Method for obtaining a deep discharge protection for a rechargeable battery, and circuit arrangement to perform the method.

0001The invention relates to a method according to the preamble of patent claim 1.

0002A method or a circuit arrangement of the type mentioned at the outset are essentially used or used in portable lights with rechargeable batteries.

0003Portable lights that are powered by rechargeable batteries are equipped with deep discharge protection. The purpose of such a measure is to protect the nickel-cadmium or lead accumulators or batteries from damaging deep discharge. Such a deep discharge occurs when battery-specific voltage values ​​are undershot during a discharge. The prior art sees deep discharge protection circuits which separate the consumer, which can be an incandescent lamp, for example, from the battery when a lower voltage limit is still reached. A restart lock prevents the consumer from restarting when the battery recovers and when the battery voltage rises. The deep discharge protection is reset by switching the lamp off and on again.

0004The disadvantage of known deep discharge protection circuits or methods is that the consumer is switched off abruptly. This protects the battery, but the disadvantages when operating in practice are obvious. This is the case when a portable lamp is used to illuminate, for example, danger spots and is switched off when the lower battery voltage value is reached. This stops the lighting of danger spots and important repair work can no longer be continued. Luminaires without deep discharge protection have one advantage: The user sees from the increasingly weaker luminous flux of the lamp that the battery capacity is slowly being exhausted and can take appropriate measures, for example leaving the danger zone, interrupting the repair work and the like. The disadvantage is that the batteries may be up to be operated below the deep discharge limit, which then results in damage up to the total failure of the battery. Lead-acid batteries, which perform significantly worse in deep-discharge behavior than nickel-cadmium batteries, are discharged to a voltage value of less than 1 volt / cell after about 10 cycles and are therefore unusable.

0005The object of the invention is to provide a method and a circuit arrangement of the type mentioned at the outset in which the disadvantages mentioned above are avoided. In particular, it should be achieved that until the final switch-off to achieve deep discharge protection, a signaling of the declining battery capacity is generated.

0006This object is achieved by the characterizing features of claim 1.

0007Further advantageous embodiments of the invention can be found in claim 2.

0008The invention thus consists in that after falling below a predetermined first value of the battery voltage, the supply voltage is switched on and off in a clocked manner, the mean voltage value at the consumer being reduced. If an incandescent lamp is used, the brightness of the incandescent lamp is reduced and the user can see the reduction in the battery capacity. If a second predetermined value is undershot, ie if there is a risk of deep discharge, then the entire battery current (consumer) is switched off.

0009Due to the pulse-length modulated clock operation in the range between the first and the second limit value depending on the battery voltage, the brightness of the lamp is reduced continuously until the switch-off time; this also helps the user to leave the danger point in good time or to stop any repair work; an unexpected turn-off of the lamp will then no longer have to be feared.

0010The circuit arrangement with which the method according to the invention is carried out can be gathered from the characterizing features of claim 3.

0011Further advantageous refinements and improvements to the circuit arrangement can be found in the further subclaims.

0012Based on the drawing, in which an embodiment of the invention is shown, the invention and further advantageous refinements and improvements are to be explained and described in more detail.

0013It shows:<ul id="ul0001" list-style="none"><li>Figure 1: A schematic block diagram representation of the circuit arrangement according to the invention,</li><li>Figure 2: a detailed representation of the circuit arrangement according to Figures 1 and</li><li>Figure 3: A graphic representation of the luminous flux over the battery voltage.</li></ul>

