Battery charger operable for selective one of a plurality of power supplies

A battery charger is configured to use selective one of two or more power supplies including a commercial AC power supply and a DC power supply. An AC cable is fixedly secured to the body of the battery charger and a DC cable is detachably connected to the body of the battery charger. A single transformer is employed that has a first primary winding to which the AC power supply is connected a first switching element, a second primary winding to which the DC power supply is connected via a second switching element, and a secondary winding to which a battery pack to be charged is coupled.

BACKGROUND

1. Field of the Invention

The present invention relates to a battery charger for charging rechargeable secondary batteries, such as nickel-cadmium batteries, lithium-ion batteries.

2. Description of the Related Art

Rechargeable secondary batteries have been widely used as a power source of portable devices, such as a cordless power tools. Conventional battery chargers for charging such secondary batteries are, in use, connected to a commercial power supply. However, when the cordless power tool is used in places where the commercial power supply is not available, the user has to bring extra batteries for replacement with the empty batteries.

To resolve the above-mentioned problem, Japanese Patent Application Publication No. 2005-245145 proposes a battery charger capable of charging secondary batteries while being supplied with power from various types of power supplies including the commercial power supply.

However, the battery charger disclosed in Japanese Patent Application Publication No. 2005-245145 accommodates a plurality of power source circuits corresponding to the number of available power supplies, so that the size of the battery charger becomes large. In addition, the secondary batteries charged by the battery charger disclosed in Japanese Patent Application Publication No. 2005-245145 are overcharged when a particular power supply is used. The secondary batteries might be physically destroyed or generate an undue amount of heat due to overcharging. Hence, battery chargers capable of safely charging the batteries have been sought in the art.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide a battery charger that can charge rechargeable batteries using selective one of a plurality of power supplies without enlarging the size of the battery charger.

It is another object of the invention to provide a battery charger configured from a simplified circuit arrangement.

To achieve the above and other objects, a battery charger according to the invention includes a body that is connectable to a battery pack containing a battery and charges the battery; a first connecting member having one end connectable to a first power supply and another end connectable to the body; and a second connecting member having one end connectable to a second power supply and another end connectable to the body.

The body may include a first voltage detector that detects a voltage generated by the first power supply; a second voltage detector that detects a voltage generated by the second power supply; and a control unit that selectively uses one of the first and second power supplies as a power source of the body in response to outputs from the first and second voltage detectors.

The body may further include a first switching element; a first switching controller connected to the first switching element for controlling the first switching element; a second switching element; a second switching controller connected to the second switching element for controlling the second switching element; and a transformer. The transformer has a first primary winding to which the first power supply is connectable via the first switching element, a second primary winding to which the second power supply is connectable via the second switching element, and a secondary winding to which the battery pack is connected.

The body may further include a charge stop circuit that generates a charge stop signal in response to a charge stop instruction received from the battery pack, wherein the charge stop circuit applies the charge stop signal to both the first and second switching controllers to stop charging the battery.

It is preferable that the control unit uses the first power supply when the output from the first input voltage detector indicates that the first power supply is connected to the first primary winding of the transformer whereas the control unit uses the second power supply when the output from the second input voltage detector indicates that the second power supply is connected to the second primary winding of the transformer.

It is further preferable that the control unit does not permit charging the battery when the outputs from the first and second input voltage detectors indicate that both the first and second power supplies are connected to the first and second primary windings of the transformer, respectively.

In addition to the first switching element, first switching controller, second switching element, second switching controller, and the transformer, the body may further include an output controller that controls a charge current or a charge voltage applied to the battery through the secondary winding of the transformer; a current/voltage setter that sets the charge current or a charge voltage applied to the battery. In this case, the control unit further controls the current/voltage setter to set the charge current or the charge voltage depending upon the first power supply and the second power supply whichever is selected, and a status of the battery instructed from the battery pack. For example, the battery pack instructs any one or all of a temperature of the battery, a number of cells constituting the battery, and a type of the battery, e.g., nickel-cadmium battery, lithium-ion battery or the like, to the control unit as the status of the battery.

