Abstract:
A circuit arrangement for detecting a switch position includes a first node configured to be connected to one phase of a power network, a third node, and a micro-controller. A switch is arranged between the first node and the third node. A resistor is arranged parallel to the switch between the first node and the third node. A connection on the micro-controller is connected to the third node. The micro-controller is programmed to compare a voltage present at the connection against a reference voltage and to determine from this comparison whether the switch is open or closed.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2012/070855, filed on Oct. 22, 2012, which claims the benefit of priority to Serial No. DE 10 2011 088 411.4, filed on Dec. 13, 2011 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     BACKGROUND 
     The disclosure relates to a circuit arrangement for detecting a switch position, to an electrical apparatus having such a circuit arrangement and to a method for detecting a switch position. 
     It is known to provide electrical devices with switches in order to switch the devices on and off. Continuously powered electrical devices, which still draw electrical energy even in the switched-off state, are also known. It is known to equip such electrical devices with apparatuses which are used to detect a switch position of the switch. By way of example, the detection can take place indirectly via a voltage present at a triac, or directly via a signal sent from the switch. In the case of all of said solutions, specially provided electrical and electronic components are necessary to detect the switch position. It is also known to connect resistors in parallel with switches in order to continuously supply power to electronics, for example in the case of machines with restart protection and current limiting at the carbon-brush apparatus. 
     SUMMARY 
     A problem addressed by the present disclosure therefore consists in providing an improved circuit arrangement for detecting a switch position. Said problem is solved by means of a circuit arrangement having the features of the disclosure. Another problem addressed by the present disclosure is to provide an electrical device having such a circuit arrangement. Said problem is solved by means of an electrical device having the features of the disclosure. A further problem addressed by the present disclosure is to specify a method for detecting a switch position. Said problem is solved by means of a method having the features of the disclosure. Preferred developments are specified in the dependent claims. 
     A circuit arrangement according to the disclosure for detecting a switch position comprises a first node, which can be connected to a phase of an electrical grid, a third node and a microcontroller. In this case, a switch is arranged between the first node and the third node. A resistor is arranged in parallel with the switch between the first node and the third node. A connection of the microcontroller is connected to the third node. The microcontroller is programmed to compare a voltage present at the connection with a reference voltage and, on the basis of said comparison, to determine whether the switch is open or closed. Advantageously, in the case of this circuit arrangement, it is possible to detect the switch position using the microcontroller without additional electronic components having to be provided. As a result, the circuit arrangement is advantageously particularly cost-effective to produce. 
     In a development of the circuit arrangement, the microcontroller has an analog-to-digital converter, wherein the reference voltage is used as reference value for the analog-to-digital converter. In this case, the microcontroller is programmed to digitize the voltage present at the connection by means of the analog-to-digital converter in order to obtain a digital value. In this case, the microcontroller is also programmed to determine, on the basis of the digital value, whether the switch is open or closed. Advantageously, an analog-to-digital converter which is present anyway in the microcontroller is then used to detect the switch position. 
     In a particularly preferred embodiment of the circuit arrangement, the connection of the microcontroller is a voltage supply connection of the microcontroller. Advantageously, no other connections of the microcontroller, in particular no IO connections of the microcontroller, are then required for detecting the switch position. 
     It is likewise preferred for the reference voltage to be an internal reference voltage of the microcontroller. Advantageously, it is then not necessary to supply the reference voltage to the microcontroller from the outside, as a result of which the design of the circuit arrangement is simplified. 
     In a development of the circuit arrangement, said circuit arrangement has a second node, which can be connected to a neutral conductor of an electrical grid. In this case, the circuit arrangement also has a seventh node, which is connected to a ground potential. In this case, an anode of a Zener diode is connected to the seventh node and a cathode of the Zener diode is connected to the third node. Furthermore, a capacitor is arranged between the third node and the seventh node. Further, a ground connection of the microcontroller is connected to the seventh node. In addition, a resistor and a diode are connected in series between the seventh node and the second node. Advantageously, the circuit arrangement can then provide, at the third node, a DC supply voltage for downstream circuit parts. 
     In an additional development of the circuit arrangement, a triac and an electric motor are connected in series between the third node and the second node. In this case, the microcontroller is designed to switch the triac. Advantageously, the microcontroller and the triac can then drive the electric motor by means of a phase gating controller for power regulation or control. 
     An electrical device according to the disclosure has a circuit arrangement of the type mentioned above. Advantageously, the electrical device can then detect a switch position of a switch without needing to have additional components for this purpose. 
     A method according to the disclosure for detecting a switch position has steps for calculating a ratio between a voltage value and a reference voltage, for detecting that the switch is open if the ratio falls below a fixed threshold value and for detecting that the switch is closed if the ratio does not fall below the fixed threshold value. Advantageously, the method can be implemented by a microcontroller. 
