KR20020033506A - DC―DC Convertor and an electronic device using the same - Google Patents

Abstract

PURPOSE: To provide a small-sized, low-cost dc-to-dc converter, and an electronic apparatus using it. CONSTITUTION: The DC-DC converter 10 is provided with an stable multivibrator 12, having a first time-constant circuit 13 for setting the on-time of its output and a second time-constant circuit 14 for setting the off-time of the output, and a switching element Q1 to be controlled by the output of the astable multivibrator 12. The duty radio of the astable multivibrator 12 is changed, in accordance with the output voltage, and consequently the output voltage is controlled. Accordingly, it is possible to reduce the size and cost of the dc-to-dc converter, since it is possible to form the converter having a simple circuit.

Description

DC-DC converter and an electronic device using the same {DC-DC converter and an electronic device using the same}

The present invention relates to a DC-DC converter and an electronic device using the same.

10 shows a circuit diagram of a conventional DC-DC converter. In FIG. 10, the DC-DC converter includes a DC power supply (Vcc), an inductance element (L1), a diode (D1) as a rectifier element, a transistor (Q1) as a switching element, resistors (R1 and R2), capacitors (C1 and C2), and a drive. The circuit 2, the reference voltage generator 3, the error amplifier circuit 4, the triangular wave generator 5, the PWM comparator 6, and the output terminal Pout.

Here, the DC power supply Vcc is connected to one end of the inductance element L1, and the other end of the inductance element L1 is connected to the collector of the transistor Q1 and the anode of the diode D1, respectively. The cathode of the diode D1 is connected to the output terminal Pout. The emitter of transistor Q1 is grounded. The capacitor C1 is connected in parallel to the DC power supply Vcc. The output terminal Pout is grounded through the capacitor C2. The output terminal Pout is grounded through the resistors R1 and R2 in order. The connection point of the resistor R1 and the resistor R2 is connected to one input of the error amplifier circuit 4. A reference voltage generator circuit is connected to the other input of the error amplifier circuit 4. The output of the error amplifier circuit 4 is connected to one input of the PWM comparator 6. A triangular wave generator circuit 5 is connected to the other input of the PWM comparator 6. The output of the PWM comparator 6 is connected to the drive circuit 2, and the output of the drive circuit 2 is connected to the base of the transistor Q1.

The DC-DC converter 1 configured as described above is a boost-type DC-DC converter, and the transistor Q1 is controlled to be ON / OFF by the drive circuit 2. The current flowing through the inductance element L1 is controlled by the transistor Q1. That is, the energy of the DC power supply Vcc is charged to the inductance element L1 when the transistor Q1 is ON, and this is discharged through the diode D1 when the transistor Q1 is OFF to output the output terminal Pout. Is output from The value of the output voltage output from the output terminal Pout is determined according to the ratio of the ON time and the OFF time of the transistor Q1.

Next, control of the output voltage will be described with reference to FIG. For example, when the ON / OFF ratio of the transistor Q1 is constant, the output voltage of the DC-DC converter 1 changes according to the voltage change of the DC power supply Vcc and the load connected to the output terminal Pout. . For this reason, it is necessary to control so that the output voltage does not change even if the voltage and load of the DC power supply Vcc change. Thus, first, the output voltage is detected by the resistors R1 and R2 and input to the error amplifier circuit 4. The reference voltage generated by the reference voltage generator 3 is also input to the error amplifier circuit 4, and the error output a corresponding to the difference is output. The error output a becomes higher as the output voltage is higher. The error output a is input to the PWM comparator 6. The PWM comparator 6 also inputs a triangular wave output b outputted from the triangular wave generating circuit 5, and the PWM comparator 6 compares the two and outputs an error output a larger than the triangular wave output b. When the triangular wave output b is larger than the L (low) level and the error output a, the comparison output c that becomes the H (high) level is output. The time variation of the error output (a), the triangular wave output (b), and the comparison output (c) is shown in FIG. 11, and the relationship is that the larger the error output (a), the triangular wave output (b) becomes the error output (a). Time becomes shorter than) so that the duty ratio of the comparison output a becomes small. On the contrary, the smaller the error output (a), the longer the time that the triangular wave output (b) is larger than the error output (a), the greater the duty ratio of the comparison output (c). The comparison output c is input to the drive circuit 2 to determine the duty ratio of the ON / OFF control of the transistor Q1 by the drive circuit 2. When the duty ratio is increased and the ON time of the transistor Q1 is long, the output voltage increases, and when the ON time is short, the output voltage decreases. In this way, when the output voltage is increased, the duty ratio of the ON / OFF control of the transistor Q1 is decreased to operate the output voltage. On the contrary, when the output voltage is decreased, the output voltage is operated to raise the output voltage to a predetermined value. Controlled.

