JP2003189613A - Dc-dc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter capable of accommodating load fluctuations and attaining reductions in size and cost. <P>SOLUTION: In this DC-DC converter 100, an output of a DC power supply 300 is turned on and off at a switching device 120 and is applied to a primary side of a transformer 110. A secondary energizing power excitation power is thereby rectified in a first rectifying diode 161 and is applied to a load 310 via a choke coil 170 and a smoothing capacitor 180. The voltage of an output terminal 193 is observed in a diversion control circuit 150, and when the load increases and the output voltage drops, a diversion circuit 163 is energized to flow an excitation current on a secondary side through a second rectifying diode 162. The current is flowed through a secondary winding reversely wound around the choke coil 170 and reduces magnetic flux density generated on the choke coil 170. Thus, the allowable magnetic flux density can be reduced to miniaturize the choke coil 170. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC which converts input DC power applied to DC power of a desired voltage.
The present invention relates to a converter, and more particularly to a small and inexpensive DC / DC converter.

[0002]

2. Description of the Related Art Regarding a conventional DC / DC converter,
This will be described with reference to FIG. The DC / DC converter 900 shown in FIG. 9 includes a transformer 902, a MOS-FET 903 that is a switching element connected in series to the primary winding Np of the transformer 902, and a switching control circuit 904 that outputs a switching signal to the MOS-FET 903.
An input filter circuit 905 connected to the primary winding Np of the transformer 902, a rectifying diode 906 connected to the secondary winding Ns of the transformer 902, and a common cathode of the secondary winding Ns and the rectifying diode. And a smoothing capacitor 908, primary DC power input terminals 911 and 912, and secondary DC power output terminals 913 and 914. Further, the DC / DC converter 900 changes the output terminal voltage to the switching control circuit 90.
4 and an output terminal voltage signal line 930 for inputting to the No. 4 and a load terminal voltage signal line 931 for inputting the terminal voltage of the load to the switching control circuit 904. In such a DC / DC converter 900, the DC power supply 9
20 is connected to the input terminals 911 and 912, and the load 921 is connected to the output terminals 913 and 914, respectively.

The DC / DC converter 9 having such a configuration
In 00, the primary DC power input from the DC power supply 920 connected to the input terminals 911 and 912 is applied to the series circuit of the primary winding Np of the transformer 902 and the MOS-FET 903 via the input filter circuit 905. To be done. Then, the secondary AC power is induced in the secondary winding Ns of the transformer 902 by the switching of the MOS-FET 903 based on the control of the switching control circuit 904,
The load 92 connected to the output terminals 913 and 914 by being rectified and smoothed by the rectifying diode 906, the choke coil 907, and the smoothing capacitor 908 to become secondary DC power.
It is output to 1.

Step-down D for generating a 12V voltage from a high voltage battery mounted on an electric vehicle or a hybrid vehicle
Assuming a C / DC converter, its output current is 1
It may exceed 00A. Therefore, a harness having a large wire diameter is used for the output harness in order to reduce the output harness resistance 922 and reduce the voltage drop. However, the harness diameter is also limited from the viewpoints of superimposition, easiness of routing the harness, and the like, and the voltage effect due to the output harness resistance 922 cannot be avoided. Therefore, in the on-vehicle DC / DC converter, the load terminal voltage signal line 931 inputs the load terminal voltage to the switching control circuit 904, and the switching control is performed so that the load terminal voltage becomes a constant voltage.

Further, assuming that the load terminal voltage signal line 931 is broken, the output terminal voltage is monitored by the switching control circuit 904 by the output terminal voltage signal line 930 from the viewpoint of fail-safe. In the switching control circuit 904, the load terminal voltage signal line 931 monitors the load terminal voltage, and when the load voltage increases due to a change in the load current, the switching of the MOS-FET 903 is controlled to reduce the output voltage, When the load voltage drops, the switching of the fly 903 is controlled to operate to increase the output voltage.

The choke coil 907 needs to have a large inductance value to store a large amount of energy in order to perform highly accurate output stabilization control from a light load current to a maximum load current. As a means, measures such as increasing the inductance value by using an amorphous core having a high saturation magnetic flux density, and increasing the inductance value by increasing the size of a ferrite core are used. However, the amorphous core is expensive, and there is a problem that the cost increases if the ferrite core is used to increase the size of the core.

Further, a step-down D for generating a 12V voltage from a high voltage battery of an electric vehicle or a hybrid vehicle, in particular.
In the C / DC converter, the required load current to be supplied to the electrical load connected to the 12V side is about 100A. Normally, the electrical component load can be divided into one that operates continuously and one that operates intermittently. When designing such a choke coil 907, a load that operates continuously and a load that operates intermittently. It was necessary to select a core with a large effective area so that the magnetic flux density due to the magnetic flux generated in the core of the choke coil would be lower than the saturation magnetic flux density even when both of them operate.

