Patent Publication Number: US-2023155364-A1

Title: Power source and method for providing an activating current

Description:
The disclosure is related to a power source and a method for providing an activating current. 
     A power source may be implemented in an automotive application, for example in an electric or hybrid vehicle. An electric or hybrid vehicle typically comprises a high voltage battery and an electric motor which is coupled to the high voltage battery via a power switch and a connection line. In the case of an electric or hybrid vehicle being involved in an accident, the high voltage battery has to be safely disconnected from the motor and other electric parts without permitting an unintended reconnection. This can typically be achieved by a disconnecting device that is inserted in the connection line of the high voltage battery to the motor and to the other electric parts of the vehicle. Such a disconnecting device typically comprises a pyrotechnic ignition element which is activated using a power source. In case of an accident the power source should operate with high reliability. 
     It is an object to provide a power source and a method for providing an activating current to a disconnecting device with increased reliability. 
     The object is achieved by the subject-matter of the independent claims. Further embodiments and developments are described in the dependent claims. 
    
    
     In an embodiment, a power source comprises an input terminal, a charging circuit, a capacitor, an electronic switching circuit, a discharge protection circuit, a control switch and a disconnecting device. The charging circuit includes an input coupled to the input terminal. The capacitor has a first electrode coupled to an output of the charging circuit. An input of the electronic switching circuit is coupled to the first electrode of the capacitor. The control switch has a first terminal which is coupled via the discharge protection circuit to the input terminal of the power source and is coupled to an output of the electronic switching circuit. The disconnecting device includes a first terminal coupled to a second terminal of the control switch. The disconnecting device may comprise a pyrotechnic ignition element. 
     Advantageously, there are two sources of current which are configured to generate an activating current that is provided to the disconnecting device. First, the activating current can be provided from the input terminal of the power source via the discharge protection circuit and the control switch to the disconnecting device. Secondly, the activating current can be provided from the capacitor via the electronic switching circuit and the control switch to the disconnecting device. Since there are two alternative ways to provide the activating current, the reliability of the power source is increased. The activating current can also be called disconnecting current. 
     In an embodiment, the discharge protection circuit is configured such that a first current is able to flow from the input terminal of the power source via the discharge protection circuit to the first terminal of the control switch. 
     In an embodiment, the discharge protection circuit is configured such that no current or approximately no current is able to flow via the discharge protection circuit to the input terminal of the power source. 
     In an embodiment, the discharge protection circuit is configured such that an energy transfer from the output of the electronic switching circuit to the input terminal is prevented. 
     In an embodiment, the discharge protection circuit comprises a diode. An anode of the diode may be coupled to the input terminal and a cathode of the diode may be coupled to the first terminal of the control switch. 
     The capacitor may be implemented as supercapacitor. 
     In an embodiment, the charging circuit comprises a decision circuit with an input coupled to the input terminal and an output coupled to the first electrode of the capacitor. 
     In an embodiment, the decision circuit may be implemented as a regulator such as a low-dropout regulator. 
     In an embodiment, the decision circuit is configured to provide a charging current to the first electrode of the capacitor in case a capacitor voltage is lower than a reference voltage. The capacitor voltage drops between the first electrode of the capacitor and a reference potential terminal. 
     In an embodiment, the charging circuit comprises a voltage converter having an input coupled via the input of the charging circuit to the input terminal of the power source and an output coupled to an input of the decision circuit. 
     In an embodiment, the electronic switching circuit is configured to provide a second current to the first terminal of the control switch only in case a capacitor voltage VC that drops between the first electrode of the capacitor and the reference potential terminal follows the equation: 
     
       
      
       VC≥k·VIT  
      
     
     wherein VIT is a terminal voltage that is tapped between the input terminal of the power source and the reference potential terminal and k is a factor. Advantageously, the electronic switching circuit is triggered to generate the second current only in case the terminal voltage is too low. 
     In an embodiment, the electronic switching circuit comprises a voltage divider coupling the input terminal of the power source to the reference potential terminal, and a control comparator having a first input connected to a divider tap of the voltage divider and a second input connected to the first electrode of the capacitor via a further input of the electronic switching circuit. An output transistor of the electronic switching circuit includes a first terminal coupled to the first electrode of the capacitor via the input of the electronic switching circuit, a second terminal coupled to the first terminal of the control switch and a control terminal coupled to an output of the control comparator. 
