Converter for rechargeable batteries, method and apparatus for converting the rechargeable battery voltage produced by a rechargeable battery

Abstract

A converter for a rechargeable battery (e.g., a lithium battery) is disclosed. In some embodiments, the converter includes a direct current (DC) / DC converter and a microcontroller unit (MCU). The DC / DC converter includes a switching circuit configured to generate a pulse-width modulated (PWM) voltage from the rechargeable battery voltage, the switching circuit configured to determine a variable duty cycle of the PWM voltage. The DC / DC converter also includes a filter circuit configured to convert the PWM voltage to a DC output voltage having an output voltage level determined according to the variable duty cycle of the PWM voltage. The MCU is configured to adjust the variable duty cycle of the switching circuit while the rechargeable battery is being discharged so that the output voltage level of the DC output voltage emulates the discharge voltage curve of a dry battery.

Description

[Technical Field]

[0001]

[0001] This application claims priority to U.S. patent application Ser. No. 17 / 885,502, filed Aug. 10, 2022, entitled "Converter for Rechargeable Batteries," the entire disclosure of which is incorporated herein by reference. [Background technology]

[0002]

[0002] Lithium batteries have a discharge voltage curve with a DC output voltage level that remains relatively constant from full capacity to full discharge. Once a lithium battery reaches full discharge, the DC output voltage level drops sharply to near 0 volts. While the lithium battery discharge voltage curve is advantageous in some situations because it is more power efficient, not all electrical devices are designed to operate with the lithium battery discharge voltage curve. For example, some electrical devices are designed to operate with dry batteries. Dry batteries have a discharge voltage curve in which the DC output voltage level drops as the battery is discharged from full charge to full discharge. In other words, the internal resistance of a dry battery increases from full charge to full discharge. In some situations, using a lithium battery to power an electrical device designed for dry batteries can damage the electrical device. [Brief explanation of the drawings]

[0003]

[0003] Aspects of the present disclosure are best understood from the following detailed description when read in conjunction with the accompanying drawings. It should be noted that, in accordance with standard industry practice, various features have not been drawn to scale. In fact, the dimensions of various features may be arbitrarily increased or decreased for clarity of illustration.

[0004] [Figure 1] FIG. 1 is a block diagram of a converter 100 according to some embodiments.

[0005] [Figure 2] FIG. 2 is a circuit diagram of a converter 200 according to some embodiments.

[0006] [Figure 3A] FIG. 3A is a graph of the voltage and current of one type of dry cell battery emulated by converter 200 of FIG. 2, according to some embodiments. [Figure 3B] FIG. 3B is a graph of the voltage and current of another type of dry cell battery emulated by converter 200 of FIG. 2, according to some embodiments. [Figure 3C] FIG. 3C is a graph of voltage and current for yet another type of dry cell battery emulated by converter 200 of FIG. 2, according to some embodiments.

[0007] [Figure 4] FIG. 4 is a flow diagram 400 illustrating a method for converting a lithium battery voltage produced by a lithium battery, according to some embodiments. DETAILED DESCRIPTION OF THE INVENTION

[0008]

[0008] In the following detailed description, reference is made to the accompanying drawings, which form a part of this specification, in which like reference numerals refer to like parts throughout and in which are shown by way of illustration embodiments that may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the embodiments is defined by the appended claims and their equivalents.

[0009]

[0009] Various operations may be described sequentially as multiple discrete acts or operations in a manner that is most helpful in understanding the claimed subject matter. However, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these operations may not be performed in the order presented. The operations described may be performed in a different order than in the described embodiment. In additional embodiments, various additional operations may be performed and / or the operations described may be omitted.

[0010]

[0010] The terms "approximately," "close," "approximately," "near," and "about" generally refer to being within + / - 10% of a target value. Unless otherwise specified, the use of ordinal adjectives such as "first," "second," and "third" to describe a common object is intended only to indicate that different instances of a similar object are being referred to and is not intended to imply that the objects so described must be in a given order, temporally, spatially, sequentially, or otherwise.

[0011] For purposes of this disclosure, the phrases "A and / or B" and "A or B" mean (A), (B), or (A and B). For purposes of this disclosure, the phrase "A, B, and / or C" means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B, and C).

[0012]

[0012] The description may use the phrases "in one embodiment" or "in an embodiment," each of which may refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," and the like, when used with respect to embodiments of the present disclosure, are synonymous.

