Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J7/00—Circuit arrangements for charging or discharging batteries or for supplying loads from batteries
  • H02J7/875—Charging or discharging for charge maintenance, battery initiation or rejuvenation

Definitions

• the invention relates to a battery discharger. It is known that a Ni-Cd rechargeable battery, if charged repeatedly when not enough discharged, cannot reach its full capacity. In order to avoid this drawback, the battery must be discharged at least once before its charge.
• Ni-MH batteries do not work under optimum conditions if they are not used during a period of approximately two months or longer. In order to avoid this drawback, it is necessary to submit such batteries to two or three charge-discharge cycles.
• the object of the invention is to provide a battery discharger which works safely and rapidly and which may be manufactured at low costs.
• This known battery discharger has two inputs for the battery, i.e. a ground input 10 and a voltage input 12.
• the voltage input 12 is connected to the first terminal 1 ⁇ of a switch 14 through a current limiter 16.
• the terminal 12 is connected to the first input 18 ⁇ of a voltage comparator 18 having a second input I82 receiving a signal Vr which is a reference voltage provided by a reference voltage generator 20.
• the second terminal 142 °f tne switch is connected to the ground terminal 10.
• the output I83 of the voltage comparator provides a signal which is applied on a control input 13 of the switch 1 .
• a LED (Light Emitting Diode) drive circuit 22 receives a current representative of the current in the switch 14 in order to provide a signal indicating whether the discharge is in operation or not.
• the reference voltage generator 20, the comparator 18 and the switch 14, which comprise different components such as transistors, as well as the LED drive current 22 are powered by an external voltage supply through a terminal
• the contact resistance between the terminals of the battery and the terminals 12 and 10 increases the discharge time because this resistance generates a periodic interruption, at a high frequency, of the discharging operation with a high intensity of discharge current.
• the contact resistance generates a voltage drop during the discharge process and the consequence of this voltage drop is that the voltage at the input 181 of comparator 18 becomes lower than Vr and, therefore, the switch 14 is opened.
• the switch 14 is opened the current through the contact resistance is null and, consequently, the voltage on the input 18]_ increases and becomes grea ' ter- tha ⁇ r " Vr " .
• the battery discharger according to the invention reduces the discharge time.
• This battery discharger comprises at least a circuit element, such as a capacitor, which extends the conduction of the discharge switch a given time before the voltage representing the battery voltage becomes lower than a reference voltage .
• the battery discharger of the invention has means for controlling the duty cycle of the oscillation which may appear during the discharge.
• the extension of the conduction time of the discharge switch is provided by the time constant of rectifier means which rectify the HF signal provided by the battery and the contact resistance.
• the rectified HF signal is compared with the reference signal and the controlled switch is on the discharge state as long as this rectified HF signal is greater than the reference signal.
• the battery discharger comprises at least a second circuit element, such as a resistor, for controlling the frequency of the oscillation which may appear during the discharge.
• This second circuit element may be a resistor in series with the battery.
• the invention eliminates an other drawback of the conventional battery discharger which is the following :
• the voltage comparator provides a control signal which has an intermediate value between, on the one hand, the value of the signal which closes completely the switch and, on the other hand, the value of the signal which opens completely the switch 14. It results that the switch takes an intermediate position, i.e. a position for which the intensity of the discharge current is reduced. The consequence of this intermediate position of the switch is also an increase of the discharge time.
• a solution to this problem would be to provide a more accurate voltage comparator, with practically no intermediate state, but this solution may be too expensive for a device of this kind and may require a specific supply voltage for an accurate comparator.
• the battery discharger includes - according to another aspect of the invention (which may be used in combination with the other aspects) - a current controller for decreasing the resistance of the discharge switch when a voltage representing the mean battery voltage is higher than a second reference voltage.
• This feature allows also to decrease the discharge time.
• the second reference voltage which controls the operation of the current controller may be different from the reference voltage which is used in cooperation with the first circuit element.
