Patent Description:
Conventional secondary battery packs flow a current whereby a minimal function of an electrical instrument can be performed even after a voltage of a secondary battery used as a power source of the electrical instrument decreases and discharge stops (for example, see patent literature <NUM>). Patent literature <NUM> describes a backup circuit as part of a power supply system mounted on a vehicle which includes, in addition to the backup circuit, also a power supply unit, a power storage unit, a power supply unit side conductive path, a power storage unit side conductive path, a first load-side conductive path, and a second load side conductive path. The backup circuit and the power storage unit constitute an in-vehicle backup device. The first load-side conductive path is a wiring portion electrically connected to a first power supply target, and is a path for supplying power to the first power supply target, while the second load-side conductive path is a wiring portion electrically connected to a second power supply target, and is a path for supplying power to the second power supply target. The first power supply target is composed of one or more in-vehicle loads, preferably an electric component whose power supply is desired even when the power supply from the power supply unit is interrupted. The power supply of the first power supply target may have a lower urgency of backup than the second power supply target. The first power supply target operates based on the power supplied from the power supply unit in a normal state, and is supplied via a first voltage conversion unit in an abnormal state. The second power supply target is composed of one or more in-vehicle loads, preferably an electric component whose power supply is desired even when the power supply from the power supply unit is interrupted. The second power supply target operates based on the power supplied from the power supply unit in the normal state, and is based on the power supplied via a second voltage conversion unit in the abnormal state.

There is thus a need to extend a period of supplying power to a load to be backed up.

Accordingly, the present disclosure provides a power control circuit and a power control method in accordance with the appended set of claims.

A power control circuit according to one or more embodiments comprises: a lithium-ion capacitor configured to be charged by power supplied by an external power source; a first protection circuit that, when power is no longer supplied from the external power source, is configured to supply a discharge current of the lithium-ion capacitor to a first load that is configured to operate using the power supplied by the external power source; and a second protection circuit that, when power is no longer supplied from the external power source, is configured to supply the discharge current of the lithium-ion capacitor to a second load that is configured to operate at a lower power consumption than the first load over at least a predetermined period. The first protection circuit is configured to stop supplying the current to the first load when a terminal voltage of the lithium-ion capacitor becomes less than a first voltage, and the second protection circuit is configured to stop supplying the current to the second load when the terminal voltage of the lithium-ion capacitor becomes less than a second voltage that is lower than the first voltage. This enables the power control circuit to stop the first load in a state wherein a charge amount of the lithium-ion capacitor is left at no less than a predetermined value when using the lithium-ion capacitor as a backup power source of the first load and the second load. As a result, a period of being able to supply power to the second load is extended. Additionally, the first voltage is set so that an electrical-charge amount that is discharged as the terminal voltage of the lithium-ion capacitor falls from the first voltage to the second voltage becomes no less than an electrical-charge amount necessary to back up the second load over the predetermined period.

According to one or more embodiments, the first protection circuit may comprise a first switching element configured to be connected between the lithium-ion capacitor and the first load. The first protection circuit may further comprise a first voltage detection circuit configured to control the first switching element. The first voltage detection circuit may be configured to be operable by a current that is supplied from the lithium-ion capacitor via the first switching element when power is no longer supplied from the external power source, maintain the first switching element in an on state when the terminal voltage of the lithium-ion capacitor is no less than the first voltage, and transition the first switching element to an off state when the terminal voltage of the lithium-ion capacitor becomes less than the first voltage. This prevents the first protection circuit from needlessly consuming power after the first load is stopped. As a result, a period of being able to supply power to the second load is extended.

According to one or more embodiments, the first protection circuit may be configured so that the lithium-ion capacitor can connect to the external power source via the first switching element, and the first switching element may be configured so that a current heading from the external power source to the lithium-ion capacitor flows even when the first switching element is transitioned to the off state. This charges the lithium-ion capacitor when the external power source is restored, regardless of a state of the first protection circuit. As a result, reversion at power restoration becomes easy.

According to one or more embodiments, the power control circuit may further comprise the external power source.

According to one or more embodiments, the lithium-ion capacitor may be mounted on a circuit board together with the first load, the lithium-ion capacitor being mounted in a position that is affected by heat generation from the first load, so that the lithium-ion capacitor is subject to a temperature increase as a heat generation amount of the first load increases, and the lithium-ion capacitor has a lower limit of the terminal voltage corresponding to the first voltage when the temperature of the lithium-ion capacitor is higher than a predetermined temperature and to the second voltage when the temperature of the lithium-ion capacitor is no greater than the predetermined temperature. This causes the lithium-ion capacitor to be utilized in a voltage range that is as wide as possible within a usage temperature range thereof. As a result, a period of being able to supply power to the second load is extended.

According to one or more embodiments, a power control circuit is provided that can extend a period of supplying power to a load to be backed up.

One or more embodiments provide a use of the of the power control circuit in an Internet of Things (IoT) gateway terminal.

One or more embodiments provide a power control method as defined in claim <NUM>.

Embodiments of the present invention will be described in comparison with comparative examples which are not covered by the scope of the appended claims.

Comparative Example <NUM> will be described below. As illustrated in <FIG>, a power control circuit <NUM> of comparative example <NUM> includes a power source <NUM>, a processor <NUM>, and an RTC (real-time clock) <NUM>. The power source <NUM> supplies power to the processor <NUM>. When the power source <NUM> becomes unable to supply power, the processor <NUM> stops operating.

The power control circuit <NUM> further includes a diode <NUM> connected in series with the RTC <NUM> and an electric double-layer capacitor <NUM> connected in parallel to the RTC <NUM>. The power source <NUM> supplies power to the RTC <NUM> via the diode <NUM> and supplies power to the electric double-layer capacitor <NUM> to charge the electric double-layer capacitor <NUM>. When the power source <NUM> becomes unable to supply power, the electric double-layer capacitor <NUM> discharges and supplies power to the RTC <NUM>. The RTC <NUM> can operate using the power discharged by the electric double-layer capacitor <NUM>. As a result, the power control circuit <NUM> can function as a backup power source for the RTC <NUM>.

