JPH09162003A - Positive temperature coefficient thyristor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the generation of a thermal-stress breaking due to a temperature difference between the temperature of the interior of a semiconductor ceramic element having positive temperature characteristics and the temperature of the surface part of the element at the time when an abrupt voltage is applied to the element by a method wherein the temperature of the element is held at a temperature higher than room temperatures by heating the element. SOLUTION: A positive temperature coefficient thyristor device 11 is constituted into a structure wherein a semiconductor ceramic element (PTC element) 3 for overcurrent protection use, which shows positive temperature characteristics, and a heater (a heating element) 12 are housed in a case 14. The heater 12 is applied by a current through lead terminals 13 and the temperature in the case 14 is made higher than room temperatures and is held at a temperature lower than a Curie point temperature. As this result, the element 3 is also held at the same temperature as that in the case 14. The nearer the temperature of the element 3 is the Curie point temperature, the better this temperature is and specially, if the temperature in the case 14 or the temperature which is held by the element 3, and the Curie point temperature are respectively assumed T and Tc, the temperature is adjusted by the heater 12 so as to satisfy the condition of Tc-60 deg.C<T<Tc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor (P) having a semiconductor ceramic element exhibiting positive temperature characteristics.
TC) device.

[0002]

2. Description of the Related Art As a conventional positive temperature coefficient thermistor device using a semiconductor ceramic element exhibiting a positive temperature characteristic (hereinafter referred to as a PTC element), for example, one having a structure shown in FIG. 2 is known. In this positive temperature coefficient thermistor device 1, electrodes 2 are provided on opposite sides of an element body 3a made of a semiconductor ceramic, and lead wires 4 are electrically connected to each electrode 2 by soldering or the like to obtain a PT.
The C element 3 is formed, and the PTC element 3 has the exterior resin 5
It is covered with.

In such a PTC element, as shown in FIG. 1, which shows the relationship between the element resistance and the temperature, the resistance value sharply increases above the Curie point temperature, so that various kinds of protection such as circuit overcurrent protection are possible. Is used for. That is, P
When an overcurrent flows through the TC element, the resistance of the PTC element causes P
Since the temperature of the TC element suddenly rises and its resistance value becomes very large, the current of the circuit in which the PTC element is inserted is cut off and the circuit is protected from overcurrent.

[0004]

When a voltage is suddenly applied to the PTC element through the lead wire of the positive temperature coefficient thermistor device as described above, the PTC element heats up and the PTC element often breaks down.

Therefore, the inventors of the present invention measured the temperature distribution inside the PTC element by using an infrared temperature analysis device in order to investigate the heat generation state of the PTC element during energization. FIG. 3 is a diagram showing the temperature distribution inside the PTC element 3 using the isotherms 6. As shown in FIG.
Since the temperature is high inside the TC element and the temperature is low on the surface of the PTC element, it is considered that the element destruction is caused by the thermal stress destruction due to the temperature difference between the inside of the element and the surface portion.

[0006] Then, when examined in detail, the mechanism of device destruction could be considered as follows. When a voltage is suddenly applied to the PTC element, the PTC element generates heat due to a current flowing through the PTC element, but the temperature inside the element becomes higher than the temperature at the surface due to a difference in heat dissipation between the inside and the surface. . When the temperature inside the element increases, the resistivity inside the element becomes higher than that at the surface, so the amount of heat generated inside the element further increases, and the heat dissipation and the increase in the resistivity inside the element increase the temperature inside the element and the surface. The temperature difference between the PTC element and the PTC element is broken due to the difference in thermal expansion between the inside and the surface of the element.

The present invention was made on the basis of the above findings obtained by the inventors of the present invention. The purpose of the present invention is to detect the inside and the surface of the semiconductor ceramic element showing a positive temperature characteristic. An object of the present invention is to provide a positive temperature coefficient thermistor device which is excellent in heat resistance fracture characteristics while avoiding thermal stress fracture due to temperature difference.

[0008]

A positive temperature coefficient thermistor device according to a first aspect of the present invention includes a semiconductor ceramic element exhibiting a positive temperature characteristic, and a semiconductor ceramic element for maintaining the temperature higher than room temperature and lower than the Curie point. And a heating element.

