Battery charger and method of charging battery

Abstract

A battery charger includes a transformer having a primary winding and a first secondary winding. A current modulation circuit is coupled in series with the primary winding, and a battery detection circuit is coupled to the first secondary winding and configured to output a connection status signal. A control circuit is coupled to receive the connection status signal and to control the current modulation circuit to control energization of the primary winding based at least in part on the connection status signal. When the battery charger is in the standby mode, a change in output of a first secondary winding of the battery coupled to the battery charger causes the battery detection circuit to change the connection state signal, which switches the battery charger from the standby mode to the charging mode. Related methods and batteries are also disclosed.

Description

Technical Field

[0001] The present invention relates to a battery charger and a method for charging a battery. Background Art

[0002] A battery charger is used to charge rechargeable batteries. Typically, such a charger is plugged into a mains power source. The battery is connected to the charger and charged according to a charging scheme, such as a constant current constant voltage scheme.

[0003] It is generally desirable to reduce the amount of power consumed by a battery charger, especially when in standby mode, and to simplify and / or reduce the cost of the battery charger circuitry. Summary of the invention

[0004] In a first aspect, there is provided a battery charger comprising:

[0005] Transformer, including:

[0006] primary winding; and

[0007] a first secondary winding;

[0008] a current modulation circuit connected in series with the primary winding;

[0009] a battery detection circuit coupled to the first secondary winding and configured to output a connection status signal; and

[0010] a control circuit coupled to receive the connection status signal and to control the current modulation circuit based at least in part on the connection status signal to control energization of the primary winding;

[0011] Wherein, when the battery charger is in standby mode, in response to a change in the output of the first secondary winding of the battery charger connected to the battery, the battery detection circuit changes the connection status signal. In the standby mode, the control circuit controls the current modulation circuit to generate a standby pulse in the primary winding. The change in the connection status signal switches the battery charger from the standby mode to the charging mode. In the charging mode, the control circuit controls the current modulation circuit to generate a power pulse in the primary winding, wherein the average power of the power pulse is higher than the standby pulse.

[0012] Using the connection status signal in this manner to control switching between standby and charging modes may allow for reduced standby power consumption, and / or reduced or simplified circuitry.

[0013] The connection status signal may include a voltage that increases in response to the battery being connected to the battery charger. For example, the detection circuit may include a charge accumulation circuit configured to generate the connection status signal based on the pulses such that:

[0014] The voltage of the connection status signal as a result of the standby pulse is insufficient to cause the battery charger to switch from the standby mode to the charging mode when the battery is not connected; and

[0015] The voltage of the connection status signal as a result of the standby pulse when a battery is connected is sufficient to cause the battery charger to switch from the standby mode to the charging mode.

[0016] This can provide a convenient mechanism for controlling the switching between standby and charging modes.

[0017] The control circuit may include a charge controller for controlling the generation of the power pulses; and the connection status signal may be configured to power the charge controller during the charging mode. This may provide a convenient, simple and / or low power mechanism for controlling the charge controller.

[0018] As a result of the charge controller being powered up due to the voltage increase of the connection status signal, the battery charger can be configured to switch from the standby mode to the charging mode. This can provide a convenient and / or simple mechanism for controlling the charge controller.

[0019] The charge controller may include:

[0020] diode; and

[0021] A capacitor connected in series with a diode;

[0022] The voltage of the connection status signal is a voltage generated at the capacitor based on the current passing through the diode.

[0023] This may provide a convenient and / or simple mechanism for generating connection status signals.

[0024] The control circuit may include an oscillator or pulse generator for generating the standby pulse. Optionally, the oscillator or pulse generator may be disabled when the battery charger is in charging mode. This helps to reduce power consumption when the charger is in standby mode.

[0025] The oscillator or pulse generator may comprise an analog oscillator circuit. Optionally, the analog oscillator circuit may comprise an RC network. This may provide a convenient, simple and / or low power way of generating pulses in standby mode.

[0026] The battery charger can be operated only in a constant current charging mode. This can simplify the circuitry of the charger, especially when combined with one or more of the previous optional aspects.

[0027] The battery charger may be configured to receive feedback indicative of a charging current, wherein during a charging mode, the battery is charged only in a constant current mode, the charging current being controlled based on the feedback. This may simplify the circuitry of the charger compared to a charger using constant current constant voltage charging, particularly when combined with one or more of the previous optional aspects.

[0028] In response to the battery management system stopping charging the battery due to the charging voltage reaching a predetermined threshold, the connection status signal can cause the battery charger to switch from the charging mode to the standby mode. This can provide a convenient and / or simple mechanism for stopping charging.

[0029] The battery charger may be configured so that the connection status signal causes the battery charger to repeatedly switch back and forth between the charging mode and the standby mode. This may provide a convenient and / or simple mechanism to ensure full charging of the battery.

[0030] The battery charger may include a second secondary winding, wherein the battery charger is configured to charge the battery via the second secondary winding.

