DE4338183A1 - Circuit for controlling a charging current circuit for an accumulator - Google Patents

Description

The invention relates to a circuit for controlling a Charging current circuit for an accumulator according to the Oberbe handle of claim 1.

In Figs. 1 and 2, the charge and discharge are a nickel-cadmium battery or a nickel-Me tall-hydride storage battery shown, that is, the gate voltage or time Akkumula cell voltage on the charging or discharging. The charging curve shows a steep increase in the battery voltage or battery cell voltage at the start of charging up to a plateau, where there is only a slight increase in the voltage over time. This is followed by a steep climb up to a maximum. Due to temperature increases due to the battery being overcharged, the battery voltage or battery cell voltage drops again after the maximum has been reached. The full charge of the battery is reached at the maximum point of the battery voltage. However, the maximum accumulator voltage is not a fixed value, but rather the maximum value of the voltage-charging time curve, which depends, inter alia, on the parameters “charging current” and “accumulator temperature” and the aging state of the accumulator.

The voltage level of the charging curve is clearly temperature-dependent pending with a negative temperature coefficient. With increasing charging current shifts the charging curve higher voltage values in the direction of the entered Arrow I, while with increasing battery temperature Cell voltage of the battery is lowered, d. H. the Charging curve has a negative temperature coefficient according to the direction of the arrow T entered.

The discharge curve of an accumulator shown in FIG. 2 shows a relatively steep drop in the accumulator voltage up to a plateau, where there is only a slight voltage drop with the discharge time. The plateau is followed by a steep drop in battery voltage down to zero voltage. As the discharge current increases, the discharge curve shifts in the direction of the arrow. Compared to the voltage level of the charging curve, the discharge curve shows a significantly lower temperature dependency.

If an accumulator is overcharged, its life becomes duration significantly reduced. To overcharge the accumulator To avoid gate cells, it is common to charge Nickel-cadmium and nickel-metal hydride cells with one to make low constant current, but thereby the charging process for a very long time, namely approx. 10 to 16 hours, at Nickel metal hydride cells last over 20 hours.

To shorten the charging time, you can switch off the charging process when the temperature rises, for example. To shorten the charging time, however, the property of the charging curve shown in FIG. 1 is mostly used by charging with a relatively high current before the maximum voltage is reached, thereby shortening the charging process and switching off the charging current at a specific cell voltage by means of a threshold switch or the charging process ended. However, the setting of a threshold value for the end of the charging process does not take into account that the maximum cell voltage changes in a relatively large range depending on the remaining capacity and the recovery phase between a discharge and charging of the battery, as well as by the aging process of the cells. Therefore, if a lower but safe threshold value is selected, the maximum capacity of the accumulator is not exhausted, while if a higher threshold value is selected there is the risk of overcharging and thus damage to the accumulator cells.

The optimal operation of an accumulator is cyclical Operation in which the accumulator is just below its span maximum loaded and then again by a possible as much as possible is unloaded, etc. make sure that the battery is not over-discharged becomes.

DE 36 26 534 A1 describes a charger for nickel kadmi um cells with a constant current source for the charging current known to switch off and stop charging a peak detector in connection with a trigger or comparator circuit is used. The trigger scarf tion is on the input side with both the output of the peak de tector as well as the accumulator cell voltage beats and switches between at a voltage difference the two input signals and ends the charging process via a shutdown logic.

As a trigger circuit in the known charger Schmitt trigger used, its transmission characteristic a switching hysteresis in the form of a voltage difference between the switch-on and the switch-off level. With the help of the Schmitt trigger, the battery is charged current abge when a certain voltage level is reached switches. As soon as the accumulator voltage by energy ent taking or self-discharge again under one by the Hysteresis of the Schmitt trigger defined switch-on level decreases, the battery charging current is switched on again.  

Because of the strong temperature dependence of the charging curve and the only slight temperature dependence of the discharge curve ve described above with reference to FIGS . 1 and 2, it is known to provide a temperature-dependent resistor at the input of the Schmitt trigger, with the aid of which the switch-off voltage is adapted to the temperature behavior of the battery becomes. However, due to the fixed setting of the switching hysteresis of the Schmitt trigger, the reclosure voltage has the same temperature dependency as the opening voltage.

