Battery protection

Abstract

A battery protection system is described. The system includes a battery and a load / charge port configured to be coupled to a load or a battery charger. Primary and secondary protection switches are coupled between the battery and the load / charge port. The system also includes a primary protection circuit configured to sense a voltage across the battery and to control the primary protection switch based on the sensed voltage. A secondary protection circuit is also configured to sense a voltage across the battery and to control the secondary protection switch based on the sensed voltage. The primary and secondary protection circuits are arranged in parallel across the battery. A method of operating the battery protection and an appliance comprising the battery protection system are also disclosed.

Description

[0001] BATTERY PROTECTION

[0002] BACKGROUND

[0003] Consumer appliances such as electronic toothbrushes, vacuum cleaners and hairdryers may be powered by rechargeable batteries. A rechargeable battery may power an appliance load, such as a motor, during use. When not in use the battery may be recharged. These operations may be controlled by a battery protection circuit. The battery protection circuit may perform various tasks, such as discharge control, battery charger detection and charge control. The battery protection circuit may do this by controlling one or more switches positioned between the battery and the load or battery charger. The battery protection circuit may also perform various protection functions, such as undervoltage protection.

[0004] SUMMARY

[0005] In a first aspect, the present disclosure provides a battery protection system, comprising: a battery; a load / charge port configured to be coupled to a load or a battery charger; a primary protection switch coupled between the battery and the load / charge port; a secondary protection switch coupled between the battery and the load / charge port; a primary protection circuit, configured to sense a voltage across the battery and to control the primary protection switch based on the sensed voltage; and a secondary protection circuit, configured to sense a voltage across the battery and to control the secondary protection switch based on the sensed voltage; wherein the primary and secondary protection circuits are arranged in parallel across the battery.

[0006] In modern electronic appliances battery protection systems may be required to include two protection circuits. The primary and secondary protection circuits may be used to perform a variety of functions, including over current protection, over temperature protection, and over and under voltage protection. In particular, the protection circuits may be used to prevent the battery from being discharged when the battery voltage drops below a certain voltage. In prior art protection systems, the primary and secondary protection circuits may be connected in series, such that the secondary protection switch is coupled between the primary protection circuit and the battery. In such an arrangement the primary protection circuit senses the battery voltage through the secondary protection switches, meaning that the battery voltage is not sensed accurately. This can lead to errors in the sensed voltage which in turn can cause the system to malfunction. In the first aspect of the disclosure, the primary and secondary protection circuits may be coupled to the battery in parallel. This allows the primary and secondary protection circuits to both sense the battery voltage accurately, meaning the sensed battery voltage is less likely to include errors and the possibility of a system malfunction is reduced.

[0007] The primary protection circuit may be coupled across the battery between the battery, and the primary and secondary protection switches. By coupling the primary protection circuit to a point in the circuit between the battery and the protection switches, there are no active devices between the battery protection circuit and the battery. This enables the battery protection circuit to sense the battery voltage more accurately. The battery protection circuit may account for passive components such as resistors and capacitors when sensing battery voltage as they are fixed. However, active devices such as switches may change their values depending on their state. For example, in some examples known from the prior art, the primary protection circuit senses battery voltage through the secondary protection switches. This leads to an apparent change in battery voltage when the switches are opened and closed. For example, the bandgap voltage of 0.7V may be added in or out of the sensed voltage depending on the switch state. The secondary protection circuit may be configured in the same way.

[0008] The primary protection circuit may be configured to detect the presence of a battery charger coupled to the load / charge port. The primary protection circuit may include a primary ground connection which may be coupled to a negative terminal of the battery. As such, the primary protection circuit may be arranged in parallel with the battery, and the secondary protection switch is located between the common ground connection and the load / charge port.

[0009] The primary protection circuit may include a battery voltage sensing connection coupled to a positive terminal of the battery. The primary protection circuit may be further configured to sense the battery voltage via the battery voltage sensing connection and the primary ground connection. The primary protection circuit may include two connections for sensing battery voltage. These connections may be coupled to the positive and negative battery terminals to enable accurate sensing of battery voltage. The secondary protection circuit may include corresponding connections configured in the same way.

[0010] The primary protection circuit may include a battery charger detection connection coupled to the load / charge port. The primary protection circuit may be further configured to detect the battery charger via the battery charger detection connection and the primary ground connection. By coupling both battery voltage sensing connections across the battery terminals, the primary protection circuit may sense battery voltage more accurately. Passive components may be positioned between the battery protection circuits and the battery, without adversely impacting battery sensing. Such components may be accurately compensated for.

[0011] The primary protection circuit may include a primary ground connection and the secondary protection circuit may include a secondary ground connection. The primary and secondary ground connections may be coupled to a negative terminal of the battery.

[0012] The primary protection switch may be coupled between a first terminal of the battery and a first terminal of the load / charge port, and the secondary protection switch may be coupled between a second terminal of the battery and a second terminal of the load / charge port. The first terminals may be positive terminals and the second terminals may be negative terminals.

[0013] The primary protection circuit may be a first integrated circuit and the secondary protection circuit may be a second integrated circuit. The use of two separate integrated circuits (ICs) may be required because of local regulations or other safety requirements. The second protection circuit IC may include the bypass circuit, meaning that primary and secondary protection circuits may be connected in parallel with the battery. The second IC therefore provides both the secondary protection circuit and the bypass circuit, enabling the system to accurately sense the battery voltage using both ICs, while also detecting the presence of a battery charger.