In the positive temperature coefficient thermistor device according to a second aspect of the present invention, the temperature of the semiconductor ceramic element exhibiting a positive temperature characteristic is Tc-60 ° C <T <Tc, where Tc is the semiconductor ceramic element. Curie point temperature T: a heating element for maintaining the temperature of the semiconductor ceramic element.

A positive temperature coefficient thermistor device according to a third aspect of the present invention has a Curie point temperature of 90 ° C. or higher and shows a positive temperature characteristic of a semiconductor ceramic element, and the temperature of the semiconductor ceramic element is Tc-40 ° C. < T <Tc, where Tc: Curie point temperature of the semiconductor ceramic element, T: heating element for maintaining the temperature of the semiconductor ceramic element.

[0011]

According to the positive temperature coefficient thermistor device of the present invention, the temperature of the semiconductor ceramic element having a positive temperature characteristic is kept higher than room temperature by heating the semiconductor ceramic element having the positive temperature characteristic. The temperature difference between the inside of the element and the surface portion can be reduced. Therefore, even when a voltage is suddenly applied, it is possible to avoid the thermal stress fracture due to the difference in thermal expansion dimension between the inside and the surface of the semiconductor ceramic element, and the positive characteristic excellent in the thermal breakdown resistance is obtained. A thermistor device can be obtained. Particularly, good flash withstand voltage test results can be obtained.

Further, since the temperature of the semiconductor ceramic element is lower than the Curie point temperature, it is possible to avoid the resistance value of the semiconductor ceramic element from becoming high resistance, and the resistance value becomes unstable due to the temperature change. Never.

The temperature T of the semiconductor ceramic element is
If the temperature is maintained in the range of Tc-60 ° C. <T <Tc, the semiconductor ceramic element can be held in a temperature region close to the Curie point, and the flash withstand voltage value of the positive temperature coefficient thermistor device can be increased.

Further, since the Curie point temperature Tc of an ordinary overcurrent protection element is 90 ° C. or higher, if the temperature T of the semiconductor ceramic element is kept within the range of Tc-40 ° C. <T <Tc. It is possible to obtain a large flash withstand voltage value that cannot be obtained normally.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

(One Embodiment of the Present Invention) FIG. 4 is a schematic view showing a positive temperature coefficient thermistor device 11 according to one embodiment of the present invention. The positive temperature coefficient thermistor device 11 has a case 14 in which a semiconductor ceramic element (PTC element) 3 and a heater (heating element) 12 that exhibit positive temperature characteristics for overcurrent protection are housed. The PTC element 3 is connected in series to a circuit (not shown) and is used to cut off the current when an overcurrent flows. Further, the heater 12 is energized from the lead terminal 13, and keeps the temperature inside the case 14 higher than room temperature and lower than the Curie temperature, and as a result, keeps the temperature of the PTC element 3 at the same temperature. This temperature T is better as it is closer to the Curie point temperature Tc of the PTC element 3, and in particular, if the temperature inside the case 14 or the temperature held by the PTC element 3 is T and the Curie point temperature is Tc, then Tc-60 ° C < It is preferable to adjust the temperature with the heater 12 so that T <Tc.

As the heater 12 for heating the PTC element 3 to maintain the temperature, it is preferable to use a positive temperature coefficient thermistor element, but a SiC heater or another heater may be used.

(PTC element flash withstand voltage test) Next, the PTC element was placed in a constant temperature bath to keep the temperature of the PTC element at various temperatures, and the flash withstand voltage value (V) of the PTC element at each temperature was obtained. . The result is shown in FIG. Here, the flash withstand voltage test is to examine whether or not the PTC element is destroyed by applying a pulsed overvoltage instantaneously. The flash withstand voltage value is the withstand voltage before the PTC element is destroyed. Point out. Further, the one shown in FIG. 1 was also measured by the inventors of the present invention, in which the temperature of the PTC element was kept at various temperatures in a constant temperature bath, and the resistance value at each temperature was measured. It is a thing.

As can be seen from FIG. 5, the flash withstand voltage value increases as the temperature of the PTC element is kept higher. This is because by holding the PTC element at a temperature higher than room temperature, the temperature difference between the inside of the element and the surface portion when a voltage is suddenly applied is reduced, the dimensional change due to thermal expansion is reduced, and the heat generated is reduced. It is considered that this is because the stress becomes small.

