JP2003174768A - Dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter wherein circuits are protected and downsizing is facilitated. <P>SOLUTION: The DC-DC converter is provided with a switching element and is so designed as to increase or decrease a direct-current voltage inputted by turning on and off the switching element and output the voltage. Change in voltage or current at a point where the voltage or current varies due to the operation of the DC-DC converter is detected. Turn-on/off of the switching element is so controlled that the detected change in voltage or current delineates a reference curve of change. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a DC-DC converter.

[0002]

2. Description of the Related Art Conventionally, a DC-device has been provided with a switching element, and by turning the switching element on and off, an input DC voltage is stepped up or down and output.
DC converters are known.

FIG. 1 is a schematic diagram of a conventional DC-DC converter.

FIG. 1 shows a step-up DC-DC converter 1 and a battery power supply 2.

The DC-DC converter 1 shown in FIG. 1 has input terminals 1a and 1b and output terminals 1c and 1d.
This DC-DC converter 1 consists of a chip LSI
Is a switching unit 13 including an N-type MOSFET 13a and a diode 13b, and a capacitor 1 connected to both ends of the switching unit 13 via a diode 12.
9 and a resistor 20 and a resistor 21 connected in series at both ends of the capacitor 19. A switching unit 13 is connected to the anode side of the diode 12 and a capacitor 19 is connected to the cathode side.

The DC-DC converter 1 also includes
Turning on the N-type MOSFET 13a of the switching unit 13,
PWM (Pulse Width Mo
The control circuit 15 is also provided. Here, the positive and negative sides of the battery power source 2 are connected to the input terminals 1a and 1b of the DC-DC converter 1, and the battery voltage Vi is applied between the input terminals 1a and 1b. On the other hand, between the positive side and the negative side, between the output terminals 1c and 1d to which the load circuit (not shown) is connected,
The voltage Vo is output.

The DC-DC converter 1 also includes
The inductor 11 connected between the input terminal 1a and the switching unit 13, and the N-type MOSFETs 13a and P
A resistor 14 connected to the WM control circuit 15 is also provided. The resistor 14 and the diode 13b are N-type M
This is for protecting the OSFET 13a. Also,
The resistors 20 and 21 are for dividing the output voltage Vo, and the capacitor 19 is for stabilizing the output voltage Vo.

Further, the DC-DC converter 1 includes a reference power source VREF17 for outputting a reference voltage and a resistor 2.
0 and the voltage determined by the resistor 21 and the reference power supply VREF
There is also provided a differential amplifier 18 that inputs both of the reference voltages output from 17 and outputs the comparison result to the PWM control circuit 15, and a soft start circuit 16 connected to the PWM control circuit 15. This soft start circuit 16
, A PWM control circuit 15 outputs a control signal for outputting a pulse waveform whose duty ratio rises in a predetermined pattern. This soft start circuit 16 causes the DC-DC converter 1 to start up. Overshoot is prevented.

FIG. 2 is a diagram showing how the input voltage is boosted by the soft start circuit while drawing an ideal boosting curve.

FIG. 2 shows an ideal rising portion of the boost curve.

In the DC-DC converter 1 shown in FIG.
The battery voltage Vi is boosted to a voltage Vo (Vi <Vo) while drawing the boosting curve shown in FIG. 2 and output.

In recent years, electronic devices such as cameras have been
There is a demand for ever-smaller size, and in order to meet this demand, DC-DC is achieved by increasing the switching frequency.
The inductors, capacitors, and the like, which are the constituent elements of the converter, have been downsized, and thus the DC-DC converter has been downsized.

[0013]

Here, in order to further reduce the size of the DC-DC converter, it is conceivable to cut off the margin for withstanding voltage in addition to increasing the switching frequency.

However, the soft start circuit described above is
Although designed according to the miniaturization of the C-DC converter, the PWM control circuit also outputs a predetermined control signal so that the PWM control circuit outputs a pulse waveform whose duty ratio rises in a predetermined pattern. Output to.

Therefore, in this DC-DC converter, if the margin for withstand voltage is removed from the inductor, the capacitor, etc., a sudden change in voltage or current occurs due to the influence of the connected load circuit. In such a case, the occurrence of overshoot cannot be prevented, and the situation may occur in which the inductor or the capacitor, whose margin for withstanding voltage is removed, is heated or damaged.

FIGS. 3 and 4 show that due to a sudden change in voltage or current on the DC-DC converter circuit,
FIG. 3 is a diagram showing a state in which boosting is performed by following a locus different from the ideal boosting curve shown in FIG. 2.

FIG. 3 shows a state in which the voltage fluctuates in the middle of boosting, and FIG. 4 shows a state in which the boosting pace suddenly rises from the middle.

