Abstract:
A circuit charges and maintains a battery. The circuit includes a microprocessor for receiving a current sense signal and a voltage sense signal. The microprocessor generates control signals for selectively operating the circuit in a charging mode and in a maintenance mode. The circuit includes a current sense circuit for measuring the battery&#39;s current consumption and generating the current sense signal responsive to the measured current consumption. The circuit includes a voltage sense circuit for measuring the battery&#39;s voltage and generating the voltage sense signal responsive to the measured battery voltage. The circuit includes a waveform generator circuit for receiving the control signals, and operating in response thereto to apply a charging signal to the battery when in the charging mode and to deactivate the charging signal when in the maintenance mode. The charging signal has an oscillating triangular waveform superimposed on a DC bias signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. §119 (e), this application claims priority from, and hereby incorporates by reference for all purposes, U.S. Provisional Patent Application Ser. No. 60/975,714, entitled PULSE CHARGING AND REJUVENATING CIRCUIT, and filed Sep. 27, 2007, U.S. Provisional Patent Application Ser. No. 60/975,707, entitled METHOD FOR PULSE CHARGING AND REJUVENATING A BATTERY, and filed Sep. 27, 2007, and U.S. Provisional Patent Application Ser. No. 60/975,701, entitled BATTERY PULSE CHARGING AND REJUVENATING CIRCUIT, and filed Sep. 27, 2007. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to electronic circuits, and more particularly the invention relates to a battery charging circuit. 
     BACKGROUND OF THE INVENTION 
     A variety of charging circuits are available for charging and maintaining rechargeable batteries. Existing charging circuits typically apply a charging signal to a battery to replenish its charge. Examples of prior art circuitry used for generating such a charging signal may be found in the U.S. Pat. Nos. 4,871,959, 5,084,664, 5,063,341, 5,276,393, and 5,633,575 and U.S. Reissue Pat. No. RE35,643, the disclosures of which are hereby incorporated by reference. 
     For increased battery life and performance, rechargeable batteries must be protected from excessive charging voltage during recharging. Thus, the battery voltage is monitored during recharging to prevent over charging. It is known that sulphates build-up on battery plates. These sulphate deposits can damage the battery&#39;s ability to hold charge and/or be recharged. At present, charging circuits do not provide an efficient means of removal of sulphates during recharging. 
     SUMMARY 
     A circuit charges and maintains a battery. The circuit includes a microprocessor for receiving a current sense signal and a voltage sense signal. The microprocessor generates control signals for selectively operating the circuit in a charging mode and in a maintenance mode. The circuit includes a current sense circuit for measuring the battery&#39;s current consumption and generating the current sense signal responsive to the measured current consumption. The circuit includes a voltage sense circuit for measuring the battery&#39;s voltage and generating the voltage sense signal responsive to the measured battery voltage. The circuit includes a waveform generator circuit for receiving the control signals, and operating in response thereto to apply a charging signal to the battery when in the charging mode and to inhibit the charging signal when in the maintenance mode. 
     The charging signal has an oscillating triangular waveform superimposed on a DC bias signal. The oscillating triangular waveform is characterized by a relatively short linear rise time followed by a substantially long linear fall time. The microprocessor operates the circuit in the charging mode if the measured battery voltage is less than a first threshold voltage. The microprocessor operates the circuit in the maintenance mode if the measured voltage exceeds the first threshold voltage and the measured current consumption is less than a first threshold current. During the maintenance mode, the microprocessor applies the oscillating triangular waveform superimposed on the DC bias signal if the measured voltage is less than a second threshold voltage. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the features, example embodiments and possible advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which: 
         FIG. 1  is a block diagram of a battery charger in accordance with an example embodiment; 
         FIG. 2  illustrates a pulse charging circuit in accordance with one embodiment; 
         FIG. 3A  illustrates a waveform generated by the pulse charging circuit in accordance with one embodiment; 
         FIG. 3B  is a waveform generated by a prior art circuit; and 
         FIG. 4  is a flow diagram of the steps for charging a battery in accordance with one embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a block diagram of a battery charger  100  in accordance with an example embodiment. The battery charger  100  is adapted to receive an AC voltage (e.g., 85-265V AC) from an AC source such as a wall outlet  110 . AC voltage from the wall outlet  110  is filtered at a filtering section  114  to reduce line emission. The filtering section  114  may include a safety fuse for over current protection. 