[0031] The standby pulses in the primary winding may induce corresponding pulses in the output of the battery charger, which may be detected by the battery management system (BMS) of the battery when the battery is connected to the battery charger for charging.

[0032] According to a second aspect, there is provided a method of charging a battery using a battery charger, the battery charger comprising a transformer having a primary winding and a first secondary winding, the method comprising:

[0033] outputting a connection status signal based on an output of the first secondary winding, the output varying based on whether the battery is connected to a battery charger for charging;

[0034] Based on the connection status signal, the current modulation circuit is controlled to control the energization of the primary winding, so that the battery charger can operate in the following modes:

[0035] a standby mode in which standby pulses are generated in the primary winding; and

[0036] a charging mode, wherein power pulses are generated in the primary winding, wherein the average power of the power pulses is higher than the standby pulses; and

[0037] The battery charger is switched from a standby mode to a charging mode in response to a change in the connection status signal due to a change in the output of the first secondary winding when the battery is coupled to the battery charger.

[0038] The method may include generating a connection status signal based on the pulses such that:

[0039] The voltage of the connection status signal as a result of the standby pulse is insufficient to cause the battery charger to switch from the standby mode to the charging mode when the battery is not connected; and

[0040] The voltage of the connection status signal as a result of the standby pulse when a battery is connected is sufficient to cause the battery charger to switch from the standby mode to the charging mode.

[0041] The method may include powering a charge controller of the battery charger with the connection status signal.

[0042] The method may include switching from the standby mode to the charging mode as a result of the charging controller being powered up due to an increase in the voltage of the connection status signal.

[0043] According to a third aspect, there is provided a battery for use with a battery charger according to any preceding claim.

[0044] The battery may include a bypass switch, the battery being configured to close the bypass switch when the battery is coupled to the battery charger according to the previous aspect.

[0045] The battery may include a battery management system configured to sense pulses at an output of a battery charger when the battery is coupled to the battery charger for charging.

[0046] The battery management system may be configured to close the bypass switch in response to sensing a pulse at the output of the battery charger when the battery management system determines that the battery requires charging.

[0047] Features described above in connection with any aspect of the invention are equally applicable to all other aspects of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a schematic circuit diagram showing a battery charger and connected batteries;

[0049] Figure 2 is a schematic circuit diagram showing another battery charger and a connected battery;

[0050] Figure 3 is a schematic circuit diagram showing another battery charger and a connected battery;

[0051] Figure 4 It is shown Figure 3 A signal diagram of a simulated operation of a battery charger; and

[0052] Figure 5 is a flow chart illustrating a method of charging a battery. DETAILED DESCRIPTION

[0053] refer to Figure 1, a battery charger 100 is shown. The battery charger 100 is used to charge a device (not shown) powered by a lithium-ion battery, such as a rechargeable hair care device or a vacuum cleaner. However, those skilled in the art will appreciate that such a battery charger may also be used to charge other types of rechargeable devices, appliances, and battery packs, including those using different battery chemistries.

[0054] The battery charger 100 includes a transformer 102. The transformer 102 includes a primary winding 104, a first secondary winding in the form of an auxiliary winding 106, and a second secondary winding 108. At least with respect to this particular embodiment, the transformer 102 takes the form of a flyback transformer, in the sense that the core and windings are optimized for a flyback converter. In other embodiments, the transformer may take any other suitable form.

[0055] The battery charger 100 includes a current modulation circuit in the form of a field effect transformer (FET) 110, whose source and drain are connected in series with the primary winding 104. Those skilled in the art will appreciate that other current modulation circuits may be used, including other semiconductor switches, and other active or passive components capable of modulating current.

[0056] The battery charger 100 includes a battery detection circuit 112 coupled to sense the output of the auxiliary winding 106 and arranged to output a connection status signal 114. As described in more detail below, the output of the auxiliary winding 106 varies based on whether a battery is coupled to the battery charger 100 for charging.

[0057] The battery charger 100 includes a control circuit 116 that is coupled to receive the connection status signal 114. The control circuit 116 is also coupled to the gate of the FET 110 so that the control circuit 116 can control the FET 110. The skilled person will appreciate that the control circuit 116 includes a gate driver circuit. As described in more detail below, the FET 110 controls the energization of the primary winding 104.

[0058] The control circuit 116 may take any suitable form. For example, the control circuit 116 may include one or more microprocessors having one or more drive outputs that control the FET 110. Alternatively, one or more functions of the control circuit 116 may be performed using dedicated analog circuits, digital controllers, or any suitable combination thereof. Figure 2 and 3 An example implementation is shown, but those skilled in the art will appreciate that the desired control may be achieved in many other ways.

[0059] The battery charger 100 includes an AC to DC conversion circuit 118 coupled to rectify and optionally filter the output of the secondary winding 108 .

[0060] The battery charger 100 includes a DC power supply 130, which may include, for example, a rectifier and a filter (not shown). The DC power supply 130 is powered by an AC mains power source (not shown).

