JPH057143A - Solid State Relay - Google Patents

Abstract

(57) [Summary] [Purpose] Solid state without reverse firing of TRIAC
Provide a relay. [Configuration] Diode stack circuit for full-wave rectification of load voltage
Path DS and two resistors R₁₃, R ₁₄Consisting of a diode
Voltage dividing circuit for dividing the full-wave rectified voltage of the stack circuit DS
And the first voltage that is turned on / off by the divided voltage.
To coupler PC₁And this first photo coupler PC₁And enter
Force terminal PI₁, PI₂The input applied to and zero
War MOSFET PT that turns on at the timing of loss₂To
Bidirectional output second photocoupler PC for output₂When,
This second photocoupler output turns the trigger current ON / OF.
F triac TC.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to solid state relays.

[0002]

2. Description of the Related Art A conventional solid state relay is shown in FIG. In this solid state relay, an AC power supply and a load are connected to the output terminals PO ₁ and PO ₂ (not shown). And the output terminals PO ₁ , P
The O _2, and a snubber circuit comprising a series circuit of a resistor R ₇ and capacitor C, and the triac TR, a diode D _1, D
_A diode stack circuit DS including ₂ , D ₃ , and D ₄ is connected in parallel. The diode stack circuit DS is a full-wave rectification circuit, and the gate resistance R ₆ of the triac TR is provided between the point b of the circuit DS and the output terminal PO _2.
Are connected. The zero cross circuit 1 is connected to the input sides of the points c and d of the diode stack circuit DS.
In this zero-cross circuit 1, a series circuit of a resistor R ₁ and a light emitting element LD of a photocoupler PC is connected to input terminals PI ₁ and PI ₂ to which an input signal is applied, while a point between points c and d of a diode stack circuit DS. A series circuit of the resistor R ₂ and the phototransistor PT of the photocoupler PC, the resistor R ₃
And a series circuit of a transistor Tr _1, a series circuit of resistors R ₁ and R _{2, and} a series circuit of a thyristor SCR and a diode D ₁ are connected in parallel to each other,
The base of ₁ is connected to the collector of the phototransistor PT, and the transistor Tr ₂ is connected to the transistor T _2.
The transistor Tr ₂ is connected in parallel to r ₁ , the collector of the transistor Tr ₂ is connected to the gate of the thyristor SCR, and the base is connected to the connection point of the resistors R ₄ and R ₅ .

In this solid state relay, when no input signal is applied to the input terminals PI ₁ and PI ₂ ,
Since the light emitting element LD of the photocoupler PC does not emit light and the phototransistor PT is OFF, the transistor Tr ₁ is ON, so that the trigger current does not flow through the thyristor SCR, the current flowing through the gate resistor R ₆ is small, and the triac TR is OFF. It is still done. When an input signal is applied, the light emitting element LD is turned on, the phototransistor PT is turned on, and the transistor Tr ₁ is turned off accordingly. In this state, if the AC signal is at a certain level, resistors R ₄ and R ₅
The transistor Tr ₂ is turned on and the thyristor SCR is still turned off by the voltage corresponding to, the current I flows through the gate resistor R, or the triac TR is not triggered.
When the AC signal falls below a certain level (zero cross point),
The transistor Tr ₂ is turned off, the trigger current I _T flows through the thyristor SCR, the current I + I _T flows through the gate resistor R ₆ , and the triac TR is turned on.

[0004]

In the above-mentioned conventional solid state relay, when the triac is triggered or not triggered, the current I of the zero-cross circuit flows into the gate of the triac, so that when the output dV / dt is large,
There has been a problem that a displacement current due to dV / dt flows in and the TRIAC is erroneously fired. This problem is particularly remarkable in the case of an L (inductance) load. The same applies at high temperatures.

The present invention has been made in view of the above problems, and an object thereof is to provide a solid state relay which does not erroneously fire a triac even when the output voltage change (dV / dt) is large. I am trying.

[0006]

A solid-state relay of the present invention comprises a diode stack circuit for full-wave rectifying a load voltage, a voltage dividing circuit for dividing the full-wave rectified voltage of the diode stack circuit, and a voltage dividing circuit. A first photocoupler that is turned on / off by the applied voltage, a second photocoupler that outputs a power MOSFET and that is turned on at a zero-cross timing by the first photocoupler and the input, and It is composed of a triac whose trigger current is turned on / off by a second photocoupler output.

In this solid-state relay, the AC signal is full-wave rectified by the diode stack circuit, and the rectified voltage is divided by the voltage dividing circuit to reach a predetermined voltage or more.
The first photo coupler turns on. When the AC signal is at zero cross, the divided voltage is equal to or lower than the predetermined voltage, and the first photo coupler is not turned on. When an input signal is applied while the first photo coupler is on, the second photo coupler does not turn on, but when there is an input signal, the zero cross point is reached, and when the first photo coupler turns off, The second photo coupler turns on, and the output power MO of the second photo coupler
The SFET turns on and the triac is triggered to turn on. In this solid state relay, the gate current flows through the triac only when it is triggered. That is, the current of the zero-cross circuit does not flow into the gate of the triac.