[0013]

[0013] A microcontroller unit (MCU) and a DC / DC converter. The DC / DC converter is configured to generate a pulse-width modulated (PWM) voltage from a rechargeable battery voltage and then convert the PWM voltage to a DC output voltage. The output voltage level of the DC output voltage is determined by the duty cycle of the PWM voltage. The MCU adjusts the duty cycle of the PWM voltage to adjust the output voltage level of the DC output voltage. The MCU is configured to adjust the output voltage level of the DC output voltage when the rechargeable battery is discharging so that the output voltage level emulates the discharge voltage curve of a dry battery.

[0014] FIG. 1 is a block diagram of a converter 100 according to some embodiments.

[0015] Converter 100 includes a microcontroller unit (MCU) 102 and a DC / DC converter 104. Converter 100 is configured to accept a rechargeable battery voltage P+ generated by a rechargeable battery (not explicitly shown in FIG. 1 ). In some embodiments, the rechargeable battery is a lithium battery. The rechargeable battery voltage P+ is a direct current (DC) voltage. For example, a lithium battery generates a rechargeable battery voltage P+ such that the DC voltage level of the rechargeable battery voltage P+ remains relatively constant while the lithium battery is discharged from a maximum power level (e.g., fully charged) to a minimum power level (e.g., fully discharged). However, once the lithium battery reaches the minimum power level, the DC voltage level of the lithium battery voltage P+ drops sharply. While the rechargeable battery discharge voltage curve of a lithium battery is advantageous in many respects, the way the lithium battery discharge voltage varies can damage electrical equipment designed for dry batteries (e.g., alkaline batteries, carbon batteries, etc.).

[0016] Converter 100 is configured to convert rechargeable battery voltage P+ to a DC output voltage VOUT having an output voltage level that emulates the discharge voltage curve of a dry battery during discharge of the rechargeable battery. In some embodiments, the emulated dry battery discharge voltage curve is the discharge voltage curve of an alkaline battery. In some embodiments, the emulated dry battery discharge voltage curve is the discharge voltage curve of a carbon battery. In some embodiments, the emulated dry battery discharge voltage curve is the discharge voltage curve of a dry battery other than an alkaline battery or a dry battery. In some embodiments, the emulated dry battery discharge voltage curve is the discharge voltage curve of an 18650 battery.

[0017]

[0017] The DC / DC converter 104 is configured to convert the rechargeable battery voltage P+ into a DC output voltage VOUT. The MCU 102 is configured to control the DC / DC converter 104 so that the output voltage level of the DC output voltage VOUT emulates the discharge voltage curve of a dry battery. The DC / DC converter 104 includes a switching circuit 106 and a filter circuit 108. The switching circuit 106 is configured to generate a pulse width modulated (PWM) voltage SW from the rechargeable battery voltage P+. The filter circuit 108 is configured to filter high frequency components from the PWM voltage SW to generate the output voltage VOUT from the PWM voltage SW.

[0018] 1, MCU 102 is configured to generate a control signal PWM that is received by DC / DC converter 104. In this embodiment, the control signal PWM is received by switching circuit 106. Switching circuit 106 is configured to determine a variable duty cycle of PWM signal SW. Using the control signal PWM, MCU 102 adjusts the variable duty cycle of PWM voltage PW so that the output voltage level of DC output voltage VOUT emulates the discharge voltage curve of a dry battery while the rechargeable battery is being discharged.

[0019] In some embodiments, an AA alkaline battery is emulated. In some embodiments, the alkaline AA is discharged at different current levels (e.g., 100 mA, 200 mA, 300 mA, 400 mA, 500 mA, 750 mA, 1000 mA, 1200 mA, 1500 mA, 2000 mA, 2500 mA, 3000 mA, etc.) at a voltage level of 0.9V. In this manner, discharge voltage curve data is obtained. In some embodiments, an AA-sized lithium battery with a USB port is discharged at the same discharge currents listed above to obtain the lithium battery discharge voltage curve. Once the alkaline and lithium battery discharge voltage curves are obtained, the logic and / or program of the MCU 102 that converts the lithium battery discharge voltage curve to an alkaline battery discharge voltage curve is determined.

[0020] FIG. 2 is a circuit diagram of a converter 200 according to some embodiments.

[0021] Converter 200 of FIG. 2 corresponds to converter 100 of FIG. 1, according to some embodiments.