However, the electric double-layer capacitor <NUM> self-discharges easily. Therefore, the electric double-layer capacitor <NUM> is not suited for a usage of backing up a load over a long period.

In <FIG>, when the electric double-layer capacitor <NUM> is substituted with a primary battery such as a button battery, the primary battery can function as the backup power source of the RTC <NUM>. However, the primary battery cannot be charged and thus needs to be replaced. Moreover, a circuit needs to be added so the primary battery starts backup when the power source <NUM> is stopped.

Furthermore, the power control circuit <NUM> can only back up the one system linked to the RTC <NUM>, and a separate backup power source needs to be provided for the processor <NUM>.

Comparative Example <NUM> will be described below. As illustrated in <FIG>, a power control circuit <NUM> of comparative example <NUM> includes a lithium-ion secondary battery <NUM>, a positive-electrode terminal <NUM>, and a negative-electrode terminal <NUM>. The lithium-ion secondary battery <NUM> may include a plurality of battery cells. A positive electrode of the lithium-ion secondary battery <NUM> is connected to the positive-electrode terminal <NUM>. A negative electrode of the lithium-ion secondary battery <NUM> is connected to the negative-electrode terminal <NUM>. The positive-electrode terminal <NUM> and the negative-electrode terminal <NUM> are connected to a load. The power control circuit <NUM> functions as a backup power source for the load by supplying a current from the positive-electrode terminal <NUM> and the negative-electrode terminal <NUM> to the load. A charging rate (SOC: state of charge) of the lithium-ion secondary battery <NUM> is positively correlated to a terminal voltage. That is, the higher the terminal voltage of the lithium-ion secondary battery <NUM>, the higher the SOC. The higher the SOC of the lithium-ion secondary battery <NUM>, the longer discharge can be performed.

The load includes a heavy load that operates at a power consumption that is no less than a predetermined value and a micro load that operates at a power consumption that is less than the predetermined value. The heavy load includes, for example, the processor <NUM>. The micro load includes, for example, the RTC <NUM>.

The negative electrode of the lithium-ion secondary battery <NUM> and the negative-electrode terminal <NUM> of the power control circuit <NUM> are connected by two parallel paths. One path includes a switch <NUM>. The other path includes a series circuit of a switch <NUM> and a resistor <NUM>. In a closed state, the switches <NUM> and <NUM> are conductive, enabling current flow in the wiring. In an open state, the switches <NUM> and <NUM> block current flow to the wiring.

The power control circuit <NUM> further includes a switch controller <NUM> that controls opening and closing of the switches <NUM> and <NUM>. The switch controller <NUM> controls the switches <NUM> and <NUM> based on a voltage of the lithium-ion secondary battery <NUM>.

The switch controller <NUM> closes the switch <NUM> and opens the switch <NUM> when the voltage of the lithium-ion secondary battery <NUM> is no less than a predetermined voltage-that is, when the SOC is no less than a predetermined value. In this situation, the terminal voltage of the lithium-ion secondary battery <NUM> is output as a voltage between the positive-electrode terminal <NUM> and the negative-electrode terminal <NUM> and applied to the load connected between the positive-electrode terminal <NUM> and the negative-electrode terminal <NUM>.

The switch controller <NUM> opens the switch <NUM> and closes the switch <NUM> when the voltage of the lithium-ion secondary battery <NUM> is less than a predetermined voltage-that is, when the SOC is less than the predetermined value. In this situation, the lithium-ion secondary battery <NUM> supplies the current to the load via wiring that includes the resistor <NUM>. The switch controller <NUM> measures the discharge current of the lithium-ion secondary battery <NUM> based on a voltage of the resistor <NUM>. When the discharge current of the lithium-ion secondary battery <NUM> becomes no less than a predetermined value, the switch controller <NUM> opens the switch <NUM> and stops the discharge of the lithium-ion secondary battery <NUM>. Upon confirming that the discharge current of the lithium-ion secondary battery <NUM> becomes less than the predetermined value, the switch controller <NUM> closes the switch <NUM> and restarts the discharge of the lithium-ion secondary battery <NUM>. This restricts the discharge current of the lithium-ion secondary battery <NUM> and extends a duration of discharge.

As for the load, when current supply stops, wiring that supplies the current to the micro load is made conductive and wiring that supplies the current to the heavy load is blocked by a means such as opening and closing the switches <NUM> and <NUM>. This controls the current supplied to the load overall to be less than the predetermined value. As a result, the switch controller <NUM> can confirm that the current that flows to the load when the switch <NUM> is closed is less than the predetermined value. In this situation, the power control circuit <NUM> can function as a backup power source for the micro load.

The power control circuit <NUM> can not only function as a backup power source for the micro load as above but also for the heavy load. The power control circuit <NUM> supplies the backup current to both the micro load and the heavy load from one system composed of the positive-electrode terminal <NUM> and the negative-electrode terminal <NUM>. In other words, in the power control circuit <NUM>, both the micro load and the heavy load drain the backup current from one system. The heavy load stops draining the current only when the heavy load per se stops operating. Therefore, an operation of the power control circuit <NUM> supplying the current to only the micro load is dependent on control of the heavy load per se.

Power consumption that does not contribute to load operation occurs at the resistor <NUM> used to measure the discharge current of the lithium-ion secondary battery <NUM>. This power consumption decreases the discharge duration of the lithium-ion secondary battery <NUM>.

The lithium-ion secondary battery <NUM> has a narrow usable temperature range and can only be used under limited conditions. When the power control circuit <NUM> is used in an environment that does not meet these conditions, a reliability thereof decreases.

The lithium-ion secondary battery <NUM> self-discharges easily. Therefore, the lithium-ion secondary battery <NUM> is difficult to store as inventory over a long period and is not suited to a usage of backing up a load over a long period.

Overcharging the lithium-ion secondary battery <NUM> causes early degradation and failure. Therefore, a charge current of the lithium-ion secondary battery <NUM> needs to be controlled by an overcharge protection circuit. Providing an overcharge protection circuit to the power control circuit <NUM> makes size reduction difficult. As a result, an installation location of the power control circuit <NUM> is limited.

