JPS6243414B2 - - Google Patents

Description

Detailed Description of the Invention This invention connects a charged capacitor in parallel with a fast-acting fuse for protecting a semiconductor device via a semiconductor switch, and connects a fast-acting fuse for protecting a semiconductor device through the semiconductor switch at the same time as a circuit abnormality is detected. The present invention relates to a circuit that protects a full-wave controlled semiconductor device from overcurrent by causing a fast-acting fuse to blow out quickly by passing a constant current of discharge from a capacitor through the circuit.

FIG. 1 is a circuit diagram showing an example of a conventional overcurrent protection circuit for a semiconductor device. It is configured to supply power from an AC power supply 1 to a load 4 through a fast acting fuse 3 and a thyristor 5, and the AC power supply 1 turns on or off the thyristor 5 during a positive half cycle (the polarity of the power supply 1 is as shown). By letting
The power supplied to the load 4 is controlled. In this circuit, when an abnormality occurs in the load 4 and the load 4 is short-circuited, a short-circuit current flows from the AC power supply 1 through the fast-acting fuse 3 and the thyristor 5, and when the fast-acting fuse 3 blows, the short-circuit current is closed. The circuit becomes open. In this operation, the fast acting fuse 3
If the full-break surge current of is larger than the rated surge current of thyristor 5 (generally, the break-off surge current of a fast-acting fuse is expressed as the value of full-break I ² t, and the rated surge current of the thyristor is also Therefore, in other words, if the total cutoff I ² t of the fast-acting fuse 3 is greater than the rating I ² t of the thyristor 5), at the time the fast ^- acting fuse 3 blows, Thyristor 5 has already been destroyed. Therefore, as a rule, fast-acting fuses 3 are used which have a total cut-off I ² t that is smaller than the rated I ² t of the thyristor 5.

However, in this case, the following problem occurs.

(1) Comparing the time constant for the junction temperature rise of the thyristor 5 and the time constant for the melting of the fast-acting fuse 3, the former is generally faster, and if you try to completely protect the thyristor 5, the current capacity is small in advance. It is necessary to use fast acting fuse 3. That is, the thyristor 5 cannot be used until its rated current reaches its maximum, and is limited by the current capacity of the fast acting fuse 3.

(2) As the current capacity of the thyristor 5 increases, the tendency described in item (1) above becomes stronger, and the current reduction rate increases in order to provide complete protection.

(3) With advances in thyristor manufacturing technology, thyristors with large current capacities have become available, but there are no commercially available fast-acting fuses that can be used with thyristors with a rated current of 1000 A (average value) or higher. , parallel connection of fast-acting fuses is required.

(4) Selection of fast-acting fuses becomes extremely complex as all conditions must be considered.

As mentioned above, there are many problems involved in selecting a fast-acting fuse, which should be the easiest to use. Further, FIG. 2 is a circuit diagram showing another example of a conventional overcurrent protection circuit for a semiconductor device, and the circuit configuration is as follows.

From the DC power supply 2 through the fast acting fuse 3, the main thyristors 5, 6, 7, 8 and the auxiliary thyristors 9,
10, 11, 12 and commutating capacitors 17, 18
Power is supplied to the load 4 via an inverter circuit consisting of commutation reactors 20 and 21. In this circuit, the operation of the inverter circuit is not directly related to the present invention and will therefore be omitted, and only related operations will be explained.

In this circuit, a power supply short circuit occurs when the load 4 is short-circuited, when the main thyristors 5 to 8 fail to commutate (fail to turn off), or when the auxiliary thyristors 9 to 12 fail to commutate, and the power supply 2, A short-circuit current flows through the fast-acting fuse 3, and when the fast-acting fuse 3 melts, this closed circuit becomes open. The problem with this circuit is
Usually, main thyristors 5 to 8 and auxiliary thyristors 9 to
The difference is that the rated surge currents of the 12 models are different. In general, main thyristors 5 to 8 carry load current, so their current capacity is large and their rated I ² t is large, but auxiliary thyristors 9 to 12 only carry commutation current, so their current capacity is small and their rated I ² t is large. small. Therefore, the surge current (determined by the main thyristor's rating I ² t) that can be tolerated when a load short circuit or commutation of main thyristors 5 to 8 fails, and the surge current that can be tolerated when auxiliary thyristors 9 to 12 fail to commutate. Since the currents (determined by the rating I ² t of the auxiliary thyristor) are different values, it would be impossible to protect the thyristors with the same fast acting fuse 3 as in this circuit.
That is, if the fast acting fuse 3 is selected according to the rating I ² t of the main thyristors 5 to 8, the auxiliary thyristors 9 to 12 cannot be protected, and the rating I ² t of the auxiliary thyristors 9 to 12
If the fast-acting fuse 3 is selected according to this, the load current will be reduced. For this reason, although the explanation will be omitted here, a method is used in which a fast-acting fuse is attached to each element (referred to as an element fuse).