     In an embodiment, the power source comprises a test circuit coupled to the disconnecting device. 
     In an embodiment, the test circuit is configured to apply a test current to the first terminal of the disconnecting device and to compare a test reference voltage with a device voltage or a voltage derived from the device voltage. The device voltage is tapped between the first terminal of the disconnecting device and the reference potential terminal. 
     In an embodiment, the test circuit comprises a source connected to the first terminal of the disconnecting device for providing a test current and a comparator having a first input that is coupled to the first terminal of the disconnecting device and a second input to which a reference voltage is provided. The source may be realized as current source or as voltage source. 
     In an embodiment, the test circuit comprises comprise an instrumentation amplifier coupling the first terminal of the disconnecting device to the first input of the comparator. 
     In an embodiment, an electric arrangement comprises the power source and a battery that is coupled to the input terminal. Moreover, the electric arrangement may comprise a battery management system having an output connected to the control terminal of the control switch. 
     In an embodiment, a method for providing an activating current comprises
         charging a capacitor by a charging circuit having an input coupled to an input terminal,   setting a control switch in a conducting state, and   providing the activating current alternatively either by providing a first current from the input terminal via an discharge protection circuit and a control switch to a disconnecting device or by providing a second current from the capacitor via an electronic switching circuit and the control switch to the disconnecting device.       

     In an embodiment, a control signal is provided to the control switch. The control signal sets the control signal in a conducting state in case of emergency. In normal operation, the control signal sets the control signal in a non-conducting state. Thus, the power source is controllable. 
     Features and embodiments that are only described in connection with the power source may also be implemented in connection with the method for providing an activating current and vice versa. 
     In an embodiment, the power source includes redundant power sources and diagnostics for a vehicle safety switch. 
     In an embodiment, the disconnecting device is realized as a pyro switch. The battery may be a conventional secondary low-voltage battery. Typically, the disconnecting device is triggered using the battery. Vehicle crash can abruptly disconnect this battery, so the disconnecting device cannot be triggered to isolate a high-voltage DC source from rest of the vehicle system. The power source described herewith aims to overcome this situation by providing a capacitor based redundant power source and a diagnostic system to monitor health of the disconnecting device. The power source results into a reliable, cost effective and compact solution for electric-vehicle applications, abbreviated as EV applications. 
     In an embodiment, a pyro switch is used in EV applications as disconnecting device because of its reliability and fast switching action, compared to other disconnecting devices or safety switches. However, it was observed in some cases that a vehicle crash leads to abrupt disconnection of the battery from the pyro switch ignitor. The battery may be a low-voltage battery, having e.g. a battery voltage of 12V. Due to this failure, an expected disconnection of the high-voltage battery, abbreviated HV battery, from the vehicle system fails which may lead to fire and explosion situations. The HV battery may have a voltage higher than 400 V. The power source described herewith proposes a capacitor based redundant power source, capable of igniting the pyro switch, when the primary power source i.e. the LV battery is not available. 
     In an embodiment, this capacitor based redundant power source is placed near to the pyro switch to avoid any such disconnection during crash condition. This capacitor can be provided as in-built part of pyro switch system or as in accessory so that a customer or an original equipment manufacturer (abbreviated OEM) has freedom to choose this redundant power source. The capacitor based power source is charged using primary LV battery having e.g. 12V. However, the power source does not replace the primary battery as a power source for the disconnecting device with the pyro ignitor unless the primary battery is unavailable. So primary LV battery always has first preference over capacitor based redundant power source. System may fail to isolate the HV battery in case of pyro ignitor failure due to unknown reasons even if power source is available (primary or redundant). To overcome this, the power source includes a pyro health diagnostic system with a resistance measurement which continuously monitors the health of pyro ignitor and generates prognostic feedback to a battery monitoring system (abbreviated BMS) or to an electronic control unit. 
