HK1143459B - Multiple mode battery charger - Google Patents

Description

Multi-mode battery charger

Technical Field

The present disclosure relates generally to battery chargers, and more particularly to multi-mode battery chargers.

Background

Electronic devices such as cellular telephones typically include an internal, rechargeable battery to allow portability. Selecting an appropriate battery charger generally requires a compromise between the specific advantages and disadvantages present in each type of charger. For example, a switch mode battery charger may operate efficiently and charge a battery relatively quickly, but may generate interference that causes noise during operation of the device. Linear mode battery chargers are significantly less efficient than switch mode battery chargers and thus may not be able to charge the battery quickly without overheating the charger. However, linear mode battery chargers generally do not introduce interference.

Drawings

The present disclosure may be better understood, and its numerous features and advantages made apparent to those skilled in the art by referencing the accompanying drawings, wherein:

FIG. 1 is a graph showing the state of charge of a battery charger;

FIG. 2 shows in partial block diagram and partial schematic form a battery charger suitable for charging a battery in accordance with the present invention;

FIG. 3 is a flow chart illustrating operation of the battery charger of FIG. 2; and

fig. 4 is a timing diagram illustrating the operation of the battery charger of fig. 2.

The use of the same reference symbols in different drawings indicates similar or identical items.

Detailed Description

A battery charger is disclosed that automatically selects between one of 4 operating modes. The battery charger may operate in a linear mode or in a switched mode, and may provide constant current or constant voltage regulation in either mode. The battery charger may automatically switch between the 4 operating modes based on a feedback signal indicative of the current delivered to the battery, the battery voltage, and the temperature, such as the temperature of the battery charger integrated circuit. The charging mode is also determined according to whether the battery charger receives power from a source of the power grid connection or from a Universal Serial Bus (USB) peripheral adapter.

Fig. 1 is a graph 100 showing the state of charge of a battery. The curve 100 has a horizontal axis representing time in hours and a vertical axis representing signal amplitude in amperes or volts as the case may be. Curve 100 includes a waveform 114 representing the current in amps provided to the battery by the battery charger, a waveform 116 representing the voltage in volts at the battery, and time references 110 and 112.

Curve 100 shows the situation where a substantially discharged battery is connected to the battery charger. The battery voltage is initially about 1 volt and increases as the battery is charged. The current delivered to the battery is maintained at an elevated level until the battery voltage approaches the nominal operating voltage of that particular battery. At time reference 110, the battery voltage increases to approximately 4.2 volts and the current delivered to the battery begins to decrease. The battery is not yet fully charged as indicated by the fact that the battery charger is still providing approximately 0.8 amps of current to the battery. As the battery approaches a fully charged state, the current delivered to the battery continues to decrease. At time reference 112, the battery is substantially fully charged and is charged at a rate of approximately 0.1 amps of current.

Fig. 2 shows in partial block diagram and partial schematic form a battery charger 200 suitable for charging a battery 270 in accordance with the present invention. The battery charger 200 includes a battery charger circuit 210, an inductor 240, a resistor 240, and a temperature sensor 280. Battery charger circuit 210 is an integrated circuit that includes an input terminal 211 for receiving a signal labeled "VCHRG", an input terminal 212 for receiving a signal labeled "COMP", an input terminal 213 for receiving a signal labeled "ENABLE", an output terminal 214 for providing a signal labeled "OUT", an input terminal 215 for receiving a signal labeled "CURRENT", an input terminal 216 for receiving a signal labeled "VOLTAGE", an input terminal 217 for receiving a signal labeled "TEMPERATURE", and an input terminal 218 for receiving a signal labeled "GND". The battery charger circuit 210 further includes a control and regulation circuit 230, a transistor 220, and a rectifier, which may take the form of a transistor 222 or a diode 224 implementing a synchronous rectifier. Control and regulation circuitry 230 includes regulation circuitry 232, control circuitry 234, and dual mode driver 236. The battery charger circuit 210 is further configured to charge the battery

Control circuit 234 has a first input connected to input terminal 212, a second input connected to input terminal 213, a third input, a first output, and a second output. Dual mode driver 236 has a first input connected to a first output of control circuit 234, a second input connected to a second output of control circuit 234, a third input connected to input terminal 211, a first output, and a second output. Transistor 220 has a drain connected to input terminal 211, a gate connected to a first output of dual mode driver 236, and a source connected to output terminal 214. Transistor 222 has a drain connected to output terminal 214, a gate connected to a second output of dual mode driver 236, and a source connected to ground. Diode 224 has a cathode connected to output terminal 214 and an anode connected to ground. The regulating circuit 232 has a first input connected to the input terminal 215, a second input connected to the input terminal 216, a third input connected to the input terminal 217, and an output connected to a third input of the control circuit 234.

