JPH0242250B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an electronic circuit that improves the dv/dt withstand capability of a high voltage thyristor switch used in a TD exchange subscriber circuit or the like.

(Prior Art) In a conventional electronic circuit of this type, as shown in FIG. and an NPN transistor 6 with its collector and emitter connected, respectively.
an emitter on the anode 2 of the thyristor 1;
It is composed of a PNP transistor 5 whose collector is connected to the base of the NPN transistor 6 and whose base is open.
A transient current flows from the constant current source 7, which is in an inactive state, and operates in the direction of driving the P gate. At this time, the base of the NPN transistor 6 is driven and operated by the transient current from the PNP transistor 5, clamping the P gate of the thyristor 1 and the cathode 3, but the collector current of the NPN transistor 6 is mA to several tens of mA
If this reaches the limit and the clamping cannot be completed, the thyristor 1 will malfunction.

Therefore, in the conventional circuit, the constant current source 7 added as a P gate drive circuit and in an inactive state
There is a drawback that it is not possible to prevent the deterioration of the dv/dt capability of thyristor 1 due to transient current from
The base of the NPN transistor 6 is connected to the PNP
Since it is driven by a small transient current from the transistor 5, the current amplification factor of the NPN transistor 6 needs to be extremely large, which has the disadvantage that process control becomes strict, especially when integrated.

(Object of the Invention) In order to eliminate such conventional drawbacks, the present invention connects a resistor between the constant current source section and the thyristor P gate, and further connects a diode between the constant current source section and the base of the NPN transistor. By connecting the thyristors, a current switch is constructed, and the thyristor's dv/dt withstand capability is increased by increasing the bypassing ability of transient currents due to dv/dt. An embodiment of the present invention will be described in detail below with reference to the drawings.

(Structure of the Invention) FIG. 2 is a diagram showing an embodiment of the electronic switch circuit of the present invention, in which 1 is a thyristor, 2 is an anode, 3 is a cathode, 4 is a drive power supply terminal, 5 is a PNP transistor, and 6 is an NPN A transistor, 7 a constant current source, and 8 a resistor constitute the same circuit as the conventional one.
A resistor 9 is connected between the constant current source 7 of this circuit and the P gate of the thyristor 1, and the anode of a diode 10 is connected to the constant current source 7, and the cathode is connected to the base of the NPN transistor 6. To operate this, the anode 2 of thyristor 1
An arbitrary voltage that does not exceed the breakdown voltage is applied to the cathode 3, and a voltage lower than the voltage applied to the anode 2 and lower than the power supply terminal 4 is applied to the cathode 3, and a current is caused to flow from the constant current source 7. A portion of the current flows through the resistor 8, but most of the current flows into the P gate of the thyristor 1, which becomes a trigger current and causes the thyristor 1 to conduct.

Next, in the above state, when the constant current source 7 is made inactive and a sudden potential change is applied to the cathode 3 in a direction lower than the applied voltage state until then, the constant current source 7 is A transient current flows through the capacitance component and through the resistor 9, and attempts to drive the P gate of the thyristor 1. However, if the transient current is large, the potential drop across the resistor 9 becomes large, and the current is shunted to the diode 10 side, causing the NPN transistor to 6
At the same time, the transient current from the PNP transistor 5 is also input to the base of the NPN transistor 6, and the collector of the NPN transistor 6 connects the transient current from the constant current source 7 and the P gate of the thyristor 1 to each junction. In order to absorb the transient current passing through thyristor 1 and clamp the voltage between the gate and cathode of thyristor 1, thyristor 1
malfunctions are prevented. In this way, thyristor 1
By applying an arbitrary voltage that does not exceed the breakdown voltage to the anode 2 of the , keeping the constant current source 7 inactive, and applying a sudden potential change to the cathode 3 in a direction lower than the power supply terminal 4, the constant current source A transient current flows through the route of the power supply terminal 4 → constant current source 7 → resistor 9 → P gate of thyristor 1 through the capacitor 7, and some of the current is bypassed through the resistor 8, but most of the transient current is , flows into the P gate of thyristor 1 and tries to cause thyristor 1 to malfunction, and at the same time, the transient current flows through resistor 9 and generates a potential drop, so the voltage at the connection point between constant current source 7 and resistor 9 is: Assuming that the transient current is i _T , the voltage between the P gate and cathode of thyristor 1 is V _GK , and the resistor 9 is R, when viewed from the cathode 3, it becomes R・i _T +V _GK , which is connected to the diode 10 (the forward potential drop is V When the transient current _i T becomes larger than the sum of the base-emitter potential drop V _BE of the NPN transistor 6 (i.e., V _F +V _BE ), the transient current i _T flows through the diode 10 and Enter the base,
The transistor 6 is amplified, allowing more collector current to flow and maintaining the saturation state, and the base of the NPN transistor 6 has a PNP
Since the transient current from transistor 5 is also input,
It is possible to flow more collector current, and since the gate and cathode of thyristor 1 can be reliably clamped, the dv/dt tolerance can be increased, and the base drive current of NPN transistor 6 is large, so the current amplification factor can be increased. Since the minimum guaranteed value can be lowered, there is no need to tighten process control when integrating.