[0061] Figure 1 A lithium-ion rechargeable battery 120 is shown, which is coupled for charging by the battery charger 100. The battery 120 includes battery cells and an optional battery management system, one embodiment of which is referred to as Figure 3 Describe it. Figure 1 In an embodiment, the battery 120 is a battery pack that can be removed from a device (not shown) with which it is intended to be used and temporarily connected to the battery charger 100 for charging, such as Figure 1 shown.

[0062] The battery charger 100 can operate in two modes. The first mode is a standby mode, in which the control circuit 116 controls the FET 110 to generate a standby pulse in the primary winding 104. The second mode is a charging mode, in which the control circuit 116 controls the FET 110 to generate a power pulse in the primary winding 104.

[0063] The average power of the power pulses is higher than the standby pulses. For example, the energy of all standby pulses averaged over a given period may be lower than the energy of the pulses averaged over a similar period when the charger is in charging mode. Optionally, the pulse frequency in standby mode may be lower than the pulse frequency in charging mode. This helps to reduce the power of the standby pulses. Alternatively or in addition, the peak voltage and / or current of the pulses in standby mode may be lower than the peak voltage and / or current in charging mode. Alternatively or in addition, the pulse duration in standby mode may be shorter than the pulse duration in charging mode.

[0064] When the battery 120 is connected to the battery charger 100 , the control circuit 116 switches the battery charger 100 from the standby mode to the charging mode in response to a change in the connection status signal 114 .

[0065] In use, the battery charger 100 is started in the standby mode and the battery 120 is not connected for charging. The control circuit 116 controls the FET 110 so that a series of pulses are applied to the primary winding 104. These pulses induce corresponding currents through the auxiliary winding 106 and the secondary winding 108. The battery detection circuit 112 determines that the output of the auxiliary winding 106 is relatively low, meaning that the battery 120 is not connected for charging. As such, the connection status signal 114 remains at a value indicating that the battery 120 is not connected to the battery charger 100, and the battery charger 100 therefore remains in the standby mode.

[0066] The battery detection circuit 112 can determine whether the output of the auxiliary winding 106 is relatively low or high in any suitable manner. For example, an analog-to-digital converter can be used to sample the output voltage of the auxiliary winding 106, and the digital value output by the analog-to-digital converter is processed to determine whether the voltage is high or low. For example, the digital value can be low-pass filtered, such as by a moving average. If the value of the moving average exceeds a threshold, the battery detection circuit 112 can conclude that the battery 120 has been connected to the battery charger 100 for charging.

[0067] Alternatively, the connection status signal 114 may take the form of an analog voltage. For example, the connection status signal 114 may include a voltage that is higher (or higher on average) when the battery 120 is connected to the battery charger 100 than when the battery 120 is not connected to the battery charger 100.

[0068] Those skilled in the art will appreciate that the battery detection circuit 112 can be configured in many other ways based on the first secondary winding (i.e. Figure 1 The output of the auxiliary winding 106 in the embodiment of the present invention determines whether the battery 120 is connected to the battery charger 100 for charging. Figure 2 and Figure 3 Specific implementations are described in greater detail.

[0069] Next, the battery 120 is connected to the battery charger 100 for charging. When connected in this manner, the battery 120 presents a voltage across the secondary winding 108 (e.g., during conduction of the output rectifier between the battery 120 and the secondary winding 108). As a result of the mirroring, this voltage across the secondary winding 108 causes the voltage / current within the auxiliary winding 106 to increase. Thus, the battery detection circuit 112 determines that the output of the auxiliary winding 106 is relatively high. The connection status signal 114 then changes to indicate that the battery 120 is connected to the battery charger 100.

[0070] The change in the connection status signal 114 causes the battery charger 100 to switch from the standby mode to the charging mode. This includes the control circuit 116 changing the way the FET 110 is controlled. Figure 1 In an embodiment, the battery charger 100 uses a flyback conversion. Thus, to switch the battery charger 100 to a charging mode, the control circuit 116 stops outputting the pulses it originally outputs and instead outputs pulses of the type typically used to drive a flyback transformer (e.g., transformer 102). The pulses applied to the primary winding 104 produce corresponding output pulses in the secondary winding 108.

[0071] Optionally, when the battery charger 100 is in the standby mode, the frequency of the flyback pulse is greater than the pulse output by the control circuit.

[0072] Skilled persons understand the operation of a flyback transformer in the context of a battery charger such as battery charger 100 and therefore the relationship between the flyback pulse applied to primary winding 104 and the output of secondary winding 108 will not be described in detail.

[0073] The output of the secondary winding 108 is supplied to an AC to DC conversion circuit 118 which rectifies the output and supplies the result to the battery 120 where it is used to charge the cells within the battery 120 , optionally under the control of a BMS.

[0074] Charging can use a constant current constant voltage charging scheme, a constant current only charging scheme, or any other suitable charging scheme. Figure 3 One embodiment of a battery 120 having a BMS and battery cells is described.

[0075] Battery charging may be terminated in any suitable manner. For example, the voltage of the battery cells of battery 120 may be measured by a BMS, and once the desired voltage is reached, the BMS terminates charging. If constant current and constant voltage are used, charging is initially performed at constant current. Once a first battery threshold voltage is reached, charging is switched from constant current to constant voltage. Charging continues at constant voltage until a second threshold voltage is reached, at which point charging stops.

