POWER TOOL INCLUDING A LOW QUIESCENT CURRENT DC LINK BUS DISCHARGE CIRCUIT

A power tool device that includes a housing, a battery pack interface configured to receive at least one battery pack, a first battery pack terminal and a second battery pack terminal, a low quiescent current direct current (“DC”) link bus discharge circuit including a DC link bus capacitance, a first DC link bus switch, and a second DC link bus switch, and a controller. The controller is configured to monitor a voltage of the first battery pack terminal, monitor a voltage of the second battery pack terminal, turn ON the first DC link bus switch and the second DC link bus switch when the voltage of the first battery pack terminal is greater than a first threshold value and the voltage of the second battery pack terminal is zero volts.

FIELD

Embodiments described herein provide battery pack powered devices.

SUMMARY

Embodiments described herein provide systems and methods that allow safe-to-touch battery pack terminals after a battery pack has been disconnected from a power tool.

Power tool devices described herein include a housing, a battery pack interface configured to receive at least one battery pack, a first battery pack terminal and a second battery pack terminal, a low quiescent current direct current (“DC”) link bus discharge circuit including a DC link bus capacitance, a first DC link bus switch, and a second DC link bus switch, and a controller. The controller is configured to monitor a voltage of the first battery pack terminal, monitor a voltage of the second battery pack terminal, turn ON the first DC link bus switch and the second DC link bus switch when the voltage of the first battery pack terminal is greater than a first threshold value and the voltage of the second battery pack terminal is zero volts.

In some aspects, the power tool devices further include a third DC link bus switch connected to the first DC link bus switch.

In some aspects, the controller is configured to activate the third DC link bus switch is when the voltage of the second terminal is greater than a battery pack presence voltage threshold value.

In some aspects, the battery pack presence voltage threshold value is 18V or less.

In some aspects, the first DC link bus switch is deactivated when the voltage of the first battery pack terminal is greater than the first threshold value and the voltage of the second battery pack terminal is greater than a second threshold value.

In some aspects, the at least one battery pack includes a first battery pack and a second battery pack.

In some aspects, the first threshold value is between 18V and 36V.

In some aspects, the first threshold value is 25V.

Power tool devices described herein include a housing, a battery pack interface configured to receive at least one battery pack, a low quiescent current direct current (“DC”) link bus discharge circuit including a discharge resistor and a discharge switch, and a controller. The controller is configured to determine when the power tool device is not in operation, implement a delay interval subsequent to it being determined that the power tool device is not in operation, activate, after the end of the delay interval, the discharge switch to discharge voltage stored on a DC link bus through the discharge resistor.

In some aspects, the controller is configured to provide a turn ON command to a controller pin after the end of the delay interval.

In some aspects, the power tool device is configured to disconnect the battery pack interface from a DC link capacitance using a solid state disconnect circuit.

In some aspects, the controller is configured determine a safe to handle state of the power tool device.

Methods of controlling a power tool device described herein include monitoring a voltage of a first battery pack terminal, monitoring a voltage of a second battery pack terminal, activating a first DC link bus switch and a second DC link bus switch when the voltage of the first battery pack terminal is greater than a first threshold value and the voltage of the second battery pack terminal is zero volts.

In some aspects, the methods further include activating a third DC link bus switch when the voltage of the second terminal is greater than a battery pack presence voltage threshold value.

In some aspects, the battery pack presence voltage threshold value is 18V or less.

In some aspects, the methods further include deactivating the first DC link bus switch when the voltage of the first battery pack terminal is greater than the first threshold value and the voltage of the second battery pack terminal is greater than a second threshold value.

In some aspects, the first threshold value is between 18V and 36V.

In some aspects, the first threshold value is 25V.

In some aspects, the methods further include determining a safe to handle state of the power tool device.

In some aspects, the methods further include connecting the first battery pack terminal to a first battery pack and the second battery pack terminal to a second battery pack.