The inductor 240 has a first terminal connected to the output terminal 214 of the battery charger circuit 210 and a second terminal connected to the input terminal 215 of the battery charger circuit 210. Resistor 250 has a first terminal connected to the second terminal of inductor 240 and a second terminal connected to input terminal 216 of battery charger circuit 210. Capacitor 260 has a first terminal connected to the second terminal of resistor 250 and a second terminal connected to ground. Battery 270 has a positive terminal connected to the second terminal of resistor 250 and a negative terminal connected to ground. The temperature sensor 280 has a first terminal connected to the input terminal 217 of the battery charger circuit 210 and a second terminal connected to ground.

The battery charger circuit 210 may operate in 4 modes: 1) switching mode with constant current regulation, 2) switching mode with constant voltage regulation, 3) linear mode with constant current regulation, 4) linear mode with constant voltage regulation. The switching mode is best suited to efficiently charge the battery at a relatively high rate. Linear modes generally produce negligible interference but are less efficient than switched modes. The control and regulation circuit 230 monitors feedback signals including the current delivered to the battery during charging, the battery voltage, and the temperature of the power consuming devices contained in the battery charger circuit 210. Furthermore, the control and regulation circuit 230 detects whether a mains-powered power supply (or another source capable of providing a relatively high current) provides the charging voltage VCHRG, or a USB peripheral adapter with relatively limited current capability provides the charging voltage VCHRG. All of this information is used by the control and regulation circuitry 230 to properly regulate between the 4 operating modes.

When the battery charger circuit 210 is operating in the linear mode, a first output of the dual mode driver circuit 236 provides a variable analog dc voltage to the gate of the transistor 220. The control and regulation circuit 230 regulates the conductivity of the transistor 220 to maintain the potential at the output terminal 214 at a desired level when the battery charger circuit 210 is operating in the constant voltage regulation mode. The control and regulation circuit 230 regulates the conductivity of the transistor 220 so that the current sourced from the output terminal 214 remains substantially constant when the battery charger circuit 210 is operating in a constant current regulation mode. When the battery charger circuit 210 is operating in the linear mode, the second output of the dual mode driver 236 is inactive and is set to ground potential and the transistor 222 remains nonconductive. When the battery charger circuit 210 operates in the linear mode, the level of the voltage at the gate of the transistor 220 determines the level of current conducted by the transistor 220. Transistor 220 thus operates in a linear mode. In the illustrated embodiment, transistor 220 is a Metal Oxide Semiconductor (MOS) field effect transistor, but in other embodiments may be a bipolar junction transistor, or another device capable of conducting current in the linear region when operating in the linear mode and switching at an appropriate frequency when operating in the switched mode.

When the battery charger circuit 210 is operating in the linear mode, the inductor 240 presents little resistance to the charging current provided at the output terminal 214. Resistor 250 is a current sense resistor. The battery charger 210 monitors the voltage between the input terminals 215 and 216 and the voltage is proportional to the current flowing through the resistor 250. Thus, the battery charger 210 obtains an indication of the current delivered to the battery 270 by monitoring the voltage across the resistor 250. The battery charger 210 monitors the voltage at the battery 270 through the input terminal 216.

When the battery charger circuit 210 operates in the switching mode, a first output of the dual mode driver 236 provides a digital Pulse Width Modulation (PWM) signal having a variable duty cycle. A second output of dual mode driver 236 provides a signal that is opposite in logic to the signal provided at the first output of dual mode driver 210. When the first output of dual mode driver 236 is at a logic high level, transistor 220 is conductive. At the same time, the second output of dual mode driver 236 is at a logic low level, which makes transistor 222 non-conductive. When the first output of dual mode driver 236 is at a logic low level, transistor 220 is non-conductive. At the same time, the second output of dual mode driver 236 is at a logic high level and makes transistor 222 conductive. When the potential at output terminal 214 drops below ground potential beyond the threshold voltage of diode 224, diode 224 becomes conductive. Transistor 222 is preferred over diode 224 in terms of preventing the signal at output terminal 214 from falling below ground when transistor 220 is suddenly turned off. In the illustrated embodiment, diode 224 is a parasitic device formed between the body and the channel of transistor 222.

