Overcurrent protection, and associated circuitry, devices, systems, and methods

Various embodiments relate to protection circuits. A protection circuit may include a first node for coupling to a first battery and a second node for coupling to a second battery. The protection circuit may also include a first path coupled between the second node and the first node and including a diode. The protection circuit may also include a second path coupled between the first node and the second node. The second path may include a first stage coupled to the first node and including a first number of thermistors coupled in parallel. The second path may also include a second stage coupled between the first stage and the second node and including a second number of thermistors coupled in parallel, wherein the first stage may be coupled in series with the second stage. Associated methods, systems, and devices are also disclosed.

TECHNICAL FIELD

This disclosure relates generally to overcurrent protection and, more specifically, to limiting an amount of current supplied to a chargeable battery, and to related circuitry, devices, systems, and methods.

BACKGROUND

Chargeable batteries are electrical batteries that can be charged, discharged into a load, and recharged many times. Chargeable batteries, such as lithium-ion (Li-Ion) batteries, include a wide range of applications, from, for example, earbuds to large backup power systems. Some chargeable batteries (e.g., a secondary battery) may be configured to receive (e.g., from a power source, such as a primary battery) a maximum charge voltage of, for example only, 25.8 volts (V) at, for example, 3 amperes (A) or less. In some scenarios, because a chargeable battery may be coupled (e.g., directly wired) to a primary battery and because a voltage (e.g., a voltage reaching as high as 29V) exhibited by the primary battery may be greater than the maximum charge voltage, an amount of current conveyed to the chargeable battery may be too great, a charge limiter built into the chargeable battery may be overwhelmed, and the chargeable battery may be damaged.

BRIEF SUMMARY

At least one embodiment of the disclosure includes an overcurrent protection circuit. The overcurrent protection circuit may include a first node for coupling to a first battery and a second node for coupling to a second battery. The overcurrent protection circuit may also include a first path coupled between the second node and the first node and including a diode having an anode coupled to the second node and a cathode coupled to the first node. Further, the overcurrent protection circuit may include a second path coupled between the first node and the second node. The second path may include a first stage coupled to the first node and including a first number of thermistors coupled in parallel. The second path may also include a second stage coupled between the first stage and the second node and including a second number of thermistors coupled in parallel. The first stage may be coupled in series with the second stage.

Another embodiment includes a method of charging a battery. The method may include receiving, at a circuit, a first current from a primary battery. Further, the method may include, responsive to the first current, conveying, via a first path of the circuit including at least one negative temperature coefficient (NTC) thermistor coupled to at least one positive temperature coefficient (PTC) thermistor, a second current to a secondary battery.

Other embodiments may include a mobile unit. A mobile unit may include a trailer and a storage box coupled to the trailer and including a primary battery. The mobile unit may also include a mast coupled to the trailer and having a first end proximate the storage box. Further, the mobile unit may include a head unit coupled to a second, opposite end of the mast. The head unit may include a secondary battery and a protection circuit comprising a number of thermistors coupled between the primary battery and the secondary battery.

DETAILED DESCRIPTION

Referring in general to the accompanying drawings, various embodiments of the present invention are illustrated to show example embodiments related to overcurrent protection. It should be understood that the drawings presented are not meant to be illustrative of actual views of any particular portion of an actual circuit, device, system, or structure, but are merely representations which are employed to more clearly depict various embodiments of the disclosure.

The following provides a more detailed description of the present invention and various representative embodiments thereof. In this description, functions may be shown in block diagram form in order not to obscure the present invention in unnecessary detail. Additionally, block definitions and partitioning of logic between various blocks is exemplary of a specific implementation. It will be readily apparent to one of ordinary skill in the art that the present invention may be practiced by numerous other partitioning solutions. For the most part, details concerning timing considerations and the like have been omitted where such details are not necessary to obtain a complete understanding of the present invention and are within the abilities of persons of ordinary skill in the relevant art.