By the way, in the DC-DC converter 1 shown in FIG. 10, since there are the error amplifier circuit 4, the triangular wave generator circuit 5, the PWM comparator 6, etc., there exists a problem that a circuit size becomes large and it becomes difficult to reduce cost. . In addition, since the circuit size is large, the IC is often made, but in such a case, since the shape becomes large and expensive, there is a problem that miniaturization is difficult in addition to the low cost.

SUMMARY OF THE INVENTION The present invention aims at solving the above problems, and provides a DC-DC converter and an electronic device using the same that can be miniaturized and reduced in cost.

In order to achieve the above object, the DC-DC converter of the present invention is unstable including a first time constant circuit for setting the OFF time of the output and a second time constant circuit for setting the ON time. A DC-DC converter comprising a multivibrator, a switching element and a rectifying element controlled by an output of the unstable multivibrator, and changing a voltage value of an input voltage as an output voltage,

An output voltage control circuit for controlling the output voltage by changing at least one of the ON time and the OFF time of the switching element by changing at least one time constant of the first and second time constant circuits according to the output voltage. It is characterized by including.

In addition, the DC-DC converter of the present invention is characterized in that an inductance element for energy charging and discharging is formed in series with the switching element.

The DC-DC converter of the present invention is characterized in that at least one of the first and second time constant circuits includes an impedance variable circuit for changing the time constant.

In addition, the DC-DC converter of the present invention is characterized in that a totem pole circuit is formed between the output of the unstable multivibrator and the switching element.

In the DC-DC converter of the present invention, the rectifier element is composed of a switch element for rectification, and the unstable multivibrator is inverted with respect to the first output and the first output for ON / OFF control of the switching element. And a second output for controlling the rectifying switch element to be turned ON when the switching element is OFF.

In addition, the DC-DC converter of the present invention is characterized in that the inclination is formed on the rising waveforms of the first and second outputs so that the switching element and the rectifying switch element are turned on at the same time with the period OFF. .

The DC-DC converter of the present invention is characterized in that a totem pole circuit is formed between the output of the unstable multivibrator and the rectifying switch element.

The DC-DC converter of the present invention is characterized in that the rectifying switch element is a MOSFET (metal oxide film semiconductor field effect transistor).

The DC-DC converter of the present invention is characterized in that the switching element is a MOSFET.

Moreover, the electronic device of this invention used the DC-DC converter in any one of the above-mentioned, It is characterized by the above-mentioned.

With this configuration, the DC-DC converter of the present invention can realize miniaturization and low cost with a simple circuit.

Further, the electronic device of the present invention can realize miniaturization and low cost.

1 is a circuit diagram showing an embodiment of the DC-DC converter of the present invention.

FIG. 2 is a characteristic diagram illustrating time variation of collector voltages and base voltages of two transistors of an unstable multivibrator used in the DC-DC converter of FIG. 1.

3 is a circuit diagram illustrating a specific example of an output voltage control circuit and an impedance variable circuit of the DC-DC converter of FIG. 1.

4 is a circuit diagram showing another embodiment of the DC-DC converter of the present invention.

5 is a circuit diagram showing still another embodiment of the DC-DC converter of the present invention.

6 is a circuit diagram showing still another embodiment of the DC-DC converter of the present invention.

FIG. 7 is a characteristic diagram illustrating time variation of signals of respective parts of the DC-DC converter of FIG. 6.

8 is a circuit diagram showing still another embodiment of the DC-DC converter of the present invention.

9 is a perspective view illustrating an embodiment of an electronic device of the present invention.

10 is a circuit diagram showing a conventional DC-DC converter.

FIG. 11 is a characteristic diagram illustrating time variation of signals of respective parts of the DC-DC converter of FIG. 10.

