Patent Description:
Many electronic devices, such as mobile phones and watches, include a battery. The batteries occasionally need to be recharged. In many cases, this can be accomplished by connecting the electronic device to a power outlet via charging cord. However, in some cases batteries can be charged wirelessly via inductive charging. The electronic device is placed adjacently to a wireless charging device that emits a charging field. Energy harvesting circuitry within the electronic device harvests energy from the charging field.

The energy harvesting circuitry may include a rectifier that converts an AC voltage to a DC charging current. In some scenarios the rectifier may not function properly and may generate excess amounts of heat. These excess amounts of heat can result in the temperature of the electronic device increasing to undesired levels.

More specifically, the invention relates to a device according to the preamble of claim <NUM>, which is known, for instance, from <CIT>. A somewhat similar solution is known from <CIT>. Also document <CIT> is of some interest for the invention.

Embodiments of the present disclosure comprise:.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS.

In the following description, certain specific details are set forth in order to provide a thorough understanding of various disclosed embodiments. However, one skilled in the relevant art will recognize that embodiments may be practiced without one or more of these specific details, or with other methods, components, materials, etc..

Unless the context requires otherwise, throughout the specification and claims which follow, the word "comprise" and variations thereof, such as, "comprises" and "comprising" are to be construed in an open, inclusive sense, that is as "including, but not limited to. " Further, the terms "first," "second," and similar indicators of sequence are to be construed as interchangeable unless the context clearly dictates otherwise.

As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. It should also be noted that the term "or" is generally employed in its broadest sense, that is as meaning "and/or" unless the content clearly dictates otherwise.

<FIG> is a block diagram of an electronic device <NUM>, in accordance with one embodiment. The electronic device <NUM> includes a load <NUM>, a rectifier <NUM>, a current sensor <NUM>, and a rectifier controller <NUM>. As will be set forth in more detail below, the components of the electronic device <NUM> cooperate to provide a DC current to the load <NUM> while promoting low power dissipation and temperature changes.

The load <NUM> may include a battery. In this case, the DC current may be a DC charging current for charging the battery. Alternatively, the load may include another type of device or circuit. In one embodiment, the load <NUM> is positioned between the rectifier <NUM> and a battery.

The electronic device <NUM> can include a mobile phone, a smartwatch, wireless headphones, smart glasses, a tablet, a laptop, or other types of electronic devices. The electronic device may be configured for wireless charging of the battery. In a wireless charging situation, the electronic device <NUM> is placed on a wireless charging device such that inductive circuitry of the electronic device <NUM> is inductively coupled to charging circuitry of the wireless charging device. The wireless charging device outputs a charging field. The electronic device <NUM> generates an AC voltage VAC from the charging field. While examples herein may refer to a situation in which the electronic device generates an AC voltage from a wireless charging device, principles of the present disclosure <NUM> extend to AC voltages generated by wired connections or in other ways.

The electronic device <NUM> includes a rectifier <NUM>. The rectifier <NUM> receives the AC voltage VAC and outputs a charging current I to the load <NUM>. In practice, the rectifier <NUM> generates a DC voltage by rectifying the AC voltage VAC. The load <NUM> draws the DC charging current I from the DC voltage generated by the rectifier <NUM>. Further details regarding the rectifier <NUM> and the charging current I will be set forth further below.

The load <NUM> may include control circuitry that limits the magnitude of the I current drawn by the load <NUM>. One reason for this can be to limit the amount of heat generated by charging a battery, in examples in which the load <NUM> is a battery or includes a battery. If too much heat is generated from charging the battery <NUM>, the temperature of the electronic device <NUM> may become very high. If the temperature of the electronic device <NUM> becomes very high, then the electronic device <NUM> may become damaged or may not function properly. Additionally, a user of the electronic device <NUM> could endure discomfort if the temperature of the electronic device becomes very high.

