Patent Publication Number: US-7586213-B2

Title: Control circuit for relay-operated gas valves

Description:
This application claims priority to PCT/EP2005/002856, filed on Mar. 17, 2005, which claims priority to DE102004045031.5 filed on Sep. 15, 2004 and to DE102004016764.8 filed on Apr. 1, 2004. 
   TECHNICAL FIELD 
   The invention relates to a control circuit for relay-operated gas valves. 
   BACKGROUND 
   Gas valves are known which are opened and closed via a relay. It is also known for such relays for opening and closing gas valves to be activated via a control device, often in the form of a microprocessor. It can be important here that the overall arrangement is failsafe, i.e. that a gas valve is only opened via a relay when the control device is in a defined state. If an undefined state of the control device is present, it is desirable that the relay not open the gas valve. For this, control circuits for relay-operated gas valves sometimes have a failsafe circuit in addition to the relay, where the failsafe circuit is connected between the control device and the relay. The failsafe circuit may help ensure the failure safety of the overall arrangement. 
   SUMMARY 
   According to one illustrative embodiment of the present invention, a control circuit may be provided that includes a relay for opening and/or closing a gas valve, and a failsafe circuit. A control device may be connectable to one or more input of the failsafe circuit, and the failsafe circuit may be adapted to only supply the relay with a voltage and/or current necessary for opening the gas valve when an input signal supplied at an input of the failsafe circuit by the control device has, for example, at least two different frequency signals succeeding each other in time. 
   In accordance with this illustrative embodiment, the relay can accordingly only open a gas valve if the signal supplied by the control device contains the two frequency signals in the time-defined order. If only one of the two frequency signals is present, the relay cannot open the gas valve. This helps ensure that the relay can only actuate the gas valve if the control device, often in the form of a microprocessor, is working properly. If the control device supplies a signal with other frequencies or a different time sequence of frequencies at the input of the failsafe circuit, the gas valve may be closed, sometimes immediately. 
   In some illustrative embodiments, the control circuit may have a charging circuit and a drive circuit for the relay. In some cases, the charging circuit has at least one capacitor, the charging circuit charging the at least one capacitor of the charging circuit upon the application or presence of a first frequency signal in the input signal. Upon the application or presence of a second frequency signal, on the other hand, the at least one capacitor of the charging circuit discharges itself. Upon the application or presence of the second frequency signal in the input signal, the drive circuit for the relay may supply the relay with a voltage and/or current necessary for opening the gas valve. 
   In some cases, the drive circuit may have at least two transistors, a base of a first transistor being connected via a resistor to the capacitor of the charging circuit, and the first transistor of the drive circuit only conducting when the capacitor of the charging circuit discharges itself upon the application of the second frequency signal in the input signal. 

   
     BRIEF DESCRIPTION 
     The invention may be more completely understood in consideration of the following detailed description of an illustrative embodiment of the present invention in connection with the accompanying drawings, without being restricted to this or other illustrative embodiments, in which: 
       FIG. 1  shows a circuit diagram of an illustrative control circuit that can be used in conjunction with relay-operated gas valves; and 
       FIG. 2  shows a timing diagram for clarifying the functioning of the illustrative control circuit of  FIG. 1 . 
   

