Patent Description:
Along with the wide use of portable electronic devices such as cellular phones, digital cameras, and laptop computers, batteries for supplying power to such portable electronic devices have been actively developed. Such a battery is provided in the form of a battery pack together with a protective circuit for controlling the charging and discharging operations of the battery, and various studies have been conducted on methods and devices for efficiently charging batteries.

Chargers are configured to charge batteries to a preset full-charge voltage. Such a full-charge voltage is set by considering the degree of deterioration of batteries according to battery voltages, but is not set by considering the degree of deterioration of batteries when the batteries are left for a long time in a state in which the batteries are charged to a full-charge voltage. However, when a battery is left for a long time in a state of being charged to a full-charge voltage, manufactured materials such as active materials and additives contained in the battery may become unstable and may accelerate deterioration of the battery. Since the full-charge voltage of batteries is set without taking this into consideration, the lifespan of the batteries is rapidly shortened when the batteries are left after being charged to the full-charge voltage.

<CIT> discloses a structure including a fuse with a heater, connected to a positive electrode side of a battery cell, as a secondary battery, a driving FET for driving the heater of the fuse and a detection control IC. When the detection control IC detects an over-charging state of the battery cell, the detection control IC drives the driving FET to fuse the heater of the fuse.

To solve the above-described problem, the present disclosure provides a battery pack configured to be charged using a diode such that the charging of the battery pack may be completed at a voltage lower than a preset voltage based on which a charger of the related art determines that the battery pack is fully charged, thereby minimizing a decrease in the lifespan of the battery pack that is caused when the battery pack is left for a long period of time at the preset voltage, and the present disclosure also provides a method of controlling charging of the battery pack.

According to the invention there is provided a battery pack according to claim <NUM>.

Optional features of the battery pack are set out in dependent claims <NUM> to <NUM>.

According to the invention there is further provided a method of controlling charging of a battery according to claim <NUM>.

Optional features of the method are set out in dependent claims <NUM> to <NUM>.

According to the battery pack and the method of controlling charging of the battery pack of various embodiments of the present disclosure, the battery pack is charged using the diode such that the charging of the battery pack may be completed at a voltage lower than a preset voltage based on which a charger of the related art determines that the battery pack is fully charged, thereby minimizing a decrease in the lifespan of the battery pack that is caused when the battery pack is left for a long period of time at the preset voltage.

In addition, since the battery pack switches the charging mode of the battery from the first charging mode to the second charging mode at an appropriate time based on the state of charge and voltage of the battery, a decrease in the charging speed of the battery may be minimized, and heating in the first diode may be minimized.

According to an aspect of the present disclosure, a battery pack includes: a battery including at least one battery cell, a first battery terminal, and a second battery terminal; a terminal unit including a first pack terminal and a second pack terminal that are connected to a charger; a discharging switch including a first switch and a diode, the first switch being connected between the first pack terminal and the first battery terminal, the diode being connected in parallel to the first switch and having a forward direction in which charging current of the battery flows; and a battery management unit configured to determine a charging mode from one of a first charging mode in which the battery is charged with charging current flowing through the first switch and a second charging mode in which the battery is charged with charging current flowing through the diode, wherein the battery management unit starts charging the battery in the first charging mode and then switches the charging mode to the second charging mode.

Advantages and features of the present disclosure, and implementation methods thereof will be clarified through the following descriptions given with reference to the accompanying drawings. However, the following embodiments of the present disclosure are non-limiting examples and may have different forms, and it should be understood that the idea and technical scope of the present disclosure cover all the modifications, equivalents, and replacements. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present disclosure to those skilled in the art. Moreover, detailed descriptions related to well-known functions or configurations will be omitted in order not to unnecessarily obscure subject matters of the present disclosure.

The terminology used herein is for explaining specific embodiments only and is not intended to limit the scope of the present disclosure. The terms of a singular form may include plural forms unless otherwise mentioned. It will be understood that terms such as "comprise," "include," and "have," when used herein, specify the presence of features, integers, steps, operations, elements, components, or combinations thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof. It will be understood that although the terms "first" and "second" are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element or component from other elements or components.

In the drawings, identical or corresponding elements are denoted with the same reference numbers, and overlapping descriptions thereof will be omitted.

<FIG> is a view schematically illustrating an internal structure of a battery pack <NUM> according to an embodiment of the present disclosure.