This will be described in detail below. In the DC / DC converter 900 shown in FIG. 9, the MOS-FET 903 which is a switching element is on / off controlled to operate so as to keep the output voltage constant. This on / off control is PWM control. It shall be carried out using Therefore, assuming that the ON / OFF duty is D, the ON time is Ton, and the maximum ON time is Tonmax, the magnetic flux density B generated in the core of the choke coil 907.
Is generally represented by the following equation (1).

[0009]

[Equation 1]   B = (ΔV × Ton) / (N × Ae) (1)

ΔV is the difference between the voltage Vin input to the choke coil 907 and the voltage Vout output. The voltage Vin input to the choke coil 907 is D
For the voltage of the DC power supply 920 of the C / DC converter 900,
It is a value obtained by multiplying the winding ratio Ns / Np of the transformer 902.
N is the number of winding turns of the choke coil.
Is the effective area of the core used in the choke coil.

Here, the operation with respect to the fluctuation of the input voltage will be described. In the DC / DC converter 900, when the voltage of the DC power supply 920 is low, the MOS-FET 90
When the ON time Ton1 of No. 3 is increased and the voltage of the DC power supply 920 is high, the ON time Ton2 is decreased to keep the output voltage constant. In each of these cases, the magnetic flux density B generated in the core of the choke coil is
It becomes like Formula (2). However, the input voltage of the choke coil 907 when the voltage of the DC power source 920 is low is Vin
1, the ON time of the MOS-FET 903 is Ton1, the input voltage of the choke coil 907 is Vin2 when the voltage of the DC power supply 920 is high, and the ON time of the MOS-FET 903 is Ton.
Set to 2.

[0012]

[Equation 2]   B = ((Vin1−Vout) × Ton1) / (N × Ae)     = ((Vin2-Vout) * Ton2) / (N * Ae) (2)

Next, the operation for the fluctuation of the output voltage will be described. Now, let the input voltage of the choke coil be Vinmax when the voltage of the DC power supply 920 is the maximum input voltage that guarantees the performance of the DC / DC converter 900. In this state, in the DC / DC converter 900 in which the load current is constant and is in the steady operation state, when the load current sharply increases due to a large number of intermittent differential electrical component loads, the load current sharply increases. The load terminal voltage falls below a certain voltage. The voltage at this time is V
outmin. In such a state, the DC / DC converter 900 returns the output voltage to the original voltage,
The duty of the MOS-FET 903 is maximized so that a large amount of power is supplied, that is, the MOS-FET 90.
The ON time Ton of 3 is set to Tonmnax to increase the output voltage. Magnetic flux density generated in the core of the choke coil at this time
max is expressed by the following equation (3).

[0014]

[Equation 3]   B = ((Vinmax−Voutmin) × Tonmax) / (N × Ae) (3)

Then, these operations will be described focusing on the output current. Now, assuming that the inductance of the choke coil is L, the input / output potential difference is ΔV, and the change amount of the output current of the choke coil is Δi, the relationship of the following expression (4) is established.

[0016]

[Equation 4]   ΔV × Ton = L × Δi (4)

The change Δi in the output current is a ripple current when the DC / DC converter is in a steady operation state, and indicates the change in the output current when the output current changes. By substituting the equation (4) into the equation (3), the following equation (5) is obtained.
Can be expressed as

[0018]

[Equation 5]   Bmax = (L × Δi) / (N × Ae) (5)

Thus, when the output current suddenly increases from the minimum current to the maximum current in the rated current range, that is, equation (5)
The magnetic flux density B generated in the core of the choke coil becomes the maximum magnetic flux density max when the Δi shown in FIG. Even in this case, it is necessary to select a core having a large effective area so that the core will not be magnetically saturated. Therefore, the size of the core becomes large and the cost becomes high.

As a conventional means for solving such a problem, for example, there is a method disclosed in Japanese Patent Laid-Open No. 9-331677. In this method, as shown in FIG. 10, the middle leg of the E-shaped core is subjected to wedge-shaped gap processing, the inductance value of the choke coil is large when the output current is small, and the inductance value is large when the output current is large. We have proposed a choke coil that has a current dependence so that is small. In such a choke coil, lines of magnetic force flowing in the choke coil are concentrated in a gap portion having a small magnetic resistance when the load current is small, and a large inductance is obtained. Further, when the load current increases, the magnetic force lines gradually flow through a wide gap with a large magnetic resistance, and the inductance decreases. Therefore, the load current until the magnetic saturation occurs can be made larger than that in the conventional core having no gap or the core having a uniform gap. In other words, when the maximum load current is specified, it is possible to select a core having a smaller effective area than the conventional core.

[0021]

However, this conventional choke coil has a complicated structure and lacks versatility, such as the need to provide a wedge-shaped dedicated gap in the middle leg of the choke coil, which is different for each specification. Met.
As a result, there is a problem that the processing becomes complicated and the processing cost becomes high.