[0014] The primary protection circuit may be further configured to open the primary protection switch when the battery voltage drops below a first threshold voltage. The secondary protection circuit may be further configured to open the secondary protection switch when the battery voltage drops below a second threshold voltage. The second threshold voltage may be less than the first threshold voltage.

[0015] The primary protection circuit may be used to prevent the battery from discharging to a load when the battery voltage drops below a first threshold. The first threshold may be a voltage below which the electronic appliance may not operate effectively. The secondary protection circuit may be used to prevent current leakage from the battery when the battery reaches a lower, second threshold voltage. This might occur if the electronic appliance is stored for long periods without being used. The secondary protection circuit prevents the battery becoming completely depleted.

[0016] The battery protection system may further comprise a resistor-capacitor (RC) network positioned between the battery voltage sensing connection and the battery positive terminal. Such an arrangement may be useful to provide filtering or current limitation to protect the primary protection circuit. Such passive elements can be accounted for by the primary protection circuit such that battery voltage may still be sensed accurately. The secondary protection circuit may also utilise an RC network.

[0017] The primary protection circuit may be further configured to detect the presence of a battery charger coupled to the load / charge port and to control the primary protection switch based at least in part on the presence of a battery charger.

[0018] In addition to providing undervoltage battery protection, the primary protection circuit may detect the presence of a battery charger and control the primary protection switch to control charging of the battery. The batery protection system may further comprise a bypass circuit coupled between the battery and the load / charge port. In a first mode the secondary protection switch may be closed and the primary protection circuit may be further configured to detect the presence of a battery charger via a primary charger detection current path which includes the secondary protection switch. In a second mode the secondary protection switch may be open and the primary protection circuit may be further configured to detect the presence of a battery charger via a secondary charger detection current path which includes the bypass circuit.

[0019] Because the primary and secondary protection circuits are arranged in parallel with respect to the battery, the secondary protection switches are located between the primary protection circuit and the load / charge port. When the secondary protection switch is closed, a current loop may be formed between the primary protection circuit and a batery charger via the secondary protection switch. This enables the primary protection circuit to detect the presence of a battery charger. However, when the battery voltage drops below the second threshold, the secondary protection switch is opened. This interrupts the current loop between the primary protection circuit and the battery charger. To address this, a bypass circuit is coupled between the battery and the load / charge port. When the secondary protection switch is open, a secondary charger detection current loop is formed via the bypass circuit, enabling the primary protection circuit to detect the presence of a battery charger.

[0020] The bypass circuit may include at least one bypass resistor and at least one bypass switch and in the second mode of operation the at least one bypass switch may be closed. The second mode of operation may be an undervoltage mode of operation in which the battery voltage drops below an undervoltage threshold. The bypass circuit may be coupled between a positive terminal of the battery and a negative terminal of the load / charge port. The secondary protection circuit may comprise the bypass circuit. The secondary charger detection current path may also include / pass through the battery. By providing a secondary protection circuit with a resistor network which acts as a bypass circuit, the secondary protection circuit itself provides the secondary charger detection current loop, reducing the complexity of the battery protection system. The primary protection circuit may be further configured to close the primary protection switch when the battery charger is detected to allow the battery charger to charge the battery.

[0021] The system may be configured to form a charging current loop during charging, via the first and second protection switches, and when the secondary protection switch is open the current flows through a body diode of the secondary protection switch. The switches may be transistors that include body diodes to enable charging of the battery even when the switches are open.

[0022] In a second aspect, the present disclosure provides a method of operating the battery protection system as described above, comprising: sensing, using the primary protection circuit, the voltage across the battery; sensing, using the secondary protection circuit, the voltage across the battery; controlling the primary protection switch, using the primary protection circuit, based on the voltage sensed by the primary protection circuit; and controlling the secondary protection switch, using the secondary protection circuit, based on the voltage sensed by the secondary protection circuit.

[0023] The method may further comprise opening the primary protection switch, using the primary protection circuit, when the battery voltage drops below a first threshold voltage. The method may further comprise opening the secondary protection switch, using the secondary protection circuit, when the battery voltage drops below a second threshold voltage. The second threshold voltage may be less than the first threshold voltage.

[0024] The method may further comprise: when the secondary protection switch is closed, detecting the presence of a battery charger using the primary protection circuit, via a primary charger detection current path that includes the secondary protection switch; and closing the primary protection switch to enable the battery to be charged.

[0025] The method may further comprise: when the secondary protection switch is open, detecting the presence of a battery charger, using the primary protection circuit, via a secondary charger detection current path that includes the bypass circuit; and closing the primary protection switch to enable the battery to be charged.

[0026] In a third aspect, the present disclosure provides an electronic appliance, comprising the battery protection system as described above.

[0027] The electronic appliance may further comprise: a battery charger dock, configured to receive a battery charger and coupled to the load / charge port; a load, coupled to the load / charge port; and a user interface, coupled to the battery protection system and configured to control the discharge of the battery to the load. The load may be an electric motor.

[0028] The primary protection switch may be two primary protection switches, including a primary charging switch and a primary discharge switch. Similarly, the secondary protection switch may be two secondary protection switches, including a secondary charging switch and a secondary discharge switch. Both primary protection switches may be coupled to the primary protection circuit and both secondary protection switches may be coupled to the secondary protection circuit. The charging switches are closed during a charging operation and the discharge switches are closed during a discharge operation. The charging and discharging switches may have opposite polarity, meaning that the charging switches block current flowing in one direction, and the discharging switches block current flowing in the opposing direction. The switches all include body diodes meaning they may pass current flowing in one direction even when open.