Another problem is that in many Cases the switch-on point of the accumulator charging current one assign certain residual energy content of the battery would like to. In the known circuit arrangement with a fixed switching hysteresis between the switch-on and the The switch-off point determines the charging current, whereby the differences difference between the switch-off and the switch-on voltage is constant.

Because of the strong non-linearity of the charging and discharging curve ve according to FIGS. 1 and 2 and an adjustment of the switch-off point of the accumulator charging current to the temperature behavior of the accumulator, so that the accumulator is always fully charged but never overcharged and the determination of the restart point at a residual energy content of approx. 20% to 70% of the accumulator in the flat plateau area of the discharge curve, the residual energy content of the accumulator fluctuates very strongly if the restart voltage is changed to the same extent as the switch-off voltage due to a constant switching hysteresis. This problem is further aggravated by the fact that the discharge curve has a significantly lower temperature coefficient than the charge curve in connection with FIG. 2.

The object of the present invention is a circuit for controlling a charging current circuit for an accumulator to create gate depending on the battery voltage at which the charging current is independent of the accumulator gate temperature at a certain residual energy content of the Battery is turned on again.

This object is achieved by the characterizing Feature of claim 1 solved.

The solution according to the invention enables a largely tem temperature-independent restart of the charging current at a certain residual energy content of the battery by the switch-on voltage is independent of the switch-off voltage adjustable and the temperature behavior of the discharge curve is customizable.

An advantageous embodiment of the invention Solution is characterized in that the switching hysteresis of the first Schmitt trigger within the switching hysteresis of the second Schmitt trigger. This ensures represents the switch-on level of the second Schmitt trigger the maximum battery voltage, d. H. switching off the Accumulator charging current determined during the start-up and  Switch-off level of the first Schmitt trigger in the whole Voltage hysteresis range of the second Schmitt trigger lies.

According to a further feature of the solution according to the invention determines the switch-on level of the second Schmitt trigger the voltage at which the charging current circuit for Stromver supply of the accumulator is switched off and the off switching level of the first Schmitt trigger the voltage at the the charging current circuit for powering the accumulator tors is turned on.

According to a further advantageous embodiment of the inventions The solution according to the invention is the exit of the first Schmitt trig gers through a resistor to the input of the second Schmitt triggers connected in such a way that the first Schmitt Trigger when switching off the input of the second Schmitt Triggers so out of tune that it also switches off.

As a result of the coupling of the two Schmitt triggers using of a resistor become the input divider resistors the second when switching off the first Schmitt trigger like this strongly disgruntled that the second Schmitt trigger too falls back to the off state. So that determines first Schmitt trigger to restart the accumulator gate charging current by releasing the to the output of the second Schmitt-Triggers connected charging current switch. The Coupling of the two Schmitt triggers using a resistor  that is only an advantageous solution. It is also other coupling elements for connecting the two Schmitt Trigger can be used.

Too strong a coupling between the two Schmitt triggers to prevent, otherwise the switching on of the first Schmitt trigger to switch on the second Schmitt trigger would lead, so that the means of the second Schmitt Triggers set maximum battery voltage According to another characteristic, more is achieved Invention the difference in the switch-off levels of both Schmitt Trigger less than the difference from their turn on level set.

The temperature dependence of the maximum accumulator span during the loading process or to determine the remaining capacity to turn on the battery charging current, but also the temperature dependence of those used in the circuit Components are made using a temperature-dependent resistor of the Schmitt trigger at the input is taken into account. With the Arrangement of a temperature-dependent resistor in the Input divider resistances of the two Schmitt triggers an adaptation of the Schmitt trigger temperature response to the Temperature response of the batteries made and thus a Temperature compensation for each of the two Schmitt triggers aims.  

In a circuit variant, only one common tempe Temperature-dependent resistance for temperature compensation both Schmitt triggers used, with the help of which the Re reference voltage for the one Schmitt trigger through direct re coupling is greatly affected while on the other Schmitt trigger is weaker. this will achieved in that the reference voltage for the second Schmitt trigger using a voltage divider over the tem temperature-dependent resistance is tapped.