Some example systems (e.g., electronic systems) may include a primary power source (e.g., a primary battery) and a secondary power source (e.g., a secondary battery). In these example systems, the primary power source, which may be configured to provide power to a load, may include, for example, a bank of absorbed glass mat (AGM) batteries in a series/parallel combination rated at, for example only, 24V and 220 AHrs. Further, the primary power source may be configured to provide power to the secondary power source (i.e., for charging the secondary power source). The secondary power source, which may include, for example, a Li-Ion battery (e.g., a 24V Li-Ion battery), may provide power to the load upon one or more events (e.g., the primary power source failing to provide a sufficient amount of power to the load, the primary power source being disconnected from the load (e.g., if one or more wires are cut or otherwise disconnected), or another event). As noted above, in some scenarios, the secondary power source may be damaged (e.g., due to too much current being conveyed to the secondary power source). It is noted that each the primary power source and the secondary power source may include any suitable type of battery chemistry, such as, AGM, flooded lead acid, lithium (e.g., lithium-ion, lithium-polymer, lithium iron phosphate, or other lithium-based chemistry), or any combination thereof, without limitation.

Various embodiments of the disclosure relate to limiting an amount of current conveyed to a battery, while not substantially limiting an amount of current conveyed from the battery. More specifically, various embodiments relate to systems, devices, circuitry, and methods associated with limiting a current conveyed from a primary battery to a secondary battery (i.e., to charge the secondary power source), while not substantially limiting a current conveyed from the secondary battery (i.e., to power an associated load (e.g., in response to the primary battery failing to provide a sufficient amount of power to the load)).

In some embodiments, a protection circuit (also referred to herein as an “overcurrent protection circuit”), which may be coupled between the primary power source and the secondary power source, may be configured to limit an amount of current conveyed from the primary power source to the secondary power source. For example, in some embodiments, a protection circuit may include a combination of positive temperature coefficient (PTC) thermistors and negative temperature coefficient (NTC) thermistors wired in a series/parallel configuration that may limit the current over a wide ambient temperature range (e.g., from approximately −20° C. to approximately +54° C., or any other temperature range). A thermistor configuration by itself may limit both a charge current (i.e., a current conveyed to the secondary battery) and a discharge current (i.e., a current conveyed from the secondary battery). To overcome the discharge current limitation, the protection circuit may also include a diode having an anode coupled to the secondary battery and a cathode coupled to, for example, a load. In one non-limiting example, the diode may include a Schottky diode (e.g., 45V, 10 A Schottky diode), which may exhibit a low forward voltage drop of, for example, 0.5V, as opposed to 0.7V for a standard silicon diode. In some examples, even with a 0.5V drop, the secondary battery may still provide a sufficient amount of power to an associated load to operate the load for at least a time period (e.g., ½ hour, 1 hour, more than 1 hour).

Embodiments of the disclosure will now be explained with reference to the accompanying drawings.

FIG.1illustrates an example system100including a first battery102, a load104, and a second battery106. In this example, first battery102(e.g., a primary battery) may provide power to load104. Further, first battery102may provide power to second battery106(e.g., a backup battery) to charge second battery106. Moreover, in response to first battery102failing to provide enough power to load104, second battery106may provide power to load104.

In some scenarios, because second battery106is coupled (e.g., directly wired) in parallel with first battery102and because of a voltage exhibited by first battery102(e.g., a voltage reaching as high as 29V), second battery106may be damaged due to too much current being conveyed to second battery106.

FIG.2illustrates an example system200, according to various embodiments of the disclosure. System200includes a first battery (also referred to as a “primary battery,” a “primary power source,” a “first battery,” a “main battery,” or some variation thereof)202, a load204, a second battery (also referred to as a “secondary battery,” a “secondary power source,” a “second battery,” a “backup battery,” or some variation thereof)206, and a protection circuit208. In this example, first battery202may provide power to load204, which, in one non-limiting example, includes a control board (also referred to herein as a “control unit” or “controller”) and possibly other devices (e.g., communication device, sensor, output device, without limitation). First battery202may receive power from any suitable source. As a non-limiting example, first battery202may receive power from a natural and/or a renewable power source, such as solar, wind, water, without limitation.

First battery202may also provide power to second battery206(i.e., via protection circuit208) to charge second battery206. Further, in response to first battery202failing to provide enough power to load204, second battery206may provide power to load204. In contrast to system100ofFIG.1, as described more fully below, protection circuit208may limit an amount of current conveyed to second battery206. Further, as also described more fully below, protection circuit208may be configured such that an amount of current conveyed from second battery206to load204is not limited by protection circuit208.

