JPH0652235U - Isolation circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize an insulation circuit with low heat generation. [Structure] (1) A light emitting element that emits light when a constant voltage E is applied when the switch contact SW is on, and an insulating circuit that transmits current when the light emitted by the light emitting element flows and current flows through the switch contact SW 2. An insulating circuit characterized in that a constant voltage E is applied by connecting a plurality of light emitting elements 111, 112, 113, 114 in series with a small current and a large voltage drop. (2) An insulating circuit characterized in that a resistance element R3 to which a constant voltage is applied is provided in parallel with a circuit in which a plurality of light emitting elements are connected in series. [Effect] It operates with a small current and generates less heat.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to an insulating circuit that electrically insulates an external circuit that sends ON / OFF information of a switch contact from an internal circuit that receives this ON / OFF information in a programmable controller or the like. It is intended to improve the consumed power as much as possible.

[0002]

[Prior art]

 In general, a signal input unit of a control device such as a programmable controller has a configuration as shown in FIG. 3, and an insulating circuit 1 such as a photocoupler electrically insulates an internal circuit from an external circuit. Here, the external circuit is a circuit for transmitting ON / OFF information of the switch contact SW, and the internal circuit is a circuit for receiving ON / OFF information of the switch contact SW.

In such a circuit, when the switch contact SW is turned on, a constant voltage E (24 V) is applied to the light emitting element (LED) 11, and a current flows through the light emitting element 11 via the resistor R1 to emit light. . This light is given to the base side of the light receiving element (photo transistor) 12. The light-receiving element 12 has its collector side connected to a power supply voltage of 5 V through a pull-up resistor R2 and its emitter side grounded. When light is received from the light-emitting element 11, a current flows, and this current is generated. Transmits the ON information of the switch contact SW.

[0004]

[Problems to be solved by the device]

 At this time, since the voltage applied to the light emitting element 11 is about 1.2 V, of the applied voltage E of 24 V, about 22.8 V is consumed as the voltage drop of the resistor R1. For this reason, most of the electric power consumed by the current flowing to the external circuit side for causing the light emitting element 11 to emit light is changed to the heat generation of the resistor R1, and there is wasteful power supply and this heat generation is also extremely large. There was a problem that heat adversely affected other circuit parts.

An object of the present invention is to solve such a problem, and an object thereof is to realize an insulating circuit that generates less heat.

[0006]

[Means for Solving the Problems]

 The present invention, which has solved the above-mentioned problems, provides a light emitting element that emits light when a constant voltage is applied when the switch contact is on, and a current flows when the light emitted by this light emitting element is received and the ON information of the switch contact is displayed. In the insulating circuit for transmitting, a plurality of light emitting elements with a small current and a large voltage drop are connected in series so that the constant voltage is applied.

A resistance element to which a constant voltage is applied may be provided in parallel with a circuit in which a plurality of light emitting elements are connected in series.

[0008]

[Action]

 The insulating circuit of the present invention, in a plurality of light emitting elements connected in series, reduces the current flowing with the applied voltage as it is and increases the voltage drop in this light emitting element portion. Further, since the resistors are connected in parallel to the light emitting element, the light emitting element does not emit light even when a low voltage is applied.

[0009]

【Example】

 FIG. 1 is a circuit diagram of an insulation circuit embodying the present invention. In this figure, the elements having the same reference numerals as the circuit elements shown in FIG. 3 have the same functions. The feature of the present invention is to use a plurality of light emitting devices with a small current and a large voltage drop. Four such light emitting devices 111, 112, 113, 114 are connected in series and a constant voltage E is applied. The main points are the points that are set.

When the switch contact SW is turned on and off, the operation is exactly the same as that of the conventional circuit. When the switch contact SW is turned on, all the light emitting elements 111, 112, 113 and 114 emit light and the light receiving element 12 An electric current flows when this light is received.

Here, in the general photocoupler shown in FIG. 3, when a current of 8 mA is passed through the light emitting element 11, there is a voltage drop of 1.2 V, and a current of 8 mA flows through the light receiving element 12. Shows the characteristics. Therefore, in the circuit of FIG. 3, when a current of 8 mA is passed through the light emitting element 11, the entire external circuit consumes power of 24 V × 8 mA = 192 mW. Of these, if the voltage 1.2 V applied to the light emitting element 11 is subtracted, the resistance is reduced. 22 in R1. Heat generation of 8 V × 8 mA = 182.4 mW is generated.

On the other hand, in the present invention shown in FIG. 1, since the light emitting elements 111, 112, 113, 114 having the characteristic of exhibiting a voltage drop of 1.2 V when a current of 2 mA is applied are used. When four units are connected in series, a voltage drop of 4.8V is obtained. Therefore, in the circuit of the present invention, power of 24V × 2mA = 48mW is consumed in the whole circuit, of which 1.2V × 4 = 4.8V applied to the light emitting elements 111, 112, 113 and 114 is subtracted, and The amount of heat generated by the resistor R1 is 0.2 V × 2 mA = 38.4 mW.

As described above, according to the circuit of the present invention, the current consumption is reduced and the power consumption is reduced. Therefore, the heat generation amount in the external circuit is also reduced.

In practice, as shown in FIG. 2, the resistor R3 is often connected in parallel to the light emitting elements 111, 112, 113, 114. This is to prevent the light emitting elements 111, 112, 113, 114 from emitting light halfway when a voltage lower than 24 V is applied to the input side of the light emitting elements 111, 112, 113, 114. Further, although the number of light emitting elements is four in the example shown in the figure, the number is not limited to four.

[0015]

[Effect of device]

 As described above, according to the insulation circuit of the present invention, compared with the conventional insulation circuit, the ratio of the power consumed by the light emitting element side to the power consumed by being applied to the circuit is conventional. Since it is larger than the above, it operates with less current and generates less heat. Therefore, it does not adversely affect other circuit parts.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an insulation circuit embodying the present invention.

FIG. 2 is another example of an insulation circuit embodying the present invention.

FIG. 3 is a circuit diagram showing a conventional insulation circuit.

[Explanation of symbols]

 1 Insulation circuit 11,111,112,113,114 Light emitting element 12 Light receiving element SW switch contact R1, R3 Resistance R2 Pullup resistance E Constant voltage

Claims (2)

[Scope of utility model registration request] 1. A light-emitting element that emits light when a constant voltage is applied when the switch contact is on, and an insulating circuit that transmits current when the light emitted by the light-emitting element flows and current flows through the switch contact. An insulating circuit characterized in that a plurality of light emitting elements with a small current and a large voltage drop are connected in series so that the constant voltage is applied. 2. The insulating circuit according to claim 1, wherein a resistance element to which the constant voltage is applied is provided in parallel with a circuit in which a plurality of the light emitting elements are connected in series.