Device and method for detecting a voltage drop

Abstract

The invention relates to a device for detecting a voltage drop between an anode connection and a cathode connection, comprising: a control capacitor, of which the first electrode is connected to the anode connection and the second electrode is connected to the cathode connection; a measuring device, which is designed to output a discharge signal depending on a potential difference detected between the anode connection and the cathode connection and a first threshold value for the potential difference on a discharge control line; a discharge circuit which is connected to the discharge control line and is designed to discharge the control capacitor depending on the discharge signal; and a control device, which is designed to detect the voltage drop by evaluating the state of charge of the control capacitor.

Claims

1. A device for detecting a voltage drop between an anode connection and a cathode connection, comprising a control capacitor, of which a first electrode is connected to the anode connection via a voltage divider and the second electrode is connected to the cathode connection; a measuring device, which is designed to output a discharge signal depending on a potential difference detected between the anode connection and the cathode connection, and a first threshold value for the potential difference on a discharge control line; a discharge circuit, which is connected to the discharge control line and is designed to discharge the control capacitor depending on the discharge signal; and a control device, which is designed to detect the voltage drop by evaluating the state of charge of the control capacitor; wherein the measuring device includes a first control switch having an input connected to the anode connection and wherein the first control switch connects the discharge control line to the cathode connection with low impedance when the input potential applied at the control input exceeds the first threshold value; wherein the first control switch is adapted to disconnect the discharge control line from the cathode connection when the input potential applied at the control input drops below the first threshold value; wherein the discharge circuit includes a second control switch including a control input connected to the discharge control line and which connects the first electrode of the control capacitor with low impedance to the second electrode of the control capacitor when the discharge control line is disconnected from the cathode connection; and wherein the control input of the second control switch is connected to the anode connection via a pull-up resistor.

2. The device according to claim 1, wherein the anode connection or the cathode connection are connectable to corresponding supply terminals of an external voltage source and wherein the external voltage source is one or multiple rechargeable battery packs.

3. The device according to claim 1, wherein the first electrode of the control capacitor is connected to the anode connection of the voltage divider.

4. The device according to claim 1 wherein the first threshold value is 10% to 90% of the nominal potential difference between the anode connection and the cathode connection.

5. The device according to one of claim 1, wherein the first control switch or the second control switch are a semiconductor switch.

6. The device according to claim 1, wherein the control device has a comparator unit adapted to compare the state of charge of the control capacitor with a second threshold value to determine a potential difference between the anode connection and the cathode connection, wherein the voltage drop is detected when the state of charge is lower than the second threshold value.

7. The device according to claim 6, wherein the second threshold value is 1% to 95% of the nominal potential difference between the anode connection and the cathode connection.

8. A battery-operated electrical machine tool, including an anode connection and a cathode connection for electrical supply, and a device for detecting a voltage drop between the anode connection and the cathode connection, the battery- operated machine tool comprising: a control capacitor, of which a first electrode is connected to the anode connection via a voltage divider and a second electrode is connected to the cathode connection; a measuring device, which is designed to output a discharge signal depending on a potential difference detected between the anode connection and the cathode connection, and a first threshold value for the potential difference on a discharge control line; a discharge circuit, which is connected to the discharge control line and is designed to discharge the control capacitor depending on the discharge signal; and a control device, which is designed to detect the voltage drop by evaluating the state of charge of the control capacitor; wherein the measuring device includes a first control switch having an input connected to the anode connection and wherein the first control switch connects the discharge control line to the cathode connection with low impedance when the input potential applied at the control input exceeds the first threshold value; wherein the first control switch is adapted to disconnect the discharge control line from the cathode connection when the input potential applied at the control input drops below the first threshold value; wherein the discharge circuit includes a second control switch including a control input connected to the discharge control line and which connects the first electrode of the control capacitor with low impedance to the second electrode of the control capacitor when the discharge control line is disconnected from the cathode connection; and wherein the control input of the second control switch is connected to the anode connection via a pull-up resistor.

