JP4001564B2 - Printed circuit board with thermistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to high-frequency dielectric heating using a magnetron such as a microwave oven, and more particularly to a thermistor that performs overheat protection of a semiconductor switching element used in an inverter.
[0002]
[Prior art]
FIG. 4 is a configuration diagram of a conventional magnetron driving power source.
In the figure, the alternating current from the commercial power supply 11 is rectified to a direct current by the rectifier circuit 13, smoothed by the choke coil 14 and the smoothing capacitor 15 on the output side of the rectifier circuit 13, and given to the input side of the inverter 16. The direct current is converted to a desired high frequency (20 to 40 kHz) by turning on and off the semiconductor switching element in the inverter 16. The inverter 16 is controlled by an IGBT (Insulated Gate Bipolar Transistor) that switches DC at high speed and an inverter control circuit 161 that drives and controls the IGBT, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed. Is done.
[0003]
The input signal of the control circuit 161 is a detected current obtained by detecting the primary current of the rectifier circuit 13 with the CT 17 , and the detected current is input to the inverter control circuit 161 and used for controlling the inverter 16. Further, a temperature sensor (thermistor) 9 ′ is attached to a heat radiating fin for cooling the IGBT, and temperature information detected by this temperature sensor is input to the inverter control circuit 161 and used for controlling the inverter 16.
[0004]
In the step-up transformer 18, a high-frequency voltage that is the output of the inverter 16 is applied to the primary winding 181, and a high-voltage voltage corresponding to the winding ratio is obtained in the secondary winding 182. A winding 183 with a small number of turns is provided on the secondary side of the step-up transformer 18 and is used for heating the filament 121 of the magnetron 12. The secondary winding 182 of the step-up transformer 18 includes a voltage doubler half-wave rectifier circuit 19 that rectifies its output. The voltage doubler half wave rectifier circuit 19 includes a high voltage capacitor 191 and two high voltage diodes 192 and 193.
[0005]
[Problems to be solved by the invention]
By the way, installation conditions such as placing microwave ovens on the top, bottom, left and right sides of the furniture and closing the air supply / exhaust port of the microwave oven, or the motor for the cooling fan of the microwave oven There may be a problem that the coil portion is disconnected and the cooling fan becomes inoperable.
In such a case, as a method for preventing the thermal breakdown of the IGBT that controls the switching of the inverter power supply, conventionally, the thermistor 9 ′ is used to stop the semiconductor IGBT before the thermal breakdown to prevent the temperature rise.
[0006]
In this case, as a method of detecting the temperature by attaching the thermistor 9 ′,
(1) There was a method of fastening together with the package portion of the IGBT 16a with a thermistor lead sensor U with glasses terminals.
However, the co- fastening method for the package part can be realized only by human work, so the number of man-hours is increased and the cost is increased accordingly.
[0007]
2) There is also a method in which the thermistor is separately screwed to the heat dissipating fin and detected from the heat dissipating fin (see, for example, Patent Document 1).
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-312182 [Patent Document 2]
Japanese Patent No. 28922454 [0009]
Fig.5 (a) is a figure which shows the attachment method of patent document 1, and is a figure which shows the state which screwed the thermistor to the radiation fin.
In the figure, 6 is a printed circuit board, 7 is a radiation fin, 8 is an IGBT, and 9 'is a thermistor.
The heat radiating part of the IGBT 8 that generates high heat is fixed to the heat radiating fins 7, and its three legs are inserted into the through holes of the printed circuit board and soldered on the opposite side. The thermistor 9 ′ is also screwed to the radiating fin 7 and takes out temperature information of the radiating fin.
However, such a screw fastening method to the heat radiating fins also increases man-hours and costs, and because the detection temperature is not the direct temperature of the IGBT but the temperature of the heat radiating fins, both the temperature detection accuracy and sensitivity are poor. There were drawbacks.
[0010]
3) Furthermore, there was a method of attaching a radial thermistor in the vicinity of the IGBT 8 on the printed circuit board (for example, see Patent Document 2).
FIG. 5B is a view showing the attachment method described in Patent Document 2.
In the figure, 6 is a printed circuit board, 7 is a radiation fin, 8 is an IGBT, and 9 'is a thermistor. This method is retrofitted in the vicinity of the printed circuit board, and has the disadvantage that the man-hour increases because it is attached by hand, and the thermal time constant of the thermistor deteriorates because it is directly affected by the cooling air.
[0011]
Furthermore, the thermistor 9 'was also attached to the vicinity A of the leg portion of the IGBT 8, but this was also retrofitted to the vicinity of the printed circuit board, and it was attached by hand, which increased man-hours and the effect of cooling air. Since it was received directly, there was a drawback that the thermal time constant of the thermistor deteriorated.
