JPH11187662A - Dc-to-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency of a transformer, to reduce a circuit scale and to reduce cost. SOLUTION: A circuit subsequent to a secondary of a transformer is constituted of a first system made of a transformer 9A and rectifying/smoothing means (10A, 11A and 12A) and a second system made of a transformer 9b and rectifying/smoothing means (10B, 11B and 12B). The output voltage of the two systems are added, and final output voltage is obtained. When input voltage is not more than a prescribed value, the voltage whose duty ratio is 100% is applied to the first system and voltage whose duty ratio is variably controlled is applied to the second system. When input voltage is larger than a prescribed value, voltage whose duty ratio is variably controlled is applied to the first system and applied voltage to the second system is set to zero. Since voltage applied to the transformers is applied in the form of the duty ratio being larger than in a former case, a loss in the transformer is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a D (Digital-to-Digital) circuit in which the loss in a transformer is reduced even when the input voltage fluctuates greatly.
It relates to a C-DC converter.

[0002]

2. Description of the Related Art FIG. 9 is a diagram showing a first conventional example of a DC-DC converter. 9, 1 is an input AC power supply, 2 is a rectifier circuit, 6 is a smoothing capacitor, 8 is an inverter, 9 is a transformer, 10 is a rectifier circuit, 11 is a smoothing inductance, 12 is a smoothing capacitor, and 13 and 14 are. Reference numeral 15 denotes a current detector, 16 denotes a load, and 17 denotes a controller.

The AC of an input AC power supply 1 is rectified by a rectifier circuit 2 and applied to an inverter 8. The inverter 8 is controlled by a signal from the controller 17, converts an applied direct current into an alternating current, and sends the alternating current to the transformer 9. Transformer 9
Has the function of insulating the input side and the output side in addition to the voltage transforming action. The output of the transformer 9 is rectified by a rectifier circuit 10, smoothed by a smoothing inductance 11 and a smoothing capacitor 12, and supplied to a load 16. The resistors 13 and 14 are voltage-dividing resistors for detecting an output voltage, divide the smoothed DC voltage,
Tell The current detector 15 is for detecting an output current, and a detection signal is also transmitted to the controller 17.

The current detection by the current detector 15 is performed to monitor the output current so as not to exceed a predetermined value. If the predetermined value is reached, the control signal from the controller 17 to the inverter 8 is adjusted,
It is prevented from increasing any further. The detection of the output voltage by the resistors 13 and 14 is performed to control the output voltage to a predetermined value. The detection voltage is the controller 1
The control signal is compared with the set voltage in 7, and a control signal to the inverter 8 is generated based on the comparison result. The control signal to the inverter is a ratio (showing how long the switching element is on in the period of the alternating current generated as an output (this is determined because the output frequency is determined)). Duty ratio). Therefore, when the output voltage is higher than a predetermined value, the ratio of the time during which the switching element of the inverter 8 is on is shortened (duty ratio is reduced), and when the output voltage is lower than the predetermined value, the ratio of the on time is increased (duty ratio). The control signal is adjusted so that

FIG. 7 is a diagram showing duty ratio control in a conventional DC-DC converter. This figure shows how to change the duty ratio when the input voltage fluctuates while trying to obtain a constant voltage as the output voltage. The vertical axis represents the input voltage (fluctuating voltage) to the inverter 8, and the horizontal axis represents the switching duty ratio of the inverter 8. Curve A is a curve representing the relationship between the input voltage and the duty ratio.
B and C are points on the curve. V _A , V _B , V
_C, respectively points A, B, the input voltage in the case of C, D _A, D _B, D _C, respectively points A, B, a duty ratio in the case of C.

Here, the output voltage to be obtained is V
_C is a rectified voltage. Thus, the duty ratio D _C when the input voltage V _C is 100% (that of the target point C in FIG. 7). When the input voltage of the inverter is higher than V _C , the output voltage is increased if the on-time ratio (duty ratio) of the switching element of the inverter remains the same as that of V _C (100%) (100%). Thus, as the input voltage is higher than V _C, the duty ratio is gradually decreased.

