CIRCUIT ARRANGEMENT FOR A SECURE DIGITAL SWITCHED OUTPUT, TEST METHOD FOR AND OUTPUT MODULE FOR THE SAME

Abstract

A circuit for a digital switched output for connecting a load which can be connected between the switched output and another output includes at least one semiconductor switch arranged with a clearance between contacts between a supply voltage connection and the switched output. At least one semiconductor switch is connected to the switched output via an inductor wherein a connecting node between the semiconductor switch and the inductor is connected to the other output via a free-running element. An output module provides automated control of the circuit. A method for testing the circuit includes controlling the semiconductor switch for operation of the load, interrupting the controlling, operating the load with energy stored in the inductor, determining whether voltage is prevented from being supplied to the load, and further controlling the semiconductor switch for further operation of the load.

Claims

1-15. (canceled)

16. A circuit having a digital switched output for connecting a load between the switched output and a second output, comprising: (a) at least one semiconductor switch connected with a supply voltage; (b) an inductor connected with said semiconductor switch and with said switched output; (c) a connecting node between said semiconductor switch and said inductor; and (d) a free-running element connected between said connecting node and said second output, whereby the circuit may be tested during operation without interrupting a voltage supplied to a load connected with said switched output.

17. A circuit arrangement as defined in claim 16, further comprising a capacitor connected between said switched output and said second output.

18. A circuit arrangement as defined in claim 16, wherein said free-running element comprises a diode.

19. A circuit arrangement as defined in any one of claim 16, wherein said free-running element comprises a transistor.

20. A circuit arrangement as defined in claim 19, wherein said transistor is connected with said connecting node.

21. A circuit arrangement as defined in claim 20, wherein said transistor is connected in parallel with said diode.

22. A circuit arrangement as defined in claim 16, wherein said second output is a ground connection.

23. A circuit arrangement as defined in claim 16, and further comprising at least one additional semiconductor switch and an additional supply voltage connection, said additional semiconductor switch being connected between said additional supply voltage connection and said second output.

24. A circuit arrangement as defined in claim 16, and further comprising a polarity protection switch connected upstream of said at least one semiconductor switch.

25. A circuit arrangement as defined in claim 16, and further comprising (a) a control and test circuit connected with said at least on semiconductor switch; and (b) a test connection, wherein said control and test circuit controls said at least one semiconductor switch and determines whether a brief blanking pulse is observable at said test connection.

26. A circuit arrangement as defined in claim 25, wherein said test connection is connected with said connecting node.

27. A circuit arrangement as defined in claim 26, wherein said test connection is connected with said switched output.

28. A circuit arrangement as defined in claim 27, wherein said control and test circuit determines a current flowing at said switched output during a blanking pulse.

29. An output module for automated control, comprises at least one digital switched output of a circuit as defined in claim 16 for controlling said at least one digital switched output.

30. A test method for a circuit including a digital switched output for connecting a load via an inductor, wherein the circuit includes at least one semiconductor switch arranged between a supply voltage connection and a switched output, comprising the steps of: (a) controlling the at least one semiconductor switch for operation of a load connected to a switched output; (b) interrupting said controlling step; (c) operating said load with energy stored in the inductor, (d) determining whether said interrupting step prevents voltage from being supplied to the load; and (e) further controlling the at least one semiconductor switch for further operation of the load connected to said switched output.

31. A method as defined in claim 30, in which said interrupting step and said determining step are carried out repeatedly.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0020] Other objects and advantages of the disclosure will become apparent from a study of the following specification when viewed in the light of the accompanying drawing, in which:

[0021] FIG. 1 is a circuit for a digital switched output according to a first embodiment;

[0022] FIG. 2 is a circuit for a digital switched output according to a second embodiment; and

[0023] FIG. 3 is a circuit for a digital switched output according to a third embodiment.

DETAILED DESCRIPTION

[0024] Referring first to FIG. 1, the circuit includes a supply voltage connection 1 to which a supply voltage V.sub.+ is applied. The supply voltage V.sub.+ relates to a reference voltage level which is formed by a ground potential GND. The ground potential is provided via a reference voltage or ground connection 1. The supply voltage V.sub.+ and the ground potential GND are provided by an external power supply (not shown).

