JPH0736696B2 - Semiconductor element protection circuit - Google Patents

Description

The present invention relates to a protection circuit for a semiconductor device, and more particularly to a power semiconductor device used as a switching device for a large current, in which the power from an overcurrent is exceeded. It relates to an electric circuit for protecting a semiconductor device.

(Prior Art) A contact switch is widely used as a device for turning on / off an electric circuit through which a large current flows, but in recent years, a contactless semiconductor switch has advantages such as no arc, no noise, and no maintenance. Have been started to use. Such a semiconductor switch has the advantages described above, but is very weak against overcurrent (especially abnormal current such as short circuit current). For example, when a current exceeding a specified value flows through a thyristor forming a semiconductor switch, the thyristor breaks down and is always turned on.

For this reason, a fast-acting fuse is inserted in an electric circuit, and when an overcurrent flows in the electric circuit, the circuit is cut off to protect the semiconductor switch. However, when such a fast-acting fuse is used, a new quick-acting fuse must be replaced with a new one in order to restore the circuit after the fast-acting fuse is blown by an overcurrent, and there is a problem that maintenance becomes complicated. It was Further, the responsiveness is not always satisfactory, and there is a problem in terms of cost due to replacement.

On the other hand, contact breakers have been tried to protect some semiconductor elements. However, such a breaker involves a mechanical operation to open the contact, and there is a time delay from the occurrence of overcurrent to the operation of the breaker. As a result, there is a problem that the responsiveness required to protect the semiconductor element is not sufficient.

(Problems to be Solved by the Invention) The present invention has been made in order to solve the above-mentioned conventional problems, and quickly turns off an electric circuit even when an overcurrent such as a short-circuit current flows, and a semiconductor switch. It is an object of the present invention to provide a protection circuit for a semiconductor element capable of surely protecting the semiconductor device and easily performing restoration.

[Structure of the Invention] (Means for Solving Problems) The present invention relates to a power semiconductor element, a breaker connected in series to the semiconductor element, and a general formula (V _1-X A _X ) ₂ O.
₃ [wherein A represents at least one metal selected from Cr, Al and Sc, and x represents 0 ≦ x ≦ 0.02], and a current limiting element having a composition represented by the formula It is a semiconductor element protection circuit.

The current limiting element having the composition represented by the above general formula has a characteristic that the resistance at room temperature is as low as 10 ⁻³ Ω · cm or less, and the resistance increases by two digits at 100 ° C., and the response is extremely high. Have.

As an element whose resistance increases with temperature rise, a BaTiO ₃ semiconductor element has been conventionally known, but such an element has a large resistance value at room temperature of 10 to 10 ² Ωcm, It is not suitable as a current limiting element incorporated in a circuit.

Next, the current limiting element having the composition of the above general formula will be described. Cr, Al, and Sc in the formula are elements necessary to exert the characteristic (PTC characteristic) of increasing the resistance when the temperature rises, and the value of x needs to be in the range of 0 ≦ x ≦ 0.02. And a more preferable range is 0.0005 ≦ x ≦ 0.015. When the value of x exceeds 0.02, the current limiting element maintains the high resistance state and does not show the PTC characteristic.

In the current limiting element having the above composition, by incorporating Fe, Cu, Ni, Co and Sn, it becomes possible to enhance the sinterability of the current limiting element. The sinterability can be improved by adding at least one of these metals in an amount of 20% by weight or less. That is, if the added amount of these metals exceeds 20% by weight, the PTC ratio will be reduced. The most preferable metal addition range is 2 to 15% by weight. Among the above metals, Sn is particularly effective because it can improve the PTC characteristics in addition to the above-mentioned improvement in sinterability. Sn is stable as a metal in the sintering temperature of 1400 to 1600 ° C. and in a sintering atmosphere, and intervenes as a liquid phase between particles of the metal oxide represented by the above formula, and can exert an effect of promoting sintering. In addition, in the sintered body after sintering, the Sn precipitate phase reduces the specific resistance in the low resistance region in the PTC characteristic,
It also has the effect of expanding the current capacity. Further, the current limiting element containing Sn has a feature that the transition temperature variable showing the PTC characteristic is small.

In the current limiting element having the above composition, Fe, Cu, Ni, Co,
By adding W or Mo separately from Sn, the crystal grains of the sintered body can be made small, and sufficient thermal shock resistance can be exhibited even when rapidly heated by an overcurrent.

Hereinafter, a protection circuit for a semiconductor device of the present invention will be described in detail with reference to FIG.

In the figure, 1 is a load, 2 is a semiconductor switch having, for example, a thyristor for turning on / off the load 1, 3 is a current limiting element having the composition of the above formula, 4 is a breaker, and the current limiting element 3 and The breakers 4 are connected in series with the semiconductor switches 2, respectively.