FIG. 8 is a diagram showing a specific example of the conventional duty ratio control, in which the vertical axis represents the voltage applied to the transformer and the horizontal axis represents time. 8 (A), 8 (B), 8 (C)
8 is a diagram showing switching at points A, B, and C in FIG. 7, respectively. T represents a half cycle of AC, and T _ON represents a time during which the switching element is on in the half cycle. Therefore, T _ON / T is the duty ratio.

FIG. 8C shows switching when the input voltage is V _C. At this time, the switching is on for the entire period of T (T = T _ON, duty ratio D _C = 100).
%). Although FIG. 8 (B) is a switching when the input voltage is V _B, since V _B is greater than V _C, the duty ratio D _B is smaller than D _C, the on-time is shortened. Although FIG. 8 (A) is the switching when the input voltage V _A, since the V _A further is greater than V _B, the duty ratio D
_A is still smaller than D _B, on-time is further shortened.

Returning to FIG. 9, current flows in the forward and reverse directions through the transformer 9 in the DC-DC converter for a time determined by the duty ratio as shown in FIG. It is known that the efficiency of the transformer becomes worse as the duty ratio becomes smaller. If the input voltage does not fluctuate much, the winding ratio of the transformer is determined based on the voltage ratio with the desired output voltage, and the duty ratio can be controlled at a value close to 100%. Therefore, in such a case, the efficiency of the transformer can be increased.

However, when the input voltage fluctuates greatly, such measures cannot be taken. Therefore, the efficiency of the transformer is inevitably reduced. Therefore, in such a case, a circuit in which a voltage converting circuit (a booster circuit or a step-down circuit) is inserted before or after the transformer to improve the efficiency of the transformer is considered. Next, it is shown.

FIG. 10 is a diagram showing a second conventional example of a DC-DC converter. The reference numerals correspond to those in FIG.
Is a current detector, 4 and 5 are resistors, and 7 is a step-down circuit. The current detector 3 is for detecting an input current, and the resistors 4 and 5 are voltage dividing resistors for detecting an input voltage.
When the current detector 3 detects that the input current has become excessive, the controller 17 takes measures to protect the DC-DC converter from overcurrent (for example, stop the control signal to the inverter 8).

The detection of the input voltage by the resistors 4 and 5 is performed to determine whether or not the step-down circuit 7 performs the step-down operation. Whether to perform the step-down operation is instructed by a signal from the controller 17. When the input voltage is large, the step-down circuit 7 performs a step-down operation. Then, the duty ratio of the inverter 8 becomes larger than when the voltage is not reduced, and the efficiency of the transformer 9 is much better than when the voltage is not reduced.

[0013] Conventional documents relating to DC-DC converters include, for example, JP-A-4-368644, JP-A-5-284744, and JP-A-5-336.
No. 749, JP-A-7-31144, and the like.

[0014]

In a DC-DC converter in which a step-down circuit or the like is inserted to maintain a high duty ratio to increase the efficiency of a transformer, the circuit scale is increased by the amount of the inserted circuit. In addition, there is a problem that the cost increases. An object of the present invention is to solve such a problem.

[0015]

According to the present invention, there is provided an inverter for converting a fluctuating input voltage into an alternating current by controlling a duty ratio, a transformer for transforming the alternating current, and a transformer for transforming the alternating current. Rectifying and smoothing means for rectifying and smoothing, voltage detecting means for detecting a DC output voltage, and a controller for controlling the duty ratio of the inverter based on a detection value from the voltage detecting means to make the DC output voltage a constant value. A DC-DC converter comprising: an inverter having a bridge configuration including first, second, and third arms; an input voltage detecting means for detecting an input voltage and inputting a detection signal to the controller; A first transformer to which an input voltage is applied through duty ratio control in the first and third arms, and rectifying and smoothing the output of the first transformer First rectifying and smoothing means, a second transformer to which an input voltage is applied through duty ratio control in the second and third arms, and a second rectifier for rectifying and smoothing the output of the second transformer. And a means for adding the output voltages of the first and second rectifying and smoothing means to obtain the DC output voltage, and applying the DC voltage to the first and second transformers according to the magnitude of the input voltage. The method of controlling the duty ratio of the applied voltage is made different.