[0025] The circuit is part of an output module which is used within an industrial automated installation. The circuit has a digital switched output 2 or is connected to the switched output, to which an output voltage V.sub.s, which can be switched on or off, is applied by the circuit. The output voltage V.sub.s again relates to the ground potential GND which is also provided at another output 2 of the circuit. The circuit is used for the secure controlled switching on or off of a load connected between the switched output 2 and the other output 2.

[0026] In this embodiment, two series-connected semiconductor switches 3, 4 are connected between the supply voltage connection 1 and the switched output 2. Metal oxide semiconductor field effect transistors (MOSFETs) are used as semiconductor switches. The semiconductor switches 3, 4 have an internal bypass diode. It is understood that instead of the MOSFETs, bipolar transistors or insulated gate bipolar transistors (IGBTs), for example, can also be used.

[0027] Two series-connected semiconductor switches 3, 4 are provided in order to increase the switching security, in particular the switch-off security.

[0028] The semiconductor switches 3, 4 are controlled via the control connection thereof (here the gate connection) by a control and test circuit 5. The control and test circuit 5 receives an input signal via an input (not shown) and switches the semiconductor switches 3, 4 on or off in accordance with the input signal.

[0029] Between the semiconductor switches 3, 4 and the switched output 2, an inductor 6 is connected and a diode 7 is connected as a switching device between the reference potential and the connecting nodes between the series connection of the semiconductor switches 3, 4 and the inductor. A capacitor 8 is connected between the outputs 2, 2.

[0030] The circuit shown in FIG. 1 is used for the controlled switching on and off of a load connected to the switched output 2 or to the other output 2. To verify that the semiconductor switches 3, 4 are functioning correctly in the switched on state, the control and test circuit 5 is configured to switch the semiconductor switches 3, 4 off and then on again to briefly blank, independently of one another, such as alternately one after the other with intermediate pauses. At the output of the series connection of the semiconductor switches 3, 4, i.e. at the connecting node to the inductor 6, a test connection 9 is arranged, the potential of which is measured and verified by the control and test circuit 5. The test connection 9 indicates whether a blanking of the control connections, i.e. the gate connections of the semiconductor switches 3, 4, has also successively led to the interruption of the clearance between contacts of the semiconductor switches 3, 4.

[0031] The blanking of one of the semiconductor switches 3, 4 leads to an interruption of the current flow between the series connection of the semiconductor switches 3, 4 and of the inductor 6. According to Lenz's law, the current flow is maintained by the dropping magnetic field of the inductor 6, as a result of which the diode 7 becomes conductive. During the brief blanking pulse, the combination of the inductor 6 and diode 7 maintains the flow of the connected load. The resulting circuit current extends via the diode 7, the inductor 6 and the load connected to the switched output 2 or to the other output 2.

[0032] The capacitor 8, which is optionally arranged parallel to the load, supports this behavior and maintains the supply voltage V.sub.+ with respect to the ground potential GND. The inductance value of the inductor 6, preferably formed by a coil with a ferrite core, is dimensioned so that for the duration of the blanking pulse, the voltage at the switched output 2 is maintained to the extent possible with only a small voltage drop. Preferably, the blanking times are in the range from several i.e 10 microseconds (s) to less than 1 s is in order to deliver even stronger currents in the range from several amps (A) through the inductor 6 for a sufficiently long time without the inductor 6 requiring an excessively high inductance value. A maximum voltage drop of approximately 5%-7% can be tolerated during the blanking time for usually connected loads. For example, a supply voltage V.sub.+ of 24 volt (V), a 1.5 V drop, can generally be tolerated. By adapting the size of the inductance value of the inductor 6, an even smaller voltage drop can be carried out, if necessary.

[0033] While the output voltage V.sub.s is substantially maintained in this manner at the switched output 2 during the blanking pulse, when the semiconductor switches 3, 4 are working correctly, the output voltage decreases at the test connection 9 to a voltage which corresponds to the breakdown voltage of the diode 7. This lowering of the supply voltage V.sub.+ to the forward voltage of the diode which is negative with respect to the ground potential at the test connection 9 and typically less than one volt, is detected by the control and test circuit 5 and evaluated as a sign of a correctly switched-off semiconductor switch 3, 4. If the voltage at the test connection 9 does not decrease, this is a sign of a defective semiconductor switch 3 and/or 4, or a sign that no load is connected to the output. The latter can also be interpreted as a potential error since it can be caused by a cable break or other issue.