<Brief description of the main parts of the drawing>

10, 20, 30, 40, 50 DC-DC converters

11 Output Voltage Control Circuit

12, 21 Unstable Multivibrator

13, 22 First time constant circuit

14, 23 2nd time constant circuit

15, 24 impedance variable circuit

31, 42 totem pole circuit

41 bootstrap circuit

51 Logic Inverting Circuit

Circuit 60 printer

Q1 transistor (switching element)

Q2, Q3, Q4, Q5 transistors

Q6, Q8 FETs (Switching Devices)

Q7 FET (Rectifier Switch Element)

D1 diode (rectifier)

L1 inductance element

Fig. 1 shows a circuit diagram of one embodiment of the DC-DC converter of the present invention. 1, the same code | symbol is attached | subjected to the part same or equivalent to FIG. 10, and the description is abbreviate | omitted.

In Fig. 1, the DC-DC converter 10 includes the drive circuit 2, the reference voltage generator 3, the error amplifier circuit 4, and the triangular wave generator circuit 5 of the conventional DC-DC converter 1 described above. ), Instead of the PWM comparator 6 and the resistors R1 and R2, the output voltage control circuit 11 and the unstable multivibrator 12 are included. The unstable multivibrator 12 is composed of a transistor Q2, a resistor and a capacitor, and includes a first time constant circuit 13 for determining the OFF time of the transistor Q2, a transistor Q3, and an impedance variable circuit ( 15) and a second time constant circuit 14 for determining the OFF time of the transistor Q3. The collector of transistor Q3 is connected to the base of transistor Q1, which is a switching element, and serves as an output terminal of the unstable multivibrator 12. The output voltage control circuit 11 is connected to the impedance variable circuit 15.

In the DC-DC converter 10 configured as described above, the unstable multivibrator 12 oscillates at the frequency and duty ratio determined by the first and second time constant circuits 13 and 14. FIG. 2 shows the time variation of the collector voltage v2c and the base voltage v2b of the transistor Q2 of the unstable multivibrator 12, the collector voltage v3c and the base voltage v3b of the transistor Q3. . The collector voltage of transistor Q3 is also the base voltage v1b of transistor Q1. As shown in Fig. 2, the transistors Q2 and Q3 are turned on and off alternately in accordance with the OFF time determined by the first and second time constant circuits 13 and 14, respectively. The collector of the transistor Q3 becomes the output of the unstable multivibrator 12, becomes L (low) level when the transistor Q3 is ON (that is, when the transistor Q2 is OFF), and the transistor ( When Q3) is OFF (that is, when the transistor Q2 is ON), the level becomes H (high). Therefore, the unstable multivibrator 12 oscillates in the OFF time determined by the first time constant circuit 13 and the ON time determined by the second time constant circuit 14 to drive the transistor Q1. In this way, the transistor Q1 is turned on and off and the DC-DC converter 10 operates.

Next, control of the output voltage of the DC-DC converter 10 will be described. In the DC-DC converter 10, the output voltage control circuit 11 detects the output voltage and outputs a signal indicating whether the output voltage is high or low with respect to a predetermined voltage in comparison with the built-in reference voltage to vary the impedance. Input to the circuit 15. The impedance variable circuit 15 changes its impedance in accordance with the signal from the output voltage control circuit 11. Specifically, for example, when the output voltage of the DC-DC converter 10 is higher than the predetermined voltage, the output voltage control circuit 11 operates to reduce the impedance of the impedance variable circuit 15. Since the impedance variable circuit 15 is a component of the time constant circuit 14 that determines the OFF time of the transistor Q3, the time constant of the time constant circuit 14 becomes small, so that the OFF time of the transistor Q3 is shortened. . The shortening of the OFF time of the transistor Q3 means that the ON time of the transistor Q1 is shortened. At this time, since there is no change in the OFF time of the transistor Q2, the OFF time of the transistor Q1 does not change. As a result, the ratio of the ON time to the sum of the ON time and the OFF time of the transistor Q1, i.e., the duty ratio, becomes small so as to lower the output voltage. On the contrary, when the output voltage is low, the impedance of the impedance variable circuit 15 is increased to increase the duty ratio of the transistor Q1 to increase the output voltage. In this way, the DC-DC converter 10 is controlled so that the output voltage becomes a predetermined voltage.