It should be understood that although certain drawings illustrate hardware and software located within particular devices, these depictions are for illustrative purposes only. Functionality described herein as being performed by one component may be performed by multiple components in a distributed manner. Likewise, functionality performed by multiple components may be consolidated and performed by a single component. In some embodiments, the illustrated components may be combined or divided into separate software, firmware and/or hardware. For example, instead of being located within and performed by a single electronic processor, logic and processing may be distributed among multiple electronic processors. Regardless of how they are combined or divided, hardware and software components may be located on the same computing device or may be distributed among different computing devices connected by one or more networks or other suitable communication links. Similarly, a component described as performing particular functionality may also perform additional functionality not described herein. For example, a device or structure that is “configured” in a certain way is configured in at least that way but may also be configured in ways that are not explicitly listed.

DETAILED DESCRIPTION

FIG.1illustrates a high-power electrical system to which multiple battery packs10,10A may be attached. The high-power electrical system includes various high-power electrical devices enabled to receive and utilize multiple battery packs, and subsequently use a quiescent circuit to allow for a discharging of a capacitor. For example, the high-power electrical system includes hand-held devices (i.e., devices configured to be supported by an operator during use) and non-hand-held devices (i.e., devices supported on a work surface or support rather than by the operator during use). Such devices include motorized power tools (e.g., a drill, an impact driver, an impact wrench, a rotary hammer, a hammer drill, a saw [a circular saw, a cut-off saw100, a reciprocating saw, a miter saw105, a table saw120, etc.], a core drill130, a breaker115, a demolition hammer compressor110, a pump, etc.), outdoor tools (e.g., a chain saw125, a string hammer, a hedge trimmer, a blower, a lawn mower, etc.), drain cleaning and plumbing tools, construction tools, concrete tools, other motorized devices (e.g., vehicles, utility carts, wheeled and/or self-propelled tools, etc.), etc. and non-motorized electrical devices (e.g., a power supply145, a light135, an AC/DC adapter140, a generator, etc.).

FIG.2illustrates a simplified block diagram of an embodiment illustrating an electronics assembly275and a motor assembly210of a power tool or power tool device200. The electronics assembly275includes circuitry to couple to several embodiments of circuits that allow for low quiescent current and safe discharge of capacitors. The electronics assembly275includes a positive power input terminal260, a negative power input terminal270, a first controller245, a second controller240, an inverter bridge225, and a trigger assembly230. The motor assembly210includes a motor215and a rotor position sensor assembly220. The electronics assembly275may also include additional user inputs, for example, a mode selector switch, a speed dial, a clutch setting unit, etc. In some embodiments, the electronics assembly275may include a power switch in addition to or in place of the trigger assembly230.

The functionality of the implemented circuit may be divided between the first controller245and the second controller240. For example, the first controller245may be a main controller of the system, whereas the second controller240is an application controller controlling one or more applications of the implemented circuit. In some embodiments, the second controller240may be a motor controller controlling operation of the inverter bridge225and the motor215, and the first controller245may be a main controller that performs other functionality of the implemented circuit. By distributing the functional load of the high-capacity and high-powered implemented circuit, and by particularly separating motor control functionality from a first controller245, thermal load is distributed among the first controller245and the second controller240. This thermal distribution thereby reduces the thermal signature of the implemented circuit.

In some embodiments, the first controller245and/or the second controller240are implemented as microprocessors with separate memories. In other embodiments, the first controller245and/or the second controller240may be implemented as microcontrollers (with memory on the same chip). In other embodiments, the first controller245and/or the second controller240may be implemented partially or entirely as, for example, field programmable gate arrays (FPGA), application specific integrated circuits (ASIC), hardware implemented state machines, etc., and the memory may not be needed or modified accordingly.

In some embodiments, the second controller240and the motor assembly210may be part of a single motor package. This motor package offers modularity for future applications. For example, multiple motor packages, each including a motor assembly210and a second controller240, may be assembled in the implemented circuit and controlled by a single first controller245.

A communication protocol may be implemented between the first controller245and the second controller240in order to maintain an uninterrupted operation of the implemented circuit. In one example, the first controller245and the second controller240may communicate over a communication bus235such as a serial peripheral interface (SPI) bus. The first controller245and the second controller240may be configured such that the first controller245and the second controller240exchange communications at a certain time interval. The time interval may be, for example, between 3 milliseconds (ms) to 15 ms. The first controller245may also communicate with a battery pack controller over a communication link265.