The ratio of the output voltage from the first rectifying / smoothing means to the output voltage from the second rectifying / smoothing means in the DC output voltage varies according to the magnitude of the input voltage to the inverter. To do. For example, when the input voltage is equal to or less than a predetermined value, a duty ratio of 100
%, A voltage controlled by varying the duty ratio is applied to the second transformer, and when the input voltage is larger than the predetermined value, a voltage controlled by varying the duty ratio is applied to the first transformer. And the voltage applied to the second transformer is controlled to be zero.

In the above-described control, the duty ratio control in the third arm of the inverter is the same as the larger duty ratio of the duty ratio control in the first and second arms performed simultaneously. It is performed at the duty ratio.

Such a DC-DC converter is used for obtaining a constant DC output voltage by using a generated voltage from a generator driven by an internal combustion engine of a vehicle as an input voltage. It is suitable as a converter.

(Summary of operation to be solved) In a DC-DC converter for obtaining a constant output voltage from a fluctuating input voltage, the duty ratio of an inverter is controlled, and the obtained AC is transformed by a transformer. Rectified and smoothed. Generally, the loss in the transformer increases as the duty ratio in the inverter decreases. DC-D of the present invention
In a C converter, two systems of a transformer and a rectifying and smoothing circuit following the transformer are provided, and their output voltages are added to obtain a final output voltage. If the input voltage is equal to or less than the predetermined value, the input voltage is applied to the first system as it is,
, A duty ratio controlled input voltage is applied.
If the input voltage is larger than the predetermined value, the input voltage controlled by the duty ratio is applied to the first system and is not applied to the second system. With this configuration, when viewed as a whole, the voltage applied to the transformer is applied with a duty ratio larger than that of the related art, so that the efficiency of the transformer is improved as compared with the related art.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a diagram showing a D according to the present invention.
It is a figure showing a C-DC converter. Reference numerals correspond to those in FIG. 10, 9A and 9B are transformers, 10A and 10B are rectifier circuits, 11A and 11B are smoothing inductances,
2A and 12B are smoothing capacitors. The parts having the same reference numerals as those in FIG. 10 perform the same operation, and thus the description thereof will be omitted.

The first difference from the conventional example shown in FIG. 10 is that the step-down circuit 7 is eliminated. The second difference is
The point is that the transformer and the rectifying / smoothing circuit following the inverter are divided into two systems, and the sum of their output voltages is used as the output voltage of the DC-DC converter. The third difference is that two systems of a transformer and a rectifying / smoothing circuit are provided.
The point is that a bridge having three sets (U, V, W) of arms is used as the inverter 8.

The input side of the transformer 9A is connected between the center connection point of the arm U and the center connection point of the arm W, and the input side of the transformer 9B is connected to the center connection point of the arm V and the arm W
Connected to the central connection point. Therefore, the transformer 9
The input voltage is applied to A during the period when both arms U and W are on, and the input voltage is applied to the transformer 9B during the period when both arms V and W are on. It is. These ON periods are times determined by duty ratio control.

FIG. 2 is a diagram showing an example of voltage application control to a transformer. Figure 2 (b) is the voltage applied to the inverter 8 indicates a voltage application control to the transformer 9A at the time of the V _K, FIG. 2 (b) shows the voltage application control to the transformer 9B in the same time. The duty ratio is assumed to be 100% in FIG. 2A and 50% in FIG. 2B. Thus, the voltage application control to the transformers 9A and 9B
Next, the reason why the two inverters 8 can perform the operations individually will be described.