[0022] According to some embodiments, converter 200 includes an MCU 202 corresponding to MCU 102 of FIG. 1. According to some embodiments, converter 200 includes a DC / DC converter 204 corresponding to DC / DC converter 104 of FIG. 1. According to some embodiments, DC / DC converter 204 includes a switching circuit 206 corresponding to switching circuit 106 of FIG. 1. According to some embodiments, DC / DC converter 204 includes a filter circuit 208 corresponding to filter circuit 108 of FIG. 1. DC / DC converter 204 also includes a charge / discharge control unit 210 and a protection circuit 212.

[0023] 2, the MCU 202 includes MCU terminals 1-16. The control signal PWM is generated from MCU terminal 12 of the MCU 202. The MCU 202 is configured to receive a feedback signal SAM_01 from the filter circuit 208 at MCU terminal 11. The MCU 202 is configured to accept a ground voltage GND (which corresponds to the lower rail voltage VSS in this embodiment) at MCU terminal 14. The MCU 202 is configured to receive an enable signal IC1 at MCU terminal 1. The MCU 202 is configured to generate an enable signal EN at MCU terminal 16. In this embodiment, the MCU 202 is an integrated circuit (IC). In some embodiments, the MCU 202 has 8, 16, 24, 32, or 64 pins. However, the MCU 202 can have any number of pins.

[0024]

[0024] The switching circuit 206 includes switching circuit terminals 1 to 16. Switching circuit terminal 1 is configured to receive an enable signal EN from MCU terminal 16 of the MCU. Switching circuit terminal 2 corresponds to power ground PGND, and switching circuit terminal 3 corresponds to analog ground AGND. Switching circuit terminal 2 and switching circuit terminal 3 are connected to receive the ground voltage GND. Switching circuit terminal 4 is configured to receive a feedback signal FB from the filter circuit 208. Switching circuit terminal 5 is configured to receive a voltage output sense signal VOS from the filter circuit 208. Switching circuit terminal 6 is configured to receive a power good signal PG from the filter circuit 208. Switching circuit terminal 7 is configured to output a PWM voltage SW. Switching circuit terminal 8 is configured to receive a rechargeable battery voltage P+ from the rechargeable battery.

[0025]

[0025] The switching circuit 206 and the filter circuit 208 are configured such that the DC / DC converter 204 shown in FIG. 2 is a step-down DC / DC converter (e.g., a buck converter). In other embodiments, the DC / DC converter 204 is configured as a step-up converter. In still other embodiments, the DC / DC converter 204 is configured as a step-up / step-down converter. The filter circuit 208 shown in FIG. 2 has an inductor L1 connected between the switching circuit terminal 7 and a node NL. In FIG. 2, the inductance of the inductor L1 is 1 μH. In other embodiments, the inductor L1 has an inductance between 1 μH and 2.2 μH.

[0026]

[0026] Node NL outputs a DC output voltage VOUT. Node NL inputs a voltage output sense signal VOS to switching circuit terminal 5. Resistor R1 is connected between node NL and node NVD. In some embodiments, resistor R1 has a resistance of 233 kOhms. In other embodiments, resistor R4 has a different value, and changing the value of resistor R4 results in changes in the values of other components in filter circuit 208.

[0027] A resistor R4 is connected between node NVD and ground node NGND. In some embodiments, resistor R4 has a resistance of 100 kilohms. In other embodiments, resistor R4 has a different value, but changing the value of resistor R4 results in changes in the values of other components in filter circuit 208.

[0028] A feedback signal FB is received from terminal NVD at switching circuit terminal 4. Resistor R2 is connected between node NL and node NPG. In some embodiments, resistor R2 has a resistance of 400-500 kilohms. In other embodiments, resistor R2 has a different value, but changes in the value of resistor R2 result in changes in the values of other components in filter circuit 208.

[0029] A power-good signal PG is input to switching circuit terminal 6 from node NPG. A termination P1 is connected between nodes NL and NPA. A capacitor C1 is connected between node NL and ground node NGND. In some embodiments, capacitor C1 has a capacitance value between 106 and 226 μF. Capacitor C1 provides filtering and helps control self-discharge. Ground node NGND is configured to receive ground voltage GND. A resistor R6 is connected between nodes NPA and NGND. A resistor R5 is connected between nodes NPA and NPA. Resistor R5 controls the brightness of the charging indicator. In some embodiments, resistor R5 has a resistance between 7.7 and 10 kilohms. In other embodiments, resistor R2 has a different value, and changing the value of resistor R2 results in changes to the values of other components in filter circuit 208.

