Window comparator and handheld power tool, electric tool, charging device and / or domestic appliance having such a window comparator

Abstract

In a window comparator (200) having a discrete, coil-less and capacitor-less structure for monitoring an input voltage (U I ), the window comparator (200) comprises at least three transistors and at least one ohmic resistor (R1 to R 10 ).

Description

Technical Field

[0001] The invention relates to a window comparator for monitoring an input voltage and a handheld power tool, an electric tool, a charging device and / or a household appliance having such a window comparator. Background Art

[0002] From the prior art electronic window comparators or two-stage threshold detectors or amplitude detector circuits for detecting voltage ranges in discrete circuit technology and in integrated circuit technology are known in a wide range of variations.

[0003] A discretely constructed amplitude detector circuit or so-called "window detector" is known from DE 24 15 098 B2. The amplitude detector circuit has a first threshold circuit, which responds to an input voltage and provides an output voltage at its output, which corresponds to the portion of the input voltage that exceeds a first voltage threshold. In addition, a second threshold circuit is provided with a higher threshold than in the case of the first threshold circuit, which responds to the input voltage and sets the output to a reference voltage point when the input voltage exceeds the threshold of the second threshold circuit. In this case, a feedback circuit is provided, which responds to the voltage at the output and provides a control voltage for the first threshold circuit, which control voltage brings the first threshold circuit out of its activated state when the output is set to the reference potential point by the second threshold circuit.

[0004] An electronic window comparator is also known from US Pat. No. 5,963,062 A. This window comparator essentially comprises a differential switching stage with a current mirror and a downstream load circuit. Summary of the invention

[0005] The invention relates to a window comparator for monitoring an input voltage, which has a discrete, coil-free and capacitor-free structure and comprises at least three transistors and at least one ohmic resistor.

[0006] The invention thus enables a circuit-technically simple and cost-effective realization of an electronic window comparator which, due to its low power requirement, is also particularly suitable for battery-powered mobile devices. Only discrete bipolar transistors or discrete unipolar MOSFETs and at least one discrete ohmic resistor are used. No failure-critical components such as electrolytic capacitors or coils with relatively low MTBF values ​​(Mean Time Between Failure) are required.

[0007] Preferably, of the at least three transistors, at least two transistors are npn transistors and at least one transistor is designed as a complementary pnp transistor. This allows a minimal structure of the circuit of the electronic window comparator to be achieved.

[0008] Preferably, the first npn transistor switches when the input voltage exceeds a first voltage threshold in the range of approximately 0.6 V to 1.2 V. Thus, the determination of the first switching threshold can be realized in a simple and uncomplicated manner.

[0009] According to an advantageous embodiment, the pnp transistor is always switched on until the input voltage is greater than a second voltage threshold, which corresponds to the operating voltage of the window comparator minus the base-emitter voltage of the pnp transistor. The second switching threshold of the window comparator can be determined thereby. In the case of common transistor parameters of bipolar small-signal transistors, in the case of an operating voltage of, for example, 3.3 V, a second voltage threshold of the order of magnitude of, for example, 2.7 V is thus obtained.

[0010] Preferably, a resistor is arranged between the base and the emitter of the pnp transistor. This makes it possible to prevent the transistor from being switched on in an undesired manner or to keep it safely in the off state.

[0011] Preferably, the operating voltage of the window comparator is in the range between 3.0 V and 3.6 V. The window comparator is therefore very suitable for monitoring charging electronics of lithium batteries or lithium polymer batteries for battery-powered devices. Particularly preferably, the operating voltage is in the order of magnitude of approximately 3.3 V, which corresponds to the common cell voltage of lithium polymer batteries.

[0012] In one embodiment, the second npn transistor is used as an inverter for the collector voltage of the first npn transistor, and the collector voltage of the pnp transistor can be simultaneously connected to ground via a seventh resistor by means of the second npn transistor. By means of the inverter or inverting stage formed by means of the second npn transistor, the output voltage of the first npn transistor associated with the first switching threshold and the output voltage of the pnp transistor associated with the second switching threshold are linked to each other, and thus a defined output voltage or a defined output signal with two switching states can be provided. In the first switching state, the output voltage of the window comparator is approximately zero volt or is at ground, i.e. the output of the window comparator is in a "low" state. When the input voltage is between the two switching thresholds, the output voltage of the window comparator is exactly equal to the operating voltage (second switching state), otherwise the output voltage of the window comparator is equal to zero volt, i.e. the output of the window comparator is in a "low" state. In the second switching state of the window comparator, the output voltage is approximately equal to the operating voltage, i.e. the output of the window comparator is in a "high" state.

