, the power loss in the circuit of the present invention can be reduced by about 40% as compared with the conventional circuit, and can be about 1 W.

FIG. 3 shows an example of waveforms of the voltage of the wiring L and the current flowing through the inductance 4 in the power supply device 1a of FIG. Note that the ripple voltage and the like are omitted in FIG. The Vsat in FIG.
Represents the saturation voltage when the device is conducting, and t1 is the switching element 3
Shows the cycle time of the operation cycle. Further, the current flowing in the inductance element 4 of FIG. 2B is as follows: the voltage across the capacitor 2b is V1 (V), the output voltage across the capacitor 5 is V2 (V), and the voltage across the resistor 22 is Is Vbe (V), the inductance value of the inductor element 4 is L (H), the forward voltage of the diode 8 due to the back electromotive force is VF (V), and the elapsed time is Δt (s), the transistor 11 becomes conductive. The charging current during the charging is expressed by the formula (2), and when the transistor 11 is cut off and charged by the counter electromotive force, the charging current is expressed by the formula (3).

[0021]

## EQU00002 ## i = (V1- (V2 + Vbe)). Times..DELTA.t / L (2)

[0022]

[Mathematical formula-see original document] i '=-(V2- (VF-Vbe)) * [Delta] t / L (3) Note that the output current and the values of the respective constants are set according to the load to be connected. For example, when the peak value of the output current is several hundred mA, the cycle t of the operation cycle is
1 is several μs to several tens μs, the inductance value of the inductance element 4 is several mH to several tens mH, the resistance value of the resistor 22 is about several Ω to several tens Ω, and the resistance value of the resistor 12 is several M.
Ω, and the resistance value of the resistor 18 may be set to about several hundreds Ω.

FIG. 4 shows an embodiment as an application circuit when the power supply device 1a of FIG. 1 is used for an electric vacuum cleaner or the like. The application circuit 50 of FIG. 4 includes a plug 51 for inputting an AC voltage (so-called “commercial power supply”) and a diode element 52 for rectifying and smoothing the AC power supply to obtain the power supply voltage of the power supply device 1a of the present invention. An input power supply circuit including an input capacitor 2c, a semiconductor device 53 such as a one-chip microcomputer that operates by being supplied with a power supply voltage from the power supply device 1a, and an interrupter circuit 54 for transmitting a control signal from the semiconductor device 53. , A drive device 60 such as a triac for controlling conduction and interruption of an AC power supply in accordance with a signal input by the interrupter circuit 54, and a drive device 60
It is composed of a load 59 such as a motor operated by an AC power source controlled by.

The connection relation of each part will be described. One end of the AC power supply is connected to the reference voltage terminal T2 of the power supply device 1a and the reference voltage (GND) side of each circuit via the plug 51, and the other end is connected to the load 59 and the anode of the diode element 52. . The power supply voltage rectified and smoothed by the diode element 52 and the input capacitor 2c is connected to the voltage input terminal T1 of the power supply device 1a of the present invention, and the output terminal T3 of the power supply device 1a is connected to the power supply voltage terminal (VDD) of the semiconductor device 53. The output S of the semiconductor device 53 is connected to the anode of the light emitting diode 56 of the interrupter circuit 54 via the resistor 55. Light emitting diode 56
The light emission output of is received by the light receiving element 57 such as a pin diode connected between the anode and the gate of the triac of the driving device 60 via the resistor 58, and the other anode of the triac is connected to the load 59. With such a circuit configuration, it is possible to easily control a load such as a motor using a commercial power supply of 100V or 220V.

The present invention is not limited to the above-described embodiments, and for example, a full-wave rectification circuit using a diode bridge circuit, a transformer with a center tap, or the like may be used in the input power supply circuit, or the input power circuit may be used. A switch circuit for operation control is provided in the power supply circuit, a display device such as a light emitting diode is provided for displaying the operation state, and the output voltage of the power supply device of the present invention is divided by a resistor or the like to supply voltage of a one-chip microcomputer or the like It may be used as. The voltage detection circuit of the monitoring circuit may have any circuit configuration as long as it can detect the current flowing through the load. Furthermore, the circuit of the present invention may be formed by using only a single electronic component, or may be formed in a semiconductor device in which only a circuit portion including a transistor, a diode and a resistor is integrated. Further, a circuit configuration using MOS transistors may be used instead of the circuit using bipolar transistors in FIG.

[0026]

According to the present invention as described above, claim 1
Since the power supply device according to the description has a simple circuit configuration, the internal loss is reduced and the heat dissipation process can be simplified. Therefore, a small and inexpensive electronic component or a part thereof is integrated into one. A power supply device can be easily formed using a small semiconductor device, and a small and inexpensive power supply device can be easily formed.

In addition, since the electric equipment according to the second aspect can easily use a small-sized and inexpensive power supply device for the power supply circuit of the semiconductor application product, the outer shape of the product is less restricted and designed. This has the effect of shortening the period, reducing the design cost, and reducing the unit price of the product.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating an embodiment of the present invention,

FIG. 2 is a waveform diagram showing characteristics of output voltage and input current according to the embodiment of the present invention,

FIG. 3 is a waveform diagram showing characteristics of main parts of the embodiment of the present invention,

FIG. 4 is a configuration diagram showing an applied device using the circuit of the present invention,

FIG. 5 is a circuit diagram showing a conventional circuit example,

FIG. 6 is a waveform diagram showing characteristics of a conventional circuit example.

[Explanation of symbols]

 1a: Power supply device 2: Input power supply circuit 3: Switching element (PNP transistor) 4: Inductance element 5: Output capacitor 6: Monitoring circuit 7: Drive circuit 8: (Flywheel) diode 9: Characteristic improvement circuit

Claims (2)

[Claims] 1. A switching element and an inductance element connected in series between a voltage input terminal and an output terminal,
A monitoring circuit for detecting a current flowing through the output terminal and preventing a current of a certain value or more from flowing, and a drive circuit for connecting and disconnecting the switching element according to a current detection result in the monitoring circuit, In a power supply device having a flywheel diode for forming a path through which a current due to the counter electromotive force of the inductance element flows when the switching element is cut off, the counter electromotive force due to the inductance element is equal to that of the flywheel diode. A power supply device having a characteristic improving circuit for turning off the switching element until the current becomes equal to or less than a current that defines a forward voltage. 2. The power supply device according to claim 1, wherein a rectified voltage of a commercial power supply is connected to the voltage input terminal, and an output capacitor for smoothing an output voltage and a semiconductor device are connected to the output terminal. Electrical equipment characterized by.