DE4333702C1 - Circuit arrangement for independent power supply of digital input circuits - Google Patents

Abstract

The invention describes a circuit arrangement for independent power supply of digital input circuits. The input load current, which every input circuit has when it is triggered by an external sensor, is used to supply all components of the input circuit with power. The invention makes an external power supply for comparators, serial interface control, optical couplers etc. unnecessary. A minimum voltage detector captures the input potential of one or more input connections and switches the voltage potential to the supply connections of all components of the input circuit. In the inactive state of the inputs, i.e. when none of the inputs of an input circuit is triggered, no current is required, so that none is supplied to any component. The essential advantages of the invention are a considerable reduction of the sensitivity to faults and reduction of the dissipated power, and therefore of the operating temperature of the input circuit.

Description

The invention describes a circuit arrangement for independent energy supply digital input circuits, especially for programmable Control devices consisting of switching stages for acquisition and adaptation as well Switching means for providing electrical input signals for logical linking within a user-specific control program for a mikropro processor-controlled functional level, the switching stages and switching means being multi-stage Input circuit are executed, the input one for each input information Comparator used, its output and other n-comparator outputs to one each Input of a parallel-serial converter is connected, which multiplexed the Input information transported to the control level, the energy requirement of Input circuit permanently operational by an external power supply unit is held.

Known input circuits can be roughly divided into two from their circuit concept Divide species.

a. Switching without external power supply to the input circuit

This type of circuit essentially consists of a voltage divider in the input circuit, on which a shunt, consisting of light emitting diode and opto-coupler arrangement, is indicated is closed. This circuit is inexpensive and requires little circuitry. The undefined switching levels, which are particularly disadvantageous due to the large ones, are disadvantageous Component tolerances occur. Furthermore, this type of circuit is only a parallel one Transfer of input information to the processor possible. The costs increase with it the number of inputs. The heat loss of the voltage divider resistors, which corresponding to the permissible input load current (typ. I = 6.. .10 mA) and the component Developed packing-tight, quickly exceeds the permissible operating temperature.

b. Circuit with external power supply for the input circuit

Here, too, the voltage divider is located in the input circuit. The exit of the  The voltage divider feeds a comparator for each input with a fixed input and Switch-off voltage. The comparator gives its information to a serial device further (see the German Patent No. 40 34 373). The comparator and possibly the on Direction, which serially transfers the information to the processor, require one Power supply. This can be done via a DC / DC converter from the 5 V logic supply generated or supplied externally. A supply via DC / DC converter is unfavorable, since this places a heavy load on the 5 V logic supply and feeds in HF components. Therefore mostly an external supply is preferred. To damage the circuit due to reverse polarity To avoid the power supply connections, an appropriate protective circuit must be used be provided. A defined switch-on and switch-off level as well as a Any information transfer to the processor, both in parallel and in series. Disadvantageous are the uneconomical manufacture of such input circuits through complex Circuit technology with discrete circuit construction. On every input circuit board two additional connections for the power supply must be provided. Furthermore the noise sensitivity of these input circuits is very high. Input circuit tested with fast transients according to IEC 801-4. This interference becomes capacitive switched to the inputs and directly to the power supply. A directly coupled one Disturbance is much stronger than an injected one. It becomes a big one in practice Expense operated with expensive measures to meet the EMC guidelines (EMC law) to become. It comes with interference filters, shielding plates and metallizing Plastics worked. The overall interference suppression measures considerably increase the effort and thus the cost of a product.

From DE 42 00 935 C1 is a circuit arrangement for the power supply of several micro-controlled analog-digital converter from a common operating voltage source known.

There are between the common operating voltage source and the analog Functional parts of the A / D converter and analog value preparation groups each micro-computer controlled all-pole disconnector and auxiliary power sources provided that the power supply of the analog modules with each open  Take over the disconnector.

However, this solution is associated with a relatively high level of circuitry complexity.

A circuit arrangement in which a microcontroller receives signals and only the energy of these signals used to power the microcontroller is in the EP 0 440 545 A1 shown and explained.

This circuit arrangement leaves open, however, as with several in parallel Input signals and especially in a circuit arrangement according to the preamble of claim 1 can be carried out.