[0076] Other charging schemes, such as constant current charging, may also be used. One such implementation is described in more detail below.

[0077] Go to Figure 2 , another embodiment of a battery charger 200 is shown. The battery charger 200 shares many features with the battery charger 100, and similar features are indicated by the same reference numerals. For clarity, Figure 2 The power supply 130 is not shown.

[0078] In the battery charger 200, the battery detection circuit 112 is indicated by a dotted line. The battery detection circuit 112 of the battery charger 200 includes a diode 122 and a capacitor 124 connected in series with the auxiliary winding 106. The connection status signal 114 is obtained from the junction between the diode 122 and the capacitor 124.

[0079] In the battery charger 200, the control circuit 116 includes a pulse generator 126 and a charge controller in the form of a flyback controller 128. The pulse generator 126 may take any suitable form, but is preferably Figure 2 In an embodiment of the present invention, a low power analog oscillator and a gate driver for the FET 110 are included. The pulse generator 126 is powered by a DC power supply 130.

[0080] Without intending to be bound by any particular power consumption value, it is contemplated that at least some embodiments enable the charger to achieve or at least approach the goal of zero standby power consumption (ZSPC), which is defined in standard IEC 62301:2011 as less than 5 mW (average power). Those skilled in the art will appreciate that this standard represents a goal, not a strict requirement. To achieve this goal, the pulse generator 126 should consume less than 5 mW of energy.

[0081] The pulse generator 126 and the flyback controller 128 receive the connection status signal 114 as control inputs.

[0082] Like the battery charger 100 , the battery charger 200 is operable in a standby mode and a charging mode.

[0083] In use, the battery charger 200 is started in standby mode, with the battery 120 not connected for charging. The pulse generator 126 controls the FET 110 so that a series of pulses are applied to the primary winding 104. The pulses induce a corresponding current through the secondary winding 108 and to a lesser extent through the auxiliary winding 106.

[0084] The auxiliary winding 106 is connected in series with the diode 122 and the capacitor 124. Thus, the voltage induced in the auxiliary winding 106 appears at the diode 122. Because the battery 120 does not provide a voltage across the secondary winding 108 when the battery charger 200 is in the standby mode, the pulse induced in the auxiliary winding 106 due to the mirrored pulse of the secondary winding 104 is not sufficient to turn on the flyback controller 128. Thus, the connection status signal 114 remains low, indicating that the battery 120 is not connected to the battery charger 200. The battery charger 200 thus remains in the standby mode, wherein the flyback controller 128 remains powered off, while the pulse generator 126 remains enabled.

[0085] Next, the battery 120 is connected to the battery charger 200 for charging. When connected in this manner, the battery 120 presents a voltage across the secondary winding 108 (e.g., when a rectifier (not shown) between the battery 120 and the secondary winding 108 is turned on). Figure 3 One method of connecting the voltage of the battery 120 to the secondary winding 108 through a rectifier is described, but those skilled in the art will appreciate that other methods of detecting battery connection may also be used.

[0086] As a result of the pulse applied to the primary winding 104, the increased voltage that the secondary winding 108 needs to provide to conduct through the rectifier 138 causes transformer magnetizing energy to flow through the auxiliary winding 106, charging the capacitor 124 through the diode 122, thereby causing the voltage (and therefore the value of the connection status signal 114) to rise.

[0087] Once the voltage at capacitor 124 reaches a sufficient level, flyback controller 128 is enabled. Those skilled in the art will appreciate a variety of ways this can be accomplished. For example, flyback controller 128 can be powered directly by DC power source 130, and connection status signal 114 can be used as an enable signal to cause flyback controller 128 to begin operation.

[0088] In the event that it is desired to further reduce power consumption during standby, the connection status signal 114 may be used to effectively wake up the flyback controller 128. For example, the connection status signal 114 may be used to activate the power supply of the flyback controller 128, thereby turning it on.

[0089] Alternatively, in Figure 2 In an embodiment of the present invention, the connection status signal 114 itself can form the power supply for the flyback controller 128. That is, when the battery 120 is not connected to the battery charger 200, the connection status signal 114 does not provide significant power to the flyback controller 128. The flyback controller 128 therefore remains "off" and actually consumes no power. When the battery 120 is connected to the battery charger 200, the connection status signal 114 charges the capacitor 124 via the diode 122. Once the voltage of the connection status signal 114 reaches a sufficiently high value, the flyback controller 128 is powered by the connection status signal 114 and begins to control the FET 110 to output a type of pulse that is typically used to drive a flyback transformer (such as the transformer 102). As described above, the flyback pulse applied to the primary winding 104 generates a corresponding output pulse in the secondary winding 108.