Since the soft start circuit is designed under the condition that the load of the load circuit is constant and is known in advance, if the load is constant as ideal, it is ideal as shown in FIG. However, if the load changes, the boosting curve may deviate significantly from the ideal curve as shown in FIG. 3 or 4. In that case, there is a risk that the inductor and the capacitor will generate heat and be damaged.

In view of the above-mentioned circumstances, the present invention is a DC-DC system capable of further miniaturization while protecting the circuit.
The purpose is to provide a converter.

[0020]

A DC-DC converter of the present invention for achieving the above object comprises a switching element, and by turning on / off the switching element, an input DC voltage is stepped up or stepped down. In a DC-DC converter that outputs the
A detector for detecting a voltage change or a current change at a point where the voltage or current changes due to the operation of the C-DC converter, and a reference change curve serving as a reference for the voltage change or the current change detected by the detector are stored. And a control unit for controlling ON / OFF of the switching element so that the voltage change or the current change detected by the detection unit draws a change curve along the reference change curve. Characterize.

In the DC-DC converter of the present invention, DC
The voltage change or the current change on the DC converter circuit is detected by the detection unit, and the switching element is turned on and off so that the voltage change or the current change follows the reference change curve. That is, in the DC-DC converter of the present invention, the actual voltage change or current change obtained by the detection unit is on the reference change curve representing the transition of the differential coefficient of an ideal step-up or step-down curve that does not burden the circuit. It is determined whether or not it is followed, and the control unit controls the switching element so that the actual voltage change or current change obtained by the detection unit follows this reference change curve. As a result, in the DC-DC converter of the present invention, the input voltage is stepped up or stepped down as little as possible while coping with the sudden voltage change or current change. Therefore, D of the present invention
According to the C-DC converter, it is possible to further reduce the size while protecting the circuit.

Here, it is preferable that the detection unit of the DC-DC converter of the present invention detects a voltage change on the input side.

In this way, for example, the temporary voltage drop of the battery voltage due to the occurrence of the inrush current can be accurately grasped, so that the accuracy of the response by the control unit can be further increased.

It is also a preferred embodiment that the detection section of the DC-DC converter of the present invention detects a voltage change on the output side.

In this way, for example, this DC-D
Since it is possible to accurately grasp a sudden voltage change on the output side due to a short circuit of the load circuit connected to the output side of the C converter, it is possible to further improve the accuracy of response by the control unit.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below.

FIG. 5 is a schematic diagram of the first embodiment of the DC-DC converter of the present invention.

FIG. 5 shows a DC-DC converter 10 for boosting and a battery power source 2. It should be noted that those shown in FIG. 5 and of the same kind as those shown in FIG. 1 are given the same reference numerals as those given in FIG.

The DC-DC converter 10 shown in FIG.
Input terminals 10a, 10b and output terminals 10c, 10d
The DC-DC converter 10 includes a switching unit 113 including an N-type MOSFET 113a and a diode 113b, and a resistor 120 connected in series with the switching unit 113. . Further, in the DC-DC converter 10, a capacitor 119 is also connected via a diode 112 to both ends of a switching unit 113 and a resistor 120 which are connected in series. A switching unit 113 is connected to the anode side of the diode 112, and a capacitor 119 is connected to the cathode side. Also,
The DC-DC converter 10 also includes a switching control circuit 115 that controls ON / OFF of the N-type MOSFET 113a that is a switching element. Here, the positive side of the battery power supply 2 is connected to the input terminal 10a of the DC-DC converter 10, the negative side of the battery power supply 2 is connected to the input terminal 10b, and the battery is connected between the input terminals 10a and 10b. The voltage Vi is applied. On the other hand, the output terminal 10c is the positive side, the output terminal 10d
Is the minus side, and between the output terminals 10c and 10d,
The voltage Vo is output.

The DC-DC converter 10 also includes an inductor 111 connected between the input terminal 10a and the switching section 113. A resistor 114 is provided between the N-type MOSFET 113a and the switching control circuit 115.
And the diode 113b are the N-type MOSFET 113
It is for protecting a. The resistor 120 is for dividing the voltage applied across the switching unit 113 and the resistor 120 connected in series.
The capacitor 119 is for stabilizing the output voltage Vo.

