SPECIFICATIONA switching arrangemenent for a current supply deviceIntrinsically safe current supply devices, such as those required, for example, in electrical installations for underground mining or explosion-proof electrical installations, have to be constructed according to accepted specifications so that the power they emit is not sufficient to produce sparks which could cause ignitions. A European StandardSpecification (50020, August 1976) also includes a classification of intrinsically safe operating means for various safety requirements by means of the designations "ia" and "ib". Accordingly, operating means of category "ia" should not be able to cause an ignition spark in normal operation following a single fault or any combination of two faults, with a safety factor of 1.5 during normal operation with one fault and with a safety factor of 1.0 with two faults.
Current limiting with the aid of semiconductors is not safe with operating means in this category, because ignition sparks as a result of the failure or destruction of semiconductors cannot be excluded.
According to the present invention, there is provided a switching arrangement for a current supply device with limitation of current and voltage so that, in normal operation, no ignition spark can be produced if a single fault or any combination of two faults occurs, the arrangement including a semiconductor component which is connected in the primary circuit of an output transformer, supplied in use with direct current, of a switching regulator and can be controlled as a function of regulating signals for current and voltage values.
Aseries regulator may be connected afterthe switching regulator and load terminals of the switching arrangement may be short-circuitable by means of a further semiconductor component as a function of boundary values of current and voltage. In this way the switching arrangement offers multiply redundant safety.
Moreover, a fuse can be connected in the primary circuit of the transformer, which switches off the switching arrangement if there are inadmissible current values.
The invention will now be described by way of example with reference to the single figure of the accompanying drawing, which shows one example of an arrangement according to the invention, connected to a rectifier.
The switching arrangement shown in the Figure is based on a rectifier 1, whose output voltage is smoothed by a capacitor 2, and meets category "ia".
The current circuit is closed via a fuse 3, theprimary winding 4 of the transformer 5 and a controllable semi-conductor component 6, for example a triac or a switching transistor. These components form a switching regulator. The secondary winding 7 of the transformer 5 supplies the loads to be connected to the output terminals 10 and 11 after rectification by a diode 12 and smoothing by a capacitor 13 via a series regulator 14. Regulating signals can be supplied to the controllable semiconductor component 6 as a function of current and voltage values in the secondary circuit of the transformer 5 via suitable coupling devices 15 and 16, for example opto-couplers.This takes place, on the one hand, via a signal amplifier 17 which converts the voltage appearing at the smoothing capacitor 13 into a regulating signal which is supplied via the coupling device 15 to the controllable semiconductor component 6. On the other hand, in respect of current, an output signal is supplied to the semiconductor component 6 via the coupling device 16 by a further signal amplifier 20, and by means of a signal amplifier 27 an output signal is supplied via the coupling device 15. A further signal amplifier 21 for voltage values and a further signal amplifier 22 for current values influence the series regulator 14.
Also, the aforementioned signal amplifier 22 controls the reference voltage of the signal amplifier 17 as a function of current so that, when an over-current occurs, the voltage at the smoothing capacitor 13 is reduced via the semi-conductor component 6.
In parallel with the output terminals 10 and 11 there is a further controllable semiconductor component 23 whose control electrode 24 may be acted upon with a triggering voltage by means of threshold value diodes 25 and 26 following inadmissible voltage values and by means of the signal amplifiers 20 and 21 following inadmissible current values.
The circuit diagram contains a number of diodes which do not have reference numerals and the purpose of which is only to decouple the outputs of the signal amplifiers in a known manner.
The circuit arrangement described has multiple safety devices whereby the conditions for intrinsic safety are maintained. The semiconductor component connected in series with the primary winding 4 of the transformer 5 is controllable as a function of current and voltage values and is connected so that the intrinsic safety cannot be impaired if it is damaged. A further safety measure for maintaining the permissible values for current and voltage is additionally provided by the controllable semiconductor component 23 between the output terminals 10 and 11. Also, the switching arrangement can be put out of operation when the fuse 3 responds, if for any reason the current rises to inadmissible levels in the primary circuit of the transformer 5. Also, the switching regulator, operated as a blocking transformer, is not capable of inducing inadmissible energy in the secondary circuit.
1. A switching arrangement for a current supply device with limitation of current and voltage so that, in normal operation, no ignition spark can be produced if a single fault or any combination of two faults occurs, the arrangement including a semiconductor component which is connected in the primary circuit of an output transformer, supplied in use with direct current, of a switching regulator and can be controlled as a function of regulating signals for current and voltage values.
2. A switching arrangement according to claim 1,
**WARNING** end of DESC field may overlap start of CLMS **.