SWITCHING CIRCUIT

Abstract: Switching circuit for electronically switching of electronic, electrical or electromechanical components by means of semiconductors, wherein energy-transfer from the switching component (2) to the switched component (8) is established through a voltage transferring component (5), which completely isolates the switching component from the switched component; and wherein the voltage transferring component consists of a transformer.

Description: SWITCHING CIRCUIT This invention relates to a circuit for electronically switching of electronic components, electrical compo¬ nents or electromechanical components by means of a semiconductor, as can be used in for instance mains switches. With the known mechanical mains switches the switching is accomplished mechanically by means of mechanical parts. Such a mechanical construction is susceptible to failure and fouling. It is more prone to this in an hostile environment. When the switch is to be used in an environment where an explosion hazard exists, costly demands are made concerning the explosion safety of the construction of the switch. The mechanical design of a switch brings also limitations with respect to the design of the housing, which makes the protection against the above-mentioned risks by means of the housing difficult and costly. Furthermore the mainte¬ nance and cleaning of a mechanical switch is difficult and costly as a result of the above. The above-mentioned shortcomings could be obviated by electronically switching the electronic, electrical or electromechanical components, such as a relay, by means of a semiconductor. However, authorities and approving offices such as KEMA and VDE refuse on the basis of safety regulations to approve electronically switching by means of semiconductors of electronic, electrical or electromechanical components in for instance switches, because in the existing systems the failure of the semiconductor can lead to excitation of the system and the switched component. It is an object of the invention to obviate the draw¬ backs of the known switches. To this end the circuit for switching of electronic, electrical or electromechanical components by means of semiconductors according to the invention is characte¬ rised by energy transfer from the switching component to the switched component by an energy transferring component, that completely isolates the switching component from the switched component. According to another characteristic of the circuit according to the invention the energy transferring component is a transformer. According to yet another characteristic of the circuit according to the invention it is provided with means in the primary circuit, by which the maximum energy trans¬ fer is limited, in such a way that the switching cir- cuit is protected in case of short circuit in the switching component. According to again another characteristic the means for limiting the maximum energy transfer in the primary circuit consist of a series resistor. In the normal condition, when the electronic, elec¬ trical or electromechanical component is to be swit¬ ched, the switching component, a semiconductor, passes an alternating current through the primary winding of a transformer, which at its turn generates an alternating current voltage in the secundary winding. This voltage, whether or not rectified, actuates the electronical, electrical or electromechanical component. In the case of short-circuiting or interruption of the switching component a direct current or no current respectively will flow through the primary winding. In both cases there will be no voltage generated in the secundary winding and the switched component can not be excited in any way. According to an embodiment of the present invention a series resistor in the primary circuit limits the maximum energy transfer, so that the switching circuit is protected in case of short circuiting of the swit- ching component, the semiconductor. Likewise, defects in possible peripheral electronic, electrical or electromechanical components can not in any way lead to excitation of the switched component. The configuration according to the invention guaranties that the electronic, electrical or electromechanical components, for instance a relay, can not be excited in any way by whatever possible defect in the switching component. The invention will now be further described with refe- rence to a drawing of an example of an embodiment of the invention. The figure relates to a diagram of a circuit for electronically switching of a relay by means of a semiconductor, as can be applied in for instance a mains switch. As illustrated in the figure the switching component 2, in this embodiment a transistor 2, is incorporated in the circuit 1. When at input 3 an alternating current voltage, with well chosen suitable characteristics, is applied, the resistor 2 will pass an alternating cur- rent to the primary winding 4 of the voltage trans¬ ferring component 5, in this example of an embodiment the transformer 5. A suitable choice of the transfor¬ mer, which will lead to a high energy-efficiency of the switching circuit is for instance a close coupled transformer in the 10 KHz range. The transformer has in that case a transfer ratio of 1:1 and low core losse which guarantees an efficient energy-transfer. In view of the low voltages no high demands are made upon the insulation between the primary and the secundary win- ding of the transformer. In this case a lOKHz. signal then has to be applied to the transformer during a very brief period. As a result of this an alternating cur¬ rent voltage is generated over the terminals of the secundary winding 6 of the transformer 5. This voltage is in this embodiment rectified by bridge rectifier 7. The voltage is then supplied into the switched compo¬ nent 8, in this embodiment a relay. In this embodiment the relay 8, which consists of an armature with two contacts 9 en 10 and an excitation coil 11, is arranged as a locking relay; when during a short period a signal in the form of the above-mentio¬ ned alternating current voltage is offered to the transistor 2, the relay 8 will be excited and will keep itself excited untill the connection between the protective contact breakers 12 and 13 is interrupted. It is possible to incorporate a contact breaker as off- switch at this place in the switching circuit. In this embodiment the switching circuit is active only for a very short period, that is only for the moment of swit- ching. In this embodiment the series resistor 14 in the primary circuit limits the maximum direct current in the primary circuit, in the event of short circuiting of the transistor 2. Furthermore in the figure a resis¬ tor 15 and a pair of capacitors 16, 17 are shown. Through conducting path 18 flows a direct current. Through conducting path 19 a signal can be given in the form of an alternating current voltage, with characte¬ ristics, that enable the current to allow the transis¬ tor 2 and the transformer 5 to perform their respective functions. The conducting path 20 is mass. In this embodiment of the invention the energy reguired for the switched component of the invention is gene¬ rated by a converter or generator circuit. There are many variations on this embodiment conceivable, which all remain within the scope of the invention; it is possible to use for the energy-generation a full bridge converter, a half bridge converter, an isolated forward converter, an isolated flyback converter, a non-isol¬ ated step up converter, a non-isolated step down con¬ verter etc. In another embodiment of the invention the various parts of the switching circuit can be integrated. More in particular it is possible to integrate the resistor 14 in the transformer 5, that functions as voltage transferring component, by choosing a suitable ohmic resistance for the primary winding 4. Furthermore an embodiment is conceivable in which the transformer 5, the eventual rectifier 7 and t .. relay 8 are integra¬ ted. In yet another embodiment the switching circuit can be combined with a piezo-electric element, that at a touch gives a voltage pulse. This voltage pulse serves as a signal for the excitation of the switching circuit. In another embodiment of the invention the switching circuit is provided with a micro-controller, in which the voltage pulse is offered to the micro-controller. In still another embodiment of the invention the micro¬ controller is provided with software. The microcontrol¬ ler processes the offered signals and at its turn controls on the basis of the software stored in the microcontroller the circuit for switching the electro¬ nic, electrical or electromechanical components by means of semiconductors, by offering a signal to the ■witching component in the form of a current, that is suitable to enable the switching component and the voltage transferring component to conduct their respec¬ tive functions. In yet another embodiment of the invention the configu- ration of the switching circuit with a piezo-electric element and a microcontroller as described above is provided with a variable current limiting device and current control system. When the variable current limiting device and the current control system are connected with the microcon¬ troller in a favourable manner, it is possible to let the microcontroller process the information from the variable current limiting device and the current con- trolsystem. By doing so, it becomes possible to make the microcontroller switch off the current on the basis of pre-chosen criteria when exceeding pre-determined values. In yet another embodiment of the invention the variable current limiting device and the current control system consist of a specially designed transformer, that consists of a few or even one turn. The wire thickness is selected such, that it is sufficient for the current that is to be measured. In this way the voltage drop over the primary winding is very small. The secundary winding is designed such, that the secundary voltage is directly proportional with the current through the primary winding. In this way the voltage on the secun¬ dary winding is a direct indication for the current in the primary winding. The secundary voltage measured in this manner is compared with an adjustable reference voltage. In summary four conditions are possible: no current, overload, short circuit and normal current. The current is rated by operating certain pre-chosen margins for the exceeding of the reference voltage at the comparison of the secundary voltage with the refe¬ rence voltage. In another embodiment of the invention in the above described configuration a status indication system, for example in the form of a display with led'3, is connec¬ ted to the microcontroller, so that --.t is possible to survey the status of the system. In yet another embodiment of the invention the configu- ration of the switching circuit with a piezo-electric element, a microcontroller, a variable current limiting device and current controlsystem and a status indicati¬ on system described above is incorpor' ed in an her¬ metically sealp' J , environment resistant housing. The invention is not limited to the above described embodiments. There are many variations conceivable in the application of the invention.