Here, an example of the specific circuit of the output voltage control circuit 11 and the impedance variable circuit 15 is shown in FIG. In Fig. 3, the output voltage control circuit 11 is composed of resistors R3, R4, R5, transistor Q4, zener diode D2, and capacitor C3. Here, the resistors R3 and R4 are connected in series between the output terminal Pout of the DC-DC converter 10 and ground. In addition, the resistor R5, the transistor Q4, and the zener diode 2 are also connected in series between the output terminal Pout and ground. The connection point of the resistors R3 and R4 is connected to the base of the transistor Q4. The capacitor C3 is connected between the connection point of the resistors R3 and R4 and the collector of the transistor Q4. Among them, the collector of the transistor Q4 serves as the output terminal of the output voltage control circuit 11. The variable impedance circuit 15 is composed of a resistor R6, a series circuit of a resistor R7 and a transistor Q5 connected in parallel thereto. Among them, the base of the transistor Q5 becomes a control terminal of the variable impedance circuit 15 and is connected to the output terminal of the output voltage control circuit 11.

In the output voltage control circuit 11 and the impedance variable circuit 15 configured as described above, the output voltage of the DC-DC converter 10 is divided and detected by the resistors R3 and R4, and is input to the base of the transistor Q4. do. Since the emitter of the transistor Q4 is maintained at a constant voltage by the zener diode D2, when the output voltage increases, the base current of the transistor Q4 increases, so that the collector voltage of the transistor Q4, that is, the impedance variable circuit ( The base voltage of the transistor Q5 of 15 decreases. When the base voltage of transistor Q5 decreases, the resistance value between the emitter and collector of transistor Q5 falls. As a result, the resistance value of the entire impedance varying circuit 15, that is, the impedance, is lowered. In this way, the output voltage control circuit 11 and the impedance variable circuit 15 operate.

In addition, the structure of an output voltage control circuit and an impedance variable circuit is not limited to this, Any circuit structure may be sufficient as long as it has the same function.

4 shows a circuit diagram of another embodiment of the DC-DC converter of the present invention. In the DC-DC converter 20 of FIG. 4, the same symbol as that of FIG. 1 is given the same symbol, and the description is abbreviate | omitted.

In FIG. 4, the DC-DC converter 20 includes an unstable multivibrator 21 in place of the unstable multivibrator 12 of the DC-DC converter 10 of FIG. 1. The unstable multivibrator 21 includes a transistor Q2, an impedance variable circuit 24, and a capacitor, and includes a first time constant circuit 22 for determining an OFF time of the transistor Q2, and a transistor Q3. And a second time constant circuit 23 composed of a resistor and a capacitor and determining the OFF time of the transistor Q3. The output voltage control circuit 11 is connected to the impedance variable circuit 24.

The DC-DC converter 20 configured as described above has only the DC-DC converter 10 that the impedance variable circuit 24 is a component of the first time constant circuit 22 that determines the OFF time of the transistor Q2. ) For this reason, in the DC-DC converter 20, the OFF time of the transistor Q1 changes with the change of the output voltage, and the ON time does not change. For this reason, the ratio of the OFF time to the sum of the ON time and the OFF time of the transistor Q1, that is, the duty ratio, is controlled so that the output voltage becomes a predetermined voltage. In this case, as opposed to the DC-DC converter 10, the impedance variable circuit 24 needs to be configured so that the resistance value increases when the output voltage is high.

5 shows a circuit diagram of still another embodiment of the DC-DC converter of the present invention.

In the DC-DC converter 30 of FIG. 5, the same symbol as that of FIG. 1 is attached | subjected, and the description is abbreviate | omitted.

In FIG. 5, the DC-DC converter 30, in addition to the configuration of the DC-DC converter 10 of FIG. 1, is an output terminal of the unstable multivibrator 12, that is, a transistor which is a collector and a switching element of the transistor Q3. A totem pole circuit 31 and a speed up circuit 32 connected in series are included between the bases of Q1.

