JP2863775B2 - Contact input circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact input circuit used for a programmable sequencer or the like, and more particularly to an improvement in low power consumption.

<Prior Art> FIG. 7 is a circuit diagram of a conventional contact input circuit used for a programmable sequencer (PC) and the like. In the figure,
n points of contact input circuits are provided in parallel on the PC, and each contact input circuit has an input resistor R connected in series with the contact SW.
has a _in, the protection resistor RB connected in parallel with the photocoupler PC and the photocoupler light-emitting diode insulates the contacts and the PC internal circuit. To emit the light-emitting diode, the external input voltage V _in is provided, which supplies a DC voltage to each contact SW.

<Problems to be Solved invention> FIG. 8 is a graph showing the relationship between the consumption and the input voltage V _in power. The photocoupler needs to supply a current of at least 2-3 mA when the contact is turned on. The external input voltage V _in are as 12V and 24V, and to 4.7kΩ in the input resistance R _in 2.2 k, relative to 24V for 12V. To expand the range of the external input voltage V _in the case of the two combined is a 3.3kΩ input resistor R _in. Then, at 12V, the minimum current required for the photocoupler can be supplied, but at 24V, the current consumption increases, and when the number of input contacts is 64 points, the power consumption exceeds 10 W, causing a thermal problem. was there. In order to avoid this, it is necessary to limit the number of contacts that are turned on at the same time. However, there has been a problem that control becomes complicated and the purpose of increasing the number of input contacts is obliterated.

An object of the present invention is to solve such a problem and to provide a contact input circuit capable of inputting a large number of contacts and having a wide allowable range of an external input voltage by reducing power consumption.

<Means for Solving the Problems> According to the present invention for achieving the above object, a switching element (Q) _in which a contact (SW) is connected to a control terminal via an input resistor (R _in ), An input circuit with a photocoupler (PC) connected to the input terminal, a pull-up resistor (Rp) connected in series to the light emitting element side of this photocoupler for each contact, and a DC voltage supplied to each contact an external DC power source (V _in) to be, is characterized by comprising a secondary output voltage and the insulating converter supplies to the light emitting element of the photo coupler.

<Operation> Each component of the present invention performs the following operation. The external DC power supply supplies electric power required for ON / OFF detection of each contact. The isolated converter supplies a current necessary for driving each photocoupler. The current supplied from an external power supply for turning on and off the switching element can be significantly (about two digits) smaller than the drive current of each photocoupler. The output voltage of the isolated converter is also the minimum voltage required to drive the photocoupler. In this way, power consumption can be reduced as a whole.

<Example> Hereinafter, the present invention will be described with reference to the drawings.

 FIG. 1 is a circuit diagram showing one embodiment of the present invention.

In FIG. 1, components having the same functions as those in FIG. 7 are denoted by the same reference numerals, and description thereof will be omitted. In the figure, the switching element Q is a transistor, the contacts SW via the input resistor R _in is connected to the base terminal. The light-emitting diode of the photocoupler PC is connected to the collector terminal (input terminal), and the other end of the light-emitting diode is connected to the insulated converter 20 via the pull-up resistor Rp.
The isolated converter 20 receives a 24 V DC voltage or a commercial AC voltage supplied to the primary side, and outputs a photocoupler driving voltage V0 to the secondary side. The secondary common is connected to the common of the external DC power supply, and the secondary output voltage V0 is supplied to the light emitting diode of the photocoupler PC via the pull-up resistor Rp, and this voltage drives the light emitting diode 1.5 to 4V which is enough voltage. Logic circuit 30
Is connected to the light receiving transistor of the photocoupler PC, and performs a necessary logical operation according to each contact signal.

The operation of the device configured as described above will now be described. When the contact SW1 is turned on, the next base current Ib flows through the base of the transistor Q1.

_{Ib = (V in -VBEQ1) /} R in (1) Then, a current flows through the light emitting diode of the photocoupler PC transistor Q1 is turned on, turned to the logic circuit 30 secondary transistor of the photocoupler PC is turned on Is transmitted.

