JP2002281748A - Dc/dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC/DC converter which can reduce generation of a leakage magnetic flux and improve the efficiency of transformer. SOLUTION: This DC/DC converter 1 comprises a transformer 2 and a temperature sensor 6 to measure a core temperature of the transformer to assure the function to control to reduce a primary current of the transformer 2 when a core temperature has exceeded the predetermined value. In this DC/DC converter 1, the first fixing metal jig 21, a temperature sensor 6 and the second fixing metal jig 22 are arranged in this sequence on the upper surface of the transformer 2, the temperature sensor 6 is held with the first fixing metal jig 21 and second fixing metal jig 22 and is then fixed to the upper surface 2a of the transformer 2. As a result, in comparison with the prior art, generation of leakage magnetic flux can be reduced, an apparatus can be reduced in size and reduction of cost can also be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter, and more particularly to a technique for easily detecting a temperature of a transformer.

[0002]

2. Description of the Related Art As a conventionally used DC / DC converter, for example, a DC / DC converter having a configuration as shown in FIG. 5 is known. DC / DC converter 101 shown in FIG.
Has a transformer 102 having a primary winding Np and a secondary winding Ns, an input filter 103 connected between the primary winding Np and the DC power supply 110, and a switching transistor 104. . Further, a switching control circuit 105 that outputs a pulse signal (PWM signal) to the transistor 104 to control on / off of the transistor 104, a temperature sensor 106 that measures the temperature of the core of the transformer 102, and a temperature sensor 106 And a temperature detecting circuit 107 for detecting when the temperature of the core of the transformer 102 becomes equal to or higher than a predetermined value and outputting a control signal to the switching control circuit 105.

A rectifying / smoothing circuit 108 for rectifying an AC voltage generated in the secondary winding Ns is connected to the secondary winding Ns, and an output of the rectifying / smoothing circuit 108 is a load 111. It is connected to the.

Next, the operation will be described. When a pulse signal is output to the base of the transistor 104 under the control of the switching control circuit 105, the transistor 104 is turned on and off by the pulse signal, and the transformer 102
Pulse current flows through the primary winding Np. This allows
A secondary AC voltage is generated in the secondary winding Ns, and the secondary AC voltage is rectified and smoothed by the rectification and smoothing circuit 108, and is supplied to the load 111 as a DC voltage. Thereby, power can be supplied to the load 111.

The core material used for the transformer 102 has a Curie point temperature. When the core material exceeds the Curie point temperature for some reason, the core does not show magnetism, so that the primary current of the transformer 102 rapidly increases. Therefore, the temperature of the core is monitored by the temperature sensor 106.

FIG. 6 is an explanatory view showing the structure of the transformer 102. As shown in FIG. 6, a temperature sensor 106 is installed on a magnetic core 102a inside a core of the transformer 102. And a primary winding Np and a secondary winding Ns.

When the temperature sensor 106 detects that the temperature of the core material has reached a set temperature lower than the Curie point temperature, the temperature detection circuit 107
The detection signal is output to the switching control circuit 105. Accordingly, the switching control circuit 105 controls the primary current of the transformer 102 to be reduced by reducing the duty ratio of the pulse signal output to the transistor 104, so that the temperature of the core material does not exceed the Curie point temperature. Can be controlled.

[0008] Such a conventional DC / DC converter 1
In FIG. 01, as shown in FIG.
a, the primary winding Np and the secondary winding Ns are connected to the temperature sensor 106.
Is wound around the magnetic core 102a in a partially expanded state.

Here, the efficiency of the transformer when the winding of the transformer is a perfect circle and when it is not a perfect circle will be described.

Since the winding of a general transformer is wound in a perfect circle around the core of the transformer, almost all of the magnetic flux generated by the current IA flowing through the primary winding passes through the core 102a. Become. The current flowing through the secondary winding is excited by the magnetic flux in the magnetic core 102a, and flows to the rectifying / smoothing circuit 108 as the secondary current IB1.

Assuming that the number of turns of the primary winding of the transformer 102 is Tp and the number of turns of the secondary winding is Ts, the following equation (1) holds.

IB1 = M1 * (Ts / Tp) * IA (1) where M1 is a coupling coefficient.

In a general transformer 102, since the coupling coefficient is approximately M1 = 1, the above equation (1) can be expressed by the following equation (2).