The present invention has been made in view of such problems, and the object of the present invention is suitable even when applied to, for example, a vehicle-mounted power supply device in which the difference between the minimum power consumption and the maximum power consumption is large. The object of the present invention is to provide a small-sized and inexpensive DC / DC converter which can cope with fluctuations.

[0023]

To achieve the above object, according to a first aspect of the present invention, there is provided a DC / DC converter according to the present invention.
The DC converter includes a transformer having a primary winding and a secondary winding, and a switching element that is connected in series to the primary winding and converts an applied DC voltage into a non-DC voltage and applies the applied DC voltage to the primary winding. A rectifying / smoothing circuit having a choke coil connected in series to the secondary winding and rectifying and smoothing a secondary alternating current excited in the secondary winding and outputting the rectified and smoothed current to a desired load. A DC converter, wherein the choke coil is connected in series to a secondary winding of the transformer and a first winding that is wound around a core in a predetermined direction, and is connected in series to a secondary winding of the transformer. And a second winding wound around the core in a direction opposite to the first winding, the output current detecting means for detecting a state of the output current,
It further has a shunt control means for controlling the current applied to the second winding of the choke coil based on the state of the detected output current.

In the DC / DC converter having such a configuration, the temporary DC voltage on the input side is applied to the series circuit of the primary winding of the transformer and the switching element, and the switching element is turned on and off, for example. An alternating voltage is excited on the secondary winding side of the transformer. And
The alternating current by the alternating voltage is rectified and smoothed by a rectifying and smoothing circuit including a choke coil having a first winding and a second winding, and then output to a desired load. At this time, the state of the current output to the load is detected by the output current detection means, and the current applied to the secondary winding of the choke coil is controlled by the shunt control means based on the detected output current state. To be done. In the choke coil, the primary winding and the secondary winding are wound in the opposite directions with respect to the core, that is, the magnetic flux generated by each winding acts so as to cancel each other. Controlling the current applied to the secondary winding in this way controls the magnetic flux density generated in the choke coil.

Although not limited to this, it is preferable that the shunt control means includes only the first winding of the choke coil when the output current is within a predetermined range. The current output from the secondary winding of is output, and when the output current increases beyond a predetermined range,
The current output from the secondary winding of the coil is shunted to the second winding of the choke coil (claim 2).

Although not limited to this,
As a specific and preferable configuration of the DC / DC converter according to the present invention, the output current detecting means detects a change in the current output from the rectifying / smoothing circuit, and the shunt control means detects the detected current. The second based on the change of the current
Control the current applied to the winding. (Claim 3) Also,
Similarly, as another specific and preferable configuration of the DC / DC converter according to the present invention, the output current detection means detects the output terminal voltage of the rectifying and smoothing circuit and the input terminal voltage of the load, The voltage drop between the rectifying and smoothing circuit and the load is detected, and the shunt control means controls the current applied to the second winding based on the detected voltage drop. (Claim 4)

Although not limited to this,
A preferred configuration of the choke coil has an E-shaped core,
The first winding and the second winding are wound around the middle leg of the E-shaped core. (Claim 5)

[0028]

According to the invention described in claims 1 to 5, the magnetic flux density of the choke coil is controlled only by passing a current through the second winding of the choke coil according to the state of the output power. be able to. Therefore, the choke coil having a simple structure using a general-purpose core can be appropriately used even in an application in which the difference between the minimum power consumption and the maximum power consumption is large. Further, since the magnetic flux density can be appropriately suppressed, the choke coil can be made compact. As a result, a small and inexpensive DC / DC converter can be provided.

In addition to this, according to the invention described in claim 2, it is possible to provide a DC / DC converter capable of appropriately coping with the case where the load current sharply increases. Further, according to the invention described in claim 3, it is possible to provide a DC / DC converter which grasps the status of the load by appropriately detecting the change in the load current and controls the magnetic flux density appropriately. .
Further, according to the invention described in claim 4, it is possible to provide a DC / DC converter which detects the voltage drop of the harness resistance to grasp the load situation and appropriately controls the magnetic flux density. According to the invention described in claim 5, it is possible to provide a DC / DC converter having a choke coil with a simple structure using a general-purpose member.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment A DC / DC converter according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a circuit diagram showing the configuration of the DC / DC converter 100 of the first embodiment. As shown in FIG. 1, the DC / D of the present embodiment
The C converter 100 includes a transformer 110 and a transformer 11.
0, which is a switching element connected in series to the primary winding Np of 0, a switching control circuit 130 which outputs a switching control signal to the MOS-FET 120, and an input filter circuit 140 which is connected to the primary winding Np of the transformer 110. , A shunt control circuit 150 that controls shunting of a current output on the secondary winding side of the transformer 110, a first rectifying diode 161 connected to the secondary winding Ns of the transformer 110, and a first rectifying diode 161 in parallel. The connected second rectifying diode 162, a shunt circuit 163 for shunting a current to the second rectifying diode 162,
The configuration is such that the choke coil 170, the smoothing capacitor 180, the input terminals 191, 192, and the output terminals 193, 194 are connected as shown.

