DE3016108A1 - VOLTAGE MEASURING - Google Patents

Description

Voltage measuring circuit

The invention relates to a voltage measuring circuit, in particular a battery voltage measuring circuit.

The electronic timepieces developed recently and put on the market use a primary battery as a power source. If this battery is so depleted that its output voltage drops below a predetermined voltage level, the electronic watch may malfunction or stall. To avoid this condition, it is necessary to determine the drop in the battery voltage to a predetermined level and at this point in time to replace the battery with a new battery. For this purpose, the circuit of a conventional electronic watch contains a voltage measuring or testing circuit shown, for example, in FIG.

The voltage measuring circuit according to FIG. 1 comprises one with the positive terminal of a battery 4 connected variable or variable resistor 2 and an n-channel field effect transistor (FET) 6, the current path connected between the variable resistor 2 and the negative terminal of the battery 4 (current path) and a gate electrode connected to the positive terminal of the battery 4. Furthermore, this contains

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This circuit is a series combination connected via the battery 4 from resistors 8 and 10. The voltage V1 at the junction between the variable resistor 2 and the field effect transistor 6 and the voltage V2 at the junction between resistors 8 and 10 are applied to the first and second, respectively Input terminal of a comparator 12 applied.

If the output voltage of the battery 4 is sufficiently high as shown in FIG. 2, that at the junction between the Variable resistor 2 and the field effect transistor 6 measured voltage V1 higher than the reference voltage V2 at the junction between the resistors 8 and 10, so that the comparator 12 of FIG. 3 has an output signal of a low level supplies. When the output voltage of battery 4 is below drops a predetermined amount, the measurement voltage V1 becomes due to the decrease in the resistance of the field effect transistor 6 lower than the reference voltage V2. As a result, the comparator 12 according to FIG. 3 provides an output signal high level, which informs the user that the battery 4 is already more depleted is.

In the voltage measuring circuit according to FIG. 1, the initial setting of the measuring voltage V1 is appropriate The size compared to the reference voltage V2 determined by the resistors 8 and 10 is important. Unless the initial setting the measuring voltage V1 is not carried out exactly, the voltage measuring circuit can detect the drop in the output voltage of the Battery 4 below the predetermined level is not high Determine the degree of reliability. For this reason, the setting of the variable resistor 2 must be made by the manufacturer take place.

Usually it is possible to increase the control range (variable range) of the control resistor 2 by increasing the manufacturing

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to reduce the accuracy of the individual circuit elements. In this case, however, it is also necessary set the measurement voltage V1 to a value in the vicinity of the reference voltage V2. Because of this, it has already been proposed to form a plurality of resistors with suitable resistance values on a semiconductor substrate and to combine these resistances with one another when the measurement voltage V1 is initially set. This method, however, where numerous resistors have to be formed on a single semiconductor chip, is also possible with the The disadvantage is that these resistors enlarge the area of the chip and are selectively coupled to one another or must be separated from each other.

The object of the invention is in particular to create a voltage measuring circuit with which the initial state can be adjusted without using a rheostat and has a simple structure.

This object is achieved by the features characterized in the attached patent claim.

In a preferred embodiment, the invention includes Voltage measuring circuit two power supply terminals, a first pn junction circuit, one side of which with the first Power supply terminal is connected and which has at least one pn junction device, one between the other side of the first pn junction circuit and the second power supply terminal switched on first power source circuit, a second pn junction circuit, one side of which is connected to the second power supply terminal, and which has at least one pn junction device, one between the other side of the second pn junction circuit and the first power supply terminal switched on two-

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th power source circuit and a comparator with a first input terminal connected to the junction between the first pn junction circuit and the first current source circuit is connected, as well as with a second input terminal, which is connected to the junction between the second pn junction circuit and connected to the second power source circuit.