Another advantageous embodiment of the invention ßen solution is characterized in that between the Ak accumulator and the control circuit a controllable scarf ter is arranged, the control connection to the voltage Source connected to supply the battery in this way is that the drive circuit only when the Switch on charging current circuit to the supply voltage source is tested.

This embodiment of the solution according to the invention provides sure that the control circuit for the charging current scarf device is only switched on when the charging current switch device is connected to a supply voltage network, see above that only in this case energy from the control circuit is consumed. This turns the energy supply into a control circuit ensured without in addition to self-ent charge the battery an energy loss due to the control circuit and thus an increase in charge-discharge cycles frequency and thus a lifetime reduction of the accumulator  tors takes place. The accumulator is used to monitor the accumulator emulator voltage through the charging electronics no energy ent pulled.

As long as no charging current flows, the energy supply becomes Control circuit by means of a parallel to the switching transistor stor the charging current circuit arranged resistor be provided, according to a further feature of the invention is dimensioned so that just as much current flows as the An control circuit consumed.

Based on an exemplary embodiment shown in the drawing The idea on which the invention is based is intended to play are explained in more detail. Show it:

Figure 1 is a schematic representation of a charging curve of a nickel-cadmium or nickel-metal-hybrid battery.

Fig. 2 is a schematic representation of an accumulator discharge curve;

Fig. 3 is a schematic block diagram of the control and charging current circuit according to the Invention with two Schmitt triggers;

Fig. 4 is a schematic block diagram of the control and charging current circuit with a coupling element for switching level detuning

Fig. 5 is a schematic representation of the accumulator voltage over time in a charge and discharge cycle with a coupling between the two Schmitt triggers of a discharge current control circuit;

Fig. 6 is a detailed circuit diagram of the circuit shown in FIGS. 3 and 4 with two temperature-dependent resistors in the inputs of the Schmitt trigger and

Fig. 7 is a detailed representation of the circuit of FIG. 6 with a common temperature dependent resistor in the inputs of the two Schmitt triggers.

Fig. 3 shows a schematic block diagram of the control and charging current circuit for an accumulator 1 , which can be connected to a feeding AC network or - with appropriate polarity - to a DC network U via a charging current circuit LS via a rectifier ter G. The switching on and off of the charging current flow from the AC or DC network U into the accumulator 1 is determined by the charging current circuit LS.

The charging current circuit LS is enabled or blocked by means of a control circuit which has two Schmitt triggers ST1 and ST2 which can be connected to the accumulator 1 via a switch S. The switch S is arranged so that it only connects the control circuit to the accumulator 1 when the circuit arrangement is connected to the DC or AC voltage supply U is. The outputs of the two Schmitt triggers ST1 and ST2 are connected to the inputs of a logic circuit or a coupling element.

In the embodiment shown in Fig. 3, the connection of the outputs of the two Schmitt triggers is made via a NAND gate NG, the output of which is connected to the control terminal of the charging current circuit LS. By linking the output signals of the two Schmitt triggers ST1 and ST2, the charging current circuit LS is always switched off when the outputs of both Schmitt triggers ST1 and ST2 emit an output signal.

Fig. 4 shows a schematic block diagram of a preferred embodiment of the control and charging current circuit device with a coupling element for switching level detuning, in which instead of a NAND gate NG shown in FIG. 3, a switching element is provided, the input side with the output of the first Schmitt trigger ST1 is connected, and controls the second Schmitt trigger ST2 on the output side. With the aid of the coupling element, the second Schmitt trigger ST2 is influenced by the first Schmitt trigger ST1, which would switch off at a lower voltage without being influenced by the first Schmitt trigger ST1.

However, the coupling element makes the second Schmitt trig ger ST2 so out of tune that when the first Schmitt trigger ST1 is forced to turn off, d. H. the second Schmitt trigger ST2 is then always in the switched off state when the first Schmitt trigger ST1 is switched off. These relationships are set out below based on the schematic representation of the accumulator chip voltage over time for a charge and discharge cycle with a coupling between the two Schmitt triggers Discharge current control circuit will be explained in more detail.