[0013] Preferably, the window comparator has a first voltage divider, which is formed by means of a first resistor on the operating voltage side and a second resistor on the ground side, at the voltage tap of which the input voltage to be monitored is applied, wherein the voltage tap is connected to the base of the first npn transistor via a fourth resistor and to the base of the pnp transistor via a third resistor. As a result, the base of the first npn transistor and the base of the complementary pnp transistor are at a defined potential even when the input of the window comparator is not connected.

[0014] Preferably, the window comparator has a second voltage divider, which is formed by means of a fifth resistor on the operating voltage side and an eighth resistor on the ground side, the voltage tap of which is connected to the collector of the first npn transistor and to the base of the second npn transistor via a ninth resistor, so that the base of the second npn transistor is at a defined potential.

[0015] In a technically advantageous embodiment, the collector of the second npn transistor is connected to ground by means of a tenth resistor, wherein the collector voltage of the second npn transistor represents the output voltage of the window comparator. Thus, a defined output signal or a defined output voltage is set.

[0016] Preferably, the first, second, fifth, seventh and ninth resistors each have a value of 1 kΩ, the third and fourth resistors each have a value of 47 kΩ, the sixth resistor has a value of 470 kΩ, and the eighth and tenth resistors each have a value of 100 kΩ. Thus, a window comparator with suitable electrical characteristics can be provided in a simple manner for most practically relevant application cases.

[0017] Preferably, the two npn transistors are each formed by a small-signal transistor, in particular a small-signal transistor of the 2N3904 type, and the one pnp transistor is formed by a small-signal transistor, in particular a small-signal transistor of the 2N3906 type. Thus, a simple, power-saving and at the same time robust window comparator is provided that is cost-effective and suitable for mass production.

[0018] The invention further relates to a handheld power tool, an electric tool, a charging device and / or a domestic appliance having at least one window comparator according to the invention, thereby enabling reliable detection of fault states in electrical signals from a plurality of electrical devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In the following description, the invention is further explained based on the exemplary embodiments shown in the drawings. The drawings show:

[0020] Figure 1 shows a schematic view of a standard window comparator according to the prior art;

[0021] Figure 2 Show Figure 1 A curve diagram showing a schematic input and output voltage variation process of a window comparator over time t;

[0022] Figure 3 An exemplary circuit diagram of a window comparator according to the present invention is shown;

[0023] Figure 4 Show Figure 3 A graph showing the input and output voltage changes measured by the window comparator. DETAILED DESCRIPTION

[0024] Figure 1 1 shows a window comparator 100 known from the prior art, which has a first operational amplifier A1 or a first differential amplifier and a second operational amplifier A2 or a second differential amplifier. The two operational amplifiers A1, A2 are preferably loaded with a unipolar operating voltage U B The first operational amplifier A1 is illustratively connected as a non-inverting comparator, while the second operational amplifier A2 is connected as an inverting comparator. The two operational amplifiers A1 and A2 are usually implemented as complex monolithic integrated circuits. B A voltage divider 110 is connected between the ground M and the ground M, which has (here only by way of example) three ohmic (voltage dividing) resistors R of equal size and arranged in series. T , so that at the first voltage tap 112 on the ground side there is preferably 1 / 3U B and preferably 2 / 3U 1 at the second voltage tap 114 on the operating voltage side. B The second voltage U2.

[0025] The input voltage V of the window comparator 100 I is applied to the positive input terminal ("+" input terminal) of the first operational amplifier A1 and the negative input terminal ("-" input terminal) of the second operational amplifier A2. 1,2 The output terminals 116 and 118 are connected in parallel and connected with the help of load resistor R L Or the so-called "pull-up" resistor and the operating voltage U B The first voltage tap 112 is connected to the negative input terminal of the first operational amplifier A1, and the second voltage tap 114 is connected to the positive input terminal of the second operational amplifier A2.

[0026] If the input voltage V Iis less than the first voltage U1, the output terminal 116 of the first operational amplifier A1 is in a "low" state, and the output terminal 118 of the second operational amplifier A2 is in a "high" state, so that the output voltage V at the output terminal 120 of the window comparator 100 is O is at approximately zero volts or at ground potential M. If the input voltage V I When the output terminal 116 of the first operational amplifier A1 is equal to the “high” state, the output terminal 118 of the second operational amplifier A2 remains unchanged in the “high” state, and the output voltage V O In fact, the working voltage U B full level.