Claims: CLAIMS 1. Switching circuit for electronically switching of electronic, electrical or electromechanical components by means of semiconductors, wherein energy-transfer from the switching component to the switched component is established through a voltage transferring compo¬ nent, which completely isolates the switching component from the switched component. 2. Switching circuit according to claim 1, wherein the voltage transferring component consists of a transfor¬ mer. 3. switching circuit according to claim 1 or 2, wherein the primary circuit is provided with means by which the maximum energy transfer is limited in such a way, that the switching circuit is secured in case of short circuiting in the switching component. 4. Switching circuit according to claim 3, wherein the means consist of a series resistor in the primary circuit. 5. Switching circuit according to the claims l to 4, wherein the energy necessary for the switched component is generated by a converter. 6. Switching circuit according to claim 1 to 5, wherein the switched element consists of a relay. 7. Switching circuit according to claim 3, 4, 5 or 6, wherein the resistor is integrated in the transformer by a suitable choice of the ohmic resistance of the primary winding of the transformer. 8. Switching circuit according to claims 1 to 7, whe: →^- in the voltage transferring component, the eventual present rectifier and the switched component are i. - grated. 9. Switching circuit according to the claims 1 to 8, wherein the switching circuit is comt-ned with a piezo¬ electric element, that gives a voltage pulse at tou¬ ching. 10. Switching circuit according to claim 9, wherein the switching circuit is combined with a microcontroller, that processes the signals offered by the piezo-elec- tric element. 11. Switching circuit according to claim 10, wherein the microcontroller offers signals to the switching circuit on the basis of the signals offered by the piezo-electric element in the form of a current, which is suitable to enable the switching component and the voltage transferring component to perform their respec¬ tive functions. 12. Switching circuit according to claim 11, wherein the configuration is extended with a variable current limiting device and current controlsystem, in such a manner that these, when in a favourable way connected to the piezo-electric element and the microcontroller, make it possible to monitor and control the current intensity. 13. Switching circuit according to claim 12, wherein the variable current limiting device and current con¬ trolsystem consist of a transformer, that is suitably constructed for that goal. 14. Switching circuit according to claim 13, wherein the configuration is extended with a status indication system in such a way that, when suitably connected with the microcontroller, it is possible to survey the status of the system. 15. Switching circuit according to claim 14, wherein the microcontroller is eguipped with software, which enables the microcontroller to control the configurati¬ on on the basis of previously determined criteria. 16. Switching circuit according to any one of the preceding claims, wherein the configuration is incorpo¬ rated completely in a completely sealed, environment resistent, housing. 17. Switcing circuit according to any one of the befo- rementioned claims, wherein this circuit is embodied in a switch, more in particular a mains switch.

Inventors: DUGOUR ROBERT GERARD, DUGOUR, ROBERT, GERARD
Applicants: DUGOUR ROBERT GERARD, DUGOUR, ROBERT, GERARD
Application year: 1995
Main classification: H03K17
IPC codes: H03K17