Abstract:
A method and an arrangement for the detection of a coil in an electronic circuit, which is operated with a direct voltage lying within a prescribed voltage range, and in which the coil together with a condenser forms an electrical oscillating circuit.

Description:
RELATED APPLICATIONS 
   This application claims priority under 35 U.S.C. §119(a) to German patent application No. 10 2006 045 319.0, filed Sep. 22, 2006, the complete subject matter of which is incorporated herein by reference in its entirety. 
   BACKGROUND OF THE INVENTION 
   The present technology, in general, concerns a method and an arrangement for the detection of a coil in an electronic circuit, which is operated with a direct voltage lying within a prescribed voltage range, and in which the coil, together with a condenser, forms an electrical oscillating circuit. 
   Circuits of this kind are in widespread use. In particular, they are operated in a voltage range between ground and a usually positive supply voltage, which is made available from an external voltage source or by means of a condenser present within the electronic circuit with appropriate voltage stabilisation. In the context of this document a coil is understood to be an electrical component with inductive properties and a condenser is understood to be an electrical component with capacitive properties, which together are able to form an electrical oscillating circuit. 
   BRIEF SUMMARY OF THE INVENTION 
   The subject of the present technology is therefore a method and an arrangement with which the presence of this coil in the electrical circuit can be ascertained. A typical use of the present technology is therefore a circuit in which the coil represents an inductive interface to an external alternating current voltage supply and/or for data transfer. Circuits of this kind are, for example, used in order to start a prescribed program sequence after the removal or short-circuiting of the coil as a triggering event. It is therefore important to be able reliably to ascertain the removal of the coil within the electronic circuit. In the event of a complete removal of the coil the coil terminals are open circuit, so that a high ohmic resistance can be ascertained between the two coil terminals. In contrast, in the event of a short-circuit of the coil terminals, however, no resistance can be ascertained. Depending on the place in which the circuit is installed it can also happen that after the removal of the coil an ohmic resistance is ascertained that corresponds to the pure ohmic resistance of the coil, if the coil terminals are dirty, for example, or come into contact with a weakly conducting medium. 
   Therefore it is not possible to come to a reliable conclusion concerning the presence or absence of a coil in the circuit by means of a simple measurement of the ohmic resistance between the coil terminals in the electrical circuit. 
   At least one aspect of the present technology is to be able to reliably detect a coil in an electrical circuit. This aspect is achieved with the features, for example, of Claims  1  and  7 . In particular, in the method according to the present technology provision is made that the electrical circuit is excited with a pulse, which during the oscillation temporarily generates a voltage value lying outside the prescribed voltage range on a first coil terminal that can be tapped on the coil. This voltage value, which can only be achieved within the electronic circuit if an electronic component with inductive properties is connected to the first coil terminal, therefore reliably indicates the presence of the coil. If on the other hand this voltage value is not ascertained, the conclusion can be drawn that no coil is connected to the first coil terminal in the electronic circuit, or that it has been removed. 
   The removal of a coil can then be ascertained particularly reliably, if this voltage value lying outside the prescribed voltage range is determined by sampling the flank of the tapped voltage signal. In particular, for this purpose a voltage signal can be generated from the voltage directly tapped at the first coil terminal, which only has a negative or positive flank in the voltage characteristic indicating the absence of the coil, if a voltage is present on the first coil terminal that lies outside the prescribed voltage range of the electronic circuit. 
   Since the occurrence of voltages lying outside the operating voltage range can often cause damage to electronic components in the electronic circuits, it is sensible for the protection of these components to protect the voltage tapped at the first coil terminal, and/or the voltage derived therefrom, via a diode. For this purpose, the diode can be preferably connected to a ground at the input of the voltage detector. A Schottky diode is particularly suitable for this purpose; this has a particularly rapid switching characteristic and possesses a smaller forward voltage than parasitic diodes of a silicon circuit connected. Hence, it is in a conducting state earlier and so protects the silicon circuit. 
   In this case, it is possible to register the voltage tapped at the first coil terminal at an input port of a microprocessor. Since only a limited voltage range, as a rule between ground and a maximum, usually positive supply voltage, can be applied to a microprocessor, that is to say, to its input ports, an input port of this kind can be reliably protected against the occurrence of high voltage of one polarity by the previously described diode. 