0014An incandescent lamp h1 is located in an incandescent lamp circuit 10, which is supplied with energy by a battery 11. In the incandescent lamp circuit 10 there is a first switch S1 in front of the incandescent lamp h1; A connecting terminal 12 of a second switch S2 is connected between the first switch S1 and the incandescent lamp, and a third switch S3 is connected in the incandescent lamp circuit 10 behind the incandescent lamp h1. Between the incandescent lamp circuit 10 and the connecting terminal 12, a leg of a differentiating element is connected, which is formed from a capacitor C and a resistor R; the other leg of the differentiator is connected to the negative pole 13 of the battery. The positive pole of the battery has the reference number 14. The other terminal 15 of the switch is connected to a line 16 which is connected to a reference circuit 17; the circuit arrangement also has a threshold switch 18, an oscillator 19 and a comparator circuit 20. Via the differentiator R / C, the threshold switch 18 is given a voltage pulse via a line 21 connected between the capacitor C and the resistor R. As a result, the threshold switch 18 closes the electronic switch S2 via the line 22 shown in broken lines. As a result, the battery voltage is identified on line 16 as U_H on. The threshold switch compares the voltage output by the reference circuit 17 with the battery voltage U_H, and then whom U_H is greater than the reference voltage U_Ref, the threshold switch on line 22 gives the "on" signal to switch S2, which then remains closed. The circuit thus supplies itself (self-holding circuit).

0015The oscillator 19 generates a triangular voltage U_Dthat from the reference voltage U_Ref controlled a maximum amplitude U_Ref + U_Dand an amplitude lowest value U_Ref - U_DHas. The triangular voltage U_D is from the comparator with the battery voltage U_H compared. Is U_H> U_Ref + U_Dthen the electronic switch S₃ is continuously switched on via the further dash-dotted line 23 and the incandescent lamp H₁ burns. If the battery voltage U drops during the discharge_batt (corresponds to U_H), so when the threshold is undershot U_Ref + U_Dthe switch S₃ is no longer turned on, but periodically with a clock ratio that corresponds to the instantaneous value of the battery voltage. As a result, the mean voltage value on the lamp H 1 is reduced; the luminous flux decreases. Appropriate dimensioning means that the luminous flux can decrease to such an extent that when the deep discharge protection limit value is reached it is only a few percent of the nominal luminous flux. The deep discharge protection is formed from the interaction of the reference circuit arrangement, the threshold switch and the switch S₂. If the battery voltage reaches the value U_H small U_Ref, then the threshold switch responds and opens the switch S₂, so that the voltage U_H disappears and the battery current drops to a few milliamps towards zero, since the lamp h1 goes out and is not switched on again.

0016Reference is now made to Figure 2. The switch S 1 is closed. Characterized flows through the differentiator, which consists of a series connection of resistors R₁, R₂, a diode V2 and a capacitor C₁ and is connected in parallel to the series connection of battery 11 and the switch S₁, a short time a current. Between the two resistors R₁ and R₂, the base of a transistor V₁ is connected, and the voltage drop across the resistor R₁ controls the base of the transistor V₁, so that it goes into the conductive state. As a result, the voltage U_H given. Between the line 16 and the negative pole of the battery 11 are a further resistor R₆ and a Zener diode V₆, which two components form the reference circuit and thus the reference voltage U_Ref form. Parallel to the resistor R₆ and the diode V₆ is a voltage divider consisting of two resistors R₅ and R₉; in a comparator V₅, the voltage divided by the two resistors R₅ and R mit with the reference voltage U_Ref compared; the minus input lies between the resistor R₆ and the diode V₆. The output of the comparator is connected to the base of a transistor V₄ and between the collector of transistor V₁ and the base of transistor V₄ is a resistor R Widerstand. If the reference value U_Ref is greater than the voltage divider value R₅ / R₉, then the transistor V₄ is controlled by the comparator V₅ in the conductive state and via resistors R₁, R₂ and diode V₂, the transistor V₁ remains conductive; the circuit supplies itself (self-holding circuit).