In the DC-DC converter 30 configured as described above, the output of the unstable multivibrator 12 is input to the totem pole circuit 31. The totem pole circuit 31 augments the output of the unstable multivibrator 12. The output of the totem pole circuit 31 is input to the base of the transistor Q1 which is a switching element via the speed up circuit 32. As a result, the switching speed of the transistor Q1 increases. In this case, the switching speed means the speed required for the transistor Q1 to change from ON state to OFF state or from OFF state to ON state. As the switching speed of the transistor Q1 increases, the switching loss of the transistor Q1 decreases. Since the switching loss of the transistor Q1 becomes a major part of the loss of the DC-DC converter 30, the efficiency of the DC-DC converter 30 can be improved by lowering the switching loss of the transistor Q1. Can be.

6 shows a circuit diagram of still another embodiment of the DC-DC converter of the present invention.

In the DC-DC converter 40 of FIG. 6, the same code | symbol is attached | subjected to the part same or equivalent to FIG. 5, and the description is abbreviate | omitted.

In Fig. 6, the DC-DC converter 40 is a step-down DC-DC converter, which has a transistor Q1, a diode D1, in the configuration of the DC-DC converter 30 of Fig. 5, The speed-up circuit 30 is removed, and FETQ6, which is a switching element, FETQ7, which is a switching element for rectification, a bootstrap circuit 41, and a totem pole circuit 42 are included.

Here, FETQ6 and FETQ7 are N-channel MOSFETs. FETQ6 is connected between the DC power supply Vcc and the inductance element L1. The output of the totem pole circuit 31 is connected to the gate of FETQ6. The bootstrap circuit 41 composed of the diode D3 and the capacitor C4 is connected between the drain and the source of the FETQ6. The collector of the NPN transistor, which is the power supply connecting portion of the totem pole circuit 31, is connected to the bootstrap circuit 41, specifically, to the connection point of the diode D3 and the capacitor C4. The connection point of FETQ6 and inductance element L1 is grounded through FETQ7. The collector of the transistor Q2 of the unstable multivibrator 12 is connected to the gate of FETQ7 via the totem pole circuit 42. As a result, the first output of the unstable multivibrator 12 is output from the collector of transistor Q3, and the second output of the unstable multivibrator 12 is output from the collector of transistor Q2.

Here, in FIG. 7, the collector voltage v2c and the base voltage v2b of the transistor Q2 of the unstable multivibrator 12, the gate voltage v7g and the drain voltage v7d of the FETQ7, and the transistor Q3 The time change of the collector voltage v3c, the base voltage v3b, and the gate voltage v6g of FETQ6 is shown, and the operation | movement of the DC-DC converter 40 is demonstrated using it together.

First, in the DC-DC converter 40, the two transistors Q2 and Q3 of the unstable multivibrator 12 alternately turn ON and OFF. At this time, the collector voltage v2c and the base voltage v2b of the transistor Q2, the collector voltage v3c and the base voltage v3b of the transistor Q3 are as shown in FIG. Compared with the case of the DC-DC converter 10 shown in FIG. 2, the inclination is formed in the rising waveform of the collector voltages v2c and v3c. The inclination of this inclination is determined by the time constant by the resistor and the capacitor connected to the collectors of the transistors Q2 and Q3, respectively. That is, the larger the time constant, the larger the slope. In addition, the DC-DC converter 10 shown in FIG. 2 also does not have any inclination at all, and is only shown as if it is rising vertically because the inclination is very steep.

The collector voltage v3c of the first output transistor Q3 is input to the totem pole circuit 31. Since the power supply connecting portion of the totem pole circuit 31 is connected to the bootstrap circuit 41, the voltage is boosted by the DC power supply Vcc, and a voltage sufficiently large with respect to the source voltage of the FETQ6 is increased by the FETQ6 in the totem pole circuit 31. Is applied to the gate. As a result, the FETQ6 is turned on and off to operate as a switching element. At this time, since the inclination is formed in the rising waveform of the collector voltage v3c of the transistor Q3, the rising waveform of the voltage v6g applied to the gate of the FETQ6 also has the inclination as shown in FIG. For this reason, it takes some time until the gate voltage v6g of FETQ6 reaches the threshold which turns on FETQ6. As a result, as shown in Fig. 7, dead time t1 occurs from the transistor Q7 to OFF until the FETQ6 is turned on.

