JPS5944731A - Current limiting breaking circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current-limiting circuit that performs current-limiting operation for overload protection in a load driving device operated by a DC power supply or an AC power supply, or for protection against a load short circuit, and in particular, a current-limiting circuit that performs a current-limiting circuit that performs a current-limiting circuit for protection against load short circuits, etc. in a load drive device operated by a DC or AC power source. This invention relates to a current limiting circuit using an inductive thyristor.

Load drive circuits, particularly load drive devices that supply DC power to a load, generally employ many current-limiting circuits that use a reverse-blocking three-terminal SIRISK, so-called normal SIRISK (hereinafter simply referred to as SIRISK). This utilizes the arc-extinguishing ability of the thyristor to cut off the circuit when a current is generated, for example, and is superior in that it is capable of high-speed operation that cannot be achieved with a breaker with a mechanical cut-off mechanism. It has a function.

The first section is a circuit diagram of a load drive device that shows an example of a conventional current-limiting breaker circuit being applied. 1 is a DC main power supply, 2 is a switch that performs switching, 3 is a load, and 4 is a cyrisk. be. Furthermore, 5 is a start switch, 6. ．． 7, 8, 9, 9
' is a resistor, 10 is a commutating capacitor, 11 is a Zuner diode, and 12 is a silice.

That is, when supplying power to the load 3 in a device that drives the load 3 by power supply from the DC main power supply 1, first the switch 2
to close the starting switch 5.

Then, a positive gate current from the DC main power supply 1 is applied to the gate of the thyristor 4 via the resistor 6, and the thyristor 4 is ignited, passing the entire resistor 7 through the load 3 and supplying the DC main power supply 1 to the gate of the thyristor 4.
〇In addition, the resistor 7 is arranged to detect the load current, and the impedance of this resistor is extremely low compared to the impedance of the load 3, so the effect on the load 3 can be ignored. . Here, due to the ignition of the thyristor 4, the commutation capacitor lO is transferred from the DC main power supply 1 to the switch 2. Resistor 8. It is charged through the thyristor 4 and the resistor 7 to the polarity shown.

From this state, when the load current increases and reaches the overcurrent detection level, the voltage drop across the resistor 7 is increased by the Zener diode 11.
The thyristor 12 is fired by exceeding the sum of the Zener voltage of and the minimum firing gate voltage of the thyristor 12. Then, the voltage of the commutating capacitor 10 is applied in the opposite direction between the anode and cathode of the thyristor 4 through the thyristor 12 and the resistor 7, so that the thyristor 4 is turned off. On the other hand, the load current is thyristor 4
The current flows from the circuit portion of the resistor 7 to the circuit portion of the commutating capacitor lO and the thyristor 12, and at the same time as charging of the commutating capacitor lO is completed in reverse to the illustrated polarity, it becomes zero, completing the circuit cutoff. Here, the resistors 9, 9' are the thyristors 4. It is added to remove gate noise of the thyristor 12 and stabilize its operation.

The operation of circuit breaking as described above will be further explained with reference to FIG.

FIG. 2 shows the time course of the load current in FIG. 1, where the vertical axis shows the load current and the horizontal axis shows time. Second
In the figure, the load current IL starts to increase from time T1,
It is shown that the overcurrent detection level IO has been reached at time T2. Therefore, at time T2, the thyristor 12 is fired as described above, so that the load current IL is commutated to the commutating capacitor 10 and the thyristor 12. Then, the voltage applied to the load 3 increases due to the initial charging voltage of the commutating capacitor 10, and the load current IL is temporarily increased. Furthermore, assuming that the voltage of the commutating capacitor 10 becomes zero at time T3, the period from time T2 to time T3 is a period in which a reverse bias is applied to the thyristor 4, and this is the turn-off time of the thyristor 4. It is necessary to do more than that. Furthermore, the current from time T3 to time T4 passes through the load 3 to the commutating capacitor 1 as described above.
0 will be charged with the opposite polarity.

Thus, the device shown in FIG. 1 has the following disadvantages.

(1) A circuit section that performs a sequence operation is required to fire the thyristor 4 at the time of starting.

(2) It is necessary to charge the commutation capacitor 10 before shutting off, which may result in failure to shut off immediately after starting.

(3) At the time of shutdown, the load current IL is temporarily increased further than the overcurrent detection level IO.

(4) The turn-off time of thyristor 4 is several tens (μ
Even if S), it takes several times as much time from the point of overcurrent detection to the completion of shutoff.