Further, the DC-DC converter 10 shown in FIG. 5 is also provided with an MPU 22. This MPU 2
2 is three A / D conversion circuits (A / Di221, A / D
m222, A / Do 223), CPU 224, RAM2
25 and a ROM 226, which are connected to the switching control circuit 115. The inductor, the capacitor and the like provided in the DC-DC converter 10 are miniaturized by increasing the frequency of the switching element and cutting off the margin for withstanding voltage. Also,
For convenience of explanation, the MPU 22 is shown in an enlarged scale. However, the MPU 22 is smaller than the DC-DC converter in size due to the size reduction of the inductor and the capacitor.
The effect of adding to the DC converter on the outer dimensions of the DC-DC converter is small.

FIG. 6 is a diagram showing a basic switching waveform input to the switching unit of the DC-DC converter of this embodiment.

The basic switching waveform C shown in FIG. 6 represents the on / off timing for the N-type MOSFET 113a which is a switching element provided in the DC-DC converter 10, and is shown in addition to the basic switching waveform C. It is calculated by using two kinds of waveforms (basic boosting waveform A and triangular waveform B).

The basic boosting waveform A is a waveform in which a rising curve is gently drawn from the left side, and the rising portion of the basic boosting waveform A is shown in FIG. Further, the triangular wave waveform B is a sawtooth waveform of a certain size.

As shown in FIG. 3, the basic switching waveform C becomes'H 'level when the basic boosting waveform A is larger than the triangular waveform B, and the basic boosting waveform A is the triangular waveform B.
The pulse waveform has an “L” level when it is smaller than the above, which is narrow at the time of starting the DC-DC converter 10 and gradually widens to a predetermined maximum pulse width with the passage of time.

The basic boost waveform A and the triangular waveform B are DC-
It is stored in the ROM 226 of the DC converter 10,
The CPU 224 outputs the basic boost waveform A and the triangular waveform B to RA.
The basic switching waveform C is calculated on M225 and output to the switching control circuit 115. When the basic switching waveform C is input to the switching control circuit 115, a current flows through the path of the inductor 111 and the N-type MOSFET 113a when the N-type MOSFET 113a is on, and a counter electromotive force generated in the inductor 111 when the N-type MOSFET 113a is off. Is added to the input voltage Vi and a current flows through the path of the diode 112 and the capacitor 119, and the boosted voltage Vo (Vo> Vi) is output between the output terminals 10c and 10d.

The ROM 226 shown in FIG. 5 stores not only the basic boost waveform A and the triangular waveform B, but also a reference change curve representing changes in the voltage change or the current change of the basic boost waveform A.

FIG. 7 is a diagram showing a reference change curve stored in the ROM of the DC-DC converter of this embodiment.

In FIG. 7, the basic boost waveform A, which is a boost curve drawn when a voltage change or a current change follows this reference change curve, is also shown by a dotted line.

In the DC-DC converter 10 of this embodiment, boosting is performed as follows so that the actual voltage change or current change detected by the MPU 22 follows this reference change curve.

First, when the DC-DC converter 10 is activated, the CPU 224 calculates a basic switching waveform based on the basic boosting waveform A and the triangular waveform B waveform stored in the ROM 226, and the N is passed through the switching control circuit 115. Type MOSFET 113a is driven, and DC-
The voltage change or current change at each node A, B, C on the DC converter circuit is detected by A / Di 221 and A / Dm.
It is converted into a digital value based on the voltage value obtained in 222 and A / Do 223. These digital values are compared with a reference value that draws a reference change curve, and if the digital value that represents the actual voltage change or current change exceeds the target value, for example, it should be performed gradually gradually. The CPU 22 gives an instruction to step on the pulse width expansion of
4 to the switching control circuit 115.

FIG. 8 is an operation flowchart of the MPU included in the DC-DC converter.

First, the DC-DC converter 1 shown in FIG.
When 0 is activated, three A / D conversion circuits (A / Di 221, A / Dm 222, A / Do 2) are started in step S1.
23) The registers provided in each are reset. The A / Di 221 is provided with registers R11 and R12 for storing a digital value obtained by A / D converting the voltage obtained at the node A.
The m222 is provided with registers R21 and R22 for storing the digital value obtained by dividing the voltage obtained at the node B by a predetermined value and A / D converting the divided value. , A / Do 223 are provided with registers R31 and R32 for storing the digital value obtained by A / D converting the voltage obtained at the node C.

In step S2, the voltage of the node A on the DC-DC converter circuit is set to the voltage A supplied to the MPU 22.
/ Di221 detects. After that, step S
Go to 3.

In step S3, the detected voltage value is A
A / R converted register R provided in A / Di 221
It is stored in the register R12 of 11 and R12. Then, it progresses to step S4.

In steps S4 and S5, D
The voltage of the node B on the C-DC converter circuit is A / Dm
At 222, the detected voltage value is divided by a predetermined resistance value, and the calculated current value is A / D converted to A / Dm.
It is stored in the register R22 of the registers R21 and R22 provided in the 222. afterwards. Go to step S6.