The battery charger circuit 210 and the inductor 240 together implement a buck regulator when operating in the switching mode. The capacitor 260 implements a filter in conjunction with the inductor 240 to minimize high frequency interference generated by the switching regulator. Resistor 250 provides an indication of the current delivered to the battery as previously described. Control and regulation circuit 230 regulates the duty cycle of dual mode driver 236 to control the charging voltage when operating in constant voltage mode or to control the charging current when operating in constant current mode. Input terminal 212 is used to provide compensation to ensure stability of the regulation control loop during operation in any mode. For example, a reactive circuit network including capacitors, inductors, or both may be connected to terminal 212.

In another embodiment, the device shown in fig. 2 may be integrated into a battery pack that includes a battery 270. Further, transistor 220, transistor 222, inductor 240, resistor 250, capacitor 260, and temperature sensor 280 may be physically integrated as part of battery charger circuit 210, or may be discrete devices separate from control and regulation circuit 230. Although shown as a single integrated circuit, in other embodiments, the battery charger circuit 210 may be implemented as multiple integrated circuits.

Fig. 3 is a flow chart 300 illustrating the operation of the battery charger 200 of fig. 2. Flow diagram 300 begins at decision block 302 where control and regulation circuit 230 determines whether the mains connected power supply, the USB peripheral adapter, or both are providing signal VCHRG. If the mains power supply (or another alternative source capable of properly supplying current, such as an automotive battery) provides the signal VCHRG, flow proceeds to block 310 where the battery charger circuit 210 operates from mains (wall) power and is disabled if a USB input is present. Flow continues to decision block 312 where the conditioning circuit 232 determines the operating temperature of the battery charger circuit 210 using the temperature sensor 280. If the operating temperature is less than 110 deg.C, flow continues to block 320 where the adjustment circuit 232 configures the control circuit 234 to operate in the linear mode.

Flow continues to decision block 322 where the regulation circuit 232 determines the voltage at the battery 270. If the battery voltage is below the nominal voltage threshold of battery 270 (4.2 volts in this example), flow continues to block 330 where control and regulation circuit 230 operates in the linear mode using constant current regulation. Flow continues to decision block 332 where the conditioning circuit 232 monitors the temperature of the battery charging circuit 210. If the temperature is still below 110 deg.C, flow returns to decision block 322. If the temperature is no longer less than 110 deg.C, flow returns to decision block 312. Returning to decision block 322, if the voltage at battery 270 is not less than 4.2 volts, flow continues to block 340 where control and regulation circuit 230 operates in linear mode using constant voltage regulation. Flow continues to decision block 342 where the conditioning circuit 232 monitors the temperature of the battery charging circuit 210. If the temperature is still below 110 deg.C, flow returns to decision block 322. If the temperature is no longer less than 110 deg.C, flow returns to decision block 312.

Returning to decision block 312, if the operating temperature is not less than 110 ℃, the flow continues to block 350 where the adjustment circuit 232 configures the control circuit 234 to operate in the switching mode. Flow continues to decision block 352 where the conditioning circuit 232 determines the voltage at the battery 270. If the battery voltage is below 4.2 volts, flow continues to block 360 where the control and regulation circuit 230 operates in switched mode using constant current regulation. Flow continues to decision block 362 where the conditioning circuit 232 determines the current delivered to the battery 270. If the battery current is not less than 500 milliamps (mA), flow returns to decision block 352. If the battery current is less than 500mA, flow continues to decision block 364 where the control and regulation circuit 230 determines the temperature of the battery charging circuit 210. If the temperature of battery charging circuit 210 is less than 80 deg.C, flow returns to decision block 312. If the temperature of the battery charging circuit 210 is not less than 80 deg.C, flow returns to decision block 352. Thus, the control and regulation circuit 230 implements temperature hysteresis.

Returning to decision block 352, if the battery voltage is not below 4.2 volts, flow continues to block 370 where the control and regulation circuit 230 operates in switched mode using constant voltage regulation. Flow continues to decision block 372 where regulation circuit 232 determines the current delivered to battery 270. If the battery current is not less than 500mA, flow returns to decision block 352. If the battery current is less than 500mA, flow continues to decision block 374 where the control and regulation circuit 230 determines the temperature of the battery charging circuit 210. If the temperature of battery charging circuit 210 is less than 80 deg.C, flow returns to decision block 312. If the temperature of the battery charging circuit 210 is not less than 80 deg.C, flow returns to decision block 352.