[0027] In the further description, the term "low" state refers to a voltage of approximately zero volts or ground potential at the input or output. In contrast, the term "high" state refers to a voltage at the input or output which is at the operating voltage U B voltage of the order of magnitude.

[0028] If the input voltage V I Finally, the output terminal 116 of the first operational amplifier A1 remains in the "high" state, while the output terminal 118 of the second operational amplifier A2 switches to the "low" state, and the output terminal 120 of the window comparator 100 switches to the low state or the output voltage V O Approximately presents the ground potential M. Only when the input voltage V I When the output voltage V of the window comparator 100 is between the two voltages U1 and U2 representing the first and second voltage thresholds, O It is almost equal to the working voltage U B , otherwise the output voltage V O Approximately zero volt.

[0029] Figure 2 Show Figure 1 An exemplary voltage profile of a window comparator 100, which is exemplarily loaded with a positive periodic and triangular input voltage V I Only when the input voltage V I The (voltage) window 122 between the first voltage U1 and the second voltage U2—in this case, 1 / 3 U B With 2 / 3U B When the output voltage is between O Only then can the working voltage U B , or the output terminal of the window comparator 100 is switched to the "high" state. Otherwise, the output voltage V OAt zero volts, or the output of the window comparator is in the "low" state.

[0030] Figure 3 The window comparator 200 according to the present invention is shown, which has a discrete, coil-free and capacitor-free structure, which includes at least three transistors and at least one ohmic resistor. As an illustration, the window comparator 200 has two bipolar npn transistors T1, T2, a bipolar complementary pnp transistor Q and exemplarily ten ohmic resistors R1 to R 10 Another exemplary configuration of the circuit of the window comparator 200 requires a minimum number of three transistors and preferably at least six ohmic resistors. However, it should be noted that the window comparator 200 may also have an arbitrarily larger number of resistors.

[0031] Working voltage U between ground M and positive rail 202 B Preferably, it lies in the range between 3.0V and 3.6V and is therefore ideally suited for battery-powered mobile devices in combination with the extremely low power requirements of the circuit of the window comparator 200. B The voltage range is preferably particularly suitable for monitoring charging electronics of lithium batteries and lithium polymer batteries.

[0032] The circuit of the window comparator 200 preferably has a first voltage divider 210, which is formed by means of a first resistor R1 on the operating voltage side and by means of a second resistor R2 on the ground side. An input voltage U is preferably applied to the input 204 of the window comparator 200, which is monitored by the window comparator. I or any electrical signal. The input 204 of the window comparator 200 is preferably electrically connected to the voltage tap 212 of the first voltage divider 210. Furthermore, the voltage tap 212 is preferably connected to the base of a single complementary pnp transistor Q via a third resistor R3 and to the base of the first npn transistor T1 via a fourth resistor R4. A resistor R6 is preferably arranged between the base and the emitter of the complementary pnp transistor Q. The resistor R6 - like the other four ohmic resistors R1, R4, R8, R9 - serves to ensure a safe shutdown, so that only current flows (if this is also provided).

[0033] The circuit of the window comparator 200 preferably also has a second voltage divider 220, which is formed by means of a fifth resistor R5 on the operating voltage side and an eighth resistor R8 on the ground side. The voltage tap 222 of the second voltage divider 220 is preferably connected to the collector of the first npn transistor T1 and to the base of the second npn transistor T2 via a ninth resistor R9. The second npn transistor T2 acts as a collector voltage U for the first npn transistor T1. T1CThe inverter 230. By means of the second npn transistor T2, the collector voltage U of the pnp transistor Q can be QC The collector of the second npn transistor T2 is connected to the ground M via the seventh resistor R7. 10 connected to ground M, wherein the collector voltage U of the second npn transistor T2 T2C represents the output voltage U of the window comparator 200 O .

[0034] The first npn transistor T1 is preferably connected to the input voltage U I exceeds a first voltage threshold ( Figure 4 U S1 ). The complementary pnp transistor Q preferably remains switched on until the input voltage U I Greater than the second voltage threshold ( Figure 4 U S2 ), the second voltage threshold corresponds to the operating voltage U of the window comparator 200. B Subtract the base-emitter voltage U of the complementary pnp transistor Q QBE Unlike the circuit of the window comparator 200 shown here only by way of example, at least two complementary pnp transistors and at least one npn transistor can also be provided, which then results in a substantially mirror-image circuit structure. Furthermore, instead of the emitter circuit shown here only by way of example, a collector circuit or base circuit of at least three transistors can be provided.