   An illustrative embodiment of the present invention will now be described in greater detail with reference to  FIG. 1  and  FIG. 2 . 
     FIG. 1  shows a control circuit  10  according to one illustrative embodiment for relay-operated gas valves. The illustrative control circuit includes a relay  11  and a failsafe circuit  12  for the relay  11 . The illustrative failsafe circuit  12  has an input  13 , at which a control device, not shown, in particular a control device such as a microprocessor, can be connected. The control device supplies an input signal at the input  13  of the failsafe circuit  12  or at the input  13  of the control circuit  10 . The failsafe circuit  12  may be adapted to then only supply at the relay  11  a voltage and/or current necessary for opening the gas valve when, for example, a signal having at least two different frequency signals succeeding each other in time is supplied at the input  13  by the control device. 
   In one illustrative embodiment, and not to be limiting, the failsafe circuit  12  of the control circuit  10  may include a charging circuit  14  and a drive circuit  15 . The illustrative charging circuit  14  includes the components surrounded by a dashed box in  FIG. 1 ; the components of the drive circuit  15  are surrounded in  FIG. 1  by a dotted and dashed box. 
   As can be seen from  FIG. 1 , the illustrative charging circuit  14  includes a capacitor  16 , with two diodes  17  and  18  connected in parallel to the capacitor  16 .  FIG. 1  shows that the cathode of the diode  18  is in contact with the anode of the diode  17 . The capacitor  16  is connected in parallel to the two diodes  17  and  18  in such a manner that the capacitor is in contact with the cathode of the diode  17  on one side and with the anode of the diode  18  on the other side. Connected between the two diodes  17  and  18  is a resistor  19 , which with interposed capacitors  20 ,  21 ,  22  and  23  is connected to the input  13  of the failsafe circuit  12 . Instead of the four capacitors  20  to  23  shown in  FIG. 1 , it is also possible to use only one capacitor, or any other number of capacitors as desired of appropriately sized capacity. 
   The illustrative drive circuit  15  includes, among other things, two transistors  24  and  25 . A first transistor  24  is connected with its base to the capacitor  16  of the charging circuit  14 , with an interposed resistor  26 . The collector of the transistor  24 , which according to the illustrative embodiment of  FIG. 1 , is developed as an NPN transistor, is connected with an interposed further resistor  27  to a supply voltage V of the control circuit  10 . With its emitter, on the other hand, the transistor  24  is connected to a ground potential or earth potential. A second transistor  25  is switched with the first transistor  24  in such a manner that the collector of the second transistor  25 , which like the first transistor  24  is developed as an NPN transistor, is connected to the base of the first transistor  24 . The emitter of the second transistor  25  is connected, like the emitter of the first transistor  24 , to the ground potential or earth potential. The base of the second transistor  25  is connected with an interposed resistor  28  to the input  13  of the control circuit  10 . 
   According to the illustrative embodiment of  FIG. 1 , the illustrative drive circuit  15  may include, in addition to the two transistors  24 ,  25  and the resistors  26 ,  27  and  28 , two Darlington transistor circuits  29  and  30 , each of which has two transistors switched in the so-called Darlington circuit. According to  FIG. 1 , the two transistors of the Darlington transistor circuit  29  are developed as NPN transistors, the two transistors of the Darlington transistor circuit  30  on the other hand being developed as PNP transistors. In the illustrative embodiment, the two Darlington transistor circuits  29  and  30  are connected together at their base and coupled to the collector of transistor  24 . It can further be seen from  FIG. 1  that the emitters of the Darlington transistor circuits  29  and  30  may also be connected to each other, a series connection of a resistor  32  and a capacitor  33  being in contact at this connection point  31  of the emitters. The collector of the Darlington transistor circuit  29  is shown connected to the potential of the supply voltage V; the collector of the Darlington transistor circuit  30 , on the other hand, is shown connected to the ground potential together with the emitters of the transistors  24  and  25 . A diode  34  is connected in parallel to the relay  11 , the diode  34  being connected with its anode coupled to the collector of the Darlington transistor circuit  29  and with its cathode coupled to the capacitor  33 . 
   As already mentioned, the illustrative control circuit  10  or the failsafe circuit  12  of the same may only supply the relay  11  with a voltage necessary for opening the gas valve when, for example, an input signal including at least two different frequency signals succeeding each other in time is supplied at the input  13  of the failsafe circuit  12  by the control device. In this case a defined operating state of the control device for opening the gas valve is present. 
   In one illustrative embodiment, and although not required, the gas valve may be only opened by the relay  11  if the signal supplied by the control device at the input  13  includes two frequency signals, namely a first frequency signal with a frequency of around 1000 kHz and a second frequency signal with a frequency of around 5 kHz, which are applied or present succeeding one another in time in such a manner in the signal supplied by the control device, that in each case a time span of around 40 ms with the first frequency signal of around 1000 kHz is followed by a time span of around 80 ms with the second frequency signal of around 5 kHz.  FIG. 2  visualizes such an input signal, as supplied by the control device, as a solid line, where in each case a time span t 1  with the frequency signal of around 1000 kHz is followed by a time span t 2  with the frequency signal of around 5 kHz. 