In such a DC / DC converter 100, the DC power supply 300 is connected to the input terminals 191, 192, and the load 310 is connected to the output terminals 193, 194. The harness wiring resistance 320 is DC / DC.
It is the wiring resistance of the harness connected to the output terminals 193 and 194 of the converter 100. In addition, in the state where the DC power source 300 and the load 310 are connected in this manner, the DC / DC
In the converter 100, the output terminals 193, 194
Is input to the switching control circuit 130 and the shunt control circuit 150 via the output terminal voltage signal line 230, and the terminal voltage of the load 310 is input to the switching control circuit 130 via the load terminal voltage signal line 231. .

Incidentally, in FIG. 1, contact point a and contact point b
Is a shunt circuit 16 for the anode of the first rectifying diode 161 connected to the secondary winding Ns of the transformer 110.
3 is an input contact, and the contact c is an input contact of an input signal for controlling the shunt circuit 163. Further, the contact point d and the contact point e are output contacts of the shunt circuit 163 with respect to the anode of the second rectifying diode 162, and the contact point f is an input contact of the output terminal voltage signal line 230 to the shunt control circuit 150, and the contact point. g is an output contact of the diversion control circuit 150 for the control signal input of the diversion circuit 163.

Such a DC / DC converter 100
The configuration of the choke coil 170 will be described with reference to FIG. As shown in FIG. 2, the choke coil 170 includes a first winding N1 (171) and a second winding N2 (17).
2) is a configuration in which it is wound around the middle leg portion 174 of the E-shaped core 173. At this time, in the second winding N2, a magnetic flux φ2 (| φ1 |> | φ2 |) is generated so as to cancel the magnetic flux φ1 generated in the core 173 when a current flows through the first winding N1. It is wound in the opposite direction to the first winding N1. The relationship between the magnetic flux φ and the magnetic flux density B is expressed by the equation (6), where S is the cross-sectional area in which the magnetic flux is generated.

[0034]

[Equation 6]   B = φ / S (6)

The structure of the shunt circuit 163 is shown in FIG.
Will be described with reference to. As shown in FIG. 3, the shunt circuit 163 is composed of two systems of MOS-FETs and resistors corresponding to both terminals of the secondary winding Ns of the transformer 110. In the shunt circuit 163 having such a configuration, the conduction states of the contact a and the contact d, and the contact b and the contact e are controlled according to the control signal applied from the shunt control circuit 150 to the contact C. Then, when it is conducting, the second rectifier diode 162 is connected to the secondary winding Ns of the transformer 110 in parallel with the first rectifier diode 161. In FIG. 3, the shunt circuit 163 is an MO.
Although it is configured by using the S-FET, this is only an example and may be configured by a transistor, a mechanical relay, or the like.

The configuration of the diversion control circuit 150 will be described with reference to FIG. The diversion control circuit 150 is shown in FIG.
As shown in FIG. 1, a first differentiating circuit 151 including a resistor R1 and capacitors C1 and C3, a second differentiating circuit 152 including a resistor R2 and a condenser C2, and a first filter circuit including a transistor Tr1, a diode D1, and a resistor R3. 1
53, a second filter circuit 154 composed of a transistor Tr2 and a resistor R4, a hysteresis comparator circuit 155 composed of resistors R5 to 7 and an amplifier A1, and a driver circuit 156 are connected as shown in the drawing.

In the shunt control circuit 150 having such a configuration, the voltage input from the output terminal voltage signal line 230 is input to the two differentiating circuits 151 and 152, and after passing the respective predetermined filters, the hysteresis comparator circuit 2
Compare at 53. As a result, the change in the voltage of the output terminal is detected, and the driver circuit 256 is controlled to be turned on / off. For example, when the output voltage is held constant, the hysteresis comparator circuit 155 is passed through the first differentiating circuit 151 and the first filter circuit 153.
The relationship between the voltage Va input to the inverting input terminal of the above and the voltage Vb input to the non-inverting input terminal of the hysteresis comparator circuit 155 via the second differentiating circuit 152 and the second filter circuit 154 is Va < Since it becomes Vb, the output of the driver circuit 156 is turned off. On the other hand, when the voltage at the output terminal decreases, which decreases the voltage Vb input to the non-inverting input terminal of the hysteresis comparator circuit 155, and the voltage relationship becomes Va> Vb, the driver circuit 156 determines that It turns on.