     The following description of figures of embodiments shall further illustrate and explain aspects of the power source and method for providing an activating current. Parts and components with the same structure and the same effect, respectively, appear with equivalent reference symbols. Insofar as parts and components correspond to one another in terms of their function in different figures, the description thereof is not repeated for each of the following figures. 
       FIGS.  1  and  2    show exemplary embodiments of an electric arrangement with a power source. 
       FIG.  1    shows an exemplary embodiment of an electric arrangement  100  with a power source  10  which comprises a disconnecting device  11 . The disconnecting device  11  comprises a pyrotechnic ignition element  12 . The pyrotechnic ignition element  12  may comprise a resistor  13 . The power source  10  comprises an input terminal  14 , a charging circuit  15  and a capacitor  16 . The input terminal  14  is coupled via the charging circuit  15  to a first electrode of the capacitor  16 . A second electrode of the capacitor  16  is connected to a reference potential terminal  18 . The capacitor  16  may be implemented as a supercapacitor. The charging circuit  15  comprises a decision circuit  19  that is connected on its output side via an output  20  of the charging circuit  15  to the first electrode of the capacitor  16 . 
     The decision circuit  19  comprises a decision transistor  21 . A first terminal of the decision transistor  21  is coupled via a voltage converter  28  of the charging circuit  15  and an input  22  of the charging circuit  15  to the input terminal  14 . A second terminal of the decision transistor  21  is connected via the output  20  of the charging circuit  15  to the first electrode of the capacitor  16 . Moreover, the decision circuit  19  comprises a decision comparator  23  having an output connected to a control terminal of the decision transistor  21 . A first input of the decision comparator  23  is coupled via the input  22  of the charging circuit  15  to the input terminal  14 . A second input of the decision comparator  23  is connected to the first electrode of the capacitor  16 . The decision circuit  19  comprises a decision voltage divider  24  having a divider tap that is connected to the first input of the decision comparator  23 . The decision voltage divider  24  comprises a first and a second divider resistor  25 ,  26  that are connected in series between the input  22  of the charging circuit  15  and the reference potential terminal  18 . The divider tap is between the first and the second divider resistor  25 ,  26 . 
     Additionally, the voltage converter  28  includes an input coupled via the input  22  of the charging circuit  15  to the input terminal  14  and an output connected to the first terminal of the decision transistor  21 . The voltage converter  28  is optional and may be replaced e.g. by a connection line, a resistor or a low-pass filter. 
     Furthermore, the power source  10  comprises an electronic switching circuit  31  that is coupled on its input side to the first electrode of the capacitor  16 . An input  38  and a further input  39  of the electronic switching circuit  31  are coupled to the first electrode of the capacitor  16 . The input  38  and the further input  39  of the electronic switching circuit  31  may be connected to each other. 
     Moreover, the power source  10  comprises a control switch  32 . The control switch  32  has a first and a second terminal  33 ,  34  and a control terminal  35 . The second terminal  34  of the control switch  32  is coupled to a first terminal  36  of the disconnecting device  11 . A second terminal  37  of the disconnecting device  11  is coupled or connected to the reference potential terminal  18 . The electronic switching circuit  31  is coupled on its output side to the first terminal  33  of the control switch  35 . The electronic switching circuit  31  comprises an output transistor  40  having a first terminal that is connected to the first electrode of the capacitor  16  via the input  38  of the electronic switching circuit  31 . A second terminal of the output transistor  40  is connected to the first terminal  33  of the control switch  32 . 
     The electronic switching circuit  31  comprises a control comparator  42  having an output connected to a control terminal of the output transistor  40 . A first input of the control comparator  42  is coupled to the input terminal  14 . A second input of the control comparator  42  is connected to the first electrode of the capacitor  16  via the further input  39  of the electronic switching circuit  31 . The electronic switching circuit  31  comprises a voltage divider  43  that couples the input terminal  14  to the reference potential terminal  18 . A divider tap of the voltage divider  43  is connected to the first input of the control comparator  42 . The voltage divider  43  of the electronic switching circuit  31  comprises a first and a second divider resistor  44 ,  45  which are arranged in series between the input terminal  14  and the reference potential terminal  18 . The divider tap of the voltage divider  43  is arranged between the first and the second divider resistor  44 ,  45 . 