The following are preferred embodiments of the invention in comparison to the prior art explained in more detail with reference to the accompanying drawing. Show it:

Fig. 1 is a circuit diagram of a previous battery voltage measuring circuit ,

2 shows a graph of the service life of a battery in relation to the battery voltage;

Fig. 3 is a graphical representation of the level change of a Output signal j of the battery voltage measuring circuit according to FIG. 1,

4 is a circuit diagram of a battery voltage measuring circuit according to the invention,

Fig. 5 is a graph showing the relationship between anode and cathode voltages of two in the circuit according to Fig. 4 provided diodes on the one hand and the battery voltage on the other hand,

FIG. 6 is a graph showing the change in level of one of the circuit of FIG. 4 corresponding to FIG Change in the battery voltage generated output signal,

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7 to 9 circuit diagrams of modified embodiments the voltage measuring circuit according to the invention and

Fig. 10 to 12 circuit diagrams of specific circuit constructions the battery voltage measuring circuit according to FIG. 4.

FIGS. 1 to 3 have already been explained at the beginning.

Fig. 4 illustrates an embodiment of the invention Battery voltage measuring circuit which has a resistor 20 connected to the positive terminal of a battery 22, a diode 24 connected in the forward direction between the resistor 20 and the negative terminal of the battery 22, one to the negative terminal of the battery 22 connected resistor 26 and one in the forward direction between the Resistor 26 and the positive terminal of the battery 22 connected diode 28 comprises. The branch 30 between the Resistor 20 and diode 24 and the junction 32 between resistor 26 and diode 28 are with a first and a second input terminal of a comparator 34 connected.

In the circuit according to FIG. 4, it should be noted that in the series circuit of the resistor 20 and the diode, the cathode of the diode 24 is connected to the negative terminal of the battery 22 so that the anode voltage of this diode 24 can be taken off as a reference voltage V, _Q , while in the series circuit of the diode 28 and the resistor 26, the anode of the diode 28 is connected to the positive terminal of the battery 22, so that the cathode voltage of this diode is applied as the measuring voltage V, p & ^m comparator 34.

In the graph of Fig. 5, the relationships are

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Gen of reference and measurement voltage to the output voltage of the battery 22 represented by the solid and dashed lines. If, as shown in FIG. 5, the output voltage ν _{χ of} the battery 22 is higher than the forward voltage drop V ₅₁ across the diode 24, the reference voltage V, _o remains practically at Vp. When the output voltage ν _{χ of} the battery 22 is higher than that Forward voltage drop Vp across the diode 28, the measurement voltage V, _{2 is} practically equal to a voltage (ν _χ - Vp). This means that when the battery _{voltage ν χ} becomes 2Vp, the reference voltage V30 and the measurement voltage V- ^ _{2 become} practically equal to each other. In other words: the measurement voltage V, ₂ is greater than the reference voltage V ^ ₀ when the battery _{voltage ν χ is} higher than 2Vp, while it becomes smaller than the reference voltage V, _Q when the battery _{voltage ν χ is} below 2Vp.

The battery voltage measuring circuit according to FIG. 4 can thus be designed in such a way that, for example, a relationship V _X q = 2Vp is given when a decrease in the battery voltage ν _χ to a critical _{value ν χ} ~ is determined. While in this case the battery _{voltage ν χ is} higher than the threshold voltage V _xc , ie 2Vp, the measurement voltage is V-, ρ - ^w; J- ^e mentioned - higher than the reference voltage V, q. In this case, the comparator 34 provides an output signal of high level as shown in FIG. When the battery _{voltage V x drops below the critical voltage V xc as} the battery 22 is gradually exhausted, the measurement voltage V, ₂ becomes smaller than the reference voltage V, q, so that the comparator of FIG. 6 generates a low level output signal. By coupling an alarm device (not shown) to the battery voltage measuring circuit in order to apply voltage to this device as a function of the change in level of the output signal of the comparator 34, it is thus possible to reliably determine the correct point in time for the replacement.

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be the battery 22 to determine.

In the circuit according to FIG. 4, the reference voltage V, and the measurement voltage V, p are determined by the electrical properties or characteristics of the diodes 24 and 28 and the output voltage of the battery 22, so that, in contrast to the previous circuit, no variable or regulating resistor is necessary for setting the measuring voltage. In addition, according to the current semiconductor manufacturing processes, diodes with the desired electrical properties can be manufactured with comparatively high precision, so that the desired critical voltage ν _χ ~ can be reliably determined.

