Patent Application
20080054846
One better embodiment thereinafter is provided to explain the charging control system for a lithium battery of the present invention.
In the present embodiment, before charging the lithium battery 20, the voltage detector 400 detects the existing voltage (VBAT) of the lithium battery 20 in advance and uses an analog-to-digital converter (ADC) set in the voltage detector 400 to convert the analog voltage value of VBAT to a digital voltage value, and then the voltage detector 400 sends the digital voltage value to the microprocessor 100 by the electric connection to judge the value. If the microprocessor 100 decides that the lithium battery 20 needs to be charged, the microprocessor 100 sends a control signal to the control unit 200, wherein the control unit 200 is a switch-control circuit (such as at least one transistor) or a switch to control the operation of the charging unit 300. When the control unit 200 receives the control signal from the microprocessor 100 to enable the charging unit 300 charge the lithium battery 20, the control unit 200 turns on to drive and enable the charging unit 300 to charge up the lithium battery 20, wherein the control signal is a pulse width modulation signal which comes from a firmware (not shown in
Referring to
If the detected VBAT value is between 3 volts and 4.1 volts, the charging process enters into the constant-current-charging stage (step 504) to use constant current of 0.5 C (1 C is equal to the expected charging capacity of lithium battery per hour, for example, if the expected charging capacity of lithium battery is 500 mAh, the charging current of 1 C equals to 500 mA) to charge the lithium battery with constant current, wherein a function of pulse width modulation from a firmware set in the microprocessor is used to modulate the duty cycle of the control unit (step 506), and depending on the duty cycle of the control unit, the power provided by the charging unit is modulated as the applicable constant current for charging the lithium battery. Then, if the VBAT value of the charged lithium battery is reached more than 4.1 volts in the predetermined charging protection time with constant current (90 minutes), the constant-current-charging stage is completed, and if the VBAT value of the charged lithium battery is not reached more than 4.1 volts in 90 minutes during the charging process with the constant current, it is indicated that there is something wrong in the charging process to fail the charging.
If the detected VBAT value is more than 4.1 volts, the charging process enters into the current-voltage-charging stage (step 504) to use constant voltage of 4.2 volts to charge the lithium battery with constant voltage, wherein the function of pulse width modulation from the firmware set in the microprocessor is used to modulate the duty cycle of the control unit (step 506), and depending on the duty cycle of the control unit, the power provided by the charging unit is modulated as the applicable constant voltage for charging the lithium battery and then to proceed the charging with constant voltage (step 508). At this time, the charging current comes down slowly and then if the charging current comes down to 0.1 C and the VBAT value of the charged lithium battery is reached to 4.2 volts in the predetermined charging protection time with constant voltage (90 minutes) (step 508), the constant-voltage-charging stage is completed, and if the VBAT value of the charged lithium battery is not reached more than 4.2 volts in 90 minutes during the charging process with the constant voltage, it is indicated that there is something wrong in the charging process to fail the charging.
Wherein, the charging protection times of the three charging stages (pre-charge stage, constant-current-charging stage and current-voltage-charging stage) are predetermined by the firmware in the microprocessor and the charging protection times can be adjusted according to the characteristic of the different lithium batteries and the timer is designed to stop charging to protect the lithium battery when a charging error is happened during the charging process.
To sum up, in the present embodiment, during the charging process of the lithium battery, the voltage detector detects the voltage of the lithium battery continuously to judge and select the corresponding charging way for the lithium battery (step 502, 504), and then the microprocessor enables the control unit depending on the function of pulse width modulation (step 506) to modulate the power provided by the charging unit as the applicable constant current or constant voltage to charge the lithium battery (step 508). Accordingly, the charging process is completed by repeating the steps 500, 502, 504, 506 and 508 continuously.
When charging the power module 30 of the hand-held apparatus 1, the voltage detecting unit of the charging control module 60 detects the existing voltage of the power module 30 and an analog-to-digital converter included in the voltage detecting unit is applied to convert the existing voltage from an analog voltage value to a digital voltage value. Then the voltage detecting unit sends the digital voltage value to the microprocessor to perform the judgment of the voltage signal.
If the microprocessor judges that the power module 30 necessary to be charged, the microprocessor sends a control signal to the control unit of the charging control module 60, wherein the control unit is a switch-control circuit (such as at least one transistor) or a switch to control the operation of a charger 2. When the control unit receives the control signal from the microprocessor to enable the charger 2 to charge the power module 30, the control unit turns on to drive the charger 2, wherein the control signal is a pulse width modulation signal which comes from the microprocessor to modulate the duty cycle of the control unit. Depending on the duty cycle of the control unit, the power provided by the charger 2 is modulated as the applicable current or voltage for power module 30. Further, the charger 2 includes a power input port, such as a plug or an universal serial bus (USB), to obtain the charging power. During the charging process, the voltage detecting unit detects the status and the voltage of the power module 30 simultaneously and continuously sends the voltage signal to the microprocessor to judge whether to complete the charge process or not.
When the voltage detecting unit detects that the voltage value is equal to or more than 4.2 volts, the microprocessor of the central control module 40 sends a control signal to order the control unit to control the charger 2 stop charging the power module 30. Understandably, the charging control module 60 and the central control module 40 complete the charging process of the power module 30 by detecting the voltage continuously and enabling the charger in the duty cycle. Further, the microprocessor of the central control module 40 includes a timer to protect the power module 30. If the power module 30 is not charged to the expected power in a predetermined time, it is indicated that there is something wrong in the charging process to fail the charging, and then the charging process is forced to stop.
To sum up, the charging control system for the lithium battery is provided in the embodiment of the present invention. The voltage detector is applied to detect the current voltage of the lithium battery and send the voltage to the microprocessor preset in the hand-held apparatus. The microprocessor is used to judge the applicable charging way of the lithium battery and the status of the charging battery in real time during the charging process, then the pulse width modulation signal is used to modulate the duty cycle of the control unit and the power provided by the charging unit is modulated as the applicable constant current for charging the lithium battery depending on the duty cycle of the control unit. Accordingly, the charging process is completed by repeating the voltage detection and the duty cycle modulation of the control unit.
Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.
