Abstract:
An electrical circuit with large creepage isolation distances is provided. In some embodiments, the electrical circuit is capable of increasing creepage isolation distances by many multiples over traditional electrical circuits. In one embodiment, an electrical circuit comprises a ground circuit optically coupled to a floating circuit, and an isolated circuit optically coupled to the floating circuit. The circuits can be optically coupled with opto-isolators, for example. The isolated circuit can have a creepage isolation distance at least twice as large as a traditional circuit. In some embodiments, “n” number of floating circuits can be optically coupled between the ground circuit and the isolated circuit to increase the total creepage isolation distance by a factor of “n”. Methods of use are also described.

Description:
INCORPORATION BY REFERENCE 
     All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference. 
     FIELD 
     The present disclosure relates generally to powering medical devices. More specifically, the present disclosure relates to obtaining sufficient creepage insulation distances required for high voltage medical devices. 
     BACKGROUND 
     Medical devices having electrical components typically must meet various electrical safety standards imposed by governing bodies (for example, in the United States, medical electrical equipment must satisfy the general standard IEC 60601-1 published by the International Electrotechnical Commission). One of the major concerns in electrical devices is electrical isolation. In applications where high voltages are used in close proximity to a patient, it can be very challenging to achieve the proper level of electrical isolation, since as the voltage used increases, the creepage distance and air clearance required must also be increased. 
     Generally, opto-isolators are used to transfer a signal over an isolation barrier, and DC to DC converters or transformers are used to transfer power over the isolation barriers. Opto-isolators currently on the market are capable of obtaining creepage insulation up to approximately 7 mm. However, in very high voltage devices, these opto-isolators are not capable of achieving the creepage insulation required by IEC 60601-1. 
       FIG. 1  illustrates an electrical circuit system  100  including a true ground circuit  102  and a single isolated circuit  104 . In  FIG. 1 , the two circuits  102  and  104  are separated by a creepage insulation distance D. Power can be transmitted between the two circuits with, for example, an isolated DC to DC converter, and the input/output signals can be transmitted between the circuits with opto-isolators  108  and  110 . As known in the art, opto-isolators are electronic devices configured to transfer electrical signals via light waves (e.g., from a light-emitting diode (LED) to a photosensor (such as a phototransistor or photoresistor). In the illustrative schematic shown in  FIG. 1 , traditional opto-isolators are typically capable of providing creepage isolation distances D up to ˜7 mm. 
     Thus, methods and systems are required for high voltage medical devices to obtain creepage isolation of at least 12 mm-14 mm. 
     SUMMARY OF THE DISCLOSURE 
     In one embodiment, an electrical circuit is provided, comprising a ground circuit, a floating circuit optically coupled to the ground circuit, the floating circuit being electrically isolated from the ground circuit by a first creepage isolation distance, and an isolated circuit optically coupled to the floating circuit, the isolated circuit being electrically isolated from the floating circuit by a second creepage isolation distance, the isolated circuit being electrically isolated from the ground circuit by a total creepage isolation distance equal to a combination of the first and second creepage isolation distances. 
     In some embodiments, the total creepage isolation distance is at least twice as large as the first creepage isolation distance. 
     In other embodiments, the circuit further comprises a first opto-isolator configured to optically couple a signal input from the ground circuit to the floating circuit. In another embodiment, the circuit further comprises a second opto-isolator configured to optically couple the signal input from the floating circuit to the isolated circuit. 
     In one embodiment, the first opto-isolator comprises a diode disposed on the ground circuit and a transistor disposed on the floating circuit. In another embodiment, the second opto-isolator comprises a diode disposed on the floating circuit and a transistor disposed on the isolated circuit. 
     In some embodiments, the circuit further comprises a first opto-isolator configured to optically couple a signal input from the isolated circuit to the floating circuit. In one embodiment, the circuit further comprises a second opto-isolator configured to optically couple the signal input from the floating circuit to the ground circuit. 
     In one embodiment, the first opto-isolator comprises a diode disposed on the isolated circuit and a transistor disposed on the floating circuit. In another embodiment, the second opto-isolator comprises a diode disposed on the floating circuit and a transistor disposed on the ground circuit. 