The above issues of the lithium-ion secondary battery <NUM> can also arise when the electric double-layer capacitor <NUM> in <FIG> is substituted with the lithium-ion secondary battery <NUM>.

As above, in the configurations of each comparative example, various improvements of the power control circuits <NUM> and <NUM> are required for backing up a load for a long period.

According to one or more embodiments, a power control circuit <NUM> (see <FIG> and the like) can back up a load over a long period. The power control circuit <NUM> may be applied to a usage of an edge computer gateway. The power control circuit <NUM> may be used in an IoT (internet of things) gateway terminal.

As illustrated in <FIG>, the power control circuit <NUM> according to one or more embodiments includes a lithium-ion capacitor <NUM>, a first protection circuit <NUM>, a second protection circuit <NUM>, and a regulator <NUM>. The lithium-ion capacitor <NUM> has one end connected to a ground point <NUM> and another end connected to the first protection circuit <NUM> and the second protection circuit <NUM>. The first protection circuit <NUM> has one end connected to the lithium-ion capacitor <NUM> and another end connected to the regulator <NUM>. The regulator <NUM> has one end connected to the first protection circuit <NUM> and another end connected to a first load <NUM>. The second protection circuit <NUM> has one end connected to the lithium-ion capacitor <NUM> and another end connected to a second load <NUM> via a diode <NUM>. The diode <NUM> is connected so that a direction heading from the second protection circuit <NUM> to the second load <NUM> is a forward direction. The power control circuit <NUM> has a node <NUM> that is positioned between the regulator <NUM> and the first load <NUM> and a node <NUM> that is positioned between the diode <NUM> and the second load <NUM>. The power control circuit <NUM> further includes a diode <NUM>. The diode <NUM> is connected between the node <NUM> and the node <NUM> so that a direction heading from the node <NUM> to the node <NUM> is a forward direction. The power control circuit <NUM> is connected to an external power source <NUM> from between the first protection circuit <NUM> and the regulator <NUM>.

The regulator <NUM> controls power supplied from the external power source <NUM> so that a voltage or a current is a predetermined value and supplies this to the first load <NUM> and the second load <NUM>. The regulator <NUM> may be configured as a switching regulator. The regulator <NUM> may be configured as a step-down switching regulator or a step-up switching regulator.

The lithium-ion capacitor <NUM> is an electricity storage device that can realize a performance that includes the advantages of both the electric double-layer capacitor <NUM> and the lithium-ion secondary battery <NUM>. The greater a quantity of an electrical charge that is charged in the lithium-ion capacitor <NUM>, the longer a time over which it can discharge. The electrical-charge amount charged in the lithium-ion capacitor <NUM> is positively correlated to a terminal voltage. That is, the higher the terminal voltage of the lithium-ion capacitor <NUM>, the greater the electrical-charge amount that is charged. As a result, the higher the terminal voltage, the longer the time over which the lithium-ion capacitor <NUM> can discharge.

The external power source <NUM> supplies power to the regulator <NUM> and can charge the lithium-ion capacitor <NUM> via the first protection circuit <NUM>. The external power source <NUM> may include a circuit that controls a charging voltage of the lithium-ion capacitor <NUM>. The external power source <NUM> may have, for example, a charging upper-limit voltage protection function for the lithium-ion capacitor <NUM>. The external power source <NUM> may control the voltage whereat the lithium-ion capacitor <NUM> is charged and a voltage applied to the regulator <NUM> to be the same voltage or different voltages.

The power supplied by the external power source <NUM> is supplied to the first load <NUM>, the second load <NUM>, and the lithium-ion capacitor <NUM>. The regulator <NUM> controls the power supplied from the external power source <NUM> to be direct-current power of a predetermined voltage and supplies this to the first load <NUM> and the second load <NUM>. The lithium-ion capacitor <NUM> is charged by the power supplied from the external power source <NUM>. The external power source <NUM> may include a charging control circuit that controls the charging of the lithium-ion capacitor <NUM>. The external power source <NUM> may control the output voltage so the lithium-ion capacitor <NUM> can be charged in a CCCV (constant current, constant voltage) mode. The regulator <NUM> can supply the direct-current power of the predetermined voltage to the first load <NUM> and the second load <NUM> regardless of the size of the voltage controlled by the external power source <NUM> to charge the lithium-ion capacitor <NUM>.

When the external power source <NUM> stops and cannot supply power, the lithium-ion capacitor <NUM> discharges and supplies power to the first load <NUM> or the second load <NUM>. The first protection circuit <NUM> and the second protection circuit <NUM> control whether to flow or block the current based on the terminal voltage of the lithium-ion capacitor <NUM>.

When the terminal voltage of the lithium-ion capacitor <NUM> is no less than a first voltage, the first protection circuit <NUM> provides conductivity between the lithium-ion capacitor <NUM> and the regulator <NUM> and supplies the power from the lithium-ion capacitor <NUM> to the regulator <NUM>. When the voltage of the lithium-ion capacitor <NUM> is less than the first voltage, the first protection circuit <NUM> provides blocking between the lithium-ion capacitor <NUM> and the regulator <NUM> and stops power supply to the regulator <NUM>.

When the voltage of the lithium-ion capacitor <NUM> is no less than a second voltage that is lower than the first voltage, the second protection circuit <NUM> provides conductivity between the lithium-ion capacitor <NUM> and the second load <NUM> and supplies the power from the lithium-ion capacitor <NUM> to the second load <NUM>. When the voltage of the lithium-ion capacitor <NUM> is less than the second voltage, the second protection circuit <NUM> provides blocking between the lithium-ion capacitor <NUM> and the second load <NUM> and stops power supply to the second load <NUM>.

As above, when the voltage of the lithium-ion capacitor <NUM> is no less than the first voltage, the first load <NUM> and the second load <NUM> can operate using the power supply from the lithium-ion capacitor <NUM>. When the voltage of the lithium-ion capacitor <NUM> is less than the first voltage and no less than the second voltage, the second load <NUM> can operate using the power supply from the lithium-ion capacitor <NUM>. Meanwhile, the first load <NUM> cannot operate without being supplied with power. When the voltage of the lithium-ion capacitor <NUM> is less than the second voltage, both the first load <NUM> and the second load <NUM> cannot operate without being supplied with power.