FIG. 7 illustrates another embodiment of the battery voltage measuring circuit according to the invention, which corresponds to that of FIG. 4 with the difference that instead of the diodes 24 and 28, Zener diodes 34 and 38 are provided. If in the circuit according to FIG. 7, the Zener voltages of the Zener diodes 44 and 48 _{are denoted by V 21} and Vyp, the reference voltage V ₁ -Q at junction 50 between resistor 20 and Zener diode 44 is practically V ₂₁ , while the measurement voltage V ₁ ^ ^at the junction between the Zener diode 48 and the resistor 26 can be expressed practically as (ν _χ - Vy ₂ ). Thus, when the critical voltage ν _{χ (} -, is set to (Vy ₁ + V ^ p), the comparator 34 can output a low level output signal at a time when the battery _{voltage ν χ} drops to the critical voltage V _xc , and in the same way as in the circuit of FIG. 4, so that the correct time for replacing the battery 22 can be determined.

The further modified battery voltage measuring circuit

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Fig. 8 corresponds to that of Fig. 4 with the difference that instead of the resistors 20 and 26 constant current sources 60 and 66 are provided. This circuit works also in the same way and with the same results as the circuit of FIG. 4.

The further modified embodiment according to FIG. 9 differs differs from the voltage measuring circuit according to FIG. 7 in that that (again) instead of the resistors 20 and 26 constant current sources 70 and 76 are used. Way of working and the effect of this circuit are the same as in the case of the voltage measuring circuit according to FIG. 4.

Figs. 10 to 12 illustrate specific examples of the detailed circuit construction of the battery voltage measuring circuit 4 in these diagrams, the respective resistors 20 and 26 are used in the circuit 4 formed by field effect transistors 120 and 126. The comparators provided are in themselves known, so that they only need to be described briefly.

In the circuit according to FIG. 10, the comparator 34 comprises p-channel and n-channel field effect transistors 130 and 132, respectively, whose respective current paths are connected in series across the battery, as well as p-channel and n-channel field effect transistors 134 and 136, their respective current paths (also) connected in series across the battery 22.

If the battery voltage V "is sufficient in this circuit is high, the field effect transistor 130 receiving the reference voltage at its gate electrode has a high resistance, while the field effect transistor 134 to which the measuring voltage is applied at its gate electrode has a low resistance. The cons

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The value of the field effect transistor 136, the gate electrode of which is connected to the source electrode of the field effect transistor 130, is high, while the resistance value of the field effect transistor 132 connected with its gate electrode to the source electrode of the field effect transistor 134 is low. The output voltage of the comparator 34 is therefore at a high level under these conditions. When the battery voltage ν _χ falls below the critical _{value ν χ (} , the resistance of the field effect transistors 132 and 134 becomes greater than that of the field effect transistors 130 and 136, so that the comparator 34 emits a low level output signal.

In the voltage measuring circuit according to FIG. 11, there is the Comparator 34 composed of p-channel field effect transistors 140 and 142 and n-channel field effect transistors 144 and 146, their respective current paths in series via the battery 22 are connected, and furthermore from p-channel field effect transistors 150 and 152 and n-channel field effect transistors 154 and 156, their respective current routes (also) are connected in series across the battery 22.

Here, if the battery voltage ν _{χ is} sufficiently high, the field effect transistors 152 and 154 have a high and a low resistance value, so that the output signal of the comparator 34 is at a low level. As a result, the field effect transistors 140 and 146 have a low and a high resistance value, respectively, so that a high voltage is applied to the gate electrodes of the field effect transistors 150 and 156. When the battery voltage ν _χ falls below the predetermined magnitude V _xc , the field effect transistors 152 and 154 go to a low and high resistance value, respectively, so that the comparator 34 produces a high level output signal.

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testifies. In this way, with this circuit, if the battery _{voltage ν χ} falls below the critical voltage _{value V xc,} an output signal of high level is generated by which an alarm device (not shown) connected to this circuit is triggered.