Referring to <FIG>, the battery pack <NUM> includes a battery <NUM>, a first battery terminal <NUM>, a second battery terminal <NUM>, a battery management unit <NUM>, a charging switch <NUM>, a discharging switch <NUM>, a first pack terminal <NUM>, and a second pack terminal <NUM>. The discharging switch <NUM> includes a first switch <NUM> and a first diode <NUM>, and the charging switch <NUM> includes a second switch <NUM> and a second diode <NUM>.

The battery <NUM> stores electricity and includes at least one battery cell <NUM>. The battery <NUM> may include one battery cell <NUM> or a plurality of battery cells <NUM> which are connected in series, parallel, or series-parallel. The number of battery cells <NUM> included in the battery <NUM> and the method of connecting the battery cells <NUM> may be determined according to a required output voltage and a required electricity storage capacity.

The battery cells <NUM> may include rechargeable battery cells other than rechargeable lead-acid battery cells. For example, the battery cells <NUM> may include nickel-cadmium battery cells, nickel metal hydride (NiMH) battery cells, lithium-ion battery cells, or lithium polymer battery cells.

The first battery terminal <NUM> and the second battery terminal <NUM> are connected to a positive (+) electrode and a negative (-) electrode of the battery <NUM>, respectively. The first battery terminal <NUM> and the second battery terminal <NUM> may be wiring patterns such as electrode patterns, connector patterns, terminal block patterns, land patterns, or pad patterns. In addition, the second battery terminal <NUM> may be connected to one of the negative and positive electrodes of the battery <NUM>, and the idea of the present disclosure is not limited to the case shown in <FIG> in which the second battery terminal <NUM> is connected to the negative electrode of the battery <NUM>. For example, when the second battery terminal <NUM> is connected to the negative electrode of the battery <NUM>, the first battery terminal <NUM> is connected to the positive electrode of the battery <NUM>, and when the second battery terminal <NUM> is connected to the positive electrode of the battery <NUM>, the first battery terminal <NUM> is connected to the negative electrode of the battery <NUM>.

The first pack terminal <NUM> and the second pack terminal <NUM> may be electrically connected to an external device (not shown). The first pack terminal <NUM> and the second pack terminal <NUM> may be wiring patterns such as electrode patterns, connector patterns, terminal block patterns, land patterns, or pad patterns. The first pack terminal <NUM> is electrically connected to the first battery terminal <NUM>, and the second pack terminal <NUM> is electrically connected to the second battery terminal <NUM>. Therefore, when the first battery terminal <NUM> is connected to the positive (+) electrode of the battery <NUM>, the first pack terminal <NUM> is a positive pack terminal, and in this case, since the second battery terminal <NUM> is connected to the negative electrode of the battery <NUM>, the second pack terminal <NUM> is a negative pack terminal.

The battery pack <NUM> is connected to an external device through the first pack terminal <NUM> and the second pack terminal <NUM>. Examples of the external device includes a load which consumes electricity received from the battery <NUM>, and a charger <NUM> (refer to <FIG>) which charges the battery <NUM> by supplying electricity to the battery <NUM>.

The discharging switch <NUM> is arranged between the second battery terminal <NUM> and the second pack terminal <NUM>. The discharging switch <NUM> is placed along a high current path through which charging current and discharging current of the battery <NUM> flow, and the discharging switch <NUM> may allow or interrupt the flow of discharging current of the battery <NUM>. The first diode <NUM> may have a forward direction in which charging current of the battery <NUM> flows, and a direction in which discharging current of the battery <NUM> flows may be the reverse direction of the first diode <NUM> such that the first diode <NUM> may interrupt the flow of discharging current. The first switch <NUM> and the first diode <NUM> may be implemented using a power MOSFET device having a vertical diffused MOS structure.

The charging switch <NUM> is arranged between the discharging switch <NUM> and the second pack terminal <NUM>. Like the discharging switch <NUM>, the charging switch <NUM> may be placed along the high current path and may allow or interrupt the flow of charging current. The charging switch <NUM> includes a second switch <NUM> and a second diode <NUM>, wherein the second diode <NUM> may have a forward direction in which discharging current flows, and a direction in which charging current flows may be the reverse direction of the second diode <NUM> such that the second diode <NUM> may interrupt the flow of charging current. The second switch <NUM> and the second diode <NUM> may be implemented using a power MOSFET device having a vertical diffused MOS structure.