In addition, the steady driving state of the P gate of the thyristor 1 (from the constant current source 7 to drive the thyristor 1,
When current is flowing through the P gate), no current should flow to the diode 10 side, so it is necessary to determine the value R of the resistor 8 so that the following formulas (1) and (2) are satisfied. be.

V _F ＋V _BE −V _GK /i _D ＞R＞ V _F ＋V _BE −V _GK ／i _T ...(1) V _F ＋V _BE −V _CE ／i _D ＞R＞ V _F ＋V _BE −V _CE /i _T ...(2) Here, equation (1) is the condition when the transient current from constant current source 7 switches to diode 10, and equation (2) is the setting value condition of resistor 9 after switching. .

Here, V _F ;forward potential drop of diode 10,
V _BE ; Base-emitter voltage of NPN transistor 6, V _GK ; Gate-cathode potential drop of thyristor 1, V _CE ; Collector-emitter voltage of NPN transistor 6, i _D ; Output current of constant current source 7 ( P gate drive current during steady state), i _T ; is a transient current from the constant current source 7 when a sudden change in potential is applied to the cathode of the thyristor 1.

Now, i _D = 0.4~0.6mA, V _F = V _GK = 0.7V, V _BE
=0.6V and V _CE =0.3V, the value of R is 500Ω to 1kΩ, taking into consideration the temperature coefficient of each element, and when integrated, it can be easily realized using a diffused resistor or the like.

(Effects of the Invention) As explained in detail above, the present invention detects transient current due to dv/dt from a constant current source, considers a current exceeding a certain value to be a malfunction current, and automatically detects this by using a resistor and a diode. Since the switch has a circuit that uses the malfunction current as the drive current of the malfunction prevention circuit, it is possible to obtain an electronic switch using a thyristor with extremely high dv/dt tolerance. Therefore, it can be used in exchange subscriber circuits, etc., which are subject to high voltage from the outside and have a lot of noise that changes rapidly.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an electronic switch implementing conventional DV/DT protection measures, and FIG. 2 is a circuit diagram showing an embodiment of the electronic switch circuit of the present invention. 1...Thyristor, 2...Anode, 3...Cathode, 4...Driver power supply terminal, 5...PNP transistor, 6...NPN transistor, 7...
Constant current source, 8, 9...resistor, 10...diode.

Claims (1)

[Claims] 1. Between the P gate and the cathode of the thyristor, connect an NPN transistor with the collector and emitter connected respectively, and connect a resistor in parallel to this, and
a PNP transistor whose collector and emitter are connected to the base of the NPN transistor and the anode of the thyristor, respectively, and whose base is open;
In a circuit in which a constant current source is connected to the P gate of the thyristor, a resistor is connected between the constant current source and the P gate of the thyristor, an anode is connected to the constant current source, and a cathode is connected to the base of the NPN transistor. An electronic switch circuit characterized in that it has a connected diode.