Accordingly, an object of the present invention is to solve these problems and to provide a printed circuit board with a thermistor which does not need to be attached by hand and is hardly affected by cooling air and has a small thermistor thermal time constant.
[0012]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned problems, and the invention of the printed circuit board with thermistor according to claim 1 is directed to an inverter unit that converts direct current into alternating current of a predetermined frequency by switching with a semiconductor switching element (16a). (16), an inverter control circuit (161) for outputting a switching voltage to the control terminal of the semiconductor switching element, and a thermistor (9) for detecting the temperature of the switching element (16a) and a resistor (163) connected in series a series circuit formed by the semiconductor switching element radiating fins (7) (16a) and attached to radiate heat from the switching element (16a), the printed circuit board formed by soldered mounted, the The series circuit of the thermistor (9) and the resistor (163) is connected to the inverter control circuit (161). The junction point potential between the thermistor (9) and the resistor (163) of the series circuit is input to the inverter control circuit (161), and the other end of the thermistor (9) and the inverter control circuit (161) ) Is directly connected to the emitter leg of the semiconductor switching element (16a), and is exposed to the same potential near the emitter leg of the semiconductor switching element (16a) exposed to the printed circuit board solder surface side of the switching element (16a). The semiconductor thermistor (9a) is directly soldered to the pattern, and the potential change caused by the resistance value change of the thermistor (9) is directly input to the inverter control circuit (161), thereby switching the semiconductor switching element (16a). It is characterized by controlling .
According to a second aspect of the present invention, in the printed circuit board with a thermistor according to the first aspect, the semiconductor switching element is an IGBT (Insulated Gate Bipolar Transistor).
According to a third aspect of the present invention, in the printed circuit board with thermistor according to the first or second aspect, the thermistor is a chip thermistor.
According to a fourth aspect of the present invention, there is provided a high frequency dielectric heating device comprising: a printed circuit board including an inverter unit, heat radiation fins and a thermistor; a step-up transformer for boosting an output voltage of the inverter unit; and an output voltage of the step-up transformer. A microwave output unit comprising a high voltage rectification unit for voltage rectification, a magnetron that radiates the output of the high voltage rectification unit as a microwave, and a heating cooking chamber that accommodates an object to be heated, and radiates from the magnetron in the high-frequency dielectric heating apparatus by supplying microwaves into the cooking chamber for heating the object to be heated that is, using a thermistor with a printed circuit board of any one of claims 1 to 3 as the printed circuit board It is characterized by that.
[0013]
According to the above invention, since the thermistor is a chip component, it can be quickly mounted by an automatic machine. Further, since this thermistor directly receives the current flowing through the IGBT leg, a value close to the junction temperature of the IGBT can be detected.
Furthermore, since the thermistor is attached not to the heat radiating fin side but to the solder surface on the back of the printed circuit board, it is not affected by cooling air. Moreover, the cost is not increased as in the conventional method.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a printed circuit board with an IGBT protection thermistor according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a configuration diagram of a magnetron driving power source according to the present invention.
In the figure, the alternating current from the commercial power supply 11 is rectified to a direct current by the rectifier circuit 13, smoothed by the choke coil 14 and the smoothing capacitor 15 on the output side of the rectifier circuit 13, and given to the input side of the inverter 16. The direct current is converted to a desired high frequency (20 to 40 kHz) by turning on and off the semiconductor switching element IGBT in the inverter 16. The inverter 16 is driven by an IGBT 16a that switches DC at high speed and an inverter control circuit 161 that controls the IGBT 16a, and the current flowing through the primary side of the step-up transformer 18 is switched on / off at high speed.
[0015]
In the step-up transformer 18, a high-frequency voltage that is the output of the inverter 16 is applied to the primary winding 181, and a high-voltage voltage corresponding to the winding ratio is obtained in the secondary winding 182. A winding 183 with a small number of turns is provided on the secondary side of the step-up transformer 18 and is used for heating the filament 121 of the magnetron 12. The secondary winding 182 of the step-up transformer 18 includes a voltage doubler full wave rectification circuit 20 that rectifies its output. The voltage doubler full-wave rectifier circuit 20 includes high-voltage capacitors 201 and 202 and two high-voltage diodes 203 and 204.
[0016]
According to the present invention, the thermistor 9 for detecting the temperature of the IGBT 16a is not directly placed on the emitter leg of the IGBT (16a), but on the printed circuit board 6 instead of on the emitter fin side of the IGBT 16a, instead of the package portion or the heat radiating fin portion of the conventional IGBT 16a. The thermistor used for soldering is soldered on the solder surface on the back of the chip, and the thermistor used is a chip thermistor.