     Furthermore, the power source  10  comprises a discharge protection circuit  50  that couples the input terminal  14  to the first input  33  of the control switch  32 . The discharge protection circuit  50  may be called “reverse discharge protection circuit”. The discharge protection circuit  50  is configured to allow a current flow in one direction only. The discharge protection circuit  50  comprises a diode  51 . For example, an anode of the diode  51  is connected to the input terminal  14  and a cathode of the diode  51  is connected to the first terminal  33  of the control switch  32 . 
     Additionally, the power source  10  comprises a test circuit  55  that is coupled to the disconnecting device  11 . A terminal of the test circuit  55  is connected to the first terminal  36  of the disconnecting device  11 . The test circuit  55  comprises a source  56  having an output connected to the first terminal  36  of the disconnecting device  11 . An input of the source  56  may be coupled to the input terminal  14 . The input of the source  56  is coupled e.g. via the discharge protection circuit  50  to the input terminal  14 . The source  56  may comprise a source resistor  57 . The source resistor  57  couples the input terminal  14  to the first terminal  36  of the disconnecting device  11 . The source  56  may be a current source. 
     Moreover, the test circuit  55  comprises a comparator  58  having a first and a second input. The second input of the comparator  58  is coupled to the first terminal  36  of the disconnecting device  11 . The test circuit  55  may comprise a test amplifier  59 . The test amplifier  59  has an input connected to the first terminal  36  of the disconnecting device  11 . An output of the test amplifier  59  is connected to the second input of the comparator  58 . The test amplifier  59  is a voltage amplifier. The test amplifier  59  may be realized as an instrumentation amplifier. 
     Furthermore, the test circuit  55  comprises a test voltage divider  60 . A divider tap of the test voltage divider  60  is connected to the first input of the comparator  58 . The test voltage divider  60  couples the input terminal  14  to the reference potential terminal  18 . The test voltage divider  60  comprises a first and a second divider resistor  61 ,  62 . The first and the second divider resistor  61 ,  62  are connected in series between the input terminal  14  and the reference potential terminal  18 . The divider tap is arranged between the first and the second divider resistor  61 ,  62 . 
     The power source  10  is part of the electric arrangement  100 . The electric arrangement  100  comprises the power source  10  and a battery  101 . The battery  101  is coupled to the input terminal  14 . Thus, the battery  101  couples the input terminal  14  to the reference potential terminal  18 . Moreover, the electric arrangement  100  comprises a battery management system  102 , abbreviated BMS. An output of the BMS  102  is connected to the control terminal  35  of the control switch  32 . An input of the BMS  102  is connected to an output of the test circuit, more specifically to an output of the comparator  58 . 
     A battery voltage VB is provided by the battery  101 . A terminal voltage VIT is tapped at the input terminal  14 . The terminal voltage VIT is equal to the battery voltage VB as long as there is no failure, such as e.g. a missing connection of the battery  101  to the input terminal  14 . The battery voltage VB can be tapped between the input terminal  14  and the reference potential terminal  18 . A capacitor voltage VC can be tapped between the first and the second electrode of the capacitor  16 . The charging circuit  15  provides a charging current IC. A first current I 1  flows through the discharge protection circuit  50 . A second current I 2  is provided by the electronic switching circuit  31 . An activating current IA is provided to the first terminal  36  of the disconnecting device  11 . The activating current IA flows through the disconnecting device  11  to the reference potential terminal  18 . A control signal SC is applied to the control terminal  35  of the control switch  32 . The control signal SC is generated by the BMS  102 . A test current IT flows through the source  56 . A device voltage VD is tapped between the first terminal  36  of the disconnecting device  11  and the reference potential terminal  18 . The comparator  58  generates a comparator signal SCOM. The generator signal SCOM is provided to the BMS  102 . 
     At the start of operation, the battery voltage VB is provided to the input terminal  14 , for example by a switch (not shown) between the battery  101  and the input terminal  14 . In the case that the battery voltage VB can be tapped at the input terminal  14 , the charging circuit  15  applies the charging current IC to the capacitor  16 . Thus, the capacitor voltage VC rises from a value of 0 V. The capacitor voltage VC rises up to a reference voltage VCP. The reference voltage VCP is applied to the first input of decision comparator  23 . The reference voltage VCP may be a predetermined reference voltage. The reference voltage VCP may be determined by the decision voltage divider  24  and the battery voltage VB. The reference voltage VCP can be tapped at the divider tap of the decision voltage divider  24 . In the case that the capacitor voltage VC reaches the reference voltage VCP, the charging current IC is zero or is approximately zero. 