IB1 = (Ts / Tp) * IA (2) On the other hand, in the above-described conventional example, as shown in FIG.
p and Ns are in a state of being partially expanded with respect to the magnetic core 102a. Therefore, due to the influence of the bulging portion, the magnetic flux passing through the core 102a of the core decreases as compared with the above-described general case (when the winding is a perfect circle).
A magnetic flux that passes outside the magnetic core 102a is generated.

A part of the magnetic flux passing outside the magnetic core 102a leaks from between the primary winding Np and the secondary winding Ns, and becomes a leakage magnetic flux. This leakage flux is caused by the secondary winding Ns
Does not contribute to the generation of the secondary current IB2 excited in the above, the coupling coefficient M2 becomes smaller than 1 (M2 <1), and the relationship between IB1 and IB2 is expressed by the following equation (3).

IB2 = M2 * (Ts / Tp) * IA <IB1 (3) From the above equation (3), it is understood that the generation of the leakage magnetic flux reduces the secondary current.

Assuming that the voltage between the terminals of the primary winding Np of the transformer 102 is VA and the voltage between the terminals of the secondary winding Ns is VB, the efficiency K in the transformer 102 can be expressed by the following equation (4). .

K = (VB * IB) / (VA * IA) (4) Since IB2 <IB1 according to the above equation (3), the efficiency of the transformer 102 is lower than the equation (4). You can see that

Therefore, it is necessary to increase the primary power in order to output a current value required from the load 111 connected to the DC / DC converter 101, and to increase the primary power, the transformer 102 Inevitably, the size of the device must be increased, which causes a problem that not only the device becomes large-scale, but also the cost increases.

Further, a temperature sensor 106 is provided inside the winding.
, Which leads to a further increase in cost.

[0021]

As described above, in the conventional DC / DC converter 101, the temperature sensor 106 is connected to the magnetic core 102a inside the core of the transformer 102.
Because it is a configuration that can be attached to the
There is a disadvantage that the efficiency of the transformer 102 is reduced.
In addition, since the temperature sensor 106 is mounted inside the winding, there is a problem that the configuration is complicated and the cost is increased.

The present invention has been made to solve such a conventional problem, and an object of the present invention is to provide a transformer capable of simplifying the configuration without lowering the efficiency of the transformer. DC / D with
It is to provide a C converter.

[0023]

Means for Solving the Problems To achieve the above object, the invention according to claim 1 of the present application has a transformer and a temperature detecting means for measuring a core temperature of the transformer, wherein the core temperature is measured. DC / DC having a function of controlling to reduce the primary current of the transformer when a predetermined value is exceeded.
In the converter, a first fixing member, the temperature detecting means, and a second fixing member are arranged in this order on an upper surface of the transformer, and the temperature is detected by the first fixing member and the second fixing member. It is characterized in that the means is clamped and fixed to the transformer.

Further, the invention according to claim 2 is the first invention.
The fixing bracket and the second fixing bracket each have a crank shape in cross section having three planes, and the temperature detecting means is sandwiched between one surface of the first fixing bracket and one surface of the second fixing bracket. Then, the transformer is fixed to the upper surface, and the other two surfaces of the first fixing bracket are used to fall from one side surface of the transformer to a transformer fixing base. The transformer is fixed to the base, and the other two sides of the second fixing bracket are used to fall down to the base from the other side of the transformer, and the second fixing bracket is fixed to the base. It is characterized by having done.

According to a third aspect of the present invention, the temperature sensing portion of the temperature detecting means is formed integrally with one of the first fixing bracket and the second fixing bracket. Features.

According to a fourth aspect of the present invention, there is provided an insulating means for insulating the second fixture and the transformer.

The invention according to claim 5 is characterized in that the temperature detecting means includes a resistor whose resistance value changes with a change in temperature.

The invention according to claim 6 is characterized in that the temperature detecting means includes a diode whose resistance value changes according to a temperature change.

[0029]

According to the first aspect of the present invention, the temperature detecting means is sandwiched between the first fixing metal and the second fixing metal, and the temperature detecting means is fixed to the upper surface of the transformer. Therefore, the occurrence of leakage magnetic flux can be reduced as compared with the conventional case where the temperature detecting means is mounted inside the winding of the transformer. Therefore, the efficiency of the transformer can be improved, the size of the entire device can be reduced, and the cost can be reduced. Also, 2
Since the temperature detecting means is sandwiched and fixed by using the two fixing brackets, the temperature detection accuracy can be improved as compared with the case where the temperature detecting means is fixed using an adhesive or a screw. .

According to the second aspect of the present invention, since the first fixing bracket and the second fixing bracket each have a crank-shaped cross section, the fixing to the base is facilitated.