In one embodiment in which the load <NUM> includes a battery, the magnitude of the charging current I is based on the current total charge of the battery. When the battery holds a very low charge, i.e. is depleted, then the battery may allow a relatively high DC charging current I. As the charge of the battery <NUM> increases, the battery may gradually decrease the magnitude of the charging current. Accordingly, as the battery approaches a fully charged state, the magnitude of the DC charging current I may become significantly reduced. While this may be beneficial in protecting the battery or the electronic device <NUM>, other difficulties may arise with the function of the rectifier <NUM> as the DC charging current I is decreased.

In one embodiment, the rectifier <NUM> operates as a synchronous rectifier. The rectifier <NUM> may include multiple switches <NUM> coupled between nodes of the AC voltage VAC and configured to rectify the AC voltage. The switches <NUM> are selectively enabled and disabled as the nodes of the AC voltage fluctuate in the periodic manner of a sinusoid or another form of AC voltage. The rectifier <NUM> may also include a plurality of diodes each coupled in parallel with one of the switches <NUM>.

It is possible that as the charging current I reduces, the voltage drop across one or more of the switches <NUM> may reduce to the point that the switch <NUM> no longer turns on when the rectifier <NUM> tries to turn on the switch <NUM> in the process of synchronous rectification. If this happens, then a substantial portion of the charging current may flow through the corresponding diode of the rectifier <NUM>. When the charging current flows through the diode, the voltage drop across the diode may be significantly higher than the desired voltage drop across the switch <NUM>. This can result in a very large amount of power dissipation across the diode. The large amount of power dissipation across the diode can cause a large increase in temperature of the electronic device <NUM>.

The electronic device <NUM> overcomes these potential problems by utilizing the current sensor <NUM>, the rectifier controller <NUM>, and by including at least one variable switch among the switches <NUM>. The variable switch <NUM> may have a variable resistance that can be selectively increased or decreased to ensure a desired voltage drop across the variable switch <NUM> as the DC charging current I changes.

The current sensor <NUM> is coupled between the rectifier <NUM> and the battery <NUM>. The current sensor <NUM> senses the magnitude of the DC charging current I. The current sensor <NUM> generates a sensor signal IS. The sensor signal IS is indicative of the magnitude of the DC charging current I. The current sensor <NUM> passes the sensor signal IS to the rectifier controller <NUM>.

The rectifier controller <NUM> is coupled to the current sensor <NUM> and receives the sensor signal IS from the current sensor <NUM>. The rectifier controller <NUM> is also coupled to the rectifier <NUM>. More particularly, the rectifier controller <NUM> is coupled to the variable switch of the switches <NUM> of the rectifier <NUM>. The rectifier controller <NUM> adjusts the resistance of the switch <NUM> based on the magnitude of the DC charging current I.

In one embodiment, as the magnitude of the charging current I decreases, the rectifier controller <NUM> increases the magnitude of the resistance of the variable switch of the switches <NUM>. Because the voltage drop across the variable switch is based on Ohm's law V = I*R, increasing the resistance of the variable switch can increase the voltage drop across the variable switch. This can ensure that the variable switch will turn on when desired.

In one embodiment, the switches <NUM> are transistors. The voltage drop across the switches <NUM> corresponds to the voltage drop between the drain and source terminals of the transistors. The voltage VS at the source terminal of the transistor is equal to VD-I*R, where VD is the voltage at the drain terminal, R is the resistance of the transistor, and I is a current flowing between the drain and source of the transistor. The transistor turns on when the VG-VS (VGS) is greater than the threshold voltage VTH of the transistor. However, if the voltage drop from the drain terminal to the source terminal was low, then VS will not be sufficiently low to turn on the transistor. This will result in much of the current flowing through the diode, as described above.

In one embodiment, the variable switch includes a plurality of transistors coupled in parallel. The parallel coupling means that the drain terminals of each of the transistors are connected together and that the source terminals of each of the transistors are connected together. The resistance of the switch is adjusted by selectively controlling the number of transistors whose gate terminals can receive a gate turn-on voltage. The rectifier controller <NUM> determines which of the parallel transistors will receive the gate turn-on voltage. When more transistors receive the gate turn-on voltage, the resistance of the switch is reduced. When fewer of the transistors receive the gate turn-on voltage, the resistance of the switch is increased. Accordingly, the rectifier controller <NUM> can control the resistance of the switch by controlling the number of parallel transistors that receive the gate turn-on voltage. This may also correspond to controlling the size of the switch by controlling the number of transistors that are enabled at any given time.