The first power supply is, for example, selected to be a commercial AC power supply, and the second power supply to be a DC power supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A battery charger in accordance with one embodiment of the invention will be described with reference to the accompanying drawings.FIG. 1is a perspective view and FIG.2is a partially cut-away top view showing a battery charger in accordance with the embodiment of the invention.FIG. 3is a right side view of the battery charger on which a battery pack to be recharged is loaded.

As shown inFIG. 1, the battery charger1has an upper housing6and a lower housing7. The upper housing6and the lower housing7constitute in combination a housing of the battery charger1. The lower housing7is shaped into a rectangular parallelepiped and has a bottom wall and a rectangular top opening. The upper housing6is adapted to cover the rectangular top opening of the lower housing7. A battery-holding portion8is formed in the upper housing6at a right half thereof. The battery-holding portion8has a sloping surface8ainclining downwards from the rear-side to the front-side of the upper housing6.

Slide rails8bare formed in the sloping surface8aof the battery-holding portion8. Top surface of each slide rail extends parallel to the sloping surface8a. A battery pack40(seeFIG. 3) has an outer surface provided with rails slidably movable on the slide rails8a.

A terminal cover9is provided at a lower portion of the sloping surface8a. Terminals are exposed to an atmosphere at the terminal cover9.

For loading the battery pack40with the battery charger1, the battery pack1is inserted in a direction indicated by an arrow on the upper surface of the upper housing6so that the rails of the battery pack1are engaged with and slidingly moves along the slide rails8bdownwards toward the front-side of the sloping surface8a. Thus, the terminals of the battery pack40are brought into electrical and physical contact with the corresponding terminals of the battery charger1.

As shown inFIG. 2, the battery charger1includes an AC cable4having one end fixedly connected to the body of the battery charger1and another end having a plug to be connected to a commercial AC power supply. The battery charger1also includes a connector34to which a DC cable3is detachably connected. The DC cable3is used to supply DC power from an external DC power supply to the battery charger1.

FIG. 4is a block diagram showing electrical arrangements of the battery charger1and the battery pack40. As described with reference toFIG. 2, the AC cable4of the battery charger1is typically connected to the commercial AC power supply5and the DC cable3is used to connect the battery charger1to the external DC power supply2when the commercial AC power supply5is not available.

An electrical arrangement of the battery pack40will firstly be described. The battery pack40includes a battery42having a prescribed number of cells connected in series. The battery pack40also includes a protection IC41, a thermal protector43for preventing undue temperature rise of the battery pack40which may occur during charging the battery42, a discrimination resistor44, an over-charge signal transmission device45, and a thermistor46. The battery pack40has positive (+), negative (−), T, LS and LD terminals to be connected to the corresponding terminals at the side of the battery charger1. The protection IC41includes an over-charge detector41aand an over-discharge/over-current detector41b.

Each cell of the battery42is connected to the protection IC41so that the protection IC can monitor the voltage developed across each cell of the battery42and an overall voltage developed across the positive and negative terminals of the battery42. The over-charge detector41aoutputs an abnormal signal to the LS terminal via the over-charge signal transmission device45when the voltage of at least one of the cells exceeds a predetermined cell voltage and when the voltage across the battery42exceeds a predetermined battery voltage. The over-discharge/over-current detector41boutputs an abnormal signal to the LD terminal when the loaded battery pack40is judged to be in an overly discharged state or when the charge current flowing in the battery42exceeds a predetermined maximum. The abnormal signal output from the LD terminal of the battery pack40will not be described further, as this signal is not directly related to the operation of the battery charger in accordance with the embodiment of the invention.