FIG. 2 is a specification diagram of a circuit specifically designed based on the present invention, which is described in comparison with the conventional circuit of FIG. Figure, 22Keiomega input resistor R _in, when the external input voltage V _in and 24V, the input current I _in flowing through the input resistor R _in is 1.1mA, and the
For a total of 64 points that consume 0.026 W per single contact input circuit, 1.68 W is consumed (~). Further, when the forward voltage V _F of the light-emitting diodes and 1.2V, 300 [Omega the resistance value of the pull-up resistor Rp, the photocoupler current Ipc When the drive voltage V0 and 3V is given by the following equation.

Ipc = (3.0−1.2) /270=0.0067 (2) That is, since it is 6.7 mA, the driving power per one photocoupler PC is 0.02 W, and it is 1.28 W at 64 points. Assuming that the efficiency is 50%, the input power of the isolated converter 20 requires 2.56 W (W). As a result, the overall power consumption is 4.25
It becomes W (). This value is less than half of 10.33 W of the conventional device, and it is understood that the power consumption is greatly reduced.

Also in the circuit of FIG. 1, also an external input voltage V _in is a 5V and a low value, the base current Ib of the transistor Q1 is given by the following equation.

_{Ib = (V in -V BE)} / R in = (5-0.7) /22X1000=0.00020 [A] (3) where, as an emitter grounded electrostatic forward current amplification factor h _FE of the transistor Q1 was 100 Also, 20 mA can be passed to the collector terminal current Ic, and it is sufficiently possible to drive the photocoupler PC. Accordingly, the scope of the external input voltage V _in is also magnified as about 5~24V by a large margin.

FIG. 3 is a circuit diagram showing a second embodiment of the present invention.
Here, a compound transistor with a built-in resistor (for example, RN1507 supplied from Toshiba Corporation) is used. When such a transistor element is used, a circuit can be formed without increasing the number of parts.

FIG. 4 is a circuit diagram showing a third embodiment of the present invention. V01, V0 insulated from the output voltage of the isolated converter 20
By providing two-systems, it is possible to input the external input voltage V _in 1, V _in 2 of two systems that are insulated from each other.

FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention. Transistor Q1 uses a PNP transistor and is configured with + common. Therefore, the output voltage V0 of the insulating converter 20 is supplied to the emitter terminal, and the common is connected to the collector terminal via the light emitting diode of the photocoupler PC and the pull-up resistor Rp. The common of the external DC power supply is connected to the output voltage V0 of the isolated converter 20, and the output voltage side is connected to a contact.

FIG. 6 is a circuit diagram showing a fifth embodiment of the present invention. And the base resistance Rb is provided between the base and the emitter of the transistor Q1, is obtained by allowing arbitrarily set the input voltage V _in the transistor Q1 is turned on.

<Effects of the Invention> As described above, according to the present invention, the photocoupler PC
In an isolated contact input circuit using
Is supplied from an isolated converter 20 provided inside, thereby reducing the power received from an external DC power supply and reducing the power consumption as a whole.

The transistor Q1 is because it is a control input contact signal, there is also an effect that the allowable range of the external input voltage V _in is enlarged.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a specification diagram of a circuit specifically designed based on the present invention, and FIGS. 3 to 6 show other embodiments of the present invention. FIG. 4 is a circuit diagram for explaining. FIG. 7 is a circuit diagram of a conventional apparatus, FIG. 8 is a graph showing the relationship between the consumption and the input voltage V _in power. 20 …… Insulated converter, 30 …… Logic circuit, PC ……
Photocoupler, Q: Transistor, R _in: Input resistance, SW: Contact, V _in: External DC power supply.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G05B 19/04-19/05

Claims (1)

(57) [Claims] A switching element (Q) having a contact (SW) connected to a control terminal via an input resistor (R _in ), and a photocoupler (P) connected to an input terminal of the switching element.
C), an input circuit provided with a pull-up resistor (Rp) for each contact connected in series to the light emitting element side of this photocoupler, and an external DC power supply (V _in ) that supplies a DC voltage to each contact
A contact input circuit, comprising: and an insulating converter that supplies a secondary output voltage to a light emitting element of each photocoupler.