Therefore, even when the temperature T of the PTC element 3 is maintained at room temperature or higher and Curie point temperature Tc or lower by heating with the heater 12 as in the positive temperature coefficient thermistor device 11, the flash withstand voltage of the PTC element 3 is maintained. It is considered that the value can be increased to prevent thermal stress destruction of the PTC element 3. However, when the PTC element 3 is kept at the Curie point temperature Tc or higher, as shown in FIG. 1, the PTC element 3 has a high resistance and the resistance value is stable because the temperature change rate of the resistance value is large. Is damaged. Therefore, it can be said that it is preferable that the PTC element 3 be maintained at a temperature as close to the Curie point temperature Tc as possible, below the Curie point temperature Tc.

(Comparison of Flash Withstand Voltage Values in Example and Comparative Example) Therefore, the flash withstand voltage value test was conducted using an actual positive temperature coefficient thermistor device instead of the constant temperature bath to confirm the effect. The positive temperature coefficient thermistor device 11 of the embodiment is shown in FIG.
The PTC element 3 having the structure as shown in FIG. 3 and having a Curie point temperature Tc of about 120 ° C. was used. The inside of the case 14 is heated to 100 ° C by the heater 12.
Held. Under these conditions, the resistance value and flash withstand voltage value of the PTC element 3 were measured. In this measurement result, as shown in Table 1, the resistance value of the PTC element 3 was 6Ω and the flash withstand voltage value was 490V.

[0021]

[Table 1]

Similarly, a Curie point temperature Tc of about 120 ° C. is obtained by using a positive temperature coefficient thermistor device having no heater.
While maintaining the PTC element at room temperature (25 ° C.), the resistance value and flash withstand voltage value of the PTC element were measured. In this measurement result, as shown in Table 1, the resistance value of the PTC element was 6Ω and the flash withstand voltage value was 280V.

Therefore, as can be seen from Table 1, the flash withstand voltage value can be improved by holding the PTC element at a temperature close to the Curie temperature Tc. It is understood that the difference in temperature between the inside of the element and the surface portion when a voltage is suddenly applied is reduced, so that a material having excellent thermal breakdown resistance can be obtained. The holding temperature T of the PTC element also applies to this embodiment, but if the Curie point temperature Tc is 90 ° C. or higher, Tc-4
Setting 0 ° C. <T <Tc is particularly desirable for improving the flash withstand voltage value.

[0024]

According to the present invention, the semiconductor ceramic element having a positive temperature characteristic is heated by the heating element to keep the temperature of the semiconductor ceramic element at a temperature higher than room temperature and lower than the Curie point. The temperature difference between the inside of the element and the surface portion can be reduced, and thermal stress fracture due to the difference in the thermal expansion dimension between the inside of the element and the surface portion can be avoided. In particular, a good flash withstand voltage test result can be obtained, and the reliability of the positive temperature coefficient thermistor device can be improved. Further, the fluctuation of the resistance value due to the temperature change (outside air when the PTC element is not operating) is eliminated.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a temperature and a resistance value in a PTC element.

FIG. 2 is a schematic sectional view showing a conventional positive temperature coefficient thermistor device.

FIG. 3 is a diagram showing the temperature distribution in the PTC element during energization by isothermal lines.

FIG. 4 is a schematic diagram showing a positive temperature coefficient thermistor device according to an embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the temperature of the PTC element and the flash withstand voltage value.

[Explanation of symbols]

3 PTC element (semiconductor ceramic element showing positive temperature characteristics) 12 heater 14 case

Claims (3)

[Claims] 1. A positive temperature coefficient thermistor device comprising: a semiconductor ceramic element exhibiting a positive temperature characteristic; and a heating element for keeping the semiconductor ceramic element at a temperature higher than room temperature and lower than the Curie point. 2. A semiconductor ceramic element exhibiting a positive temperature characteristic, and a temperature of the semiconductor ceramic element is Tc−60 ° C. <T <Tc, where Tc: Curie point temperature of the semiconductor ceramic element T: the semiconductor ceramic element A positive temperature coefficient thermistor device equipped with a heating element for maintaining the temperature of. 3. A semiconductor ceramic element having a Curie point temperature of 90 ° C. or higher and exhibiting positive temperature characteristics, and the temperature of the semiconductor ceramic element is Tc−40 ° C. <T <Tc, where Tc: the semiconductor ceramic Curie point temperature of element T: Positive temperature coefficient thermistor device provided with a heating element for maintaining the temperature of the semiconductor ceramic element.