[0029] The battery protection system may include a single, bidirectional current path for charging and discharging the battery. The current path may include the primary and secondary protection switches. In view of this, the system may utilise pairs of unipolar transistors, such as MOSFETs, or may utilise bidirectional switches.

[0030] In a further aspect of the invention, a battery protection system is disclosed that may be configured to perform battery charger detection. The system may include a charger detection circuit that, in use, may be configured to form a primary charger detection current loop with a battery charger. The charger detection circuit may form part of the primary protection circuit. The primary charger detection current loop may be a current path that includes the primary protection circuit and the secondary protection switch. The battery protection system may also include a battery protection circuit that disconnects the battery from a battery charger port when the battery is in an undervoltage condition. The battery protection circuit may form part of the secondary protection circuit. The battery protection circuit may be configured to disconnect the battery from the battery charger port using the secondary protection switch. When the battery is disconnected from the battery charger port the primary charger detection current loop is blocked by the open secondary protection switch. The system may be further configured to provide a secondary charger detection current path between the charger detection circuit and the battery charger when the battery is in the undervoltage condition, thereby enabling the charger detection circuit to detect the battery charger. The secondary charger detection current path may include the battery and the bypass circuit, which forms part of the secondary protection circuit, thereby avoiding the open secondary protection switch.

[0031] The battery protection system may be particularly useful in smaller electronic appliances, such as an oral care device (e.g., an electronic toothbrush). Alternatively, it may also be used in other electronic appliances, including floorcare appliances (e.g., stick vacuum cleaners) or haircare appliances (e.g., hair dryers).

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure l is a system diagram showing a battery protection system in accordance with a first embodiment of the disclosure;

[0034] Figure 2 is a flow chart showing a first method of operation of the system shown in Figure 1;

[0035] Figure 3 is a flow chart showing a second method of operation of the system shown in Figure 1; Figure 4 is a system diagram showing the battery protection system shown in Figure 1 during the second method of operation;

[0036] Figure 5 is a further system diagram showing the battery protection system shown in Figure 1 during the second method of operation; and

[0037] Figure 6 is a system diagram showing a battery protection system in accordance with a second embodiment of the disclosure.

[0038] DETAILED DESCRIPTION

[0039] Figure 1 shows a battery protection system 100 in accordance with an embodiment of this disclosure. The battery protection system 100 includes a battery 102, which may be a rechargeable battery. The battery 102 may be a lithium-ion rechargeable battery or may use any other suitable rechargeable battery technology. The battery 102 may be a single-cell device or may be a multi-cell device. The battery protection system 100 is configured to control the charging and discharging of the battery 102. Additionally, the battery protection system 100 may be configured to perform various protection mechanisms, such as undervoltage protection, overvoltage protection and thermal protection.

[0040] The battery 102 is coupled to a pair of battery terminals 104A and 104B. The battery terminals include a positive battery terminal 104A and a negative battery terminal 104B. The battery protection system 100 may also comprise a load / charge port which is configured to be coupled to a load or a battery charger. The battery charger may be a wireless charger, and the load / charge port may be coupled to a wireless charging interface. The load / charge port includes a positive load / charge terminal 106A and a negative load / charge terminal 106B. The battery protection system 100 may form part of a consumer appliance, such as a vacuum cleaner or hairdryer, in which case the load / charge port may be coupled to a motor of that appliance. The consumer appliance may include a user interface to control discharge of the battery 102 to the load. The user interface is not shown in Figure 1 in the interests of clarity. The battery 102 may operate under a range of voltages. In this embodiment, the battery 102 is rated to operate at up to 4.35V. This is a typical voltage for lithium-ion batteries used in consumer appliances.

[0041] The positive battery terminal 104A is coupled to the positive load / charge terminal 106A via a positive power rail 108 A. The negative battery terminal 104B is coupled to the negative load / charge terminal 106B by a negative power rail 108B. To control charging and discharging of the battery 102, a pair of primary protection switches are provided along the positive power rail 108 A. The primary protection switches include a primary charge switch 110A and a primary discharge switch HOB. In addition, a pair of secondary protection switches are provided along the negative power rail 108B. The secondary protection switches include a secondary charge switch HOC and a secondary discharge switch 110D. The primary and secondary protection switches may be MOSFETs or other suitable transistors or switches. As noted above, the battery protection system 100 may be used to control the charging and discharging of the battery 102. The direction of current flow along the positive and negative power rails 108 A, 108B will be different depending upon the mode of operation. As MOSFETS are unipolar devices, two switches are required along each power rail, each having opposing polarity. In an alternative embodiment it may be possible to use bi-directional transistors, in which case only a single device would be required along each power rail. Furthermore, the battery protection system 100 may be configured only for charging the battery 102 in which case only a single unipolar switch may be required.

[0042] The battery protection system 100 further comprises a primary protection circuit 112A and a secondary protection circuit 112B. Two protection circuits may be required owing to electrical regulations in certain countries, or to provide more advanced protection routines. The primary protection circuit 112A is coupled to primary protection switches 110A, 110B. The secondary protection circuit 112B is coupled to secondary protection switches HOC, 110D. Although differences in the operation of the primary and secondary protection circuits will become apparent in the remainder of this description, both circuits may also perform certain common functions such as undervoltage protection, overvoltage protection and thermal protection. Furthermore, the primary and secondary protection circuits 112A, 112B may be implemented as separate integrated circuits. Each circuit may include various pins though which the switches may be controlled and through which various voltages and currents may be sensed. Although in this embodiment separate integrated circuits are used, it may be possible to implement the same functionality using discrete circuit components.