On the other hand, the collector voltage v2c of the transistor Q2 which is the second output is input to the totem pole circuit 42. The augmented second output from the totem pole circuit 42 is applied to the gate of FETQ7. As a result, the FETQ7 is turned ON and OFF. At this time, since a slope is formed in the rising waveform of the collector voltage v2c of the transistor Q2, the rising waveform of the voltage v7g applied to the gate of the FETQ7 also has a slope as shown in FIG. For this reason, it takes some time until the gate voltage v7g of FETQ7 reaches the threshold at which FETQ7 is turned on. As a result, as shown in Fig. 7, the dead time t2 occurs from the transistor Q6 being turned off until the FETQ7 is turned on.

In this way, the FETQ6 and the FETQ7 are turned on and off alternately with the dead time t1, t2 at which both are simultaneously turned off. The dead time t1 and t2 are created by forming a slope in the rising waveforms of the collector voltages v2c and v3c of the transistors Q2 and Q3. This is to prevent the short circuit through the FETQ6 and FETQ7.

In this way, when FETQ6 is ON, FETQ7 is OFF, so current flows from the DC power supply Vcc to the output terminal Pout through the FETQ6 and the inductance element L1. Therefore, as shown in Fig. 7, when the FETQ6 is ON, the drain voltage v7d of the FETQ7, that is, the source voltage of the FETQ6, becomes almost the same voltage as the DC power supply Vcc.

On the other hand, when FETQ6 is OFF, FETQ7 turns ON, so that current flows through the FETQ7 and the inductance element L1 through the FETQ7 and the inductance element L1 due to the excitation energy accumulated in the inductance element L1. . In other words, the FETQ7 operates as a synchronous rectifying element that flows current in one direction in synchronism with switching of the FETQ6. For this reason, as shown in Fig. 7, when the FETQ6 is OFF, the source voltage of the FETQ6, that is, the drain voltage v7d of the FETQ7 becomes a negative value slightly lower than the ground voltage.

Also, in the dead time t1 from when FETQ6 is turned OFF to FETQ7 is turned on, and in dead time t2 from when FETQ7 is turned OFF to FETQ6 is turned ON, a current flows through the FETQ7 to the inductance element L1. Since the MOSFET FETQ7 has a body diode, a current flows from the ground toward the output terminal Pout. When FETQ7 is ON and dead time (t1, t2), the value of the drain voltage (v7d) of FETQ7 changes, which is the case where the current passes through the body diode compared to the case where the current passes through FETQ7 in the ON state. This voltage drop is large.

In the DC-DC converter 40 of the present invention configured as described above, one of the two outputs originally possessed by the unstable multivibrator 12 is used as the first output and used for switching the FETQ6 which is the switching element. The synchronous rectification circuit is configured by using two outputs for switching the FETQ7, which is a switching element for rectification. For this reason, since it is not necessary to use expensive control IC etc. for control of a rectifying switch element, the synchronous rectification type DC-DC converter can be implemented at low cost. In addition, since a space for mounting a control IC or the like is not required, miniaturization of a circuit board and, moreover, the DC-DC converter itself can be realized. Of course, it is also possible to realize a low loss characteristic of the synchronous rectification circuit.

8 shows a circuit diagram of still another embodiment of the DC-DC converter of the present invention. In the DC-DC converter 50 of FIG. 8, the same symbol as that of FIG. 6 is given the same symbol, and the description is abbreviate | omitted.

In FIG. 8, the DC-DC converter 50 removes the bootstrap circuit 41 from the DC-DC converter 40 of FIG. 6, installs FETQ8, which is a P-channel MOSFET, in place of FETQ6, and also unstable multi A logic inversion circuit 51 is included between the first output of the vibrator 12 and the totem pole circuit 31. The collector of the NPN transistor, which is the power supply connecting portion of the totem pole circuit 31, is connected to the DC power supply Vcc.

In the DC-DC converter 50, since the switching element is replaced with FETQ8, which is a P-channel MOSFET, the gate voltage of FETQ8 does not need to be higher than the source voltage, so that the bootstrap circuit 41 is not necessary. Instead, since the logic of ON / OFF with respect to the signal applied to the gate of FETQ8 is inverted with FETQ6, a logic inversion circuit 51 for inverting the logic of the first output is required.

Also in the DC-DC converter 50 configured as described above, the operation is performed in almost the same manner as in the case of the DC-DC converter 40 to achieve the same effect.

