JPH0427219Y2 - - Google Patents

Description

[Detailed description of the invention] <Field of industrial application> The present invention relates to the improvement of an AC switch circuit that uses a bidirectional thyristor to open and close a commercial AC power supply, etc., and in particular increases the gate current of the reverse blocking thyristor. The present invention relates to an AC switch circuit that ensures trigger operation and at the same time reduces leakage current of the AC switch circuit.

<Prior Art> When opening and closing an AC circuit, it is desirable to close the circuit when the voltage is low in order to prevent the generation of noise due to the effects of inductance and capacitance in the circuit.

FIG. 1 is a circuit diagram showing a conventional embodiment of this type of zero-crossing method.

An AC power source P and a load L are connected in series to the outside of input terminals 1a and 1b of the AC switch circuit.
A bidirectional thyristor _Q1 is connected between input terminals 1a and 1b. Input terminals 1a and 1b are connected to AC terminals 2a and 2b of diode bridge _D1 via resistors _R1 and _R2 , respectively. The gate G of the bidirectional thyristor _Q1 is connected to the AC terminal 2b of the diode bridge _D1 . The DC terminal 3a of the diode bridge _D1 is connected to the anode 2 of the reverse blocking thyristor _Q2 , and the DC terminal 3b is connected to the cathode. A resistor R ₃ , a phototransistor Q ₃ and a resistor R ₄ are connected in series and a voltage _{V 1 is} applied between the anode and cathode of the reverse blocking thyristor Q 2 . Phototransistor Q ₃ and resistor R ₄
The connection point and the gate of reverse blocking thyristor _Q2 are connected. A capacitor C is installed between the gate and cathode of reverse blocking thyristor Q ₂ to prevent misfiring of reverse blocking thyristor Q ₂ due to surge voltage transmitted to the gate via the capacitance between the anode and gate of reverse blocking thyristor Q ₂ . ₂ are connected. The voltage V ₂ across the series circuit of the phototransistor Q ₃ and the resistor R ₄ is the zener diode D ₂ and the resistor
Applied to the series circuit of R ₅ and zener diode D ₂
The voltage V ₃ at the junction of resistor R ₅ and resistor R 5 is applied to the base of zero detection transistor Q ₄ . The collector of zero detection transistor _Q4 is a phototransistor
At the base of Q ₃ , its emitter is a reverse blocking thyristor.
Each is connected to the cathode of Q ₂ . A capacitor _C1 is connected between the collector of the zero detection transistor _Q4 and the emitter of the phototransistor _Q3 . The phototransistor _Q3 is turned on and off by the optical signal 4, and the result appears across the load L as a voltage _V4 .

The phototransistor Q ₃ constitutes a photocoupler together with the light emitting diode D ₃ . The light emitting diode _D3 is connected to the signal input terminals 5a, 5b via a resistor _R6 , and the input signal S for closing the bidirectional thyristor _Q1 is applied to the signal input terminals 5a, 5b.

FIG. 2 is a waveform diagram showing waveforms at various parts of the circuit shown in FIG. The operation of the circuit shown in FIG. 1 will be described below with reference to FIG.

First, when the input signal S is not applied to the phototransistor _Q3 (the off state in Figure 2a), the phototransistor _Q3 is off, and no current flows through the gate of the reverse blocking thyristor _Q2 , resulting in reverse blocking. Thyristor _Q2 is off. Therefore, no current flows through the gate of the bidirectional thyristor _Q1 , and no voltage _V4 (FIG. 2e) appears across the load L either. In this case, a diode bridge is connected to the voltage of AC power supply P between the anode and cathode of reverse blocking thyristor _Q2 .
A voltage V ₁ (FIG. 2b) appears with a waveform that is double rectified by D ₁ . Voltage V ₁ is applied to Zener diode D ₂ via resistor R ₃ , so when the value of voltage V ₁ is large, it is clamped by Zener diode D ₂ , and when it is below the Zener voltage, it is clamped by Zener diode D 2.
D ₂ is turned off and the waveform of voltage V ₁ remains unchanged as voltage V ₂
(Fig. 2c) appears at the cathode of the zener diode _D2 . Also, zero detection transistor _Q4
When the voltage at the base of V ₃ is higher than the rising voltage between the base and emitter, it is clamped almost to the rising voltage, and when it is lower than the rising voltage, the voltage waveform is turned off (FIG. 4d).