[0043] The primary protection circuit 112A includes a charge control pin 114A which is coupled to the primary charge switch 110A and a discharge control pin 114B which is coupled to the primary discharge switch HOB. Furthermore, the primary protection circuit 112A includes a battery sense pin / battery voltage sensing connection 114C and a ground pin / primary ground connection 114D. The battery sense pin 114C is coupled to the positive battery terminal 104A. The ground pin 114D is coupled to the negative battery terminal 104B. These connections enable the primary protection circuit 112A to sense the voltage of the battery 102.

[0044] The primary protection circuit 112A is connected in parallel with the battery 102, using the battery sense pin 114C and the ground pin 114D, to sense the voltage of the battery 102. Furthermore, the battery sense pin 114C and the ground pin 114D are connected between the battery 102 and the primary and secondary protection switches 110A-D. It should be noted that in Figure 1 there are no passive components between the primary protection circuit 112A and the battery 102. However, passive components may be provided between the battery 102 and the primary protection circuit 112A, for example to provide current limitation, while still enabling the primary protection circuit 112A to accurately measure the voltage of the battery 102. This is because the values of any passive components can be accounted for by the primary protection circuits 112A. Furthermore, because battery sense pin 114C and ground pin 114D are coupled between the battery 102 and the primary and secondary protection switches 110A-D, no active components are positioned between the battery 102 and the primary protection circuit 112A. Because the voltage drop across active components may vary depending on their state (for example the bandgap voltage of 0.7V in a transistor), avoiding having such components between the primary protection circuit 112A and the battery 102 improves the ability of the primary protection circuit 112A to accurately measure the voltage of the battery 102. The primary protection circuit 112A also includes a charger sense pin / battery charger detection connection 114E which is coupled to the positive load / charge terminal 106A. The charger sense pin 114E is used for charger detection.

[0045] The secondary protection circuit 112B includes a charge control pin 116A which is coupled to the secondary charge switch HOC and a discharge control pin 116B which is coupled to the secondary discharge switch HOD. Furthermore, the secondary protection circuit 112B includes a battery sense pin 116C and a ground pin / secondary ground connection 116D. The battery sense pin 116C is coupled to the positive battery terminal 104A. The ground pin 116D is coupled to the negative battery terminal 104B. These connections enable the secondary protection circuit 112B to sense the voltage of the battery 102.

[0046] The secondary protection circuit 112B is connected in parallel with the battery 102, using the battery sense pin 116C and the ground pin 116D, to sense the voltage of the battery 102. Furthermore, the battery sense pin 116C and the ground pin 116D are connected between the battery 102 and the primary and secondary protection switches 110A-D. It should be noted that in Figure 1 there are no passive components between the secondary protection circuit 112B and the battery 102. However, passive components may be provided between the battery 102 and the secondary protection circuit 112B, for example to provide current limitation or filtering, while still enabling the secondary protection circuit 112B to accurately measure the voltage of the battery 102. This is because the values of any passive components can be accounted for by the secondary protection circuit 112B. Furthermore, because battery sense pin 116C and ground pin 116D are coupled between the battery 102 and the primary and secondary protection switches 110A-D, no active components are positioned between the battery 102 and the secondary protection circuit 112B. Because the voltage drop across active components may vary depending on their state (for example the bandgap voltage of 0.7V in a transistor), avoiding having such components between the secondary protection circuit 112B and the battery 102 improves the ability of the secondary protection circuit 112B to accurately measure the voltage of the battery 102. The secondary protection circuit 112B also includes a charger sense pin 116E which is coupled to the negative load / charge terminal 106B. This pin may be used by the secondary protection circuit 112B to perform electrostatic discharge detection or charger polarity faults. The secondary protection circuit 112B further comprises a bypass circuit 118. The bypass circuit 118 provides a switchable current path between the battery sense node 116C and the charger sense pin 116E. The bypass circuit 118 may be a switch and a resistor, formed in series between the battery sense pin 116C and the charger sense pin 116E.

[0047] It should be noted that, depending upon the implementation of the circuit, various passive circuit components such as resistors, capacitors and inductors, may be used at various points in the circuit. Such components may be used for current sensing or current limiting. The passive components may be provided as discrete components within the circuit, or they may be provided as integrated components within the integrated circuits that constitute the primary and secondary protection circuits. Such components are omitted in the present embodiment in the interest of clarity.

[0048] The battery protection system 100 is configured to prevent excessive discharge of the battery 102. This is achieved by sensing when the battery’s voltage drops below one or more thresholds and disconnecting it from the load / charge port. This is known as undervoltage protection.

