JPH01319324A - Solid-state relay - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution by connecting a base of a photo transistor(TR) of a zero cross detection circuit to a connecting point of a base voltage setting via a diode. CONSTITUTION:A zero cross detection circuit ZC has a photo TR with a base terminal coupled with a light emitting diode PD provided to an input side circuit 2, the base of the photo TR is connected to a 1st connecting point (f) of voltage division resistors R1, R2 for base voltage setting via diodes D1, D2. Moreover, the collector of the photo TR is connected to a 2nd connecting point (g) of voltage division resistors R3, R4 for SCR trigger voltage setting. Thus, the signal transmission and zero cross detection are attained in common by the single photo TR to simplify the circuit constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a solid state relay (SSR) used for controlling power supply to loads such as motors and heaters in industrial equipment and general consumer equipment.

<Prior art and its problems> There are cases where it is necessary to apply a solid state relay to control two loads to contradictory states, such as turning one of the loads on and turning the other one off. For example, this applies to the case where a motor is driven by switching between forward rotation and reverse rotation. In order to meet such demands, attempts have been made in the past to combine a normally on operation type and a normally off operation type to facilitate operation switching control and to simplify the circuit configuration. There is. As a normally-on solid state relay used for this purpose, there is a conventional one having the configuration shown in FIG.

In the figure, 2° is an input end circuit into which a signal for controlling on/off operation is input, 4o is an output side circuit that turns on/off the load power supply AC in response to the input signal, and both circuits 2°, 4o is coupled via a photocoupler 6°. The input side circuit 2° includes a pair of input terminals r, St, and a photocoupler 6 to which signals for on/off operation control are input manually.
It consists of a light emitting diode PD that makes up the input terminal ■
1. ■.

A DC power supply E and a switch SW are connected to the terminal. On the other hand, the output side circuit 4° has a pair of output terminals P1, P,
A bidirectional switching element (TRIAC in this example) THY connected via THY, and this TRIAC THY
a trigger circuit TC that turns on and off the load power supply AC, a zero-cross detection circuit ZCo that operates the trigger circuit TC near the zero-cross point of the voltage of the load power supply AC, a phototransistor T that constitutes the photocoupler 6°, and a snubber for surge absorption. and a circuit SC. The zero-crossing detection circuit ZCo is composed of a switching transistor T connected to a phototransistor T, and resistors R3 to R4, and is configured to set the trigger circuit TC to a non-operating state when an input signal is applied. There is. Note that RL is a load such as a motor and a heater.

In the above configuration, when the switch SW is off and no input signal is applied, the phototransistor TI is off and the switching transistor T is also in an off state with no base current flowing. When the voltage of the load power supply AC gradually rises from Ov and the potential of the voltage dividing point of the resistors R1 and R4 reaches the operating potential of the SIRISK SCH of the trigger circuit TC, the SIRISK SCR is turned on. Then, the triac THY is triggered and turns on, so the output terminal P1
, P, are turned on, and the load RL is energized. On the other hand, when the switch SW is turned on and an input signal is applied to the input terminal circuit 2, the phototransistor T is turned on, and the base current flows through the switching transistor T until the voltage of the load power supply AC approaches OV. Switching transistor T! turns on. As a result, the voltage applied to the gate of the thyristor SCR becomes lower than the trigger voltage, so the thyristor SCR turns off, and therefore the triac THY is not triggered, and the output terminal P
1 and Pt, the load RL is not energized in an off state.

By the way, in the conventional configuration described above, it was necessary to provide a switching transistor T separately from the phototransistor T in the zero-cross detection circuit ZCO, which not only complicated the circuit configuration but also caused an increase in cost. .

<Purpose of the Invention> The present invention has been made in view of the above circumstances, and provides a normally-on operation type solid state relay without impairing the function of the zero-cross detection circuit.
The purpose is to further simplify the circuit configuration.

<Configuration and Effects of the Invention> In order to achieve the above object, the present invention adopts the following configuration.

That is, in the present invention, a zero cross detection circuit for a solid state relay has a phototransistor with a base terminal coupled to a light emitting element provided in an input side circuit, and the base of the phototransistor is connected to the base of the phototransistor. It is characterized by being connected via a diode to the connection point of the voltage dividing resistor for voltage setting.

According to the above configuration, a single phototransistor can serve both signal transmission and zero-cross detection, so a conventional switching transistor can be omitted. Therefore, it is possible to simplify the circuit configuration and reduce costs.

<Embodiment> FIG. 1 is a circuit configuration diagram of a normally-on operation type solid state relay according to an embodiment of the present invention.

The solid state relay 1 of this embodiment includes an input side circuit 2 into which a signal for on/off operation control is input, and a load power supply AC (alternating current) turned on/off in response to the input signal to this input side circuit 2. and an output side circuit 4 that is turned off, both circuits 2.
4 are coupled via a photocoupler 6.

The above-mentioned input side circuit 2 consists of a pair of input terminals ■1 and ■1 into which on-off operation control signals are input, a resistor R8, and a light emitting element (in this example, a light emitting diode) PD that constitutes a photocoupler 6. A DC power supply E and a switch SW are connected to input terminals I and I.

On the other hand, the output side circuit 4 includes a bidirectional switching element (TRIAC' in this example) THY connected to the load power supply AC via a pair of output terminals P and SP, and a trigger that turns ON/OFF this TRIAC THY. The trigger circuit TO detects the zero cross point of the voltage of the circuit TC and the load power supply AC.
It is equipped with a zero-cross detection circuit ZC for operating the circuit, and a snubber circuit SC for absorbing surges.