FIG. 3 is a diagram showing a current path to the transformer and switching of the inverter. The reference numerals correspond to those in FIG. 1, and 8U1, 8U2, 8V1, 8V2, 8W1, 8
W2 is a transistor constituting the inverter 8. FIG. 3A shows a path when a positive voltage is applied to the transformers 9A and 9B, and FIG. 3B shows a path when a negative voltage is applied. The path indicated by the dotted arrow indicates the current path. FIGS. 3C to 3H show the transistors 8U1 to 8W.
FIG. 4 is a diagram showing the on / off status of the second embodiment.

First, the paths for applying a positive voltage to the transformers 9A and 9B are as follows, as shown in FIG. Transformer 9A: Transistor 8U1 → Transformer 9A → Transistor 8W2 Transformer 9B: Transistor 8V1 → Transformer 9B → Transistor 8W2 The transistor 8W2 is a path in any case.

Accordingly, the duty ratio of 10
When applying a voltage of 0%, the transistor 8U1 is set to have a duty ratio of 1 as shown by a waveform C-1 in FIG.
The control is performed at 00%, and the transistor 8W2 is also controlled at a duty ratio of 100% as shown by the waveform H-1 in FIG. On the other hand, at the same time, the duty ratio 50
% Voltage is applied, the waveform E of FIG.
As shown in FIG.
% And the transistor 8W2 also has a duty ratio of 50%
I would like to say that the transistor 8
W2 is controlled at a duty ratio of 100%. The reason is,
This is because the transistor 8W2 also serves as a current path to the transformer 9A, and it is necessary to satisfy that requirement. That is, the transistor 8W2 is controlled in accordance with the larger duty ratio.

The paths for applying a negative voltage to the transformers 9A and 9B are as follows, as shown in FIG. Transformer 9A: Transistor 8W1 → Transformer 9A → Transistor 8U2 Transformer 9B: Transistor 8W1 → Transformer 9B → Transistor 8V2 The transistor 8W1 is a path in any case. The duty ratio control when a negative voltage is applied to the transformers 9A and 9B is performed in the same manner as when a positive voltage is applied, and thus a detailed description is omitted. The waveforms related to the operation in this case are shown in FIG.
The waveform F-1 in FIG. 3F and the waveform G-1 in FIG. 3G are referred to.

Returning to FIG. 1, the transformers 9A and 9B
Output voltages of the rectifier circuits 10A and 10B, the smoothing inductances 11A and 11B, and the smoothing capacitor 1 respectively.
The DC output terminals are rectified and smoothed by 2A and 12B, added in such a manner that their DC output terminals are connected in series, and applied to both ends of the resistors 13 and 14 and the load 16. The final output voltage is divided and detected by the resistors 13 and 14, and the detection signal is input to the controller 17. The controller 17 compares the output voltage with a predetermined set voltage and controls the switching of the inverter 8 so that the output voltage becomes the voltage (duty ratio control).

In controlling the duty ratio of the inverter 8, in the present invention, the voltage applied to the transformers 9A and 9B is supplied in a manner that the duty ratio is not so small so that the loss in the transformer does not become large. for that reason,
Depending on the magnitude of the input voltage to the inverter 8, the duty ratio control of the voltage applied to the transformer 9A and the transformer 9
The duty ratio control of the voltage applied to B is made different.
Next, it will be described.

FIG. 4 is a diagram showing duty ratio control in the present invention. The vertical axis indicates the input voltage to the inverter 8, and the horizontal axis indicates the duty ratio. Curve a is the transformer 9
A curve relating to the control of the applied voltage to A, a curve B relating to the control of the applied voltage to the transformer 9B, and a curve C relating to the control of the applied voltage in the conventional DC-DC converter having only one transformer. (Corresponding to curve A in FIG. 7).

The input voltage V ₁ is an input voltage at which a predetermined constant output voltage is obtained to the load 16 when applied to the transformers 9A and 9B at a duty ratio of 100%.
Voltage V ₃ is trans 9A only the duty ratio of 100%
Is applied to the load 16 to obtain a predetermined constant output voltage. Input voltage V ₂ is slightly smaller input voltage than V _3. Voltage V _M is the maximum input voltage expected. The values of V ₁ and V ₃ can be set to appropriate constant values by appropriately determining the winding ratio of the transformers 9A and 9B.