     In some embodiments, the first creepage isolation distance is approximately 7 mm. In another embodiment, the second creepage isolation distance is approximately 7 mm and the total creepage isolation distance is approximately 14 mm. 
     In one embodiment, the ground circuit, floating circuit, and double isolated circuit are disposed on a printed circuit board. 
     An electrical circuit is provided, comprising, a ground circuit, a first floating circuit optically coupled to the ground circuit, the first floating circuit being electrically isolated from the ground circuit by a first creepage isolation distance, a second floating circuit optically coupled to the first floating circuit, the second floating circuit being electrically isolated from the first floating circuit by a second creepage isolation distance, and a triple isolated circuit optically coupled to the second floating circuit, the triple isolated circuit being electrically isolated from the second floating ground circuit by third creepage isolation distance, the triple isolated circuit being isolated from the ground circuit by a total creepage isolation distance equal to a combination of the first, second, and third creepage isolation distance, 
     In some embodiments, the total creepage isolation distance is at least three times as large as the first creepage isolation distance. 
     In one embodiment, the circuit further comprises a first opto-isolator configured to optically couple a signal input from the ground circuit to the first floating circuit. In another embodiment, the circuit further comprises a second opto-isolator configured to optically couple the signal input from the first floating circuit to the second floating circuit. In an additional embodiment, the circuit further comprises a third opto-isolator configured to optically couple the signal input from the second floating circuit to the triple isolated circuit. 
     In some embodiments, the first opto-isolator comprises a diode disposed on the ground circuit and a transistor disposed on the first floating circuit. In another embodiment, the second opto-isolator comprises a diode disposed on the first floating circuit and a transistor disposed on the second floating circuit. In an additional embodiment, the third opto-isolator comprises a diode disposed on the second floating circuit and a transistor disposed on the triple isolated circuit. 
     A method of increasing a creepage isolation distance in an electrical circuit is also provided, comprising optically coupling a ground circuit to a floating circuit to electrically isolate the floating circuit from the ground circuit by a first creepage isolation distance, and optically coupling an isolated circuit to the floating circuit to electrically isolate the isolated circuit from the floating circuit by a second creepage isolation distance, and to electrically isolate the isolated circuit from the ground circuit by a total creepage isolation distance equal to a combination of the first and second creepage isolation distances. 
     In some embodiments of the method, optically coupling comprises optically coupling with an opto-isolator. In another embodiment, the total creepage isolation distance is approximately 14 mm. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the claims that follow. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIG. 1  illustrates an electrical circuit having a ground circuit and a single isolated circuit. 
         FIG. 2  illustrates an electrical circuit having a ground circuit, a floating circuit, and a double isolated circuit. 
         FIG. 3  is a schematic drawing of one embodiment of a printed circuit board layout including the circuits described above in  FIG. 2 . 
         FIG. 4  illustrates a 3D view of the printed circuit board of  FIG. 3 . 
         FIG. 5  illustrates one embodiment which can provide an isolation creepage distance of n times a single isolation distance (e.g. n times 7 mm of creepage distance for conventional opto-isolators). 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure describes and illustrates effective and inexpensive methods and systems for obtaining a wide range of creepage isolation distances. These methods and systems are particularly well suited for high-voltage medical device applications where large creepage isolation distances are required by law or statute. 
       FIG. 2  illustrates a schematic electrical diagram of one embodiment of an electrical circuit  200  configured to provide large (e.g., up to 14 mm) creepage isolation distances. The electrical circuit can be disposed on, for example, a printed circuit board. As shown in  FIG. 2 , circuit  200  can include ground circuit  202 , floating circuit  203 , and double isolated circuit  204 . Power can be transmitted from the ground circuit  202  to the double isolated circuit  204  via a pair of isolated DC to DC converters  206   a  and  206   b . The input/output signals can be transmitted from the ground circuit  202  to the double isolated circuit  204  via opto-isolators  208   a  and  208   b  (signal input) and opto-isolators  210   a  and  210   b  (signal output). 