     A high voltage rectification and step down section  118  is coupled to the filtering section  114 . The high voltage rectification and step down section  118  provides full-wave rectification of the AC voltage and produces a pulsating DC voltage. For example, the high voltage rectification and step down section  118  may rectify the 85-265V AC to a 120-375V pulsating DC. As will be appreciated, the full-wave rectification of a sinusoidal wave produces a pulsating DC voltage. Capacitors are used to filter or smooth out the DC voltage. 
     In one implementation, the high voltage rectification and step down section  118  converts the 120-375V DC into a regulated low voltage (e.g., 15V regulated DC). It will be appreciated that the 15 Volts DC is suitable for driving charging current into a typical 12V lead acid battery. In one implementation, a switching circuit and a step down transformer is used to convert the 120-375V DC voltage into the 15V regulated DC. 
     A microprocessor regulator section  122  and a microprocessor controller section  134  cooperatively generate a pulse control signal. It will be understood that the microprocessor regulator section  122  and the microprocessor controller section  134  may be incorporated, or merged, in a single device or they may be implemented as separate devices. The microprocessor regulator section  122  receives the 15V regulated DC and generates a 3.3V regulated DC to power and operate the microprocessor (as well as perhaps, other circuitry). The microprocessor controller section  134  monitors voltage and current of an external battery being charged through sensing circuits,  126  and  130 , and responsive to the monitored voltage and current generates the pulse control signal  137 . In one implementation, the microprocessor controller section  134  receives a current sense signal  135  from a charge current sense unit  126  and receives a voltage sense signal  136  from a voltage sense unit  130 . In one implementation, the voltage sense signal  136  may represent a composite voltage, which may be computed from the battery voltage and the charging terminal output voltage. In response to the current sense signal  135  and the voltage sense signal  136 , the microprocessor controller section  134  generates the pulse control signal  137 . A pulse charging section  138  receives the pulse control signals  137  and in response generates a battery charging waveform, which is applied to a positive and a negative terminal,  142  and  146 , of the external battery. 
     In one implementation, the pulse charging section  138  may be implemented with a pulse charging circuit comprising a pulse transformer.  FIG. 2  illustrates a pulse charging circuit  200  having a pulse transformer  234 . The pulse transformer  234  has a primary winding  235  and a secondary winding  236 . The primary winding  235  has three terminals: terminal # 1 , terminal # 4 , and terminal # 3  (center tap). A pulse source  214  (e.g., regulated 15V DC) is coupled to the center tap (terminal # 3 ) of the primary winding  234  through a limiting resistor  218 . A transistor  246  includes a collector junction  247  coupled to the terminal # 4  of the primary winding and includes an emitter junction  248  coupled to ground, thus providing a current flow path from the terminal # 4  to the ground when the transistor  246  is turned ON. A resistor network formed by resistors  238  and  242 , coupled between the terminal # 1  of the primary winding and the ground, provide another current flow path from the terminal # 1  of the primary winding to the ground. The resistors  238  and  242  are coupled to a base junction  249  of the transistor  246 . When a current flows from the terminal # 1  and through the resistors  238  and  242 , a base current is supplied to the base junction  249  to turn ON the transistor  246 . 
     As will be appreciated, when the transistor  246  is turned ON, current flows from the center tap (terminal # 3 ) through the terminal # 4  and into the ground. When the transistor  246  is turned OFF, current flows from the center tap (terminal  3 ) through the terminal  1 , the resistors  238  and  242  and into the ground. 
     As discussed before, when current flows from the terminal # 1  through the resistors  238  and  242 , the transistor  246  is turned ON, causing the transistor  246  to allow current to flow from the terminal # 4  through the transistor  246  and into the ground. Due to the conduction of current through the transistor  246 , current does not flow through the resistors  238  and  242 , thus removing the necessary base current from the base junction  249 . Consequently, the transistor  246  turns OFF, which in turn causes the current to flow again through the resistors  238  and  242 . Thus, the resistors  238  and  242  and the transistor  246  induce oscillation at the primary winding  235  of the pulse transformer  234 . 
     In one implementation, a pulse control signal  222  (which may be the pulse control signal  137  shown in  FIG. 1 ) generated by the microprocessor (shown in  FIG. 1 ) is utilized to turn OFF the oscillation in the primary winding  235 . Specifically, the pulse control signal  222  is coupled to a gate junction  231  of a transistor  230  to turn ON the transistor  230 , which in turn pulls the base junction  249  of the transistor  246  to ground. A resistor  226  couples a 3.3V source to the gate junction  231 . When the transistor  230  is turned ON, the transistor  246  turns OFF, thus halting the oscillation. 