In one example, battery may initially be substantially depleted. The electronic device <NUM> is placed in close proximity to a wireless charging device. The electronic device <NUM> generates the AC voltage VAC from the wireless charging device via inductive coupling. The battery initially draws a relatively high DC charging current I. Because the DC charging current I is high, the rectifier controller <NUM> reduces the resistance of a variable switch by enabling all of the parallel transistors of the switch. As the level of charge of the battery gradually increases, the battery draws a smaller DC charging current I. The current sensor <NUM> senses the reduced charging current I and provides the sensor signal IS to the rectifier controller <NUM>. The rectifier controller disables one or more of the transistors of the variable switch, thereby effectively increasing the resistance of the switch in ensuring that the switch can continue to be turned on and off reliably. As the battery nears a full charge, the DC charging current I may be very small. The rectifier controller may only enable a single transistor of the variable switch, thereby increasing the resistance of the switch to the maximum in ensuring that the switch can turn on and off properly even at the low value of the DC charging current I.

<FIG> is a schematic diagram of a rectifier <NUM>, in accordance with one embodiment. The rectifier <NUM> of <FIG> is one example of the rectifier <NUM> of <FIG>. The rectifier <NUM> includes a first input node that receives a first AC input voltage VAC1. The rectifier <NUM> includes a second input node that receives a second AC input voltage VAC2. VAC2- VAC1 corresponds to the AC voltage VAC. The rectifier <NUM> generates a rectified DC voltage VRECT and outputs a DC charging current I.

The rectifier <NUM> includes a first transistor T<NUM>, the second transistor T<NUM>, a third transistor T<NUM>, and a fourth transistor T<NUM>. The drain terminal of the transistor T<NUM> is connected to the first input node and receives the voltage VAC1. The source terminal of the transistor T<NUM> is coupled to the output node of the rectifier <NUM>. The output node applies the rectified voltage VRECT and the DC charging current I. The drain terminal of the transistor T<NUM> is coupled to the second input node and receives the input voltage VAC2. The source terminal of the transistor T<NUM> is coupled to the output terminal of the rectifier <NUM>.

The drain terminal of the transistor T<NUM> is coupled to the second input terminal and receives the second input voltage VAC2. The source terminal of the transistor T<NUM> is coupled to ground. The drain terminal of the transistor T<NUM> is coupled to the first input terminal and receives the voltage VAC1. The source terminal of the transistor T<NUM> is coupled to ground.

The rectifier <NUM> includes four diodes D<NUM>-D<NUM>. Each diode is coupled in parallel with a respective one of the transistors T<NUM>-T<NUM>. The anode of the diode D<NUM> is coupled to VAC1. The cathode of the diode D1 is coupled to the output terminal of the rectifier <NUM>. The anode of the diode D<NUM> is connected to VAC2. The cathode of the diode D<NUM> is connected to the output terminal of the rectifier <NUM>. The anode of the diode D<NUM> is coupled to ground. The anode of the diode D<NUM> is coupled to ground. The cathode of the diode D<NUM> is coupled to VAC1.

The rectifier <NUM> includes a comparator <NUM>. The output terminal of the comparator <NUM> is coupled to the gate terminal of the transistor T<NUM>. The inverting input of the comparator <NUM> is coupled to VAC2. The noninverting input of the comparator <NUM> is coupled to ground.

The rectifier <NUM> includes a comparator <NUM>. The output of the comparator <NUM> is coupled to the gate terminal of the transistor T<NUM>. The inverting input of the comparator <NUM> is coupled to VAC1. The noninverting input of the comparator <NUM> is coupled to ground.