   The illustrative control circuit  10  may work in such a manner that upon the application or presence of the first frequency signal of around 1000 kHz at the input  13  of the failsafe circuit  12 , the charging circuit  14  charges the capacitor  16  of same. During the application of the second frequency signal of around 5 kHz at the input  13 , on the other hand, the capacitor  16  of the charging circuit  14  cannot be charged, but instead during the time span in which the second frequency signal of around 5 kHz is applied, a discharge of the capacitor  16  of the charging circuit  14  takes place through the resistor  26  and the base of the transistor  24 . It should further be noted that during the time span in which the second frequency signal of around 5 kHz is applied at the input  13 , there may be a generally rectangular 5 kHz signal at the connection point  31 . Thereby, on the one hand, the capacitor  33  of the drive circuit  15  is charged over the diode  34 , and on the other hand there is a discharge over the relay  11 . In the discharge, a direct current may flow through the relay  11 . In the time span in which the first frequency signal of around 1000 kHz is applied, the capacitor  33  of the drive circuit  15  can also discharge over the relay  11 . In the illustrative embodiment, the transistor  24  of the drive circuit  15  is only conducting if from the discharge of the capacitor  16  a current flows at its base. 
   During the time span in which the first frequency signal with the relatively high frequency of around 1000 kHz is applied at the input  13 , the capacitor  16  of the charging circuit  14  is indeed being charged, but the drive circuit  15  is not conducting because of, for example, the so-called feedback capacity of the transistor  25  and because of the relatively large resistor  28 . In the illustrative embodiment, the drive circuit  15  is only conducting when, during the time span in which the second frequency signal with the relatively low frequency of 5 kHz is applied at the input  13 , the capacitor  16  of the charging circuit  14  discharges through the resistor  26  and the base of the first transistor  24 . The charging and discharging of the capacitor  16  of the charging circuit  14  during the time spans t 1  and t 2  with the different frequency signals is represented in  FIG. 2  by the broken line  35 . As can be seen from  FIG. 2 , the capacitor  16  is charged during the time span t 1  in which the first frequency signal of around 1000 kHz is applied, while a discharge of the capacitor  16  occurs during the time span t 2  in which the second frequency signal of around 5 kHZ is applied. 
   By supplying a signal at the input  13  of the control circuit  10 , in which the signal includes the two frequency signals of around 1000 kHz and around 5 kHz succeeding each other in a defined time, a voltage and/or current necessary to open the gas valve can be permanently supplied at the relay  11 . In the time span in which the first frequency signal of around 1000 kHz is applied at the input  13 , the capacitor  33  of the drive circuit  15  discharges, as a result of which the voltage and/or current necessary to open the gas valve is maintained at the relay  11 . During the time span for which the second frequency signal of around 5 kHz is applied at the input  13  and the capacitor  16  of the charging circuit  14  discharges, the drive circuit  15  is conducting and there is a rectangular 5 kHz signal at the connection point  31 . As a result of this, on the one hand the capacitor  33  is charged over the diode  34 , and on the other hand there is a discharge over the relay  11 . In the discharge a direct current flows through the relay  11 . During the presence of the first frequency signal of around 1000 kHz, the transistor  25  is continuously conducting, as a result of which the voltage at the emitters of the Darlington transistor circuits  29  and  30  becomes high. Since during the time span in which the first frequency signal of around 1000 kHz is applied at the input  13 , the voltage necessary to open the gas valve is maintained at the relay  11  by the discharge of the capacitor  33 , this time typically should be shorter than the discharge time of the capacitor  33 . 
   The actual design of the control circuit described above is up to the person skilled in the art who is addressed here. In the especially preferred embodiment, the capacitance of the capacitor  16  of the charging circuit is 10 μF, the capacitance of each of the capacitors  20 ,  21 ,  22 ,  23  is 100 pF. The capacitance of the capacitor  33  of the drive circuit is preferably 47 μF. The resistor  19  is preferably sized at 1 kΩ, the resistor  28  at 1 MΩ. The resistor  26  is preferably 47 kΩ, the resistor  27  100 kΩ. The resistor  32  is preferably 51Ω. The supply voltage V is 24 V. With this sizing for the circuit components, the discharge time of the capacitor  16  through the resistor  26  is about 116 ms, its charge time is about 40 ms. 
   REFERENCE NUMBER LIST 
   
       
         10  Control circuit 
         11  Relay 
         12  Failsafe circuit 
         13  Input 
         14  Charging circuit 
         15  Drive circuit 
         16  Capacitor 
         17  Diode 
         18  Diode 
         19  Resistor 
         20  Capacitor 
         21  Capacitor 
         22  Capacitor 
         23  Capacitor 
         24  Transistor 
         25  Transistor 
         26  Resistor 
         27  Resistor 
         28  Resistor 
         29  Darlington transistor circuit 
         30  Darlington transistor circuit 
         31  Connection point 
         32  Resistor 
         33  Capacitor 
         34  Diode