[0090] exist Figure 2 In the embodiment of the present invention, the detection circuit (i.e., the diode 122 and the capacitor 124) can be considered as a charge accumulation circuit, which is configured to generate a connection status signal based on the received pulse, such that:

[0091] The voltage of the connection status signal as a result of the standby pulse is insufficient to cause the battery charger to switch from the standby mode to the charging mode when the battery is not connected; and

[0092] The voltage of the connection status signal as a result of the standby pulse when a battery is connected is sufficient to cause the battery charger to switch from the standby mode to the charging mode.

[0093] The connection status signal 114 simultaneously (or slightly delayed) goes "high" causing the pulse generator 126 to be "turned off". The pulse generator 126 may be turned off in any suitable manner. For example, a comparator may monitor the connection status signal 114 against a reference voltage and disable the pulse generator 126 when the connection status signal 114 is above the reference voltage.

[0094] The battery charger 200 uses a constant current charging scheme, rather than a constant current constant voltage charging scheme. Figure 3 As shown, the operation of this charging scheme will now be described with reference to another embodiment of a battery charger 300. The battery charger 300 shares many features with the battery charger 100, and similar features are indicated by the same reference numerals. In fact, the battery charger 300 is the same as the battery charger 200, but includes many additional implementation details, which will now be described.

[0095] exist Figure 3 In the embodiment, the battery 120 includes a battery management system (BMS) 132 connected to the battery cells 134. The battery cells 134 are conventional lithium-ion battery cell arrays and will not be described in detail. The BMS 132 includes hardware that controls the charging of the battery cells 134 and may include, for example, a controller such as a microprocessor (not shown), a voltage sensing circuit (not shown), and / or any other suitable analog and / or digital circuitry required to implement the described functions. Such circuits are well understood by the skilled person and therefore will not be described in more detail.

[0096] The battery 120 also includes a bypass field effect transistor (FET) 136 that is controlled by the BMS 132, as described in more detail below.

[0097] Compared to the battery charger 200 , the battery charger 300 includes many other components. Figure 3 The conversion circuit 118 shown in dashed outline in FIG. 1 includes an output rectifier 138 for rectifying the output of the secondary winding 108 , and an output capacitor 140 for smoothing the output of the output rectifier 138 .

[0098] The battery charger 300 includes a first current feedback circuit 142 for providing feedback indicating the current charging current to the flyback controller 128 so that the flyback controller 128 can control the output to keep the current constant. In a manner well known to those skilled in the art, feedback is provided by an optocoupler 143 to maintain current isolation.

[0099] The battery charger 300 includes a second current feedback circuit 144 for providing feedback of the current flowing through the FET 110. The second current feedback circuit enables the flyback controller 128 to control the FET 110 during charging so that the transformer 102 is not saturated and the FET 110 is not overloaded.

[0100] The output of the second current feedback circuit 144 is also provided as an input to a first comparator 160. The first comparator 160 is also provided with a first reference input 162. The output of the first comparator 160 controls a switch 164, as described in more detail below.

[0101] Figure 3 Also shown is one way in which the pulse generator 126 may be implemented. The pulse generator 126 includes a controlled current source 166 coupled in series with a capacitor 168. The controlled current source 166 is enabled / disabled by the connection status signal 114 so that the pulse generator 126 only generates pulses when the battery charger 100 is in standby mode. Those skilled in the art will appreciate that the controlled current source 166 is merely one example of a mechanism for controlled charging of the capacitor 168, and any other suitable circuit may be used instead.

[0102] The junction between the controlled current source 166 and the capacitor 168 is coupled by means of a switch 170 to control the gate of the FET 110. The switch 170 is controlled by the output of a second comparator 172. The second comparator 172 accepts as input a second reference 174 and a junction between the controlled current source 166 and the capacitor 168. The connection status signal 114 is supplied to the second comparator 172 as an enable signal.

[0103] When the battery charger 120 is in the standby mode, the pulse generator 126 has three states.

[0104] In the first state, FET 110 is off, switch 170 is open, and switch 164 is open. This is a charging state during which capacitor 168 is charged by controlled current source 166 until the voltage of capacitor 168 exceeds the voltage of second reference 174. This causes a change in the output of second comparator 172, causing pulse generator 126 to enter the second state in which switch 170 is closed.

[0105] In the second state, capacitor 168 charges the gate of FET 110 via switch 170, turning on FET 110. The current through FET 110 begins to increase according to the DC power supply 130 voltage and the flyback primary inductance. When the current measured by the second current feedback circuit 144 is higher than the reference 162 connected to the first comparator 160, the output of the first comparator 160 changes state, causing switch 164 to close, thereby placing the pulse generator 126 in the third state.

[0106] In the third state, the switch 164 discharges the capacitor 168 and the gate of the FET 110. The FET 110 turns off, and the falling voltage at the capacitor 168 again changes the output of the second comparator 172, causing the pulse generator 126 to return to the first state.

[0107] When the battery charger 100 is in the standby mode, the first, second and third states are cycled through.

