CN119631273A

CN119631273A - Battery charger and method for charging battery

Info

Publication number: CN119631273A
Application number: CN202380059282.XA
Authority: CN
Inventors: M·巴蒂斯塔凯泽
Original assignee: Dyson Technology Ltd
Current assignee: Dyson Technology Ltd
Priority date: 2022-08-23
Filing date: 2023-08-15
Publication date: 2025-03-14
Also published as: GB202212249D0; GB2621980A; WO2024042427A1

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. The control circuit is 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. When the battery charger is in the standby mode, the battery detection circuit is caused to change the connection state signal in response to a change in the output of the battery coupled to the first secondary winding of the battery charger, which switches the battery charger from the standby mode to the charging mode. Related methods and batteries are also disclosed.

Description

Battery charger and method for charging battery

Technical Field

The present invention relates to a battery charger and a method of charging a battery.

Background

The battery charger is used to charge a rechargeable battery. Typically, such chargers plug into the mains power supply. The battery is coupled to a charger and is charged according to a charging scheme, such as a constant current constant voltage scheme.

It is generally desirable to reduce the amount of power consumed by a battery charger, particularly when in standby mode, and to simplify and/or reduce the cost of the battery charger circuitry.

Disclosure of Invention

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

a transformer, comprising:

primary winding, and

A first secondary winding;

A current modulation circuit coupled 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 a standby mode, the control circuit controls the current modulation circuit to generate a standby pulse in the primary winding in response to a change in the output of the battery coupled to the first secondary winding of the battery charger causing the battery detection circuit to change the connection state signal, the change in the connection state signal switching the battery charger from the standby mode to a charging mode in which 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.

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

The connection status signal may include a voltage that is increased in response to the battery being coupled to the battery charger. For example, the detection circuit may include a charge accumulation circuit configured to generate the connection state 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 state signal as a result of the standby pulse is sufficient to cause the battery charger to switch from the standby mode to the charging mode when the battery is connected.

This may provide a convenient mechanism for controlling switching between standby and charging modes.

The control circuit may include a charge controller for controlling the generation of the power pulse, 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.

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

The charge controller may include:

diode, and

A capacitor connected in series with the diode;

Wherein the voltage of the connection status signal is a voltage generated at the capacitor based on the current through the diode.

This may provide a convenient and/or simple mechanism for generating the connection status signal.

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

The oscillator or pulse generator may comprise an analog oscillator circuit. Alternatively, 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.

The battery charger may operate only in a constant current charging mode. This may simplify the circuitry of the charger, especially when combined with one or more of the previous optional aspects.

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.

The connection status signal may cause the battery charger to switch from the charging mode to the standby mode in response to the battery management system stopping charging the battery due to the charging voltage reaching a predetermined threshold. This may provide a convenient and/or simple mechanism for stopping charging.

The battery charger may be configured such that the connection status signal repeatedly switches the battery charger back and forth between the charging mode and the standby mode. This may provide a convenient and/or simple mechanism to ensure full charge of the battery.

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

The standby pulse in the primary winding may induce a corresponding pulse in the output of the battery charger that is detectable by a Battery Management System (BMS) of the battery when the battery is coupled to the battery charger for charging.

According to a second aspect, there is provided a method of charging a battery using a 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 coupled to a battery charger for charging;

Controlling the current modulation circuit based on the connection status signal, thereby controlling energization of the primary winding such that the battery charger may operate in:

A standby mode in which a standby pulse is generated in the primary winding, and

A charging mode in which a power pulse is generated in the primary winding, wherein the average power of the power pulse is higher than the standby pulse, and

The battery charger is switched from the standby mode to the 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.

The method may include generating a connection status signal based on the pulse such that:

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

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 the voltage increase of the connection state signal.

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

The battery may comprise a bypass switch, the battery being configured to close the bypass switch when coupling the battery to the battery charger according to the previous aspect.

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

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 needs to be charged.

The features described above in connection with any aspect of the invention are equally applicable to all other aspects of the invention.