[0049] Figure 2 is a flow chart showing the process that occurs as the battery 102 is discharged. In a normal mode of operation, all the primary and secondary protection switches 110A-D are closed and the battery 102 may discharge to a load via the load / charge port (S200). The maximum battery voltage may be 5V, as noted above, and operating voltage range may be 2.5V to 5V. These voltages are not intended to be limiting, and the actual range of operation will depend on the battery type and the appliance powered by the battery 102. The battery protection system 100 has an operating voltage range, with a minimum operating voltage and a maximum operating voltage. In this case, the minimum operating voltage is 2.5V and the maximum operating voltage is 5V. The primary and secondary protection circuits 112A and 112B monitor the battery voltage and this information is used to control the operation of the primary and secondary protection switches. When the battery voltage drops below the minimum operating voltage / a first threshold voltage, the primary protection circuit 112A opens the primary protection switches 110A, HOB (S202). This prevents any further discharge of the battery 102 to the load. This is known as undervoltage protection, and the minimum operating voltage is also referred to as the first undervoltage threshold. At this point, the battery 102 may not be used to power a load until it has been charged. In this embodiment, when the primary protection switches 110A, HOB are open and the secondary protection switches HOC, 110D are closed, the negative load / charge terminal 106B is connected to the negative battery terminal 104B, or ground. The negative load / charge terminal 106B is therefore at 0V. As the positive load / charge terminal 106A is isolated from the positive battery terminal 104 A by the open primary protection switches 110A, 110B, it floats to the same voltage as the negative load / charge terminal 106B; i.e. 0V.

[0050] Even when the battery 102 has been disconnected from the load by the primary protection switches 110A, 110B, current leakage may occur through the negative battery terminal 104B. The secondary protection switches HOC, 110D initially remain closed, allowing a current leakage path towards the negative load / charge terminal 106B. Current leakage of this type is typically sufficiently low that over short periods of time, it does not significantly drain the battery. However, over time, the battery 102 may discharge to a point where it can no longer be recharged. For example, if the appliance that incorporates the battery protection system 100 is put into long-term storage, current leakage from the battery 102 could render the battery unusable.

[0051] In view of this, when the battery voltage drops below a second undervoltage threshold / second threshold voltage, the secondary protection circuit 112B opens the secondary discharge switch 110D (S204). This prevents discharge of the battery 102 via the negative load / charge terminal 106B. In this embodiment, the second undervoltage threshold is 2.35 V. The secondary charge switch 110C remains closed in this scenario. It is not necessary to open the secondary charge switch 110C to prevent current leakage, and as will be described below, leaving this switch closed is helpful for battery charging, which may occur later.

[0052] In addition to sensing the battery voltage, the primary protection circuit 112A also performs battery charger detection via charger sense pin 114E. To perform battery charger detection, the primary protection circuit 112A requires a connection to the positive load / charge terminal 106A and to the negative load / charge terminal 106B. When the secondary protection switches are both closed (i.e. after the battery voltage drops below the first undervoltage threshold but not the second), the ground pin 114D is able to form a current path to the negative load / charge terminal 106B. Hence, in this scenario the primary protection circuit 112A can detect when a battery charger is present. However, once the secondary discharge switch HOD is open, a current path is no longer formed between the ground pin 114D and the negative load / charge terminal 106B. In view of this, the secondary protection circuit 112B includes the bypass circuit 118.

[0053] When the second undervoltage threshold is passed, the secondary protection circuit 112B puts the bypass circuit 118 into closed circuit, forming a current path between the battery sense pin 116C and the charger sense pin 116E (S206). The bypass circuit may be a switch and a resistor, formed in series between the battery sense pin 116C and the charger sense pin 116E. The resistor may have a value in the range of 250kQ to 3500kQ. In this embodiment, the resistor takes a value of 1250kQ. The resistor may be a resistor network, rather than a single resistor.

[0054] After the battery voltage drops below the second undervoltage threshold, the secondary discharge switch HOD is opened and the bypass circuit 118 is switched into closed circuit. When the battery voltage drops below the second undervoltage threshold (e.g., dropped to 2.25V), the negative load / charge terminal 106B is pulled up to the same voltage as the positive battery terminal 104 A because of the current path formed through the bypass circuit 118 in the secondary protection circuit 112B. In addition, because the positive load / charge terminal 106A is still isolated from the positive battery terminal 104A, but coupled to the negative load / charge terminal 106B via the load, it also floats to the battery voltage (e.g., 2.25V). Figure 3 is a flow chart showing the process that occurs when a charger is connected to the load / charge port when the battery voltage is below the second undervoltage threshold.

[0055] A charger (not shown) is coupled across the load / charge port (S300). The charger may for example be a 5V battery charger suitable for use with lithium-ion rechargeable batteries. The battery voltage initially remains at 2.25V. The negative load / charge terminal 106B is still coupled to the positive battery terminal 104 A via the bypass circuit 118, and therefore also remains at 2.25V. The battery charger adds 5V to this value to bring the positive load / charge terminal 106A to 7.25V. This voltage may then be sensed by the charger sense pin 114E. However, for the primary protection circuit 112A to perform charger detection, a current path must be formed between the charger and the primary protection circuit 112 A.

[0056] Figure 4 shows the battery protection system 100 of Figure 1 with the charger detection current path 400 highlighted. Some of the reference numerals from Figure 1 are omitted for clarity. As can be seen, because the current path via the open secondary protection switches HOC, HOD is blocked, a current path is formed through the bypass circuit 118, via the battery 102 and into the ground pin 114D of the primary protection circuit 112 A.

[0057] Once the battery charger is connected, the primary protection circuit 112A detects that the charger is present and closes the primary charge switch 110A (S302). Primary discharge switch 110B remains open. Owing to the body diode of the primary discharge switch 110B a charging current may flow from the positive load / charge terminal 106A to the positive battery terminal 104 A. Similarly, the secondary protection switches HOC, 110D have not changed state, with the secondary charge switch HOC closed and the secondary discharge switch 110D open. The body diode of the secondary discharge switch 110D enables charging current to flow from the negative battery terminal 104B to the negative load / charge terminal 106B. The battery charger is therefore able to charge the battery 102 (S304). Figure 5 shows the battery protection system 100 of Figures 1 and 4 with the charging current path 500 highlighted. As shown in Figure 5, the charging current path 500 is in the form of a charging current loop. The positive load / charge terminal 106A drops to a level above 2.25V and the negative terminal drops below zero volts, owing to the voltage drop across the body diode of secondary discharge switch HOD.