[0108] Those skilled in the art will appreciate that various forms of feedback may be provided to the flyback controller 128 in lieu of (or in addition to) the first current feedback circuit 142 and the second current feedback circuit 144. For example, charging current regulation may be performed by the flyback controller 128 based on feedback from the primary winding 104. Any such feedback may be based on current and / or voltage, depending on the charging scheme (e.g., current-based or voltage-based). Furthermore, those skilled in the art will appreciate that current may be estimated based on voltage, and thus current feedback may take the form of voltage (or vice versa). Any other available signal may also be used to estimate current, either directly or indirectly.

[0109] The battery charger 300 includes a buffer or active clamp circuit 146 which operates in a manner known to those skilled in the art and will not be described in further detail.

[0110] In the standby mode, the battery charger 300 operates in the same manner as described with respect to the battery charger 200 .

[0111] When the battery 120 is coupled to the charger 300 (when charging), the BMS 132 senses a standby pulse from the secondary winding 108. In response to the sensed pulse (and if the BMS 132 determines that the battery cell 134 needs to be charged), the BMS 132 controls the bypass FET 136 to close, which in turn allows the voltage from the battery cell 134 to be applied to the secondary winding 108 via the output rectifier 138. During the conduction phase of the output rectifier 138, the auxiliary winding 106 mirrors the voltage increase on the secondary winding 108. This increased voltage on the auxiliary winding 106 powers up the flyback controller 128 and disables the pulse generator 126, as described in more detail above.

[0112] As a result of the flyback controller 128 controlling the FET 110, the pulses supplied to the primary winding 104 generate output pulses in the secondary winding 108. The output pulses are rectified by the output rectifier 138 and filtered by the output capacitor 140 to provide DC power to the BMS 132. The BMS 132 uses the DC power to power itself and control the charging of the battery cell 134.

[0113] Those skilled in the art will appreciate that this sequence will only occur when the battery charger 100 is powered (i.e., plugged into the mains and, if necessary, turned on) when the battery 120 is connected to the battery charger 100. In some embodiments, the BMS 132 may be operated in a low power or standby mode. If the battery 120 is connected to the battery charger 100 when the battery charger 100 is not powered, the absence of pulses at the secondary winding 108 means that the BMS 132 will not be awakened from its low power or standby mode and therefore will not close the FET 110 to initiate the flyback conversion mode and thus initiate charging of the battery 120.

[0114] If the battery charger is powered up when the battery 120 is connected to it, the standby pulses described above will begin, causing pulses to appear at the secondary winding 108. These pulses wake the BMS 132 from its low power / standby mode and continue switching the flyback charging mode as described above.

[0115] Those skilled in the art will understand that Figure 3 As shown, any BMS may not be inserted between the conversion circuit 118 and the battery cell 134. Instead, the BMS may be connected in parallel with the battery cell 134 and configured to sense factors related to the charging of the battery cell 134 (e.g., optionally including the current battery cell voltage and charging current), and to control elements such as the bypass FET 136.

[0116] The battery 120 is charged by the battery charger 300 using a suitable constant current. The voltage required to maintain the constant current increases as the battery cell 134 is charged. Once the voltage reaches a first threshold, the BMS 132 disconnects the battery cell 134 and turns on the bypass FET 136 so that the charging current no longer flows through the battery cell 134.

[0117] The flyback controller 128 determines that the battery 120 is no longer being charged. This determination may be made in any suitable manner, such as through feedback from the auxiliary winding 106, or through a comparator (not shown) connected to the output of the charger 300. Based on this determination, the flyback controller 128 stops generating the flyback control signal for the FET 110.

[0118] When the flyback controller 128 is turned off, the output capacitor 140 needs to discharge faster than the flyback controller capacitor to avoid starting to charge again due to the mirroring of the voltage in the output capacitor 140. Those skilled in the art will appreciate that there are a number of ways to achieve this.

[0119] For example, current leakage can be designed into the charger (e.g., by connecting a resistor). The values ​​of capacitor 124 and output capacitor 140 can be selected in conjunction with such designed current leakage to ensure that the voltage at output capacitor 140 drops fast enough relative to the voltage at capacitor 124 to ensure that charging does not restart.

[0120] An alternative approach is to add circuitry that increases the current drain at the charger output to discharge the output capacitor 140 once charging is stopped by the BMS 132. There are a number of ways to achieve this controlled current drain, including using a non-linear impedance (such as a Zener diode or a voltage reference) or a comparator, or an optocoupler between the flyback controller power rail (i.e., the connection status signal 114) and the output capacitor 140.

[0121] Another alternative is to add a circuit within the battery 120 , controlled by the BMS 132 , to reduce the voltage of the output capacitor 140 when the BMS stops charging the battery cell 134 .

[0122] Once the voltage of the connection status signal 114 drops sufficiently, the pulse generator 126 is restarted and begins outputting standby pulses again, as described above. The BMS 132 receives pulses from the charger 300 as described above, and may choose to restart charging depending on the charging state of the battery cell 134. In this case, the BMS turns off the FET 136 and repeats the above process.

[0123] The typical result of this sequence is a relatively long initial constant current charge cycle (assuming the battery has a relatively low initial charge), followed by one or more relatively short constant current charge cycles. When the BMS 132 eventually determines that charging is no longer required, the FET 136 remains off and no further charging occurs.