In the voltage measuring circuit according to FIG. 12, the comparator 34 comprises one connected to the positive terminal of the battery 22 Constant current source 160, a series combination of a p-channel and an η-channel field effect transistor 162 or 164 and a series combination of a p-channel and an n-channel field effect transistor 166 or 168, where these series combinations between the other terminal of the constant current source 160 and the negative terminal of the battery 22 are switched on. Furthermore, a series combination of a p- and an n-channel field effect transistor170 or 172 and a series combination of a p-channel and an n-channel field effect transistor 174 and 176, respectively, are provided, with these series combinations are connected via the battery 22. The gate electrode of the field effect transistor 172 is with the gate and drain electrodes of the field effect transistor 164 and with the gate electrode of the field effect transistor 168 connected while the gate electrode of the field effect transistor 176 to the drain electrode of the field effect transistor 168 and the gate electrode of the field effect transistor 174 is connected to the gate and source electrodes of the field effect transistor 170.

If the battery voltage Vy is sufficiently high, is at the gate electrode of the field effect transistor 166 a high voltage, so that the field effect transistor 166 has a higher resistance than the field effect transistor 162. As a result, high or low voltages are applied to the relevant gate electrodes of the field

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Effect transistors 172 and 176 applied, which consequently have a high and a low resistance value, so that the comparator 34 emits an output signal of high level. When the battery _{voltage ν χ} drops below the critical voltage V _xc , the resistance of the field effect transistor 162 is greater than that of the field effect transistor 166. As a result, the field effect transistors 172 and 176 go to a high and a low resistance value, so that the comparator has a signal low Levels generated.

As can be seen from the circuit diagrams of FIGS. 10 to 12, the voltage measuring circuit according to the invention can be formed on a single chip, while the diodes 24 and 28 can be produced in such a way that they provide the critical voltage ν for setting a desired or intended magnitude of the critical voltage _χ ρ have the required properties.

Although the invention has been described above in connection with preferred embodiments, it is in no way restricted thereto. While, for example, in the embodiments according to FIGS. 4 and 8, two diodes 24 and for setting the critical voltage ν _{χ (} -, are provided, these diodes 24 and 28 can each be replaced by a combination of diodes connected in series Zener diodes 44 and 48 according to FIGS. 7 and 9 are each replaced by a series connection of Zener diodes.

Furthermore, it is possible for each of the diodes 24 and 28 in the embodiments according to FIGS. 4 and 8 to be a Zener diode and each of the resistors 20 and 26 in the circuits of Figs. 4 and 7 by a constant current source substitute.

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Claims (1)

Henkel, Kern, Feiler & Haiuei patent attorneys Möhlstrasse 37 D-8000 Munich TOKYO SHIBAURA DENKI KABUSHIKI KAISHA, Te'ffl? 0529802 h'rlfd Kawasaki-shi, Japan Telegrams: ellipsoid 55Pi56-3 / wa April 25, 1980 PATENT CLAIM Voltage measuring circuit with two power supply terminals, one connected between the two power supply terminals first voltage generating circuit for supplying an output voltage which is dependent on one between the two Voltage applied to the power supply terminals varies, a second voltage generating circuit connected between these two terminals for generating a voltage with a practically fixed level and a comparator circuit for comparison the output voltages of the two voltage generation circuits, characterized in that the first voltage generating circuit (26; 28; 48; 66; 76) has a first pn junction circuit (28; 48) having a terminal connected to the first power supply terminal and at least one pn junction device and a first current source circuit (26; 66; 76) connected between the other terminal of the first pn junction circuit (28; 48) and the second power supply terminal is switched on and an output voltage at the junction between the first pn junction circuit (28; 48) and the first Power source circuit (26; 66; 76) generated, and that the second - 2 03 0 044/089 8 Voltage generating circuit (20; 24; 44; 6O; 70) a second pn junction circuit (24; 44) with one with the second Power supply terminal connected terminal and with at least one pn junction device and a second Current source circuit (20; 60; 70), which between the other terminal of the second pn junction circuit (24; 44) and the first power supply terminal is on and an output voltage at the junction between the second pn junction circuit (24; 44) and the second current source circuit (20; 60; 70) to the comparator circuit (34). 0300U / 0898