[0035] The first, second, fifth, seventh and ninth resistors (i.e., R1, R2, R5, R7, R9) preferably have a value of 1 kΩ, respectively. The third and fourth resistors R3, R4 preferably measure a value of 47 kΩ, respectively. The sixth resistor R6 preferably has a value of 470 kΩ, and the eighth and tenth resistors R8, R9 preferably have a value of 1 kΩ, respectively. 10 Depending on the requirements placed on the window comparator 200, resistors R1 to R 10 It should be noted that the illustrative ten resistors can also be constructed from a plurality of resistors, so that for example the resistor R1 having a value of 1 kΩ by way of example can also be formed from two resistors having a value of 0.5 kΩ, and so on.

[0036] Preferably, the two npn transistors T1, T2 are each formed by means of a small-signal transistor, in particular a small-signal transistor of the 2N3904 type, and a complementary pnp transistor Q is also formed by means of a small-signal transistor, in particular a small-signal transistor of the 2N3906 type. In order to further reduce the power requirement of the window comparator 200, for example, a unipolar MOSFET can be used when at least one complementary MOSFET is used. The window comparator 200 according to the invention is optimally suitable for identifying fault states of all types of electrical signals. This is advantageous because, if, for example, only the electrical signal is checked for a "high" state or a "low" state, then in the case of a simple and obvious component defect for the subsequent circuit part, it is no longer possible to identify whether a fault situation exists or not.

[0037] For example, if a voltage divider formed by means of two ohmic resistors is considered, two possible fault states arise in the fault analysis. In the case of a fault, the voltage tap of the voltage divider to be monitored can have a voltage of zero volts or be at the level of the operating voltage. This fault situation can be caused, for example, by a high-resistance solder joint. Caused by a wire break, a burnt-out and therefore high-resistance resistor, a short circuit in a (wire) resistor, etc. Such electrical fault states can be reliably detected by means of the window comparator 200, since when the input voltage U I If the input voltage U is in the interval between the first voltage threshold and the second voltage threshold and therefore no fault condition mentioned above is present, the output terminal 206 of the window comparator 200 switches to the "high" state. I If the voltage is less than the first voltage threshold or greater than the second voltage threshold, the output terminal 206 of the window comparator 200 switches to a “low” state, which indicates the presence of one of the above-mentioned fault conditions.

[0038] The window comparator 200 according to the invention is therefore suitable for various applications within the scope of monitoring electrical signals, for example for measuring physical variables, in particular temperature, humidity, air pressure, path, angle, light, rotation speed or velocity, etc. Due to the minimal power requirement of the window comparator 200, the window comparator is also intended for signal monitoring in mobile, battery-powered devices, in particular handheld power tools and electric tools.

[0039] Particularly preferably, the window comparator 200 can be used in electronics for speed regulation and for sensor monitoring. It can thus be checked whether the electrical connection of the sensor to the downstream electronics is fault-free, i.e. whether the sensor is still electrically "present", in particular without interruptions and / or short circuits, and therefore does not provide any distorted Sensor signals. Wire breaks and / or cold welds of sensors monitored by means of the window comparator 200 can also be detected. In addition, the use of the window comparator 200 in the field of voltage signal monitoring in charging devices and household appliances is suitable. In addition, the window comparator 200 can be used in vacuum cleaners in order to monitor the selected power level, such as weak, medium, strong, in terms of suction power, in order to determine in particular whether the power level selected by the user is also permanently maintained.

[0040] Figure 4 Shows the allocation Figure 3 250 of the input and output voltage profiles of the window comparator 200. The time t in seconds is plotted on the abscissa of the graph 250, while the ordinate shows the voltage U in volts in the range from approximately zero volts to approximately 3.3 volts, for example. Figure 3 The input voltage U of the window comparator I The input voltage U has an approximately wedge-shaped or sawtooth-shaped variation over time t and is shown as a dotted line. Due to its sawtooth characteristic, the input voltage U I The rising speed is relatively high in the interval between t1 and t2 , and the falling speed is relatively low in the range between t3 and t4 .

[0041] The two voltage thresholds U of the window comparator 200 S1 , U S2 and the operating voltage U of the window comparator 200 B Here, the first voltage threshold U S1 is about 1.1 volts, and the second voltage threshold U S2 is at about 2.7 V. The supply voltage or feed voltage of the window comparator 200 is preferably at 3.3 V.