[0124] Figure 4 It is shown Figure 3 Signal diagram of the operation of a battery charger. Four signal traces are shown:

[0125] 1. A charging current ILOAD passes through the battery 120.

[0126] 2. The voltage Vbat of the battery 120.

[0127] 3. The voltage VDD of capacitor 124.

[0128] 4. The output voltage Vout of the charger 300.

[0129] During the period until time 5.0, charger 300 is in standby mode. Due to the lack of voltage on secondary winding 108, the mirror pulse generated by pulse generator 126 in primary winding 104 produces a relatively small pulse 156 at the output of charger 300 (ie, at capacitor 140).

[0130] The battery 120 is connected to the battery charger 300 at time 5.0. The BMS 132 detects the pulse 156 at the output of the charger 300 and in response (and assuming the BMS 132 determines that the battery 120 needs charging), closes the bypass FET 136. This connects the battery cell 134 voltage across the secondary winding 108, as shown by the slight drop 158 in Vbat at this point and the increase 180 in the voltage Vout at the output of the charger 300.

[0131] As described above, the presence of the battery voltage on the secondary winding 108 increases the voltage developed on the auxiliary winding 106 due to the mirroring of the standby pulse, which results in charging of the capacitor 124 via the diode 122. This is reflected in Figure 4 Because FET 136 is closed, battery 120 sees a current pulse 186, such as Figure 4 The ILOAD signal is shown in Figure 1.

[0132] At approximately time 5.25, VDD rises to voltage 184, which is high enough to power up flyback controller 128. Flyback controller 128 begins controlling FET 110, causing the voltage on and current through primary winding 104 to rise. When FET 110 turns off, the current through primary winding 104 suddenly decreases, creating a current in secondary winding 108. This type of flyback conversion is well known to those skilled in the art and will not be described in detail.

[0133] The output of secondary winding 108 is rectified by output rectifier 138 and filtered by output capacitor 140. The resulting filtered DC charges battery 120. The charging current remains constant, as shown by the relatively constant value of ILOAD during the charging period between times 5.25 and 6.0 (approximately).

[0134] It should be understood that actual charging time will usually be longer than Figure 4 The periods shown are much longer. This is because for explanatory purposes, Figure 4 Represents the behavior of a simulated battery charger.

[0135] The flyback controller 128 controls the constant current based on feedback received via the first current feedback circuit 142. To maintain a constant current, the voltage applied to the battery 120 needs to increase during charging, as shown by the rising value of Vbat between times 5.25 and 6 (approximately).

[0136] Once the voltage Vbat of the battery 120 reaches the first threshold 38.5V at approximately time 6.0, the battery cell 134 is disconnected by the BMS 132 turning off the FET 136. The output voltage increases briefly after the battery cell 134 is disconnected. The resulting increase in voltage at the flyback controller 128 is detected and the flyback circuit 128 is disabled as described above.

[0137] After the charging voltage stops, Vbat will drop slightly.

[0138] Due to the discharge of the corresponding capacitors, the values ​​of VDD and Vout decrease as described above.

[0139] Once VDD drops sufficiently (at approximately time 6 . 3 ), the pulse generator 126 begins to operate, and low voltage pulses 156 are again supplied by the pulse generator 126 to the primary winding 104 .

[0140] If the BMS 132 determines that further charging of the battery cell 134 is required, the process is repeated as described above.

[0141] Go to Figure 5 , a flow chart representing a method 148 for charging a battery is shown. The method 148 uses a battery charger including a transformer having a primary winding and a first secondary winding. Battery chargers 100, 200, and 300 are examples of such battery chargers, although other suitable battery chargers and charger types may also be used.

[0142] The method 148 includes outputting 150 a connection status signal based on the output of the first secondary winding, the output varying based on whether the battery is connected to a battery charger for charging. As described above, the connection status signal 114 is an example of such a connection status signal.

[0143] The method 148 includes controlling 152 a current modulation circuit based on the connection status signal to control energization of the primary winding such that the battery charger can operate in the following modes:

[0144] a standby mode in which standby pulses are generated in the primary winding; and

[0145] A charging mode in which power pulses are generated in the primary winding, wherein the average power of the power pulses is higher than the standby pulses.

[0146] The method 148 includes switching 154 the battery charger from a standby mode to a charging mode in response to a change in the connection status signal while the battery is coupled to the battery charger.

[0147] Although the embodiments describe the use of flyback conversion, those skilled in the art will appreciate that other embodiments may use different converter types. Non-limiting examples of such converter types include active clamp flyback converters, flyback converters with synchronous rectification, forward converters, buck converters, and bridge converters with transformers.