As described above, in some embodiments, the second controller240controls the operation of motor215through the inverter bridge225. The first controller245is communicatively coupled to the trigger assembly230. The trigger assembly230may include, for example, a potentiometer, a distance sensor, etc., to determine and provide an indication of the distance the trigger is pulled to the first controller245. The first controller245reads and processes the trigger information and provides the trigger information to the second controller240. The second controller240is communicatively coupled to the rotor position sensor assembly220. As described above, the rotor position sensor assembly220provides an absolute rotational position of the rotor and/or the rotational speed of the rotor. The second controller240performs an open loop or closed loop control of the motor215through the inverter bridge225based on the signals received from the first controller245(e.g., trigger information) and the rotor position sensor assembly220. In some embodiments, the first controller245and the second controller240are communicatively coupled to the rotor position sensor assembly220to provide redundancy for monitoring rotation speed.

FIG.3illustrates an embodiment 300 of a portion of the inverter bridge225that controls the power supply to the three-phase (e.g., U, V, and W) of the motor215of the power tool device200. The inverter bridge300includes gate drivers305, high-side FETs310, and low-side FETs315for each phase of the motor215. The high-side FETs310and the low-side FETs315are controlled by the corresponding gate drivers305.

In some embodiments, the inverter bridge300may include more than one high-side FET310and more than one low-side FET315per phase in order to provide redundant current paths for each phase. AlthoughFIG.3illustrates only one set of a gate driver305, a high-side FET310, and a low-side FET315, the inverter bridge300includes three sets of gate drivers305, high-side FETs310, and low-side FETs315, one for each phase of the motor215.

The high-side FETs310receive battery power supply at the drain of the high-side FETs310. The source of the high-side FETs310is connected to the motor215(e.g., phase coil of the motor215) to provide battery power supply to the motor215when the high-side FETs310are closed. In other words, the high-side FETs310are connected between the battery power supply and the motor phase coil.

The drain of the low-side FETs315is connected to the motor215(e.g., phase coils of the motor215) and the source of the low-side FETs315is connected to ground. In other words, the low-side FETs315are connected between the motor phase coil and ground. The low-side FETs315provide a current path between the motor phase coils and ground when closed.

When the FETs310,315are closed (or ON), the FETs310,315allow a current flow through the phase coils. In contrast, when the FETs310,315are open (or OFF), the FETs310,315prevent a current flow through the phase coil. The FETs310,315are characterized by a relatively high drain-source breakdown voltage (e.g., between 120 V to 220 V), a relatively high continuous drain current (e.g., between 50 A to90A), a relatively high pulsed drain current (e.g., over 300 A), and a drain-source on-state resistance (RDS (on)) of less than 15 m22.

In contrast, FETs used in existing power tool devices were not rated for such high voltage and current characteristics. Accordingly, existing power tool devices would not be capable of handling such high current and voltage characteristics.

The gate drivers305provide a gate voltage to the FETs310,315to control the FETs310,315to open or close. The gate drivers305receive an operating power supply (e.g., a low-voltage power supply) from the battery pack10,10A. The gate drivers305also receive control signals, one each for the high-side current path and the low-side current path, from the second controller240. The gate drivers305provide a control gate voltage (e.g., from the low-voltage power supply) to the FETs310,315based on the control signals received from the second controller240.

In some embodiments, the second controller240and the gate drivers305may control only the low-side FETs315to operate the motor215. In other embodiments, the second controller240and the gate drivers305may control only the high-side FETs310to operate the motor215. In other embodiments, the second controller240and the gate drivers305alternate between controlling the high-side FETs310and the low-side FETs315to operate the motor215and to distribute the thermal load between the FETs310,315.

In some embodiments, the inverter bridge300may also include a current sensor provided in the current path to detect a current flowing to the motor215. The output of the current sensor is provided to the second controller240. The second controller240may control the motor215further based on the output of the current sensor.

With reference toFIG.2, a discharge switch255is provided on a current path between the power terminals and the inverter bridge300of the implemented circuit. The discharge switch255may be implemented using, for example, a metal-oxide-semiconductor field effect transistor (MOSFET). When the discharge switch255is open, current flow is stopped between power terminals and the inverter bridge300.