As can be seen from the curves a and b in FIG.
The duty ratio control according to the present invention is performed in the following two cases according to the input voltage to the inverter 8. (1) a duty ratio control voltage when the input voltage is applied to V ₃ or less when the transformer 9A ... 10
0% (that is, along the portion from the point E to the point F in the curve A). Duty ratio control of the voltage applied to the transformer 9B: Performed along the curve B. (2) The input voltage is V ₃ In the case of a larger value, the duty ratio control of the voltage applied to the transformer 9A is performed along the portion from the point F to the point G in the curve A. The duty ratio control of the voltage applied to the transformer 9B is 0%.
(That is, the input voltage to the transformer 9B is set to zero. In other words, the control is performed along the portion from point H to point P on the vertical axis).

[0033] Note that whether or not the input voltage to the inverter 8 is V ₃ or less, the input voltage coming detected by resistors 4 and 5 is determined in comparison with V ₃ by the controller 17. Thus, for example, in the case that the input voltage is V ₃ or less, the transistors of the inverter 8, a transistor for supplying a voltage applied to the transformer 9A is turned on so that the duty ratio of 100%. The duty ratio of the transistor for supplying the applied voltage to the transformer 9B is appropriately changed (according to the curve B) so that the output voltage detected by the resistors 13 and 14 becomes a predetermined value. Next, the duty ratio control in the present invention will be described for some specific examples.

FIG. 5 is a diagram showing a specific example of duty ratio control in the present invention. Voltage V _1, V _2, V _M corresponds to that of FIG. 5 (1), 5 (2), 5
(3) indicates that the input voltage V of the inverter 8 is V ₁ ,
When V _2, V _M, shows the waveform of the voltage applied to transformer 9A, 9B. The case of FIG. 5A (V = V ₁ ) corresponds to the case of the point E in FIG. 4, and the duty ratio of 10 is applied to both the transformers 9A and 9B.
A voltage controlled at 0% is applied.

In the case of FIG. 5B (when V = V ₂ ),
Focusing on an intersection of the dashed line of V ₂ in FIG. 4, intersect at a 100% duty ratio and the curve b, intersect at the duty ratio D _2% the curve b. Therefore, a voltage controlled at a duty ratio of 100% is applied to the transformer 9A, and the duty ratio D ₂ is applied to the transformer 9B.
A voltage controlled in% is applied. The duty ratio is small when looking at only the transformer 9B, but is not small when looking at the entire transformer including the transformer 9A. Therefore, the loss of the entire transformer is smaller than that of the conventional transformer.

The case of FIG. 5 (3) (in the case of V = V _M) is,
This corresponds to the case of point G in FIG. 4, and a voltage controlled at a duty ratio D _M % is applied only to the transformer 9A. Since the voltage applied to the transformer 9B is set to zero, the duty ratio of the transformer 9A has a correspondingly large value.
Therefore, the loss in the transformer 9A is reduced. As described above, the circuit after the transformer is divided into two systems, and finally added to obtain an output voltage, and the duty ratio control of the voltage supplied to the two systems is made different depending on the magnitude of the input voltage. However, the loss when viewed from the whole transformer is smaller than before.

As described above, the DC-DC converter according to the present invention can operate the transformer 9A,
Although 9B can operate in an efficient state as a whole, an example suitable for using such a DC-DC converter will be described below. FIG. 6 is a diagram showing a usage example of the DC-DC converter of the present invention. In FIG. 6, 31 is a pulley, 32 is an engine, 33 is an intake pipe, 34 is an exhaust pipe, 35 is a turbocharger, 36 is a compressor blade, 37 is a rotor, 38 is a stator,
39 is a turbocharger rotating electric machine, 40 is a turbine blade, 41 is a belt, 42 is a pulley, 43 is a vehicle generator, 44 is a controller, 45 is a power unit, and 46 is DC
-DC converter, 47 is a battery, 48 is a load.