[0042] Until time t1 (illustratively and merely by way of example 0.033 s), the input voltage U I Below the first voltage threshold U S1 And the output voltage U O = 0. At the first time point t1, the input voltage U I Reaching the first voltage threshold U S1 , and the output terminal of the window comparator 200 switches to the "high" state, that is, the output voltage U at the output terminal of the window comparator 200 is O Almost reaches the operating voltage U of the window comparator 200 B At time t2 (illustratively and only by way of example, 0.083 s), the input voltage U I Exceeding the second voltage threshold U S2, whereby the output of the window comparator 200 switches back to the "low" state again, and the output voltage U O At time t3 (illustratively and only exemplarily 0.290 s), the input voltage U I falls below the second voltage threshold U S2 , so that the output terminal of the window comparator 200 switches to the "high" state again, and the output voltage U O The operating voltage value of approximately 3.3 V is reached. At time t4 (illustratively and merely by way of example 0.770 s), the input voltage U at the input of the window comparator 200 is I falls below the first voltage threshold U S1 , whereby the output of the window comparator 200 is set to the "low" state, and an output voltage U of approximately zero volt is obtained at the output of the window comparator O .

[0043] In addition, it can be seen from the graph 250 that the output voltage U O The edge steepness is largely related to the sawtooth input voltage U I The rise and fall speeds are independent, so that for the signal of the subsequent electronic circuit part of the window comparator 200, the output voltage U O The output signal of the window comparator 200 is available.

Claims

1. A window comparator (200), the window comparator (200) having a function for monitoring an input voltage U I A circuit having a discrete, coil-free and capacitor-free structure, characterized in that: The window comparator includes at least three transistors and at least five ohmic resistors. The input terminal (204) of the window comparator (200) is electrically connected to a voltage tap (212) of a first voltage divider (210), and the voltage tap (212) is connected to the base of a single complementary pnp transistor (Q) via a first resistor (R3) and to the base of a first npn transistor (T1) via a second resistor (R4). wherein a voltage tap (222) of the second voltage divider (220) is connected to the collector of the first npn transistor (T1) and to the base of the second npn transistor (T2) via a third resistor (R9), The collector of the second npn transistor (T2) is connected to the collector of the second npn transistor (T2) by means of a fourth resistor (R 10 ) is connected to ground (M), wherein the collector voltage U of the second npn transistor (T2) T2C represents the output voltage U of the window comparator (200) O , wherein the first npn transistor (T1) is configured to I Exceeding a first voltage threshold U in the range of 0.6V to 1.2V S1 When switching, The pnp transistor (Q) is configured to be always on until the input voltage U I Greater than the second voltage threshold U S2 The second voltage threshold corresponds to the operating voltage U of the window comparator (200). B Subtract the base-emitter voltage U of the pnp transistor (Q) QBE , The collector voltage U of the pnp transistor (Q) can be simultaneously adjusted by means of the second npn transistor (T2). QC The current is led to ground (M) via a sixth resistor (R7), wherein the sixth resistor (R7) is arranged between the collector of the pnp transistor (Q) and the collector of the second npn transistor (T2).

2. The window comparator according to claim 1, characterized in that: Among the at least three transistors, at least two transistors are npn transistors (T 1,2 ) and at least one transistor is constructed as a complementary pnp transistor (Q).

3. The window comparator according to claim 1 or 2, characterized in that: A fifth resistor (R6) is arranged between the base and the emitter of the pnp transistor (Q).

4. The window comparator according to claim 1 or 2, characterized in that: The working voltage U of the window comparator (200) B It is in the range between 3.0V and 3.6V.

5. The window comparator according to claim 3, characterized in that: The second npn transistor (T2) is used as a collector voltage U for the first npn transistor (T1) T1C An inverter (230) is provided.

6. The window comparator according to claim 5, characterized in that: The window comparator (200) has a first voltage divider (210) formed by a resistor (R1) on the operating voltage side and a resistor (R2) on the ground side, and an input voltage U to be monitored is applied to a voltage tap (212) of the first voltage divider. I .

7. The window comparator according to claim 6, characterized in that: The window comparator (200) has a second voltage divider (220) which is formed by means of a further resistor (R5) on the operating voltage side and a further resistor (R8) on the ground side.

8. The window comparator according to claim 1 or 2, characterized in that: The first npn transistor (T1) and the second npn transistor (T2) are formed as small signal transistors, and the pnp transistor (Q) is formed as a small signal transistor.

9. The window comparator according to claim 8, characterized in that: The first npn transistor (T1) and the second npn transistor (T2) are formed by small signal transistors of the 2N3904 type.

10. The window comparator according to claim 8, characterized in that The pnp transistor (Q) is formed as a small signal transistor of the 2N3906 type.

11. A handheld power tool, an electric tool, a charging device and / or a domestic appliance having at least one window comparator (200) according to any one of the preceding claims.

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