The temperature information (resistance value) of this thermistor lowers the potential at the connection point with the resistor 163 as the temperature of the IGBT (16a) rises, and this potential at the connection point is input to the inverter control circuit 161 to function to suppress heating.
[0017]
FIG. 2 shows a printed circuit board to which a chip thermistor is attached according to the present invention. In the figure, 6 is a printed circuit board, 7 is a radiation fin, 8 is an IGBT, and 9 is a chip thermistor.
The heat radiating part of the IGBT 8 that emits high heat is fixed to the heat radiating fin 7, and its three legs are inserted into through holes of the printed circuit board and soldered on the opposite side (back side, solder side). It can be seen that a chip thermistor is used as the thermistor 9 and is soldered directly to the vicinity of the leg portion of the IGBT 16a (the same pattern potential) on the solder surface on the back side of the printed circuit board 6 instead of the radiating fin side.
[0018]
By adopting such a configuration, since the thermistor is a chip component, it can be quickly mounted by an automatic machine, and since this thermistor directly receives the current flowing through the IGBT leg, a value close to the junction temperature of the IGBT can be detected. . Furthermore, since the thermistor is attached not to the heat radiating fin side but to the solder surface on the back of the printed circuit board, it is not affected by cooling air. Moreover, the cost is not increased as in the conventional method.
[0019]
FIG. 3 shows the power control waveform of the IGBT in the case where the thermistor is placed near the legs of the diode bridge (a) and the case of the present invention placed in the vicinity of the legs of the IGBT, and the temperature control waveform of each IGBT ( It is a diagram showing c).
In the diagrams (a) and (b), the vertical axis represents the input current, and the horizontal axis represents the time. In FIG. 3C, the vertical axis is the IGBT temperature, the horizontal axis is the time, T0 is the target (reference) temperature of the IGBT, T1 and T1 ′ are the maximum and minimum values of the temperature control waveform of FIG. 3B according to the present invention. The values T2 and T2 ′ indicate the maximum value and the minimum value of the temperature control waveform in the case of FIG.
[0020]
In FIG. 3C, when an inverter is operated by passing a current through the IGBT, the temperature of the IGBT rises and eventually reaches the target temperature T0 at time to.
(A): When the thermistor is placed in the vicinity of the diode bridge leg, even if the IGBT temperature reaches the target temperature T0, heat conduction to the thermistor is poor and the thermistor cannot immediately detect this. Then, it is finally detected that the target temperature is reached at time t2 (at this time, the temperature of the IGBT is greatly increased to T2), and the current flowing through the IGBT is reduced (t2 in FIG. 1A). At this time, the temperature of the IGBT starts to decrease, and finally the thermistor detects that the temperature has decreased below the target temperature T0 at a temperature T2 ′ that is lower than the target temperature T0 (at this time, the temperature of the IGBT greatly decreases to T2 ′). ) Increase the input current. This is repeated below. As described above, according to the temperature detection method of the conventional method, the detected temperature fluctuates within a wide range between the maximum temperature T2 and the minimum temperature T2 ′. Therefore, the power control interval of the IGBT becomes large (see FIG. A), and the input It was difficult to finely control the current.
(B) On the other hand, when the thermistor is placed in the vicinity of the leg portion of the IGBT according to the present invention, the temperature of the IGBT is transferred to the thermistor with good thermal conductivity and sensitivity, and the thermistor reaches the target temperature T0 at the time t1 immediately after that. (The IGBT temperature at this time has risen slightly to T1), and the input current is reduced (t1 in FIG. 4B). At this time, the temperature of the IGBT starts to fall, and the thermistor quickly detects this at a temperature T1 ′ that is lower than the target temperature T0 (at this time, the temperature of the IGBT slightly drops to T1 ′), and increases the input current. Hereinafter, this is repeated in a short cycle (see FIG. 5B).
As described above, according to the temperature detection method using the thermistor placed in the vicinity of the leg portion of the IGBT according to the present invention, the temperature of the IGBT can be maintained within a slight range between the maximum temperature T1 and the minimum temperature T1 ′.
[0021]
By arranging the thermistor in the vicinity of the emitter terminal of the IGBT in this way, the temperature is detected in response to the temperature change of the IGBT, so the temperature is detected compared to the case where the thermistor is arranged at the base of the diode bridge at the same potential. Becomes accurate, and the temperature detection level can be set to the last minute temperature of the IGBT.
