JP3174363B2 - Thyristor ignition circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thyristor starting circuit suitable for controlling an AC switch corresponding to a load having a wide power factor.

[0002]

2. Description of the Related Art In an apparatus using a thyristor in a high-voltage system, a firing energy is obtained by using a voltage between both ends of the thyristor, and the firing energy is supplied to a gate of the thyristor by an optical pulse to operate the thyristor. A thyristor firing circuit for firing is used, and the present applicant has previously filed an application as Japanese Patent Application No. 2-45001. As shown in FIG. 2, the prior invention has an ignition capacitor (C2) for accumulating ignition energy, a voltage suppression circuit for always suppressing the voltage of the ignition capacitor (C2) to a certain value or less, and an ignition command light. When a forward voltage is applied to the anode of the main thyristor (SCR), a snubber resistor (R1) and a voltage dividing capacitor (C1) that also serves as a snubber are provided. , The ignition capacitor (C
2) The ignition energy is stored.

When the phototransistor (PTR) receives a firing command light signal, a current flows through the base of the transistor (TR1) connected to the phototransistor (PTR) and Darlington through the phototransistor (PTR), and the transistor (TR)
1) is in the 0N state, the energy stored in the firing capacitor (C2) is supplied to the gate of the main thyristor (SCR), and the main thyristor (SCR) is fired.

However, in this circuit, a surge voltage is applied to the anode electrode of the main thyristor (SCR) due to switching surge at start-up or other phenomena, and the ignition capacitor is turned off.
When a steep voltage is applied to (C2), the phototransistor (PTR) becomes conductive due to the avalanche effect, and the current flows through the transistor (T2) even though the firing command optical signal is not issued.
R1), the transistor (TR1) turns ON,
There is a problem that energy is supplied to the gate of the main thyristor (SCR) and the main thyristor (SCR) may be ignited incorrectly.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned conventional problems. Even when a surge voltage is applied to the anode of the main thyristor, the phototransistor does not conduct, and the ignition command light signal is output. Has been completed to provide a thyristor firing circuit that supplies energy to the gate of the main thyristor and fires the main thyristor only when is applied.

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides an ignition capacitor and an ignition capacitor for accumulating ignition energy by obtaining an ignition power supply from an anode electrode of a main thyristor. A voltage suppression circuit that constantly suppresses the voltage of the capacitor to a fixed value or less, and a phototransistor that is turned on in response to the firing command optical signal. In the thyristor firing circuit that supplies the gate of the thyristor, a capacitor is connected between the base and collector of the transistor in the voltage suppression circuit,
It is characterized in that a resistor is connected between the emitters.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the illustrated circuit. In the circuit shown in FIG. 1, the main thyristor
A resistor (R1) for snubber, a voltage dividing capacitor (C1) also serving as a snubber, and a gate circuit connected in series are connected in parallel between the anode and cathode of (SCR). The voltage suppression circuit in the gate circuit is provided with a switching transistor (TR2).
A capacitor (C5) is connected between the collector and base of (TR2), and a resistor (R7) is connected between the base and emitter.

When a forward voltage is applied to the main thyristor (SCR), the current flows through a snubber resistor (R1), a voltage dividing capacitor (C1), a resistor (R8), and a diode (D2), and a firing capacitor (C2).
Is charged. The voltage at both ends of the firing capacitor (C2) is divided by the resistor (R3) and the resistor (R2), and the voltage of the resistor (R2) is applied to the second pin of the logic circuit (IC). When the voltage of pin 2 of the logic circuit (IC) exceeds a certain threshold, the logic circuit (IC)
Pin 5 becomes High state and turns on transistor (TR2)
Therefore, the current flows to the cathode side without applying a voltage exceeding a certain level to the firing capacitor (C2), and when the voltage of pin 2 of the logic circuit (IC) falls below the threshold value, the logic The 5th pin of the circuit (IC) becomes Low state and the transistor (T
R2) is turned off, so the firing capacitor (C
In 2), a constant voltage is always applied.

When the firing command optical signal is input to the phototransistor (PTR) while the firing capacitor (C2) is charged as described above, the phototransistor (PTR)
Flows current through the gate of the transistor (TR1) and turns on the transistor (TR1), so the energy stored in the firing capacitor (C2) is supplied to the gate of the main thyristor (SCR) through the transistor (TR1). Main thyristor (SCR)
Is set to a firing state.

[0010] Further, the main thyristor (SC
When a surge voltage is applied to the anode electrode of (R), the current is correspondingly increased by the snubber resistor (R1), the voltage dividing capacitor (C1),
After passing through the capacitor (C5), it flows into the base of the transistor (TR2) and turns on the transistor (TR2). No more than a certain voltage is applied to the capacitor (C2). At this time, the voltage across the capacitor (C5) gradually increases due to the resistance (R7),
Eventually, when the capacitor (C5) becomes charged, the capacitor
There is no current flowing into the base of the transistor (TR2) through (C5) and the transistor (TR2) is turned off. Is to be retained.

The voltage across the firing capacitor (C2) also rises with the voltage rise due to the charging of the capacitor (C5), but the resistor (R8) and the capacitor (C2) constitute an integrating circuit. Therefore, the rate of increase is lower than that of the voltage of the capacitor (C4), which prevents a sharp voltage from being applied to the ignition capacitor (C2).
(PTR) The current due to the avalanche effect flows and the transistor (T
R1) does not malfunction when ON
(PTR) Ignition capacitor only by ignition optical signal
The energy of (C2) is supplied to the gate of the main thyristor (SCR) to fire the main thyristor (SCR).

[0012]

As is apparent from the above description, according to the present invention, even if a surge voltage due to switching surge at start-up or other phenomena is applied between the anode and cathode of the main thyristor, the transistor of the voltage suppression circuit will be described. Is turned on and a surge current flows to the cathode side, so that no steep voltage is applied to the firing capacitor, so that no avalanche effect occurs in the phototransistor and the thyristor firing circuit does not malfunction. For this reason, the main thyristor can be reliably fired only by the firing command light signal, and the thyristor-applied product can be used safely even in a high-voltage system where switching surges at the start occur. . Therefore, the present invention is extremely large in that it contributes to industrial development as a thyristor ignition circuit that solves the conventional problems.

[Brief description of the drawings]

FIG. 1 is a thyristor firing circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional thyristor firing circuit.

[Explanation of symbols]

 SCR: Main thyristor C2: Firing capacitor PTR: Phototransistor C5: Capacitor R7: Resistance

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yuji Yonega 2-1203, Hazen, Meito-ku, Nagoya City, Aichi Prefecture (58) Field surveyed (Int. Cl. ⁷ , DB name) H03K 17/73 H02M 1 / 08 301 H02M 3/00

Claims (1)

(57) [Claims] 1. The voltage of an ignition capacitor (C2) for obtaining ignition power from an anode electrode of a main thyristor (SCR) and storing ignition energy, and the voltage of the ignition capacitor (C2) is always lower than a certain value. And a phototransistor (PTR) that conducts upon receiving the firing command optical signal. The firing capacitor is activated by the conduction of the phototransistor (PTR).
The firing energy stored in (C2) is transferred to the main thyristor (SCR)
In the thyristor firing circuit that supplies the gate of the thyristor, a capacitor (C5) is connected between the base and collector of the transistor (TR2) of the voltage suppression circuit, and a resistor (R7) is connected between the base and emitter. Thyristor firing circuit.