     The voltage converter  28  provides a down conversion. The voltage converter  28  is implemented as Buck converter or Buck-Boost converter. Thus, the voltage converter  28  is realized as a direct-current to direct-current converter, abbreviated as DC-to-DC converter. The voltage converter  28  may be realized as a capacitive converter or an inductive converter. A voltage at the output of the voltage converter  28  may be less than the battery voltage VB. 
     At normal operation of the electric arrangement  100  or of a vehicle comprising the electric arrangement  100 , the control signal SC sets the control switch  32  in a non-conducting state. Thus, the disconnecting device  11  is not triggered. The activation current IA only has the value of the test current IT; thus, the activation current IA does not activate the disconnecting device  11 . 
     An emergency operation of the electric arrangement  100  is different from the normal operation of the electric arrangement  100 . The emergency operation may e.g. occur in the case of an accident of the vehicle. 
     At the emergency operation, the control signal SC sets the control switch  32  in a conducting state. The BMS  102  generates the control signal SC with a triggering value e.g. in case of an accident. The power source  10  achieves that the activating current IA immediately obtains a value that triggers the disconnecting device  11 . In the case of triggering of the disconnecting device  11  the pyrotechnic ignition element  12  is activated and interrupts a power connection line (not shown) between a high voltage battery and a motor or other electric parts of the vehicle (not shown). The activating current IA either results from the first current I 1  or results from the second current I 2 . A value IA of the activating current can be calculated as follows: 
         IA=I 1+ I 2+ IT,    
     wherein I 1  is a value of the first current, I 2  is a value of the second current and IT is a value of the test current. In case the test current IT can be neglected, the value IA of the activating current can be calculated as follows: 
         IA=I 1+ I 2 
     In the emergency operation with regular operation of the power source  10 , the activating current IA has the value of the first current I 1 . Thus, in the emergency operation with regular operation of the power source  10 , the battery  101  generates the first current I 1 . The first current I 1  flows from the input terminal  14  via the discharge protection circuit  50  and the control switch  32  to the disconnecting device  11 . 
     In the emergency operation, a failure of the battery  101  or of a connection line between the battery  101  and the input terminal  14  may occur resulting in an alternative operation of the power source  10 . In the emergency operation with alternative operation of the power source  10 , the first current I 1  has a small value, e.g. zero or approximately zero, and the activating current IA approximately or exactly has the value of the second current I 2 . 
     The electronic switching circuit  31  is configured to detect whether the terminal voltage VIT is sufficient for generating the first current I 1 . The electronic switching circuit  31  compares a voltage derived from the terminal voltage VIT with the capacitor voltage VC. The terminal voltage VIT generates a threshold voltage VT at the divider tap of the voltage divider  43  of the electronic switching circuit  31 . The control comparator  42  compares the threshold voltage VT with the capacitor voltage VC. In the case that the threshold voltage VT is less than the capacitor voltage VC, the control comparator  42  sets the output transistor  40  into a conducting state. Thus, the second current I 2  flows from the first electrode of the capacitor  16  via the output transistor  40  and the control switch  32  to the disconnecting device  11 . In the case that the threshold voltage VT is higher than the capacitor voltage VC, the control comparator  42  sets the output transistor  40  into a non-conducting state; thus, the second current I 2  has approximately or exactly the value zero. 
     Thus, the second current I 2  is only generated with a value sufficient to trigger the disconnecting device  11  in the case that the first current I 1  is zero or is too low. The capacitor voltage VC is only used to generate the activating current IA in the case that a terminal voltage VIT tapped at the input terminal  14  is too low. Thus, either the terminal voltage VIT or the capacitor voltage VC is used to generate the activating current IA. Alternatively, the activating current IA mainly results from the second current I 2  and results only to a small extent from the first current I 1  (e.g. in case of a partial failure of the battery  101  or of connection lines of the battery  101 ). Advantageously, a high reliability of the power source  10  is achieved. 