(5) Since the reverse bias time of the thyristor 4 depends on the load 3, it may become impossible to shut off when the load impedance decreases due to an accident or the like.

Furthermore, as various semiconductor products are being adopted for loads or devices connected to them, these semiconductor products generally have a relatively low overcurrent resistance, so the conventional thyristors used in the above-mentioned Current-limiting current cutoff circuits have not been satisfactory in terms of performance, and there has been a desire for circuits with even more advanced performance.

In view of the above-mentioned points, the present invention provides a current-limiting cut-off circuit having a simple structure and improved performance by skillfully utilizing an electrostatic induction thyristor. Hereinafter, the present invention will be explained based on the drawings. Figures 3 and 4 are explanatory diagrams of an electrostatic induction thyristor (hereinafter referred to as 8I thyristor) shown to facilitate understanding of the present invention, and forward blocking characteristics. FIG.

That is, the SI thyristor has an anode electrode (A), a cathode electrode (K), and a gate electrode (G) as shown in No. 31.
It is a type of three-terminal thyristor, and is a self-extinguishing element that can be extinguished by flowing a reverse current through its gate. In FIG. 3, VGK indicates the voltage between the gate and the cathode, YAK indicates the voltage between the anode and the cathode, and 1 indicates the anode current.

Here, in terms of forward characteristics, SI risks can be roughly divided into normally closed type and normally open type.

First, in Fig. 4(a), when the gate-cathode voltage vGx is zero (Vox = 0), the SI thyristor is in the firing state, and even if the anode current IA increases, the anode-cathode voltage VAK remains constant. It has an extremely small voltage, and furthermore, the gate-cathode voltage VGK is set to a negative value Vl (Vo
When x=V1<o), even if the anode-cathode voltage vλK increases, only a very small leakage current flows in one anode current, and good blocking characteristics are achieved. Furthermore, when this anode-cathode voltage YAK exceeds a certain value vB, the anamide current IA becomes a breakdown region where it rapidly increases, and eventually ignition occurs. Cathode voltage VG
It is shown that it can be increased by increasing K in the negative direction.
Since the ignition state occurs when the cathode voltage VOIC is zero, it can be called a normally closed circuit type 8I cyrisk.

Next, the voltage VOX between the gate and cathode is zero (Vciic=0), which also exists as shown in FIG.
0), and in order to fire it, the gate-cathode voltage VGK must be set to a positive value v, similar to a thyristor.
2 (vGK=v2>o). This can be said to be a normally open type 8I thyristor in contrast to the above-mentioned normally closed type SI thyristor.

FIG. 5 is a circuit diagram showing an embodiment to which the present invention is applied, in which 9", 97 are resistors, 13 is a normally closed SI thyristor having the characteristics shown in FIG. 4 (,), 14 is a normally open type SI SIRISK having the characteristics shown in Fig. 4(b), and 15 is a DC constant voltage source as an auxiliary DC power supply.0 In Fig. 1, the same symbols as in Fig. 1 are the same components. That is, in the circuit configuration shown in this way, the starting circuit part is removed compared to the device shown in FIG.
The difference is that the thyristor 14 is replaced with the SI thyristor 14. The operation of this is as follows.

In FIG. 5, when the switch 2 is closed for starting, the S
Since the gate and cathode of the I thyristor 13 are connected through a resistor 9'', the gate-cathode voltage vGK
becomes zero, ignition occurs without the need for any other starting circuit, and power is supplied to the load 3 from the DC main power supply 1. At this time, the SI thyristor 14 is connected to the resistor 9"
', the gate and cathode are short-circuited, the voltage VGK between the gate and the cathode becomes zero, and the arc is extinguished, and the DC constant voltage source 15 does not supply power anywhere.

Now, the load current increases and reaches the overcurrent detection level1.
When the voltage drop across the resistor 7 exceeds the Zener voltage of the Zener diode 11 and the voltage between the gate and cathode of the SI thyristor 14 becomes positive, the SI thyristor 14 fires. A reverse current is applied between the gate and cathode of the SI thyristor 13 through the SI thyristor 14 and the resistor 7, and the gate reverse current flows, thereby extinguishing the SI thyristor 13 and cutting off the load current.