Returning to decision block 302, if only the USB adapter provides signal VCHRG, flow continues to decision block 380 where control and regulation circuit 230 operates from USB power. Flow continues to decision block 382 where the control and regulation circuit 230 determines the temperature of the battery charging circuit 210. If the temperature of battery charging circuit 210 is less than 110 deg.C, flow continues to decision block 384 where regulation circuit 232 determines the voltage at battery 270. If the battery voltage is not below 4.2 volts, flow continues to block 386 and the control and regulation circuit 230 operates in the switching mode using constant voltage regulation. Flow continues to decision block 388 where the control and regulation circuit 230 determines the temperature of the battery charging circuit 210. If the temperature of battery charging circuit 210 is less than 110 deg.C, flow returns to decision block 384. If the temperature of the battery charging circuit 210 is not less than 110 deg.C, flow returns to decision block 382. Returning to decision block 384, if the battery voltage is not less than 4.2 volts, flow continues to block 391 and the control and regulation circuit 230 operates in switched mode using constant current regulation.

Returning to decision block 382, if the temperature of battery charging circuit 210 is not less than 110 ℃, flow continues to decision block 390 where regulation circuit 232 determines the voltage at battery 270. If the battery voltage is below 4.2 volts, flow continues to block 391 and the control and regulation circuit 230 operates in switched mode using constant current regulation. Flow continues to decision block 392 where regulation circuit 232 determines the voltage at battery 270. When the voltage at the battery 270 is not less than 4.2 volts, the flow returns to block 382. Returning to decision block 390, if the voltage of battery 270 is not less than 4.2 volts, flow continues to block 395 and control and regulation circuit 230 operates in switched mode using constant voltage regulation. Flow continues to decision block 396 where the control and regulation circuit 230 determines the temperature of the battery charging circuit 210. If the temperature of the battery charging circuit 210 is less than 80 deg.C, flow returns to decision block 382. If the temperature of battery charging circuit 210 is not less than 80 deg.C, flow continues to decision block 397 where regulation circuit 232 determines the voltage at battery 270. If the voltage at the battery 270 is less than 4.2 volts, flow returns to block 395. If the voltage at the battery 270 is not less than 4.2 volts, flow returns to block 382.

The preceding example illustrates one embodiment of a battery charger that monitors battery voltage, charging current, charger temperature, and power supply power to dynamically adjust the operating mode of the battery charger. Note that the control and regulation circuit 230 regulates the operating mode that is best suited for the particular product implementation, battery type, ambient temperature, and particular operating conditions. In another embodiment, the transition from the switched mode to the linear mode is based on a battery current that is a desired fraction of a current threshold that previously caused the transition to the switched mode. In yet another embodiment, the control and regulation circuitry 230 may include additional sensors. For example, conditioning circuit 232 may monitor additional temperature sensors in close proximity to battery 270 to determine the temperature of battery 270.

Fig. 4 is a timing diagram 400 illustrating the operation of the battery charger 200 of fig. 2. Timing diagram 400 has a horizontal axis representing time in seconds and a vertical axis representing current, voltage, and temperature, optionally in amps, volts, and degrees celsius. Timing diagram 400 includes waveform 410 labeled "VGATE", waveform 420 labeled "TEMPERATURE", waveform 430 labeled "CURRENT", waveform 410 represents the signal provided by dual mode driver 236 to the gate of transistor 220, waveform 420 represents the TEMPERATURE provided by TEMPERATURE sensor 280, and waveform 430 represents the CURRENT delivered to battery 270. Timing diagram 400 further includes a temperature threshold 422 representing a temperature of 110 ℃, a temperature threshold 424 representing a temperature of 80 ℃, a current threshold 432 representing a current of 500mA, and time references 450, 460, and 470.

At time reference 450, the battery charger circuit 210 operates in a linear mode using constant current regulation, such as shown at block 330 of fig. 3. Dual mode driver 236 changes VGATE420 to keep signal CURRENT substantially constant and transistor 220 therefore provides a substantially constant CURRENT to battery 270. The linear mode of operation is less efficient than the switch mode and may cause overheating of the battery charger circuit 210. At time reference 460, the TEMPERATURE of the battery charger circuit 210 increases to 110 ℃ corresponding to the TEMPERATURE threshold 422 as indicated by signal TEMPERATURE 420. This is represented by decision block 332 in fig. 3. The voltage at battery 270 is less than 4.2 volts (not shown) so the determination at decision block 352 is positive. The regulation circuit 232 responds to this high temperature condition by configuring the control and regulation circuit 230 to operate in a switching mode using constant current regulation, such as represented by block 360 of fig. 3.

When operating in the switching mode, the control and regulation circuit 230 provides the signal VGATE410 as a PWM signal having a duty cycle operable to maintain a desired constant charging current. Shortly after time reference 470, the voltage at battery 270 reaches 4.2 volts (not shown) and the charging CURRENT indicated by signal CURRENT begins to decrease. At time reference 470, signal CURRENT drops below 500mA, shown by CURRENT threshold 432, as represented by decision block 362 in fig. 3. Also, the temperature of the battery charger circuit 210 decreases below 80 ℃, as indicated by decision block 364 in fig. 3, below the temperature threshold 424. The voltage at battery 270 has reached 4.2 volts, so regulation circuit 232 configures control and regulation circuit 230 to operate in a linear mode using constant voltage regulation, as represented by decision block 340 in fig. 3. The battery charger circuit 210 continues to operate in this state until the charging current, battery voltage, or charger temperature changes, causing a mode change according to the flow chart of fig. 3.

