JPS5825232B2 - Overvoltage detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overvoltage detection circuit, and particularly to an overvoltage detection circuit suitable for protecting semiconductor rectifying elements (thyristors).

In semiconductor rectifiers, which have been rapidly developing in recent years, how to protect semiconductor rectifier elements from abnormal voltages caused by various causes has become an important issue because the overvoltage resistance of semiconductors is low.

One of these protection means is to detect an overvoltage of a semiconductor rectifying element and apply appropriate protection (for example, firing a thyristor to which an overvoltage is applied).

As described above, when protecting the semiconductor rectifying element by detecting overvoltage, it is desirable that the overvoltage be detected quickly and electrically isolated.

FIG. 1 shows a conventional overvoltage detection circuit.

Terminals 1 and 2 indicate overvoltage detection terminals, and an overvoltage detection object 3 is connected between both terminals 1 and 2.

An example of the object to be detected 3 is a main thyristor of a semiconductor rectifier.

Overvoltage is detected as a light amount by a series connection body of a resistor 4 connected between terminals 1 and 2 and light emitting diodes 10 and 11 connected in antiparallel.

That is, as the voltage applied between the terminals 1 and 2 increases, the amount of light emitted by one of the light emitting diodes 10 and 11 increases depending on the polarity of the voltage.

This amount of light is detected by a light detection circuit 50 through the light guide 40, and an overvoltage detection signal is obtained by a level detection circuit 51 when a signal (for example, voltage) corresponding to the amount of light exceeds a preset level.

This detection signal is converted into a protection control signal that activates the gate amplifier of the thyristor to fire the thyristor, for example.

However, in the above conventional method, since the resistor 4 has a linear characteristic and most of the voltage between terminals 1 and 2 is applied to the resistor 4, the voltage and current of the detection circuit is reduced as shown in FIG. The characteristics are also almost linear, and there are few changes in current (changes in light amount), making it difficult to detect with high precision.

In particular, since the amount of light emitted by the light emitting diode 10,110 and the detection sensitivity of the photodetector circuit 50 are temperature dependent, overvoltage detection settings are affected by temperature and are prone to malfunction due to noise.

Some improved conventional circuits improve detection sensitivity by using a nonlinear resistance element as the resistor 4 and having the voltage-current characteristics shown in FIG.

If we look only at the vicinity of , it is susceptible to noise due to its linear characteristics, and we were unable to improve accuracy.

An object of the present invention is to provide a highly accurate overvoltage detection circuit.

In the overvoltage detection circuit of the present invention, at least one of the resistor 4 or the light emitting semiconductor elements such as the light emitting diodes 10 and 11 has negative resistance characteristics.

Examples of the present invention will be described in detail below.

FIG. 4 shows an embodiment of the present invention, and the same parts or parts having the same functions as those in FIG. 1 are designated by the same reference numerals.

In FIG. 4, the resistor 4 is composed of the following elements.

That is, a nonlinear resistance element 20 having voltage-current characteristics shown by the broken line A in FIG. 5, and an antiparallel connection that is connected in series to this nonlinear resistance element 20 and has a natural breakover at voltage v2 as shown by the dotted line B in FIG. thyristor 2L22 and overvoltage detection setting value V.

It consists of a voltage dividing resistor 5 having a value such that the voltage dividing between the nonlinear resistance element 20 and the thyristors 21 and 22 becomes vl:V2.

With such a configuration, the resistor 4 can have the voltage-current characteristics shown by the solid line C in FIG.

That is, the voltage applied to the resistor 4 is V.

When it exceeds V2, the voltage of the thyristors 21 and 22 also exceeds V2, and depending on the voltage polarity, one of them undergoes a natural breakover, and the current flows from 11 to 2 through the negative resistance region.

It has a negative resistance characteristic of rapidly increasing.

Note that the overvoltage detection level is set by both circuit elements 20, 21,
22 and the resistance value of the voltage dividing resistor 5.

Next, a resistor 6 is connected in series to the light emitting diode 10.11, and a constant voltage diode 23.24 connected in anti-series is provided in parallel with this connection body.

These resistors 6 and constant voltage diodes 23 and 24 are used to limit the current flowing through the light emitting diodes 10 and 11 and to protect the light emitting diodes io and i1, and when applied to a device where the detection voltage does not become extremely high. can be omitted.