   According to the present technology, it is particularly advantageous if the tapping of the voltage at the first coil terminal takes place by means of electrical components that are part of a rectifier circuit. In this case, the coil can provide the inductive connection of the electronic circuit to an upstream circuit, for energy supply, for example, and/or programming. At the same time, the action of the rectifier thereby provides a protective function for the input port of the microprocessor, which in particular with the previously described diode limits the possible input voltages at the port connection to a permissible voltage range. 
   Part of such a rectifier circuit can be an NPN transistor, via which the voltage present at the first coil terminal is tapped. For this purpose the NPN transistor is preferably operated inversely and in a grounded-base circuit. In this manner, the input port lying behind the NPN transistor can be protected from high voltages lying above the maximum supply voltages. Therefore, the use of an NPN transistor is also sensible if the latter is not part of a rectifier circuit. 
   According to a particularly advantageous embodiment of the method according to the present technology, the voltage tapped at the first coil terminal and, for example, present at the input port of the microprocessor, can also be drawn on for determination of the frequency of an alternating voltage externally applied onto the coil, for example if the quartz stabilisation of the electronic circuit is not sufficiently accurate. In this way, the signal can be used for the calibration of the frequencies used and even for the detection of modulations in the information transfer, for example, in the context of a programming function. 
   In particular, in an arrangement according to the present technology for the detection of a coil in an electronic circuit with a coil and a condenser that together form an electronic oscillating circuit, operated with a direct voltage within a prescribed voltage range, for the solution of the task according to the present technology provision is made that a first coil terminal of the coil is connected to a pulse generator for the generation of a pulse, and has a voltage detector for the detection of a voltage value lying outside the voltage range of the direct voltage. This arrangement can be used particularly advantageously for the execution of the previously described method. 
   According to the present technology it is particularly advantageous if the voltage detector is connected via an NPN transistor to the first coil terminal, wherein the NPN transistor, on account of the higher electrical strength of the collector-base junction compared with the emitter-base junction, is preferably operated in inverse mode. 
   Furthermore, a Schottky diode can be connected to a ground between the NPN transistor, that is to say, its emitter terminal, and the voltage detector. By means of this arrangement voltages present below the prescribed voltage range, within which the electronic circuit is operated, can be isolated such that the tapped voltage signal can be connected to the input port of a microprocessor that is in particular driven with the supply voltage. 
   The port inputs and/or outputs of the microprocessor are then, in particular, the voltage detector and/or the pulse generator. 
   According to a particularly preferred form of embodiment of the present technology, a rectifier is connected downstream of the electrical oscillating circuit that contains the coil. This is equivalent of the coil being able to be an interface of the electronic circuit to an upstream circuit, which in particular generates an alternating voltage for energy supply to and/or programming of the electronic circuit. 
   Thereby, the NPN transistor can be part of the rectifier and in particular can undertake the task of one of the diodes of a rectifier bridge circuit of four diodes. 
   The method according to the present technology, as well as the arrangement that can in particular be introduced for execution of the method, are suitable for detecting particularly reliably the removal of a coil from an electronic circuit. Therefore, they can be particularly advantageously used if the removal of the coil is drawn on as a triggering event for a procedure that takes place subsequently, for example, the execution of a program inputted within the electronic circuit. 
   Further advantages, features and possible applications of the present technology ensue from the following description of an example of embodiment and the drawing. Thereby all described and/or figuratively represented features form, separately or in any combination, the subject of the present technology, also independently of their summary in the claims or their back references. 

   
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  shows an electronic circuit with coil detection according to the present technology; 
       FIG. 2  shows examples of voltage characteristics at the coil terminals S 1  and S 2  as well as at the emitter output of the NPN transistor V 4  from  FIG. 1 ; 
       FIG. 3  shows the voltage signal tapped at the coil terminal S 1  in the presence of a coil; 
       FIG. 4  shows the voltage signal tapped at the coil terminal S 1  after a high ohmic separation of the coil; 
       FIG. 5  shows the voltage signal tapped at the coil terminal S 1  with a short-circuited coil, and 
       FIG. 6  shows the voltage signal tapped at the coil terminal S 1  when the coil is replaced with a resistance. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows an electronic circuit with a microprocessor D 1 . The complete electronic circuit is supplied with energy via an interactive interface, which has a transmitter coil LS and a receiver coil L. Furthermore the interface serves for programming of the microprocessor D 1 . For this purpose, the receiver coil L receives an alternating field from an external commutating coil LS, represented in  FIG. 1  by arrows between the coil LS and the coil L. The energy thereby transferred is rectified in a manner described in more detail in what follows, and stored in a condenser C 3 . A voltage controller V 8  downstream of the condenser C 3  then supplies the complete electronic circuit for a certain time with a stabilised output voltage Ub on the basis of the energy stored in the condenser C 3 . 