[0034] In an alternative design of the circuit, the switched output 2 is used as a test connection. In this design, no lowering to the low voltage value of the breakdown voltage of the diode 7 is detected by the control and test circuit 5, but only a slight lowering is detected because the inductor 6 and the capacitor 8 exhibit an exponential discharge behavior. Even if the inductor 6 and diode 7, and optionally the capacitor 8, are suitable for maintaining the output voltage V.sub.s at the switched output such that an included load can be passed on without a problem, a detectable lowering of the voltage V.sub.s at the switched output 2 occurs nevertheless.

[0035] When measuring the voltage at the capacitor 8, the value of the current flowing at the output or whether any current flows at all at the output can be noted. The determined current value or current flow can also be monitored to, among other things, provide information regarding any problems during the connection of the load, such as a line break.

[0036] FIG. 2 is a diagrammatic circuit diagram a second embodiment of a circuit for a digital switched output. In this figure as well as in the following FIG. 3, identical reference numerals mark identical or equivalent elements as those of FIG. 1.

[0037] In the basic design, the circuit represented in FIG. 2 corresponds to the circuit represented in FIG. 1.

[0038] In contrast to the embodiment example of FIG. 1, a transistor 10, such as a MOSFET, is arranged parallel to the diode 7. In the embodiment of FIG. 1, the diode 7 represents an uncontrolled free-running element which becomes conductive during a blanking of one of the semiconductor switches 3, 4 due to the potentials formed at the connections thereof.

[0039] The transistor 10 thus also represents a free-running element having the same function as the diode 7. For this purpose, it is controlled by the control and test circuit 5 synchronously with the blanking pulses. The passage resistance of the transistor 10 is so low that in the conductive state, there is only a slight, negligible voltage drop across the transistor 10. Accordingly, energy losses that occur in the circuit of FIG. 1 at the diode 7 and that can lead to heating of the diode 7 are avoided. Small energy losses also lead to the load connected to the switched output 2 being supplied for a longer time by the energy stored in the inductor 6 or in the capacitor 8. In the case of a predetermined length of the blanking pulses, the inductor 6 and the capacitor 8 can thus be dimensioned with lower inductance or capacity values.

[0040] Another difference from the embodiment of FIG. 1 is the series connection of the polarity protection switches 11 connected upstream of the semiconductor switches 3, 4. This polarity protection switch could be formed passively by a diode; however, in this case, a MOSFET transistor is used for decreasing voltage drops.

[0041] FIG. 3 shows another embodiment of a circuit according to the invention for a digital switched output. In this embodiment, the output is switched at all of the poles.

[0042] There are supply voltage connections 1, 1 for a positive voltage supply V.sub.+ and a ground potential GND, respectively. Each of these supply voltage connections 1, 1 is connected via a respective semiconductor switch 3 or 4 to the output of the circuit. Accordingly, the two poles of the output are connected and marked in FIG. 3 as switched output 2 or additional switched output 2 with corresponding output voltages V.sub.s+ or V.sub.s.

[0043] A control and test circuit 5 controls the two semiconductor switches 3, 4. The voltage applied between two test connections 9, 9 is determined during a blanking pulse.

[0044] A polarity protection 11 is connected downstream of the positive supply voltage connection 1.

[0045] The circuit including inductor 6, diode 7 and capacitor 8, which enables the supply of the load connected to the switched output 2, 2 in the blanking pulses of the control and test circuit 5, is designed similarly to those of FIGS. 1 and 2, wherein the inductor 6 is connected upstream of the switched output 2, and wherein, via the diode 7, the node between the semiconductor circuit 3 and a connection of the inductor 6, is connected to the other switched output 2. The capacitor is connected parallel to the switched outputs 2, 2.

[0046] A transistor 10 is connected parallel to the diode 7 and controlled during the blanking pulse by the control and test circuit 5 and used in addition to the diode 7 as a free-running element.

[0047] During switching off of the switched output 2, 2, a separation from the supply voltage V.sub.+ or GND is carried out at all of the poles. The advantage of the separation at all the poles is that an external short circuit of a line which leads away from the switched output 2 and which permanently applies the supply voltage V.sub.+ to the load does not represent a security loss since the line leading away from the other switched output 2 is also switched off.