9. The electrical machine tool according to claim 8, further comprising a restart protection device for protection against an uncontrolled restart of the electrical machine tool after a voltage drop, wherein the restart protection device is connected to the device for detecting the voltage drop.

10. A method for detecting a voltage drop between an anode connection and a cathode connection, whereupon the state of charge of a control capacitor is evaluated in order to detect the voltage drop, a first electrode of the control capacitor being connected to the anode connection and a second electrode of the control capacitor being connected to the cathode connection, wherein the control capacitor is discharged depending on a potential difference, which is detected between the anode connection and the cathode connection, and a first threshold value for the potential difference; wherein the method further comprises utilizing a measuring device that includes a first control switch having an input connected to the anode connection and wherein the first control switch connects a discharge control line to the cathode connection with low impedance when the input potential applied at the control input exceeds the first threshold value; wherein the control switch is adapted to disconnect the discharge control line from the cathode connection when the input potential applied at the control input drops below the first threshold value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The following FIGURE shows a preferred exemplary embodiment of the invention, in which individual features of the present invention are shown in combination with one another. Features of the exemplary embodiment can also be implemented separately from one another and can therefore be readily connected by a person skilled in the are to form further reasonable combinations and subcombinations.

(2) FIG. 1 shows a circuit diagram of a battery-operated electrical machine tool having a device for detecting a voltage drop within the scope of a restart protection device.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(3) FIG. 1 schematically shows a battery-operated electrical machine tool 1 and a rechargeable battery pack 2 which is connected to the electrical machine tool 1 for providing a supply voltage V.sub.BAT for the electrical machine tool 1.

(4) The rechargeable battery pack 2 and the electrical machine tool 1 each have a rechargeable battery pack interface 3 for connecting the rechargeable battery pack 2 to the electrical machine tool 1. It is pointed out here that the invention can also be advantageously suitable for use with multiple rechargeable battery packs 2 in order to increase the provided supply voltage V.sub.BAT and/or to increase the operating time during the use of the electrical machine tool 1. Multiple rechargeable battery packs 2 can, more particularly, be connected in series, although in principle these can also be connected in parallel.

(5) The rechargeable battery pack 2 can have one or multiple rechargeable battery cells 4, which are connected, for example, in series and, overall, generate the supply voltage V.sub.BAT. The rechargeable battery pack 2 shown has, for example, a supply line 5 and a ground line GND, which are connected to the electrical machine tool 1 via the rechargeable battery pack interface 3 for supplying the electrical machine tool 1.

(6) The electrical machine tool 1 shown has an anode connection 6 and a cathode connection 7 or GND, between which the supply voltage V.sub.BAT is applied. In order to compensate for overvoltages, a buffer capacitor C.sub.B, more particularly an electrolyte capacitor, is provided between the anode connection 6 and the cathode connection 7. The buffer capacitor C.sub.B is not absolutely necessary within the scope of the invention, however; the invention is particularly advantageously suitable for use with an electrical machine tool 1 which has a buffer capacitor C.sub.B of this type.

(7) Moreover, the electrical machine tool 1 has an operating switch 8 for selectively switching an electric motor M of the electrical machine tool 1 on or off. The operating switch 8 can be lockable in its switched-on position.

(8) In order to prevent an undesirable restart of the electric motor M, for example, when the operating switch 8 is locked, after a voltage drop of the supply voltage V.sub.BAT, a restart protection device 9 is provided, which includes the device 10 (described in the following) for detecting the voltage drop between the anode connection 6 and the cathode connection 7.

(9) The device 10 for detecting the voltage drop has a control capacitor C.sub.K, of which the first electrode is connected to the anode connection 6 and the second electrode is connected to the cathode connection 7. The control capacitor C.sub.K is therefore charged in the case of a rechargeable battery pack 2 being inserted into the electrical machine tool 1 and when supply voltage V.sub.BAT is present. In the exemplary embodiment, the charging of the control capacitor C.sub.K is delayed due to the use of an upstream primary charging resistor R.sub.L1. The primary charging resistor R.sub.L1 forms, with a secondary charging resistor R.sub.L2, a first voltage divider 11 and, therefore, also limits the maximum achievable charging voltage of the control capacitor C.sub.K. The primary charging resistor R.sub.L1 can be dimensioned, for example, such that the control device 12 (described in the following) and/or further electrical components of the electrical machine tool 1 have sufficient time for a boot process in order to reliably detect a restart protection event. The use of a primary charging resistor R.sub.L1 or of the first voltage divider 11 is optional, in principle.