     The oscillation in the primary winding  254  of the transformer  234  induces AC voltage at terminals  6  and  7  of the secondary winding  236 . A transistor  274  in series with a resistor  278  is coupled between the terminals  6  and  7  of the secondary winding. Thus, when the transistor  274  is turned on, current flows from the terminal  6  through and the transistor  274  to the terminal  7 . An R-C network formed by resistors  258  and  262  and a capacitor  270  is coupled to a base junction  275  of the transistor  274 . Diodes  254  and  266  couple the R-C network to the terminals  6  and  7 , respectively. The diode  266  functions as a half-bridge rectifier blocking a return path of the AC current. The diode  254  clips the oscillating signal wave at 15+ volts causing the base junction  275  of the transistor  274  to slowly conduct to ground via the R-C network formed by the resistor  262  and the capacitor  270 . A diode  282  in conjunction with the resistor  278  and the transistor  274  produces a pulse waveform at an output terminal  290 . A DC bias signal is added to the pulse waveform, and the resulting pulse waveform superimposed on the DC bias signal is applied to the external battery (not shown in  FIG. 2 ). The pulse waveform superimposed on the DC bias signal is also referred to as the battery charging signal. The battery charging signal is characterized as a triangular or sawtooth signal superimposed on a DC bias signal. As will be explained further, depending on the battery condition, the circuit  200  is either operated in a charging mode or in a maintenance mode. In the charging mode, the battery charging signal (i.e., the triangular or sawtooth signal superimposed on the DC bias signal) is applied to the battery. In the maintenance mode, the battery&#39;s settling voltage is continuously monitored. If the battery&#39;s settling voltage falls below a threshold value, the charging signal is turned ON until the battery&#39;s settling voltage reaches the threshold value. The charging signal is turned OFF or removed when the battery&#39;s settling voltage reaches the threshold value. 
     The R-C network causes a slow, tapered linear pinch off of transistor  274 &#39;s conductance so as to control the pulse shape. The diode  282  prevents the external battery from discharging through the circuit  200 . A resettable fuse  286  may be connected in series with the diode  282  for short circuit protection. In one implementation, the pulse control signal  137  (shown in  FIG. 1 ) is used to control a switch  202  to remove the DC bias signal from the output terminal  290 . A diode  293  connected in series with the switch  292  prevents the battery from discharging through the switch  292 . It will be understood that the DC bias signal may be selectively removed from the output terminal  292  using a variety of other circuitry. 
       FIG. 3A  illustrates a waveform  300  generated by the pulse charging circuit  200 . As discussed above, the slow, tapered linear pinch off of the transistor  274 &#39;s conduction results in a triangular or sawtooth waveform. The triangular or sawtooth waveform  300  is superimposed on a DC bias signal  308 , and the resulting battery charging waveform is a triangular or sawtooth waveform superimposed on a DC bias signal. The battery charging waveform is also referred to herein as a pulse modulated waveform or a pulse modulated signal. The triangular or sawtooth waveform  300  is characterized by a relatively short linear rise time  302  (e.g., 412 million V/sec) followed by a substantially long linear fall time  304  (e.g., 40 million V/sec). It will be understood that the pulse charging circuit  200  can be modified to generate the triangular waveform having other rise time and fall time values. In one implementation, the ratio of the rise time to fall time is approximately 1:10, thus resulting in a relatively short rise time and a substantially long fall time. The waveform  300  has a frequency between 30-50 KHz. The short linear rise time  302  and a substantially long linear fall time  304  of the triangular or sawtooth waveform  300  provides a larger area under the curve, which enables the waveform  300  to possess increased charging and desulphating capability. The short linear rise time  302  and the relatively long linear fall time  304  of the triangular or sawtooth waveform  300  provide increased desulphating voltage and current to the external battery being charged. It will be appreciated, the increased desulphating voltage and current removes sulphates from the lead plates of the battery, thus improving battery condition. 
     In one implementation, the pulse charging circuit  200  is operated in a charging mode and a maintenance mode. During the charging mode (when the pulse control signal  222  is active and the DC bias signal is active), the triangular or sawtooth waveform  300  is superimposed on the positive DC bias signal (e.g., 15V DC)  308 . As discussed before, the triangular or sawtooth waveform  300  provides increased desulphating voltage and current to the battery. As will be appreciated, during the charging mode, the base line of the waveform is the DC bias voltage. 