By blocking power supply to the first load <NUM> when the voltage of the lithium-ion capacitor <NUM> becomes less than the first voltage, the power control circuit <NUM> can stop the first load <NUM> in a state wherein a charge amount of the lithium-ion capacitor <NUM> is left at no less than a predetermined value. This secures a power amount that can be supplied to the second load <NUM>. As a result, a period of being able to supply power to the second load <NUM> is extended.

As above, the power control circuit <NUM> according to one or more embodiments can function as a backup power source that supplies power to the first load <NUM> and the second load <NUM> when the external power source <NUM> becomes unable to supply power. Moreover, when the charge amount of the lithium-ion capacitor <NUM> is decreased, the power control circuit <NUM> can supply power with priority to the second load <NUM>, which needs to be operated over at least a predetermined period. As a result, the power control circuit <NUM> can back up the second load <NUM> over the predetermined period while functioning as a backup power source of the first load <NUM> and the second load <NUM>.

The second load <NUM> includes a clock circuit such as an RTC. When applied to a usage of an edge computer gateway, the power control circuit <NUM> supplies backup power to an IoT terminal. The IoT terminal communicates with a server or the like and thereby uploads data to the server. The communication between the IoT terminal and the server or the like is synchronized by the clock. Therefore, in running the IoT terminal, the clock operation is included as one of the operations to be maintained with priority. The power control circuit <NUM> according to one or more embodiments can meet specifications of a backup power source in a usage of an edge computer gateway.

The first load <NUM> includes a processor or the like. The first load <NUM> may be configured to consume a power amount that the lithium-ion capacitor <NUM> can supply in about several dozen seconds. Meanwhile, the second load <NUM> may be configured to consume the power amount that the lithium-ion capacitor <NUM> can supply over about half a year or no less than about one year. That is, the power consumption of the second load <NUM> may be orders of magnitude smaller than the power consumption of the first load <NUM>. By doing so, even if the IoT terminal adopting the power control circuit <NUM> is installed in a position that is difficult to be accessed by a worker or the like, continued functioning as a backup power source for the second load <NUM> is enabled until the worker makes repairs after power is no longer fed from the external power source <NUM>.

The second load <NUM> may include a storage device such as an SRAM (static random-access memory). When power supply from the external power source <NUM> stops, the storage device serving as the second load <NUM> may quickly store information being processed by the processor or the like. This enables the processor to restart operations based on the information from before the stop when power supply from the external power source <NUM> restarts.

The second voltage corresponds to a lower-limit voltage established as a specification of the lithium-ion capacitor <NUM>. When the lithium-ion capacitor <NUM> discharges until the terminal voltage of the lithium-ion capacitor <NUM> becomes less than the lower-limit voltage, a possibility of the lithium-ion capacitor <NUM> failing increases.

The first voltage is set based on the power consumption of the second load <NUM> and the time for which the second load <NUM> is backed up. That is, the first voltage is set so that an electrical-charge amount that is discharged as the terminal voltage of the lithium-ion capacitor <NUM> falls from the first voltage to the second voltage becomes no less than an electrical-charge amount necessary to back up the second load <NUM> over the predetermined period.

As illustrated in <FIG>, the first protection circuit <NUM> includes a voltage detection circuit <NUM>, a switching element <NUM>, and terminals <NUM> and <NUM>. The voltage detection circuit <NUM> is also referred to as a first voltage detection circuit. The switching element <NUM> is also referred to as a first switching element. The first protection circuit <NUM> is configured to be connectable to the lithium-ion capacitor <NUM> by the terminal <NUM>. The first protection circuit <NUM> is configured to be connectable to the regulator <NUM> and the external power source <NUM> by the terminal <NUM>. The first protection circuit <NUM> is connected to the ground point <NUM> by the voltage detection circuit <NUM>. The first protection circuit <NUM> operates using a voltage applied between the terminal <NUM> or <NUM> and the ground point <NUM>.

In one or more embodiments, it is supposed that the switching element <NUM> includes a p-channel MOSFET (metal-oxide-semiconductor field-effect transistor). The switching element <NUM> may include an n-channel MOSFET. The switching element <NUM> may include a transistor other than a MOSFET and may include a switch IC (integrated circuit) or the like. The switching element <NUM> is conductive in an on state and provides blocking in an off state.

The voltage detection circuit <NUM> includes a comparator <NUM>, a reference voltage source <NUM>, and resistor voltage dividers <NUM> and <NUM>. The resistor voltage dividers <NUM> and <NUM> are connected in series between the terminal <NUM> and the ground point <NUM>. The resistor voltage dividers <NUM> and <NUM> divide the voltage applied between the terminal <NUM> and the ground point <NUM>. The voltage applied between the terminal <NUM> and the ground point <NUM> that is divided by the resistor voltage dividers <NUM> and <NUM> is also referred to as a first divided voltage. The first divided voltage is applied to a node <NUM> positioned between the resistor voltage divider <NUM> and the resistor voltage divider <NUM>. The reference voltage source <NUM> is connected between the terminal <NUM> and the ground point <NUM> and outputs a first reference voltage.

The comparator <NUM> has input terminals connected to the reference voltage source <NUM> and the node <NUM> and an output terminal connected to a gate of the switching element <NUM>. The comparator <NUM> is connected between the terminal <NUM> and the ground point <NUM> and operates using the voltage applied between the terminal <NUM> and the ground point <NUM>. When the switching element <NUM> is in the on state and causing the terminal <NUM> and the terminal <NUM> to be conductive, the comparator <NUM> may operate using a voltage applied from the terminal <NUM> or a voltage applied from the terminal <NUM>. The comparator <NUM> has two input terminals and one output terminal. The comparator <NUM> outputs from the output terminal a signal based on a result of comparing the first reference voltage and the first divided voltage input to the input terminals.