The rectifier <NUM> includes a level shifter <NUM>. The level shifter <NUM> is coupled between the gate terminal of the transistor T<NUM> and the output of the comparator <NUM>. When the output of the comparator <NUM> is low, the level shifter <NUM> supplies a low-voltage to the gate terminal of the transistor T<NUM>. When the output of the comparator <NUM> is high, the level shifter <NUM> boosts the high voltage of the comparator <NUM> to an even higher boosted voltage value. The utility of this will be described further below.

The rectifier <NUM> is a synchronous rectifier that operates in a synchronous mode. In the synchronous mode, the transistors T<NUM>-T<NUM> are turned on and off in such a manner that all current flows primarily through the transistors T<NUM>-T<NUM> rather than through the diodes D<NUM>-D<NUM>. The transistors T<NUM> and T<NUM> are controlled by the comparator <NUM>. When the output of the comparator <NUM> is low, the transistor T<NUM> is turned off. When the output of the comparator <NUM> is high, the transistor T<NUM> is turned on. The transistors T<NUM> and T<NUM> are controlled by the output of the comparator <NUM>. When the output of the comparator <NUM> is low, the transistors T<NUM> and T<NUM> are turned off. When the output of the comparator <NUM> is high, the transistors T<NUM> and T<NUM> are turned on.

Further description of the operation of the rectifier <NUM> will be made with reference to <FIG> includes graphs illustrating the values of signals associated with the rectifier <NUM> of <FIG>, in accordance with one embodiment. The graph <NUM> illustrates the voltages VAC1 and VAC2. As can be seen in <FIG>, VAC1 and VAC2 alternate between high and low values. In practice, the AC voltages VAC1 and VAC2 may have other forms than shown in the graph <NUM>. For example, VAC1 and VAC2 may be substantially sinusoidal in one embodiment. The graph <NUM> also illustrates the rectified voltage VRECT. While the graph <NUM> illustrates the rectified voltage VRECT having approximately the same value as the positive amplitudes of VAC1 and VAC2, in practice, VRECT may be slightly lower than the positive amplitudes of VAC1 and VAC2.

The graph <NUM> illustrates the output voltage V<NUM> of the comparator <NUM>. The output voltage V<NUM> of the comparator <NUM> is high when VAC1 is greater than the rectified voltage VRECT and VAC2 is less than <NUM> V. Otherwise, the output voltage V<NUM> of the comparator <NUM> is low. Accordingly, the transistors T<NUM> and T<NUM> are on when VAC1 is greater than the rectified voltage VRECT and VAC2 is less than <NUM> V, otherwise the transistors T<NUM> and T<NUM> are off.

The graph <NUM> illustrates the output voltage V<NUM> of the comparator <NUM>. The output voltage V<NUM> of the comparator <NUM> is high when VAC2 is greater than the rectified voltage VRECT and VAC1 is less than <NUM> V. Otherwise, the output voltage V<NUM> of the comparator <NUM> is low. Accordingly, the transistors T<NUM> and T<NUM> are on when VAC2 is greater than the rectified voltage VRECT and VAC1 is less than <NUM> V, otherwise the transistors T<NUM> and T<NUM> are off.

Returning to <FIG>, as described in relation to <FIG>, the current level charge of the battery <NUM> determines the magnitude of the charging current I. When the battery <NUM> is at a low level of charge, the charging current I may be relatively high. When the battery <NUM> approaches full charge, the charging current I may be relatively low. The voltage drop between the source and drain terminals of the transistors T<NUM>-T<NUM> is based on the magnitude of the current flowing through the transistors T<NUM>-T<NUM> and the on-resistances of the transistors T<NUM>-T<NUM>. The currents flowing through the transistors T<NUM>-T<NUM>.

As described previously in relation to <FIG>, if the charging current I flowing through the transistors T<NUM>-T<NUM> is very small, such as when the battery <NUM> is approaching full charge, the voltage drops across the transistors T<NUM> and T<NUM> may not be sufficiently large to ensure a high enough gate to source voltage VGS to ensure that the transistors T<NUM> and T<NUM> turn on, even when the outputs of the comparators <NUM> and <NUM> go high.