Next, if the voltage V ₁ is large during the transition period T (Figure 2 a) when the input signal S changes from off to on, the zero detection transistor Q ₄ is already on and the base of the phototransistor Q ₃ is turned on. Since it is short-circuited, no current flows through the gate of the reverse blocking thyristor _Q2 and it is in the OFF state. Bidirectional thyristor Q ₁ is therefore off and no voltage V ₄ appears at load L (FIG. 1e). This shows that the bidirectional thyristor Q ₁ does not turn on even if the input signal S is applied when the voltage V ₁ is large. If the input signal S is applied when the voltage V ₁ is small and the voltage V ₂ is approximately below the zener voltage of the zener diode D ₂ , then
Since zero detection transistor _Q4 is in the off state,
Current flows through the phototransistor _Q3 to the gate of the reverse blocking thyristor _Q2 , and the reverse blocking thyristor
Q ₂ is made conductive, producing a voltage V ₄ across the load L.
Therefore, only when the input signal S is applied and the value of the voltage V ₁ is less than or equal to a predetermined value, the bidirectional thyristor Q ₁
is ignited.

Once the bidirectional thyristor Q ₁ is fired, it conducts current through the load L and produces no voltage V ₄ as long as the input signal S is applied (FIG. 2e). When the input signal S turns off in a conductive state, the bidirectional thyristor Q ₁ turns off at the first point where the current crosses zero after turning off.

The capacitor _C1 is for preventing misfire of the reverse blocking thyristor _Q2 due to the dark current of the phototransistor Q3. That is, when the optical signal 4 is off, the dark current of the phototransistor _Q3 flows from the collector-base of the phototransistor _Q3 to the capacitor _C1 and the resistor _R4 , which charges the capacitor _C1 , but there is no zero detection. When the transistor _Q4 turns on, the charge in the capacitor _C1 is discharged, and the voltage across the capacitor _C1 , that is, the voltage between the base and emitter of the phototransistor _Q3 , _Vbe , is limited to a constant value (Fig. 2 f). ), by selecting the off period and off duty of the zero detection transistor _Q4 so that this value is less than the rising voltage of the phototransistor Q3, it is possible to prevent misfiring of the reverse blocking thyristor _Q2 due to dark current.

However, the AC switch circuit shown in FIG. 1 has the following drawbacks.

The leakage current between the anode and gate of the reverse blocking thyristor _Q2 is, for example, 20 microamps, and the gate
If the threshold voltage is 0.3 volts, then the resistance R ₄
is 0.3V/20×10 ^-6 (μA) or less, for example, 10kΩ, and the reverse blocking thyristor due to leakage current is selected.
Prevents mis-ignition of _Q2 . Here, reverse blocking thyristor Q ₂ when phototransistor Q ₃ is on
When the anode voltage V ₁ of the reverse blocking thyristor Q 2 is set to 10 volts and the gate voltage of the reverse blocking thyristor Q ₂ is set to 1 volt or more to perform a trigger operation, the resistor R ₃ is replaced with a resistor.
The value should be selected to be less than 10 times _R4 , for example 50 kilohms. By the way, when such a constant is set, when the phototransistor _Q3 is off and the reverse blocking thyristor _Q2 is off, the device leakage current is:
The current flowing through resistor R ₃ , zener diode D ₂ , and resistor R ₅ is given by the voltage of power supply P is 100 volts, 50
When using a commercial power source such as Hertz, the current is 2 milliamps or more. Such numerical values are generally selected when the operating ambient temperature range is about 0 to 45°C.

However, if the upper limit of the operating ambient temperature range is set to 100
℃, the leakage current of reverse blocking thyristor _Q2 is
increased to 100 microamps, etc., and further gate
The threshold voltage also drops to 0.2 volts, etc. This can be countered by selecting the resistors R ₄ and R ₃ to be small, but this has the disadvantage of resulting in an increase in device leakage current.

<Purpose of the invention> In view of the above-mentioned prior art, it is an object of the present invention to provide an AC switch circuit that ensures the trigger operation of a reverse blocking thyristor and has less device leakage current.