[0148] Although various aspects have been described with reference to various embodiments, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

Claims

1. A battery charger comprising: Transformer, including: primary winding; and a first secondary winding; a current modulation circuit connected in series with the primary winding; a battery detection circuit coupled to the first secondary winding and configured to output a connection status signal; and a control circuit coupled to receive the connection status signal and to control the current modulation circuit based at least in part on the connection status signal to control energization of the primary winding; Wherein, when the battery charger is in standby mode, in response to the battery being connected to the battery charger, a change in the output of the first secondary winding causes the battery detection circuit to change the connection status signal. In the standby mode, the control circuit controls the current modulation circuit to generate a standby pulse in the primary winding. The change in the connection status signal switches the battery charger from the standby mode to the charging mode. In the charging mode, the control circuit controls the current modulation circuit to generate a power pulse in the primary winding, wherein the average power of the power pulse is higher than the standby pulse.

2. The battery charger according to claim 1, wherein: The connection status signal includes a voltage that increases in response to the battery being coupled to the battery charger.

3. The battery charger according to claim 2, wherein: The detection circuit includes a charge accumulation circuit configured to generate the connection status signal based on the pulse so that: The voltage of the connection status signal as a result of the standby pulse when the battery is not connected is insufficient to cause the battery charger to switch from the standby mode to the charging mode; and The voltage of the connection status signal as a result of the standby pulse when a battery is connected is sufficient to cause the battery charger to switch from the standby mode to the charging mode.

4. A battery charger according to any preceding claim, wherein: The control circuit includes a charge controller for controlling the generation of power pulses; and The connection status signal is configured to power a charge controller during a charging mode.

5. The battery charger according to claim 4, wherein: The battery charger is configured to switch from a standby mode to a charging mode as a result of the charging controller being powered on due to an increase in the voltage of the connection status signal.

6. The battery charger according to any one of claims 3 to 5, wherein: The charging controller comprises: diode; and A capacitor connected in series with a diode; The voltage of the connection status signal is a voltage generated at the capacitor based on the current passing through the diode.

7. A battery charger according to any preceding claim, wherein: The control circuit comprises an oscillator or a pulse generator for generating a standby pulse.

8. The battery charger according to claim 7, wherein: When the battery charger is in charging mode, the oscillator or pulse generator is disabled.

9. The battery charger according to claim 7 or 8, wherein: The oscillator or pulse generator comprises an analog oscillator circuit.

10. The battery charger according to claim 9, wherein: The analog oscillator circuit includes an RC network.

11. A battery charger according to any preceding claim, operating in a constant current charging mode only.

12. The battery charger of claim 11 configured to receive feedback indicative of a charging current, wherein: During the charging mode, the battery is charged only in constant current mode, and the charging current is controlled based on the feedback.

13. The battery charger according to claim 12, wherein: In response to the battery management system stopping charging the battery due to the charging voltage reaching a predetermined threshold, the connection status signal causes the battery charger to switch from the charging mode to the standby mode.

14. The battery charger of claim 13, configured such that the connection status signal causes the battery charger to repeatedly switch back and forth between a charging mode and a standby mode.

15. A battery charger according to any preceding claim, comprising a second secondary winding, wherein the battery charger is configured to charge the battery via the second secondary winding.

16. A battery charger according to any preceding claim, wherein: The standby pulse in the primary winding induces a corresponding pulse in the output of the battery charger which can be detected by a battery management system (BMS) of the battery when the battery is connected to the battery charger for charging.

17. A method of charging a battery using a battery charger, the battery charger comprising a transformer having a primary winding and a first secondary winding, the method comprising: outputting a connection status signal based on an output of the first secondary winding, the output varying based on whether the battery is connected to a battery charger for charging; Based on the connection status signal, the current modulation circuit is controlled to control the energization of the primary winding, so that the battery charger operates in the following modes: a standby mode, in which standby pulses are generated in the primary winding; and a charging mode, wherein power pulses are generated in the primary winding, wherein the average power of the power pulses is higher than the standby pulses; as well as The battery charger is switched from a standby mode to a charging mode in response to a change in the connection status signal due to a change in the output of the first secondary winding when the battery is coupled to the battery charger.

18. The method of claim 17, comprising generating the connection status signal based on the pulse such that: The voltage of the connection status signal as a result of the standby pulse is insufficient to cause the battery charger to switch from the standby mode to the charging mode when the battery is not connected; and The voltage of the connection status signal as a result of the standby pulse when a battery is connected is sufficient to cause the battery charger to switch from the standby mode to the charging mode.

19. A method according to claim 17 or 18, comprising using the connection status signal to power a charge controller of a battery charger.

20. The method of claim 19, comprising switching from a standby mode to a charging mode as a result of the charging controller being powered up due to an increase in the voltage of the connection status signal.

21. A battery for use with a battery charger according to any one of claims 1 to 16.

22. A battery according to claim 21, comprising a bypass switch, the battery being configured to close the bypass switch when the battery is connected to a battery charger according to any one of claims 1 to 17 for charging.

23. The battery of claim 22, comprising a battery management system configured to sense pulses at the output of the battery charger when the battery is coupled to the battery charger for charging.

24. The battery according to claim 23, wherein The battery management system is configured to close the bypass switch in response to sensing a pulse at the output of the battery charger when the battery management system determines that the battery requires charging.

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