[0030] A capacitor C5 is connected between the node NOI and the ground node NGND. A feedback signal SAM OI is input to the MCU terminal 11 from the node NOI.

[0031] The feedback signal level of the feedback signal SAM OI indicates the output voltage level of the DC output voltage VOUT. The feedback signal level of the feedback signal FB also indicates the output voltage level of the DC output voltage VOUT. The switching circuit 206 is configured to control the switching on and off of the PWM voltage in response to the feedback signal level of the feedback signal FB from the filter circuit 208. In some embodiments, the switching circuit includes an error amplifier, and the feedback signal FB is a high-impedance input to the error amplifier. The error amplifier compares an internal reference voltage VREF with the feedback signal FB. Resistors R1 and R4 are a voltage divider that provides a set value for the output voltage. In response to the difference between the feedback voltage level of the feedback signal FB and the reference voltage VREF reaching a set value, the switching circuit 206 turns off the PWM voltage SW. In response to the difference between the feedback voltage level of the feedback signal FB and the reference voltage VREF being greater than a set value, the switching circuit 206 turns on the PWM voltage SW. In this manner, the switching circuit 206 is configured to control the switching on and the switching off of the PWM voltage SW in response to the feedback signal level of the feedback signal FB from the filter circuit 208. In this manner, the switching circuit 206 determines the duty cycle of the PWM voltage.

[0032] 2, the MCU 202 is configured to generate a PWM control signal PWM applied to the feedback signal FB to adjust the feedback signal level so that the DC output voltage VOUT emulates the discharge voltage curve of a dry battery while the rechargeable battery is being discharged. By applying the PWM control signal PWM to the feedback signal FB, the difference between the feedback voltage level of the feedback signal FB and the reference voltage VREF in the switching circuit 206 is adjusted, thereby allowing the MCU 202 to control the duty cycle of the switching signal. In this way, the MCU 202 controls the output voltage level of the DC output voltage VOUT so that the output voltage level emulates the discharge voltage curve of a dry battery. The feedback signal SAM_OI is input to the MCU 202, whereby the output voltage level is adjusted to a target DC voltage level set according to the emulated discharge output voltage curve.

[0033] To apply the PWM control signal PWM, the PWM control signal is applied through resistor R7. In some embodiments, resistor R7 has a resistance value of 10-20 kilohms. Resistor R7, along with capacitor C4, is referred to as an integrated resistor. In other embodiments, resistor R7 has a different value, but changing the value of resistor R7 results in changes in the values of other components within filter circuit 208.

[0034]

[0034] Resistor R7 is connected between MCU terminal 12 and node NFB. Capacitor C4 is connected between node NFB and ground node NGND. The capacitance C4 is 10^3p-10^4p. Capacitor C4 is charged by the PWM control signal PWM. Diode D2 is connected between node NFB and node NVB. Node NVB is connected to switching circuit terminal 4, which receives feedback signal FB. As a result, a voltage generated by charging capacitor C4 is applied to node NVD, which increases or decreases the voltage of feedback signal FB. In this way, the PWM control signal PWM adjusts feedback signal FB, thereby adjusting the duty cycle of switching signal SW.

[0035]

[0035] The MCU 202 is configured to enable the switching circuit 206. The switching circuit 206 is configured to be enabled in response to the enable signal EN being in a first state and to be disabled in response to the enable signal EN being in a second state. The charge / discharge control unit 210 is configured to detect when the rechargeable battery is being discharged and to enable the MCU 202 in response to detecting the discharge of the rechargeable battery. The MCU 202 is configured to enable the switching circuit 206 in response to being enabled by providing the enable signal EN in the first state.

[0036]

[0036] The charge / discharge control unit 210 detects undervoltage / overvoltage / overcurrent of the rechargeable battery and performs protection control. The charge / discharge control unit 210 detects whether a load is connected at the management unit terminal 4. The charge / discharge control unit 210 is configured to generate an enable signal IC1 from the management unit terminal 4 to be applied to node NCRG. The management unit terminal 4 and the MCU terminal 1 are both connected to node NCRG. When no load is connected, the charge / discharge control unit 210 generates the enable signal IC1 in a disabled state. In response, the MCU 202 generates the enable signal EN to disable the switching circuit 206. However, when a load is connected, the charge / discharge control unit 210 generates the enable signal IC1 in an enabled state. In response, the MCU 202 generates the enable signal EN to enable the switching circuit 206.