0017The oscillator circuit is formed from a resistor R₁₀, one leg of which is connected between the Zener diode and the resistor R₆, a resistor R₁₁ which is in series with the resistor R₁₀, a resistor R₇ which is in series with the resistor R₁₁ and whose another leg is connected to line 16, a resistor R₁₂, which is connected in parallel to the minus input and the output of a comparator V₅ʹ, whose positive input is connected between the resistors R₁₀ and R₁₁ and whose output is also switched on between the resistors R₇ and R₁₁, and a capacitance C₃, which lies between the minus input of the comparator V₅ʹ and the minus pole of the battery. The resistor R₁₂ is with one leg between the minus connection of the comparator V₅ʹ and the capacitance C₃ and with the other leg at the output of the comparator V₅ʹ. This oscillator circuit generates a triangular voltage U_D a capacity which is the maximum of<maths id="math0001"><img file="EP0240883A2_D0001.tif" /></maths> and a low of<maths id="math0002"><img file="EP0240883A2_D0002.tif" /></maths> owns. The frequency of the oscillator is determined by the resistors R₁₂, R₁₀, R₁₁ and R₇ and the capacitance C₃ and is due to appropriate dimensioning of these parts between 100 to 500 Hertz. This triangular voltage U_D is fed to the positive input of a further comparator V₅ʺ; the negative connection of the comparator V₅ʺ is at the center tap of a potentiometer R₁₃, which is connected to the line U via further resistors R₈ and R₁₄_H and on the other hand is connected to the negative pole of the battery. This triangular voltage U_D is from the comparator V₅ʺ on the voltage divider R₈, R₁₃, R₁₄ with the voltage U_H compared. Is this divided voltage from U_H above the maximum value of U_DThen the base of a transistor V₇ is driven via a voltage divider at the output of the comparator V₅ʺ from the two resistors R₁₅ and R₁₆, so that the transistor V₇, whose emitter is connected to line 16, is conductive and via a voltage divider in the collector circuit Resistors R₁₇ and R₁₈ the switching transistor V₈ continuously conductive; the base of the transistor is connected to the collector V₇ via the resistor R₁₆. Parallel to the base-emitter path of the transistor V₈ is the resistor R₁₈. A capacitance C₄ lies parallel to the basic collector path. If the transistor V₈ is conductive, the light bulb h1 burns. If the battery voltage drops in the course of the discharge, the voltage U also drops_H from. If this voltage at the inverting input of the comparator V₅ʺ falls below the maximum value of U_D, then a pulse length modulated signal appears at the output of the comparator V₅ʺ. The two transistors V₇ and V₈ are now operated clocked. The clock ratio depends on U_H and determines the direct current average by the light bulb h1. The luminous flux increases disproportionately as the voltage U decreases_H or U_batt from.

0018If the battery voltage drops further, then the voltage at the non-inverting input of the comparator V₅ also drops. If this falls below the value of U_Ref, then the comparator V₅ switches to zero and the transistor V₄ blocks; so that the transistor V₁ is driven into the blocking state via the diode V₂, the resistor and the resistor R₂. The circuit thereby takes the supply voltage U_H, which creates deep discharge protection with a restart lock. The entire circuit can only be reactivated by opening and reclosing the switch S 1.

0019The following is achieved by the method according to the invention or by the circuit arrangement according to the invention:

0020If the battery voltage is high enough, the lamp is switched on continuously. If the cell voltage, for example of a nickel-cadmium battery, drops to a value of less than 1 volt / cell during the discharge, the luminous flux of the incandescent lamp is reduced disproportionately. This shows the user that the battery capacity is at an end. By reducing the lamp current, the remaining capacity is used to extend the burning time. Shortly before the deep discharge protection responds, the luminous flux has such small values ​​that the user may switch off the lamp himself.

0021In a special embodiment of a battery with four nickel-cadmium cells, the luminous flux is reduced when the battery voltage is less than 4 volts, ie 1 volt / cell. At 0.9 volts / cell the luminous flux is still approx. 5% and at this value, ie at 3.6 volts battery voltage, the deep discharge protection responds. Reference is made here to Figure 3. The luminous flux curve of a 4.8 volt, 5 watt incandescent lamp, depending on the battery voltage, can be seen in full. The dotted line runs exactly on the solid line up to a battery voltage of 3.9 volts. If the battery voltage drops further, ie, the capacity decreases, the current through the consumer drops disproportionately due to the circuit arrangement according to the invention up to the value of 3.6 volt battery voltage. At this voltage, the deep discharge protection responds and disconnects the lamp h1 from the battery.