Drawings

Fig. 1 is a schematic circuit diagram showing a battery charger and a connected battery;

FIG. 2 is a schematic circuit diagram showing another battery charger and connected battery;

FIG. 3 is a schematic circuit diagram showing another battery charger and connected battery;

fig. 4 is a signal diagram illustrating a simulated operation of the battery charger of fig. 3, and

Fig. 5 is a flowchart illustrating a method of charging a battery.

Detailed Description

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

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. With respect to at least this particular embodiment, the transformer 102 takes the form of a flyback transformer in the sense that the core and windings are optimized for use in a flyback converter. In other embodiments, the transformer may take any other suitable form.

The battery charger 100 includes a current modulation circuit in the form of a Field Effect Transformer (FET) 110 having its source and drain coupled 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.

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 the battery is coupled to the battery charger 100 for charging.

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

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 with dedicated analog circuits, digital controllers, or any suitable combination thereof. Fig. 2 and 3 illustrate example embodiments, but those skilled in the art will appreciate that the desired control may be achieved in many other ways.

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.

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

Fig. 1 shows a lithium ion rechargeable battery 120 coupled for charging by a battery charger 100. The battery 120 includes a battery cell and an optional battery management system, one embodiment of which is described with reference to fig. 3. In the embodiment of fig. 1, battery 120 is a battery pack that is removable from the device (not shown) with which it is intended to be used and temporarily coupled to battery charger 100 for charging, as shown in fig. 1.

The battery charger 100 may 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.

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

When the battery 120 is coupled 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.

In use, the battery charger 100 is activated in a standby mode and the battery 120 is not coupled for charging. The control circuit 116 controls the FET 110 such that a series of pulses is 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 coupled for charging. In this way, the connection status signal 114 remains at a value that indicates that the battery 120 is not coupled to the battery charger 100, and thus the battery charger 100 remains in the standby mode.

The battery detection circuit 112 may 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 may be used to sample the output voltage of the auxiliary winding 106, and the digital value of the analog-to-digital converter output is processed to determine whether the voltage is high or low. For example, the digital values may be low pass filtered, such as by moving average. If the value of the moving average exceeds the threshold, the battery detection circuit 112 may conclude that the battery 120 has been coupled to the battery charger 100 for charging.

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

Those skilled in the art will appreciate that the battery detection circuit 112 may determine whether the battery 120 is coupled to the battery charger 100 for charging from the output of the first secondary winding (i.e., the auxiliary winding 106 in the embodiment of fig. 1) in many other ways. Specific embodiments will be described in more detail below with reference to fig. 2 and 3.

Next, the battery 120 is coupled to the battery charger 100 for charging. When coupled in this manner, battery 120 presents a voltage across secondary winding 108 (e.g., during output rectifier conduction between battery 120 and secondary winding 108). As a result of the mirroring, this voltage on the secondary winding 108 results in an increase of the voltage/current in the auxiliary winding 106. In this way, 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 coupled to the battery charger 100.

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 manner in which the FET 110 is controlled. In the embodiment of fig. 1, the battery charger 100 uses flyback conversion. Thus, to switch the battery charger 100 to the charging mode, the control circuit 116 stops outputting the pulse it originally outputted, but outputs a type of pulse that is typically used to drive a flyback transformer (e.g., the transformer 102). The pulses applied to the primary winding 104 produce corresponding output pulses in the secondary winding 108.

Alternatively, the flyback pulses have a frequency greater than the pulses output by the control circuit when the battery charger 100 is in the standby mode.

The skilled person will understand the operation of the 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.

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

The charging may use a constant-current constant-voltage charging scheme, a constant-current-only charging scheme, or any other suitable charging scheme. One embodiment of the battery 120 having the BMS and the battery cells is described below with reference to fig. 3.

Battery charging may be terminated in any suitable manner. For example, the voltage of the battery cells of the battery 120 may be measured by the BMS, and the BMS terminates the charging once the desired voltage is reached. If a constant current and constant voltage are used, the charging is initially performed at a constant current. Once the 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.

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

Turning to fig. 2, another embodiment of a battery charger 200 is shown. The battery charger 200 shares a number of features with the battery charger 100 and like features are designated with the same reference numerals. For clarity, power supply 130 is not shown in fig. 2.