When the first divided voltage is no less than the first reference voltage, the comparator <NUM> outputs from the output terminal a signal that performs a control whereby the switching element <NUM> enters the on state. When the switching element <NUM> is an FET, the comparator <NUM> outputs a signal having a voltage no less than a gate threshold voltage of the FET. When the first divided voltage is no less than the first reference voltage, the comparator <NUM> may place the switching element <NUM> in the on state by outputting the same voltage as the terminal <NUM> or <NUM>. The switching element <NUM> maintains the on state by receiving, in the on state, the signal that performs the control whereby the on state is entered. The switching element <NUM> transitions to the on state by receiving, in the off state, the signal that performs the control whereby the on state is entered.

When the first divided voltage is less than the first reference voltage, the comparator <NUM> outputs from the output terminal a signal that performs a control whereby the switching element <NUM> enters the off state. When the switching element <NUM> is an FET, the comparator <NUM> outputs a signal having a voltage less than a gate threshold voltage of the FET. When the first divided voltage is less than the first reference voltage, the comparator <NUM> may place the switching element <NUM> in the off state by outputting the same voltage as the ground point <NUM>. The switching element <NUM> transitions to the off state by receiving, in the on state, the signal that performs the control whereby the off state is entered. When the switching element <NUM> transitions to the off state, the comparator <NUM> becomes unable to receive a voltage and no longer operates. When the comparator <NUM> becomes unable to receive a voltage and no longer operates, it outputs no signal. A state wherein the comparator <NUM> outputs no signal is deemed to be a state wherein the comparator <NUM> is outputting the signal that places the switching element <NUM> in the off state. Therefore, when the comparator <NUM> outputs no signal, the switching element <NUM> enters the off state. As a result, the switching element <NUM> is maintained in the off state after transitioning from the on state to the off state. The switching element <NUM> is also maintained in the off state when the switching element <NUM> was originally in the off state.

The voltage detection circuit <NUM> is configured so the first divided voltage is no less than the first reference voltage when the terminal voltage of the lithium-ion capacitor <NUM> is no less than the first voltage. Specifically, in the voltage detection circuit <NUM>, resistance values of the resistor voltage dividers <NUM> and <NUM> and the first reference voltage output by the reference voltage source <NUM> are appropriately set.

As illustrated in <FIG>, the second protection circuit <NUM> includes a voltage detection circuit <NUM>, a switching element <NUM>, and terminals <NUM> and <NUM>. The voltage detection circuit <NUM> is also referred to as a second voltage detection circuit. The switching element <NUM> is also referred to as a second switching element. The second protection circuit <NUM> has the terminal <NUM> connected to the lithium-ion capacitor <NUM> and the terminal <NUM> connected to the second load <NUM>. The second protection circuit <NUM> has the voltage detection circuit <NUM> connected to the ground point <NUM>. The second protection circuit <NUM> operates using a voltage applied from the terminal <NUM> or <NUM>.

In one or more embodiments, it is supposed that the switching element <NUM> is a p-channel MOSFET. It is supposed that the voltage detection circuit <NUM> is configured identically to the voltage detection circuit <NUM> of <FIG>. The voltage detection circuit <NUM> generates a second divided voltage that is a division between the terminal <NUM> or <NUM> and the ground point <NUM>. The voltage detection circuit <NUM> generates a second reference voltage.

When the second divided voltage is no less than the second reference voltage, the voltage detection circuit <NUM> outputs a signal that performs a control whereby the switching element <NUM> enters an on state. When the switching element <NUM> is an FET, the voltage detection circuit <NUM> outputs a signal having a voltage no less than a gate threshold voltage.

When the second divided voltage is less than the second reference voltage, the voltage detection circuit <NUM> outputs a signal that performs a control whereby the switching element <NUM> enters an off state. When the switching element <NUM> is an FET, the voltage detection circuit <NUM> outputs a signal having a voltage less than a gate threshold voltage.

The voltage detection circuit <NUM> is configured so the second divided voltage is no less than the second reference voltage when the terminal voltage of the lithium-ion capacitor <NUM> is no less than the second voltage. The second reference voltage may be identical to the first reference voltage. In this situation, a resistance value of a resistor voltage divider included in the voltage detection circuit <NUM> may be set so the second divided voltage is identical to the first divided voltage. The first reference voltage and the second reference voltage being made identical enables the reference voltage source <NUM> to be shared between the voltage detection circuits <NUM> and <NUM>.

Change over time in the terminal voltage of the lithium-ion capacitor <NUM> is described with reference to the graph illustrated in <FIG>. The horizontal axis represents time. The vertical axis represents the terminal voltage of the lithium-ion capacitor <NUM>.

The lithium-ion capacitor <NUM> is charged so the terminal voltage is V0 up to time T0 and starts discharging from time T0. At the discharge starting point (time T0), the terminal voltage of the lithium-ion capacitor <NUM> steps down according to a voltage drop due to an internal resistance of the lithium-ion capacitor <NUM>. The terminal voltage of the lithium-ion capacitor <NUM> decreases due to discharge and decreases to a first voltage V1 at time T1.

When the terminal voltage of the lithium-ion capacitor <NUM> becomes the first voltage V1, the first protection circuit <NUM> provides blocking between the lithium-ion capacitor <NUM> and the regulator <NUM>. Meanwhile, the second protection circuit <NUM> maintains conductivity between the lithium-ion capacitor <NUM> and the second load <NUM>. This maintains power feeding to the second load <NUM> but stops power feeding to the first load <NUM>.

Stopping power feeding to the first load <NUM> causes a discharge current of the lithium-ion capacitor <NUM> to decrease. The decrease in the discharge current causes the voltage drop due to the internal resistance of the lithium-ion capacitor <NUM> to decrease. As a result, the terminal voltage of the lithium-ion capacitor <NUM> steps up at time T1. The first load <NUM> stops operating at a timing when power feeding stops. The terminal voltage of the lithium-ion capacitor <NUM> stepping up enables the first protection circuit <NUM> to once again provide conductivity between the lithium-ion capacitor <NUM> and the regulator <NUM>. In this situation, the first load <NUM> may be configured so as to not restart operations automatically. For example, the first load <NUM> may be configured to be able to communicate with the external power source <NUM> and be configured to restart operations when a signal representing that the external power source <NUM> has restarted power supply is acquired. This makes a phenomenon wherein the switching element <NUM> of the first protection circuit <NUM> changes between the on state and the off state in short increments (phenomenon corresponding to chattering arising in a relay or the like) less likely to occur.