DC / DC converter 1 having such a configuration
The operation of 00 will be described. DC / DC converter 1
At 00, primary DC power is input from DC power supply 300 connected to input terminals 191, 192. DC /
The primary DC power input to the DC converter 100 is switched via the input filter circuit 140 according to the switching control signal output from the switching control circuit 130, and the MOS-FET 120 and the transformer 11.
0 in a series circuit with a primary winding Np. MOS-
The secondary AC power excited in the secondary winding Ns of the transformer 110 by the switching of the FET 120 becomes DC power by the first rectifying diode 161, the choke coil 170, and the smoothing capacitor 180, and the output terminals 193, 1
It is output from 94 to the load 310.

In such a DC / DC converter 100, when the output voltage is controlled to the constant voltage Vout, it is input to the inverting input terminal of the hysteresis comparator circuit in the shunt control circuit 150 shown in FIG. Since the relationship Va <Vb is established between the voltage Va and the voltage Vb input to the non-inverting input terminal, the driver circuit 1
The output of 56 is turned off. Then, this output is input to the gate of the MOS-FET of the shunt circuit 163 as shown in FIG. 3, and the MOS-FET of the shunt circuit 163 is maintained in the off state. As a result, the secondary exciting current excited in the secondary winding of the transformer 110 flows through the first rectifying diode 161 and the first winding N1 of the choke coil 170.
Current flows through the second rectifier diode 162 and the second winding N2 of the choke coil 170.

On the other hand, when the load current increases while the output voltage is controlled to the constant voltage Vout, the output voltage decreases. The reduced output voltage at this time is defined as Vout-low. Due to this change in the output voltage, in the shunt control circuit 150 shown in FIG. 4, the voltage Vb input to the non-inverting input terminal of the hysteresis comparator circuit decreases, and becomes lower than the voltage Va input to the inverting input terminal Va. When the relation is> Vb, the output of the driver circuit 156 is turned on. The period in which the driver circuit 156 is turned on in the driver circuit 156 is set to a desired period by adjusting each constant in the differentiation circuit and the hysteresis comparator circuit in the shunt control circuit 150.

The output of the driver circuit 156 is
Since it is input to the gate of the MOS-FET of the shunt circuit 163 as shown in FIG. 3, the MOS-FET is turned on, and the secondary exciting current excited in the secondary winding of the transformer 110 becomes the first The current is shunted to the rectifying diode 161 and the second rectifying diode 162, and the first choke coil 170 is divided.
A current flows through both the winding N1 and the second winding N2.
As described above with reference to FIG. 2, the choke coil 170
In the above, since the winding directions of the first winding N1 and the second winding N2 are opposite to each other, the magnetic flux φ1 generated in the core 173 of the choke coil 170 due to the current flowing through the first winding N1 and The magnetic fluxes φ2 generated in the core 173 due to the current flowing through the second winding N2 have their directions canceling each other. Further, the absolute values of the respective magnetic fluxes have a relationship shown in the following expression (7).

[0042]

[Equation 7]   | Φ1 |> | φ2 | (7)

Therefore, the core 17 of the choke coil 170
The magnetic flux φ3 generated in 3 is given by the following equation (8).

[0044]

[Equation 8]   φ3 = φ1-φ2 (8)

Therefore, when a current is also applied to the second winding N2, the magnetic flux φ generated in the choke coil 170 is generated.
3 will decrease. The choke coil 170
When the cross-sectional area of the middle leg 174 is S, the magnetic flux density B in the middle leg 174 is expressed by the following formula (9) from formula (6) and formula (8).
become that way.

[0046]

[Equation 9]   B = φ3 / S (9)

In such a DC / DC converter 100, a waveform diagram of the output current, the output voltage, the magnetic flux density, and the shunt control signal when the output voltage drops due to the sudden increase of the load current is shown in FIG. ~ Fig. 5 (D). DC
In the / DC converter 100, FIG.
As shown in (D), when the output voltage drops temporarily due to a sudden increase in the load at time T1, the MOS-FET 12 returns the output voltage V to the original constant voltage.
The ON time Ton of 0 is set to be long, the output current I increases, and the magnetic flux density B also starts to increase.

However, at time T2, for example, the shunt control circuit 150 detects this output voltage drop, and the shunt circuit 163 is turned on by this, so that the choke coil 170 via the second rectifier diode 162 is turned on. Two
A current will also flow through the winding N2. As a result, since the magnetic flux generated in the first winding N1 and the magnetic flux generated in the second winding N2 cancel each other, the choke coil 170
The magnetic flux density generated in the middle leg 174 sharply decreases to about B3. After that, the magnetic flux density B increases in proportion to the current I.