[0058] Figure 6 shows a battery protection system 1000 in accordance with a further embodiment of the disclosure. The battery protection system 1000 has several features in common with the battery protection system 100 of Figure 1. However, the battery protection system 1000 includes several additional features, as will be explained in the following.

[0059] The battery protection system 1000 includes a single-cell battery 1002, which in this embodiment is a rechargeable lithium-ion battery having a rating of 5V. The battery 1002 is coupled to a positive battery terminal 1004A and a negative battery terminal 1004B. The battery protection system 1000 also comprises a positive load / charge terminal 1006A and a negative load / charge terminal 1006B. The load / charge terminals 1006A, 1006B may be coupled to a load 1007, however the load does not form part of the battery protection system 1000.

[0060] The positive battery terminal 1004A is coupled to the positive load / charge terminal 1006A via a positive power rail 1008 A. The negative battery terminal 1004B is coupled to the negative load / charge terminal 1006B by a negative power rail 1008B. The battery protection system 1000 also comprises a pair of primary protection switches, including a primary charge switch 1010A and a primary discharge switch 1010B. In addition, a pair of secondary protection switches are provided along the negative power rail 1008B. The secondary protection switches include a secondary charge switch 1010C and a secondary discharge switch 1010D. The primary and secondary protection switches may be MOSFETs or other suitable transistors or switches.

[0061] The battery protection system 1000 further comprises a primary protection circuit 1012A and a secondary protection circuit 1012B. The primary protection circuit 1012A may be an integrated circuit (IC), such as the MAX17330 by Analog Devices, Inc. of Wilmington, Boston, U.S.A. The MAX17330 is a stand-alone battery charger and protector IC. The MAX17330 includes several features which are not relevant to this disclosure, but which may be utilised in an implementation of the battery protection system 1000. The features which are relevant to this disclosure will be described in the following. The secondary protection circuit 1012B may be an IC, such as the S-82D1A by ABLIC Inc. of Tokyo, Japan. The S-82D1 A is a battery protection IC.

[0062] The primary protection circuit 1012A is coupled to primary protection switches 1010A and 1010B. The secondary protection circuit 1012B is coupled to secondary protection switches 1010C and 1010D. The primary protection circuit 1012A includes a charge control pin 1014A which is coupled to the primary charge switch 1010A. The charge control pin provides charge FET control (CHG) in the MAX17330. The primary protection circuit also includes a discharge control pin 1014B which is coupled to the primary discharge switch 1010B. The discharge control pin 1014B provides discharge FET control (DIS) in the MAX17330.

[0063] The primary protection circuit 1012A includes a battery sense pin 1014C and a ground pin 1014D. In the MAX17330 the battery sense pin 1014C is the battery connection (BATT) and the ground pin 1014D is the ground connection (GND). The battery sense pin 1014C is coupled to the positive battery terminal 1004A. The ground pin 1014D is coupled to the negative battery terminal 1004B. The MAX17330 datasheet recommends an external resistor and capacitor network to be coupled to the battery and ground connections for effective operation. In this embodiment, the battery protection system 1000 includes a resistor R1 between the battery sense pin 1014C and the positive battery terminal 1004A. The resistor may take a value of 10Q, although may take a value from IQ to 100Q. Furthermore, a capacitor Cl, which may have a value of 0.1 pF, is positioned in bypass between the battery sense pin 1014C and ground. Cl may take a value from O.OlpF to I F. The primary protection circuit 1012A takes account of R1 and Cl and may accurately sense the battery voltage. No active components are located between the battery sense pin 1014C and the battery, enabling accurate and constant sensing of battery voltage.

[0064] The primary protection circuit 1012A also includes a charger sense pin 1014E which is coupled to the positive load / charge terminal 1006A. This is the pack positive terminal or system positive terminal (PCKP) in the MAX17330. In this embodiment, a current limiting resistor R2 is positioned between the charger sense pin 1014E and the positive load / charge terminal 1006A. R2 may have a value in the range of 100Q to lOkQ, although in this embodiment the value is IkQ.

[0065] The primary protection circuit 1012A may also include a current sense negative pin 1014F and a current sense positive pin 1014G. These pins correspond to the CSN and CSP inputs in the MAX17330. These pins are connected across a current sense resistor R3 which is arranged in series with the primary protection switches along the positive power rail 1008 A. These inputs enable the primary protection circuit 1012A to measure charging current, which may be helpful during a charging mode. As this aspect of the MAX17330 is not directly relevant to the operation of the battery protection system 1000 according to this disclosure, further details will not be provided here.

[0066] The primary protection circuit 1012A also includes a thermistor connection pin 1014H. This is the TH pin in the MAX17330. This pin may be connected to a thermistor T2 for sensing battery temperature. The thermistor may take a value in the range of lOkQ to lOOkQ, and in this case takes a value of lOOkQ.

[0067] The secondary protection circuit 1012B includes a charge control pin 1016A which is coupled to the secondary charge switch 1010C and a discharge control pin 1016B which is coupled to the secondary discharge switch 1010D. The charge control pin 1016A provides the charge control FET function (CO) of the S-82D1A. The discharge control pin 1016B provides the discharge control FET function (DO) of the S-82D1A.