   By modulation of the carrier signal of the magnetic alternating field between the coils LS, L data can also be transferred to the electronic circuit. The data transfer can in principle take place in both directions and in  FIG. 1  is schematically indicated by the programming interface PS, which forwards the programming information contained in the modulated carrier signal to the input port P 1  of the microprocessor D 1 . The programming interface PS receives any feedback signals from the microprocessor D 1  via the output port P 2 . Programming interfaces PS of this kind are of known art and are therefore not elucidated in what follows. 
   After the programming of the microprocessor D 1  via the inductive interface with the coils LS, L the microprocessor D 1  after the removal of the receiver coil L is designed to execute a program, corresponding to the programmed-in parameters, which triggers a reaction at an output port Pi of the microprocessor D 1  as a function of the programmed parameters. The removal of the coil L after the programming at the first and second coil terminals S 1  and S 2  is therefore designed to be used as a start signal for the execution of the program inputted into the microprocessor D 1 . 
   In order to be able to achieve the detection of the missing coil L with a high reliability, various galvanic conducting states at the coil terminals S 1  and S 2  must be detected after the removal of the coil L. The removal of the coil can for example take place as a rupturing of the coil in the event of a detonation of munitions, or similar, so that the exact state in the region of the coil terminals S 1  and S 2  is not known exactly. In particular, after the rupturing of the coil the coil terminals S 1  and S 2  can not only have a high ohmic resistance, but can also be short-circuited, or have an ohmic resistance whose value lies near that of the ohmic resistance of the coil L itself. 
   Therefore, the solution according to the present technology for coil detection is based on the detection of inductive properties of the coil L, which not only measures the ohmic resistance of the coil to check for its presence, but can draw conclusions as to whether the inductance of the coil L is present or not. 
   For this purpose a positive voltage pulse is outputted from the microprocessor D 1  at its output port P 3  via a Schottky diode V 6 , which pulse excites the sub-circuit formed by the two condensers C 1  and C 2  and the coil L such that the oscillatory system of the electrical circuit formed by the coil L and the condenser C 1  also generates voltages that are negative relative to the ground potential, and otherwise do not occur in the electronic circuit supplied with the positive output voltage, i.e. supply voltage Ub. 
   The sub-circuit formed by the condensers C 1  and C 2  and the coil L is in principle already of known art (cf. Speiser, “Impulsschaltungen” [“Pulse circuits”], Springer Verlag 1963, page 133,  FIG. 150   b ), wherein in the circuits of known art the voltage, bipolar relative to ground, is then rectified by means of a diode such that only the negative pulse components are outputted. A circuit of this kind cannot be used directly for the detection of the presence of the coil under the constraint of a limited operating voltage range. 
   If the evaluation of the voltage tapped at the coil terminal S 1  is designed to take place via an input port P 4  of the microprocessor D 1 , which is particularly advantageous from the point of view of practical implementation of the electronic circuit, it is particularly necessary to protect the port. Since the microprocessor is a digital component, it can only process or output voltages at its input or output ports that lie between ground and its operating voltage Ub, as a rule a positive voltage. Negative voltages can therefore not be applied at its input ports, since they could destroy the microprocessor. For exactly the same reason, however, high positive voltages that lie above the operating voltage Ub must also be avoided at the input ports, 
   In the implementation of the detection circuit according to the present technology with a microprocessor D 1  protective devices are therefore necessary for the input and/or output ports P 3  and P 4  of the microprocessor D 1 , which connect the microprocessor D 1  with the coil terminals S 1  and S 2  for the necessary measurements. During the energy supply and programming procedures alternating voltages can occur at these coil terminals S 1  and S 2 , which in magnitude clearly lie above the positive operating voltage Ub, or alternatively lie in the negative range. The input ports and/or outputs P 3  and P 4  of the microprocessor D 1  must therefore on the one hand be protected against the high alternating voltages of the programming and energy supply procedures, and on the other hand any negative measured voltage that occurs at the coil terminal S 1  and provides evidence of the presence of the coil L, is to be changed in polarity or limited such that the input port P 4  can also detect the occurrence of negative voltages. 
