A BATTERY CHARGING APPARATUS AND A METHOD THEREOF
FOR AN AUTOMOBILE
Field of the invention
[0001] The present invention relates to Automobile battery charging process.
Prior Art [0002] In automobiles, there is a battery to provide power to electrical systems. It would normally be charged while the vehicle is running from the power supplied by an alternator coupled to engine. A rectifier is provided to convert alternator's output to unidirectional current. In a rectifier-filter/charger setup, the current from the source is always spiky and during a short interval each half cycle, a high current pulse has to flow to effectively charge the battery. For this purpose, the alternators need to be over-rated than usual power demand. As a result of which, the alternator output current is discontinuous.
[0003] The block schematic shown in figure 1 depicts the conventional battery charging system in vehicles. The alternator/dynamo provides an alternating voltage (I phase system or can be 3-phase system). The rectifier converts it in to fluctuating DC voltage and a controller/ regulator controls the charging current. In this kind of circuit, current will flow from alternator only when the alternator voltage is higher than the battery terminal voltage plus the forward drop in rectifier. The simplified schematic and voltage and current waveforms shown in figure 2 elaborate this. Charging current controller/regulator may make the charging current ICh continuous, but it will be done so by having a capacitive filter, which would further increase the peak current demand from the alternator. [0004] Therefore, there is a need for a method for charging an automobile battery overcoming the disadvantages listed above. The need to overrate the alternator should be obviated and the alternator output current should be continuous and in phase with the alternator voltage.
OBJECT OF THE INVENTION [0005] An objective of the invention is to make output current continuous, sinusoidal and in phase with the alternator voltage.

[0006] Another objective of the invention is to increase alternator and battery life
by reducing its heating.
[0007] Yet another objective of the invention is to reduce the alternator over rating
and hence the size, weight and cost.
[0008] Yet another objective of the invention is to increase battery life by
increasing the controlling of the charging current.
[0009] Accordingly, the present invention provides a method for charging
automobile battery comprising a power factor correction circuit having an
inductance having a first end receiving a first voltage, a switch having one end
coupled to the second end of the inductance and the other end coupled to a low
voltage, a first diode which has an anode coupled to the second end of the
inductance L, and a capacitor.
[0010] The present invention, therefore, provides a method for charging the
automobile battery as a result of which the source current can be made sinusoidal
and continuous - reduces the harmonics radiation. The alternator over-rating and
hence the size, weight and cost can be reduced. The heating of alternator would be
reduced, increasing its life. The voltage Vo is regulated. Hence regulating charging
current is easier. Charging current to the battery is free of spikes - reduced heating
and electrolyte boiling - better battery life. As the output voltage of the PFC stage
is higher than input, a constant charging voltage can be maintained at any value of
alternator voltage, which would keep varying with engine RPM, i.e., the vehicle
speed.
BRIEF DESCRIPTION OF THE DRAWINGS [0011] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to various embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. [0012] Figure 1 depicts a conventional charging system in an automobile

[0013] Figure 2 depicts current and voltage waveforms in conventional charging
set-up of figure 1.
[0014] Figure 3 illustrates the PFC automobile battery charger working principle,
in accordance with an embodiment of the invention.
[0015] Figure 4 illustrates the voltage and current waveforms in PFC charger, in
accordance with an embodiment of the invention.
[0016] Figure 5 illustrates equivalent circuit for switch-Off duration in PFC
charger, in accordance with an embodiment of the invention.
DETAILED DESCRIPTION OF INVENTION [0017] Various embodiments of the present invention provide a method for charging automobile battery.
[0018] Figure 3A is a boost converter circuit diagram of a power factor correction circuit according to the invention. The power factor correction circuit 300 includes an inductor (7), a switch (5), a first diode (4) and a first capacitor (6). The inductor (7) has a first end and a second end. The first end is for receiving a first voltage Vin. The switch (5) has one end coupled to the second end of the inductor (7) and has the other end coupled to a low voltage, such as a ground voltage. The power control chip is for receiving the spread spectrum synchronization signal and accordingly controlling the switch (5) to be turned on/off by using a control signal in order to improve the power factor. The first diode (4) has an anode coupled to the second end of the inductor (7). The first capacitor (6) has one end coupled to a cathode of the first diode (4) for generating a second voltage Vout and has the other end coupled to the low voltage. The switch (5) is, such as, a metal oxide semiconductor field effect transistor (MOSFET) with a gate for receiving the control signal, a drain coupled to the second end of the inductor (7), and a source coupled to the low voltage.
[0019] Figure 3B shows the flow of current in the power factor correction circuit 300 when switch is closed. While the switch is closed, the current in the inductor (7) will be rising and all the input voltage appears across the inductor, storing the output energy form alternator in inductor in the form of magnetic field. It may be

apparent to a person skilled in the art that the inductor current In flows through the switch to the ground.
10020] Figure 3C shows the flow of current in the power factor correction circuit 300 when switch is open. When the switch opens, current starts falling and di/dt-the rate of current change is of opposite direction. Now the magnetic field in the inductor too starts collapsing and results in a back-emf in inductor to be induced in opposite direction to that while switch was closed. The equivalent circuit for the duration of switch's OFF state is as shown in figure 5. The induced voltage and input voltage add together to make output voltage higher. It may be apparent to a person skilled in the art that the back EMF adds to Vin boosting the output voltage. [0021] The schematic in figure 3 depicts a boost converter type of PFC circuit whose output voltage is greater than input voltage. Its functioning is as described above in detail. The switch (5) is operated at a very higher frequency compared to frequency of alternator output.
[0022] In accordance with an embodiment of the invention, the waveforms in figure 4 illustrate the relationship between voltage and currents in a PFC charger system. As shown in figure 4, the current from the alternator will be continuous, less peaky, reducing the burden of peak load on alternator. [0023] The source current can be made sinusoidal and continuous - reduces the harmonics radiation. The alternator over-rating and hence the size, weight and cost is reduced. The heating of alternator would be reduced, increasing its life. The voltage Vo is regulated. Hence regulating charging current is easier. Charging current to the battery is free of spikes - reduced heating and electrolyte boiling -better battery life. As the output voltage of the PFC stage is higher than input, a constant charging voltage can be maintained at any value of alternator voltage, which would keep varying with engine RPM, i.e., the vehicle speed. [0024] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims mat follow.

We claim:
1. An electronic apparatus for charging a battery of an automobile, the
apparatus comprising a power factor correction circuit, the power
correction circuit having:
a. an inductor, the inductor having a first end and a second end, the
first end receiving a first voltage;
b. a switch, the switch having one end coupled to the second end of
the inductor and the other end coupled to a low voltage, the switch
being operated at a very high frequency compared to frequency of
alternator output;
c. a first diode, the first diode having an anode coupled to the second
end of the inductor; and
d. a capacitor.
2. The electronic apparatus for charging a battery of an automobile according to claim 1, wherein while the switch is closed all the input voltage appears across the inductor.
3. The electronic apparatus for charging a battery of an automobile according to claim 1, wherein while the switch is open a back-emf in inductor is induced in the direction opposite to that while switch is closed.