     During the maintenance mode, the charging signal (i.e., the triangular or sawtooth waveform superimposed on the DC bias signal) is deactivated or removed and the battery&#39;s settling voltage is continuously monitored. If the battery&#39;s settling voltage falls below a threshold value, the charging signal is turned ON until the battery&#39;s settling voltage reaches the threshold value. The charging signal is turned OFF or removed when the battery&#39;s settling voltage exceeds the threshold value. 
     In one implementation, a microprocessor generates the control signal  137  to selectively operate the pulse charging circuit  200  in the charging mode and the maintenance mode. The charging algorithm may be stored in a memory which is either within the microprocessor or provided as a separate component connected to the microprocessor. For example, the pulse control signal  222  (also the signals  137 ) may be generated by the microprocessor. 
       FIG. 3B  is a waveform  320  generated by a pre-existing circuit. The waveform  320  has a frequency of approximately 8 KHZ and exhibits a logarithmic fall time  322 , resulting in a comparatively smaller area under the curve than the area under the curve of the triangular or sawtooth waveform  300 . 
       FIG. 4  is a flow diagram of the steps for charging a battery in accordance with one embodiment. The flow starts in step  404  in which an external battery is connected to a charger circuit in accordance with the embodiments discussed above. In step  408 , the battery is tested or analyzed to determine if the battery is defective. If the battery is found to be defective, the battery is disconnected in step  412  and the flow returns to step  404 . If the battery is found not to be defective, the flow moves to step  416  in which the charger circuit is operated in a charging mode. 
     As discussed before, depending on the charge level of the battery and in response to the pulse control signal  222 , the charger is operated in a charging mode or in a maintenance mode. During the charging mode, a positive DC charging voltage (e.g., 15V DC) is added to a triangular or sawtooth waveform, and the resulting signal is applied to the battery. The signal is characterized by the triangular or sawtooth waveform superimposed on the DC bias signal. The triangular or sawtooth waveform desulphates the battery by removing sulphate buildup on the lead plates. 
     In step  420 , real time data related to the battery voltage and current is acquired. In one implementation, voltage and current values are stored in a memory coupled to the microprocessor. In step  424 , LED indicator settings are determined based on the acquired data, and LED indicators are set to indicate the battery&#39;s status. For example, the LED indicators may indicate that the charging circuit is in a charging mode or in a maintenance mode. 
     In step  428 , a comparison is made whether the battery voltage is less than a first threshold voltage (e.g., 14.2V DC). In one implementation, a composite value of the voltage reading of the battery and the charger is used to estimate the voltage. If the composite value of the voltage reading is less than 14.2V DC, the flow returns to step  420 . If the composite value of the voltage reading is equal or greater than 14.2V DC, the flow moves to step  432  wherein a determination is made regarding the current consumption of the battery. The current consumption of the battery can be determined from the data acquired in step  420 . Referring back to step  432 , if the current consumption is greater than a first threshold current (e.g., 0.75 Amp), the flow returns to step  420 . Thus, it will be appreciated that if the battery is drawing more than 0.75 Amp, the battery is considered not fully charged by the pulse charging circuit (although the battery voltage satisfies the first threshold) and the flow returns to step  420 . 
     If the current consumption is less than or equal to 0.75 Amp (along with the high battery voltage), the battery is considered fully charged, and the flow moves to step  436 , wherein the charger circuit is switched to the maintenance mode. In step  440 , the triangular waveform superimposed on the DC bias signal is deactivated or turned OFF. In step  444 , the battery&#39;s settling voltage is compared to a second threshold voltage. If the battery&#39;s settling voltage falls below a second threshold voltage (e.g., 13.6V DC), the flow moves to step  448  wherein the triangular waveform superimposed on the DC bias signal is applied to the battery and the flow subsequently returns to step  444 . If the battery&#39;s settling voltage level remains equal to or above 13.6V DC, the flow returns to step  440 . 
     While the charging method and operation is described in connection with lead acid batteries, it will be understood that the charging method and operation disclosed herein may also be used in connection with other battery types. 
     It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. It is also within the spirit and scope of the present invention to implement a program or code that can be stored in a machine-readable medium to permit a computer to perform any of the methods described above. 
     As used in the description herein and throughout the claims that follow, “a”, “an”, and “the” includes plural references unless the context clearly dictates otherwise. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. 
     The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention. 
     Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation or material to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims and/or to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. Thus, the scope of the invention is to be determined solely by the appended claims.