The vehicle generator 43 is a normal vehicle-mounted generator driven by the engine 32 via the pulley 31, the belt 41, and the pulley 42. Turbocharger 3
5 rotates the turbine blade 40 by the exhaust gas from the exhaust pipe 34, rotates the compressor blade 36 using the rotational force, and takes in external air into the intake pipe 33. The turbocharger rotating electric machine 39 is a rotating electric machine incorporated in the turbocharger 35, and a rotor 37 is attached to a rotating shaft of the turbocharger 35, and a stator 38 is provided in a housing of the turbocharger 35.
Is attached. The rotation of the rotor 37 causes the stator 38 to rotate.
, An electromotive force is induced, and the generated voltage is taken out to the outside.

The generated voltage from the vehicle generator 43 and the turbocharger rotating electric machine 39 is introduced to the power section 45. The power unit 45 has a built-in DC-DC converter 46 and converts the voltage into a voltage required by the vehicle. The conversion control is performed by the controller 44. The converted voltage is supplied to a battery 47, an electric load 48 in the vehicle, and the like. The rotation speed of the vehicle generator 43 greatly varies depending on the condition of the engine rotation speed. In particular, in the present embodiment, the speed is increased at a high speed (3 to 5 times) in consideration of supplying a voltage to the turbocharger rotating electric machine 39 at the time of starting, so that the generated voltage from the vehicle generator 43 greatly fluctuates. I do.
Therefore, it is suitable to use the DC-DC converter of the present invention as the DC-DC converter 46 built in the power unit 45. That is, even if the input voltage fluctuates greatly, the duty ratio can be used without making the duty ratio too small, so that the loss in the transformer can be reduced.

[0040]

As described above, according to the DC-DC converter of the present invention, the following effects can be obtained. (Effects of Claims 1 and 2) In a DC-DC converter, a transformer and a rectifying / smoothing circuit following the transformer are provided in two systems, and their output voltages are added to obtain a final output voltage. The duty ratio control for generating the voltage to be applied to the system and the duty ratio control for generating the voltage to be applied to the second system are made different depending on the magnitude of the input voltage. In consideration of the above, the voltage applied to the transformer is applied with a larger duty ratio than in the past,
Transformer efficiency is improved. Since a step-down circuit or the like becomes unnecessary, the circuit scale is reduced and the cost is reduced. Furthermore, since the circuit from the transformer to the portion that adds the output voltage is composed of two systems, the voltage shared by each system is small, and circuit elements such as diodes that constitute the circuits of each system are replaced with low withstand voltage devices. You can do it. Therefore, the cost is reduced in this aspect as well.

(Effect of Claim 3) When the input voltage is equal to or lower than a predetermined value, the first transformer has a duty ratio of 1
The input voltage controlled at 00% is applied, and the input voltage to the second transformer is controlled so that the duty ratio is variable. When the input voltage is higher than a predetermined value, the input voltage to the first transformer is reduced. Since the duty ratio is controlled so as not to be applied to the second transformer, when viewed as a whole, the voltage applied to the transformer is applied with a larger duty ratio than in the past, and the efficiency of the transformer is increased. Is improved.

(Effect of the Invention of Claim 4) A required inverter can be configured with a smaller number of circuit elements as compared with the case where an inverter having a bridge configuration including two arms is individually provided for each system. Costs can be reduced.

According to the fifth aspect of the present invention, a DC-DC converter for obtaining a constant DC voltage by using a generated voltage of a vehicle generator or a turbocharger rotating electric machine as an input has a constant DC voltage even if the input voltage greatly varies. It is demanded that the DC-DC converter of the present invention satisfies these conditions, and that the DC-DC converter of the present invention satisfies those conditions. It is suitable for.

[Brief description of the drawings]

FIG. 1 is a diagram showing a DC-DC converter according to the present invention.