The battery management unit <NUM> may sense the current, voltage, or temperature of the battery <NUM>, and may obtain information such as the remaining electricity, lifespan, and state of charge (SOC) of the battery <NUM> based on the sensed information. For example, the battery management unit <NUM> may measure the voltage and temperature of the battery cells <NUM> using sensors. In addition, the battery management unit <NUM> may monitor the voltage between the first pack terminal <NUM> and the second pack terminal <NUM> to detect whether the charger <NUM> is connected.

The battery management unit <NUM> may turn off at least one of the charging switch <NUM> and the discharging switch <NUM> when the battery <NUM> is likely to be exposed to danger. The battery management unit <NUM> may control the charging switch <NUM> and the discharging switch <NUM> to protect the battery <NUM> when the battery <NUM> is overdischarged or overcharged or there is a possibility of overcurrent, overvoltage, or overheating.

When it is detected that the voltage of the battery <NUM> is equal to or less than a certain value, the battery management unit <NUM> turns off the first switch <NUM> of the discharging switch <NUM> to prevent overdischarging of the battery <NUM>. When the first switch <NUM> is turned off, the battery <NUM> is not discharged, but charging current may flow to the battery <NUM> through the first diode <NUM>.

Similarly, the battery management unit <NUM> turns off the second switch <NUM> of the charging switch <NUM> to prevent the battery <NUM> from being overcharged. When the second switch <NUM> is turned off, the battery <NUM> is not charged, but discharging current may flow through the second diode <NUM>. In addition, the battery management unit <NUM> may open both the first switch <NUM> and the second switch <NUM> to interrupt charging current and discharging current when the battery <NUM> is exposed to danger due to overheating or overcurrent.

According to an embodiment, the battery management unit <NUM> may determine one of a first charging mode and a second charging mode as the charging mode of the battery <NUM>. The first charging mode is a mode for charging the battery <NUM> in a state in which the first switch <NUM> is turned on to allow charging current to flow to the battery <NUM> through the first switch <NUM>. The second charging mode is a mode for charging the battery <NUM> in a state in which the first switch <NUM> is turned off such that charging current flows via the first diode <NUM>.

When the charger <NUM> is connected between the first pack terminal <NUM> and the second pack terminal <NUM>, the battery <NUM> may be charged in the first charging mode up to a voltage corresponding to a voltage applied between the first pack terminal <NUM> and the second pack terminal <NUM>. In the second charging mode, the battery <NUM> may be charged up to a target voltage that is lower than the voltage applied between the first pack terminal <NUM> and the second pack terminal <NUM> by a preset voltage. The preset voltage is a voltage dropped by the first diode <NUM> according to the characteristics of the first diode <NUM>. Details of the preset voltage will be described below with reference to <FIG>.

<FIG> is a view schematically illustrating the structure and characteristic curve of a diode.

Referring to <FIG>, the diode is formed by bonding a P-type semiconductor and an N-type semiconductor. The diode allows current to flow in a direction from the P-type semiconductor to the N-type semiconductor, but does not allow current to flow in the opposite direction.

In the diode, the number of free electrons and the number of holes decrease at a junction interface, thereby forming an insulating region. Specifically, the density difference between free electrons and holes at the junction interface causes the free electrons to diffuse to the P-type semiconductor and holes to diffuse to the N-type semiconductor, thereby forming a depletion layer by recombination of the free electrons and the holes. The diode has an electric field formed in the depletion layer, and the electric field prevents the depletion layer from expanding further. As a result, in the diode, the electric field causes a potential difference between both ends of the depletion layer, which is called a diffusion voltage Vb. The diffusion voltage Vb is about <NUM> V in a germanium semiconductor and about <NUM> V in a silicon semiconductor.

Referring to the graph shown in <FIG>, when a forward voltage is applied to the diode, for example, when a positive (+) power source terminal is connected to the P-type semiconductor and a negative (-) power source terminal is connected to the N-type semiconductor, free electrons and holes of the depletion layer migrate to original positions in the diode. When the forward voltage is equal to or higher than the diffusion voltage Vb, electrons and holes may freely move through the depletion layer, and thus current may flow. In this case, a voltage drop occurs between both ends of the diode in an amount equal to the diffusion voltage Vb. The diffusion voltage Vb is the preset voltage described with reference to <FIG>. The preset voltage is maintained at a constant level regardless of the magnitude of current flowing through the diode. For example, when the diffusion voltage Vb of the diode is <NUM> V, the diffusion voltage is maintained at <NUM> V regardless of whether the current flowing through the diode is <NUM> A or 2A. That is, when a forward voltage is applied to the diode, a constant voltage drop of <NUM> V occurs between both ends of the diode regardless of the magnitude of current.