To address this issue, the rectifier <NUM> utilizes variable resistance transistors for the transistors T<NUM> and T<NUM>. As the charging current I decreases, the rectifier controller <NUM> increases the resistance of the transistors T<NUM> and T<NUM> to provide a sufficiently large voltage drop between the drain and source terminals to ensure that the source voltages will be low enough that the transistors T<NUM> and T<NUM> will turn on when the comparators <NUM> and <NUM> go high.

The rectifier controller <NUM> controls the resistances of the transistors T<NUM> and T<NUM> to be relatively low when the charging current I is relatively large. This can help avoid unduly large power dissipations at the transistors T<NUM> and T<NUM> when the charging current I is high. Further details regarding the variable transistors T<NUM> and T<NUM> are provided in relation to <FIG>.

In one embodiment, the transistors T<NUM> and T<NUM> are not variable resistance transistors. Instead, the level shifters <NUM> ensures that the transistor T<NUM> will turn on when the output of the comparator <NUM> is high, even if there is a small charging current I and a correspondingly low voltage drop across the transistor T<NUM>. The level shifter <NUM> shifts the high-voltage output from the comparator <NUM> to a high enough level to ensure that the gate to source voltage VGS of the transistor T<NUM> is sufficient to turn on the transistor T<NUM> regardless of the magnitude of the charging current I. The level shifter <NUM> shift the high-voltage output from the comparator <NUM> to a high enough level to ensure that the gate to source voltage VG a sum of the transistor T<NUM> is sufficient to turn on the transistor T<NUM> regardless of the magnitude of the charging current I.

In one embodiment, the high voltage VDD output by the comparator <NUM> is between <NUM> V and <NUM> V. The level shifter <NUM> boosts the high-voltage by a value between <NUM> V and <NUM> V. In an example in which VDD is <NUM> V and the level shifter boost the high-voltage by <NUM> V, then when the output of the comparator <NUM> goes high, the level shifter <NUM> supplies <NUM> V the gate terminal of the transistor T<NUM>. Other voltages for VDD and for the boost provided by the level shifter <NUM> can be utilized without departing from the scope of the present disclosure.

<FIG> is a schematic diagram of the variable transistor T<NUM> of <FIG>, in accordance with one embodiment. The variable transistor T<NUM> includes a plurality of transistors M<NUM>-M<NUM> coupled in parallel with each other. In particular, the drain terminals of the transistors M<NUM>-M<NUM> are all coupled to VAC2. The source terminals of the transistors M<NUM>-M<NUM> are all coupled to ground. The gate terminals of the transistors M<NUM>-M<NUM> can be selectively coupled or decouple from the output of the comparator <NUM> by operation of a respective control switches SC1-SC5.

The total resistance of the transistor T<NUM> is based on the number of the transistors M<NUM>-M<NUM> that are enabled by the rectifier controller <NUM>. The rectifier controller <NUM> can reduce the resistance of the transistor T<NUM> by enabling more of the transistors M<NUM>-M<NUM>. The rectifier controller can increase the resistance of the transistor T<NUM> by enabling fewer of the transistors M<NUM>-M<NUM>.

The rectifier controller <NUM> (see <FIG>) controls the operation of the control switches SC1-SC5 responsive to the magnitude of the charging current I as sensed by the current sensor <NUM>. The rectifier controller <NUM> enables or disables any of the transistors M<NUM>-M<NUM> by closing or opening the corresponding control switches SC1-SC5. For example, if the magnitude of the charging current I is such that the rectifier controller <NUM> determines that the transistors M<NUM> and M<NUM> should be enabled while the transistors M<NUM>-M<NUM> should be disabled, then the rectifier controller <NUM> closes the control switches SC1 and SC2 and opens the control switches SC3-SC5. The result is that the gate terminals of the transistors M<NUM> and M<NUM> are coupled to the output of the comparator <NUM>, while the gate terminals of the transistors M<NUM>-M<NUM> are disconnected from the output of the comparator <NUM>.

