Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-04-27
2002-04-09
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S284000, C323S901000
Reexamination Certificate
active
06369561
ABSTRACT:
TECHNICAL FIELD
The present invention refers to a DC-DC converter usable as a battery charger and to a method for charging a battery.
BACKGROUND OF THE INVENTION
For charging batteries, for example batteries of cell phones, the use of DC-DC converters operating as battery chargers and able to perform various charging algorithms for NiCd, NiMH and TiIon batteres is known.
FIG. 1
illustrates a known step-down DC-DC converter usable as a battery charger.
The DC-DC converter, indicated as a whole by the reference number
1
, comprises a switch
2
, for example formed of a MOS transistor, the opening and closing whereof is controlled by a driving stage
4
, and presenting a first terminal connected to a supply line
6
biased at the voltage VCC and a second terminal connected, via a diode
8
, to ground; an inductor
10
and a sense resistor
12
series-connected between the second terminal of the switch
2
and a node
14
, which is in turn connected, via a diode
16
, to a positive pole of the battery
18
to be charged, which presents its negative pole connected to ground; a capacitor
20
connected between the node
14
and ground; and a voltage divider
22
, formed of two resistors
24
,
26
, connected in parallel to the battery
18
, and presenting an intermediate node
28
on which it supplies a voltage VFB proportional, through the division ratio, to the voltage VBAT present between the poles of the battery.
The DC-DC converter
1
further comprises a filtering stage
30
, typically including an operational amplifier, presenting a first input and a second input terminals connected across the sense resistor
12
, and an output terminal supplying the filtered voltage VFR present across the sense resistor
12
; a differential current error amplifier
32
presenting an inverting terminal connected to the output terminal of the filtering stage
30
, a non-inverting terminal receiving a reference voltage VR, and an output terminal connected to an output node
34
through a decoupling diode
36
presenting the anode terminal connected to the output node
34
and the cathode terminal connected to the output terminal of the current error amplifier
32
; and a differential voltage error amplifier
42
presenting an inverting terminal connected to the intermediate node
28
of the voltage divider
22
and receiving from the latter the voltage VFB, a non-inverting terminal receiving a reference voltage VREF, and an output terminal connected directly to the output node
34
.
In particular, the battery charsing current IBAT depends upon the reference voltage VR, which is generated by causing a constant current supplied by a current generator
40
connected in series to a resistor
37
, to flow in the resistor
37
itself, the voltage present across the resistor
37
is then taken.
The current error amplifier
32
and the voltage error amplifier
42
are moreover biased through respective bias current generators
44
,
46
supplying, respectively, a bias current IP and a bias current IV, both of which arc constant.
Finally, the DC-DC converter
1
comprises a zero-pole compensation network
48
including a resistor
50
and a capacitor
52
series-connected between the output node
34
and ground; and a differential comparator
54
known as PWM (Pulse Width Modulator) comparator, presenting an inverting terminal receiving a comparison voltage VC which has a sawtooth waveform, a non-inverting terminal connected to the output node
34
, and an output terminal connected to the input of the driving stage
4
of the switch
2
, basically operating as pulse width modulator and supplying at an output a voltage having a square waveform, the duty cycle whereof is a function of the voltage present on the output node
34
itself.
The operation of the DC-DC converter
1
is known and will here be referred to solely as regards the aspects necessary for understanding the problems lying at the basis of the present invention.
In particular, during the battery charging phase, the current error amplifier
32
prevails over the voltage error amplifier
42
, and the DC-DC converter
1
operates in current regulation mode, behaving as a constant current generator.
During the current regulation phase, the battery charging current IBAT causes a voltage drop across the sense resistor
12
, and this voltage, filtered by the filtering stage
30
so as to obtain the mean value thereof, is supplied to the current error amplifier
32
, which operates to regulate this voltage so that it may assume a value equal to that of the reference voltage VR present on its own non-inverting terminal.
In parallel to the current error amplifier
32
there operates the voltage error amplifier
42
, and in particular the current error amplifier
32
prevails over the voltage error amplifier
42
as long as the voltage VFB is lower than the reference voltage VREF, i.e., as long as the differential input voltage &Dgr;V=VREF−VFB present between its input terminals is negative, thus determining the unbalancing of the voltage error amplifier
42
.
In detail, the current error amplifier
32
and the voltage error amplifier
42
are designed so that, during the current regulation phase, the diode
36
is on, and the current error amplifier
32
controls, through the comparator
54
, the duty cycle of the signal issued by the comparator
54
so as to render the voltages present on its inverting and non-inverting terminals equal.
The current error amplifier
32
performs a negative feedback. In fact, a possible variation in the battery charging current IBAT results in an unbalancing of the current error amplifier
32
, with consequent variation in the voltage of the output node
34
, and hence of the duty cycle of the output signal of the comparator
54
, which acts to restore the programmed value of the battery charging current IBAT.
During the current regulation phase, the battery
18
is thus charged with a constant current according to the value programmed via the current generator
40
and the resistor
36
, and the battery voltage VBAT increases progressively towards the full charge value.
In the vicinity of this full charge value, the battery charging current IBAT starts decreasing until it zeroes, after which the DC-DC converter
1
enters the voltage regulation phase in which the voltage error amplifier
42
prevails over the current error amplifier
32
and controls the battery voltage.
In particular, during transition from the current regulation phase to the voltage regulation phase, the voltage error amplifier
42
is balanced, the voltage of the output node
34
decreases progressively until the diode
36
is off, and the battery charging current IBAT decreases, thus unbalancing the current error amplifier
32
.
One drawback of the DC-DC converter
1
described above lies in the circuit topology which causes the evolution of its operation from the current regulation phase to the voltage regulation phase to depend to a large extent upon the transcharacteristic of the differential input stage of the voltage error amplifier, a dependence which results in the DC-DC converter
1
not being able to supply a battery charging current IBAT that is constant up until the battery full charge voltage is reached.
SUMMARY OF THE INVENTION
The disclosed embodiments of the present invention provide a DC-DC converter usable as a battery charger, which is able to supply a battery charging current that is constant up until the battery full charge voltage is reached.
A further aspect of the disclosed embodiments of the present invention is providing a method for charging a battery that makes it possible to supply to the battery a charging current that is constant up until the battery full charge voltage is reached.
In accordance with the disclosed embodiments of the invention, a DC-DC converter usable as a battery charger is provided, including a current error amplifier means and voltage error amplifier means connected in parallel to control the charging phase of a battery, and a gradual turning off means gradually turning off the cur
Marino Filippo
Pappalardo Salvatore
Pulvirenti Francesco
Berhane Adolf Deneke
Jorgenson Lisa
SEED IP Law Group PLLC
STMicroelectronics S.r.l.
Tarleton E. Russell
LandOfFree
Method and apparatus for charging a battery does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for charging a battery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for charging a battery will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2932791