<Configuration of the present invention> The configuration of the present invention that achieves this purpose relates to an AC switch circuit, which includes a bidirectional thyristor connected in series to a load, and a voltage at the anode corresponding to the voltage across the bidirectional thyristor. - A reverse blocking thyristor provided between the cathode and controlling the gate current of the bidirectional thyristor, and at least a first resistor, a second resistor having a higher resistance value than the first resistor, and a constant voltage element between the anode and the cathode. A buffer transistor and a phototransistor for igniting the reverse blocking thyristor with an optical signal are provided between the first series circuit connected in series, the connection point of the first resistor and the second resistor, and the cathode of the reverse blocking thyristor. a second series circuit connected in series, and a zero detection transistor that absorbs the base charge of the phototransistor to turn off the phototransistor when the collector voltage of the buffer transistor is above a predetermined value, and turns off when the collector voltage of the buffer transistor is below a predetermined value. A connection point between the second resistor and the constant voltage element is connected to the base of the buffer transistor.

<Example> Hereinafter, an example of the present invention will be described based on the drawings. Note that parts having the same functions as those in the prior art are given the same numbers, and redundant explanations will be omitted.

FIG. 3 is a circuit diagram showing an embodiment of the present invention. The circuit shown in Figure 3 is different from the circuit shown in Figure 1 by adding a resistor between the resistor R ₃ and the zener diode D ₂ .
The difference is that _R7 is inserted, and a buffer transistor _Q5 is further inserted between the connection point of resistors _R3 and _R7 and the phototransistor _Q3 . The collector of the buffer transistor Q ₅ is at the connection point with the resistors R ₇ and R ₃ , the emitter is at the collector of the phototransistor Q ₃ , and the base is at the connection point between the resistor R ₇ and the zener diode.
Each is connected to the connection point with D ₂ . resistance
_R7 is selected to have a larger value than resistor _R3 .
With this configuration, the current to the zener diode D ₂ for zero detection and the zero detection transistor Q ₄ is limited by the high resistance resistor R ₇ , and the gate from the phototransistor Q ₃ to the reverse blocking thyristor Q ₂ is limited. Since the current can flow through the resistance value R ₃ ,
It is possible to reduce the device leakage current when the phototransistor _Q3 is off, and to increase the gate current to the reverse blocking thyristor _Q2 when the phototransistor _Q3 is on, thereby enabling stable trigger operation. As a result, the allowable value of device leakage current can be increased by setting the resistor R ₄ to 1 kilohm, that is, 1/10 of that in the case of FIG. 1.

Next, the operation of buffer transistor _Q5 will be explained with reference to the waveform diagram of FIG. FIG. 4 shows a case where the load L is an inductance load and the current has a phase lag of 90° compared to the voltage. Figure a shows the on/off state of the input signal S, and figure b shows the on/off state of the phototransistor _Q3 . Figure c shows reverse blocking thyristor _Q2
Figure d shows the voltage V ₁ between the anode and cathode of , and the current flowing through the reverse blocking thyristor Q ₂ . Figure e shows the on/off state of the zero detection transistor _Q4 . In the figures a to e, the portions indicated by dotted lines are shown for reference as waveforms at each portion when there is no input signal S and the phototransistor _Q3 continues to be in the off state.

Input signal S is off (off state in Figure 4 a)
Now, phototransistor _Q3 is off (Figure 4b)
and since reverse blocking thyristor _Q2 is off,
The voltage V ₁ between the anode and cathode of the reverse blocking thyristor Q ₂ is a double-wave rectified voltage (Fig. 4c) obtained by rectifying the AC power supply P by the diode bridge D ₁ , and the current flowing through the reverse blocking thyristor Q ₂ is is zero (Fig. 4d). In this state, it does not depend on the on/off state of the zero detection transistor _Q4 .

However, when the input signal S is turned on,
When the voltage _V2 becomes lower than the predetermined value, the zero detection transistor _Q4 turns off (Fig. 4e), so
Phototransistor _Q3 is on (Figure 4b)
The reverse blocking thyristor _Q2 is triggered in synchronization with this ( _tON in FIG. 4) and becomes conductive. Therefore, the voltage V ₁ becomes zero (Fig. 4c), and the current flowing through the reverse blocking thyristor Q ₂ lags the voltage V ₁ by 90° due to the inductance load L, as shown in Fig. 4d. It becomes an electric current. Reverse blocking thyristor Q ₂
In the initial state when the switch is on, the period is long due to the delay in the rise of the current. At the point where the current becomes zero, the reverse blocking thyristor _Q2 tries to turn off, but since the phototransistor _Q3 is on, it turns on again. This state is shown in FIG. 4c as a whisker-shaped voltage corresponding to the point where the current becomes zero (FIG. 4d). Since the voltage _V1 is zero when the reverse blocking transistor _Q2 is in the on state, the zero detection transistor _Q4 remains in the off state (FIG. 4e).