Basically, the invention is based on the idea that in each input, if he is controlled by a sensor, an input load current flows. This load current flows through a resistor and only generates heat. But if the load current is successful Supply of components in the input circuit (e.g. comparators, serial Interface, opto-coupler arrangement) to supply, then an external power supply there is no need for this.

The invention is therefore based on the object of a circuit arrangement for input to create circuits by using an external power supply to supply everyone Components of the input circuitry are completely dispensed with, which reduces interference immunity significantly improved, the power loss limited and thus a cost and functionality-optimized solution is achieved.

This object is achieved in that the energy supply for the Operational readiness of the input circuit is generated independently by that, at least voltage applied to an input terminal from a minimum voltage Detector detects and for energy supply for the active functional phase of all components the input circuit is used and each input connection via one Decoupling diode is connected to a potential line.  

The decoupling diodes make the mutual influence of two or more active inputs excluded.

The minimum voltage detector is expediently a semiconductor switch and consists of a transistor, two resistors and a Zener diode, the Dimensio the zener diode defines the switching threshold of the transistor. Here is the zener diode dimensioned such that at least at the minimum HIGH voltage (according to ICE 1131- 2, limit type 1 = 15 volts at 24 V Ue) activates the transistor switch, which switches the Voltage potential of the active input as supply voltage for the components provides.

The potential line carries a constant one when the input voltage is constant Supply current for the components of the input circuit. Therefore forms the potential line the input of the minimum voltage detector and the output of the minimum voltage detector is with the supply connections of all components of the input circuit connected.

An exemplary embodiment of the invention is described below in connection with the Drawing described.

It shows

Fig. 1 is a schematic diagram of a multi-stage input circuit, which reproduces the circuit arrangement according to the invention as a whole and

Fig. 2 shows the circuit diagram of an exemplary minimum voltage detector as used in the circuit arrangement according to the invention.

Fig. 1 shows a schematic circuit diagram of an input circuit, which reproduces the circuit arrangement according to the invention as a whole. The input circuit is preferably arranged on a plug-in module that is inserted into a rack. The module has the input connections INP1 on the front. . .INPn on. These connections can be designed as plug or screw connections. A sensor level, not shown in the drawing, supplies a binary signal that has either HIGH or LOW potential. The connector side of the module is connected to a bus system that connects all modules within a rack to a control unit. The input circuit Fig. 1 consists of several input circuits ES1. . .ESn, a parallel-serial converter 3 , an opto-coupler arrangement 4 and a minimum voltage detector 2 . The outputs of each input circuit ES1. . .ESn are performed in parallel on a parallel-serial converter (PSW) 3 . The PSW 3 scans the input information of the input circuits ES1. . .ESn cyclically and outputs serial information in a multiplex process via an opto-coupler arrangement 4 designed as a galvanic isolating element and via the bus system as status information to a central unit, which further processes this constant information. The input circuits ES1. . .ESn are all constructed and dimensioned the same. They each consist of two resistors R1, R2 connected as voltage dividers and a comparator K1. . .Kn. The voltage divider brings the input voltage potential to a rough voltage level, which is provided by the downstream comparator K1. . .Kn is defined on an information signal. The circuit arrangement described so far is known and only requires a description in order to explain the essence of the invention in more detail. The input signals of the input connections INP1. . .INPn are connected to a common potential bus 6 . So that the input potentials do not influence each other, each input circuit has ES1. . .ESn a diode D1. . .Dn on, which works as a decoupling element and in the reverse direction from the potential bus 6 to the input terminals INP1. . .INPN is switched. All input potentials are collected via this potential bus 6 and fed to a minimum voltage detector 2 . The minimum voltage detector 2 is dimensioned such that at a minimum HIGH voltage value (according to IEC 1131-2, at Ue = 24 volts and limit value type 1 this value is 15 volts), the voltage potential on the potential collecting line 6 to all supply connections Vcc of the components K1. . .Kn, PSW 3 and opto-coupler arrangement 4 switches.