The battery charger circuit 210 is operable to charge the battery 270 while the associated electronic device is operating. Also, the battery charger circuit 210 may provide power to the electronic device when the user removes the battery. The battery charger circuit 210 responds appropriately to fluctuating current demands by adopting the appropriate operating mode.

The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the claims. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims (10)

1. A battery charger circuit (210), comprising:

a transistor (220) having a first current electrode for receiving a charging voltage, a control electrode for receiving a first control signal, and a second current electrode for providing an output voltage;

a rectifier (222/224) having a first terminal coupled to the second current electrode of the transistor (220) and a second terminal coupled to a supply voltage terminal; and

a control and regulation circuit (230) having a first input for receiving a first feedback signal indicative of temperature, a second input for receiving a second feedback signal indicative of battery voltage, and a first output for providing said first control signal,

the control and regulation circuit (230) operates in a switching mode if the battery voltage is less than a voltage threshold, the control and regulation circuit (230) changing from the switching mode to a linear mode if the battery voltage substantially reaches the voltage threshold and if the temperature is below a first temperature threshold.

2. The battery charger circuit (210) of claim 1, wherein said control and regulation circuit further operates in a constant voltage mode if said battery voltage substantially reaches said voltage threshold.

3. The battery charger circuit (210) of claim 1, wherein the control and regulation circuit (230) selectively performs the following when the charging voltage is provided by a first type of charging source: the control and regulation circuit (230) operates in the switching mode if the battery voltage is less than the voltage threshold, and the control and regulation circuit (230) changes to the linear mode if the battery voltage substantially reaches the voltage threshold and if the temperature is below a second temperature threshold.

4. The battery charger circuit (210) of claim 3, wherein said control and regulation circuit (230) further operates in said linear mode regardless of said battery voltage if said temperature is less than said first temperature threshold when said charging voltage is provided by a second type of charging source.

5. The battery charger circuit (210) of claim 1, wherein the control and regulation circuit (230) further comprises a third input for receiving a third feedback signal indicative of current flowing into the battery, and if the battery voltage is less than the voltage threshold, the control and regulation circuit operates in a switched constant current mode using the third feedback signal.

6. A battery charger circuit (210), comprising:

a transistor (220) having a first current electrode for receiving a charging voltage, a control electrode for receiving a first control signal, and a second current electrode for providing an output voltage;

a rectifier (222/224) having a first terminal coupled to the second current electrode of the transistor (220) and a second terminal coupled to a supply voltage terminal; and

a control and regulation circuit (230) having a first input for receiving a first feedback signal indicative of temperature, a second input for receiving a second feedback signal indicative of battery voltage, and a first output for providing said first control signal,

when the battery charging source is of a first type, the control and regulation circuit (230) operates in a linear mode if the temperature is less than a first temperature threshold, otherwise the control and regulation circuit (230) operates in a switched mode; and

when the battery charging source is of a second type, the control and regulation circuit (230) operates in a switching mode if the battery voltage is less than a voltage threshold, the control and regulation circuit (230) changing from the switching mode to the linear mode if the battery voltage substantially reaches the voltage threshold and if the temperature is below the first temperature threshold.

7. A method of charging a battery comprising the steps of:

measuring the temperature;

measuring a voltage of the battery;

operating a battery charger circuit (210) in a switched mode if the voltage is less than a voltage threshold; and

the battery charger circuit (210) changes from the switching mode to a linear mode if the temperature is below a first temperature threshold and the voltage substantially reaches the voltage threshold.

8. The method of claim 7, wherein:

the step of operating the battery charger circuit (210) in the switched mode comprises: operating the battery charger circuit in a switched constant current mode if the temperature is less than the first temperature threshold; and

the method further comprises the following steps: if the temperature is not less than the first temperature threshold and the voltage is not less than the voltage threshold, operating the battery charger circuit (210) in a switched constant voltage mode.

9. The method of claim 8, wherein the step of operating the battery charger circuit (210) in the switched constant current mode comprises:

maintaining in the switched constant current mode until the voltage rises above the voltage threshold.

10. The method of claim 8, further comprising the steps of:

the operation and the change are performed if the battery charging source is of a first type and not of a second type.