JPH0414269A - Photo coupler - Google Patents

Abstract

PURPOSE:To supply a trigger current of constant value to an input circuit independently of the power supply voltage, by connecting a constant current element in series with a light emitting diode, which constant current element supplys a driving current of constant value independently of the voltage value of a power supply which applies a driving voltage to the input circuit. CONSTITUTION:When a control signal (e) is delivered to an input circuit 7, a conduction state is obtained and the driving voltage of a power supply 12 is supplied to an input circuit 7. A constant current flows in a light emitting element 2 through a constant current element 22, and the light emitting element 3 generates light. Said light is received by a photo detector 3, and a signal is outputted from an output circuit 8. Hence a photo coupler wherein the limitation caused by the input power supply voltage value is very little and general- purpose properties are high can be realized, by applying the input circuit 7 having constant current characteristics to a photo coupler. By replacing said circuit with a constant current element, a highly reliable device can be obtained, and structural miniaturization is enabled.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an improvement in the input circuit of an optical coupling device such as a photocoupler or a solid state photorelay.

<Prior Art> As a conventional optical coupling device, a solid state relay (hereinafter abbreviated as SSR) is shown in FIG. 4.5.

In Figure 4, l is the SSR circuit, and 2 is G as a light emitting element.
An infrared light emitting diode made of aAs or the like, 3 a phototriac element as a light receiving element that receives the light emitted from the infrared light emitting diode 2 and conducts an AC current;
Built-in zero cross circuit 4. 5 is a main triac element, which is selected depending on the magnitude of the load current.

Reference numeral 6 denotes an input current limiting resistor, and an input circuit 7 is formed from the light emitting diode 2. Ma1ko, light receiving element 3
An output circuit 8 is formed from the zero cross circuit 4 and the main triac element 5.

Incidentally, the light emitting diode 2, the phototriac 3, and the zero cross circuit 4 are built into one element to form an ignition phototriac element T.

Further, as peripheral circuits, a load circuit II consisting of a load 9 and an AC power source 10, a DC power source 12, an input driving transistor j3, and a base driving resistor 14 of the transistor 13 are included.
There is an input control circuit 15 consisting of.

The positive electrode of the DC power supply 12 is connected to the input terminal a of the SSR circuit 1, and the collector terminal of the transistor 13 is also connected to the input terminal a.

A load 9 is connected to the specific power terminal C of the SSR circuit, and an AC power source 10 is also connected to the output terminal d.

The SSR circuit 1 configured as described above is as shown in FIG.
After the main triac element 5, ignition phototriac element T, input current limiting resistor 6, and lead terminals 17 to 20 are placed on the printed wiring board 16 by soldering or the like,
The circuit portion is covered with an exterior resin 2I such as Evokin resin.

Note that lead terminals 17 and 18 correspond to input terminals a and b, and lead terminals 19 and 20 correspond to output terminals c and d, respectively.

Next, the operation of the SSR will be explained. Control signal e is H
At the high level, the base current is supplied to the transistor I3 via the base drive resistor 14, and the transistor I3
3 is in a conductive state and is an input terminal a-b consisting of an infrared light emitting diode 2 and an input current limiting resistor 6 connected in series.
Input voltage Vc is applied between them.

Now, the current 11n flowing through the infrared light emitting diode 2 is given by the following equation.

Resistance value Vc of Rin input current limiting resistor 6: Voltage value of DC power supply 11 VF (LED): Forward drop voltage V of infrared light emitting diode 2 ce (sat): ) Collector-emitter saturation voltage of transistor 13 (1) In the equation, the current Iin must be selected to a value that is greater than or equal to the trigger current required to excite (conduct) the SSR phototriac element 3 and less than or equal to the maximum rated current of the infrared light emitting diode 2. It won't happen.

Now, if the minimum trigger current required to make the SSR conductive is I F T (minX minimum trigger current), then VF (LED) is approximately I V and Vce (sat) is a constant value of approximately 0.3 ■. Therefore, from equation (1), in order to keep the trigger current above the minimum trigger current and below the maximum rated current of the infrared light emitting diode 2, the input current limiting resistor 6 must be set for each voltage value Vc of the DC power supply 12 used. Is it necessary to have different resistance values?