In the above embodiments, the output voltage is controlled by changing the time constant of either the first time constant circuit or the second time constant circuit. However, for example, the time constant of the first time constant circuit is greatly increased. The output voltage can be controlled by changing both the time constants of the first and second time constant circuits, for example, by reducing the time constant of the second time constant circuit, and achieving the same effect. Further, by changing both time constants, the total time of the ON time and the OFF time of the switching element can be made substantially constant, that is, the output voltage can be controlled to be almost constant.

In addition, in each of the above embodiments, the configuration using the unstable multivibrator in the step-up and step-down DC-DC converter circuits has been described. As long as the DC voltage is input and output as a DC voltage, any circuit configuration such as an inverted type may be used, and the same effects as in the case of the boost type and the step-down type are achieved.

In the above embodiments, the DC-DC converter circuit including the inductance element has been described. However, the DC-DC converter circuit without the inductance element such as a charge pump circuit may be used. To achieve.

9 shows a perspective view of one embodiment of an electronic device of the invention. In Fig. 9, the printer 60, which is one of the electronic devices, uses the DC-DC converter 10 of the present invention as part of the power supply circuit.

As described above, by using the DC-DC converter 10 of the present invention, the switching power supply circuit can be downsized and reduced in cost, so that the printer 60 itself can be downsized and lower in price.

In the printer 60 shown in Fig. 9, the DC-DC converter 10 shown in Fig. 1 is used, but the DC-DC converters 20, 30, 40, shown in Figs. 4, 5, 6, and 8, 50) can be used, and the same effect is achieved.

In addition, the electronic device of the present invention is not limited to a printer, and includes all electronic devices that require a DC power source having a stable voltage such as a notebook computer and a portable information device.

According to the DC-DC converter of the present invention, the switching element is controlled by an unstable multivibrator including a first time constant circuit for setting the OFF time and a second time constant circuit for setting the ON time, and according to the output voltage. By controlling the output voltage by changing the time constant of at least one of the first and second time constant circuits, the circuit configuration can be simplified, and the size and the cost can be reduced.

In addition, by constituting a synchronous rectification circuit for controlling the switching element and the rectifying switch element, respectively, with the first and second outputs inverting each other of the unstable multivibrator, it is possible to achieve miniaturization, low cost, and low loss.

In addition, according to the electronic device of the present invention, it is possible to reduce the size and the price by using the DC-DC converter of the present invention.

Claims (10)

An unstable multivibrator including a first time constant circuit for setting an OFF time of an output and a second time constant circuit for setting an ON time, and controlled by an output of the unstable multivibrator A DC-DC converter, comprising a switching element and a rectifying element, wherein the DC-DC converter changes the voltage value of the input voltage to an output voltage. An output voltage control circuit for controlling the output voltage by changing at least one of the ON time and the OFF time of the switching element by changing the time constant of at least one of the first and second time constant circuits according to the output voltage. DC-DC converter comprising a. The DC-DC converter according to claim 1, wherein an inductance element for energy charging and discharging is formed in series with the switching element. The DC-DC converter according to claim 1 or 2, wherein at least one of the first and second time constant circuits includes an impedance variable circuit for changing the time constant. The DC-DC converter according to any one of claims 1 to 3, wherein a totem pole circuit is formed between the output of said unstable multivibrator and said switching element. 5. A first output according to any one of claims 1 to 4, wherein the rectifying element comprises a rectifying switch element, and wherein the unstable multivibrator controls ON / OFF of the switching element, and with respect to the first output. And a second output for inverting and controlling the rectifying switch element to be turned on when the switching element is turned off. 6. The DC-DC according to claim 5, wherein a slope is formed in the rising waveforms of the first and second outputs so that the switching elements and the rectifying switch elements are alternately turned on with a period in which the switching elements are simultaneously turned off. Converter. The DC-DC converter according to claim 5 or 6, wherein a totem pole circuit is formed between the output of the unstable multivibrator and the rectifying switch element. The DC-DC converter according to any one of claims 5 to 7, wherein the rectifying switch element is a MOSFET (metal oxide film semiconductor field effect transistor). The DC-DC converter according to any one of claims 1 to 8, wherein the switching element is a MOSFET. An electronic device comprising the DC-DC converter according to any one of claims 1 to 9.