     Ground circuit  202  can be in optical/electrical communication with floating circuit  203 , and floating circuit  203  can be in optical/electrical communication with double isolated circuit  204 . The opto-isolators used for coupling the circuits can be electronic devices configured to transfer electrical signals via light waves (e.g., from a light-emitting diode (LED) to a photosensor (such as a phototransistor or photoresistor). Opto-isolators typically have an LED as an input and various components at the output (e.g., mosfet, IGBT, logic gate, triac, Darlington, etc). 
     As shown in  FIG. 2 , opto-isolator  208   a  can comprise a diode in ground circuit  202  optically coupled to a transistor in floating circuit  203  for communicating signal inputs from the ground circuit to the floating circuit. Similarly, opto-isolator  210   a  can comprise a diode in floating circuit  203  optically coupled to a transistor in ground circuit  202  for communicating signal outputs from the floating circuit to the ground circuit. A similar configuration can communicate signal inputs and outputs from the floating circuit to the double isolated circuit, namely, opto-isolator  208   b  comprising a diode in the floating circuit optically coupled to a transistor in the double isolated circuit, and opto-isolator  210   b  comprising a diode in the double isolated circuit optically coupled to a transistor in the floating circuit. 
     In one embodiment, the electrical circuit of  FIG. 2  comprises a ground circuit  202 , a floating circuit  203  optically coupled to the ground circuit via opto-isolators  208   a  and  210   a , the floating circuit being electrically isolated from the ground circuit by a first creepage isolation distance D 1 , and an isolated circuit optically coupled to the floating circuit via opto-isolators  208   b  and  210   b , the isolated circuit being electrically isolated from the floating circuit by a second creepage isolation distance, the isolated circuit being electrically isolated from the ground circuit by a total creepage isolation distance equal to a combination of the first and second creepage isolation distances. 
     The electrical circuit  200  of  FIG. 2  can be configured to optically couple a signal input from the ground circuit to the floating circuit, and to optically couple the signal input from the floating circuit to the isolated circuit. Similarly, the electrical circuit of  FIG. 2  can be configured to optically couple a signal input from the isolated circuit to the floating circuit, and to optically couple the signal input from the floating circuit to the ground circuit. 
     The floating circuit is isolated from the ground and isolated circuits because there is no physical point of contact between the floating circuit and either the ground or isolated circuits. Instead, the floating circuit is optically coupled to both the ground and isolated circuits. The values of the resistors in the floating circuit are calculated using ohms law and depend on the LED forward current, LED voltage drop, and VCC voltage. In some embodiments, very fast opto-isolators with logic output can be used to keep delays less than 10 ns. 
     In  FIG. 2 , the addition of floating circuit  203  between ground circuit  202  and double isolated circuit  204  allows system  200  to essentially double the creepage isolation distances obtainable with a single conventional opto-isolator. In  FIG. 2 , the creepage isolation distance effectively becomes D 1 +D 2 , or 2×D. Since conventional opto-isolators are capable of approximately ˜7 mm of creepage isolation, the system of  FIG. 2  is capable of providing up to approximately ˜14 mm of creepage isolation. It should be understood that if opto-isolators are capable of providing more than the ˜7 mm of creepage isolation, the circuit systems described herein would still be capable of providing double the creepage isolation distances obtainable with a single opto-isolator. 
       FIG. 3  is a schematic drawing of one embodiment of a printed circuit board layout including the circuits described above in  FIG. 2 . In  FIG. 3 , printed circuit board  301  can include ground circuit  302 , floating circuit  303 , and double isolated circuit  304 . Ground circuit  302  can be electrically isolated from floating circuit  303  via opto-isolator  308 . Similarly, double isolated circuit  304  can be electrically isolated from floating circuit  303  via opto-isolator  310 . As shown in the diagram, this embodiment provides a creepage isolation distance of 7.24 mm+7.43 mm for a total of approximately 14.73 mm of isolation. 