     In the case that the control switch  32  is set in a non-conducting state, the test current IT generates a value of the device voltage VD that mainly depends on the resistance value of the resistor  13  of the pyrotechnic ignition element  12 . A value of the device voltage VD follows the equation: 
     
       
      
       VD=IT·R,  
      
     
     wherein R is a resistance value of the resistor of the pyrotechnic ignition element  13  and IT is a value of the test current. The device voltage VD or a voltage derived from the device voltage VD is provided to the second input of the comparator  58 . A test reference voltage VRT is provided to the first input of the comparator  58 . The test reference voltage VRT is generated by the test voltage divider  60 . The test amplifier  59  may amplify the device voltage VD and generate the voltage that is applied to the second input of the comparator  58 . 
     Thus, the comparator  58  compares the device voltage VD or a voltage depending on the device voltage VD with the test reference voltage VRT. The test reference voltage VRT may have a predetermined value. The comparator  58  generates a comparator signal SCOM indicating whether the device voltage VD is lower or higher than the test reference voltage VRT. In the case that the device voltage VD is lower than the test reference voltage VRT, the comparator signal SCOM indicates a failure inside the disconnecting device  11 , such as, for example, resulting from a short circuit inside the disconnecting device  11 . 
     In an alternative embodiment, the test circuit  55  may comprise a further comparator. The comparator  58  and the further comparator form a window comparator for comparing the device voltage VD or a voltage depending on the device voltage VD with the test reference voltage VRT and a further test reference voltage. The disconnecting device  11  has a failure in case the device voltage VD or a voltage depending on the device voltage VD is outside of a voltage region that is between the test reference voltage VRT and the further test reference voltage. 
     In  FIG.  1   , the battery  101  is implemented as a conventional LV battery source. The disconnecting device  11  may be realized as a pyro ignitor. The ignition is controlled via the control signal SC generated by the BMS  102  and provided to the control switch  32 . In event of vehicle crash and the battery  101  being not disconnected, the battery  101  provides the required activating current IA to the pyro ignitor element  12  via the discharge protection circuit  50  and the control switch  32 . The activating current IA can be named ignition current. The capacitor  16  is fabricated as a supercapacitor. The capacitor  16  acts as redundant power source. Charging of the capacitor  16  is done using the charging circuit  15 . The charging circuit  15  starts charging the capacitor  16 , when the LV battery  101  is first connected in or to the power source  10 . After a first charging cycle of the capacitor  16 , the capacitor  16  always remains charged and acts as the redundant power source for the pyrotechnic ignition element  12 . In the event of vehicle crash when LV battery  101  abruptly disconnects, the electronic switching circuit  31  detects this situation and connects the redundant power source (supercapacitor  16 ) to the pyrotechnic ignition element  12  via the control switch  32 . The pyrotechnic ignition element  12  may be named pyro ignitor element. 
     The discharge protection circuit  50  prevents a reverse current flow from the capacitor  16  to other battery connected accessories or devices. Thus, the discharge protection circuit  50  realizes a reverse discharge protection circuit. 
     The test circuit  55  may be named health monitoring section of the diagram. The source  56  connected to the battery  101  ensures to pass a minimum test current IT through the pyro ignitor element  12 . This test current IT is sufficient enough to check the continuity (via resistance measurement) of the resistor  13  that realizes a pyro ignitor filament. The device voltage VD generated across the pyro ignitor filament is amplified using the test amplifier  59  implemented as instrumentation amplifier. The comparator  58  compares this voltage with the test reference voltage VRT to verify the filament health and generates a comparator signal SCOM for the BMS  102  and/or an electronic circuit unit. With these two circuits, i.e. redundant power source and health monitoring system  55 , the disconnecting device  11  is made more reliable and robust. 
     The power source  10  may use only discrete electronic components to make it compact and achieve a cost effective solution. Alternatively, parts of the power source  10  may be realized as an integrated circuit. For example, the charging circuit  15 , the electronic switching circuit  31 , the discharge protection circuit  50 , the control switch  32  and the test circuit  55  may be integrated on one or several integrated circuits. Furthermore, the power source  10  may be designed as in-built part of the pyro switch itself or as an additional accessory. 