In one embodiment, each of the transistors M<NUM>-M<NUM> have a same on-resistance. Accordingly, each of the transistors M<NUM>-M<NUM> may have a same size. The size of the transistors M<NUM>-M<NUM> corresponds to the width the length ratio W/L of the channel regions of the transistors M<NUM>-M<NUM>. If each of the transistors of the same with the length ratio W/L in the same general structures and doping profiles, then each of the transistors M<NUM>-M<NUM> will have substantially the same on-resistance.

In one embodiment, the transistors M<NUM>-M<NUM> on-resistances. This may mean that the transistors M<NUM>-M<NUM> may have different widths the length ratios. The rectifier controller <NUM> can selectively enable one or more of the transistors M<NUM>-M<NUM> in order to achieve a desired on-resistance.

While <FIG> illustrates an embodiment of the variable transistor T<NUM>, the variable transistor T<NUM> may have substantially the same components as the variable transistor T<NUM>, including one or more transistors that can be selectively enabled.

While the description describes adjusting the on-resistance of the variable transistors T<NUM> and T<NUM>, as set forth above, this may correspond to adjusting the sizes of the transistors T<NUM> and T<NUM>. The sizes of the transistors T<NUM> and T<NUM> can be adjusted by selectively enabling or disabling various of the individual transistors that make up the variable transistors T<NUM> and T<NUM>.

Adjusting the size of a variable transistor may correspond to adjusting the width to length ratio of the transistor. If each of the transistors M<NUM>-M<NUM> has a same length and they are connected in parallel, then enabling or disabling transistors subsets of the transistors M<NUM>-M<NUM> does not effectively change the length of the channel of the variable transistor T<NUM>. However, enabling or disabling M<NUM>-M<NUM> does change the width of the channel of the variable transistor T<NUM>. In particular, enabling additional of the transistors M<NUM>-M<NUM> increases the width of the channel of the variable transistor T<NUM>, thereby reducing the on-resistance of the variable transistor T<NUM>. Disabling additional of the transistors M<NUM>-M<NUM> decreases the width of the channel of the variable transistor T<NUM>, thereby increasing the on-resistance of the variable transistor T<NUM>.

As described previously, if the transistors T<NUM>-T<NUM> do not turn on at the appropriate time due to reductions in the charging current I, this can result in increased amounts of heat generation and corresponding large changes in temperature. This is because currents will primarily flow through the diodes D<NUM>-D<NUM> if the transistors T<NUM>-T<NUM> do not turn on properly. This corresponds to operating the rectifier <NUM> in diode mode. Diodes typically have relatively large voltage drops and dissipate more power for a given amount of current than does the same amount of current flowing through MOSFETs.

In one example, the change in temperature ΔT in an electronic device based on current flowing through the rectifier in the synchronous operation can be approximated by the following relationship: <MAT> where R is the on-resistance of the transistors, I is the current flowing through the transistors, and θj is a package thermal resistance associated with the packaging of the rectifier <NUM>. If the current is <NUM> amp and the on-resistance is <NUM> mΩ, the voltage drop across the rectifier switch is 20mV. The comparators <NUM> and <NUM> are able to operate correctly to maintain the on and off states of the rectifier switches. If θj is <NUM>/W, then ΔT is about <NUM> in this mode.

In another example, the change in temperature ΔT in an electronic device based on current flowing through the rectifier in diode mode because the rectifier switch resistance is too low such that the comparators <NUM> and <NUM> cannot operate correctly (i.e. currents are flowing through the diodes D<NUM>-D<NUM> rather than through the transistors T<NUM>-T<NUM>) can be approximated by the following relationship: <MAT> where V is the voltage drop across the diodes D<NUM>-D<NUM>. If the current I is <NUM> amp as in the previous case, the voltage drop across the diodes is <NUM> V, and θj is <NUM>/W, then ΔT is about <NUM>°. This corresponds to a relatively large change in temperature compared to operation in the synchronous mode.