Fig. 5 shows a temporal representation of the accumulator voltage, the switching behavior of the Schmitt trigger ST1 and ST2 and the resulting charging current to explain the operation of the circuit shown in FIG. 4, wherein the switching hysteresis of the first Schmitt trigger ST1 is set that the switch-on level is lower than the switch-on level of the second Schmitt trigger ST2, while the switch-off level of the second Schmitt trigger ST2 is set at a lower voltage level than the switch-off level of the first Schmitt trigger ST1. The hysteresis of the second Schmitt trigger ST2 is thus selected such that the switch-on and switch-off level of the first Schmitt trigger ST1 lies in the voltage hysteresis range of the second Schmitt trigger ST2.

The following numerical example is intended to illustrate the relationships shown in FIG. 5.

Assuming that the maximum charge voltage of the accumulator tors 4 volts and the minimum discharge voltage of the accumulator tors is 2 volts, the first Schmitt trigger switches For example, ST1 turns on at 3 volts and off at 2 volts. Of the The switching level of the second Schmitt trigger ST2 is then like this set that when the first Schmitt trigger is switched off ST1 the second Schmitt trigger ST2 at 5 volts on and at Turns off 2.5 volts. When the first is switched on Schmitt trigger ST1 switches the second Schmitt trigger ST2 at 4 volts on and at 1.5 volts off, d. H. there is a Voltage level shift of the switching level of the second Schmitt-Triggers ST2 through the coupling via the coupling element ment.

These values, which are assumed as examples, result starting from an empty accumulator the following function wise.

Both Schmitt triggers ST1 and ST2 are in the out switched state, so that when the switching train is switched on sistor charging current flows into the accumulator and the accumulator mulator voltage rises. With a battery voltage of 3 volts (U 1) turns the first Schmitt trigger ST1 on and detunes the second Schmitt trigger ST2 so that his switch-on level drops from 5 volts (U₃) to 4 volts (U₂). Since the first Schmitt trigger ST1 has no direct influence on the switching transistor, the accumulator span increases on.  

The second Schmitt trigger ST2 switches on an accumulator gate voltage of 4 volts (U₂), so that the switching transi stor locked and the charging current is switched off. It follows the discharge phase of the accumulator, in which the first Schmitt Trigger ST1 at 2 volts (U₄) as the first of the two Schmitt trigger turns off, as long as the first Schmitt trigger ST1 is in the switched-on state, the switch-off level of the second Schmitt trigger ST2 is low ger, namely 1.5 volts (U₅).

By switching off the first Schmitt trigger ST1 but the switch-off level of the second Schmitt trigger ST2 is like this detuned that he is above the current battery voltage of 2 volts, namely 2.5 volts. Therefore, the second Schmitt trigger ST2 immediately off, because the momen tane battery voltage is lower than this switch off gel is. The charging current is thus switched on again Battery voltage rises and the prescribed process expires again.

Fig. 5 illustrates that the difference between the switch-off thresholds of both Schmitt triggers ST1 and ST2 is less than the difference between the two switch-on thresholds, which relates to the detailed circuit arrangement according to FIGS . 6 and 7 for the coupling of both Schmitt triggers via a coupling resistor is important.

Fig. 6 shows a detailed circuit diagram of the block circuit device according to FIG. 4, the blocks shown in FIG. 4 in the detailed circuit arrangement according to FIG. 6 being framed by dash-dotted lines.

In the circuit arrangement according to FIG. 6, the given down-transformed mains DC or mains alternating voltage U is rectified via a rectifier bridge G with the diodes 41 to 44 . In parallel to the DC voltage clamps of the rectifier bridge G, the series connection of the accumulator 1 is connected to the load connections of a transistor 2 , which is part of the charging current circuit LS. The charging current circuit LS also has a first control transistor 3 , the collector of which is connected to the accumulator 1 and whose emitter is connected to the base of the switching transistor 2 via a resistor 6 , in parallel with its base-emitter path a resistor 7 is switched .