Unlike this, when a reverse voltage is applied to the diode, for example, when a negative (-) power source terminal is connected to the P-type semiconductor and a positive (+) power source terminal is connected to the N-type semiconductor, the depletion layer becomes larger and free electrons and holes are collected at both ends of the diode. In this case, the free electrons and holes are not unable to move through the depletion layer in the diode, and thus current does not flow. In addition, when a voltage equal to or greater than a breakdown voltage Va is applied across both ends of the diode, the diode is broken, and reverse current flows.

According to an embodiment, in the second charging mode, the battery <NUM> is charged up to the target voltage that is lower than a voltage applied between the first pack terminal <NUM> and the second pack terminal <NUM> by the preset voltage. In the second charging mode, the battery <NUM> is charged with charging current that flows through the first diode <NUM> and the second switch <NUM>. The battery <NUM> is supplied with a voltage which is lowered by the preset voltage at the first diode <NUM>. Meanwhile, the magnitude of diffusion voltage remains unchanged within a certain range of current flowing through the first diode <NUM>. For example, when the charger <NUM> charges the battery pack <NUM> at a constant voltage of <NUM> V, the battery <NUM> is charged up to <NUM> V which is lowered from <NUM> V by <NUM> V. That is, the battery <NUM> is charged to a voltage which is lower than the voltage applied by the charger <NUM> by the voltage drop at the diode.

Unlike this, in the first charging mode, the battery <NUM> is charged up to a voltage corresponding to the voltage applied by the charger <NUM>. In the first charging mode, charging current flows through the first switch <NUM> and the second switch <NUM>. The voltage drop at the first switch <NUM> and the second switch <NUM> is negligibly small, and thus the battery <NUM> is charged up to a voltage corresponding to the voltage applied by the charger <NUM>. For example, when the charger <NUM> charges the battery pack <NUM> at a constant voltage of <NUM> V, the battery <NUM> may be charged up to <NUM> V.

Meanwhile, as the charging by the charger <NUM> proceeds, the magnitude of charging current flowing through the battery <NUM> decreases, and thus, when the charger <NUM> detects a current less than a preset current, the charger <NUM> determines that the battery <NUM> is completely charged. Hereinafter, for each of illustration, the case in which the charger <NUM> detects that the battery <NUM> is completely charged will be described as a state in which the battery <NUM> is fully charged.

<FIG> is a graph illustrating the degree of deterioration of the battery <NUM> according to the number of times that the battery <NUM> is fully charged and left for a certain period of time.

Referring to <FIG>, the vertical axis refers to the capacity of the battery <NUM>, and the horizontal axis refers to the number of times that the battery <NUM> is charged.

The charger <NUM> charges the battery <NUM> in a constant-current charging mode in which a constant charging current is applied to the battery pack <NUM> and in a constant-voltage charging mode in which a constant charging voltage is applied to the battery pack <NUM>. The charger <NUM> starts to charge the battery <NUM> in the constant-current charging mode, and when it is determined that the battery <NUM> reaches a certain voltage or a certain state of charge (SOC), the charger <NUM> changes the charging mode from the constant-current charging mode to the constant-voltage charging mode. Meanwhile, the charger <NUM> may apply various square-wave charging currents to the battery pack <NUM>, and this case is also included in the constant-current charging mode. The idea of the present disclosure is not limited to the constant-current charging scheme.

The charger <NUM> is set in advance to charge the battery <NUM> up to a full-charge voltage at which the lifespan of the battery <NUM> is not shortened and the battery <NUM> is not damaged. To this end, the charger <NUM> applies the full-charge voltage to the battery pack <NUM> in the constant-voltage charging mode. For example, when seven battery cells <NUM> connected in series are charged, if the voltage for safely charging each of the battery cells <NUM> is <NUM> V, the full-charge voltage is set to be <NUM> V.

However, the battery <NUM> may be left unused for a certain period of time after being charged up to the full-charge voltage. For example, the battery pack <NUM> may be included in an electric bicycle or an electric vehicle. The battery pack <NUM> included in an electric bicycle or an electric vehicle may be left for a long time in a fully-charged state, for example, when the user of the electric bicycle or vehicle is asleep. Such a situation in which the battery <NUM> is left for a long time may be repeated every day, and thus the situation in which materials such as active materials and additives included in the battery cells <NUM> of the battery <NUM> are left for a long time in an unstable state may be repeated, thereby accelerating deterioration of the battery <NUM>. This may be clearly understood from a first curve L1 and a second curve L2 shown in <FIG>.