In the battery charger 200, the battery detection circuit 112 is indicated by a broken 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 taken from the junction between the diode 122 and the capacitor 124.

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 in the embodiment of fig. 2, includes a low power analog oscillator and a gate driver for FET 110. The pulse generator 126 is powered by a DC power supply 130.

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

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

As with the battery charger 100, the battery charger 200 may operate in a standby mode and a charging mode.

In use, the battery charger 200 is activated in a standby mode and the battery 120 is not coupled for charging. The pulse generator 126 controls the FET 110 such that a series of pulses is applied to the primary winding 104. The pulse induces a corresponding current through the secondary winding 108 and, to a lesser extent, through the auxiliary winding 106.

The auxiliary winding 106 is connected in series with a diode 122 and a capacitor 124. In this way, the voltage induced in the auxiliary winding 106 appears at the diode 122. Because the battery 120 does not provide a voltage on the secondary winding 108 when the battery charger 200 is in standby mode, the pulses induced in the auxiliary winding 106 due to the secondary winding 104 mirroring the pulses are insufficient to cause the flyback controller 128 to turn on. In this way, the connection status signal 114 remains low, indicating that the battery 120 is not coupled to the battery charger 200. The battery charger 200 thus remains in a standby mode in which the flyback controller 128 remains powered off and the pulse generator 126 remains enabled.

Next, the battery 120 is coupled to the battery charger 200 for charging. When coupled in this manner, battery 120 presents a voltage across secondary winding 108 (e.g., when a rectifier (not shown) between battery 120 and secondary winding 108 is on). One way of coupling the voltage of the battery 120 to the secondary winding 108 through a rectifier is described below with reference to fig. 3, but one skilled in the art will appreciate that other ways of detecting battery connection may be employed.

As a result of the pulse applied to the primary winding 104, the secondary winding 108 needs to be provided with an increased voltage conducted through the rectifier 138 causing transformer magnetizing energy to flow through the auxiliary winding 106, charging the capacitor 124 through the diode 122, resulting in a rise in voltage (and thus the value of the connection status signal 114).

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

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.

Alternatively, in the embodiment of fig. 2, the connection status signal 114 itself may 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 consumes virtually 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 pulse that is typically used to drive a flyback transformer (e.g., 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.

In the embodiment of fig. 2, the detection circuit (i.e., diode 122 and capacitor 124) may be considered a charge accumulation circuit configured to generate a connection state signal based on the received pulse such that:

The simultaneous (or slightly delayed) change of the connection status signal 114 to "high" causes the pulse generator 126 to "turn off". The pulse generator 126 may be turned off in any suitable manner. For example, the 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.

The battery charger 200 uses a constant current charging scheme instead of a constant current constant voltage charging scheme. As shown in fig. 3, 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 a number of features with the battery charger 100 and like features are designated with the same reference numerals. In practice, the battery charger 300 is identical to the battery charger 200, but includes many additional implementation details, which will now be described.

In fig. 3, the battery 120 includes a Battery Management System (BMS) 132 connected to a battery cell 134. The battery cells 134 are conventional lithium ion battery cell arrays and will not be described in detail. The BMS 132 includes hardware to control the charging of the battery cells 134 and may include, for example, a controller such as a microprocessor (not shown), voltage sensing circuitry (not shown), and/or any other suitable analog and/or digital circuitry required to perform the described functions. Such a circuit is well understood by the skilled person and will therefore not be described in more detail.

The battery 120 also includes a bypass Field Effect Transistor (FET) 136 controlled by the BMS 132, as described in more detail below.

The battery charger 300 includes many other elements relative to the battery charger 200. The conversion circuit 118, shown in dashed outline in fig. 3, 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.

The battery charger 300 includes a first current feedback circuit 142 for providing feedback to the flyback controller 128 indicating the present charging current so that the flyback controller 128 can control the output to keep the current constant. Feedback is provided through optocoupler 143 to maintain galvanic isolation in a manner well known to the skilled artisan.

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 flyback controller 128 to control FET 110 during charging such that transformer 102 is not saturated and FET 110 is not overloaded.