When the output current becomes constant at time T3, the magnetic flux density B also becomes constant, but the shunt circuit 163 is also on while the driver circuit 156 is on due to the circuit setting in the shunt control circuit 150. Since a part of the output current flows in the second winding N2 of the choke coil 170, the magnetic flux density B in the middle leg portion 174 of the choke coil 170 is equal to the magnetic flux of the first winding N1 and the second winding N2. The magnetic flux due to the line N2 becomes constant at a small level that cancels each other out. Then, when the driver circuit 156 is turned off by the circuit setting in the shunt control circuit 150, the shunt circuit 163 is also turned off, and the output current flows only through the first winding N1. As a result, the magnetic flux density B of the middle leg 174 rapidly increases to the normal magnetic flux density B5.

For comparison, the state of change of the magnetic flux density B in the conventional DC / DC converter 900 illustrated in FIG. 9 is shown by a broken line in FIG. 5 (C). As shown,
In the DC / DC converter 900, the magnetic flux density generated in the core 173 of the choke coil 170 increases as it is with the increase of the output current, and increases to the magnetic flux density B4 larger than the magnetic flux density B5 when the output current is constant. Will be done.

As described above, in the DC / DC converter 100 according to the present embodiment, the magnetic flux density generated during the period when the output voltage is lower than the maximum magnetic flux density B4 conventionally generated under the same conditions. Is clearly small, and is smaller than the magnetic flux density B5 generated when the magnetic flux density is controlled to be constant. Therefore, as the core 173 of the choke coil 170, which is required to have a saturation magnetic flux density corresponding to this, a core having a smaller effective cross-sectional area than before can be used, and the core 173 of the choke coil 170, that is, the choke coil 170. The coil 170 can be downsized.
As a result, a small and inexpensive DC / DC converter can be provided.

Further, unlike the conventional method illustrated in FIG. 10, it is not necessary to perform special processing such as providing a wedge-shaped gap, and therefore, the choke coil 1 using a general-purpose core is used.
70 can be configured. Also, the inductance value can be made variable. Therefore, the choke coil 170 can be manufactured at a low cost, and a cheaper DC
A / DC converter can be provided. Also, DC
In the / DC converter 100, the choke coil 1
By generating magnetic flux in the opposite direction at 70, the magnetic flux density can be actively controlled, and it becomes possible to suppress the output voltage fluctuation at the time of sudden load change.

The relationship between the inductance L and the magnetic flux density B, which is derived from Ampere's law, is given by the following equation (10).

[0054]

[Equation 10]   L = A × B × N / I (10)

Here, A is the cross-sectional area of the portion where the winding is wound. From the equation (10), the inductance L decreases as the magnetic flux density B decreases. Therefore, in the DC / DC converter 100 of the present embodiment, since the magnetic flux density can be reduced, the inductance becomes smaller, and the inductance becomes smaller.
The response of the load current can be improved.

Second Embodiment A DC / DC converter according to a second embodiment of the present invention will be described with reference to FIGS. 6 to 8. FIG. 6 is a circuit diagram showing the configuration of the DC / DC converter 100b according to the second embodiment. As shown in FIG. 6, the basic configuration of the DC / DC converter 100b of the second embodiment is almost the same as the configuration of the DC / DC converter 100 of the first embodiment described above with reference to FIG. Is the same. However, the DC / DC converter 100b according to the second embodiment is
The configuration of the shunt control circuit 250 and the point that the load terminal voltage signal line 231 is also input to the shunt control circuit 250 together with the switching control circuit 130 are different from the DC / DC converter 100 of the first embodiment. Below, D
The description of the same configuration as the C / DC converter 100 is omitted, and only the points related to this difference will be described.

First, the diversion control circuit 250 will be described. FIG. 7 is a diagram showing the configuration of the diversion control circuit 250 of the DC / DC converter 100b. Shunt control circuit 250
Are resistors R11 to R14 and the amplifier A1 to which the output terminal voltage signal line 230 and the load terminal voltage signal line 231 are input.
1, a differential amplifier circuit 251, a resistor R15, a differential circuit 252 including a capacitor C11, and a resistor R1.
6, R17 and amplifier A12, a hysteresis comparator circuit 253, a constant voltage circuit 254, a resistor R1
It has an inverter circuit 255 and a driver circuit 256 which are composed of 8, R19 and an amplifier A13.

In the shunt control circuit 250 having such a configuration, the differential amplifier circuit 251 detects the difference in voltage between the output terminal voltage signal line 230 and the load terminal voltage signal line 231,
The differential value Va obtained by differentiating this in the differentiating circuit 252 is used in the constant voltage circuit 25 in the hysteresis comparator circuit 253.
4 output voltage Vref. That is, by detecting a voltage drop in the harness wiring resistance 320 and comparing it with a reference value, it is determined whether or not the secondary winding side output current of the transformer 110 is shunted to the second rectifying diode 162 side. . Then, the comparison result, which is the determination result, is inverted in the inverter circuit 255 and used for the on / off control of the driver circuit 256.