A discharge controller250controls the discharge switch255(that is, opens and closes the discharge switch255). The discharge controller250may be a logic circuit, a hardware implemented state machine, an electronic processor, etc. The discharge controller250receives inputs from the first controller245, the second controller240, and the trigger and provides a control signal to the discharge switch255. The discharge controller250may also provide a status indication to the first controller245indicating whether the discharge switch255is open or closed.

Several techniques may be contemplated to implement a discharge control scheme of the power tool device200using the discharge switch255besides the main embodiments that include a low quiescent current circuit. In one example, the discharge controller250may be an AND gate that implements a logic system with inputs from the first controller245, the second controller240, and the trigger assembly230. The discharge controller250may close the discharge switch255only when the trigger, the first controller245, and the second controller240provide controls signals to close the discharge switch255.

In some embodiments, it may be desirable to close the discharge switch255to operate the motor34when the trigger is operated and the first controller245and the second controller240are ready for the operation. In these embodiments, the discharge controller250may close the discharge switch255from the trigger, the first controller245, and the second controller240. Accordingly, when one of the first controller245and the second controller240generates an interrupt due to detecting a problem, or when the trigger is released, the discharge controller250opens the discharge switch255to prevent current flow to the inverter bridge300. In some embodiments, when the first controller245or the second controller240detects an overvoltage condition, an overcurrent condition, an overheating condition, etc., the first controller245or the second controller240may generate or terminate a signal to the discharge controller250to open the discharge switch255.

FIG.4illustrates a tool terminal block400including a positive power terminal425, a ground terminal435, a low-power terminal430, a positive transmission terminal405, a negative transmission terminal410, a positive receiver terminal420, and a negative receiver terminal415. The positive power terminal425and the ground terminal435are connected to power terminals (i.e., a positive battery terminal and a ground terminal) of the battery pack10,10A to receive a main discharging current for the operation of the implemented circuit. The low-power terminal430receives a low-power voltage supply from a low-power terminal of the battery pack10,10A to power certain functions of the tool.

The positive transmission terminal405, the negative transmission terminal410, the positive receiver terminal420, the negative receiver terminal415may together be referred to as “communication terminals” of the implemented circuit. The communication terminals allow for differential communication between the battery pack10,10A and the power tool device200. In other embodiments, the tool communication terminals follow a full-duplex standard (for example, RS485 standard).

Referring back toFIG.2, the positive power terminal425and the ground terminal435are electrically coupled to the inverter bridge225and provide a current path to operate the motor215. The communication terminal (i.e., the positive transmission terminal405, the negative transmission terminal410, the positive receiver terminal420, and the negative receiver terminal415may be coupled to first controller245, for example, through a power tool device transceiver. The communication terminal provides the communication link265between the first controller245and a battery pack controller.

FIG.5Aillustrates an embodiment of a battery pack500A. The battery pack500A includes a housing505A, a user interface portion510A for providing a state-of-charge indication for the battery pack500A, and a device interface portion515A for connecting the battery pack500A to a device (e.g., a power tool). The battery pack500A includes a plurality of battery cells within the housing505A.

FIG.5Billustrates another embodiment of a battery pack500B. The battery pack500B includes the battery housing530comprising a wall having an inside surface and an outside surface. The inside surface defines an internal cavity. The outside surface includes a top surface portion515B and a bottom portion. The battery cells disposed within the cavity are connected in series to battery contacts505B. The contacts505B are disposed on the top surface portion515B, within a battery contacts housing extension510B. The housing extension510B is configured to matingly engage with one or more power tools or powered accessories. A battery charge level indicator520is also disposed on the housing, while additional battery charging, monitoring, and indication components are disposed within the cavity. As shown inFIG.5B, two tabs535are coupled to the housing530for releasably securing the housing530to a power tool. Corresponding features to those described above with respect to the battery pack500A can also be included in the battery pack500B.

FIG.6illustrates a battery terminal block600for interfacing with the tool terminal block400of the power tool device200. The battery terminal block600is operable to electrically connect the battery pack10,10A and the power tool device200and, as illustrated, includes a positive battery terminal640, a ground terminal630, a charger terminal635, a low-power terminal625, a positive transmission terminal605, a negative transmission terminal610, a positive receiver terminal620, and a negative receiver terminal615. The positive battery terminal640and the ground terminal630are connectable to power terminals (i.e., positive power terminal425and ground terminal435) of the power tool device200. The charger terminal635and the ground terminal630are connected to charging terminals of a charger and receive charging current to charge the battery cells of the battery pack10. In some embodiments, the battery pack terminals630,640may be made of F-Tec material (a copper, phosphorus material) to offer battery thermal distribution capabilities and durability.