       FIG. 4  illustrates a 3D view of the printed circuit board of  FIG. 3 . Printed circuit board  401  includes all of the same features of the PCB layout of  FIG. 3 , including ground circuit  402 , floating circuit  403 , and double isolated circuit  404 , and opto-isolators  408  and  410 . PCB  401  also illustrates the input/output signal path from ground circuit  402 , through floating circuit  403 , to double isolated circuit  404  and back. During a PCB layout process, it is important that the creepage requirements are met throughout the entire PCB. The circuits shown in  FIGS. 3 and 4  satisfy the requirement of having a minimum of ˜14 mm of creepage distance throughout the entire PCB. 
     The embodiments described above can be further applied to providing even larger isolation creepage distances by using multiple floating circuits.  FIG. 5  illustrates one embodiment which can provide an isolation creepage distance of n times a single isolation distance (e.g. n times 7 mm of creepage distance for conventional opto-isolators). In  FIG. 5 , multiple floating circuits are disposed between the ground circuit  502  and the isolated circuit  504 . The amount of creepage distance desired determines the number of floating circuits used. For example, to achieve approximately 21 mm of creepage distance with a conventional opto-insulator, a total of two floating circuits can be used between the ground and isolated circuits. The input/output signals can be optically transmitted from the ground circuit, through the floating circuits, to the isolated circuit, via opto-insulators  508   a / 510   a  through  508   n +1/ 510   n+ 1. Similarly, n+1 DC/DC converters can transfer power from the ground circuit, through the floating circuits, to the isolated circuit. This configuration provides for a total isolation creepage distance of n times the amount of isolation provided by a single opto-insulator. For example, assuming an opto-isolator capable of providing 7 mm of isolation, two floating circuits would provide ˜21 mm of isolation, three floating circuits would provide ˜28 mm of isolation, and so forth. 
     Referring to  FIG. 5 , an electrical circuit with two floating circuits (and a total of ˜21 mm of isolation with conventional opto-isolators) can be described. In this embodiment, the electrical circuit of  FIG. 5  comprises a ground circuit  502 , a first floating circuit  203   a  optically coupled to the ground circuit via opto-isolators  508   a  and  510   a , the floating circuit being electrically isolated from the ground circuit by a first creepage isolation distance D 1 , a second floating circuit  203   n +1 optically coupled to the first floating circuit via opto-isolators  508   b  and  510   b , the second floating circuit being electrically isolated from the ground circuit by a first creepage isolation distance D 1  and a second creepage isolation distance D 2 , the electrical circuit further comprising an isolated circuit optically coupled to the second floating circuit via opto-isolators  508   n +1 and  510   n+ 1, the isolated circuit being electrically isolated from the floating circuit by a third creepage isolation distance, the isolated circuit being electrically isolated from the ground circuit by a total creepage isolation distance equal to a combination of the first, second, and third creepage isolation distances. 
     In this example, the circuit can be configured to optically couple a signal input from the ground circuit to the first floating circuit, to optically couple the signal input from the first floating circuit to the second floating circuit, and to optically couple the signal input from the second floating circuit to the isolated circuit. Similarly, the electrical circuit of  FIG. 5  can be configured to optically couple a signal input from the isolated circuit to the second floating circuit, to optically couple the signal input from the second floating circuit to the first floating circuit, and to optically couple the signal input from the first floating circuit to the ground circuit 
     As for additional details pertinent to the present invention, materials and manufacturing techniques may be employed as within the level of those with skill in the relevant art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts commonly or logically employed. Also, it is contemplated that any optional feature of the inventive variations described may be set forth and claimed independently, or in combination with any one or more of the features described herein. Likewise, reference to a singular item, includes the possibility that there are plural of the same items present. More specifically, as used herein and in the appended claims, the singular forms “a,” “and,” “said,” and “the” include plural referents unless the context clearly dictates otherwise. It is further noted that the claims may be drafted to exclude any optional element. As such, this statement is intended to serve as antecedent basis for use of such exclusive terminology as “solely,” “only” and the like in connection with the recitation of claim elements, or use of a “negative” limitation. Unless defined otherwise herein, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The breadth of the present invention is not to be limited by the subject specification, but rather only by the plain meaning of the claim terms employed.