   According to the present technology, this is to be implemented simply and with preferably few components. The protective function for the microprocessor D 1  is essentially implemented by means of an NPN transistor, which is operated inversely and in a grounded-base circuit. In inverse operation, the transistor V 4  tolerates positive voltages on its collector that is connected with the coil terminal S 1 , such as occur in the programming and energy supply phase, without these voltages being passed through to the input port P 4 . In contrast, negative voltages at the coil terminal S 1  make the collector-base diode of the NPN transistor V 4  conducting. In this case, the transistor V 4  therefore acts as a functional partner of the diode V 2 , with positive voltages on the coil terminal S 2  and negative voltages on the coil terminal S 1 . On the basis of this function, the collector-base diode of the transistor V 4  together with the diodes V 1  to V 3  therefore forms a bridge rectifier of known art for alternating voltages during the programming phase, with the aid of which the energy supply and programming phases of the microprocessor D 1  can be managed. 
   If the NPN transistor V 4  were to be used in a grounded-base circuit that was not inversely operated, the maximum possible positive voltage at the coil terminal S 1  would lie at approximately 6 volts, since otherwise the emitter-base junction of the transistor V 4  would break down. In contrast, as a result of the use of the collector-base junction as a control diode of the inverse grounded-base circuit the electric strength of this input rises to the maximum collector voltage of the transistor V 4 . 
   In the inverse circuit, the current amplification of the transistor V 4  is indeed significantly less, but with a conducting collector-base diode it is in each case sufficient to bring the emitter of the transistor V 4 , connected with the input port P 4  of the microprocessor D 1 , from the positive operating voltage Ub to a negative potential of a diode voltage, for example of U P4 =−0.7 volts. In order that any parasitic input diode present at the input port P 4  of the microprocessor D 1  cannot become conducting as a result of this negative voltage, a Schottky diode V 9  connected to ground is inserted between the emitter of the transistor V 4  and the input port P 4 ; this ensures that the voltage present at the input port P 4  is greater than U P4 =−0.4 volts, i.e. that it has a lower limit. The microprocessor D 1  can cope with this negative voltage range, in particular for a short time. 
   In this manner, it is possible according to the present technology to excite the electrical oscillating circuit with a pulse such that during the oscillation a voltage value is temporarily generated on the coil that lies outside the prescribed voltage range, namely a negative voltage value. This voltage value can be ascertained directly at the input port P 4  of the microprocessor D 1 . This advantageous circuit is achieved with few additional electronic components, because the NPN transistor V 4  for the tapping of the negative voltage at the coil terminal S 1  is at the same time part of a bridge rectifier during the programming operation of the electronic circuit. 
   For the elucidation of the operation according to the present technology, typical voltage characteristics are elucidated in what follows in more detail with the aid of  FIGS. 2 to 6 . 
     FIG. 2  shows the voltage characteristics during the programming phase at the coil terminals S 1  and S 2  and also the voltage tapped at the coil terminal S 1  that via the emitter output of the transistor V 4  is present at the input port P 4  of the microprocessor D 1 . 
   As is expected during the programming phase in which an alternating voltage is applied to the coil L, the characteristic of this alternating voltage appears at the coil terminals S 1  and S 2 , wherein the voltage range extends approximately from −2 V up to +30 V. The high voltages at the coil terminal S 1  are lowered by the NPN transistor V 4  to an operating voltage of 1.8 V, The negative voltages, which are passed through the NPN transistor, are limited by the Schottky diode V 9  to a small negative voltage of the order of −300 mV. Therefore, the voltages tapped at the coil terminal S 1  can also be applied to the input port P 4  during the programming phase. 
   The frequency of the alternating voltage represented in  FIG. 2 , which is generated by an external programming unit, is quartz-stabilised as a rule. If for technical reasons (starting characteristics, mechanical robustness, etc.) the cycle time of the electronic microprocessor circuit cannot be quartz-stabilised, a calibration of the possibly inexact oscillator of the microprocessor circuit could be managed to a quartz-accurate carrier frequency, for example, via the input port P 4  of the microprocessor D 1 , in order to implement an exact time function, for example. 
   Also a modulation carrier signal could be detected directly via the input port P 4 , instead of via the separate programming interface PS, in order to decode the programming information. In this manner, the electronic circuit can overall be further simplified. 
   When the programming phase is complete the detection phase begins for the detection of a removal of the coil L, as a result of a coil rupture, for example. For this purpose the microprocessor D 1 , firstly with a positive voltage at the output port P 5 , switches a MOSFET transistor V 5  permanently into the conducting state, in order to fix the coil terminal S 2  at ground potential. During the programming phase, the MOSFET transistor V 5  was blocked by a 0-signal in order to enable the bridge rectification of the carrier. The maximum permissible drain voltage of the MOSFET transistor V 5  must be higher than the maximum voltage occurring at the coil terminal S 2 . 