[0037]

[0037] The MCU 202 controls the duty cycle change by calculating the capacity of the rechargeable battery to simulate a dry battery. In some embodiments, the charge / discharge control unit 210 is a 4054 or 4057 linear charging IC. In some embodiments, the charge / discharge control unit 210 presets a current limit value during charging of the rechargeable battery. In one embodiment, the current limit value for charging the rechargeable battery is 300 mA. When the rechargeable battery is in a charging state, the charge / discharge control unit 210 controls the light-emitting diode (LED) D3 to illuminate red. Resistor R5 is connected between the input terminal 214 and the anode of LED D3. The cathode of LED D3 is connected to node NCRG. When the rechargeable battery is fully charged or saturated, LED D3 illuminates green. When no load is connected, the charge / discharge control unit 210 enters a low-power mode and periodically detects whether a load is connected.

[0038]

[0038] The protection circuit 212 is configured to protect the rechargeable battery during charging and discharging to prevent damage to the battery caused by overload or overcharging.

[0039] 3A-3C are graphs of voltage and current for three different types of dry cell batteries emulated by converter 200 of FIG. 2, according to some embodiments.

[0040] The horizontal axes in Figures 3A, 3B, and 3C represent time. In this example, the unit of time is minutes. The upper parts of Figures 3A, 3B, and 3C show discharge voltage curves of the output voltage VOUT when a rechargeable battery is being discharged. Therefore, the output voltage level of the output voltage VOUT is shown on the horizontal axis at the top of Figures 3A, 3B, and 3C. As shown, the voltage level continuously decreases over time as each battery is discharged. As shown at the top of Figures 3A, 3B, and 3C, the initial portion 300 of the curve decreases the output voltage level such that the speed (e.g., first derivative) increases but the acceleration (e.g., second derivative) decreases. The middle portion 302 of the curve decreases the output voltage level such that the speed (e.g., first derivative) remains constant but the acceleration (e.g., second derivative) does not increase. Therefore, the middle portion 302 is linear. The final portion 304 of the curve reduces the output voltage level such that the velocity (e.g., first derivative) increases but the acceleration (e.g., second derivative) increases, and thus the discharge voltage curve approximates an S-curve.

[0041]

[0041] The bottom of Figures 3A, 3B, and 3C show current levels for three different constant discharge currents (500 mA in Figure 3A, 1000 mA in Figure 3B, and 1500 mA in Figure 3C). According to some embodiments, higher current levels result in shorter voltage curves, while lower current levels result in longer voltage curves, as shown in Figures 3A, 3B, and 3C.

[0042]

[0042] Various discharge current curves and discharge voltage curves are used to design the MCU 202.

[0043] FIG. 4 is a flow diagram 400 illustrating a method for converting a rechargeable battery voltage generated by a rechargeable battery, according to some embodiments.

[0044]

[0044] Flow diagram 400 includes blocks 402-406. In some embodiments, blocks 402-406 are performed by converter 100 of Figure 1 or converter 200 of Figure 2. The flow begins at block 402.

[0045] In block 402, a pulse width modulated (PWM) voltage is generated from the rechargeable battery voltage. In some embodiments, the PWM voltage is the PWM voltage SW of Figures 1 and 2. In some embodiments, the PWM voltage is generated by switching circuit 106 of Figure 1 or switching circuit 206 of Figure 2. Flow then proceeds to block 404.

[0046] In block 404, the PWM voltage is converted to a direct current (DC) output voltage having an output voltage level determined according to a variable duty cycle of the PWM voltage. In some embodiments, the DC output voltage is the DC output voltage VOUT of FIGS. 1 and 2. In some embodiments, the filter circuit 108 of FIG. 1 or the filter circuit 208 of FIG. 2 converts the PWM voltage to the DC output voltage. Flow then proceeds to block 406.

[0047] In block 406, while the rechargeable battery is being discharged, the variable duty cycle is adjusted so that the output voltage level of the DC output voltage emulates the discharge voltage curve of a dry battery. In some embodiments, the variable duty cycle is adjusted by MCU 102 of FIG. 1 or MCU 202 of FIG. 2.

[0048] The foregoing outlines features of several embodiments so that those skilled in the art may better understand aspects of the present disclosure. Those skilled in the art will appreciate that they may readily use this disclosure as a basis for designing or modifying other processes and structures which carry out the same purposes and / or achieve the same advantages as the embodiments presented herein. Those skilled in the art will also appreciate that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the present disclosure.