Next, the operation of the DC / DC converter 100b having such a configuration will be described. In the DC / DC converter 100b, first, the input terminals 191, 1
Primary DC power is input from a DC power supply 300 connected to 92. The input primary DC power is input to the MOS-FET 120 and the transformer 1 via the input filter circuit 140.
It is applied to a series circuit with 10 primary windings Np. Then, the secondary AC power excited in the secondary winding Ns of the transformer 110 by the switching of the MOS-FET 120 is
It is converted into DC power by the first rectifying diode 161, choke coil 170, and smoothing capacitor 180, and output to the load 310 from the output terminals 193 and 194.

Such a DC / DC converter 100b
In the case where the output voltage is controlled to the constant voltage Vout, there is no voltage drop in the harness wiring resistance 320, the output of the differential amplifier circuit 251 of the shunt control circuit 250 is constant, and the voltage obtained by differentiating the signal is The relationship between Va and the output voltage Vref of the constant voltage circuit 254 is Va <Vref. Therefore, the driver circuit 256 is in the OFF state, and the MOS of the shunt circuit 163 whose gate is input to the driver circuit 256 is used.
The state of the FET is also off. As a result, the secondary excitation current excited in the secondary winding of the transformer 110 is
Of the second rectifying diode 162 and the first winding N1 of the choke coil 170.
And does not flow into the second winding N2 of the choke coil 170.

For example, in such a state, if the output voltage suddenly increases, the voltage drop at the harness wiring resistance 320 becomes large, so that the voltage Va is obtained by differentiating the output signal of the differential amplifier circuit 251 of the shunt control circuit 250. The relationship with the output voltage Vref of the constant voltage circuit 254 is Va> Vref. Therefore, the output signal of the hysteresis comparator circuit 253 is inverted, the driver circuit 256 is turned on, and this is input to the gate of the shunt circuit 163.
The state of the S-FET is also turned on. The driver circuit 2
For the engine in which 56 remains on, the differential amplifier circuit 2
By adjusting the constants of 51, the differentiating circuit 252, the hysteresis comparator circuit 253, and the constant voltage circuit 254, it is possible to arbitrarily set them.

As a result, the secondary exciting current excited in the secondary winding Ns of the transformer 110 is divided into the first rectifying diode 161 and the second rectifying diode 162,
The first winding N1 and the second winding N of the choke coil 170
It flows into both of the two. Hereafter, the action caused by this is
This is the same as the first embodiment described above with reference to equations (7) to (9).

In the DC / DC converter 100b,
The output current I and the differential circuit 25 in the shunt control circuit 250 when the output voltage drops due to the sudden increase of the load current
8A to FIG. 8 regarding the output voltage Va of No. 2, the magnetic flux density B, and the diversion control signal applied to the diversion circuit 163.
It shows in (D). In the DC / DC converter 100b, as shown in FIGS. 8 (A) to 8 (D), when the output voltage temporarily decreases due to a sudden increase in the load at time T1, the output voltage is kept constant. The ON time Ton of the MOS-FET 120 is set to be long in order to restore the voltage. At time T2, the diversion control circuit 150
If this output voltage drop is detected, the shunt circuit 163 is turned on by this, and the second winding N2 of the choke coil 170 is turned on via the second rectifying diode 162.
The current will also flow. As a result, the first winding N
1 and the magnetic flux generated in the second winding N2 cancel each other, so that the middle leg portion 1 of the choke coil 170
The magnetic flux density generated at 74 sharply decreases to B3. After that, the magnetic flux density increases in proportion to the current.

Even at the time T3, even if the output current becomes constant, the shunt circuit 1 remains in operation while the driver circuit 156 is turned on by the circuit setting in the shunt control circuit 150.
63 is also in the on state, part of the output current flows through the second winding N2 of the choke coil 170, and the middle leg portion 174 of the choke coil 170 has a constant magnetic flux density. Then, when the driver circuit 156 is turned off by the circuit setting in the shunt control circuit 150, the shunt circuit 163 is also turned off, and the output current flows only through the first winding N1. As a result, the magnetic flux density B of the middle leg 174 rapidly increases to the normal magnetic flux density B5.

In the conventional DC / DC converter 900 illustrated in FIG. 9, the magnetic flux density generated in the core 173 of the choke coil 170 increases as the output current increases, as indicated by the broken line in FIG. 5 (C). Along with that, the magnetic flux density increases as it is, and the magnetic flux density B4 is larger than the magnetic flux density B5 when the output current is constant.

As described above, also in the DC / DC converter 100b of the present embodiment, the magnetic flux density generated during the period when the output voltage is decreasing is smaller than the conventional one, and a core having a small cross-sectional area is used for the choke coil. be able to.
Further, the inductance value can be made variable by using a general-purpose core. Therefore, the choke coil 17
0 can be manufactured in a small size and at a low cost, and by extension, a small and inexpensive DC / DC converter can be provided.
It is also possible to improve the response of the load current and appropriately suppress the output voltage fluctuation when the load suddenly changes.