That is, the full-charge voltage of the charger <NUM> is set by considering only the degree of deterioration of the battery <NUM> according to a charging voltage without considering a decrease in the lifespan of the battery <NUM> when the battery <NUM> is left in a fully-charged state for a certain period of time.

The first curve L1 and the second curve L2 show the degree of decrease in the lifespan of the battery <NUM> for the cases in which the battery cells <NUM> are used after being left for a certain period of time at different voltages. The first curve L1 shows the degree of decrease in the lifespan of the battery <NUM> when the battery <NUM> is charged up to the full-charge voltage set in the charger <NUM> of the related art and is then left for a certain period of time, and the second curve L2 shows the degree of decrease in the lifespan of the battery <NUM> when the battery <NUM> is charged up to a voltage (hereinafter referred to as a target voltage) which is lower than the full-charge voltage of the charger <NUM> of the related art by the preset voltage described with reference to <FIG> and is then left for the certain period of time. As described above, the preset voltage refers to the voltage drop at the first diode <NUM>, and the target voltage is a voltage obtained by subtracting the preset voltage from the full-charge voltage. In addition, the certain period of time is a time period during which the battery <NUM> is left in a state in which the battery <NUM> is connected to the charger <NUM> of the related art after being completely charged by the charger <NUM>, and the certain period of time may be <NUM> hours or longer.

When the battery <NUM> is left for the certain period time in a state in which the battery <NUM> is completely charged and connected to the charger <NUM>, the degree of deterioration of the battery <NUM> and the degree of decrease in the lifespan of the battery <NUM> are referred to as a combine cycle life. That is, the first curve L1 shows the combine cycle life of the battery <NUM> when the battery <NUM> is charged to the full-charge voltage set in the charger <NUM>, and the second curve L2 shows the combine cycle life of the battery <NUM> when the battery <NUM> is charged to the target voltage.

For example, when the battery cells <NUM> reach <NUM> V after being charged up to the full-charge voltage set in the charger <NUM>, the first curve L1 indicates the combine cycle life of the battery cells <NUM> in a state in which the battery cells <NUM> are completely charged to <NUM> V, and the second curve L2 indicates the combine cycle of the battery cells <NUM> in a state in which the battery cells <NUM> are completely charged to <NUM> V.

When the first curve L1 and the second curve L2 are compared with each other, the deterioration of the battery <NUM> occurs relatively slowly when the battery <NUM> is charged to a voltage lower than the full-charge voltage set in the charger <NUM> of the related art. Considering this, it is necessary to readjust the full-charge voltage set in the charger <NUM> of the related art to increase the lifespan of the battery <NUM>. However, this method is not easy because costs increase to redesign or replace the charger <NUM>. According to the embodiment of the present disclosure, although the battery pack <NUM> is connected to the charger <NUM> of the related art, charging of the battery <NUM> may be completed at a voltage lower than the full-charge voltage set in the charger <NUM> by using the first diode <NUM> and the first switch <NUM> included in the discharging switch <NUM>, and thus it may be possible to guarantee a long lifespan of the battery <NUM> even by considering the combine cycle life of the battery <NUM>.

According to the embodiment of the present disclosure, in the second charging mode, the battery pack <NUM> may be charged to the target voltage which is lower than the full-charge voltage set in the charger <NUM> by using the first diode <NUM> and the first switch <NUM> included in the discharging switch <NUM>. As described with reference to <FIG>, in the second charging mode, the battery pack <NUM> may turn off the first switch <NUM> to cause charging current to flow through the first diode <NUM> such that a voltage lower than the full-charge voltage applied by the charger <NUM> of the related art may be applied to the battery <NUM>. In this case, the battery <NUM> has a combine cycle life according to the second curve L2, not the first curve L1. That is, it is possible to reduce a decrease in the lifespan of the battery <NUM> by completing charging of the battery <NUM> in the second charging mode instead of completing charging of the battery <NUM> in the first charging mode.

In other words, even when the full-charge voltage of the charger <NUM> of the related art is set without considering the combine cycle life of the battery <NUM>, the battery pack <NUM> may charge the battery <NUM> only up to the target voltage which is lower than the full-charge voltage of the charger <NUM> by using the first diode <NUM>, and thus rapid deterioration of the battery <NUM> occurring when the battery <NUM> is left for a long period of time after being fully charged may be prevented.