Also in step S6 and step S7, D
The voltage of the node C on the C-DC converter circuit is A / Do.
The voltage value detected in A.223 and A / D converted is A / Do.
It is stored in the register R32 of the registers R31 and R32 provided in the H.223. After that, the process proceeds to step S8, and it is determined whether or not data is stored in both of the two registers provided in each of the three A / D conversion circuits.

If it is determined in step S8 that neither of them has been stored, the process proceeds to step S9 and 3
The registers provided in each of the two A / D conversion circuits are respectively shifted, and for example, the register R1 of the registers R11 and R12 provided in the A / Di 221 is used.
If data is stored only in 2, this register R
The data stored in 12 will be shifted to the register R11. Then, it progresses to step S12.

On the other hand, when it is determined in step S8 that both are stored, the process proceeds to step S10, and the CPU 224 calculates the voltage change or the current change based on the data stored in both registers. Then, in step S11, the reference value recorded in the ROM 226 is read, and in step S12, the voltage change or current change is compared with the reference value. In step S13, the CPU 224 issues an instruction reflecting the comparison result to the switching control circuit 115.
Issued to. Then, it progresses to step S14.

In step S14, the registers are shifted. Thereby, for example, the data stored in the register R12 is written in the register R11 provided in the A / Di 221. Then, step S1
Go to 5.

In step S15, it is determined whether or not the DC-DC converter 10 is powered off.
If it is turned off, this program is terminated, and if it is not turned off, the process returns to step S2.

In the present embodiment described above, DC-DC
It is determined whether or not the voltage change or the current change of the node on the converter circuit follows the reference change curve. If not, the MPU 22 controls the switching elements to be turned on and off. Therefore, according to the present embodiment, it is possible to further reduce the size while protecting the circuit.

Next, a second embodiment of the DC-DC converter of the present invention will be described.

FIG. 9 is a schematic diagram of a second embodiment of the DC-DC converter of the present invention.

FIG. 9 shows the step-down DC-DC converter 50 and the battery power source 2. It should be noted that those shown in FIG. 9 and of the same kind as those shown in FIG. 5 are given the same reference numerals as the reference numerals given in FIG.

The DC-DC converter 50 shown in FIG.
This DC-DC converter 5 consists of a chip LSI
0 has input terminals 50a and 50b and an output terminal 50.
c and 50d are provided. Further, the DC-DC converter 50 includes a first switching unit 53 including an N-type MOSFET 53a and a diode 53b, and a resistor 57 connected in series with the first switching unit 53.
Is also provided. Further, in the DC-DC converter 50, a capacitor 59 also has an inductor 51 on both ends of the first switching unit 13 and the resistor 57 which are connected in series.
Connected through. Here, the input terminals 50a, 5
The positive and negative sides of the battery power supply 2 are connected to 0b, and the battery voltage Vi is applied between the input terminals 50a and 50b. On the other hand, the output terminal 50c is on the positive side, the output terminal 50d is on the negative side, and the output terminal 5
The voltage Vo is output between 0c and 50d.

Further, in the DC-DC converter 50, the second switching section 63 including the P-type MOSFET 63a and the diode 63b, which is connected between the input terminal 50a and the first switching section 53, and the first
A synchronous rectification DC / DC converter 54 to which the switching unit 53 and the second switching unit 63 are connected is also provided. Descriptions of the other elements provided in FIG. 9 are omitted because they overlap with the description in FIG. The inductor, the capacitor, and the like provided in the DC-DC converter 50 are also downsized by increasing the frequency of the switching element and removing the margin for withstanding voltage. Further, for convenience of explanation, MPU2
Although FIG. 2 is illustrated in an enlarged manner, compared with the miniaturization of the outer size of the DC-DC converter by miniaturization of the inductor and the capacitor, the addition of the MPU22 to the DC-DC converter can reduce the outer size of the DC-DC converter. The impact is slight.

Here, the step-down action in the DC-DC converter 50 of this embodiment will be described.

In the synchronous rectification DC / DC converter 54 provided in the DC-DC converter 50, the MPU 22
When the pulse waveform input from is “H”, P-type MO
When the SFET 63a is off and the n-type MOSFET 53a is on, and when the pulse waveform input from the MPU 22 is'L ', control is performed so that the p-type MOSFET 63a is on and the n-type MOSFET 53a is on. P-type MOSFET 63a is on and N-type MOSFET
When 53a is off, the battery power source 2 is connected to the P-type MOSFET.
63a, the inductor 51, and the capacitor 59, a current flows, and then the P-type MOSFET 63a is turned off and the N-type M
When the OSFET 53a is on, a current flows through the path of the inductor 51, the capacitor 59, and the N-type MOSFET 53a, and the output voltage V is reduced between the output terminals 50c and 50d.
o (Vo <Vi) occurs.