(Operation) In the electric circuit shown in FIG. 1, when an abnormality occurs in the load 1 and an overcurrent starts to flow in the circuit, the current limiting element 3 responds at high speed to start the operation, and the overcurrent is equal to or less than a predetermined value. Limited to. Since the current limiting element 3 having the composition represented by the above general formula has extremely high responsiveness, it exhibits a current limiting effect within 1/4 cycle. If the current limiting against the overcurrent is continued only by such a current limiting element 3, the temperature further rises due to Joule heat, the resistance decreases and the current limited to a small value increases again, so-called current limiting effect. Disappear. However,
By connecting the breaker 4 together with the current limiting element 3 to the semiconductor switch 2 in series, the resistance of the current limiting element 3 starts to decrease, that is, the breaker 4 starts to operate before the current limiting effect begins to disappear. The circuit can be kept off within / 2 cycles. Therefore, the current limiting element 3 having high responsiveness
By combining this with the breaker 4 that cuts off the circuit within 1/2 cycle, which has a relatively low responsiveness, those current limiting cutoff functions are well superimposed, resulting in extremely high speed when overcurrent flows. The current-time product (I ² · t) is greatly reduced by limiting the current with the current, and as a result, the electric circuit can be quickly turned off to reliably protect the semiconductor switch 2. Thus, both the current limiting element 3 and the breaker 4 are necessary for protection of the semiconductor switch 2, and it is difficult to effectively protect the semiconductor switch 2 from overcurrent even if only one of them is used. Become. If a high-speed current limiting breaker having a high contact dissociation speed is used as the breaker, the current limiting action of the current limiting element can be more effectively exhibited.

Further, by combining the current limiting element 3 and the breaker 4, it is possible to achieve an additional effect that the breaker 4 can cut off a current exceeding the rated breaking capacity.

Further, after the current limiting element 3 is cooled to room temperature, the breaker 4
By turning on, the circuit can be quickly restored, and the operability can be improved as compared with the conventional protection circuit using the fast-acting fuse.

(Embodiment of the Invention) An embodiment of the present invention will be described below with reference to FIG.

Example Semiconductor switch (current carrying capacity; 40 A, allowable current time product; I ² ·
t = 3200A ² sec) 2, composition is (V _0.997 Cr _0.003 ) ₂ O ₃ +5
Current limiting element made of% Sn (shape; 5 mm × 5 mm × 30 mm, resistance;
About 10 mΩ) 3 and a commercially available high-speed current limiting breaker (rated breaking capacity: 220 V-2.5 kA) 4 were respectively incorporated into the load 1 as shown in FIG. 1 to form an electric circuit.

Comparative Example An electric circuit having the same configuration as that of the above-described example (incorporating only the high-speed current limiting breaker) except that the current limiting element was omitted was constructed.

Therefore, regarding the electric circuits of the present example and the comparative example, 220
A short circuit test was conducted under V and 3.5 kA short circuit conditions (estimated short circuit current waveform shown in a in FIG. 2). As a result, in the electric circuit of the comparative example, the breaking current waveform shown in c in FIG. 2 is obtained, and the current-time product (I ² · t) is 8000 A ² · sec. The allowable current-time product of the semiconductor switch incorporated in the circuit (3200A ² sec) greatly exceeded. When the semiconductor switch of the comparative example was examined after the test, it was confirmed that the semiconductor switch was broken while the ON state was maintained. On the other hand, in the electric circuit of this embodiment, the second
The cutoff current waveform is the current limiting current waveform shown in b in the figure, and the current-time product (I ² · t) is 1900A ² · sec, and the allowable current-time product (3200A ² · sec) of the semiconductor switch 2 incorporated in the circuit is It was well below. That is, in the present embodiment, it is understood that the difference between the breaking current waveform b and the breaking current waveform c of the comparative example (hatched portion in the figure) is the current limiting effect of the current limiting element 3.
When the semiconductor switch 2 of this example was examined after the test,
It was undamaged and sound. Further, the short circuit test was repeatedly performed 10 times on the electric circuit of this example, but no abnormality of the semiconductor switch 2 was observed, and the current limiting element 3 and the high speed current limiting breaker 4 completely protected from overcurrent. Was confirmed.

Although the semiconductor switch has been described as an example of the power semiconductor element in the above-described embodiment, it can be similarly applied to protection of a semiconductor rectifying element and the like.

[Effects of the Invention] As described in detail above, according to the present invention, even if an overcurrent such as a short-circuit current flows, the electric circuit is quickly turned off to reliably protect the power semiconductor element, and the circuit can be easily restored. It is possible to provide a protection circuit for a semiconductor element that can be implemented.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an electric circuit of the present invention, and FIG. 2 is a waveform diagram showing a current during a short-circuit current test in the electric circuits of the present embodiment and the comparative example. 1 ... Load, 2 ... Semiconductor switch, 3 ... Current limiting element,
4 ... Breaker, a ... Estimated short-circuit current waveform, b ... Breaking current waveform of electric circuit of this embodiment, c ... Breaking current waveform of electric circuit of comparative example incorporating only breaker.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Masafumi Iida 2121 Nawa, Asahi-cho, Mie-gun, Mie Stock company Toshiba Mie factory (72) Sadaaki Mori 2121 Nawao, Asahi-cho, Mie-gun, Mie Share type Toshiba Mie Factory (56) References JP-A-62-164498 (JP, A)

Claims (1)

[Claims] 1. A power semiconductor device, a breaker connected in series to the semiconductor device, and a general formula (V _1-X A _X ).
₂ O ₃ [wherein A represents at least one metal selected from Cr, Al and Sc, and x represents 0 ≦ x ≦ 0.02] and a current limiting element having a composition represented by Characteristic semiconductor element protection circuit.