(10) The primary charging resistor R.sub.L1 can be, for example, 470 k and the secondary charging resistor can be 27 k when the supply voltage V.sub.BAT is nominally 36 volts (for example, provided by two series-connected rechargeable battery packs 2). The primary charging resistor R.sub.L1 can be, for example, 240 k and the secondary charging resistor can be 27 k when the supply voltage V.sub.BAT is nominally 18 volts or 10.8 volts (for example, provided by a single rechargeable battery pack 2).

(11) The capacitance of the control capacitor C.sub.K can be, for example, 2 F. Any type of design can be provided.

(12) The provided device 10 includes a measuring device 13, which is designed to output a discharge signal y depending on a potential difference, which is detected between the anode connection 6 and the cathode connection 7, and a first threshold value for the potential difference on a discharge control line 14.

(13) For this purpose, the measuring device 13 has a first controlled switch 15, which is in the form of an n-channel MOSFET in the exemplary embodiment. The control input or the gate terminal of the first switch 15 is connected to the anode connection 6 via a second voltage divider 16. The first switch 15 is designed to connect the discharge control line 14 to the cathode connection 7 with low impedance when the input potential applied at the control input exceeds the first threshold value. In the normal state, i.e., in the case of a sufficient voltage supply, the discharge control line 14 is therefore connected to the cathode connection 7 with low impedance. When the first threshold value is fallen below, i.e., in a case of a voltage drop of the supply voltage V.sub.BAT, the discharge control line 14 is switched to zero potential, however, which corresponds to the discharge signal y in the exemplary embodiment.

(14) The device can be flexibly configured by dimensioning the first switch 15 and the second voltage divider 16 and adapted, for example, for use with the buffer capacitor C.sub.B. The first threshold value can be, for example, 10% to 90% of the nominal supply voltage V.sub.BAT, preferably 20% to 80% and particularly preferably 30% to 70%. The divider ratio of the second voltage divider 16 can preferably be designed such that the first switch 15 switches the discharge control line 14 to be potential-free even prior to the maximum residual discharge (for example, 5 volts at a supply voltage V.sub.BAT of 36 volts or 4.3 volts at a supply voltage V.sub.BAT of 18 volts or 10.8 volts) of the buffer capacitor C.sub.B, wherein, simultaneously, the permissible operating range of the electrical machine tool (for example, 30 volts to 42 volts at a supply voltage V.sub.BAT of 36 volts, 15 volts to 21 volts at a supply voltage of V.sub.BAT of 18 volts, or 9 volts to 12.6 volts at a supply voltage V.sub.BAT of 10.8 volts).

(15) For example, the residual discharge of the buffer capacitor C.sub.B can be up to 4.3 volts at a nominal operating voltage of 10.8 volts or 18 volts. In this case, it can be provided that the switching of the first switch 15 begins at a detected potential difference of 9.33 volts downward and a complete disconnection of the discharge control line 14 from the cathode connection 7 has taken place, at the latest, at a residual potential of 5.73 volts. The primary resistor R.sub.M1 of the second voltage divider 16, which is shown and is connected to the anode connection 6, can therefore be, for example, 2.33 M, and the secondary resistor R.sub.M2 of the second voltage divider 16, which is connected to the cathode connection 7, can be 1.0 M.

(16) According to one further example, the residual discharge of the buffer capacitor C.sub.B can be up to 5.0 volts at a nominal operating voltage of 36 volts. In this case, it can be provided that the switching of the first switch 15 begins at a detected potential difference of 26 volts downward, and a complete disconnection of the discharge control line 14 from the cathode connection 7 has taken place, at the latest, at a residual potential of 16 volts. The primary resistor R.sub.M1 of the second voltage divider 16, which is shown and is connected to the anode connection 6, can therefore be, for example, 4.0 M, and the secondary resistor R.sub.M2 of the second voltage divider 16, which is connected to the cathode connection 7, can be 470 M.