The ground terminal630may form a common reference between the battery pack10,10A and the power tool device200. The low-power terminal625provides a low-power voltage supply to the power tool device200to power certain functions of the power tool device200. For example, the low-power voltage supply may be used to power the first controller245, the second controller240, the gate drivers305, indicators (e.g., LEDs), a communication module, etc., of the power tool device200.

The positive transmission terminal605, the negative transmission terminal610, the positive receiver terminal620, and the negative receiver terminal615may together be referred to as “battery communication terminals” of the battery pack10,10A. The battery communication terminals allow for differential communication between the battery pack10and the power tool device200or charger. The battery communication terminals and the communication terminals of the power tool device200together may be referred to as the communication link265. In other embodiments, the communication terminals follow a full-duplex standard (for example, RS485 standard).

FIG.7is a simplified block diagram of the battery pack10,10A. The battery pack10,10A includes battery cells755, a battery controller760, a low-power generator725, and a battery transceiver765. The battery controller760may be implemented in ways similar to the first controller245and the second controller240.

In some embodiments, a battery discharging switch715is connected between the battery cells755and the positive battery terminal730. The battery controller760is operable to control (e.g., open and close) the discharging switch715to control discharge of the battery cells755. In some embodiments, a charging switch710may also be connected between the battery cells755and the charger terminal705. The battery controller760is operable to control (e.g., open and close) the charging switch710to control charging of the battery cells755. In some embodiments, when the discharging switch715and the charging switch710are implemented using MOSFETs, two MOSFETS, in series, may be used as the discharging switch715and the charging switch710. This allows the discharging switch715and the charging switch710to prevent any current flow in either direction when the discharging switch715and the charging switch710are open.

The discharging switch715and the charging switch710may be implemented using bi-polar junction transistors, field-effect transistors (FETs), etc. In some embodiments, the discharging switch and the charging switch710may be connected on the ground-side of the battery cells755between the battery cells755and the ground terminal790. In some embodiments, the ground terminal790may be split into a charging path ground terminal and a discharging path ground terminal.

The low-power generator725is connected between the battery cells755and the low-power terminal720. The low-power generator725provides a low-power voltage supply at the low-power terminal720to the power tool device200. In some embodiments, the battery controller760may provide control signals to the low-power generator725to control the operation of the low-power generator725.

In the illustrated example, the battery transceiver765is implemented as a differential communication transceiver (e.g., Texas Instruments SN65HVD7 Full Duplex RS-485 Transceiver). The battery transceiver765receives a transmission signal735from the battery controller760and sends a receiver signal750to the battery controller760.

The battery transceiver765is also connected to the communication terminals (770,775,780, and785). When the battery pack10transmits a communication signal to the power tool device200or charger, the battery controller760sends a transmission enable signal740in addition to a transmission enable signal740to the battery transceiver765. When the battery transceiver765receives the transmission enable signal740, the battery transceiver765converts the transmission signal735to complementary transmission signals at the positive transmission terminal770and the negative transmission terminal775. When the battery transceiver765receives a receiver enable signal745from the battery controller760, the battery transceiver765receives complementary signals from the positive receiver terminal780and the negative receiver terminal signal750to the battery controller760. The power tool device200may similarly include a power tool device transceiver that interacts with the first controller245in a similar way to provide communications with the battery controller760.

In other embodiments, rather than the battery transceiver765, the battery pack10may include separate transmitting and receiving components, for example, a transmitter and a receiver.

The battery controller760communicates with the first controller245through the battery terminals via the communication link265(e.g., an RS-485 link). The communication link265between the battery controller760and the first controller245may be used for battery pack10,10A and power tool device200authentication or to exchange other information (e.g., discharge capabilities of the battery pack10,10A). The first controller245and the battery controller760may be configured such that the first controller245and the battery controller760exchange communications at a certain time interval. The time interval may be, for example, between 3 ms to 15 ms.