In addition, the voltage distributed to the circuit consisting of these elements 10, 11, 6, 23, and 24 is sufficiently small compared to the voltage distributed to the resistor 4, and the voltage-current characteristics of the entire overvoltage detection circuit are approximately the same. The characteristic is shown by the solid line C in Figure 5.

In such an overvoltage detection circuit, V is applied between terminals 1 and 2.

Even if the overvoltage above is applied and the voltage applied to the constant voltage diode 23 or 24 is within the constant voltage characteristic value range, the polarity of the overvoltage causes the light emitting diode 10 to
．． The current of either one of 11 is from 11 to I.

The amount of light emitted increases rapidly as well.

Therefore, the level detection circuit 51 is connected to the voltage i11 and ■.

By setting the comparison reference level at a level corresponding to (preferably approximately midway between o and 11), overvoltage can be reliably detected even if the difference from the normal voltage is small. , detection errors due to noise, fluctuations in the set detection level, etc. are eliminated, and highly accurate detection is possible.

In addition, in the above embodiment, since the overvoltage of the detected object 3 in the high voltage section is detected, the light guide 4
Although the case where the light from the light emitting diodes 10 and 11 is guided to the photodetection circuit 50 using an insulating pipe such as 0 is shown, if the insulating potential difference is low, the light may be directly detected using a photocoupler or the like.

Further, in this embodiment, overvoltages of both polarities can be detected, but if the voltage polarity of the detected object 3 is determined, one of the light emitting diode and the constant voltage diode thyristor can be omitted.

Furthermore, if the maximum overcurrent value approximately determined by the maximum overvoltage value and the nonlinear resistor 20 does not exceed the allowable value of the light emitting diode, the resistor 6 and the constant voltage diodes 23 and 24 may be omitted.

Further, in this embodiment, instead of the thyristors 21 and 220, a single thyristor having a bidirectional natural breakover characteristic may be used.

Furthermore, the light emitting diodes 10 and 11 themselves can be provided with the same characteristics as the circuit shown in the embodiment by using a light emitting semiconductor element having a negative resistance characteristic and a natural breakover characteristic.

In this case, the resistor 4 in FIG. 4 may be a nonlinear resistance element.

FIG. 6 shows another embodiment of the invention.

The difference between this figure and FIG. 4 is that the thyristors 21 and 22 with natural breakover characteristics are replaced with reverse conductive thyristors 25 and 26, and they are connected in series, and both thyristors 25 and 26 have voltage dividing resistors 1 and 26. , 8 are connected in parallel.

By doing this, in addition to the effects shown in Figure 4,
The overvoltage detection level in the direction of rain flow is independently set by voltage dividing resistors 1 and 1, respectively.
8, and also has the feature that it is not necessary to align the natural breakover voltages of the two thyristors 2L22.

In addition, in the embodiment shown in FIG. 6, various modified circuits can be constructed as in the case of FIG. 4.

Furthermore, the thyristor 2L22 can be replaced by a thyristor that does not have reverse conductivity and a diode provided in antiparallel.

As explained above, the overvoltage detection circuit according to the present invention
By employing elements with negative resistance characteristics in the overvoltage detection circuit, the detection level has the advantage of high accuracy.

[Brief explanation of drawings]

Figure 1 is a block diagram showing a conventional overvoltage detection circuit, Figure 2 is a diagram showing voltage-current characteristics in Figure 1, Figure 3 is a diagram showing improved voltage-current characteristics in Figure 1, and Figure 4 is a diagram showing improved voltage-current characteristics in Figure 1. 5 is a block diagram showing one embodiment of the present invention, FIG. 5 is a diagram for explaining the voltage-current characteristics in FIG. 4, and FIG. 6 is a block diagram showing another embodiment of the present invention. Meter: object to be detected, 4: resistor, 5, 7, 8: voltage dividing resistor, 10, 11: light emitting diode, 20...
Nonlinear resistance element, 21, 22...thyristor, 25,
26... Reverse conducting thyristor, 40... Light guide, 50... Light detection circuit, 51... Level detection circuit.

Claims (1)

[Claims] 1. In an overvoltage detection circuit that detects an overvoltage applied to a series connection of a resistor and a light emitting semiconductor element based on the amount of light emitted by the light emitting semiconductor element, the resistor includes a nonlinear resistance element, and the resistor or the light emitting semiconductor An overvoltage detection circuit characterized in that at least one of the elements has negative resistance characteristics.