This invention was made in view of the above points, and is a full-wave control semiconductor device that supplies power from an AC power source to a load via a fast acting fuse and an anti-parallel thyristor, which is connected in parallel to the AC power source. A series circuit of a diode, a capacitor charged by the rectified output of this diode, and a resistor, the negative terminal on the DC side connected to the positive charging terminal of the capacitor, and the positive terminal on the DC side connected to the negative charging terminal of the capacitor. A full-wave positive-shaping bridge circuit with thyristors whose AC ends are connected to both ends of a fast-acting fuse, an overcurrent detector connected in series with the load, and when this overcurrent detector detects an abnormality in the load current. A gate trigger circuit that selects the one that discharges the charge in the capacitor in the thyristor of the bridge circuit with the same polarity as the load current conduction polarity according to the conduction polarity of the load current, and supplies a trigger signal to each selected thyristor. The present invention provides an overcurrent protection circuit for a semiconductor device which speeds up the blowing of a fast-acting fuse and eliminates the above-mentioned conventional drawbacks.

The details of the present invention will be explained below with reference to FIG. 3 showing an embodiment.

In the figure, an AC power supply 1 is connected to a load 4 via a fast acting fuse 3 and anti-parallel thyristors 5 and 6.
In addition, full-wave control is performed in which the flow angles of the thyristors 5 and 6 are controlled by a general circuit (not shown in the diagram) according to each half-wave polarity of the AC power source 1. Therefore, the power supplied to the load 4 can be increased or decreased.

In addition, a full-wave rectification type bridge circuit including thyristors 13 to 16 is provided, and a series circuit including a diode 25, a capacitor 19, and a resistor 30 connected in parallel to the power source 1 is provided.
The capacitor 19 is charged by the rectified output of the diode 25 via the resistor 30 as shown in the charging polarity, and the anodes of the thyristors 14 and 16 forming the bridge circuit are connected to the capacitor 19 as the DC negative terminal of the bridge circuit. The cathodes of the thyristors 13 and 15 constituting the bridge circuit are connected to the charging negative terminal of the capacitor 19 as the DC positive terminal of the bridge circuit, and the anode of the thyristor 13 and the cathode of the thyristor 14 Common connection point with cathode and anode of thyristor 15 and thyristor 16
The common connection with the cathode of is connected to both ends of the fast-acting fuse 3 as the AC end of the bridge circuit.

On the other hand, a gate trigger circuit 31 is provided to supply a trigger signal to the thyristors 13 to 16, and an overcurrent detector 32 is connected in series with the load 4. Gate trigger circuit 31 when an abnormality is detected
responds, and selects one of the thyristors 13 to 16 of the bridge circuit that discharges the charge in the capacitor 19 with the same polarity as the load current conduction polarity. A trigger signal is supplied to each thyristor.

Therefore, in response to the detection of a surge current or the like, a trigger signal is supplied to any two of the thyristors 13 to 16 as follows.

That is, when the surge current has a polarity that passes through thyristor 5, a trigger signal is given to thyristors 14 and 15, and when the surge current has a polarity that passes through thyristor 6, a trigger signal is given to thyristors 13 and 16. As a result, the discharge current of the capacitor 19 is added to the surge current in the current of the fast acting fuse 3, and the fast acting fuse 3 is blown out more quickly.
As a result, each thyristor can be completely protected even if the total cutoff I ² t of the fast acting fuse 3 is greater than the rated I ² t of the thyristors 5 and 6. Note that the fast-acting fuse 3 is blown when the capacitor 1
9 discharge current (determined by capacitor capacity and charging voltage).

As explained above, according to the present invention, the apparent fusing characteristics of the fast-acting fuse (fusing characteristics seen from the load side)
Since the value of I ² t) can be freely selected,
It can be used as a very effective means in circuits that use a mixture of thyristors with different rated surge currents, or in cases where it is impossible to obtain a fast-acting fuse that matches the rated surge current of the thyristors.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional overcurrent protection circuit, Fig. 2 is a circuit diagram showing another example of a conventional overcurrent protection circuit, and Fig. 3 is an example of an overcurrent protection circuit according to the present invention. FIG. Note that the same reference numerals in the figures indicate the same or corresponding parts. In the figure, 1 is an AC power supply, 2 is a DC power supply, and 3
is a fast acting fuse, 4 is a load, 5 to 16 are thyristors, 19 is a capacitor, 25 is a diode, 30
is a resistor, 31 is a gate trigger circuit, and 32 is an overcurrent detector.

Claims (1)

[Claims] 1. In a full-wave control semiconductor device that supplies power from an AC power supply to a load via a fast-acting fuse and an anti-parallel thyristor, a diode connected in parallel to the AC power supply and a capacitor charged by the rectified output of the diode and a resistor, a DC side negative terminal is connected to the charging positive terminal of the capacitor, a DC side positive terminal is connected to the charging negative terminal of the capacitor, and an AC terminal is connected to both ends of the fast acting fuse. a full-wave rectifier type bridge circuit using a thyristor, an overcurrent detector connected in series with the load, and when the overcurrent detector detects an abnormality in the load current, A gate trigger circuit that selects one of the thyristors of the bridge circuit that discharges the charge charged in the capacitor with the same polarity as the conduction polarity of the load current and supplies a trigger signal to each of the selected thyristors. Features: Overcurrent protection circuit for semiconductor devices.