FIG.8illustrates a low quiescent current DC link bus discharge circuit800for the power tool200. The circuit800includes a battery pack negative terminal805(e.g., a lowest potential terminal connected to the battery packs500A,500B), an intermediate voltage terminal810(e.g., corresponding to the battery pack positive voltage of a first battery pack500A,500B), and a DC link bus terminal815(e.g., a highest potential terminal connected to the battery packs500A,500B). When two battery packs are connected to the power tool200, the DC link bus terminal815corresponds to a combined, series voltage of the two battery packs (e.g., 36V-40V). When either battery pack is removed from its battery pack receiving interface of the power tool200, the voltage of the DC link bus terminal can remain high if the DC link bus capacitance is charged. A discharge transistor hold-up capacitor820is charged when the voltage at the DC link bus terminal815is greater than a first threshold value (e.g., 25V, between 18V and 36V, etc.) and the voltage at the intermediate voltage terminal is greater than a second threshold value (e.g., 18V, 10V-18V, etc.). The discharge transistor hold-up capacitor820can be charged to a DC link voltage value of, for example, 10-15V. The voltage at the intermediate voltage terminal810will be greater than or approximately equal to the second threshold value when the first battery pack500A,500B is attached to the power tool200or if the second battery pack500A,500B is attached to the power tool200and the discharge transistor hold-up capacitor820is charged.

Switches825and830(e.g., bi-polar junction transistors, FETs, MOSFETs, etc.) are configured for asymmetric switching of a first DC link switch835and a second DC link switch840. The second DC link switch840is turned ON or activated if the voltage of the intermediate voltage terminal810is greater than a battery pack presence voltage threshold value (e.g., 10V), which indicates that a first battery pack500A,500B is connected to the power tool200. In some embodiments, the first DC link switch835is a PMOS transistor and the second DC link switch840is an NMOS transistor. When the second DC link switch840is ON, a DC link discharge switch845(e.g., bi-polar junction transistors, FETs, MOSFETs, etc.) is correspondingly turned OFF. In some embodiments, the DC link discharge switch845is an NMOS transistor. When the first battery pack500A,500B is removed from the power tool200, the second DC link switch840is turned OFF.

The first DC link switch835being OFF or deactivated ensures a low quiescent current for the power tool200(e.g., below a threshold quiescent current value, such as less than or equal to 5 micro-Amps [“μA”]). The first DC link switch835is turned ON or activated if the voltage at the DC link terminal815is greater than the first threshold value (e.g., greater than 25V) and the voltage at the intermediate voltage terminal810is zero (0) voltages. Such a situation occurs when the DC link bus capacitance (not show) is charged and both first and second battery packs500A,500B are removed or detached from the power tool200. In such an instance, with the first DC link switch835ON, and the second DC link switch840OFF (because the first battery pack500A,500B is removed), the DC link discharge switch845is turned ON or activated. When the DC link discharge switch845and the first DC link switch835are both ON, the discharge transistor hold-up capacitor820is discharged to ground. With the discharge transistor hold-up capacitor820being discharged, there is no risk or arcing or shock from, for example, a user contacting the battery pack receiving terminals of the power tool200(e.g., corresponding to the DC link bus terminal815and the intermediate voltage terminal810). InFIG.8, the DC link bus capacitance is illustratively shown as capacitor850. Although only one capacitor850is illustrated to represent the DC link bus capacitance, the capacitor850can represent an aggregation of capacitance on the DC link bus from multiple capacitors or other sources of capacitance.

FIG.9illustrates a low quiescent current capacitance discharge method900. The battery pack powered power tool200can receive multiple (e.g., two) battery packs and can be switched ON by a user (STEP905), which initiates an operation of the battery pack powered power tool200. This activates the battery packs connected to the circuit800illustrated in inFIG.8(STEP910) to discharge current for powering the power tool200. The terminals of the battery packs are electrically coupled to the circuit800ofFIG.8at the terminals805,810,815, and the battery pack powered tool200monitors the DC link bus terminal815and the intermediate voltage terminal810. Once the user ends their task or operation with the power tool200, the power tool operation is ceased (STEP915), therefore power is no longer needed to be transferred from the battery packs to the power tool200. As described above, the first DC link switch835being OFF ensures a low quiescent current for the power tool200. As a result, if the battery packs500A,500B remain attached to the power tool200, the quiescent current drawn by the power tool200will be very low (e.g., less than 5 μA).