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

Fig. 3 also illustrates one manner 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 such that the pulse generator 126 generates pulses only when the battery charger 100 is in the standby mode. Those skilled in the art will appreciate that controlled current source 166 is merely one example of a mechanism for controlled charging of capacitor 168, and that any other suitable circuit may alternatively be used.

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

The pulse generator 126 has three states when the battery charger 120 is in the standby mode.

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

In the second state, the capacitor 168 charges the gate of the FET 110 via the switch 170, turning on the FET 110. The current through FET 110 begins to increase depending on 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 the switch 164 to close, thereby placing the pulse generator 126 in a third state.

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

The first, second and third states cycle through when the battery charger 100 is in the standby mode.

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

The battery charger 300 includes a buffer or active clamp 146 that operates in a manner known to those skilled in the art and will not be described in greater detail.

In standby mode, the battery charger 300 operates in the same manner as described for the battery charger 200.

When the battery 120 is coupled to the charger 300 (when charged), the BMS 132 senses the standby pulse from the secondary winding 108. In response to the sensing 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 on phase of the output rectifier 138, the auxiliary winding 106 mirrors the voltage increase on the secondary winding 108. This increased voltage on auxiliary winding 106 powers up flyback controller 128 and disables pulse generator 126 as described in more detail above.

As a result of flyback controller 128 controlling FET 110, the pulse supplied to primary winding 104 generates an output pulse within secondary winding 108. The output pulses are rectified by an output rectifier 138 and filtered by an output capacitor 140 to provide DC power to the BMS 132. The BMS 132 uses the DC power to power itself and controls the charging of the battery cells 134.

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

If the battery charger is powered up when the battery 120 is coupled to the battery charger, the standby pulse will begin, causing a pulse to appear at the secondary winding 108. These pulses wake the BMS 132 from its low power/standby mode and continue to switch flyback charging modes as described above.

Those skilled in the art will appreciate that any BMS may not be interposed between the conversion circuit 118 and the battery cells 134 as shown in fig. 3. Instead, the BMS may be connected side-by-side with the battery cells 134 and configured to sense factors related to the charging of the battery cells 134 (e.g., optionally including the present battery cell voltage and charging current), and to control elements such as the bypass FET 136.

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

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

When flyback controller 128 is off, output capacitor 140 needs to discharge faster than the flyback controller capacitor to avoid starting to charge again due to the mirror of the voltage in output capacitor 140. Those skilled in the art will appreciate that there are numerous ways in which this can be accomplished.

For example, current leakage may be designed into the charger (e.g., by connecting a resistor). The values of capacitor 124 and output capacitor 140 may be selected in conjunction with the current leakage of this design to ensure that the voltage at output capacitor 140 drops sufficiently fast relative to the voltage at capacitor 124 to ensure that charging does not restart.

An alternative approach is to add a circuit to increase current consumption 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 leakage, including the use of a non-linear impedance (e.g., zener diode or voltage reference) or comparator, or an optocoupler between the flyback controller power rail (i.e., the connection status signal 114) and the output capacitor 140.

Another alternative is to add a circuit within the battery 120 that is controlled by the BMS 132 to reduce the voltage of the output capacitor 140 when the BMS stops charging the battery cells 134.

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 the pulse from the charger 300 as described above, and may choose to restart the charging according to the state of charge of the battery cells 134. In this case, the BMS turns off the FET 136 and repeats the above-described process.

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 needed, the FET 136 remains off and charging no longer occurs.

Fig. 4 is a signal diagram illustrating the operation of the battery charger of fig. 3. Four signal traces are shown:

1. charging current ILOAD through battery 120.

2. The voltage Vbat of battery 120.

3. Voltage VDD of capacitor 124.

4. The output voltage Vout of the charger 300.

During the period up to time 5.0, the charger 300 is in standby mode. The mirror pulse generated by the pulse generator 126 in the primary winding 104 produces a relatively small pulse 156 at the output of the charger 300 (i.e., at the capacitor 140) due to the lack of voltage on the secondary winding 108.

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 to be charged), closes the bypass FET 136. This connects the cell 134 voltage on the secondary winding 108, as shown by the slight drop 158 in Vbat at this point and the increase 180 in voltage Vout at the output of the charger 300.