Claims

1. 1. A converter for a rechargeable battery configured to generate a rechargeable battery voltage, the converter comprising: a direct current (DC) / DC converter; a microcontroller unit (MCU); Equipped with The DC / DC converter a switching circuit configured to generate a pulse width modulated (PWM) voltage from the rechargeable battery voltage, the switching circuit configured to define a variable duty cycle of the PWM voltage; a filter circuit configured to convert the PWM voltage to a DC output voltage having an output voltage level determined according to the variable duty cycle of the PWM voltage; Including, The MCU, and adjusting the variable duty cycle of the switching circuit while the rechargeable battery is being discharged so that the output voltage level of the DC output voltage emulates a discharge voltage curve of a dry battery.

2. 2. The converter according to claim 1, wherein the discharge voltage curve of the dry battery is the discharge voltage curve of an alkaline battery or a carbon battery.

3. the switching circuit is configured to control switching on and switching off of the PWM voltage in response to a feedback signal level of a feedback signal from the filter circuit; the MCU is configured to generate a PWM control signal applied to the feedback signal to adjust the feedback signal level so that the DC output voltage emulates the discharge voltage curve of the dry battery while the rechargeable battery is being discharged. The converter of claim 1 .

4. The converter of claim 1 , wherein the MCU is configured to enable the switching circuit.

5. a charge / discharge control unit configured to detect when the rechargeable battery is being discharged and to enable the MCU in response to detecting the discharge of the rechargeable battery, the MCU being configured to enable the switching circuit in response to being enabled; 5. The converter of claim 4.

6. 6. The converter of claim 5, wherein the charge / discharge control unit is configured to disable discharging of the rechargeable battery in response to a rechargeable battery discharge current having a current level above a threshold current limit.

7. 6. The converter of claim 5, wherein the charge / discharge control unit is configured to detect when a load is connected to receive the DC output voltage from the filter circuit.

8. The converter of claim 1 , wherein the switching circuit and the filter circuit are configured such that the DC / DC converter is a step-down DC / DC converter.

9. 2. The converter of claim 1, wherein the rechargeable battery is a lithium battery.

10. 1. A method for converting a rechargeable battery voltage produced by a rechargeable battery, comprising: generating a pulse width modulated (PWM) voltage from the rechargeable battery voltage; converting the PWM voltage to a direct current (DC) output voltage having an output voltage level determined according to a variable duty cycle of the PWM voltage; adjusting the variable duty cycle while the rechargeable battery is being discharged so that the output voltage level of the DC output voltage emulates the discharge voltage curve of a dry battery; A method comprising:

11. 11. The method of claim 10, wherein the discharge voltage curve of the dry battery is the discharge voltage curve of an alkaline battery or a carbon battery.

12. controlling the switching on and the switching off of the PWM voltage in response to a feedback signal level of a feedback signal from the filter circuit; generating a PWM control signal applied to the feedback signal to adjust the feedback signal level so that the DC output voltage emulates the discharge voltage curve of the dry battery while the rechargeable battery is being discharged; The method of claim 10 further comprising:

13. The method of claim 10 further comprising the step of enabling a switching circuit that switches the PWM voltage on and the PWM voltage off.

14. detecting when the rechargeable battery is being discharged; enabling a microcontroller unit (MCU) in response to detecting discharge of the rechargeable battery, the MCU being configured to enable the switching circuit in response to being enabled. The method of claim 13.

15. Disabling discharge of the rechargeable battery in response to a rechargeable battery discharge current having a current level exceeding a threshold current limit.

15. The method of claim 14, further comprising:

16. Detecting when a load is connected to receive the DC output voltage.

15. The method of claim 14, further comprising:

17. generating the PWM voltage from the rechargeable battery voltage by a switching circuit; generating the DC output voltage from the PWM voltage by a filter circuit; The method of claim 10, comprising:

18. 18. The method of claim 17, wherein the switching circuit and the filter circuit are configured as a step-down DC / DC converter.

19. The method of claim 10, wherein the rechargeable battery is a lithium battery.

20. 1. An apparatus comprising: a rechargeable battery configured to generate a rechargeable battery voltage; a converter configured to convert the rechargeable battery voltage to a DC output voltage having an adjustable output voltage level; a controller configured to adjust the adjustable output voltage level of the DC output voltage while the rechargeable battery is being discharged such that the adjustable output voltage level emulates a discharge voltage curve of a dry battery; An apparatus comprising:

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