• he invention concerns a battery discharger " ⁇ mprxs ⁇ ng " ar cottro ⁇ ed ⁇ switch: which: is c nducti e- for- discharging a battery when the voltage, of this battery is greater than a first reference voltage, wherein the controlled switch is periodically opened and closed due to the fact that the voltage representing the battery voltage which is used to control the switch, has a greater value when the switch is "off” than when the switch is "on”, and wherein at least a circuit element is provided in order to extend the on period of the switch when a voltage representing the voltage battery is higher than the first reference voltage.
• the circuit element comprises at least a capacitor. In another embodiment, the circuit element comprises a rectifier for rectifying the alternating voltage representing the battery voltage.
• the battery discharger may comprise a second circuit element for controlling the frequency at which the switch is alternatively on and off.
• the second circuit element is such that the frequency at which the switch is alternatively on and off decreases when the battery- capacity decreases.
• a display is provided which blinks at a frequency representative of the frequency of the on and off switching.
• the switch is such that its conduction state depends on the value of a control voltage, the switch being in an intermediate conduction state when the voltage representing the battery voltage is close to the first reference voltage, and the battery discharger comprises a current controller which puts the switch into a full conduction state when the voltage representing the battery voltage is greater than a second reference value.
• the current controller may comprise a rectifier.
• the battery discharge may comprise terminals for measuring the voltage provided by the rectifier in order to check the battery voltage.
• the switch may comprise a transistor.
• the invention relates also to the application of the battery discharger for the discharge of Ni-MH and/or Ni-Cd batteries .
• the invention is also useful for the discharge of batteries of electronic portable devices.
• figure 1 represents a conventional battery discharger
• figure 2 is a schematic representation of an embodiment of a discharger according to the invention
• figure 3 represents a detailed embodiment of the discharger represented on figure 2
• figure 4 represents a discharger similar to the one shown on figure 3, but with a supplemental function
• figure 5 is a drawing similar to figure 2, but for another embodiment
• figure 6 represents a detailed embodiment of the discharger represented on figure 5
• figure 7 is a diagram showing one aspect of the operation of the embodiment of figure 5 or 6.
• the battery to be discharged (not shown) is connected between terminals 32 and 34, terminal 34 being the ground terminal.
• the voltage terminal 32 is connected to the input of a voltage dropper 36, which is, for instance, a resistor, and the output of this voltage dropper is connected to the first input 38 ] _ of a comparator or, current controller, 38 presenting a second input 382 on which is applied a reference voltage Vr2 provided by the output 402 of a reference voltage generator 40.
• a voltage dropper 36 which is, for instance, a resistor
• the output of the voltage dropper 36 is connected to a time constant element 44 which is also connected to the output of the voltage comparator 42.
• the circuit 50 is a LED drive and display circuit which is similar to the LED drive and display circuit 22 of figure 1.
• the voltage dropper, or resistor, 36 has the function, together with the time constant element 44, to impose a given frequency to the oscillation described with reference to figure
• the voltage dropper, or resistor, 36 may be omitted when there is a significant contact resistance between the battery and terminals 32 and 34.
• the voltage dropper 36 or simply the contact resistance (when the voltage dropper 36 is omitted) , together with time constant element 44, determines the frequency of the oscillation which is proportional to the voltage of the battery.
• the current controller 3 " 8 comprises a transistor Ti having—its—emitter " connected to a terminal of a voltage divider including two resistors R2 and R3. These resistors are also components of the reference voltage generator 40.
• the reference voltage generator 40 has an input connected to a terminal 51 on which is applied the DC power supply of the battery discharger.
• this DC voltage supply is 1.6 V.
• the generator 40 comprises, between the terminal 51 and the ground terminal 34, a PNP transistor Ql having its emitter connected to terminal 51 trough a resistor R4 and its collector connected to the ground 34.
• the base of transistor Ql is connected to terminal 51 trough a resistor Rl, and to the ground through resistors R2 and R3 in series.
• the base of transistor Ql is also connected to the ground 34 trough a diode Dl.
• the first reference voltage Vr ⁇ appears on the emitter of transistor Ql and the second reference voltage Vr2 appears at the connection terminal between resistors R2 and R3, i.e. on the emitter of transistor Ti of current controller 38