However, the input signal S changes from on to off, and the current flowing through reverse blocking thyristor _Q2 becomes zero.
At the point when it turns off (t _OFF in Figure 4 e), the voltage
V ₁ reaches its maximum value (Fig. 4c), and voltage V ₂ also reaches its maximum value. Here, suppose buffer transistor Q ₅
If the phototransistor Q ₃ has a collector-base electrode capacitance of, for example, 20 picofarad, the capacitance of the capacitor C ₁ is 500 picofarad, and the voltage V ₂ is selected so that the resistor R ₇ is larger than the resistor R ₃ . Therefore, if it is 100 volts, the base voltage of phototransistor _Q3 is 100×20/(20+500)
When a voltage exceeding 3.8 volts is applied, the phototransistor _Q3 causes erroneous conduction regardless of the optical signal 4. However, at this time, the zero detection transistor Q ₄ is also in a state of conduction, so there is a competition situation in which either the photo transistor Q ₃ or the zero detection transistor Q ₄ tries to conduct, and as a result, the reverse blocking thyristor Q ₂ becomes erroneously conductive. This causes a problem in which the power is turned off normally in some cases and in other cases it turns off normally. Therefore, buffer transistor
Q ₅ is inserted as shown in Figure 3, and the surge current due to high voltage V ₂ flows through the capacitance between the collector and base of the buffer transistor Q ₅ to the Zener diode, and the zero detection transistor Q ₄ conduction and avoid the race conditions mentioned above. On the other hand, when phototransistor Q ₃ is turned on by optical signal 4, resistor Q ₃ , buffer transistor Q ₅ ,
Current flows through the phototransistor _Q3 , causing no current to the zener diode _D2 . That is,
Zero detection transistor Q ₄ is not made conductive during the period from t _ON to t _OFF in FIG. 4.

<Effects of the invention> As explained above in detail along with the examples,
According to the present invention, the current for zero detection and the current for gate drive are divided by two types of resistors, the first resistor and the second resistor, and the current for driving the reverse blocking thyristor is divided into two types. By supplying the power through the far transistor, the permissible leakage current of the reverse blocking thyristor can be increased, and at the same time, the leakage current of the device can be reduced.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional AC switch circuit, Fig. 2 is a waveform diagram showing waveforms of each part of the circuit shown in Fig. 1, Fig. 3 is a circuit diagram showing an embodiment of the present invention, and Fig. 4 4 is a waveform diagram showing the states of each part of the circuit shown in FIG. 3. FIG. Q ₁ ... Bidirectional thyristor, Q ₂ ... Reverse blocking thyristor, Q ₃ ... Photo transistor, Q ₄ ... Zero detection transistor, Q ₅ ... Buffer transistor, L ... Load, P ... AC power supply, S...Input signal, _C1 , _C2 ...Capacitor, _R1 to _R7 ...Resistance.

Claims (1)

[Scope of utility model registration request] Bidirectional thyristor connected in series with load L
Q ₁ , a reverse blocking thyristor Q ₂ which is provided with a voltage corresponding to the voltage across the bidirectional thyristor Q ₁ between its anode and cathode to control the gate current of the bidirectional thyristor Q ₁ , and the anode and the cathode. A first resistor _R3 , a second resistor _R7 having a higher resistance value than the first resistor _R3 , and a constant voltage element _D2 are interposed therebetween.
and a third resistor _R5 are connected in series,
a buffer transistor Q ₅ having a collector connected to a connection point between the first resistor R ₃ and the second resistor R ₇ and a base connected to the connection point between the second resistor R ₇ and the constant voltage element D ₂ ; A phototransistor Q3 whose collector is connected to the emitter of the buffer transistor _Q5 , a capacitor _C1 connected between the base and the emitter, and which is opened and closed by the optical signal ₄ ;
A fourth resistor _R4 , one end of which is connected to the emitter of the phototransistor _Q3 and the other end connected to the cathode of the reverse blocking thyristor _Q2 , is connected to the constant voltage element _D2 and the third resistor _R5 . a zero detection transistor Q4 whose base and emitter are connected between the point and the cathode of the reverse blocking thyristor _{Q2 ,} and whose collector is connected to the base of _the phototransistor _Q3 ; An AC switch circuit characterized in that opening and closing of the reverse blocking thyristor _Q2 is controlled by a voltage across both ends.