According to the third aspect of the present invention, the temperature detecting means is the first type.
Or the second fixture is integrally molded, so that it is possible to avoid occurrence of troubles such as dropping out of the temperature detecting means.

According to the fourth aspect of the present invention, since the insulating means is disposed between the second fixture and the transformer, it is possible to improve the insulation between the second fixture and the transformer.

According to the fifth aspect of the present invention, since a temperature-dependent resistor is used as the temperature detecting means, the transformer temperature can be accurately measured.

According to the sixth aspect of the present invention, since a temperature-dependent diode is used as the temperature detecting means, the transformer temperature can be accurately measured.

[0035]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a configuration of a DC / DC converter 1 according to one embodiment of the present invention. As shown in FIG. 1, the DC / DC converter 1 includes a transformer 2 having a primary winding Np, a secondary winding Ns, and a temperature sensor 6 for measuring a temperature of a core portion, and a primary winding of the transformer 2. An input filter 3 is provided between Np and the input terminal 91, and a switching transistor 4 is provided between the primary winding Np and the input terminal 92.

A switching control circuit 5 connected to the base of the transistor 4 for outputting a switching pulse signal having a desired duty ratio to the transistor 4 by PWM control, and a transformer 2 detected by the temperature sensor 6 And a temperature detection circuit 7 that outputs this detection signal to the switching control circuit 5 when the temperature of the core portion exceeds a temperature set lower than the Curie point temperature of the core material. Two input terminals 91, 9
2 is connected to the DC power supply 10.

The secondary winding Ns is formed by the secondary winding N
rectifies and smoothes the secondary voltage generated at the output terminal 9
3, 94, which are connected to a rectifying and smoothing circuit 8 for outputting to
The two output terminals 93 and 94 are connected to the load 11.

FIG. 2 is an explanatory diagram schematically showing the configuration of the transformer 2 shown in FIG. As shown in the figure, a primary coil Np and a secondary coil Ns are wound around a magnetic core 2a inside the core of the transformer 2.

The transformer 2 is fixed on a base 9 (a housing part of the DC / DC converter 1), and further has a first crank-shaped cross section so as to cover the upper surface 2b and the side surface 2c of the transformer 2. Are provided. The first fixture 21 is fixed to the base 9 with screws 23. Here, the “upper surface of the transformer 2” is the upper surface when the surface formed by the base 9 faces the horizontal direction and the transformer 2 is fixed thereon. Therefore, if the surface formed by the base 9 is oriented in the vertical direction, the left surface or the right surface of the transformer 2 is the “upper surface” in the present invention.

Further, a temperature sensing portion (temperature detecting means) 27 for measuring the core temperature is provided on the upper surface 21a of the first fixing member 21 provided on the upper surface 2b of the transformer 2. . Further, an insulating heat-dissipating sheet (insulating means) 25 having an L-shaped cross section is provided so as to cover the side surface 2d of the transformer 2.

Further, a second fixing bracket 22 having a crank-shaped cross section is provided so as to cover the upper side of the temperature sensing section 27 and the surface of the insulating heat dissipation sheet 25.
7 is firmly sandwiched between the upper surface 21a of the first fixture 21 and the upper surface 22a of the second fixture 22, and is fixed to the transformer 2. The upper surface 21a of the first fixture 21, the upper surface 22a of the second fixture 22, and the temperature sensor 27 constitute the temperature sensor 6 shown in FIG. The second fixture 22 is fixed to the base 9 with a screw 24, and the screw 24 is attached to the second fixture 2.
In order to prevent electrical conduction between the base 2 and the base 9, a part thereof is designed to be covered with an insulating material such as a resin.

Since the second fixture 22 is fixed to the transformer 2 via the insulating heat dissipation sheet 25,
While securing the heat radiation of the transformer 2, the second fixture 2
2 and the transformer 2 are insulated.

Further, electric wires 26a and 26b for taking out an output signal of the temperature sensor 6 are connected to the first fixture 21 and the second fixture 22, respectively.
6b is connected to the temperature detection circuit 7 (see FIG. 1).

FIG. 3 shows a temperature sensor 6 according to this embodiment.
FIG. 3 is a circuit diagram showing a specific configuration of a temperature detection circuit 7. As shown in the figure, the temperature sensor 6 includes a thermistor,
It has a temperature sensing part 27 configured as a temperature-dependent resistor such as a posistor, a temperature measuring resistor, or a PTC element.