The first and second embodiments described above are described for facilitating the understanding of the present invention, and do not limit the present invention in any way. Each element disclosed in these embodiments includes all design changes and equivalents within the technical scope of the present invention, and various suitable and various modifications are possible. For example, the method for detecting the decrease in the output voltage is not limited to the method shown in the shunt control circuit 150 or the shunt control circuit 250 described above, and it may be detected by any other method. Further, on the primary side of the transformer 110, the input DC voltage is switched by the MOS-FET 120 to be converted into an AC voltage. However, this MOS-FET 120 may be a normal transistor. Further, the method is not limited to the method using such a switching element, and DC-AC conversion may be performed by a converter having a mechanical operating unit or the like.

[Brief description of drawings]

FIG. 1 is a DC / D according to a first embodiment of the present invention.
It is a circuit diagram which shows the structure of a C converter.

FIG. 2 is a diagram showing a structure of a choke coil of the DC / DC converter shown in FIG.

3 is a circuit diagram showing a configuration of a shunt circuit of the DC / DC converter shown in FIG.

4 is a circuit diagram showing a configuration of a shunt control circuit of the DC / DC converter shown in FIG.

5 is a waveform diagram for explaining the operation of the DC / DC converter shown in FIG.

FIG. 6 is a DC / D according to a second embodiment of the present invention.
It is a circuit diagram which shows the structure of a C converter.

7 is a circuit diagram showing a configuration of a diversion control circuit of the DC / DC converter shown in FIG.

FIG. 8 is a waveform diagram for explaining the operation of the DC / DC converter shown in FIG.

FIG. 9 is a circuit diagram showing a configuration of a conventional DC / DC converter.

10 is a diagram showing a structure of a choke coil of the conventional DC / DC converter shown in FIG.

[Explanation of symbols]

100 ... DC / DC converter 110 ... trance 120 ... MOS-FET 130 ... Switching control circuit 140 ... Input filter circuit 150 ... Shunt control circuit 151 ... First differentiation circuit 152 ... Second differentiation circuit 153 ... First filter circuit 154 ... Second filter circuit 155 ... Hysteresis comparator circuit 156 ... Driver circuit 161 ... First rectifying diode 162 ... Second rectifying diode 163 ... Shunt circuit 170 ... Choke coil 171 ... First winding (N1) 172 ... Second winding (N2) 173 ... Core 174 ... Middle leg 180 ... Smoothing capacitor 191, 192 ... Input terminals 193, 194 ... Output terminal 230 ... Output terminal voltage signal line 231 ... Load terminal voltage signal line 250 ... Dividing control circuit 251 ... Differential amplifier circuit 252 ... Differentiating circuit 253 ... Hysteresis comparator circuit 254 ... Constant voltage circuit 255 ... Inverter circuit 256 ... Driver circuit 300 ... DC power supply 310 ... Load 320 ... Harness wiring resistance

Claims (5)

[Claims] 1. A transformer having a primary winding and a secondary winding, and a switching element connected in series with the primary winding and converting an applied DC voltage into a non-DC voltage and applying the non-DC voltage to the primary winding. And a rectifying / smoothing circuit that has a choke coil connected in series to the secondary winding and that rectifies and smoothes a secondary alternating current excited in the secondary winding and outputs the rectified and smoothed secondary alternating current to a desired load. A DC / DC converter, wherein the choke coil includes a core part, a first winding connected in series to a secondary winding of the transformer, and wound around the core part in a predetermined direction; Output current detection for detecting a state of the output current, which is connected in series to the secondary winding, and has a core and a second winding wound in a direction opposite to the first winding Means, based on the state of the detected output current, Further comprising a DC / DC converter and a shunt control means for controlling the current applied to the second winding of Kukoiru. 2. The shunt control means outputs the current output from the secondary winding of the coil only to the first winding of the choke coil when the output current is within a predetermined range. The current output from the secondary winding of the coil is shunted to the second winding of the choke coil when the output current increases beyond a predetermined range. DC / DC converter. 3. The output current detection means detects a change in the current output from the rectifying / smoothing circuit, and the shunt control means applies a current to the second winding based on the detected change in the current. The current to be applied is controlled.
Alternatively, the DC / DC converter described in 2. 4. The output current detecting means detects a voltage drop between the rectifying and smoothing circuit and the load by detecting an output terminal voltage of the rectifying and smoothing circuit and an input terminal voltage of the load, The shunt control means controls the current applied to the second winding on the basis of the detected voltage drop.
Alternatively, the DC / DC converter described in 2. 5. The choke coil has an E-shaped core,
The DC according to any one of claims 1 to 4, wherein the first winding and the second winding are wound around a middle leg of the E-shaped core.
/ DC converter.