JPS64772B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching circuit for interrupting an electric path using a semiconductor switching element such as a thyristor or a triax.

[Prior Art] Conventionally, there is one shown in FIG. 1 as this type of device. This device combines the advantages of both by using a non-contact semiconductor switching element and a mechanical contact with a large current capacity, and is characterized in that switching can be performed without arcing.

Specifically, 1 is an AC power supply, 2 is a load, 3 is a thyristor connected in series to these series circuits,
4 is a DC power supply, 5 is an operating switch, and 6 is a relay, which receives an input signal by closing the operating switch 5 and is excited by this input signal. ra,
rb is a normally open contact of the relay 6, whose operation timing is staggered; the contact ra is connected between the gate of the thyristor 3 and the AC power source 1, and the contact rb is connected in parallel to the thyristor 3. When the operating switch 5 is closed and the relay 6 is energized, the contact ra is closed first, causing a gate current to flow through the gate of the thyristor 3, turning it on. After that, contact rb closes after a delay.
Due to the zero crossing of the load (alternating current), thyristor 3
The potential difference between both ends becomes zero, turning it off, and from then on the load current flows through contact rb. Therefore, since the thyristor 3 is in an instantaneous ON state for a maximum of half a cycle without generating an arc, the current capacity is small and there is no heat generation.

[Problem to be solved by the invention] However, in the conventional case, the contact point rb
When the thyristor 3 is closed and a load current is flowing through it, since this is a mechanical contact, the contact resistance increases and a potential difference may occur between both ends of the thyristor 3.
This potential difference is IL×R, where IL is the load current and R is the contact resistance. When this potential difference exceeds a predetermined value, a gate current flows to the gate and turns on the thyristor 3, which generates heat and causes extreme There was a problem that it would burn out if it did.

The present invention has been made in view of the above reasons, and its purpose is to eliminate such problems,
The purpose of the present invention is to provide a switching circuit that can extend the life of a thyristor.

[Means for Solving the Problems] In order to solve the problems, the switching circuit of the present invention includes a three-terminal thyristor 3 connected in series to a series circuit of an AC power source 1 and a load 2, and a switching circuit that is excited by an input signal. The first contact rx of the relay is normally open and connected in parallel to the three-terminal thyristor 3. The second contact ry is connected between the gate of the 3-terminal thyristor 3 and the AC power source 1, and its state based on the state where the relay 6 is demagnetized is normally open or 3-terminal so that no gate current flows. It is also connected to the electric circuit parallel to the terminal thyristor and is normally closed to short-circuit the three-terminal thyristor 3, and the third contact rz of the relay is normally open and has its own state based on the state in which the relay 6 is energized. In order to prevent gate current from flowing,
When the second contact ry is normally open, the second
When relay 6 is connected in parallel to contact ry and is energized, second contact ry, first contact
Contact rx and third contact rz operate in this order, and relay 6
When is demagnetized, the third contact rz, the first contact
It is designed to operate in the order of rx and second contact ry.

[Function] When the relay 6 is excited to cause current to flow through the load 2, the second contact ry is activated (reversed) to flow the gate current, turns on the 3-terminal thyristor 3, and flows the load current IL through it. The first contact rx is then actuated (inverted) and also carries the load current IL, and the third contact rz is actuated (inverted) to prevent the gate current from flowing, after which the zero crossing of the load current IL occurs. The 3-terminal thyristor 3 turns off, and the load current
IL flows only to the first contact rx.

In this state, the three-terminal thyristor 3 is short-circuited by the second contact ry and the third contact rz, or by the third contact rz, so it cannot be turned on even if a potential difference occurs between both ends. do not have.

[Example] Hereinafter, a first example of the present invention will be described based on FIGS. 2 and 3. Incidentally, the same parts as those of the conventional one shown in FIG. 1 are given the same reference numerals, and the explanation thereof will be omitted.

rx, ry, rz are 3 linked to relay 6
When relay 6 is energized,
The second contact ry, the first contact rx, and the third contact rz operate (reverse) in this order, and when the relay 6 is demagnetized, the third contact rz, the first contact rx, and the second contact ry
It is designed to operate (reverse) in the following order.

The first contact rx of relay 6 is normally open and 3
It is connected in parallel to the terminal thyristor 3.

The second contact ry of the relay 6 is normally closed and connected between the gate of the three-terminal thyristor 3 and the AC power supply 1. This second contact ry is in its own state (closed state) based on the state in which the relay 6 is demagnetized.
In order to prevent the gate current from flowing,
It is also connected to the electrical circuit that is parallel to the 3-terminal thyristor, so in that state, the 3-terminal thyristor 3
is shorted.

The third contact rz of relay 6 is normally open and the second
is connected in parallel with the contact ry. This third contact rz acts to prevent gate current from flowing in its own state (closed state) based on the state in which the relay 6 is energized. In other words, the third contact rz is the second contact when the relay 6 is demagnetized.
It acts like a contact point ry.