Here, resistors 9" and 9#' are resistors 9" and 9#' shown in FIG.
Similar to ゜9', it removes gate noise and ensures that the gate-cathode voltage vGx during normal operation is zero.
Furthermore, since the reverse impedance between the gate and cathode of the 8I thyristor 13 becomes extremely high after the 8I thyristor 13 is turned off, the resistor 9'' is configured to control the minimum anode current required to maintain the closed circuit state after the SI thyristor 14 is fired. Thyristor 14
The action of I/) is further explained with reference to Figure 6. Figure 6 shows the load current over time in Figure 5, which is expressed on the same scale as Figure 2. ◇In other words, the load current IL begins to increase from time T1, and at time T2 the overcurrent detection level ■0
When the 8I thyristor 14 is fired and the gate reverse current of the SI thyristor 13 flows, the anode current of the SI thyristor 13 and therefore the load current IL is rapidly decreased by 1. It drops to a fraction of the overcurrent detection level IO. Furthermore, S.I.
The anode current of the thyristor 13 decreases relatively slowly after time T3' and reaches zero at time T4' to complete the cutoff.The behavior from time T2 to time T4' is mainly due to the elements of the SI thyristor 13. It depends on the characteristics, and is extremely unlikely to be influenced by the characteristics of the load 3. Also, from time T2 to time T3'
The time until Ta2 is normally about 1 (μS).
force) up to time point T4' is a number (μS), and this is expressed as the second
Compared to what is shown in the figure, the operation is one order of magnitude faster.

In the device shown in FIG. 5 with such improved performance, if the load 3 is inductive, it is of course necessary to take measures against the surge voltage caused by the rapid cutoff as described above, but this is not explained here. Although not shown, it is possible to sufficiently deal with this problem by making full use of conventional techniques such as flywheel diodes and surge absorbers. Note that it is also possible to replace the SI thyristor 14 with a thyristor.

Here, since SI Cyrisk has a faster turn-on time during ignition than Cyrisk, SI Cyrisk is suitable for such applications.
It can be said that Cyrisk is favorable. Further, the load current detector may be a hook shown in the example using the simplest resistor, but it may also be a direct current transformer (DCCT) or other types. Furthermore, the overcurrent level detection is not limited to a tuner diode, but may be other types. And it is possible to easily select the device for obtaining these load currents and detecting their levels depending on the desired accuracy and continuity of current detection.

In this way, the advantages of the apparatus plate shown in FIG. 5 can be enumerated.

(1) By using a normally closed SI thyristor element in the main circuit, a circuit section that performs the sequence operation at startup becomes unnecessary, and it is possible to immediately enter the operating state simply by closing the switch.

(2) Since there is no shutdown preparation operation, it is possible to shut off even immediately after startup.

(3) No increase in load current due to commutation operation as shown in FIG. 2 occurs.

(4) From overcurrent detection to completion of shutoff
) enables high-speed current limiting.

(5) It is possible to avoid the influence of load on the shutoff operation.

(6) Consists of a simple circuit-off configuration.

(By using the 71SI Zyristor, the voltage between the anode and cathode when energized is lower than that of the normal type Sylestor, resulting in high efficiency.

On the other hand, a drawback is that it requires an auxiliary DC power supply, which is necessary to supply a gate reverse current of a magnitude comparable to the load current when the main circuit SI risk is extinguished. The flow time is about 1 (μS), and since there are few applications that require a high-frequency green return action, it can be realized, for example, by using an extremely small-capacity power supply and a capacitor connected in parallel to this output. It's not really a problem.

Although the device thus constructed in FIG. 5 is shown as an example of a load driving device using a DC power source, it can also be easily applied to an AC circuit based on the above technical concept. An example of this is shown in FIG.

FIG. 7 is a circuit diagram showing only the load current path of an AC circuit to which the present invention is applied, in which 16 is an AC main power supply and 17 is a diode bridge. In the figures, the same reference numerals as in FIGS. 1 and 5 indicate parts having the same functions. Here, the peripheral part of the gate circuit of the SI thyristor 13 is omitted because it is the same as that shown in FIG. 5. In other words, in the device shown in FIG. It is configured so that it is converted and flows to the SI thyristor 13 and the resistor 7. Therefore, it is clear that such a device can also perform the current limiting operation in the same manner as the device shown in FIG.

As explained above, according to the present invention, it is possible to provide a current-limiting circuit having a simple circuit configuration with improved performance and capable of performing current-limiting operation for overload protection or load short-circuit optometry.

[Brief explanation of drawings]

Claims (1)

[Claims] The output of the current detector has a predetermined value between a normally closed electrostatic induction thyristor connected in series with the load, a current detector that detects the load current, and the gate and cathode of the normally closed electrostatic induction thyristor. 1. A current-limiting cut-off circuit comprising: a switching element that closes the normally closed electrostatic induction thyristor to extinguish the arc when the voltage is exceeded; and a series connection body consisting of a DC power supply.