For example, when the charger <NUM> of the related art is designed to charge the battery <NUM> including seven battery cells <NUM> to a voltage of <NUM> V, the battery <NUM> is charged to <NUM> V in the first charging mode and thus each of the battery cells <NUM> is charged to <NUM> V. In the second charging mode, the battery <NUM> is charged up to the target voltage which is lowered by the first diode <NUM>, and when the voltage drop at the first diode <NUM> is <NUM> V, the battery <NUM> is charged up to <NUM> V and thus each of the battery cells <NUM> is charged up to <NUM> V. Thus, when charging of the battery <NUM> is completed in the second charging mode, the lifespan of the battery <NUM> decreases less according to the second curve L2 than in the case in which the lifespan of the battery <NUM> decreases according to the first curve L1 as a result of charging in the first charging mode.

Thus, according to the embodiment of the present disclosure, the battery pack <NUM> may lower the full-charge voltage at which charging of the battery <NUM> is completed by using the first diode <NUM> without replacing the charger <NUM> of the related art, and thus the lifespan of the battery <NUM> may be increased.

<FIG> is a view illustrating the flow of charging current in the battery pack <NUM> in the first charging mode according to an embodiment of the present disclosure, and <FIG> is a view illustrating the flow of charging current in the battery pack <NUM> in the second charging mode according to an embodiment of the present disclosure.

Referring to <FIG>, in the first charging mode, a charging current Ic flows through the first pack terminal <NUM>, the battery <NUM>, the first switch <NUM>, the second switch <NUM>, and the second pack terminal <NUM>.

Since voltage drops at the first switch <NUM>, the second switch <NUM>, and a wire are negligibly small, a voltage sensed across the first pack terminal <NUM> and the second pack terminal <NUM> corresponds to a voltage sensed across the first battery terminal <NUM> and the second battery terminal <NUM>. For example, when a voltage applied between the first pack terminal <NUM> and the second pack terminal <NUM> is <NUM> V, a voltage between the first battery terminal <NUM> and the second battery terminal <NUM> is also <NUM> V.

In this case, the battery <NUM> is charged to the full-charge voltage described with reference to <FIG>. That is, since the voltage between the first battery terminal <NUM> and the second battery terminal <NUM> corresponds to the voltage between the first pack terminal <NUM> and the second pack terminal <NUM>, the battery <NUM> is charged to a voltage corresponding to the full-charge voltage applied by the charger <NUM>.

Referring to <FIG>, since the first switch <NUM> is turned off in the second charging mode, a charging current Ic' flows through the first pack terminal <NUM>, the battery <NUM>, the first diode <NUM>, the second switch <NUM>, and the second pack terminal <NUM>.

When the charging current Ic' flows in the forward direction of the first diode <NUM>, a voltage drop occurs corresponding to a diffusion voltage of the first diode <NUM> according to the internal characteristics of the first diode <NUM>. For example, when the first diode <NUM> includes silicon, the diffusion voltage is <NUM> V, and the voltage between the first battery terminal <NUM> and the second battery terminal <NUM> is lower than the voltage between the first pack terminal <NUM> and the second pack terminal <NUM> by <NUM> V. In addition, the diffusion voltage remains unchanged although the magnitude of current flowing through the first diode <NUM> varies.

According to an embodiment, the first switch <NUM> and the first diode <NUM> are located between the second pack terminal <NUM> and the second battery terminal <NUM> which is a negative (-) terminal of the battery <NUM>. In this case, the first switch <NUM> includes an N-channel MOSFET. The N-channel MOSFET may be fabricated at lower costs than a P-channel MOSFET, and it is also possible to remove the possibility of counter electromotive force occurring when the first switch <NUM> and the first diode <NUM> are arranged between the first pack terminal <NUM> and the first battery terminal <NUM> which is the positive a positive (+) terminal of the battery <NUM>.

According to an embodiment, in the second charging mode, the battery <NUM> is fully charged to the target voltage which is lower than the full-charge voltage by the voltage drop at the first diode <NUM>. In this case, when the battery <NUM> is charged close to the target voltage, the charging current flowing in the battery <NUM> becomes lower than the preset current, and the charger <NUM> may determine that the battery <NUM> is fully charged.