     Alternatively, the source  56  is realized as voltage source. 
     In an alternative embodiment, not shown, the discharge protection circuit  50  comprises a switch. Thus, the diode  51  is replaced by the switch. The switch is controlled by the signal at the output of the control comparator  42 . The switch is set in a conducting state by said signal in case the output transistor  40  is set in a non-conducting state and vice versa. 
     In an alternative embodiment, not shown, the disconnecting device  11  is coupled via a current sink (e.g. a resistor) to the reference potential terminal  18 . 
       FIG.  2    shows a further exemplary embodiment of an electric arrangement  100  with a power source  10  which is a further development of the embodiment shown in  FIG.  1   . The charging circuit  15  comprises a reference voltage source  80  that is connected to the first terminal of the decision comparator  23 . The reference voltage source  80  replaces the decision voltage divider  24  shown in  FIG.  1   . Thus, the reference voltage source  80  generates the reference voltage VCP. The charging current IC flows in case the capacitor voltage VC is less than the reference voltage VCP. Advantageously, after first charging of the capacitor  16 , the capacitor voltage VC has a value independent from the value of the battery voltage VB. 
     The test circuit  55  comprises a reference voltage generator  82 . The reference voltage generator  82  replaces the test voltage divider  60  shown in  FIG.  1   . Thus, the test reference voltage VRT is generated by the reference voltage generator  82 . Advantageously, the comparison of the device voltage VD with the test reference voltage VRT is independent from the value of the battery voltage VB. 
     The source  56  may be configured to provide the test current IT independent from the value of the battery voltage VB. For example, the source  56  may be supplied by the reference voltage generator  82 . 
     The battery  101  is a low voltage battery of the electric arrangement  100 . Alternatively, the battery  101  may be a high voltage battery, e.g. the high voltage battery of the vehicle. A down converter of the electric arrangement  100  may couple the battery  101  to the input terminal  14 . 
     The decision comparator  23  and the control comparator  42  are implemented as comparators. The decision transistor  21  and the output transistor  40  are fabricated as transistors, for example as field-effect transistors such as e.g. metal-oxide-semiconductor field-effect transistors. The control switch  32  may be fabricated as electronic switch, for example as transistor (e.g. as field-effect transistor such as e.g. metal-oxide-semiconductor field-effect transistor), thyristor or silicon controlled rectifier. 
     The embodiments shown in  FIGS.  1  and  2    as stated represent example embodiments of the power source and method for providing an activating current; therefore, they do not constitute a complete list of all embodiments according to the improved power source and method. Actual power sources may vary from the embodiments shown in terms of parts, structures and shape, for example. 
     REFERENCE NUMERALS 
     
         
           10  power source 
           11  disconnecting device 
           12  pyrotechnic ignition element 
           13  resistor 
           14  input terminal 
           15  charging circuit 
           16  capacitor 
           18  reference potential terminal 
           19  decision circuit 
           20  output 
           21  decision transistor 
           22  input 
           23  decision comparator 
           24  decision voltage divider 
           25 ,  26  divider resistor 
           28  voltage converter 
           31  electronic switching circuit 
           32  control switch 
           33  first terminal 
           34  second terminal 
           35  control terminal 
           36  first terminal 
           37  second terminal 
           38 ,  39  input 
           40  output transistor 
           42  control comparator 
           43  voltage divider 
           44 ,  45  divider resistor 
           50  discharge protection circuit 
           51  diode 
           55  test circuit 
           56  source 
           57  source resistor 
           58  comparator 
           59  test amplifier 
           60  test voltage divider 
           61 ,  62  divider resistor 
           80  reference voltage source 
           82  reference voltage generator 
           100  electric arrangement 
           101  battery 
           102  battery management system 
         IA activating current 
         IC charging current 
         IT test current 
         I 1  first current 
         I 2  second current 
         VB battery voltage 
         VC capacitor voltage 
         VCP reference voltage 
         VD device voltage 
         VIT terminal voltage 
         VRT test reference voltage 
         VT threshold voltage 
         SC control signal 
         SCOM comparator signal