[0068] The secondary protection circuit 1012B also includes a battery sense pin 1016C and a ground pin 1016D. The battery sense pin 1016C is the positive power supply (VDD) of the S-82D1A and the ground pin 1016D is the negative power supply (VSS) of the S-82D1A. The battery sense pin 1016C is coupled to the positive battery terminal 1004 A. The ground pin 1016D is coupled to the negative battery terminal 1004B. As with the primary protection circuit 1012A, the secondary protection circuit 1012B may include a resistor R4 between the battery sense pin 1016C and the battery positive terminal 1004 A. A bypass capacitor C2 may be positioned between the battery sense pin 1016C and ground. In one embodiment, R4 may take a value of 330Q and C2 may take a value of 0.1 pF. The value of R4 may be in the range of 270Q to 1.2kQ. The value of capacitor C2 may be in the range of 0.068pF to 2.2pF. The secondary protection circuit 1012B may accurately sense the battery voltage, taking into account the values of R4 and C2. No active components are located between the battery sense pin 1016C and the battery 1002, enabling accurate and constant sensing of battery voltage.

[0069] The secondary protection circuit 1012B also includes a charger sense pin 1016E which is coupled to the negative load / charge terminal 1006B via resistor R5. This pin corresponds to the external negative connection (VM) in the S-82D1A. R5 may take a value in the range of 300Q to 1.5kQ, and in this embodiment may have a value of 470Q. The primary function of the VM input in the S-82D1A is to provide electrostatic discharge (ESD) protection and protection for reverse charger connection. However, this pin also provides the undervoltage protection current path for charger detection, as described above.

[0070] The secondary protection circuit 1012B also includes a thermistor connection pin 1016F. This is the TH pin in the S-82D1A. This pin may be connected to a thermistor T1 for sensing battery temperature. The thermistor may take a value in the range of lOkQ to 100kQ, and in this case takes a value of 100kQ.

[0071] The secondary protection circuit 1012B also includes an overcurrent detection pin (VINI) 1016G. An overcurrent detection resistor R6 is placed in series with the negative power rail 1008B and between the battery negative terminal 1004B and the secondary protection switches 1010C, 1010D. R6 may take a value of 1.5mQ and enables the secondary protection circuit 1012B to perform overcurrent detection.

[0072] The secondary protection circuit 1012B further comprises a bypass circuit 1018. The bypass circuit 1018 provides a switchable current path between the battery sense node 1016C and the charger sense pin 1016E. The bypass circuit 1018 may be a switch and a resistor (not shown), formed in series between the battery sense pin 1016C and the charger sense pin 1016E. In an alternative embodiment, the bypass circuit may be located external to the secondary protection circuit. The bypass circuit may include a bypass resistor formed in series with a bypass switch. The bypass circuit may be coupled between the positive power rail and the negative power rail. The bypass circuit may be coupled to the positive power rail between the positive battery terminal and the primary protection switches. The bypass circuit may be coupled to the negative power rail between the secondary protection switches and the negative load / charge terminal. The bypass switch may be a MOSFET and may be coupled to the secondary discharge pin. When the secondary discharge switch is opened when the battery voltage drops below the secondary undervoltage threshold, the bypass switch may be closed, enabling a current path to be formed between the positive battery terminal and the negative load / charge terminal.

[0073] In a further embodiment, the secondary protection circuit 112B may not be required to use the bypass circuit 118, or the bypass circuit may be omitted completely. As described above, the battery protection system 100 is operated to prevent leakage from the battery 102 when the battery voltage drops below a second undervoltage threshold. This is achieved by opening the secondary protection switch HOD. By doing this, charger detection is inhibited. The bypass circuit 118 is used to form a current path between the primary protection circuit 112A and the negative load / charger port 106B to enable charger detection in this scenario. In some applications, the current leakage from the battery may be sufficiently low that there is no need to open secondary protection switch HOD to prevent battery discharge. In this case, a current path between the primary protection circuit 112A and the negative load / charge port 106B is maintained, and the bypass circuit is not required. This current path may be referred to as a primary charger detection current path and the battery protection system may be considered to be in a first mode; whereas, the current path 400 shown in Fig. 4 may be referred to as a secondary charger detection current path (including the bypass circuit) and the battery protection system may be considered to be in a second mode. This arrangement provides a simpler implementation of the parallel protection circuit topology in cases where battery leakage is not a significant issue. The battery protection system may be particularly useful in smaller electronic appliances, such as an oral care device (e.g., an electronic toothbrush). Alternatively, it may also be used in other electronic appliances, including floorcare appliances (e.g., stick vacuum cleaners) or haircare appliances (e.g., hair dryers).

[0074] An electronic appliance may include a battery charger dock, configured to receive a battery charger. The dock may be coupled to the load / charge port. The dock may be a wireless or wired dock. The appliance may include a load, coupled to the load / charge port. The load may be an electric motor. The appliance may also include a user interface, coupled to the battery protection system and configured to control the discharge of the battery to the load. For example, the user interface may include an on / off switch, configured to switch the motor on and off.

Claims

CLAIMS1. A battery protection system, comprising: a battery; a load / charge port configured to be coupled to a load or a battery charger; a primary protection switch coupled between the battery and the load / charge port; a secondary protection switch coupled between the battery and the load / charge port; a primary protection circuit, configured to sense a voltage across the battery and to control the primary protection switch based on the sensed voltage; and a secondary protection circuit, configured to sense a voltage across the battery and to control the secondary protection switch based on the sensed voltage; wherein the primary and secondary protection circuits are arranged in parallel across the battery.