<Problems to be Solved by the Invention> As in the prior art described above, in the input circuit of the optical coupling device, the trigger current is controlled using the resistor 6, so the input current limiting resistor must be set for each power supply voltage used by the user. Therefore, the optical coupling device is a highly specialized product. From the producer's perspective, this is a factor that greatly limits production planning and management.

Furthermore, in consideration of versatility, optical coupling devices without input current limiting resistor 6 have been commercialized, but in this case, it is necessary for the user to calculate the resistance value of the input current limiting resistor based on the voltage value of the DC power supply. There is.

■External parts require more parts. (It may be necessary to add an input current limiting resistor.) There were other inconveniences such as poor usability.

In view of the above, an object of the present invention is to provide an optical coupling device that can supply a constant value of trigger current to an input circuit for any power supply voltage value.

<Means for Solving the Problems> The means for solving the problems according to the present invention, as shown in FIG. In an optical coupling device constituted of an output circuit 8 having a light receiving element 3 that receives light and outputs a signal, the driving voltage is constant regardless of the voltage value of the power supply 12 that applies a driving voltage to the input circuit 7. A constant current element 22 that supplies current is connected in series with the light emitting element 2.

<Function> In the problem solving means described above, when the control signal e is output to the input circuit 7, it becomes conductive and the driving voltage of the power supply 12 is supplied to the input circuit 7.

Then, a constant current flows through the light emitting element 2 by the constant current element 22, the light emitting element 2 emits light, and the light receiving element 3 receives this light, whereby a signal is output from the output circuit 8.

By applying an input circuit having constant current characteristics to an optical coupling device, it is possible to realize a highly versatile optical coupling device that is extremely limited by the input power supply voltage value. In addition, by replacing conventional resistors with constant current elements,
Not only can the device be made highly reliable, but it can also be structurally miniaturized, which was not possible with conventional resistors.

<Example> Hereinafter, an example in which the present invention is applied to a solid state relay (SSR) will be described based on the drawings.

FIG. 1 is an input circuit diagram of an optical coupling device showing an embodiment of the present invention, FIG. 2 is a structural diagram of the optical coupling device, and FIG. 3(a)
is a current-voltage characteristic diagram of a constant current element, (b) is a current-voltage characteristic diagram of a light emitting element, and (c) is a current-voltage characteristic diagram between input terminals of an input circuit.

Note that the same reference numerals are given to functional parts that are the same as before.

The optical coupling device of this embodiment includes an input circuit 7 including a light emitting element 2 that emits light in response to a control signal e, and an output circuit 7 including a light receiving element 3 that receives light emitted from the light emitting element 2 and outputs a signal. A constant current element 22 is connected in series with the light emitting element 2 to supply a constant value of driving current regardless of the voltage value of the power supply 12 that applies the driving voltage to the input circuit 7. .

The light emitting element 2 is made of an infrared light emitting diode such as GaAs, and together with the constant current element 22, an input circuit 7 having input terminals a and b is formed.

The constant current element 22 is an N-channel depletion field effect transistor (FET) whose gate G and source 8 are short-circuited (vcs=OV), and the constant current shown in FIG. 3(a) is have characteristics. In the figure, I
D is the drain current, and VDS is the drain-source voltage. The drain D of the constant current element 22 is connected to the cathode terminal of the light emitting diode 2, and the gate G and source S
The connection point is connected to the input terminal. The input terminal S is connected to the collector terminal of the input driving transistor I3 of the 5SRI.

Further, the anode terminal of the light emitting diode 2 is connected to the input circuit 7.
is connected to input terminal a of.

The light receiving element 3 and the output circuit 8 have the same structure as the conventional one as shown in FIG. An output circuit 8 is formed.

The output terminal C is connected to the load 9, and the output terminal d is connected to the AC power source IO. Note that the other configurations are the same as the conventional one.

In the above configuration, a control signal e is output from a system control circuit such as a microcomputer.

When the level is W, the base potential of the transistor 13 is lowered to near the ground potential via the base drive resistor 14, and the transistor 13 is turned off. Therefore, input terminals a and b of the SSR are in an open state, no current flows through the infrared light emitting diode 2, and the output of the SSR is in an off state.

On the other hand, when the control signal e goes high, a base current flows between the base and emitter of the transistor 13 via the base drive resistor I4, making the transistor I3 conductive. Therefore, from the DCi source 12 to the input terminal a of the SSR
A voltage Vc-1v'ce(sat) is supplied between -b.