The battery discrimination resistor44is connected between the negative terminal of the battery42and the T terminal. The discrimination resistor44has a specific resistance value depending upon the battery42used in the battery pack40. More specifically, the resistance of the discrimination resistor44is set to indicate the type of the battery42and the number of cells constituting the battery42. The thermistor46is disposed in contact with or in the vicinity of the battery42to detect the temperature of the battery42. The output of the thermistor46can be derived from the terminal LS.

Next, an electrical arrangement of the battery charger1will be described.

The battery charger1is a computer-controlled device including the microcomputer23. Although not shown, the microcomputer23includes a CPU, a ROM, a RAM, an input port and an output port. To the input port of the microcomputer23, connected are a battery temperature detector26, a discrimination resistance detector27, a charge stop circuit28, a DC input voltage detector21, a constant voltage circuit22, and a battery voltage detector30. To the output port of the microcomputer23, connected are a first switching controller12via a fist photo-coupler15, a second switching controller19, a current/voltage setter25, a fan motor32via a fan motor driver29, and a display33.

Among the components connected to the input port of the microcomputer23, the battery temperature detector26has an input connected to an LS terminal of the battery pack40and detects the temperature of the battery42based on the resistance value of the thermistor46. The discrimination resistance detector27has an input connected to a T terminal of the battery pack40and detects the resistance value of the discrimination resistor44contained in the battery pack40. The microcomputer23determines the type of the battery and the number of cells based on the resistance value of the discrimination resistor44detected by the discrimination resistance detector27. Based on the resistance value of the discrimination resistor44and further on the temperature of the battery42detected by the battery temperature detector26, the microcomputer23determines the charge current or a set value for effecting the constant voltage control and outputs a corresponding instruction to the current/voltage setter25.

The charge stop circuit28is connected to the LS terminal of the battery pack40and receives an abnormal signal from the over-charge detector41ain the protection IC41of the battery pack40through the over-charge signal transmission device45when the over-charge detector41adetects that any of the battery cell or the battery42as a whole is brought to an over-charge condition. In this case, the charge stop circuit28outputs a charge stop signal to the microcomputer23. The charge stop signal is also sent to the first switching controller12via the first photo-coupler15, and to the second switching controller19, so that charge of the battery is stopped.

The battery voltage detector30is connected to the positive terminal (+) of the battery charger1to detect the voltage across the battery42. The voltage detected by the battery voltage detector30is applied not only to the microcomputer23but also to a constant-current/constant-voltage controller24to be described later. The battery charger1further includes a charge current detector31interposed in the negative line of a second rectifying/smoothing circuit20to be described later. The charge current detector31detects the charge current flowing in the battery42and applies the detected value to the constant-current/constant voltage controller24.

The constant-current/constant-voltage controller24controls the first and second switching controllers12and19based on the outputs from the battery voltage detector30, charge current detector31, and the current/voltage setter25. The current/voltage setter25sets a charge current to be flowed in the battery42and a set value for effecting a constant voltage control in accordance with an output from the microcomputer23.

The battery charger1includes a high-frequency transformer17having a first primary winding17a, a second primary winding17b, and a secondary winding17c. The commercial AC power supply5is connected to the first primary winding17avia a first rectifying/smoothing circuit10. The first rectifying/smoothing circuit10includes a diode bridge (not shown) and a capacitor (not shown). The diode bridge makes use of four diodes in a bridge arrangement to achieve full-wave rectification. The capacitor smoothes the DC output from the diode bridge. The output of the first rectifying/smoothing circuit10is connected to the first primary winding17aof a high-frequency transformer17through a first switching element11. An FET is used in this embodiment as the first switching element11.

The second primary winding17bof the high-frequency transformer17is connectable to the DC power supply2through the connector34. A diode35is interposed in the positive line of the DC power supply2, and a second switching element18is connected between the second primary winding17band the negative line of the DC power supply2. An FET is used in this embodiment as the second switching element18.