It is noted that system200is provided as an example system and other system configurations are within the scope of the disclosure. For example,FIG.3illustrates a system300in accordance with various embodiments of the disclosure. Like system200ofFIG.2, system300ofFIG.3includes protection circuit208coupled between first battery202and second battery206; however, in system300, a load is not coupled between first battery202and second battery206. For example, second battery206may be coupled to a load (not shown inFIG.3) independent of protection circuit208.

FIG.4depicts another example system400, according to various embodiments of the disclosure. System400includes a first battery402, a second battery406, and a protection circuit408, which is one example of protection circuit208ofFIG.2and/orFIG.3. In this example, protection circuit208, which is coupled between first battery402and second battery406, includes a resistor R coupled in parallel with a diode D. As will be appreciated by a person having ordinary skill, a diode conducts current primarily in one direction (i.e., a diode has low (ideally zero) resistance in one direction, and high (ideally infinite) resistance in the other).

In one example wherein resistor R includes a 1.5 Ohm, 10 W resistor, and diode D includes, for example, a Schottky diode, protection circuit408may limit a charge current (i.e., conveyed to second battery406) to around 4 A, while allowing a discharge current (i.e., conveyed from second battery406) to remain at about 8 A. In another example, resistor R may include a 2 Ohm, 50 W resistor, and diode D may include an OnSemi™ Schottky diode (e.g., 45V 8 A Axial) with a forward drop of approximately 550 mV at approximately 8 A.

In one non-limiting example, a charge voltage range may be from approximately 25.2V (minimum) under normal operating conditions with first battery402in a “float” stage to approximately 29V (maximum) when first battery402is in an “absorb” stage. In this example, the maximum power dissipated by resistor R during float charging may be approximately 25 W (hence the 50 W resistor rating). Also, in some examples, it may be assumed that a voltage at second battery406may originally be at approximately 15V, and therefore, in this example, the maximum charge voltage requirement is approximately 14V (i.e., 29V-15V) that will be dropped across resistor R. Thus, at approximately 25 W, the maximum current through resistor R is approximately 1.78 A, and therefore, in this example, resistor R has a resistance of approximately 7.8 Ohms.

FIG.5depicts an example device500, in accordance with various embodiments of the disclosure. Device500, which may include circuitry, includes a node (also referred to as an “input”)502, a node (also referred to as an “output”)504, a path506, and a path508. In some examples, node502may be coupled to a battery (e.g., a primary battery (e.g., first battery202; seeFIG.2)) and node504may be coupled to a battery (e.g., a secondary battery (e.g., second battery206; seeFIG.2)). For example, path506, which may also be referred to as a “charging path,” may include a number of resistive elements. More specifically, for example, path506may include a number of thermistors. Yet more specifically, as described more fully below, path506may include a plurality of thermistors in a series/parallel configuration. For example, path508, which may also be referred to as a “discharging path,” may include a diode. In another example, path508may include a switch (i.e., rather than a diode), which may be opened during a charge phase (i.e., while a battery coupled to node504is being charged) and closed during a discharge phase (i.e., while the battery coupled to node504is powering a load).

With reference to another example device600ofFIG.6, according to some examples, path506may include a first stage610including a number of thermistors (e.g., one or more negative temperature coefficient (NTC) thermistors (e.g., in parallel) and/or one or more positive temperature coefficient (PTC) thermistors (e.g., in parallel)) and a second stage612including a number of thermistors (e.g., one or more negative temperature coefficient (NTC) thermistors (e.g., in parallel) and/or one or more positive temperature coefficient (PTC) thermistors (e.g., in parallel)). As will be appreciated by a person having ordinary skill in the art, PTC and NTC thermistors are temperature-dependent resistors, wherein a resistance of a PTC thermistor increases with an increasing temperature and decreases with a decreasing temperature, and a resistance of a NTC thermistor decreases with an increasing temperature and increases with a decreasing temperature. Although various embodiments described herein use and/or include thermistors, the disclosure is not so limited and other suitable temperature dependent resistance devices may be used in addition to or in place of one or more thermistors.