Here, in the input circuit 7 of the SSR, the infrared light emitting diode 2
The voltage-current characteristics of the constant current element 22 are the curves shown in FIG. 3(b), and the voltage-current characteristics of the constant current element 22 are the curves shown in FIG. 3(a).

In FIG. 3(b), IF is the forward current of the infrared light emitting diode 2, and VF is the forward voltage drop.

The constant current value Tin in Fig. 3(a) can be controlled depending on the process conditions, and must be at least the minimum trigger current I F T (min) of the phototriac 3 and below the maximum rated current of the infrared light emitting diode 2. set to the value.

FIG. 3(c) shows the current-voltage characteristics when the light emitting diode 2 and the constant current element 22 having the characteristics shown in FIGS. 3(a) and 3(b) are connected in series, and the DC power supply voltage of the input circuit 7 Vc
If is more than (VF I +VDS I), constant current (
-1in) characteristics. Here, VFI is the forward voltage drop value of the GaAs infrared light emitting diode 2, which is approximately 10 to 1.
3V, VDS I is a voltage at which the constant current element 22 starts constant current characteristics, and in the case of the field effect transistor of this embodiment, it can be set to 1 to 2V. Note that the maximum value of VC is determined by the withstand voltage between the drain and source of the field effect transistor (50 V or more is possible, and can sufficiently cover the current commonly used voltage of 5 to 24 V).

Then, a constant current Iin flows through the infrared light emitting diode 2,
The light emitting diode 2 emits light, and this light excites the phototriac 3, making the phototriac 3 conductive.

Then, a trigger current is applied to the gate of the main triac 5, the main triac 5 becomes conductive, and the AC power source 0 is applied to the load 9.

Therefore, by applying an input circuit with constant current characteristics to an optical coupling device, a highly versatile optical coupling device (capable of covering all voltage values of power supply systems that can be used at present) with extremely few restrictions due to the voltage value of the power supply. can be realized.

In addition, by replacing conventional resistors with semiconductor devices such as field-effect transistors for constant current elements, it is possible to create highly reliable devices, and it is also possible to achieve structural miniaturization that could not be achieved with conventional resistors. becomes.

It should be noted that the present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in this embodiment, the cathode of the infrared light emitting diode 2 and the train of the field effect transistor 22 are connected, and the anode of the infrared light emitting diode 2 is connected to the output terminal a, and the source/gate connection point of the field effect transistor 22 is input. The source/gate connection point of the field effect transistor 22 is connected to the anode of the infrared light emitting diode 2, and the drain of the field effect transistor 22 is connected to the input terminal a of the infrared light emitting diode 2. The cathodes of the input terminals may be connected to the respective input terminals.

<Effects of the Invention> As is clear from the above description, the present invention includes an input circuit including a light emitting element that emits light in response to a control signal, and a light receiving element that receives light emitted from the light emitting element and outputs a signal. A constant current element is connected in series with the light emitting element to supply a constant value of drive current regardless of the voltage value of the power supply that applies the drive voltage to the surface input circuit. A constant current can be passed through the light emitting element regardless of the voltage value of the power supply, and a highly versatile optical coupling device can be realized with extremely few limitations due to the input power supply voltage value. In addition, it has the advantage of being able to provide a device with higher reliability than conventional resistors, and also has the advantage of being able to be made smaller in size, which was not possible with conventional resistors.

[Brief explanation of drawings]

FIG. 1 is an input circuit diagram of an optical coupling device showing an embodiment of the present invention, FIG. 2 is a structural diagram of the optical coupling device, and FIG. 3(a)
is a current-voltage characteristic diagram of a constant current element, (b) is a lightning-voltage characteristic diagram of a light-emitting element, (c) is a current-voltage characteristic diagram between input terminals of an input circuit, and Figure 4 is a conventional diagram. The circuit diagram of the optical coupling device shown in FIG. 5 is also a structural diagram thereof. 2: light emitting element, 3: light receiving element, 7. Input circuit, 8 output circuit, 12. Power supply, 22. Constant current element.

Claims (1)

[Claims] In the optical coupling device, the input circuit includes an input circuit including a light emitting element that emits light in response to a control signal, and an output circuit including a light receiving element that receives light emitted from the light emitting element and outputs a signal. An optical coupling device characterized in that a constant current element that supplies a constant value of drive current regardless of the voltage value of a power source that applies a drive voltage to the light emitting element is connected in series with the light emitting element.