   The microprocessor D 1  next outputs at the output port P 3  periodic individual pulses, each of a few microseconds duration, as can be detected in the first trace of  FIG. 3 . These are forwarded via the Schottky diode V 6  and a resistance R 1  to the circuit with the condensers C 2 , C 1  and the coil L, in order to generate negative voltages corresponding exactly to the electrical oscillation at the coil terminal S 1 , if the coil L is connected to the coil terminals S 1  and S 2 , because in these circumstances the exciting energy oscillates backwards and forwards between the energy stores of the coil L and condenser C 1 . 
   The Schottky diode V 6  thereby protects the port P 3  of the microprocessor D 1  in the programming phase against high positive voltages and generates only a slight voltage drop, when the excitation pulses are outputted in the detection phase. 
   As can be detected in the second trace of  FIG. 3 , the circuit formed by the condensers C 1 , C 2  and the coil L, as caused by the excitation pulses of the output port P 3  corresponding to the signal tapped at the coil terminal S 1 , reacts with a damped, bipolar voltage pulse. As soon as the voltage tapped at the coil terminal S 1  becomes negative, the NPN transistor V 4  becomes conducting and its emitter voltage, forwarded to the input port P 4  of the microprocessor D 1 , translates from a positive voltage derived from the operating voltage Ub to the negative clamping voltage of the Schottky diode V 9 . The voltage present at the port P 4  can be extracted from the bottom trace of  FIG. 3 . This negative flank of the signal present at the input port P 4 , detectable in  FIG. 3 , is detected by the microprocessor D 1  as an intact connected coil, and could for example also be used for the purpose of moving the microprocessor D 1  into a current-saving sleep mode, out of which it is woken after a fixed time by an internal timer interrupt for the output of a new excitation pulse. This procedure can be repeated until negative flanks no longer occur on the voltage signal present at the input port P 4  in reaction to an excitation pulse. 
   The absence of the negative flank of the signal at the input port P 4  then defines the point in time of the removal of the coil L, and can thus be used as a start signal for an application program that has been programmed in the microprocessor D 1 . 
   With the aid of  FIGS. 4 ,  5  and  6  the behaviour of the detection circuit after an excitation pulse is represented for the case in which no coil L is connected to the coil terminals S 1  and S 2 . 
   in  FIG. 4  the behaviour is represented when the coil L has been removed with a high ohmic resistance from the coil terminals S 1  and S 2 , between which therefore no conduction takes place. Since the system is now no longer capable of oscillation, no negative voltage any longer occurs at the coil terminal S 1 . Therefore the NPN transistor V 4  is no longer conducting and the input port P 4  remains as a result of the pull-up resistance R 2  at a positive voltage potential as a function of the operating voltage Ub. 
     FIGS. 5 and 6  show the corresponding behaviour with short-circuited coil terminals S 1  and S 2 . In the voltage characteristic represented in  FIG. 5  the coil terminals S 1  and S 2  have been short-circuited with a very low resistance; in contrast in the case of the voltage characteristic according to  FIG. 6  they are short-circuited with a 75-ohm resistance. In both cases, the voltage present at the input port P 4  corresponds to the voltage level prescribed by the operating voltage Ub. No negative voltage occurs at the coil terminal S 1  and also therefore no negative flank occurs on the voltage signal present at the input port P 4 . 
   Therefore, the proposal according to the present technology for the detection of a coil L in an electronic circle is also very robust in the cases in which the coil L has been replaced by an ohmic resistance between the coil terminals S 1  and S 2 . 
   REFERENCE SYMBOL LIST 
   
       
       
         
           Dl microprocessor 
           L receiver coil 
           S 1 , S 2  first and second coil terminals of the receiver coil 
           LS transmitter coil 
           C 1  to C 3  condensers 
           V 1  to V 3  diodes 
           V 4  NPN transistor 
           V 5  MOSFET transistor 
           V 6  Schottky diode 
           V 7  diode 
           V 8  voltage regulator 
           V 9  Schottky diode 
           Ub operating voltage 
           PS programming interface 
           P 1  to P 5  input ports, output ports of the microprocessor 
           Pi output port for initialisation of a downstream function 
           R 1 , R 2  resistances