FIG.7depicts an example layout700, according to various embodiments of the disclosure. Layout700, which may include a top view of a printed circuit board (PCB) layout, depicts a number of (i.e., three in this non-limiting example) PTC thermistors702coupled in parallel, a number of (i.e., two in this non-limiting example) NTC thermistors704coupled in parallel, and a diode706. Layout700further depicts a node (e.g., input node)710for coupling to a load and/or a primary battery, and a node712for coupling to a secondary battery (i.e., a chargeable battery).

FIG.8illustrates an example circuit800, according to various embodiments of the disclosure. For example, protection circuit208(see e.g.,FIG.2and/orFIG.3) may include circuit800. Circuit800includes a first stage810including a first thermistor R1and a second thermistor R2. In some examples, each of thermistor R1and thermistor R2includes an NTC thermistor. In other examples, each of thermistor R1and thermistor R2includes a PTC thermistor.

Circuit800further includes a second stage812including a third thermistor R3, a fourth thermistor R4, and a fifth thermistor R5. In some examples, each of thermistor R3, thermistor R4, and thermistor R5includes a PTC thermistor. In other examples, each of thermistor R3, thermistor R4, and thermistor R5includes an NTC thermistor.

It is noted that although first stage810is illustrated as having two thermistors, the disclosure is not so limited, and first stage810may include any suitable number of thermistors. Similarly, it is noted that although second stage812is illustrated as having three thermistors, the disclosure is not so limited, and second stage812may include any suitable number of thermistors. Circuit800further includes a diode820coupled between a node (also referred to herein as an “input”)802and a node (also referred to therein as an “output”)804.

As will be appreciated, during a charging phase (i.e., while a battery coupled to node804is charged), a current may flow through first stage810and second stage812, and current will not flow from node802to node804via diode820(i.e., because diode may not allow current in the reverse direction). Further, during a discharging phase (i.e., while a battery coupled to node804provides power to a load), a current may flow from node804to node802via diode820, and little, if any, current will flow from node804to node802via second stage812and first stage810. In other words, in at least some examples, during the charging phase, all current conveyed from node802to node804flows through the thermistor network of first stage810and second stage812, and during the discharging phase, all current conveyed from node804to node802flows through diode820. Therefore, during the discharging phase, a current conveyed from node804to node802may not be limited by the thermistor network of first stage810and second stage812.

Each thermistor of circuit800may include any suitable default resistance. As a non-limiting example, each of thermistor R1and thermistor R2, which in one specific example includes an NTC thermistor, may include a default resistance of approximately 7.0 ohms (e.g., at room temperature). Further, as a non-limiting example, each of thermistor R3, thermistor R4, and thermistor R5, which in one specific example includes a PTC thermistor, may include a default resistance of approximately 3.0 ohms (e.g., at room temperature). Diode820may include any diode, such as a silicon diode, a Schottky diode (e.g., 10 A Schottky diode), or any other suitable diode.

In one non-limiting contemplated operation, node802may receive an input voltage in the range of approximately 22.6 volts to approximately 29 volts. Further, in this non-limiting contemplated operation, circuit800may generate an output voltage in the range of approximately 15 volts to approximately 25.6 volts.

Although thermistors R1and R2are described as having the same default resistance value and thermistors R3, R4, and R5are described as having the same default resistance value, the disclosure is not so limited. Rather, each of thermistor R1, R2, R3, R4, and R5may have any default resistance value that may or may not be the same as or similar to a resistance value of another thermistor of circuit800. Moreover, although thermistors in a stage (e.g., stage810or stage812) are described as being the same type of thermistor (i.e., either PTC or NTC thermistors), the disclosure is not so limited. Rather, each of thermistor R1, R2, R3, R4, and R5may be any type of thermistor (i.e., PTC or NTC) regardless of a type of another thermistor of circuit800.