A second rectifying/smoothing circuit20is connected to the secondary winding17cof the transformer17and the output from the second rectifying/smoothing circuit20is connected to the positive and negative terminals of the battery pack40, thereby charging the battery42contained in the battery pack40.

The first switching controller12is connected to the first switching element11and changes the width or duration of a driving pulse applied to the first switching element (FET)11in accordance with an instruction from the microcomputer23so that the output voltage of the second rectifying/smoothing circuit20is controlled. Likewise, the output port of the microcomputer23is also connected to the second switching controller19. The second switching controller19changes the width or duration of a driving pulse applied to the second switching element (FET)18in accordance with an instruction from the microcomputer23so that the output voltage of the second rectifying/smoothing circuit20is controlled.

The charging circuit1further includes an AC input voltage detector13and an auxiliary power source circuit14. The AC input voltage detector13detects the AC voltage applied from the commercial AC power supply5. The detection output from the circuit13is applied to the microcomputer23through the second photo-coupler16. The auxiliary power source circuit14is connected across the first rectifying/smoothing circuit10and supplies a prescribed voltage Vcc to the microcomputer23through a constant voltage circuit22. The voltage Vcc is also applied to the over-charge signal transmission device45.

The DC input voltage detecting circuit21is connected to the positive line of the second primary winding17bfor detecting that the DC power supply2is connected to the battery charger1through the connector34.

The fan motor32is used for cooling the battery pack40. The fan motor32is controlled by the microcomputer23depending on the status of the battery pack40and input status of the commercial AC power supply5or the DC power supply2. When a battery mounted on a vehicle is used as the DC power supply3, it may be desirable to stop driving the fan motor33during charging the battery pack40for the sake of preserving silence in the vehicle.

The display33is configured from one or more LEDs which indicate the charging statuses of the battery pack40and input statuses of the commercial AC power supply5and the DC power supply2.

Next, operation of the battery charger1will be described with reference to the flowchart shown inFIGS. 5A and 5B.

When the battery charger1is powered by the commercial AC power supply5or DC power supply2, the prescribed voltage Vcc is applied to the microcomputer23through the auxiliary power source14and the constant voltage circuit22, whereupon initial settings of the microcomputer23are implemented (step101). Then, the display33indicates that the battery charger1is in a start-up status or a ready status (step102) by, for example, emitting red light from an LED.

Next, the microcomputer23turns off both the first and second switching controllers12and19so that no output voltage is generated from the second rectifying/smoothing circuit20(step103). The microcomputer23then judges whether the input voltage from the commercial AC power supply5is available or not based on the input supplied from the AC input voltage detector13via the second photo-coupler16(step104). When the microcomputer23determines that the AC power supply5is available (step104: YES), further judgment is made based on the output from the DC input voltage detector21whether or not the input voltage from the DC power supply2is available (step105). When the microcomputer23determines that no input voltage from the DC power supply2is available (step105: NO), the microcomputer23sets the battery charger1to be operable with an AC mode (step106).

When the microcomputer23determines that the commercial AC power supply5is not available (step104: NO), further judgment is made as to whether or not the DC power supply2is available (step107). When the DC power supply2is available (step107: YES), the microcomputer23sets the battery charger1to be operable with a DC mode (step108).

Subsequently, the microcomputer23judges whether or not the voltage from the DC power supply2is abnormal (step109). When the microcomputer23finds no abnormality in the voltage of the DC power supply2(step109: NO), the routine proceeds to step112whereas when the microcomputer23finds that the voltage of the DC power supply2is abnormal (step109: YES), the microcomputer23controls the display33to indicate that the power supply is not available or abnormal (step111) by, for example, flickering red light emitted from the LED, whereupon the routine returns to step103. When the voltage at the DC power supply2is abnormally low, charging the battery pack40is not performed to prevent the DC power supply2, e.g., car battery, from being overly discharged.