That is, in the DC-DC converter 50,
When the first switching unit 53 is turned on, the second switching unit 63 is turned off, and when the first switching unit 53 is turned off, the synchronous rectification DC / DC converter 54 is turned on so that the second switching unit 63 is turned on. It operates to reduce the input voltage. By gradually increasing the ON time of the first switching unit 53, the voltage is gradually lowered.

Hereinafter, a pulse waveform (not shown) which is narrow at the time of starting the DC-DC converter 50 and gradually widens to a predetermined maximum pulse width with the passage of time is synchronized from the MPU 22 to the DC-DC converter 50 of this embodiment. Rectified DC
A case where the basic switching waveform is input to the / DC converter 54 will be described.

In the DC-DC converter 50, when the switching waveform is input, the actual voltage change or current change detected by the CPU 224 is changed to the ROM 22.
It is determined whether or not the reference change curve stored in 6 is being followed. If the actual current change or voltage change does not follow the reference change curve, for example, the CPU 224 issues an instruction, for example, to temporarily step the pulse width expansion that would otherwise be gradually performed. It is output to the DC converter 54.

The operation of the MPU 22 in this embodiment is the same as that in the first embodiment, and will not be repeated.

Also in the second embodiment of the DC-DC converter of the present invention described above, it is judged whether the voltage change or the current change of the node on the DC-DC converter circuit follows the reference change curve, and the trace is made. If not, the CPU 224 controls the on / off of the switching element.

Therefore, according to the second embodiment of the present invention, it is possible to further reduce the size while protecting the circuit.

In the first and second embodiments, the battery power source is described as an example of the DC power supply source, but the present invention is not limited to this, and the DC power is supplied from the AC-DC converter. However, the effect of the present invention cannot be denied.

[0067]

As described above, the DC-D of the present invention
According to the C converter, it is possible to further reduce the size while protecting the circuit.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a conventional DC-DC converter.

FIG. 2 is a diagram showing how the input voltage is boosted by the soft start circuit while drawing an ideal boost curve.

FIG. 3 is a diagram showing a state in which boosting draws a locus different from an ideal boosting curve as shown in FIG. 2 due to a rapid change in voltage or current.

FIG. 4 is a diagram showing a state in which boosting draws a locus different from an ideal boosting curve as shown in FIG. 2 due to a rapid change in voltage or current.

FIG. 5 is a schematic diagram of a first embodiment of a DC-DC converter of the present invention.

FIG. 6 is a diagram showing a basic switching waveform input to the switching unit of the DC-DC converter of this embodiment.

FIG. 7 is a diagram showing a reference change curve stored in a ROM of the DC-DC converter of the present embodiment.

FIG. 8 is an MPU provided in a DC-DC converter.
3 is an operation flowchart of FIG.

FIG. 9 is a schematic diagram of a second embodiment of a DC-DC converter of the present invention.

[Explanation of symbols]

1, 10, 50 DC-DC converters 1a, 1b, 10a, 10b, 50a, 50b Input terminals 1c, 1d, 10c, 10d, 50c, 50d Output terminals 2 Battery power supplies 11, 51, 111 Inductors 12, 112, 13b, 113b Diode 13,113 Switching part 13a, 113a N-type MOSFET 14, 20, 21, 55, 56, 57, 114, 120
Resistor 15 PWM (Pulse Width Module)
control circuit 16 soft start circuit 17 reference power supply VREF 18 differential amplifier 19, 59, 119 capacitor 22 MPU 221 A / Di 222 A / Dm 223 A / Do 224 CPU 225 RAM 226 ROM 53 first switching unit 53a N-type MOSFET 53b, 63b Diode 54 Synchronous rectification DC / DC converter 63 Second switching unit 63a P-type MOSFET

Claims (3)

[Claims] 1. A DC-DC converter comprising a switching element, and turning on / off the switching element to step up or step down an input DC voltage and output the DC voltage. A detection unit that detects a voltage change or a current change at a point where a voltage or a current changes due to an operation; A DC-controlling unit for controlling ON / OFF of the switching element so that a voltage change or a current change detected by the detection unit draws a change curve along the reference change curve. DC converter. 2. The DC-DC converter according to claim 1, wherein the detection unit detects a voltage change of an input of the DC-DC converter. 3. The DC-DC converter according to claim 1, wherein the detection unit detects a voltage change in the output of the DC-DC converter.