As will be appreciated by a person having ordinary skill in the art, circuit800may limit the current over a wide ambient temperature range. More specifically, for example, at some temperatures (e.g., at or around −12° C.) a resistance of one or more NTC thermistors of a circuit (e.g., circuit800) may significantly increase to limit an amount of current conveyed to an output (e.g., output node804). Further, for example, at some temperatures (e.g., at or around +40° C.) a resistance of one or more PTC thermistors of a circuit (e.g., circuit800) may significantly increase to limit an amount of current conveyed to an output (e.g., output node804). In one specific example configuration, circuit800may limit the current over a wide ambient temperature range from approximately −20° ° C. to approximately +54° ° C. However, it will be appreciated that by, for example, varying the configuration and/or the size of one or more thermistors of circuit800, other temperature ranges may fall within the scope of the disclosure.

FIG.9depicts another example system900, in accordance with various embodiments of the disclosure. System900includes a primary battery902, a load904, a secondary battery906, a protection circuit908, and a cord reel910. As non-limiting examples, primary battery902may include a bank of absorbed glass mat (AGM) batteries, secondary battery906may include a Li-Ion battery, and load904may include a control board, and possibly other electrical devices. Protection circuit may include protection circuit208(see e.g.,FIG.2and/orFIG.3) and/or circuit800ofFIG.8.

FIG.10depicts another example system1000including a unit1002, in accordance with various embodiments of the disclosure. Unit1002, which may also be referred to herein as a “mobile unit,” a “mobile security unit,” a “live unit,” a “physical unit,” or simply a “unit,” may include one or more sensors (e.g., cameras, weather sensors, motion sensors, noise sensors, without limitation)1004and one or more output devices1006(e.g., lights, speakers, electronic displays, without limitation).

In some embodiments, unit1002may include a mobile unit, which may or may not be used for security and/or surveillance. In these and other embodiments, unit1002may include a portable trailer1008, a storage box1010, and a mast1012coupled to a head unit1014, which may include for example, one or more batteries, one or more cameras, one or more lights, one or more speakers, and/or one or more microphones. According to some embodiments, a first end of mast1012may be proximate storage box1010and a second, opposite end of mast1012may be proximate, and possibly adjacent, head unit1014. More specifically, in some embodiments, head unit1014may be coupled to mast1012an end opposite an end of mast1012proximate storage box1010.

In some examples, unit1002may include one or more primary batteries (e.g., within storage box1010) and one or more secondary batteries (e.g., within head unit1014). In these embodiments, a primary battery positioned in storage box1010may be coupled to a load and/or a secondary battery positioned within head unit1014via a cord reel, such as cord reel910ofFIG.9.

In some embodiments, unit1002may also include one or more solar panels1016, which may provide power to one or more batteries of unit1002. More specifically, according to some embodiments, one or more solar panels1016may provide power to a primary battery within storage box1010. Although not illustrated inFIG.10, unit1002may also include one or more additional power sources, such as one or more generators (e.g., fuel cell generators). In some embodiments, a primary power source may include a battery charger that is configured to be plugged into, for example, a shore power (e.g., 100 VAC) electrical outlet.

As noted above, in the event that a primary battery (e.g., primary battery902ofFIG.9) fails to provide sufficient power to a load (e.g., load904ofFIG.9), a secondary battery (e.g., secondary battery906ofFIG.9) may take over (i.e., provide power to the load). As a non-limiting example, secondary battery906may provide enough power (e.g., to load904and/or other devices) to continue to operate unit1002for an amount of time (e.g., ½ hour, 1 hour, without limitation) (e.g., such that pertinent data can be collected by unit1002regarding the reason for the failure of primary battery902).

FIG.11is a flowchart of an example method1100of charging a battery. Method1100may be arranged in accordance with at least one embodiment described in the disclosure. Method1100may be performed, in some embodiments, by a device or system, such as system200(seeFIG.2), system300(seeFIG.3), system400(seeFIG.4), device500(seeFIG.5), device600(seeFIG.6), layout700(seeFIG.7), circuit800(seeFIG.8), system900(seeFIG.9), unit1002(seeFIG.10), or another device or system. Although illustrated as discrete blocks, various blocks may be divided into additional blocks, combined into fewer blocks, or eliminated, depending on the desired implementation.