When the microcomputer23determines that both the commercial AC power supply5and the DC power supply2are available (step104: YES; step105: YES), the microcomputer23turns off both the first and second switching controllers12and19(step110). In such a case, the microcomputer23controls the display33to indicate that the power supplies are connected in error or to prompt the operator to check the connections of the power supplies (step111) by, for example, flickering red light emitted from the LED, whereupon the routine returns to step103.

When both the commercial AC power supply5and the DC power supply2are accidentally connected to the battery charger1, the microcomputer23prohibits charging the battery. Because the use of the high-frequency transformer17and the constant-current/constant-voltage controller24concurrently in both the AC and DC modes makes the output voltage from the second rectifying/smoothing circuit20unstable.

When the microcomputer23determines that neither the AC power supply5nor the DC power supply2is available (S104: NO; S107: NO), the microcomputer23turns off both the first and second switching controllers12and19(step110) and controls the display33to indicate a connection error of the power supplies or to prompt the operator to check the connections of the power supplies by, for example, flickering red light emitted from the LED (step111).

After setting the battery charger1to either the AC mode (step106) or the DC mode (step108), the microcomputer23judges whether or not the battery pack40has been loaded in the battery charger1(step112). When it is determined that the battery pack40has not been loaded (step112: NO), a charge completion flag and a charge continuation flag are reset (steps113and114), whereupon the routine returns to step102.

When the microcomputer23determines that the battery pack40has been loaded in the battery charger1(step112: YES), then the microcomputer23judges whether the charge continuation flag has been set (step115). When the microcomputer23determines that the charge continuation flag has been set (step115: YES), the routine skips to step118. On the other hand, when the microcomputer23determines that the charge continuation flag has not been set (step115: NO), then the microcomputer23further judges whether the charge completion flag has been set (step116). When the microcomputer23determines that the charge completion flag has been set (step116: YES), the routine returns to step103. On the other hand, when the microcomputer23determines that the charge completion flag has not been set (step116: NO), the microcomputer23determines the type of the battery42and the number of battery cells based on the output from the discrimination resistance detector27(step117). Subsequently, the microcomputer23checks the temperature of the battery based on the output from the battery temperature detector26(step118). When the microcomputer23finds that the battery is at a high temperature (step118: YES), the microcomputer23controls the display33to alert the operator that the battery is at a high temperature or to indicate that the charge has been complete (step119), whereupon the routine returns to step103.

When the microcomputer23determines that the temperature of the battery is not high (step118: NO), the microcomputer23makes further determination as to whether or not the battery charger1is to be operated under the AC mode (step120). If negative, the microcomputer23determines that the battery charger1is to be operated under the DC mode (step123), and sets a value to carry out a constant voltage control or a constant current control (step124). In step124, an optimum value for carrying out the constant voltage control or constant current control is selected based on the output from the discriminating resistance detector27. Specifically, the charge current to implement the constant current control is selected to be lower when operated with the DC power supply2than when operated with the commercial AC power supply5. This is because the power supplied from the DC power supply2is generally smaller than the power supplied from the commercial AC power supply5. Further, it is desirable to set the charge current smaller as the number of battery cells increases. By so setting the charge current, charging efficiency can be enhanced and the service life of the battery pack40can be prolonged.

After execution of step124, the microcomputer23turns on the second switching controller19(step125) and thereafter the processing in step126is executed.

When the microcomputer23determines in step120that the battery charger1is to be operated under the AC mode, the microcomputer23sets a value for the constant voltage control or constant current control when using the commercial AC power supply5(step121). In step121, an optimum value for carrying out the constant voltage control or constant current control implemented under the AC mode is selected based on the output from the discriminating resistance detector27. Specifically, the charge current to implement the constant current control is selected to be larger when operated with the AC power supply5than when operated with the DC power supply2.