2. A battery protection system according to claim 1, wherein the primary protection circuit is coupled across the battery between the battery, and the primary and secondary protection switches.

3. A battery protection system according to claim 2, wherein the primary protection circuit is further configured to detect the presence of a battery charger coupled to the load / charge port.

4. A battery protection system according to claim 3, wherein the primary protection circuit includes a primary ground connection which is coupled to a negative terminal of the battery.

5. A battery protection system according to claim 4, wherein the primary protection circuit includes a battery voltage sensing connection coupled to a positive terminal of the battery, the primary protection circuit being further configured to sense the battery voltage via the battery voltage sensing connection and the primary ground connection.

6. A battery protection system according to claim 5, wherein the primary protection circuit includes a battery charger detection connection coupled to the load / charge port, the primary protection circuit being further configured to detect the battery charger via the battery charger detection connection and the primary ground connection.

7. A battery protection system according to any one of claims 4 to 6, wherein the secondary protection circuit includes a secondary ground connection, wherein the primary and secondary ground connections are coupled to a negative terminal of the battery.

8. A battery protection system according to any one of the preceding claims, wherein the primary protection switch is coupled between a first terminal of the battery and a first terminal of the load / charge port, and the secondary protection switch is coupled between a second terminal of the battery and a second terminal of the load / charge port.

9. A battery protection system according to claim 8, wherein the first terminals are positive terminals and the second terminals are negative terminals.

10. A battery protection system according to any one of the preceding claims, wherein the first protection circuit is a first integrated circuit and the second protection circuit is a second integrated circuit.

11. A battery protection system according to any one of the preceding claims, wherein the primary protection circuit is further configured to open the primary protection switch when the battery voltage drops below a first threshold voltage.

12. A battery protection system according to claim 11, wherein the secondary protection circuit is further configured to open the secondary protection switch when the battery voltage drops below a second threshold voltage.

13. A battery protection system according to claim 12, wherein the second threshold voltage is less than the first threshold voltage.

14. A battery protection system according to any one of the preceding claims, wherein the primary protection circuit is further configured to detect the presence of a battery charger coupled to the load / charge port and to control the primary protection switch at least in part based on the presence of a battery charger.

15. A battery protection system according to claim 14, further comprising: a bypass circuit coupled between the battery and the load / charge port.

16. A battery protection system according to claim 15, wherein: in a first mode the secondary protection switch is closed and the primary protection circuit is further configured to detect the presence of a battery charger via a primary charger detection current path which includes the secondary protection switch; and in a second mode the secondary protection switch is open and the primary protection circuit is further configured to detect the presence of a battery charger via a secondary charger detection current path which includes the bypass circuit.

17. A battery protection system according to claim 16, wherein the bypass circuit includes at least one bypass resistor and at least one bypass switch and in the second mode of operation the at least one bypass switch is closed.

18. A battery protection system according to claim 17, wherein the second mode of operation is an undervoltage mode of operation in which the battery voltage drops below an undervoltage threshold.

19. A battery protection system according to any of claims 15 to 18, wherein the bypass circuit is coupled between a positive terminal of the battery and a negative terminal of the load / charge port.

20. A battery protection system according to any of claims 15 to 19, wherein the secondary protection circuit comprises the bypass circuit.

21. A battery protection system according to any of claims 16 to 20, wherein the secondary charger detection current path also includes the battery.

22. A battery protection system according to any of claims 14 to 21, wherein the primary protection circuit is further configured to close the primary protection switch when the battery charger is detected to allow the battery charger to charge the battery.

23. A battery protection system according to claim 22, wherein the system is configured to form a charging current loop during charging, via the first and second protection switches, and when the secondary protection switch is open the current flows through a body diode of the secondary protection switch.

24. A method of operating the battery protection system of any of claims 1 to 23, comprising: sensing, using the primary protection circuit, the voltage across the battery; sensing, using the secondary protection circuit, the voltage across the battery; controlling the primary protection switch, using the primary protection circuit, based on the voltage sensed by the primary protection circuit; and controlling the secondary protection switch, using the secondary protection circuit, based on the voltage sensed by the secondary protection circuit.

25. A method according to claim 24, further comprising: opening the primary protection switch, using the primary protection circuit, when the battery voltage drops below a first threshold voltage.

26. A method according to claim 25, further comprising: opening the secondary protection switch, using the secondary protection circuit, when the battery voltage drops below a second threshold voltage.

27. A method according to claim 26, wherein the second threshold voltage is less than the first threshold voltage.

28. A method according to any of claims 24 to 27, further comprising: when the secondary protection switch is closed, detecting the presence of a battery charger using the primary protection circuit, via a primary charger detection current path that includes the secondary protection switch; and closing the primary protection switch to enable the battery to be charged.

29. A method according to claim 24 when dependent on claim 15, further comprising: when the secondary protection switch is open, detecting the presence of a battery charger, using the primary protection circuit, via a secondary charger detection current path that includes the bypass circuit; and closing the primary protection switch to enable the battery to be charged.

30. An electronic appliance, comprising the battery protection system of any of claims 1 to 23.

31. An electronic appliance according to claim 30, further comprising: a battery charger dock, configured to receive a battery charger and coupled to the load / charge port; a load, coupled to the load / charge port; and a user interface, coupled to the battery protection system and configured to control the discharge of the battery to the load.

32. An electronic appliance according to claim 31, wherein the load is an electric motor.

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