Moreover, since the temperature of the IGBT can be detected accurately and quickly, the power control of the IGBT can be made fine, the power down period can be shortened, and the inverter output can be stabilized as much as possible. Therefore, since the IGBT temperature can be monitored with high sensitivity, the target temperature in FIG. (C) can be accurately grasped, and accordingly, the power control in FIG. (B) can be made finer than in the case of FIG. By doing so, the temperature of the IGBT is stabilized as shown in the (b) IGBT temperature diagram of FIG. 7C, power control is facilitated, and the influence on cooking performance is reduced.
[0022]
【The invention's effect】
As described above, according to the present invention, an inverter circuit that switches direct current with an IGBT and converts it into alternating current of a predetermined frequency, a heat dissipating fin that attaches the IGBT and dissipates heat emitted from the IGBT, and a temperature of the IGBT In a printed circuit board that is mounted and soldered with a thermistor for detecting the thermistor, the thermistor is soldered to an IGBT leg by soldering the thermistor to or near the leg exposed on the printed circuit board solder surface side of the IGBT. Because the current flowing through the part is directly received, a value close to the junction temperature of the IGBT can be detected, and the thermistor is not mounted on the heat dissipation fin side but the solder surface on the back of the printed circuit board, so it is not affected by cooling air, so it is an accurate IGBT The temperature can be detected.
In addition, since the mounting location is the IGBT emitter leg, high insulation is not required, and the thermistor is an inexpensive and ultra-compact chip thermistor that can be quickly mounted by an automatic machine and does not increase the cost as in the past. There is also an effect.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a magnetron drive power supply with a thermistor according to the present invention.
FIG. 2 is a front view of a printed circuit board with a thermistor according to the present invention.
FIG. 3 shows an input current control waveform when the thermistor is placed in the vicinity of the leg of the diode bridge (a) and in the case of the present invention placed near the leg of the IGBT, and a temperature control waveform of each IGBT ( It is a diagram showing c).
FIG. 4 is a configuration diagram of a conventional magnetron drive power supply with a thermistor.
5A is a front view of a printed circuit board with thermistor described in Patent Document 1, and FIG. 5B is a front view of the printed circuit board with thermistor described in Patent Document 2. FIG. It is a perspective view.
[Explanation of symbols]
7 Radiation fin 8 IGBT
9 Thermistor 11 Commercial power supply 12 Magnetron 13 Rectifier circuit 14 Choke coil 15 Smoothing capacitor 16 Inverter 161 Inverter control circuit 18 Step-up transformer 181 Primary winding 182 Secondary winding 183 Filament heating winding 19 Half-wave rectification circuit 20 Full-wave rectification Circuits 201 and 201 High-voltage capacitors 203 and 204 High-voltage diode

Claims (4)

An inverter unit for switching direct current with a semiconductor switching element to convert it into alternating current of a predetermined frequency, an inverter control circuit for outputting a switching voltage to a control terminal of the semiconductor switching element, a thermistor and a resistor for detecting the temperature of the switching element In a printed circuit board formed by mounting and soldering a series circuit formed by serial connection and a heat radiation fin for dissipating heat emitted from the switching element by attaching the semiconductor switching element,
The series circuit of the thermistor and a resistor is connected to both ends of the inverter control circuit, and a connection point potential between the thermistor and the resistor of the series circuit is input to the inverter control circuit, and the other end of the thermistor and the inverter control One end of the circuit is directly connected to the emitter leg of the semiconductor switching element, and the thermistor is soldered directly to the same potential pattern in the vicinity of the emitter leg of the semiconductor switching element exposed on the printed circuit board solder surface side of the switching element. A printed circuit board with a thermistor, wherein the switching of the semiconductor switching element is controlled by directly inputting a potential change caused by a change in resistance value of the thermistor to the inverter control circuit . 2. The printed circuit board with a thermistor according to claim 1, wherein the semiconductor switching element is an IGBT (Insulated Gate Bipolar Transistor). 3. The printed circuit board with thermistor according to claim 1, wherein the thermistor is a chip thermistor. A printed circuit board comprising an inverter unit, heat radiation fins, and a thermistor, a step-up transformer that boosts the output voltage of the inverter unit, a high-voltage rectifier unit that rectifies the output voltage of the boost transformer, and the high-voltage rectifier unit A microwave output unit composed of a magnetron that radiates the output of
A high-frequency dielectric heating apparatus that heats the object to be heated by supplying microwaves radiated from the magnetron to the heating cooking room, and as the printed board. Item 4. A high-frequency dielectric heating apparatus using the printed circuit board with thermistor according to any one of items 1 to 3.

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