     In a development of the method, the ratio is calculated by digitizing the voltage value, wherein the reference voltage is used as reference value for the digitization. Advantageously, the digital signal can then be processed further in a simple manner. 
     In an expedient embodiment of the method, the voltage value is acquired by means of a voltage supply connection of a microcontroller. Advantageously, no other electronic components are then necessary in addition to the microcontroller in order to implement the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will now be explained in more detail on the basis of the attached FIGURE, in which: 
         FIG. 1  shows a circuit arrangement for detecting a switch position. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a circuit diagram of a circuit arrangement  100 . The circuit arrangement  100  can be used, for example, in an electrical device in order to detect a switch position of a switch of the electrical device. The electrical device can be, for example, a power tool, for example a drill or an angle grinder. 
     The circuit arrangement  100  has a first circuit node  110  and a second circuit node  120 . The nodes  110 ,  120  are intended to be connected to an AC grid. In this case, the first node  110  is connected to a phase (L) of the electrical grid and the second node  120  is connected to a neutral conductor (N) of the AC grid, or vice versa. 
     A switch  200  is arranged between the first node  110  of the circuit arrangement  100  and a downstream third node  130  of the circuit arrangement  100 . The switch  200  can be closed in order to conductively connect the first node  110  to the third node  130 . The switch  200  can be opened in order to interrupt a direct connection between the first node  110  and the third node  130 . The switch  200  can be, for example, a power switch of an electrical device in which the circuit arrangement  100  is provided. 
     A standby line  210  is connected in parallel with the switch  200 , with a standby resistor  220  being arranged in said standby line. The standby line  210  comprising the standby resistor  220  is thus likewise arranged between the first node  110  and the third node  130 . The standby line  210  is used to supply electrical voltage to the electronics in which the circuit arrangement  100  is arranged, even in the switched-off state, that is to say when the switch  200  is open. Such a voltage supply even in the switched-off state is necessary in the case of many electrical devices with continuously powered electronics. The standby resistor  220  can be used to limit a current flow in the switched-off state of the electrical device. The standby resistor  220  arranged in the standby line  210  is also used to detect the switch position of the switch  200 , as explained below. 
     A switch can also be arranged between the second node  120  and downstream circuit parts of the circuit arrangement  100 . A switch arranged between the second node  120  and downstream circuit parts can be coupled to the switch  200  such that the two switches always have a uniform switch position. However, a switch arranged between the second node  120  and downstream circuit parts of the circuit arrangement  100  can be omitted, as in the example illustrated in  FIG. 1 . 
     The circuit arrangement  100  has a switched-mode power supply  300  which is used to generate a DC supply voltage at the third node  130 . Said DC supply voltage can be used by an electrical device in which the circuit arrangement  100  is arranged to supply power to other circuits and components. 
     The switched-mode power supply  300  has a seventh circuit node  170  which is connected to a ground potential  190 . A Zener diode  310  is arranged between the third node  130  and the seventh node  170 . In this case, the anode  311  of the Zener diode  310  is connected to the seventh node  170 . The cathode  312  of the Zener diode  310  is connected to the third node  130 . A capacitor  320  is also arranged between the third node  130  and the seventh node  170 . The capacitor  320  is therefore connected in parallel with the Zener diode  310 . The capacitor  320  can be, for example, an electrolytic capacitor. In addition, a series circuit comprising a resistor  330  and a diode  340  is arranged between the seventh node  170  and the second node  120 . In this case, an anode  341  of the diode  340  is oriented in the direction of the seventh node  170 , while a cathode  342  of the diode  340  is oriented in the direction of the second node  120 . In the exemplary embodiment illustrated in  FIG. 1 , the resistor  330  is arranged between the seventh node  170  and an eighth node  180 . The diode  340  is arranged between the eighth node  180  and the second node  120 . The sequence of resistor  330  and diode  340  could also be changed, however. 
     The diode  340  of the switched-mode power supply  300  causes the capacitor  320  to be charged up only during one half-cycle of an AC voltage present between the first node  110  and the second node  120 . During each second half-cycle of the AC voltage present between the first node  110  and the second node  120 , the diode  340  turns off. The resistor  330  acts as current limiter. The Zener diode  310  limits the maximum electrical voltage to which the capacitor  320  is charged. For this purpose, the breakdown voltage of the Zener diode  310  can be, for example, 5.1 V. 