The temperature detection circuit 7 has a comparator circuit 33, and the minus (inverted) input terminal of the comparator circuit 33 is connected to one end of the temperature sensing section 27. Further, the negative input terminal is also connected to the output terminal of the constant current source 32. Further, the comparator circuit 33
Is connected to the other end of the temperature sensing section 27 via a constant voltage generating circuit 31 that outputs a reference voltage Vref.

The comparator circuit 33 compares the supply voltage Vout to the minus input terminal with the supply voltage Vref to the plus input terminal. If the voltage Vout is smaller than the voltage Vref, the comparator circuit 33 returns " On the other hand, when the voltage Vout is higher than the voltage Vref, an "L" level signal is output.

Next, the operation of the present embodiment configured as described above will be described. When the switching control circuit 5 shown in FIG. 1 is driven to supply a rectangular pulse signal to the base of the transistor 4, the transistor 4 turns on and off in synchronization with the rectangular pulse. A voltage output from the DC power supply 10 is supplied to the primary winding Np of the transformer 2 via the input filter 3 when the transistor 4 is turned on and off.

Accordingly, an AC secondary current flows through the secondary winding Ns, and an AC secondary voltage is generated at both ends of the secondary winding. Then, the secondary voltage is rectified and smoothed by the rectification and smoothing circuit 8 and supplied to the load 11. By such an operation, the voltage supplied from the DC power supply 10 can be converted into a desired voltage value and supplied to the load.

As shown in FIG. 2, a temperature sensor 6 having a temperature sensing portion 27 is mounted on the upper surface 2b of the transformer 2, so that the temperature of the core portion of the transformer 2 is controlled by the temperature sensing portion 27. Is measured.

When the DC / DC converter 1 is operating stably, the temperature of the transformer 2 detected by the temperature sensing section 27 is a temperature sufficiently lower than the Curie point temperature in the core section of the transformer 2. It is. At this time, the reference voltage Vref shown in FIG. 3 and the voltage Vout (referred to as Vout1) generated in the temperature sensing section 27 are as follows: Vref> Vout1
The reference voltage Vref is set such that Therefore,
The output signal of the comparator circuit 33 is at the “H” level, and an “H” level signal is output to the switching control circuit 5 shown in FIG.

By this signal, the switching control circuit 5
Outputs a pulse signal (PWM signal) having a normal duty ratio to the transistor 4.

On the other hand, if the temperature of the core section of the transformer 2 rises for some reason, the temperature sensing section 27 has a positive temperature dependency, so that the voltage Vout generated in the temperature sensing section 27.
(This is referred to as Vout2). The relationship between the voltage Vout2 and the reference voltage Vref is represented by Vref
When <Vout2, the output signal of the comparator circuit 33 is inverted and becomes “L” level. As a result, an “L” level signal is output to the switching control circuit 5.

In accordance with this signal, the switching control circuit 5 controls the duty ratio of the output pulse signal so as to decrease, thereby reducing the primary current flowing through the primary winding Np of the transformer 2. As a result, the temperature of the core portion of the transformer 2 decreases, and falls below the Curie point temperature. In this way, control can be performed so that the temperature of the transformer 2 does not exceed the Curie point temperature.

In this way, the DC /
Since the DC converter 1 is configured to detect the temperature of the core using the temperature sensor 6 fixed to the core of the transformer 2, the DC converter 1 is arranged in a winding inside the core as in the related art. As compared with the case, it is possible to solve the problem that the leakage magnetic flux is generated. In addition, since the generation of the leakage magnetic flux can be prevented, the secondary voltage can be effectively generated, and when obtaining the same output, the transformer 2 can be downsized compared to the related art. This makes it possible to reduce the size, space, and cost of the entire apparatus. In addition, since the operation of inserting the temperature sensor into the winding is not required, the production is facilitated.

Further, as means for fixing the temperature sensing portion 27,
Adhesives and screws are not used, and two fixing brackets 21,
Since it is configured so as to be sandwiched and fixed at 22, the temperature can be detected with high accuracy. That is, in the method of fixing using an adhesive, the thermal resistance value changes due to the adhesive, so that the accuracy of temperature detection is reduced. In the method of fixing with screws, the thickness of the fixing brackets 21 and 22 is increased. Although it is necessary to increase the cost, such a problem can be solved by adopting a configuration in which the temperature sensing portion 27 is sandwiched between the two fixing brackets 21 and 22 as in the present embodiment. it can.