In this circuit example it is assumed that the input voltage potential Ue, which is generated by one or more sensors on one or more input terminals INP1. . .INPn is switched, is 24 volts. The typical input load current IE _LAST for the input circuits ES1. . .ESn is assumed to be 4 mA each and the current consumption I _{switching of} all components of the input circuit is assumed to be 6 mA each. The total input current IE _tot depends on the number of driven input circuits ES1. . .ESn and is calculated using the formula:

The entire input current IE _tot is supplied by an external voltage source via the sensors. All components K1. . .Kn, voltage divider R1-R2, PSW 3 , minimum voltage detector 2 and the light-emitting diode of the opto-coupler arrangement 4 are connected to a common reference potential BP, which also has a common reference to the external current source. With a constant input voltage potential of 24 volts, the current consumption I _switch remains the same, which results from the sum of the partial currents ID1. . .IDn composed.

In the event that all input circuits ES1. . .ESn of the input circuit Fig. 1, that is, an input module are inactive, ie no input voltage potential at the input connections INP1. . .INPn or all inputs are open, so none of the components K1. . .Kn, PSW 3 and opto-coupler arrangement 4 supplied with energy. The LED of the opto-coupler arrangement 4 remains off and the output of the opto-coupler transistor carries a static LOW signal. In this case, the entire input circuit advantageously does not require any current.

Fig. 2 shows the circuit diagram of an exemplary minimum voltage detector, as applied in the inventive circuit arrangement. It consists of a pnp transistor T1, a first resistor Rv1, a second resistor Rv2 and a Zener diode Zn1. As already described, the minimum voltage detector 2 is dimensioned in such a way that it switches through at a minimum high voltage value. The transistor T1 then becomes conductive when the Zener voltage of the Zener diode Zn1 is exceeded plus the threshold voltage of the transistor T1. The potential bus 6 is connected directly to the input 7 of the minimum voltage detector 2 and thus directly to the emitter E of the transistor T1 and to a connection of the resistor Rv1. The second connection of the resistor Rv1 is connected to the base B of the transistor T1 and a connection of the resistor Rv2, the second connection of which is connected to the cathode of the Zener diode Zn1, the anode of which is connected to the reference potential BP. If its base voltage reaches a value of type <0.7 volts, the emitter-collector path of transistor T1 becomes low-resistance. The potential of the potential bus 6 is thus connected directly to the supply connections Vcc of all components of the input circuit, the collector C of the transistor T1 being connected directly to all supply connections Vcc.

Claims (4)

1.Circuit arrangement for the independent power supply of digital input circuits, in particular for programmable control devices, consisting of switching stages for detection and adaptation as well as switching means for providing electrical input signals for the logic combination within a user-specific control program for a microprocessor-controlled functional level, the switching stages and switching means being designed as a multi-stage input circuit are, which uses the input of a comparator for each input information, the output and further n-comparator outputs are each connected to an input of a parallel-serial converter, which transports the input information to the control level in a multiplex process, the energy requirement of the input circuit being controlled by an external Energy supply unit is kept permanently operational, characterized in that
that the energy supply for the operational readiness of the input circuit ( Fig. 1) is generated automatically by the voltage potential applied to at least one input connection (INP1.. .INPn) by a minimum voltage detector ( 2 ) and for energy supply for the active functional phase of all components of the Input circuit ( Fig. 1) is used
and that each input connection (INP1 ... INPn) is connected via a decoupling diode (D1 ... Dn) to a potential bus ( 6 ). 2. Circuit arrangement according to claim 1, characterized in that the minimal voltage detector ( 2 ) is a semiconductor switch and consists of a transistor (T1), a first resistor (Rv1), a second resistor (Rv2) and a Zener diode (Zn1), wherein the dimensioning of the Zener diode (Zn1) defines the switching threshold of the transistor (T1). 3. Circuit arrangement according to claims 1 and 2, characterized in that the potential bus ( 6 ) is connected directly to the input ( 7 ) of the minimum voltage detector ( 2 ). 4. Circuit arrangement according to claims 1 to 3, characterized in that the output ( 8 ) of the minimum voltage detector ( 2 ) with the supply connections (Vcc) of all components K1. . .Kn, PSW, opto-coupler arrangement 4 ) of the input circuit ( Fig. 1) is connected.