• a capacitor CI is connected at the input of the battery discharger, between terminals 51 and 34, in order to filter any high frequency noise which may originate from the power supply.
• the voltage comparator 42 comprises two NPN transistors 52 and 54. The emitters of these transistors 52 and 54 are connected to the ground trough a resistor R5. The collector of transistor 52 is connected to terminal 51. The collector of transistor 54 is connected to supply terminal 51 through a resistor R6. The output of the comparator 42 appears at the collector of transistor 5 . The base of this transistor 54 is connected to resistor 36 through a resistor R7. The terminal of resistor R7 which is connected to resistor 36 is connected to an input of time constant circuit 44. The latter comprises a capacitor C3 connected between resistor 36 and the " contro ⁇ ⁇ p " ⁇ 67-of " Hswit;h ⁇ c ⁇ rcui-t-4 " 6 " . A capacitor C2 is provided between the base of transistor 52 and ground in order to protect this transistor 52 from noise.
• the switch circuit 46 comprises a control transistor TS1 of the PNP type having its emitter connected to supply terminal 51 and its collector connected to the base of the main transistor TS2 of this circuit 46 through a resistor R9.
• the transistor TS2 is of the NPN type and has its emitter connected to the ground and its collector connected to resistor 36 trough an other resistor R15 which constitutes the current limiter 48.
• a LED (light emitting diode) 60 has its anode connected to terminal 51 and its cathode connected to the collector of a transistor TL of the LED driver circuit 50 through a resistor R12.
• the base of this transistor TL is connected to the collector of transistor TSl trough a resistor R10 and to ground through a resistor Rll.
• the current controller 38 comprises a diode D3 having its anode connected to the terminal of resistor 36 opposed to terminal 32 and its cathode connected to ground 34 trough a resistor R13 ; this cathode is also connected to the base of transistor Ti and a capacitor C6 is connected between the base of transistor Ti and ground.
• the diode D3, capacitor C6 and resistor R13 of the current controller 38 convert the voltage provided by the battery during the oscillation period to a DC voltage provided at the base of transistor Ti.
• the circuit represented on figure 3 operates as follows :
• the voltage Vr ⁇ provided at the emitter of transistor Ql of reference generator 40 is 1.25 V in this example. This value is determined by the anode voltage of diode Dl plus the junction- oltage- ⁇ f -- b-ase ⁇ tter -- ⁇ " f — txa ⁇ si " sto ⁇ 21 " .
• the second reference voltage Vr2 appearing between resistors R2 and R3 is determined by the value of these resistors and by the value of the forward voltage of Dl. In this example this voltage Vr2 is 0.23 V.
• the discharger is off when the battery voltage is 1.05 V.
• the voltage comparator 42 operates as follows : when the voltage at the base of transistor 54 is lower than Vr ⁇ (the voltage applied on the base of transistor 52) this transistor 54 is switched off. When the voltage on this base of transistor 54 is greater than Vr ] _ the transistor 54 is switched on and the voltage of its collector drops. Consequently the voltage on the base of transistor TSl of switch circuit 46 becomes lower than the voltage on the emitter minus the emitter/base voltage of this same transistor and, therefore, this transistor becomes conductive. As a result the voltage on the base of transistor TS2 (the main transistor of switch circuit 46) increases and this transistor TS2 becomes conductive. Therefore the battery discharges trough transistor TS2 when the battery voltage is practically superior to the reference voltage Vr ⁇ _. Transistor TL of circuit 50 is "on" when transistor
• TSl and TS2 of the switch circuit 46 are on (conductive) .
• the LED (Light Emitting Diode) 60 produces light signalling that the battery is under discharge.
• Capacitor C3 of time constant circuit 44 increases the time of conduction of the switches TSl and TS2 in the switch circuit 46 when the battery voltage is superior to the reference voltage Vr ⁇ . In that case the voltage at the output of comparator 42, i.e. the voltage on the collector of transistor 54, decreases. Without the presence of capacitor C3 this would entail the immediate switching off of transistors TSl and TS2. But capacitor C3 is loaded during the conduction of transistor TSl and the conduction of Transistor 54.
• capacitor C3 is charged during the conduction time of TSl according to the fOl ⁇ owing " " " path- r TSl—emitte —and— ase-;—the—capacito —C3 " , resistor R7, the base-emitter of transistor 54 and resistor R5.
• the voltage of C3 increases during the charge and when the base voltage of TSl reaches its switch off voltage (the voltage of emitter of TSl minus emitter/base voltage of TSl) TSl is switched off. Since the transistor Ti is taking the base current of TSl at a mean battery voltage (as explained hereinafter) which is higher than Vr2 and as, also, transistor 54 is taking the base current of TSl at a battery voltage which is higher than Vrl, the charging time of C3 is longer than its discharging time i.e. the conductive duration of TSl and TS2 is longer.