In the above embodiment, the temperature sensor 27 is disposed between the upper surface 21a of the first fixing member 21 and the upper surface 22a of the second fixing member 22, and the temperature sensor 6
Has been described, but the first fixture 21
Upper surface 21a or the upper surface 2 of the second fixture 22
It is also possible to form so that either side of 2a is raised and the temperature sensing part 27 is mounted on this part. According to such a configuration, it is possible to prevent a problem that the temperature sensing portion 27 falls off due to long use.

FIG. 4 is an explanatory diagram showing a modification of the circuit (temperature sensor 6 and temperature detection circuit 7) shown in FIG. As shown in the drawing, this modified example is different from the above-described embodiment in that a diode having temperature dependency is used instead of the resistor as the temperature sensing portion 27 '.

Also in this configuration, the temperature of the core of the transformer 2 is measured by using the temperature dependency of the diode, and when the temperature of the core exceeds a predetermined value, the switching control circuit 5 Thus, the duty ratio of the output pulse signal can be controlled to be reduced, and the same effect as in the above-described embodiment can be obtained.

Further, in the above-described embodiments and modified examples, the example in which a resistor or a diode having a positive temperature dependency is used has been described. However, a resistor or a diode having a negative dependency may be used. Is also possible.
In this case, since the resistance of the resistor changes so as to decrease as the core temperature rises, this change is detected and the core temperature is set to a temperature set lower than the Curie point temperature. What is necessary is just to detect whether it reached.

Although the DC / DC converter according to the present invention has been described based on the illustrated embodiment, the present invention is not limited to this, and the configuration of each unit may be any configuration having the same function. Can be replaced with something.

For example, in the DC / DC converter according to the present embodiment, an example in which the transistor 4 is used as a switching element has been described. However, the present invention is not limited to this. It is also possible to use switching elements.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a DC / DC converter according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a configuration of a transformer used in the DC / DC converter according to the embodiment.

FIG. 3 is a circuit diagram showing a specific configuration of a temperature sensor and a temperature detection circuit according to the embodiment.

FIG. 4 is a circuit diagram showing a modification of the temperature sensor and the temperature detection circuit according to the embodiment.

FIG. 5 is a circuit diagram showing a configuration of a conventional DC / DC converter.

FIG. 6 is an explanatory diagram showing a configuration of a transformer used in a conventional DC / DC converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DC / DC converter 2 Transformer 2a Magnetic core 2b Top surface 2c Side surface 2d Side surface 3 Input filter 4 Transistor 5 Switching control circuit 6 Temperature sensor 7 Temperature detection circuit 8 Rectification smoothing circuit 9 Base 10 DC power supply 11 Load 21 First fixing bracket 21a Upper surface 22 Second fixing bracket 22a Upper surface 23, 24 Screw 25 Insulating heat dissipation sheet 26a, 26b Electric wire 27, 27 'Temperature sensing part 31 Constant voltage generating circuit 32 Constant current source 33 Comparator circuit 91, 92 Input terminal 93, 94 output terminal

Claims (6)

[Claims] 1. A transformer and a temperature detecting means for measuring a core temperature of the transformer, and a function of controlling a primary current of the transformer to be reduced when the core temperature exceeds a predetermined value. In the DC / DC converter provided, a first fixture, the temperature detecting means, and a second fixture are arranged in this order on an upper surface of the transformer, and
A DC / DC converter characterized in that the temperature detecting means is sandwiched between the fixing bracket and the second fixing bracket and fixed to the transformer. 2. The first fixing member and the second fixing member each have a crank shape in cross section having three planes, and one surface of the first fixing member and one surface of the second fixing member. Thus, the temperature detecting means is sandwiched and fixed to the upper surface of the transformer, and the other two surfaces of the first fixing bracket are used to fall from one side surface of the transformer to a transformer fixing base. Fixing the first fixture to the base, using the other two surfaces of the second fixture to fall from the other side of the transformer to the base, 2. A fixing bracket is fixed to the base.
4. The DC / DC converter according to 1. 3. The temperature sensing part of the temperature detecting means,
3. The DC / DC converter according to claim 1, wherein the DC / DC converter is formed integrally with one of the fixing bracket and the second fixing bracket. 4. 4. The DC / DC converter according to claim 1, further comprising insulating means for insulating the second fixing bracket from the transformer. 5. The DC / DC converter according to claim 1, wherein said temperature detecting means includes a resistor whose resistance value changes according to a temperature change. 6. The DC / DC device according to claim 1, wherein said temperature detecting means includes a diode whose resistance value changes according to a temperature change.
converter.