In order to ensure that the terminals of the power tool200are safe for a user to touch when the battery packs500A,500B are removed, the voltage of the DC link bus terminal815and the voltage of the intermediate voltage terminal810(shown in and described with respect toFIG.8) are monitored (STEP925) to detect if one or both of the battery packs has been removed (i.e., detached) from the power tool200. If the voltage at the DC link bus terminal815is above, for example, the first threshold value (e.g., 25V) and the voltage at the intermediate voltage terminal810is greater than the second threshold value (e.g., 18V), the controller240,245can determine that two battery packs are connected to the power tool200. If the high-side battery pack (e.g., corresponding to the highest potential terminal at the DC link bus) is removed from the power tool200and the low-side battery pack is removed with the discharge transistor hold-up capacitor820being charged (e.g., to 10V-15V), the controller240,245will measure a voltage at the DC link bus terminal815that is greater than the first threshold value (e.g., 25V) and a voltage at the intermediate voltage terminal810that is zero (0) volts. In such a situation, the discharge transistor hold-up capacitor820is discharged by the DC link discharge switch845(STEP930), as described above with respect toFIG.8. Once the discharge transistor hold-up capacitor820is discharged, the battery pack terminals of the power tool200are safe to the touch (STEP935).

FIG.10illustrates another embodiment of a circuit for safely discharging DC link capacitors or capacitance.FIG.10illustrates a DC link capacitor discharge circuit1000that includes a discharge resistor1005, a controller pin1010(e.g., from the controller240,245), and a discharge switch1015(e.g., a FET) for connecting the discharge resistor1005to ground1020. When battery packs (e.g., two battery packs) are connected to the power tool200, the combined series voltage of the battery packs corresponds to the voltage of the DC link bus of the power tool200. The positive end of the discharge resistor1005is connected to the DC link bus. During operation of the power tool200, the battery packs are connected to the DC link bus by a solid state disconnect circuit to provide power for driving a motor. However, when operation of the tool has ended, the solid state disconnect circuit can be used to disconnect the battery pack voltage from the DC link bus. The voltage from the DC link capacitance can then be discharged by the DC link capacitor discharge circuit1000. For example, after a predetermined time delay following the end of operation of the power tool200(e.g., after sensed trigger release, after a motor has stopped rotating, etc.), the controller240,245is configured to provide an ON signal to the controller pin1010to turn on the discharge switch1015. After the discharge switch1015is turned ON, the charge stored by the DC link capacitance for the DC link bus is discharged through the discharge resistor1005. As a result of the discharge switch1015being OFF, the quiescent current drawn by the power tool200will be very low (e.g., less than 5 μA).

FIG.11illustrates a control process1100for the circuit ofFIG.10. The user first connects the plurality of battery packs500A,500B to the power tool200(STEP1105), and subsequently turns the power tool200ON (STEP1110). By turning the power tool200ON, the battery packs are activated (STEP1110) and will provide power to a motor of the power tool200. In operation, a solid state disconnect circuit (e.g., main power tool power switch) connects the battery pack voltage to the DC link bus to allow for driving a motor of the power tool200. Once the user finishes working with the power tool, the power tool operation is ceased (STEP1115), stopping the motor of the power tool200. Power tool operation may be halted through a variety of different methods and/or systems (e.g., releasing a trigger, predetermined halting control, etc.). The battery pack voltages are then disconnected from the DC link capacitance (STEP1120) using the solid state disconnect circuit. After the battery pack voltage is disconnected from the DC link bus and DC link bus capacitance, a delay interval or period is set in the controller240,245(STEP1125). At the end of the delay interval or period, the controller240,245provides a turn ON command to the controller pin1010(STEP1130) in order to discharge the DC link capacitance's voltage through a discharge resistor1005(STEP1135). Once the DC link capacitance are discharged, the battery pack terminals of the power tool200are safe to touch (STEP1140).

Thus, embodiments described herein provide, among other things, systems and methods to discharge DC link bus capacitance to ensure safe to touch battery terminals. Various features and advantages are set forth in the following claims.