The above zero-cross detection circuit ZC has a phototransistor Tr with a base terminal coupled to the light emitting diode PD provided in the input side circuit 2, and the base of the phototransistor Tr is connected to a divided voltage for base voltage setting. A diode DI is connected to the first connection point f of the resistor RI and Rt.
Connected via Dt. Further, the collector of the phototransistor Tr is connected to a second connection point g of voltage dividing resistors R1 and R4 for setting a gate trigger voltage of a Cyrisk SCR, which will be described later. And phototransistor T
When r is off, the potential V at the second connection point g is smaller than the potential V1 at the first connection point r.
The values of each resistor R7, R2, R8, and R4 are set. The trigger circuit TC consists of a thyristor SCR, a bridge circuit DB for full-wave rectification, and a resistor R6.
operating potential V. is set in advance to be smaller than the potential Va required for the phototransistor Tr to turn on when it is not receiving light. In addition, snubber circuit SC
consists of a resistor R5 and a capacitor C1. In addition, RL
is the load of the motor, heater, etc.

Next, the operation of the solid state relay having the above configuration will be explained with reference to the timing chart shown in FIG. 2 and the waveform diagram of the load power supply shown in FIG. 3.

(i) State in which no human input signal is applied (period indicated by symbol a in FIG. 2) In this state, the switch SW of the DC power supply E is off, and the light emitting diode PD of the input side circuit 2 is turned off. Therefore, as shown in FIG. 3, when the load power supply AC voltage gradually increases from Ov, the potential vl at the first connection point r reaches the potential Va required to turn on the phototransistor Tr. The potential V at the second connection point g is the thyristor S
CR operating voltage V. Therefore, the gate of the thyristor SCR is turned on before the phototransistor Tr is turned on, and thereby the triac THY is also turned on. Therefore, conduction occurs between the output terminals PISPt and the load RL is energized.

(ii) State immediately after application of input signal (period indicated by the reference numerals in FIG. 2) When the switch SW of the DC power supply E is turned on and an input signal is applied to the input side circuit 2, the light emitting diode PD emits light. Along with this, the base current of the phototransistor Tr increases, so the potential vb required to turn on the phototransistor Tr decreases relatively, causing the thyristor SC to
Operating potential of R■. The phototransistor Tr is turned on below.

As a result, the potential ■ of the second connection point g changes to the thyristor SC.
Operating potential V of H. It becomes below. However, triac T
Due to its characteristics, HY does not turn off immediately, but remains on until the holding current drops below. In other words, the load RL is energized until the load power supply AC voltage becomes close to OV. Then, the device enters the off state only when the current becomes equal to or less than the holding current.

(iii) Continuous application of input signal (period indicated by symbol C in FIG. 2) In this state, a certain amount of time has passed since the switch SW of the DC power supply E was turned on, and the phototransistor Tr is Since light from the light emitting diode PD is received, the potential vb required to turn on the phototransistor Tr is lower than the operating potential V0 of the thyristor SCH. Then, while the phototransistor Tr is on, the second
Since the potential at the connection point g becomes lower than the operating potential V0 of the thyristor SCR, the thyristor SCR cannot be turned on, and therefore the triac THY is also in an off state. therefore,
There is no conduction between the output terminals P, , P, and no current is applied to the load RL.

(Iv) State immediately after the input signal is turned off (period indicated by symbol d in Fig. 2) In this state, the switch sw of the DC power supply E is off and no human input signal is applied, so the light emitting diode PD of the output side circuit 2 goes out. Therefore, as shown in Figure 3,
Potential Va required for phototransistor Tr to turn on
is the potential required for the thyristor scR to operate. However, when the voltage of the load power supply AC is larger than the potential Va required to turn on the phototransistor Tr, the phototransistor Tr maintains the on state. Therefore, the potential V! of the second connection point g! is Sairisk SC
The operating potential of R is V. Since the following is true, the thyristor SCR cannot be turned on, and the triac THY is also in an off state.

Therefore, there is no conduction between output terminals P1 and P22, and load RL
energization is not performed. Then, in the next period indicated by the symbol a in FIG. 2, when the voltage of the load power supply AC gradually increases from oV, the thyristor SCR turns on before the phototransistor Tr turns on. THY will be turned on.

[Brief explanation of the drawing]

1 to 3 show embodiments of the present invention, in which FIG. 1 is a circuit configuration diagram of a normally-on operation type solid state relay, FIG. 2 is a timing chart of the solid state relay shown in FIG. 1, and FIG. FIG. 3 is an explanatory diagram showing the relationship between the operating potentials of the phototransistor and thyristor and the output waveform of the load power supply. Further, FIG. 4 is a circuit diagram of a conventional normally-on operation type solid state relay. 1...Solid state relay, 2...Input side circuit, 4...Output side circuit, ZC...Zero cross detection circuit, Tr...Phototransistor, TC...Trigger circuit, THY... Triac.

Claims (1)

[Claims] (1) An input side circuit into which a signal for on/off operation control is input, and an output side circuit that turns on/off a load power supply in response to this input signal, and the output side circuit includes the A solid that includes a bidirectional switching element connected to a load power supply, a trigger circuit that turns on and off the switching element, and a zero-cross detection circuit that detects a zero-crossing point of the load power supply voltage and operates the trigger circuit. In the state relay, the zero-cross detection circuit has a phototransistor with a base terminal coupled to a light emitting element provided in the input side circuit, and the base of the phototransistor is connected to a base terminal for setting a base voltage of the phototransistor. A solid state relay characterized by being connected to the connection point of a voltage dividing resistor via a diode.