The operation of this device will be explained with reference to FIG.
Now, when the operation switch 5 is closed and the relay 6 is energized to cause current to flow through the load 2, the second contact ry is activated (reversed = open) to flow the gate current, and the 3-terminal thyristor 3 is turned on. Load current IL is applied to , and then the first contact rx is activated (reversed = closed)
Then, the third contact rz is activated (reversed = closed) to short-circuit the 3-terminal thyristor 3 and prevent the gate current from flowing, and then the load current IL becomes zero. 3 due to crossover
The terminal thyristor 3 is turned off, and thereafter the load current IL flows only through the first contact rx.

In this operation, the time during which the 3-terminal thyristor 3 is turned on does not exceed half a cycle, and in this state, the 3-terminal thyristor 3 is short-circuited by the third contact rz, so even if a potential difference occurs between both ends. However, it never turns on.

On the other hand, when the operation switch 5 is opened to demagnetize the relay 6 in order to cut off the load current IL, the third contact rz is activated (reversed = open), generates a gate current, and turns on the 3-terminal thyristor 3. The load current IL is passed through this as well, and then the first contact rx is activated (reversed = open) to prevent the load current IL from flowing through it, and the second contact ry is activated (reversed = closed). By doing so, the 3-terminal thyristor 3 is short-circuited to prevent the gate current from flowing, and then the 3-terminal thyristor 3 is turned off due to the zero crossing of the load current IL, and the load current IL is cut off.

Even in this operation, the time during which the three-terminal thyristor 3 is turned on does not exceed half a cycle.

FIG. 4 shows a second embodiment of the invention. The second contact ry of the relay 6 of this device is connected between the gate of the three-terminal thyristor 3 and the AC power supply 1, and its state based on the state in which the relay 6 is demagnetized is such that no gate current flows. , as always open. In addition, the third contact rz of the relay 6 is normally open, and its own state (closed state) based on the state in which the relay 6 is excited is connected to the three-terminal thyristor 3 in order to prevent the gate current from flowing. They are connected to form a parallel electrical path together with the second contact ry.

This device also operates in substantially the same manner as the first embodiment.

FIG. 5 shows a third embodiment of the present invention. This can be called a modification of the first embodiment, and the second contact ry and third contact rz of the relay 6 share a movable contact. Although these two contacts ry and rz may not be said to be strictly parallel, they have substantially the same effect as in the first embodiment, so
Parallel in the present invention also includes this.

FIG. 6 shows a fourth embodiment of the present invention. This can also be called a modification of the first embodiment, and the first contact rx and the second contact ry of the relay 6 share a movable contact. This also has the same effect as the first embodiment.

[Effects of the Invention] Since the switching circuit of the present invention is constructed as described above, the three-terminal thyristor is only turned on for a very short time between the time when the load current begins to flow and the time when it is cut off, thereby preventing heat generation and burnout. In addition, while the load current is flowing through the first contact, the 3-terminal thyristor is short-circuited by the second contact and/or the third contact, so no gate current flows. Therefore, the 3-terminal thyristor will not be turned on inadvertently,
Therefore, the problems of the conventional method can be eliminated and the life of the thyristor can be extended.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a conventional example, FIG. 2 is a circuit diagram showing a first embodiment of the present invention, FIG. 3 is a waveform diagram showing its operation, and FIG. 4 is a circuit diagram showing a first embodiment of the present invention. FIG. 5 is a circuit diagram showing a third embodiment of the present invention, and FIG. 6 is a circuit diagram showing a fourth embodiment of the present invention. 1...AC power supply, 2...Load, 3...3-terminal thyristor, 6...Relay, rx...1st relay
ry...the second contact of the relay, rz...the third contact of the relay.

Claims (1)

[Claims] 1. Consisting of a three-terminal thyristor connected in series to a series circuit of an AC power source and a load, a relay excited by an input signal, and three contacts interlocked with the relay, The first contact of the relay is normally open and connected in parallel to the three-terminal thyristor, and the second contact of the relay is connected between the gate of the three-terminal thyristor and the AC power supply, and the relay is demagnetized. In order to prevent the gate current from flowing, the self state based on the state is normally open or normally closed which is also connected to the electric circuit parallel to the 3-terminal thyristor and short-circuits the 3-terminal thyristor, and the third contact of the above relay In order to prevent the gate current from flowing in the self state based on the state in which the relay is normally open and the relay is energized, the electrical circuit that is parallel to the three-terminal thyristor when the second contact is normally open is connected to the second contact. When the second contact is normally closed, it is connected in parallel with the second contact, and when the relay is energized, the second contact and the first The contact and the third contact operate in this order, and when the above relay is demagnetized, the third contact and the first contact operate.
A switching circuit that operates in the order of the first contact and the second contact.