From time T1 onward, the lithium-ion capacitor <NUM> discharges so as to flow a current needed for the operations of the second load <NUM>. Therefore, the discharge current from time T1 onward is less than the discharge current at time T1 and before. Due to the decreased discharge current, the terminal voltage of the lithium-ion capacitor <NUM> decreases more gradually than at time T1 and before and decreases to a second voltage V2 at time T2.

When the terminal voltage of the lithium-ion capacitor <NUM> becomes the second voltage V2, the second protection circuit <NUM> provides blocking between the lithium-ion capacitor <NUM> and the second load <NUM>. This stops power feeding to the second load <NUM>.

As above, the power control circuit <NUM> according to one or more embodiments can function as a backup power source that supplies power to the first load <NUM> and the second load <NUM> when the external power source <NUM> becomes unable to supply power. Moreover, when the charge amount of the lithium-ion capacitor <NUM> is decreased, the power control circuit <NUM> can supply power with priority to the second load <NUM>, which needs to be operated over at least the predetermined period. As a result, the power control circuit <NUM> can back up the second load <NUM> over the predetermined period while functioning as a backup power source of the first load <NUM> and the second load <NUM>.

The power control circuit <NUM> according to one or more embodiments controls opening and closing of the switching elements <NUM> and <NUM> based on the terminal voltage of the lithium-ion capacitor <NUM>. Meanwhile, the power control circuit <NUM> of comparative example <NUM> has the resistor <NUM> for detecting the discharge current of the lithium-ion secondary battery <NUM>. The resistor <NUM> increases power consumption that does not contribute to load backup. Moreover, a circuit per se of the switch controller <NUM> also consumes power. Increased power consumption in the power control circuit <NUM> shortens the period for which the load can be backed up. The power control circuit <NUM> according to one or more embodiments can make the period for which the load can be backed up longer than the power control circuit <NUM> of comparative example <NUM>.

The lithium-ion capacitor <NUM> is operable in a wider temperature range than the lithium-ion secondary battery <NUM>. Therefore, if the lithium-ion capacitor <NUM> were substituted with the lithium-ion secondary battery <NUM>, a temperature range wherein the power control circuit <NUM> can operate would be narrowed. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments can make the operable temperature range wider than a configuration of being provided with the lithium-ion secondary battery <NUM>. As a result, high convenience can be realized.

The lithium-ion secondary battery <NUM> self-discharges easily due to a phenomenon wherein dendritic lithium metal is deposited therein. Meanwhile, the lithium-ion capacitor <NUM> is less likely to self-discharge. Moreover, the electric double-layer capacitor <NUM> self-discharges more easily than the lithium-ion capacitor <NUM>. Therefore, if the lithium-ion capacitor <NUM> were substituted with a lithium-ion secondary battery <NUM> or electric double-layer capacitor <NUM> of the same charge capacity, the period wherein the power control circuit <NUM> functions as a backup power source would be shortened. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments can make the period of functioning as a backup power source longer than a configuration of being provided with a lithium-ion secondary battery <NUM> or electric double-layer capacitor <NUM> of the same capacity. As a result, high convenience can be realized.

The lithium-ion secondary battery <NUM> degrades and becomes more likely to fail regardless of whether overcharging or over-discharging occurs. Meanwhile, the lithium-ion capacitor <NUM> does not degrade and become more likely to fail even if overcharging occurs. Therefore, if the lithium-ion capacitor <NUM> were substituted with the lithium-ion secondary battery <NUM>, the power control circuit <NUM> would need to be further provided with an overcharging monitoring circuit. Adding an overcharging monitoring circuit could increase a size or cost of the power control circuit <NUM>. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments does not need an overcharging monitoring circuit. As a result, a configuration can be simplified.

Over-discharge protection of the lithium-ion capacitor <NUM> is realized by the power control circuit <NUM> being provided with the first protection circuit <NUM> and the second protection circuit <NUM>. That is, the power control circuit <NUM> can avoid over-discharge by controlling the terminal voltage of the lithium-ion capacitor <NUM> to not become less than the second voltage.

If the lithium-ion capacitor <NUM> were substituted with the lithium-ion secondary battery <NUM>, a p-channel MOSFET would have an insufficient performance as the switching element <NUM> connected to the lithium-ion secondary battery <NUM>. Therefore, an n-channel MOSFET would be used. Using an n-channel MOSFET would necessitate a circuit of the lithium-ion secondary battery <NUM> to be switched on a ground side. Performing switching on the ground side could cause instability due to a state arising wherein the circuit is not grounded. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments can operate stably as a result of performing switching on a high side applied with a voltage instead of performing switching on a ground side. As a result, high convenience can be realized.

The lithium-ion capacitor <NUM> can have a longer life than the lithium-ion secondary battery <NUM>. Therefore, the power control circuit <NUM> can be configured on an assumption of not replacing the lithium-ion capacitor <NUM>. When configured on an assumption of not replacing the lithium-ion capacitor <NUM>, the power control circuit <NUM> can be configured more easily than a replaceable configuration. If the lithium-ion capacitor <NUM> were substituted with the lithium-ion secondary battery <NUM>, the power control circuit <NUM> would need to be configured so the lithium-ion secondary battery <NUM> is replaceable. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments can decrease a maintenance frequency. As a result, high convenience can be realized.

If the power control circuit <NUM> were provided with a primary battery for supplying power to the second load <NUM> as a configuration separate from the lithium-ion capacitor <NUM> that backs up the first load <NUM>, the power control circuit <NUM> would need to be provided with a circuit for connecting the primary battery to the second load <NUM>. Such a circuit could complicate the power control circuit <NUM> and be more expensive than the second protection circuit <NUM>. Moreover, after the primary battery ends discharge, the power control circuit <NUM> would become unable to function as a backup power source of the second load <NUM>. By being provided with the lithium-ion capacitor <NUM>, the power control circuit <NUM> according to one or more embodiments can be configured less expensively and operate over a longer period than a configuration of being provided with a primary battery. As a result, high convenience can be realized.