(17) The provided device 10 also has a controllable discharge circuit 17, which is designed to discharge the control capacitor C.sub.K. The discharge circuit 17 is connected to the discharge control line 14 for receiving the discharge signal y and is designed to discharge the control capacitor C.sub.K depending on the discharge signal y.

(18) For example, it can be provided that the discharge circuit 17 establishes a high-impedance connection between the two electrodes of the control capacitor C.sub.K when a control input of the discharge circuit 17 is switched to the potential of the cathode connection 7 and otherwise establishes a low-impedance connection between the electrodes of the control capacitor C.sub.K.

(19) As is shown, the discharge circuit 17 can have a second controlled switch 18 for this purpose, namely one further n-channel MOSFET in the exemplary embodiment. The control input of the second switch 18 can be connected to the discharge control line 14, optionally via a series resistance (not shown) of, for example, 47 k.

(20) Provided that the discharge control line 14 is pulled by the measuring device 13 to the potential of the cathode connection 7 during normal operation, the second switch 18 has high impedance on the output side. On the other hand, if the discharge signal y is applied on the discharge control line 14, which is equivalent, in the exemplary embodiment, to a potential-free state of the discharge control line 14 on the part of the first switch 15, the control input of the second switch 18 is connected to the anode connection 6 via the pull-up resistor RP shown in FIG. 1. The pull-up resistor RP can be, for example, 4.7 M.

(21) In this way, the control capacitor C.sub.K is short-circuited by the discharge circuit 17 when the measuring device 13 detects a voltage drop of the supply voltage V.sub.BAT. The control capacitor C.sub.K is therefore discharged. This takes place even when a buffer capacitor C.sub.B is present and, for the case in which multiple rechargeable battery packs 2 are present, also when only a portion of the rechargeable battery packs 2 is connected to the electrical machine tool 1.

(22) Finally, the provided device 10 includes a control device 12, which is designed to detect the voltage drop by evaluating the state of charge of the control capacitor C.sub.K. The control device 12 is preferably designed to be digital, for example, as a microcontroller of the electrical machine tool 1. An appropriately suitable computer program can be run on the control unit 12 with control commands that prompt the control device 12 to carry out the provided method.

(23) In order to detect the state of charge by means of the control device 12, the first electrode of the control capacitor C.sub.K, which, for example, is connected in the normal mode to the anode connection 6, is fed to the control device 12, more particularly via a first analog-to-digital converter 19.

(24) The control device 12 can include a comparator unit 20, which is designed to compare the state of charge of the control capacitor C.sub.K with a second threshold value S for the potential difference between the anode connection 6 and the cathode connection 7. The voltage drop is preferably detected when the state of charge of the control capacitor C.sub.K is less than the second threshold value S, since it can then be assumed that the control capacitor C.sub.K has recently discharged.

(25) The second threshold value S can be optionally fed to the control device 12 via a second analog-to-digital converter 21 and can result, for example, depending on the actual supply voltage V.sub.BAT, as a divider ratio of the supply voltage V.sub.BAT, for example, on the basis of a third voltage divider 22, in the ratio R.sub.C1=470 k to R.sub.C2=27 k (at a nominal supply voltage V.sub.BAT of 36 volts) or R.sub.C1=240 k to R.sub.C2=27 k (at a nominal supply voltage V.sub.BAT of 18 volts or 10.8 volts). Preferably, the divider ratio of the third voltage divider 22 corresponds to the divider ratio of the first voltage divider 11. Particularly preferably, the resistors of the first voltage divider 11 and of the third voltage divider 22 are selected such that the following applies: R.sub.L1=R.sub.C1 and R.sub.L2=R.sub.C2.

(26) When a voltage drop is detected, the control device 12 can provide a control signal 23, wherein the restart protection device 9 selectively blocks or releases the start-up of the electric motor M depending on the control signal 23.