• the charge and discharge of C3 is repeated until the battery voltage becomes smaller than Vrl.
• the oscillation frequency is determined by the time constant of capacitor C3 and the equivalent resistance of transistor 54 and resistor R5 when the battery voltage is substantially higher than reference voltage Vrl; it is also determined by the equivalent resistance of transistor Ti and resistor R3.
• the rectified voltage provided by diode D3, resistor R13 and capacitor C6 of current controller 38 is practically equal to the average battery voltage.
• this rectified voltage, which appears on the base of transistor Ti is greater than the reference voltage V2 plus the junction voltage of base/emitter of transistor Ti, this transistor Ti is switched on. Therefore the voltage on collector of transistor Ti decreases.
• the voltage on the base of transistor TSl dc a H T—whfch -" n rts ⁇ te "- ⁇ TSl and TS2.
• This current controller contributes also to make the switch on duration of the oscillation duty ratio longer and to the decrease of the discharge time of the battery.
• resistor R14 is selected to limit the base current of TSl. In an embodiment the oscillation stops only when the battery voltage is close to full discharge and the LED (Light Emitting Diode) is switched off.
• the LED Light Emitting Diode
• the battery may be removed when LED (Light Emitting Diode) becomes dark.
• capacitor C3 With a proper value of capacitor C3, it is possible to select the frequencies of blinking of the diode in such a way that the blinking is not visible when the battery is fully charged and the blinking becomes visible as soon as the charge of the battery has decreased, and the blinking is at a very low frequency when the battery is nearly completely discharged.
• the battery discharger which has been described is very simple. It does not need the use of complex IC S such as microprocessors. The discharging time is reduced and the discharge and the voltage are controlled accurately.
• This battery discharger can also be used for checking the residual battery capacity, for instance through the blinking frequency of a diode.
• Figure 4 represents a battery charger with a checking function.
• the frequency of the oscillation may be the maximum when the battery is fully charged and the minimum when it is discharged.
• this frequency will be selected at 43 Hz for full capacity 1.25 V, 17 Hz at 1.2 V, 5 Hz at 1.15 V and stop at 1.10 V.
• the battery discharger may be combined with a conventional battery charger.
• a conventional trickle battery charger slow speed charger
• the circuit shown on figure 3 or figure 4 is built on a printed circuit board with contacts for receiving a charging voltage on a battery charger and the contacts are connected to the terminals 51 and 34, a full and inexpensive charge/discharge combined system can be realized.
• the elements which have the same function as the corresponding elements in figure 2 bear the same reference numerals.
• the voltage comparator 82 comprises an input 822 receiving the reference voltage Vrl and another input 82]_ receiving the output of a rectifier 84 which rectifies the voltage provided by the voltage dropper 36.
• a filter 86 is provided between the output of voltage dropper 36 and the control input 463 of switch 46. 2 by the fact that comparator 82 provides two-state output signals with practically no intermediate state. Therefore, the switch 46 has also practically no intermediate state.
• the comparator 86 comprises an operational amplifier 90 in the form of an integrated circuit, and the rectifier 84 includes a capacitor C ⁇ 3 and a resistor R3 in parallel and a diode D13.
• a resistor R5 is connected between the output of the operational amplifier and one of its inputs.
• the rectifier 84 provides a saw tooth signal 92 which, during a substantial part t ⁇ of each period of the HF signal, has a value superior to reference voltage Vrl. Therefore, the switch 46 is ON during this substantial part ti of each HF period.
• the duration t ] _ is mainly determined by the values of C13 and 'i3-
• the filter 86 comprises a capacitor C]_4 which has practically no influence on duration t]_.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Charge And Discharge Circuits For Batteries Or The Like (AREA)
• Secondary Cells (AREA)

Priority Applications (1)

Applications Claiming Priority (4)

Publications (2)

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• 2001
  • 2001-10-08 EP EP01402591.0A patent/EP1280252B1/en not_active Expired - Lifetime
• 2002
  • 2002-07-15 WO PCT/EP2002/007862 patent/WO2003010870A2/en not_active Ceased
  • 2002-07-15 CN CNB028141490A patent/CN1326305C/zh not_active Expired - Fee Related
  • 2002-07-15 JP JP2003516140A patent/JP4191029B2/ja not_active Expired - Fee Related

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