After execution of step121, the first switching controller12is turned on (step122), and the microcomputer23controls the display33to indicate that the charging operation is continuing by, for example, emitting orange light. To this effect, two LEDs, one emitting red light and the other emitting green light, are simultaneously lit. Then, the charge continuation flag is set (step127), and charging the battery is commenced while applying a constant voltage or constant current to the battery. The charge to the battery is controlled by the first or second switching controller12or19based on the output from the constant-current/constant-voltage controller24.

More specifically, when the battery is charged with the DC power supply3, the second switching element (FET)18is driven in accordance with the output from the second switching controller19, so that the output from the second rectifying/smoothing circuit20is controlled to produce a predetermined voltage or current. At this time, a voltage is also developed across the winding17a, however, this voltage is blocked by a rectifying diode (not shown) provided in the first rectifying/smoothing circuit10. Thus, the operator does not get an electrical shock even if he or she touches the plug (not shown) of the AC cable. The first switching element11is maintained off by the first switching controller12, so the plug of the AC cable is safe for the operator.

Subsequently, the microcomputer23judges whether or not the battery42has reached a full charge condition (step129). As is well known in the art, various methods are available for detecting the full charge condition. For example, a so-called −ΔV detection is used for detecting the full charge condition of nickel-cadmium batteries, in which it is determined that the battery has reached the full charge condition when a predetermined voltage drop occurs after reaching the peak voltage at the end of charge. Another method for detecting the full charge condition includes detecting a rate of battery temperature rise or a gradient of battery temperature during a predetermined interval, i.e., ΔT/Δt, and determining that the battery has reached the full charge condition when an abrupt increase of ΔT/Δt is detected. Determination in step129for determining that the battery has reached the full charge condition may be made using one or more full charge detecting methods.

For the battery pack40containing a lithium ion battery, it is necessary to control the battery so that a voltage across each cell of the lithium ion battery does not exceed a predetermined voltage (for example, 4.2V) when the battery is charged under the constant voltage control or constant current control well known in the art. It is further necessary to implement the full charge detection when the charge current falls below a full charge discrimination value during charging the battery under the constant current control.

When determination is made in step129that the battery has not yet reached the full charge condition (step129: NO), the routine returns to step104, whereas when determination is made that the battery has reached the full charge condition (step129: YES), the charge continuation flag is reset (step130) and the display33is controlled to indicate that charging the battery has been completed (step131) by emitting green light from an LED. Subsequently, the charge completion flag is set (step132) and the routine returns to step103.

As described above, the embodiment of the invention provides an easy-to-use battery charger that can automatically use selective one of two power supplies for charging the rechargeable batteries without increasing the size of the battery charger.

While the invention has been described in detail with reference to a specific embodiment thereof, it would be apparent to those skilled in the art that many modifications and variations may be made therein. For example, the embodiment describe above is configured to selectively use two power supplies, however, the circuit arrangement can be modified so that three or more power supplies can be selectively used.

In the embodiment described above, it is desirable that the display33be controlled to provide different indications during charging depending upon the remaining period of time up to completion of charge. For example, the display33may be configured from an LED and switched from continuous lighting to flickering when the remaining predicted period of time up to completion of charge becomes a prescribed time, thereby facilitating the operator to recognize the progress of charge.

Further, it is desirable that depending upon the type of power supply used, the lighting condition of an LED (display) be changed. For example, the LED may be flickered when the DC power supply is used, and a flickering interval may be changed as the charging progresses. On the other hand, when the AC power supply is used, the LED of the display33may be continuously lit. By flickering the LED when the DC power supply is used, consumption of energy in the DC power supply can be suppressed. This is particularly advantageous when a vehicle battery is used as the DC power supply for the battery charger.

In the above described embodiment, the DC cable is attachable to and detachable from the body of the battery charger. Hence, the DC cable can be detached from the body of the battery charger and put aside when the AC cable is frequently or continuously used.

While in the above described embodiment the AC cable is fixedly attached to the body of the battery charger, it may be modified so as to be attachable to and detachable from the body of the battery charger.