The base of the first control transistor 3 is connected via a resistor 5 to the collector of a second control transistor 4 , the emitter of which is connected to the output of the switch S, while the base of the second control transistor 4 is connected via a resistor 8 to the output of the drive circuit connected is.

The switch S to connect the driving circuit to the battery voltage only for power coupling of the circuit arrangement of FIG. 5 has a transistor 30 having its emitter connected to the accumulator 1 and its collector connected to the supply line for the drive circuit-jointed, while the base of transistor 30 is connected via a resistor 33 to the connection of a series connection of a capacitor 31 to a diode 32 , which are connected in parallel to a diode 42 of the rectifier bridge GB with cathode-side connection of the diode 32 to an AC voltage connection of the rectifier bridge GB.

The diode 32 ensures that a base current is only delivered to the transistor 30 when the circuit is connected to the supplying AC or DC network. The capacitor 31 serves to buffer the base current of the transistor 30 so that the transistor 30 is continuously controlled during the connection of the circuit to the supplying direct or alternating voltage network. The drive circuit is then coupled to the accumulator 1 via the small residual resistance of the transistor 30 .

The first Schmitt trigger ST1 of the drive circuit is formed from two transistors 11 , 12 whose emitters are connected to reference potential, while their collectors are connected via resistors 13 , 15 to the voltage supply line, ie the output of the switch S. The base of the one transistor 11 is additionally connected to the collector of the other transistor 12 , while the base of the transistor 12 is connected to the input E1 and via a resistor 14 to the output A1 of the first Schmitt trigger ST1, which is through the collector of the other transistor 11 is formed.

At the input of the first Schmitt trigger ST1, a voltage divider network is connected, the stands from the series circuit of a voltage-dependent resistor 17 with a parallel resistor 16 and two further opposites 18 , 19 is formed, the connection of the two resistors 18 , 19 den Input E1 of the first Schmitt trigger ST1 forms.

The structure of the second Schmitt trigger ST2 corresponds to that of the first Schmitt trigger ST1 and consists of two transistors 21 , 22 with collector resistors 23 , 25 and a resistor 24 arranged between the input E2 and the output A2 of the second Schmitt trigger ST2. The voltage divider network of the second Schmitt trigger ST2 consists of resistors 26 , 28 , 29 connected in series with a voltage-dependent resistor 27 connected in parallel with the resistor 26 .

The temperature-dependent resistors 17 , 27 of the two Schmitt triggers ST1, ST2 have a positive temperature coefficient. The resistors 16 , 26 connected in parallel with the temperature-dependent resistors 17 , 27 serve to linearize the temperature response.

The two Schmitt triggers ST1 and ST2 are coupled to one another via a coupling resistor 9 , so that the first Schmitt trigger ST1 influences the switching levels of the second Schmitt trigger ST2 and the output of the second Schmitt trigger ST2 behaves in such a way that it can only control the switching transistor 2 via the transistor 4 serving as an impedance converter and the transistor 3 serving as an inverter.

A network consisting of a transistor 50 , a resistor 51 and a capacitor 53 is used for the switch-on delay and prevents the charging current from being switched on every time the circuit is coupled to the DC or AC voltage supply, even if the battery voltage is has not yet reached the lower switching threshold. In this network circuit, the emitter of the transistor 50 is connected to the voltage supply line and its collector is connected via a resistor 52 to the input E2 of the second Schmitt trigger ST2, while its base is connected to the connection of the resistor 51 to the capacitor 53 , which are connected to the voltage connections of the control circuit.

A parallel to the collector-emitter path of the Schalttransi stors 2 resistor 10 ensures the Stromversor supply of the drive circuit ensures as long as the second control transistor 4 is blocked.

The detailed circuit arrangement shown in FIG. 7 is constructed in the same manner as the circuit arrangement according to FIG. 6 described above . It has the same function as the circuit arrangement according to FIG. 6 and serves to fulfill the same task. The same components are denoted by the same reference numerals, so that reference can be made to the description of the circuit according to FIG. 6.