Method1100may begin at block1102, wherein a first current is supplied from a first battery to a protection circuit, and method1100may proceed to block1104. For example, the first battery may include a primary battery of a system (e.g., battery202(seeFIG.2and/orFIG.3) and/or battery902(seeFIG.9)). Further, for example, the first battery, which may include a bank of AGM batteries, may be positioned in a storage box (e.g., storage box1010ofFIG.10) of a mobile unit (e.g., unit1002ofFIG.10). For example, the protection circuit may include protection circuit208(seeFIG.2and/orFIG.3), protection circuit800(seeFIG.8) and/or protection circuit908(seeFIG.9).

At block1104, responsive to the first current, a second current may be conveyed to a second battery via a path of the protection circuit (i.e., to charge the second battery). In at least some examples, the path of the protection circuit (e.g., charging path506(seeFIG.5and/orFIG.6)) may include at least one positive temperature coefficient (PTC) thermistor coupled to at least one negative temperature coefficient (NTC) thermistor. As noted above, the protection circuit may include protection circuit208(seeFIG.2and/orFIG.3), protection circuit800(seeFIG.8) and/or protection circuit908(seeFIG.9). For example, the second battery may include a secondary battery of a system (e.g., battery206(seeFIG.2and/orFIG.3) and/or battery906(seeFIG.9)). Further, for example, the second battery, which may include a Li-Ion battery, may be positioned in a head unit (e.g., head unit1014ofFIG.10) of a mobile unit (e.g., unit1002ofFIG.10). As will be appreciated, the second current (i.e., the current conveyed to the second battery) may be less than the first current conveyed from the first battery to the protection circuit.

Modifications, additions, or omissions may be made to method1100without departing from the scope of the present disclosure. For example, the operations of method1100may be implemented in differing order. Furthermore, the outlined operations and actions are only provided as examples, and some of the operations and actions may be optional, combined into fewer operations and actions, or expanded into additional operations and actions without detracting from the essence of the disclosed embodiment. For example, method1100may include one or more acts wherein a current is conveyed from the secondary battery to a load via another path of the protection circuit that may include a diode. For example, the current conveyed from the second battery to the load may be greater than the current conveyed to the second battery (i.e., from the first battery and via the protection circuit). As another example, method1100may include one or more acts wherein the primary battery is charged via energy received from a renewable source (e.g., a solar panel or a fuel cell), shore power, or other energy source.

As will be appreciated by persons having ordinary skill in the art, in contrast to conventional systems, devices, circuitry, and methods, which require complex and costly circuitry using active components (e.g., A/D converters, comparator circuitry, uProcessors, FETs, etc.) to monitor the voltage and current (i.e., for providing overcurrent protection), various embodiments disclosed herein provide overcurrent protection via inexpensive passive components (e.g., one or more thermistors and possibly a diode), which may be more robust than active circuit components.

As will be appreciated, temperature differences of a system may affect optimal and dangerous charging currents. Lithium batteries may be particularly sensitive to certain charging currents (e.g., when the Lithium battery is too cold or too warm). It is noted that, due to the various charge current profiles of all batteries, and especially Lithium chemistries, the thermal dynamic nature of various disclosed embodiments may adjust the charging currents based on temperature. Accordingly, various embodiments may exhibit improvements (e.g., in safety and/or functionality) over existing technologies.

In accordance with common practice, the various features illustrated in the drawings may not be drawn to scale. The illustrations presented in the disclosure are not meant to be actual views of any particular apparatus (e.g., circuit, device, system, etc.) or method, but are merely idealized representations that are employed to describe various embodiments of the disclosure. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., circuit, device, or system) or all operations of a particular method.

Additionally, the use of the terms “first,” “second,” “third,” etc., are not necessarily used herein to connote a specific order or number of elements. Generally, the terms “first,” “second,” “third,” etc., are used to distinguish between different elements as generic identifiers. Absence a showing that the terms “first,” “second,” “third,” etc., connote a specific order, these terms should not be understood to connote a specific order. Furthermore, absence a showing that the terms “first,” “second,” “third,” etc., connote a specific number of elements, these terms should not be understood to connote a specific number of elements.

The embodiments of the disclosure described above and illustrated in the accompanying drawings do not limit the scope of the disclosure, which is encompassed by the scope of the appended claims and their legal equivalents. Any equivalent embodiments are within the scope of this disclosure. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combinations of the elements described, will become apparent to those skilled in the art from the description. Such modifications and embodiments also fall within the scope of the appended claims and equivalents.