FIG. 2 is a diagram showing an example of voltage application control to a transformer.

FIG. 3 is a diagram showing a current path to a transformer and switching of an inverter.

FIG. 4 is a diagram showing duty ratio control in the present invention.

FIG. 5 is a diagram showing a specific example of duty ratio control in the present invention.

FIG. 6 is a diagram showing a usage example of the DC-DC converter of the present invention.

FIG. 7 is a diagram showing duty ratio control in a conventional DC-DC converter.

FIG. 8 is a diagram showing a specific example of conventional duty ratio control.

FIG. 9 is a diagram showing a first conventional example of a DC-DC converter.

FIG. 10 is a diagram showing a second conventional example of a DC-DC converter.

[Explanation of symbols]

1: input AC power supply, 2: rectifier circuit, 3: current detector,
4, 5: resistor, 6: smoothing capacitor, 7: step-down circuit,
8. Inverter, 8U1, 8U2, 8V1, 8V2, 8
W1, 8W2: Transistor, 9, 9A, 9B: Transformer, 10, 10A, 10B: Rectifier circuit, 11, 11A,
11B: Smoothing inductance, 12, 12A, 12B
... Smoothing capacitors, 13,14 ... Resistance, 15 ... Current detector, 16 ... Load, 17 ... Controller, 31 ... Pulley, 32 ... Engine, 33 ... Intake pipe, 34 ... Exhaust pipe, 3
5 Turbocharger 36 Compressor blade
37 ... rotor, 38 ... stator, 39 ... turbocharger rotating electric machine, 40 ... turbine blade, 41 ... belt, 4
2 ... pulley, 43 ... vehicle generator, 44 ... controller,
45 power unit, 46 DC-DC converter, 47
Battery, 48 ... _{load, V A, V B, V} C ... input voltage,
D _A , D _B , D _C , D _M ... duty ratio

Claims (5)

[Claims] An inverter for converting a fluctuating input voltage into an alternating current by controlling a duty ratio; a transformer for transforming the alternating current; rectifying and smoothing means for rectifying and smoothing the transformed alternating current; and detecting a direct current output voltage. A DC-DC converter comprising: a voltage detecting means; and a controller for controlling a duty ratio of the inverter based on a detection value from the voltage detecting means to make the DC output voltage a constant value. And an input voltage detecting means for detecting an input voltage and inputting a detection signal to the controller, and a duty ratio control in the first and third arms. A first transformer to which an input voltage is applied via the first transformer, a first rectifying and smoothing means for rectifying and smoothing an output of the first transformer,
A second transformer to which an input voltage is applied through a duty ratio control in a third arm, a second rectifying and smoothing means for rectifying and smoothing the output of the second transformer, and the first and second rectifiers Means for adding the output voltage of the smoothing means to the DC output voltage, and varying the duty ratio of the voltage applied to the first and second transformers according to the magnitude of the input voltage. A DC-DC converter. 2. The ratio of the output voltage from the first rectifying / smoothing means to the output voltage from the second rectifying / smoothing means in the output voltage obtained by addition is determined by the magnitude of the input voltage to the inverter. 2. The DC-DC converter according to claim 1, wherein the DC-DC converter is changed according to the following. 3. When the input voltage is lower than a predetermined value, the first
A voltage with a duty ratio of 100% is applied to the transformer
A voltage controlled by varying the duty ratio is applied to the second transformer, and when the input voltage is greater than the predetermined value, the first
3. The DC-DC converter according to claim 2, wherein a voltage controlled by varying the duty ratio is applied to the transformer, and the voltage applied to the second transformer is zero. 4. The duty ratio control in the third arm includes:
4. The DC-DC converter according to claim 1, wherein the duty ratio control in the first and second arms is performed at the same duty ratio as the larger duty ratio. 5. The DC-DC converter according to claim 1, wherein a generated voltage from a generator driven by an internal combustion engine of the vehicle is used as an input voltage.