Patent Publication Number: US-2012043925-A1

Title: Protection circuit for battery and battery charger apparatus using the same

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a protection circuit for batteries and a battery charger apparatus using the protection circuit. 
     2. Description of the Related Art 
     In known art, a rechargeable battery protection circuit is employed to protect the rechargeable battery from overcharging, overdischarging, and so forth. However, if a fully charged rechargeable battery loses even a little of its overall charge, the rechargeable battery may be necessarily re-charged once more when connected to a charging apparatus such as an adapter. This results in unnecessary frequent charging and reduces lifetime of the rechargeable battery. 
     Therefore, a new type of protection circuit is desired to overcome the above-mentioned shortcomings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of a battery charge apparatus. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
       The FIGURE is a circuit diagram of a battery charger apparatus in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to the FIGURE, a battery charger apparatus  100  includes a charge circuit  12  and a protection circuit  13 . The charge circuit  12  receives power, such as +110V DC power, through a power input port  6 , and charges a rechargeable battery (not shown) electrically connected thereto. The protection circuit  13  enables or disables the charge circuit  12  according to the battery voltage of the rechargeable battery. In the embodiment, the battery charger apparatus  100  is a power adapter or a battery charger. 
     The protection circuit  13  includes a voltage-threshold generating unit  20 , a comparing unit  10 , a feedback unit  30 , and a reset unit  40 . The voltage-threshold generating unit  20  is configured for receiving power through the power input port  6 , and generates a threshold voltage. The comparing unit  10  is configured for comparing the threshold voltage with the battery voltage and generates a charging enable signal or a charging disable signal according to the comparison. In this way a threshold voltage can be set that prevents battery charging from occurring when there is only a minor difference between actual charge of a battery and full capacity. The feedback unit  30  is configured for feeding back the charging enable signal or the charging disable signal to the comparing unit  10 . During the charging process of the rechargeable battery, the comparing unit  10  continuously outputs the charging enable signal according to the feed back charging enable signal, or continuously outputs the charging disable signal according to the feed back charging disable signal. 
     In the embodiment, the voltage-threshold generating unit  20  includes a first resistor R 1  and a second resistor R 2  connected in series. One end of the first resistor R 1  is connected to the power input port  6  and the other end is connected the resistor R 2  to form a first node M between the first resistor R 1  and the second resistor R 2 . The second resistor R 2  is connected between the first node and the ground. One input port of the comparing unit  10  is connected to the first node. The threshold voltage is the voltage drop across the resistor R 1 . In an alternative embodiment, the voltage-threshold generating unit  20  is a rheostat. In the other alternative embodiment, the resistor R 1  or R 2  is a rheostat, or both resistor R 1  and R 2  are rheostats for providing an adjustable threshold voltage to the comparing unit  10 , for use with different types of batteries. 
     The comparing unit  10  receives the threshold voltage through a first input port  1  and the battery voltage through a second input port  2 , and then outputs the charging enable signal or the charging disable signal through an output port  4 . The charging enable signal is output to the charge circuit  12  on the condition that the amplitude of the threshold voltage is lower than that of the battery voltage; and the charging disable signal is output to the charge circuit  12  on the condition that the amplitude of the threshold voltage is equal to or higher than that of the battery voltage. In the embodiment, the output port  4  is also grounded via a resistor R 9 , the charging enable signal is a low level signal, and the charging disable signal is a high level signal. The comparing unit  10  is a hysteresis comparator that also includes a power input port  3  for receiving power and a grounding terminal  5 . 
     The charge circuit  12  is activated to charge the rechargeable battery in response to the charging enable signal, and does not charge the rechargeable battery or stops charging the rechargeable battery in response to the charging disable signal. 
     The second input port  2  of the comparing unit  10  is also grounded through a third resistor R 3  and a fourth resistor R 4  connected in series. The battery voltage is transmitted to the comparing unit  10  via a second node N between the third resistor R 3  and the fourth resistor R 4 . 
     The feedback unit  30  is connected between the second input port  2  and the output port  4 . In the embodiment, the feedback unit  30  is a resistor. A sixth resistor R 6  is connected between the power input port  3  and the output port  4 . 
     The reset unit  40  is configured for resetting the comparing unit  10  and includes an NPN type transistor Q, a seventh resistor R 7 , and an eighth resistor R 8 . The reset unit  40  resets the comparing unit  10  in response to a pulse signal through an input terminal  7 . In the embodiment, the resetting signal is a high-level pulse, which is supplied by an electronic apparatus (not shown). The base of the transistor Q is connected to the input terminal  7  through the seventh resistor R 7 , the collector is connected to the node M, and the emitter is grounded. The eighth resistor R 8  is connected between the base and the emitter of the transistor Q. 
     With such configuration, the battery voltage is input to the second input port  2  of the comparing unit  10  after the rechargeable battery voltage is connected to the apparatus  100 . The comparing unit  10  outputs the charging enable signal to the charge circuit  12  if the rechargeable battery voltage is lower than the threshold voltage. The charge unit circuit  12  charges the rechargeable battery in response to the charging enable signal. The comparing unit  10  outputs the charging disable signal to the charge circuit  12  if the rechargeable battery voltage is equal to or higher than the threshold voltage. The charge unit circuit  12  does not charge the rechargeable battery or stops charging the rechargeable battery in response to the charging disable signal. 
     When a high-level pulse is input to the reset unit  40  through the input terminal  7 , the transistor Q is turned on in response to the high-level pulse, which results in the first node M being grounded. Therefore, the first input port  1  is grounded via the first node M. The comparing unit  10  is reset to restart the apparatus  100  when the apparatus  100  goes into an endless loop. 
     It is understood that the disclosure may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.