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 the capacitor 124 being charged via the diode 122. This is reflected in the rise 182 of VDD in fig. 4. Because FET 136 is closed, battery 120 sees a current pulse 186, as shown by ILOAD signal in fig. 4.

At about time 5.25, vdd rises to a voltage 184 that is high enough to power up the flyback controller 128. Flyback controller 128 begins to control FET 110 such that the voltage across primary winding 104 and the current through it rise. When FET 110 turns off, the current through primary winding 104 suddenly decreases, creating a current in secondary winding 108. Flyback conversion of this type is well known to those skilled in the art and will therefore not be described in detail.

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

It should be appreciated that the actual charge time will typically be much longer than the period shown in fig. 4. This is because for purposes of explanation, fig. 4 shows the behavior of a simulated battery charger.

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

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

After the charging voltage stops, vbat will drop slightly.

The values of VDD and Vout drop due to the discharge of the corresponding capacitors, as described above.

Once VDD drops sufficiently (at about time 6.3), the pulse generator 126 begins to operate and the low voltage pulse 156 is again supplied by the pulse generator 126 to the primary winding 104.

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

Turning to fig. 5, a flow chart is shown that represents a method 148 of charging a battery. The method 148 uses a battery charger that includes a transformer having a primary winding and a first secondary winding. The battery chargers 100, 200, and 300 are examples of such battery chargers, although other suitable battery chargers and charger types may also be used.

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

Method 148 includes controlling 152 the current modulation circuit based on the connection status signal to control energization of the primary winding such that the battery charger may operate in:

A charging mode in which a power pulse is generated in the primary winding, wherein the average power of the power pulse is higher than the standby pulse.

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

While 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 clamped flyback converters, flyback converters with synchronous rectification, forward converters, buck converters, and bridge converters with transformers.

While aspects have been described with reference to various embodiments, those skilled in the art will appreciate that the invention may be embodied in many other forms.

Claims

1. A battery charger, comprising:

a transformer, comprising:

primary winding, and

A first secondary winding;

A current modulation circuit coupled in series with the primary winding;

Wherein when the battery charger is in a standby mode, in response to the battery being coupled to the battery charger, the change in the output of the first secondary winding causes the battery detection circuit to change the connection state 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 state signal switching the battery charger from the standby mode to a 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 of claim 1, wherein the connection status signal comprises a voltage that increases in response to the battery being coupled to the battery charger.

3. The battery charger of claim 2, wherein the detection circuit comprises a charge accumulation circuit configured to generate the connection state signal based on the pulse such that:

4. A battery charger as claimed in 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 the charge controller during a charging mode.

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

6. The battery charger of any one of claims 3 to 5, wherein the charge controller comprises:

diode, and

A capacitor connected in series with the diode;

Wherein the voltage of the connection status signal is a voltage generated at the capacitor based on a current through the diode.

7. A battery charger as claimed in any preceding claim, wherein the control circuit comprises an oscillator or pulse generator for generating a standby pulse.

8. The battery charger of claim 7, wherein the oscillator or pulse generator is disabled when the battery charger is in a charging mode.

9. The battery charger of claim 7or 8, wherein the oscillator or pulse generator comprises an analog oscillator circuit.

10. The battery charger of claim 9, wherein the analog oscillator circuit comprises an RC network.

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

12. The battery charger of claim 11, 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.

13. The battery charger of claim 12, wherein the connection state signal causes the battery charger to switch from the charging mode to the standby mode in response to the battery management system stopping charging the battery as a result of the charging voltage reaching a predetermined threshold.

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

15. A battery charger as claimed in 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 as claimed in 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 coupled to the battery charger for charging.

17. A method of charging a battery using a battery charger, the battery charger including a transformer having a primary winding and a first secondary winding, the method comprising:

Controlling the current modulation circuit based on the connection status signal, thereby controlling energization of the primary winding such that the battery charger operates in:

18. The method of claim 17, comprising generating the connection status signal based on the pulse such that:

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

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 a voltage increase of the connection status signal.

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

22. The battery of claim 21, comprising a bypass switch configured to close when the battery is coupled to the battery charger of 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 an output of the battery charger when the battery is coupled to the battery charger for charging.

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