According to an embodiment, the battery management unit <NUM> may start charging of the battery <NUM> in the first charging mode and may switch the mode of charging to the second charging mode when a preset condition is satisfied during charging of the battery <NUM>. When the battery <NUM> is continuously charged in the second charging mode, the voltage drop at the first diode <NUM> may cause a decrease in the charging speed of the battery <NUM> and heating in the first diode <NUM>. To minimize a decrease in the charging speed of the battery <NUM> and heating in the first diode <NUM>, the battery management unit <NUM> may switch the charging mode of the battery <NUM> from the first charging mode to the second charging mode when the voltage or charging current of the battery <NUM> satisfies a preset condition.

The preset condition may be set by considering the time and characteristics when the charger <NUM> switches from a constant-current charging mode to a constant-voltage charging mode. For example, the charger <NUM> may switch from the constant-current charging mode to the constant-voltage charging mode when the voltage of the battery cells <NUM> of the battery <NUM> is within the range of <NUM> V to <NUM> V, or the state of charge (SOC) of the battery <NUM> is within the range of <NUM>% to <NUM> %. In this case, the battery management unit <NUM> may determine that the preset condition is satisfied when the voltage of the battery <NUM> reaches a value ranging from <NUM> V to <NUM> V or the state of charge (SOC) of the battery <NUM> reaches a value ranging from <NUM>% to <NUM>%.

In addition, since the charger <NUM> applies a constant voltage to the battery pack <NUM> in the constant-voltage charging mode, when the battery management unit <NUM> detects application of a constant voltage, the battery management unit <NUM> may determine that the preset condition is satisfied.

Furthermore, since charging current output from the charger <NUM> gradually decreases while the charger <NUM> switches from the constant-current charging mode to the constant-voltage charging mode, the battery management unit <NUM> may switch from the first charging mode to the second charging mode when the battery management unit <NUM> detects that the charging current output from the charger <NUM> gradually decreases from a constant value.

In addition, the battery management unit <NUM> may determine that the preset condition is satisfied when it is determined, based on variations in the voltage and charging current of the battery <NUM>, that the battery <NUM> will soon reach the target voltage.

According to an embodiment, the battery management unit <NUM> may switch the charging mode of the battery <NUM> from the first charging mode to the second charging mode based on the voltage of the battery cells <NUM>. The battery management unit <NUM> measures the voltage of at least one of the battery cells <NUM> and determines whether the battery <NUM> reaches a preset reference voltage based on the voltage of the at least one battery cell <NUM> and the number of battery cells <NUM> included in the battery <NUM>. For example, when the voltage of one of the battery cells <NUM> is <NUM> V and the battery <NUM> includes seven battery cells <NUM>, the battery management unit <NUM> may detects <NUM> V as the voltage of the battery <NUM> and may determine whether the voltage of the battery <NUM> is equal to or greater than the preset reference voltage.

Meanwhile, the preset reference voltage may be set with reference to the characteristics of the first diode <NUM> and the full-charge voltage of the charger <NUM>. For example, when the voltage drop at the first diode <NUM> is <NUM> V and the full-charge voltage of the charger <NUM> is <NUM> V, the preset reference voltage may be set to be between <NUM> V and <NUM> V. In this case, the battery management unit <NUM> may change the charging mode of the battery <NUM> from the first charging mode to the second charging mode before the battery <NUM> reaches the target voltage of <NUM> V.

According to an embodiment, the battery management unit <NUM> may switch from the first charging mode to the second charging mode when a current lower than a preset reference current is sensed. The preset reference current may be set by considering the difference between the target voltage and the full-charge voltage. As the battery <NUM> is charged, the difference between the voltage between the first battery terminal <NUM> and the second battery terminal <NUM> and the voltage between the first pack terminal <NUM> and the second pack terminal <NUM> applied by the charger <NUM> is reduced, and thus charging current output from the charger <NUM> is also gradually reduced such that the battery management unit <NUM> may sense, based on the variation in the charging current, that the battery <NUM> will soon reach the target voltage. For example, when the full-charge voltage is <NUM> V, the target voltage is 19V, and the charging current is <NUM> mA when the voltage of the battery <NUM> is near <NUM> V, the preset reference current may be set to be between <NUM> mA and <NUM> mA.

In this case, the battery pack <NUM> may charge the battery <NUM> to the target voltage which is lower than the full-charge voltage without affecting the constant-current, constant-voltage charging by the charger <NUM>. That is, the battery management unit <NUM> only charges the battery <NUM> with a voltage lower than a voltage applied by the charger <NUM> in a state in which the first switch <NUM> is turned off and a voltage drop occurs at the first diode <NUM>. Therefore, since the connection between the battery <NUM> and the charger <NUM> is not forcibly interrupted, the charger <NUM> may still charge the battery <NUM> with a constant voltage even though the first switch <NUM> is turned off.