The only difference of the circuit arrangement of FIG. 7 compared to that of FIG. 6 is that only a temperature-dependent resistor is provided, which is provided in the voltage divider network in the input of the first Schmitt trigger ST1, while the second Schmitt trigger ST2 to a voltage divider formed from the resistors 16 and 26 in parallel to the temperature-dependent opposing stand 17 is connected. By a suitable choice of the resistance values of the resistors 26 to 29 at the input of the second Schmitt trigger ST2 and the resistors 16 to 19 at the input of the first Schmitt trigger ST1, a temperature response of the switching levels of both Schmitt triggers ST1 and ST2 is realized which corresponds to the desired one comes close enough.

Both circuit arrangements described above according to FIGS. 6 and 7 enable a mutually independent he ge setting switch-on and switch-off level of the charge current circuit and adapted to the temperature behavior of the discharge control of the battery charging circuit. This ensures that the charging current switches on again independently of the temperature at a certain residual energy content, while at the same time there is a maximum charging adapted to the temperature response of the battery.

To reduce the energy consumption of the control circuit when not connected to a direct or alternating voltage the drive circuit becomes the control circuit activated only when the circuit to the feeding end AC and DC voltage network is connected so that an energy loss of the accumulator essentially only through the self-discharge of the accumulator.

Claims (12)

1. Circuit for controlling a charging current circuit for an accumulator as a function of the accumulator voltage, characterized by two coupled Schmitt triggers (ST1, ST2) that can be connected to the accumulator voltage and have switching hysteresis that can be set independently of one another. 2. Circuit according to claim 1, characterized in that the switching hysteresis of the first Schmitt trigger (ST1) inside half the switching hysteresis of the second Schmitt trigger (ST2) lies. 3. A circuit according to claim 1 or 2, characterized in that the switch-on level of the second Schmitt trigger (ST2) determines the voltage at which the charging current circuit (LS) for supplying power to the battery ( 1 ) is switched off and the switch-off level of the first Schmitt -Triggers (ST1) determines the voltage at which the charging current circuit (LS) for the power supply of the battery ( 1 ) is switched on. 4. Circuit according to at least one of the preceding claims, characterized in that the output of the first Schmitt trigger (ST1) is connected via a coupling resistor ( 9 ) to the input of the second Schmitt trigger (ST2) in such a way that the first Schmitt -Trigger (ST1) when switched off detunes the input of the second Schmitt trigger (ST2) so that it also switches off. 5. Circuit according to at least one of the preceding claims che, characterized in that the difference of the off switching level of both Schmitt triggers (ST1, ST2) lower than is the difference between their switch-on levels. 6. Circuit according to at least one of the preceding claims, characterized in that the inputs (E1, E2) of the Schmitt trigger (ST1, ST2) can be connected to the battery voltage via a temperature-dependent resistor ( 17 , 27 ). 7. Circuit according to claim 6, characterized in that the inputs (E1, E2) of the Schmitt trigger (ST1, ST2) are each connected to a voltage divider network, which have a temperature-dependent resistor ( 17 , 27 ). 8. A circuit according to claim 6, characterized in that the inputs (E1, E2) of both Schmitt triggers (ST1, ST2) are connected to a voltage divider network which has a temperature-dependent resistor ( 17 ). 9. Circuit according to at least one of the preceding claims, characterized in that the output (A2) of the second Schmitt trigger (ST2) is connected to the base of a control transistor ( 4 ) which connects the control connection in series to the accumulator ( 1 ) switched Schalttran sistors ( 2 ) drives. 10. Circuit according to at least one of the preceding claims, characterized in that a controllable switch ter (S) is arranged between the accumulator ( 1 ) and the control circuit, the control connection to the voltage source (U) for supplying the accumulator ( 1 ) is closed in such a way that the control circuit is only switched on when the charging current circuit (LS) is connected to the supply voltage source (U). 11. The circuit according to at least one of the preceding claims, characterized in that the control circuit is connected to ground or reference potential via a resistor ( 10 ) connected in parallel with the charging current connections of the switching transistor ( 2 ). 12. The circuit according to claim 11, characterized in that the resistance value of the resistor ( 10 ) is dimensioned such that as much current flows through the resistor ( 10 ) as the drive circuit consumes.