<FIG> is a graph illustrating the changes in resistance for the variable transistor T<NUM> based on changes in the charging current I. The rectifier controller adjusts the on-resistance of the variable transistor T<NUM> responsive to the magnitude of the charging current I. When the charging current is less than the value I<NUM>, the variable transistor T<NUM> has an on-resistance of R<NUM>. When the charging current I has a value greater than or equal to I<NUM> and less than I<NUM>, the on-resistance is R<NUM>. When the charging current I has a value greater than or equal to I<NUM> and less than I<NUM>, the on-resistance is R<NUM>. When the charging current I has a value greater than or equal to I<NUM> and less than I<NUM>, the on-resistance is R<NUM>. When the charging current I has a value greater than or equal to I<NUM>, the on-resistance is R<NUM>.

In one example, I<NUM> is about <NUM> mA, I<NUM> is about <NUM> mA, I<NUM> is about <NUM> mA, and I<NUM> is about <NUM> mA. In one example, R<NUM> is about <NUM>Ω, R<NUM> is about <NUM>Ω, R<NUM> is about <NUM>Ω, R<NUM> is about <NUM> ohm, and R<NUM> is about <NUM>Ω. Other values for the charging current I and the on-resistance can be utilized without departing from the scope of the present disclosure.

Referring again to <FIG>, in one embodiment, the level shifters <NUM> and <NUM> are not present. Instead, a third comparator is coupled to the gate terminal of the transistor T<NUM>. In particular, the output of the third comparator is coupled to the gate terminal of the transistor T<NUM>, the inverting input of the third comparator is coupled to VAC1, and the noninverting input of the third comparator is coupled to ground. In this case, the transistor T<NUM> is a variable transistor substantially similar to the variable transistor T<NUM>. A fourth comparator is coupled to the gate terminal of the transistor T<NUM>. The output of the fourth comparator is coupled to the gate terminal of the transistor T<NUM>, the inverting input of the fourth comparator is coupled to VAC2, and the noninverting input of the fourth comparator is coupled to ground. In this case, the transistor T<NUM> is a variable transistor substantially similar to the variable transistor T<NUM>.

<FIG> is a flow diagram of a method <NUM> for operating an integrated circuit, in accordance with one embodiment. The method <NUM> can utilize components, systems, and processes described in relation to <FIG>. At <NUM>, the method <NUM> includes receiving an AC voltage at a rectifier. At <NUM>, the method <NUM> includes rectifying the AC voltage with the rectifier. At <NUM>, the method <NUM> includes outputting a DC current with the rectifier. At <NUM>, the method <NUM> includes sensing a magnitude of the DC current. At <NUM>, the method <NUM> includes adjusting a resistance of a switch of the rectifier based on the magnitude of the DC current.

<FIG> is a flow diagram of a method <NUM> for operating an integrated circuit, in accordance with one embodiment. The method <NUM> can utilize components, systems, and processes described in relation to <FIG>. At <NUM>, the method <NUM> includes outputting a DC current with a rectifier. At <NUM>, the method <NUM> includes sensing a magnitude of the DC current. At <NUM>, the method <NUM> includes selectively enabling, responsive to the magnitude of the DC current, one or more of a plurality of parallel-coupled transistors of a switch of the rectifier.

Claim 1:
A device (<NUM>), comprising:
a rectifier (<NUM>) including a first switch (<NUM>, T3, T4) having a variable resistance;
a current sensor (<NUM>) coupled to an output of the rectifier (<NUM>); and
a rectifier controller (<NUM>) coupled to an output of the current sensor (<NUM>) and to the first switch (<NUM>, T3, T4),., wherein the rectifier (<NUM>) is configured to output a current (I), wherein the current sensor (<NUM>) is configured to sense a magnitude of the current and to output a sensor signal (Is) indicative of the magnitude of the current (I), and the rectifier controller (<NUM>) is configured to receive the sensor signal (Is) and to adjust a resistance of the first switch (<NUM>, T3, T4) responsive to sensor signal (Is),
characterized in that the rectifier controller (<NUM>) is configured to adjust the resistance of the first switch (<NUM>, T3, T4) with an inverse relationship to the magnitude of the current (I).