     In the example illustrated in  FIG. 1 , the circuit arrangement  100  additionally comprises an electric motor  400  which can be driven by means of a triac  430 . The electric motor  400  can be an electric motor of an electrical device, for example a drill. The triac  430  and the electric motor  400  are connected in series. In the example shown in  FIG. 1 , the triac  430  is arranged between the third node  130  and a fourth node  140  of the circuit arrangement. In this case, a first electrode  431  of the triac  430  is connected to the third node  130 . A second electrode  432  of the triac  430  is connected to the fourth node  140 . The electric motor  400  is arranged between the fourth node  140  and the second node  120 .  FIG. 1  illustrates a series circuit comprising the electric motor  400 , a first coil  410  and a second coil  420 . In this case, the first coil  410  is arranged between the fourth node  140  and a fifth node  150  of the circuit arrangement  100 . The electric motor  400  is arranged between the fifth node  150  and a sixth node  160  of the circuit arrangement  100 . The second coil  420  is arranged between the sixth node  160  and the second node  120 . 
     Moreover, the circuit arrangement  100  comprises a microcontroller  500 . In the example shown in  FIG. 1 , the microcontroller  500  has a connection  501 , a ground connection  502  and a control connection  503 . The ground connection  502  is connected to the seventh node  170  and hence to the ground potential  190 . The control connection  503  is connected to a control electrode  433  of the triac  430 . The connection  501  is connected to the third node  130  of the circuit arrangement  100 . 
     By means of the control connection  503  and the control electrode  433  of the triac  430 , the microcontroller  500  can switch the triac  430  into a conducting state between the first electrode  431  and the second electrode  432 . This is used by the microcontroller  500  to drive the electric motor  400  by means of a phase gating controller and to regulate or to control the power of the electric motor  400 . 
     The connection  501  of the microcontroller  500  is preferably a voltage supply connection of the microcontroller  500 . Therefore, the microcontroller  500  is supplied with energy via the connection  501 . According to the disclosure, the microcontroller  500  also detects, via the electrical voltage present at the connection  501  of said microcontroller, whether the switch  200  is open or closed. 
     If the switch  200  of the circuit arrangement  100  is open, some of the electrical voltage which is present at the first node  110  of the circuit arrangement  100  is dropped across the standby resistor  220 . As a result, the voltage present at the third node  130  of the circuit arrangement  100  is lower than the voltage present at the first node  110  of the circuit arrangement  100 . If the switch  200  of the circuit arrangement  100  is closed, however, the standby resistor  220  is short-circuited, with the result that there is practically no voltage drop across the standby resistor  220 . In this case, the electrical voltage present at the third node  130  substantially corresponds to the electrical voltage present at the first node  110  of the circuit arrangement  100  and is greater than the electrical voltage present at the third node  130  when the switch  200  is open. 
     The microcontroller  500  has an internal reference voltage. Additionally, the microcontroller  500  has the possibility of digitizing, by means of an analog-to-digital converter, the voltage value of the electrical voltage present at the connection  501  of said microcontroller and of using the internal reference voltage of the microcontroller  500  as reference value in this case. A procedure such as this is described, for example, in the document “Application Note AN1072” by Microchip. The digital value supplied by the analog-to-digital converter of the microcontroller  500  then gives a ratio of the magnitude of the voltage present at the connection  501  of the microcontroller  500  to the magnitude of the reference voltage. The actual value of the reference voltage is unimportant here, as long as the reference voltage is constant, less than the voltage present at the connection  501  and greater than the ground potential. 
     The digital value supplied by the analog-to-digital converter of the microcontroller  500  has different values depending on whether the switch  200  is open or closed. If the switch  200  is closed, the ratio of the voltage at the connection  501  to the reference voltage of the microcontroller  500  is higher and the digital value has a high value. If the switch  200  is open, the ratio of the voltage present at the connection  501  of the microcontroller  500  to the reference voltage of the microcontroller  500  is lower and the digital value has a lower value. The microcontroller  500  compares the digital value to a threshold value stored in the microcontroller  500 . If the digital value is below the fixed threshold value, the microcontroller  500  infers from this that the switch  200  is open. Otherwise, the microcontroller  500  concludes that the switch  200  is closed. 
     A particular advantage of the circuit arrangement  100  consists in that no additional components and no additional connections of the microcontroller  500  are necessary for detecting the position of the switch  200 . All components of the circuit arrangement  100  are necessary for operating an electrical device which has the circuit arrangement  100 , even without the possibility of detecting the position of the switch  200 . The connection  501  of the microcontroller  500  must be connected to the third node  130  of the circuit arrangement  100  anyway in order to supply the microcontroller  500  with electrical voltage. In addition, according to the disclosure, the position of the switch  200  can be detected merely by means of suitable programming of the microcontroller  500 . 
     By way of example, the microcontroller  500  can use the knowledge of the position of the switch  200  to implement restart protection of an electrical device in which the circuit arrangement  100  is provided.