[0008]

The present invention will be described in more detail with reference to the following examples. FIG. 1 is a circuit diagram of a solid state relay showing an embodiment of the present invention. The solid-state relay of this embodiment has a snubber circuit composed of a resistor R ₁₇ and a capacitor C _{1 at} output terminals PO ₁ and PO ₂ to which an AC power source and a load (not shown) are connected, a triac TR,
A diode stack circuit DS including diodes D ₁ , D ₂ , D ₃ , and D ₄ is connected in parallel with each other. A gate resistor R ₁₆ is connected between the gate and cathode of the triac TR, and a resistor R ₁₅ and a photocoupler P are provided between the gate of the triac TR and the output terminal PO _1.
A series circuit of the output power MOSFET PT ₂ of C ₂ is connected. The diode stack circuit DS ′ is a full-wave rectifier circuit, and the zero-cross circuit 2 is connected to points c and d of this diode stack circuit DS.

The zero-cross circuit 2 has resistors R ₁₃ and R connected between the points c and d of the diode stack circuit DS.
_A voltage dividing circuit composed of ₁₄ series circuits, and a light emitting element LD ₁ of a photocoupler PC ₁ connected in parallel with the resistor R ₁₄ .
Further, a resistor R connected between the input terminals PI ₁ and PI _2
11, the light emitting element LD ₂ of the photocoupler PC _2, the series circuit and, further also resistor R ₁₂ in series circuit of the phototransistor PT ₁ of the photocoupler PC ₁ which is connected between the input terminal PI ₁ and PI ₂ of the transistor Tr ₁₁ It consists of and. The collector of the phototransistor PT ₁ of the photocoupler PC ₁ is connected to the base of the transistor Tr ₁₁ .

Next, the operation of the solid state relay of this embodiment will be described. When an AC signal is applied to the output terminals PO ₁ and PO ₂ via a load, the diode stack circuit DS performs full-wave rectification, and the voltage corresponding to the signal is divided by the resistors R ₁₃ and R ₁₄ , and the photocoupler is used. When the divided voltage applied to the light emitting element LD ₁ of PC ₁ is equal to or higher than a predetermined level, the light emitting element LD ₁ emits light. As a result, the phototransistor PT ₁ is turned on. When the AC signal applied to the diode stack circuit DS is close to zero level, the voltage divided by the resistors R ₁₃ and R ₁₄ is 0 or very small, and the light emitting element LD ₁ does not emit light. PT ₁ also does not turn on. In any case,
Under the condition that the input signal is not applied to the input terminals PI ₁ and PI ₂ , the phototransistor PT of the photocoupler PC ₁
Photo coupler PC ₂ regardless of whether ₁ is ON or OFF
A current does not flow in the light emitting element LD ₂ of, and therefore the output power MOSFET PT ₂ of the photocoupler PC ₂ does not turn ON,
Triac TR is also not triggered. Therefore, under the condition that the input signal is not applied, the current I of the zero level crossing circuit 2 is
It is flowed in a separated state without being flown to the gate of the triac TR.

[0011] Now, when the input signal is applied to the input terminal PI _1, PI _2, there AC signal above a predetermined level, under a state where the light-emitting element LD ₁ of the photocoupler PC ₁ is emitting light, the phototransistor PT ₁ Is ON, therefore the transistor Tr ₁₁ is OFF, and the light emitting element LD ₂ does not light up despite the application of the input signal.
The output power MOSFET PT ₂ also does not turn on, no current flows through the gate resistance R ₁₆ of the triac TR, and the triac TR is not triggered. However, when the input signal continues to be applied and the AC signal becomes 0 level, the light emitting element LD ₁ of the photocoupler PC ₁ does not light up, and the phototransistor PT ₁ is off at this timing, so the transistor Tr ₁₁ is in the ON state, and accordingly, a current flows through the path of the resistor R ₁₁ , the light emitting element LD ₂ and the transistor Tr ₁₁ through the input terminal PI ₁ , and the light emitting element LD ₂ is turned on. By this lighting, the output power MOSFET P
A current also flows through T ₂ , where the Transac TR is triggered. After the trigger, this AC signal causes an output current to flow through the triac TR.

[0012]

According to the present invention, a power MOSFET photocoupler is used in a triac trigger circuit.
Since the current I of the zero-cross circuit is prevented from flowing into the gate of the triac, even if the output change d
Even when V / dt is large, the triac does not reverse-fire, so that it is strong against an L load such as a motor or a solenoid. Further, since C and R of the snubber circuit can be reduced accordingly, the outer shape of the slip state relay can be reduced. Further, there is an advantage that the reverse ignition is eliminated even when the triac becomes hot.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a solid state relay according to an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional solid state relay.

[Explanation of symbols]

2 Zero cross circuit PI ₁ , PI ₂ Input terminal PO ₁ , PO ₂ output terminal TR TRIAC DS Diode stack circuit PC ₁ , PC ₂ Photo coupler PT ₂ Output power MOSFET R ₁₃ , R ₁₄ Dividing resistance

Claims (1)

Claim: What is claimed is: 1. A diode stack circuit for full-wave rectifying a load voltage, a voltage dividing circuit for dividing a full-wave rectified voltage of the diode stack circuit, and ON / O by the divided voltage.
The first photocoupler that performs FF, and the first photocoupler and the input turn on at the zero-cross timing.
A solid-state relay including a bidirectional output second photocoupler having a power MOSFET as an output and a triac whose trigger current is turned ON / OFF by the second photocoupler output.