In the first protection circuit <NUM>, the voltage detection circuit <NUM> is connected to the terminal <NUM>, which is connected to the lithium-ion capacitor <NUM>, via the switching element <NUM>. That is, the voltage detection circuit <NUM> can receive supply of the discharge current from the lithium-ion capacitor <NUM> via the switching element <NUM>. The first protection circuit <NUM> places the switching element <NUM> in the off state when the terminal voltage of the lithium-ion capacitor <NUM> becomes less than the first voltage. In this situation, the discharge current of the lithium-ion capacitor <NUM> does not flow to the voltage detection circuit <NUM>. By placing the switching element <NUM> in the off state, the first protection circuit <NUM> no longer consumes power. In this situation, compared to when the voltage detection circuit <NUM> is connected to the terminal <NUM> without passing through the switching element <NUM>, the first protection circuit <NUM> no longer consumes the current of the lithium-ion capacitor <NUM>. That is, the first protection circuit <NUM> no longer needlessly consumes power after the first load <NUM> is stopped. As a result, the period wherein the lithium-ion capacitor <NUM> can supply the current to the second load <NUM> is extended.

In the second protection circuit <NUM> as well, the voltage detection circuit <NUM> is connected to the terminal <NUM>, which is connected to the lithium-ion capacitor <NUM>, via the switching element <NUM>. This causes the second protection circuit <NUM> to no longer consume the current of the lithium-ion capacitor <NUM> after the terminal voltage of the lithium-ion capacitor <NUM> becomes less than the second voltage. As a result, a further decrease in the terminal voltage of the lithium-ion capacitor <NUM> can be avoided. When the terminal voltage of the lithium-ion capacitor <NUM> is less than the second voltage and decreases further, the lithium-ion capacitor <NUM> becomes easily degraded. Therefore, suppressing a decrease in the terminal voltage of the lithium-ion capacitor <NUM> leads to suppressing degradation of the lithium-ion capacitor <NUM>.

As above, when the terminal voltage of the lithium-ion capacitor <NUM> becomes less than the first voltage, the switching element <NUM> enters the off state. As a result, the voltage detection circuit <NUM> no longer operates.

Here, it is supposed that the external power source <NUM> restarts power supply when the terminal voltage of the lithium-ion capacitor <NUM> is less than the first voltage and the switching element <NUM> is in the off state. It is supposed that the switching element <NUM> is a p-channel MOSFET.

When the external power supply <NUM> supplies power at a voltage no less than the first voltage, the switching element <NUM> enters the on state. In this situation, the current that heads from the external power source <NUM> to the lithium-ion capacitor <NUM> can flow in a channel of the p-channel.

When charging the lithium-ion capacitor <NUM> under CCCV (constant current, constant voltage) control, the external power source <NUM> may supply power at a voltage less than the first voltage according to the terminal voltage of the lithium-ion capacitor <NUM>. In this situation, the switching element <NUM> remains in the off state. By the switching element <NUM> (p-channel MOSFET) being in the off state, the current that heads from the external power source <NUM> to the lithium-ion capacitor <NUM> cannot flow in the channel of the p-channel MOSFET.

However, as illustrated in <FIG>, the p-channel MOSFET has a parasitic diode 16a. The parasitic diode 16a is also referred to as a body diode. The switching element <NUM> (p-channel MOSFET) is connected so that a forward direction of the parasitic diode 16a is a direction heading from the terminal <NUM> to the terminal <NUM>. The current that heads from the external power source <NUM> to the lithium-ion capacitor <NUM> can flow through the parasitic diode 16a. This enables the power control circuit <NUM> according to one or more embodiments to cause the external power source <NUM> to restart charging of the lithium-ion capacitor <NUM> without needing a special circuit for restarting charging. As a result, the power control circuit <NUM> is configured as a simple circuit.

As above, according to the power control circuit <NUM> according to one or more embodiments, the external power source <NUM> can charge the lithium-ion capacitor <NUM> regardless of whether the switching element <NUM> (p-channel MOSFET) is in the on state or the off state.

It is supposed that the lithium-ion capacitor <NUM> is substituted with the lithium-ion secondary battery <NUM>. In this situation, to restrict overcharging of the lithium-ion secondary battery <NUM>, it is necessary for no current to flow in the parasitic diode 16a. Therefore, when the lithium-ion secondary battery <NUM> is substituted in, two MOSFETs connected in series so mutual source-drain directions are reversed are adopted as the switching element <NUM>. This causes no current to flow in the parasitic diode 16a when the switching element <NUM> is in the off state, and the lithium-ion capacitor <NUM> is not charged. Therefore, it is only by being provided with the lithium-ion capacitor <NUM> that the power control circuit <NUM> according to one or more embodiments can restart charging, regardless of whether the switching element <NUM> is in the on state or the off state, when the external power source <NUM> restarts power supply. As a result, reversion at power restoration becomes easy. Moreover, restarting charging by the power control circuit <NUM> can be realized by a simple circuit.

An upper limit and the lower limit of the terminal voltage of the lithium-ion capacitor <NUM> is established according to a usage temperature of the lithium-ion capacitor <NUM>. When the lithium-ion capacitor <NUM> is used in a temperature range of T1min to T1max, the upper limit and the lower limit of the terminal voltage are respectively defined as V1max and V1min. Meanwhile, when the lithium-ion capacitor <NUM> is used in a temperature range of T2min to T2max, the upper limit and the lower limit of the terminal voltage are respectively defined as V2max and V2min. Here, it is supposed that T1max is higher than T2max. It is supposed that V1min is lower than V2min. Under these suppositions, the lower limit of the terminal voltage of the lithium-ion capacitor <NUM> differs between a situation wherein the temperature of the lithium-ion capacitor <NUM> exceeds T2max and a situation wherein this is no greater than T2max. Referring to T2max as a predetermined temperature, the lower limit of the terminal voltage is lower in a situation wherein the temperature of the lithium-ion capacitor <NUM> is no greater than the predetermined temperature compared to a situation wherein the temperature of the lithium-ion capacitor <NUM> exceeds the predetermined temperature.