In an embodiment, the battery management unit <NUM> may turn on the first switch <NUM> when the charger <NUM> is not connected between the first pack terminal <NUM> and the second pack terminal <NUM>. When the charger <NUM> is not connected between the first pack terminal <NUM> and the second pack terminal <NUM>, the battery management unit <NUM> may turn on the first switch <NUM> to allow discharging of the battery <NUM>.

<FIG> is a flowchart illustrating a method of controlling charging of the battery pack <NUM> according to an embodiment of the present disclosure.

Referring to <FIG>, the flowchart shows sequential operations performed by the battery pack <NUM> illustrated in <FIG>. Therefore, the above descriptions of the components shown in <FIG> may be applied to the method described below with reference to the flowchart of <FIG> even though the descriptions are not repeated in the following description.

Referring to <FIG>, the battery pack <NUM> may detect whether the charger <NUM> is connected for charging the battery <NUM>. The battery pack <NUM> starts a charging operation when the charger <NUM> is connected (S101).

When the charger <NUM> is connected to the battery pack <NUM>, the battery <NUM> is charged as charging current flows through the first switch <NUM> toward the battery <NUM> or the second pack terminal <NUM> (S103).

The battery pack <NUM> may sense whether or not a preset condition is satisfied. As described with reference to <FIG>, the preset condition is set by considering the state of charge or voltage of the battery <NUM> or variations in the charging current output from the charger <NUM> during switching from a constant-current charging mode to a constant-voltage charging mode. In addition, whether or not the preset condition is satisfied may be determined based on a preset voltage or current indicating that the voltage of the battery <NUM> will soon reach a target voltage (S105).

When the preset condition is satisfied, the battery pack <NUM> turns off the first switch <NUM> to cause charging current to flow through the first diode <NUM>. That is, the battery pack <NUM> turns off the first switch <NUM> to change the charging mode of the battery <NUM> to the second charging mode in which the battery <NUM> is charged with charging current flowing through the first diode <NUM>. A full-charge voltage applied by the charger <NUM> is not directly applied to the battery <NUM>, but is dropped at the first diode <NUM> and then applied to the battery <NUM>. In this case, the battery <NUM> enters a fully charged state in which the battery <NUM> is only charged up to the voltage dropped at the first diode <NUM> (S107).

In the second charging mode, the battery pack <NUM> senses whether the charger <NUM> is electrically disconnected (S109).

The battery pack <NUM> turns on the first switch <NUM> when electrical connection with the charger <NUM> is not detected. Since the battery pack <NUM> is not discharged with the first switch <NUM> being turned off, when it is necessary to discharge the battery <NUM> after the charger <NUM> is disconnected, the battery pack <NUM> may turn on the first switch <NUM> for preparing a discharging operation (S111).

In this manner, since the battery pack <NUM> uses the first diode <NUM>, the battery pack <NUM> may be charged only up to the target voltage which is lower than the full-charge voltage without replacing the charger <NUM> of the related art, and deterioration of the battery <NUM> may be minimized.

Claim 1:
A battery pack (<NUM>) comprising:
a battery (<NUM>) comprising at least one battery cell (<NUM>), a first battery terminal (<NUM>), and a second battery terminal (<NUM>);
a first pack terminal (<NUM>) and a second pack terminal (<NUM>) that are connected to a charger (<NUM>);
a discharging switch (<NUM>) comprising a first switch (<NUM>) and a diode (<NUM>), the first switch (<NUM>) being connected between the second pack terminal (<NUM>) and the second battery terminal (<NUM>), the diode (<NUM>) being connected in parallel to the first switch (<NUM>) and having a forward direction in which charging current of the battery (<NUM>) flows; and
a battery management unit (<NUM>) configured to determine a charging mode from one of a first charging mode in which the battery (<NUM>) is supplied with a voltage corresponding to a voltage applied between the first pack terminal (<NUM>) and the second pack terminal (<NUM>), using charging current flowing through the first switch (<NUM>) and a second charging mode in which the battery (<NUM>) is supplied with a target voltage that is lower than the voltage applied between the first pack terminal (<NUM>) and the second pack terminal (<NUM>) by a preset voltage, using charging current flowing through the diode (<NUM>),
characterised in that
the battery management unit (<NUM>) is configured to start charging the battery (<NUM>) in the first charging mode and then switch the charging mode to the second charging mode when the battery is charged to a preset reference voltage that is lower than the target voltage.