As a specific example, when the lithium-ion capacitor <NUM> is used in a temperature range of -<NUM> to +<NUM>, the upper limit and the lower limit of the terminal voltage may be respectively defined as <NUM> V and <NUM> V. Meanwhile, when the lithium-ion capacitor <NUM> is used in a temperature range of -<NUM> to +<NUM>, the upper limit and the lower limit of the terminal voltage may be respectively defined as <NUM> V and <NUM> V. In this example, each variable above is represented as follows:.

As illustrated in <FIG>, the lithium-ion capacitor <NUM> may be mounted on a circuit board <NUM> together with the first load <NUM>. It is supposed that the lithium-ion capacitor <NUM> is mounted in a position that is affected by heat generation from the first load <NUM>. In this situation, the temperature of the lithium-ion capacitor <NUM> increases due to heat generation from the operations of the first load <NUM>. That is, the greater a heat generation amount of the first load <NUM>, the higher the temperature of the lithium-ion capacitor <NUM>.

When the first load <NUM> is operating, the temperature of the lithium-ion capacitor <NUM> is more likely to exceed the predetermined temperature. Meanwhile, when the first load <NUM> is stopped, the temperature of the lithium-ion capacitor <NUM> is more likely to remain no greater than the predetermined temperature.

Here, it is supposed that the predetermined temperature is <NUM>. Applying this supposition to the specific example above, when the temperature of the lithium-ion capacitor <NUM> exceeds <NUM>, the lower limit of the terminal voltage is <NUM> V. When the temperature of the lithium-ion capacitor <NUM> is no greater than <NUM>, the lower limit of the terminal voltage is <NUM> V.

It is further supposed that the first voltage is set to <NUM> V and the second voltage is set to <NUM> V. Under this supposition, when the terminal voltage of the lithium-ion capacitor <NUM> becomes less than the first voltage and the first protection circuit <NUM> blocks power supply to the first load <NUM>, the first load <NUM> stopping causes the temperature of the lithium-ion capacitor <NUM> to become more likely to remain less than the predetermined temperature. This makes it less likely for the terminal voltage of the lithium-ion capacitor <NUM> to fall below the lower limit even if power supply to the second load <NUM> continues through the second protection circuit <NUM> and the terminal voltage of the lithium-ion capacitor <NUM> decreases to the second voltage.

It can be said that the lithium-ion capacitor <NUM> is allowed to be mounted in the position that is affected by the heat generation from the first load <NUM> when the relationship between the temperature and terminal-voltage lower limit of the lithium-ion capacitor <NUM> and the first voltage and second voltage in the example above is met. The conditions to be met can be reworded as (a) and (b) below:.

By allowing the lithium-ion capacitor <NUM> to be mounted in the position that is affected by the heat generation from the first load <NUM>, restrictions relating to mounting the power control circuit <NUM> are decreased. Moreover, it becomes easy to integrate components mounted on the circuit board <NUM>. As a result, a smaller size and a decreased cost can be realized for the power control circuit <NUM>. Moreover, the lithium-ion capacitor <NUM> is utilized in a voltage range that is as wide as possible within the usage temperature range thereof. As a result, the period of being able to supply power to the second load <NUM> is extended.

It is supposed that the first load <NUM> consumes the power amount that the lithium-ion capacitor <NUM> can supply in about several dozen seconds. Here, it is supposed that the first load <NUM> is a processor. When power supply from the external power source <NUM> stops, the first load <NUM> detects the stopping of the external power source <NUM> and starts a stopping process for the first load <NUM> per se. By completing the stopping process while power is being supplied from the lithium-ion capacitor <NUM>, the first load <NUM> can perform stopping so as to be able to safely restart operations when power supply restarts. The first voltage may be set so the lithium-ion capacitor <NUM> can be made to continue to discharge until the first load <NUM> can complete the stopping process.

After the first load <NUM> stops itself, the regulator <NUM> no longer needs to supply power to the first load <NUM>. As illustrated by the dashed line in <FIG>, the first load <NUM> may be connected to the regulator <NUM> by a communication line <NUM>. The first load <NUM> may output a discharge stop signal to the regulator <NUM> via the communication line <NUM>. The regulator <NUM> may stop the operation of outputting the power discharged by the lithium-ion capacitor <NUM> to the first load <NUM> and the second load <NUM> based on the discharge stop signal from the first load <NUM>. This decreases, among power consumed by the power control circuit <NUM>, power consumed by the regulator <NUM>. Decreasing the power consumed by the power control circuit <NUM> increases the power amount that the lithium-ion capacitor <NUM> can supply to the second load <NUM>. As a result, the period of being able to supply power to the second load <NUM> is extended.

Claim 1:
A power control circuit (<NUM>) comprising:
a lithium-ion capacitor (<NUM>) configured to be charged by power supplied by an external power source (<NUM>);
a first protection circuit (<NUM>) configured to supply, to a first load (<NUM>) that is configured to operate using power supplied by the external power source (<NUM>), a first discharge current of the lithium-ion capacitor (<NUM>) when the power is no longer supplied from the external power source (<NUM>); and
a second protection circuit (<NUM>) configured to supply, to a second load (<NUM>) that is configured to operate using power supplied by the external power source (<NUM>), a second discharge current of the lithium-ion capacitor (<NUM>) when the power is no longer supplied from the external power source (<NUM>), wherein
the second load (<NUM>) is configured to operate at a lower power consumption than the first load (<NUM>) over at least a predetermined period,
the first protection circuit (<NUM>) is configured to stop supplying the first discharge current to the first load (<NUM>) when a terminal voltage of the lithium-ion capacitor (<NUM>) becomes less than a first voltage,
the second protection circuit (<NUM>) is configured to stop supplying the second discharge current to the second load (<NUM>) when the terminal voltage of the lithium-ion capacitor (<NUM>) becomes less than a second voltage that is lower than the first voltage, and
the first voltage is set so that an electrical-charge amount that is discharged as the terminal voltage of the lithium-ion capacitor (<NUM>) falls from the first voltage to the second voltage becomes no less than an electrical-charge amount necessary to back up the second load (<NUM>) over the predetermined period.