Regulator circuit and control method thereof

Details Regulator circuit and control method thereof Regulator circuit and control method thereof

2002-03-21

2004-12-07

Vu, Bao Q. (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C323S274000, C320S128000, C320S140000

Reexamination Certificate

active

06828764

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a regulator circuit for adjusting an output voltage to predetermined DC voltage and maintaining thereat. More specifically, it relates to a DC regulator circuit for charging a battery which is to be connected to an output terminal and for applying predetermined DC voltage to a load.
2. Description of Related Art
MPU, LSI, IC used in various electric appliances, other semiconductor devices, drive motors such as HDD, FDD, and the like work using DC voltages of DC 5V, 3.3V and the like as their power source. Therefore, electric appliances as such need a DC/DC converter for converting a current voltage converted from AC 100V or the like via an AC adapter into a desirable current voltage value. Furthermore, as system gets further complicated, there may be some cases that various kinds of power source system may be needed and that an output voltage from a DC/DC converter is further converted by another DC/DC converter. Taking conversion voltage difference, required power source capacity and accuracy, and the like into consideration, these DC/DC converters are constituted by switching regulators or series regulators, in general.
In recent years, there have been some cases that, instead of an AC adapter, rechargeable batteries as DC power source are used for portable electric appliances such as note-type personal computers and cellular phones. In the above system, an electric appliance is connected to an AC adapter and the like for recharging operation. For controlling flow of charging current to a battery, battery voltage in a fully charged state and the like, a charging control device is provided for the portable electric appliances.
FIG. 13
shows a conventional charging control device
100
. In the charging control device
100
, switching control of a PMOS driver Tr
1
is conducted. Thereby, a coil L
1
and a capacitor C
1
smooth out DC voltage outputted from an AC adapter
102
and the smoothed DC voltage is charged to a battery
101
via a charging current detecting resistance RS
1
. A diode D
1
is a fly-back diode for regenerating charging current ICHG.
Switching control of the PMOS driver Tr
1
is conducted by a charging control circuit
111
. An amplifier
112
amplifies terminal voltage of the charging current detecting resistance RS
1
. An error amplifier
116
amplifies voltage difference between reference voltage V
1
and the amplified terminal voltage of the charging current detecting resistance RS
1
as error amplification, as well as outputs control voltage for constant current charging. Furthermore, resistance elements R
110
and R
120
divide output voltage VO at a charging-control-device output terminal VO that is a battery-side terminal of the charging current detecting resistance RS
1
. An error amplifier
118
amplifies electrical potential difference between reference voltage V
2
at a reference-voltage terminal V
2
and the divided voltage of the output voltage VO as error amplification, as well as outputs control voltage for constant voltage charging. The above two kinds of control voltage are inputted to a comparator
120
and compared with an oscillating signal from an oscillator (OSC)
122
there. Thereby, a switching duty is determined. In case control voltage for constant current charging derived from the error amplifier
116
determines a switching duty, constant current charging is controlled and charging current ICHG for the battery
101
is adjusted to a predetermined value of charging current ICHGM. In case control voltage for constant voltage charging derived from the error amplifier
118
determines a switching duty, constant voltage charging is controlled and the output voltage VO is kept at a predetermined value of full charging voltage VBAT
0
so as to carry out charging.
According to a charging control method of the charging control circuit
111
shown in
FIG. 13
, the error amplifier
116
controls charging current ICHG for the battery
101
until charging begins and a value of output voltage VO at the charging-control-device output terminal VO reaches full charging voltage VBAT
0
. Thereby, charging is carried out rapidly with a predetermined value of charging current ICHGM. When charging to the battery
101
further goes on and the output voltage VO at the charging-control-device output terminal VO reaches full charging voltage VBAT
0
, a value of control voltage for constant current charging outputted from the error amplifier
116
and that for constant voltage charging from the error amplifier
118
reverse. As a result, charging control is switched from constant current control to constant voltage control. Charging operation further goes on with the output voltage VO at the charging-control-device output terminal VO kept at full charging voltage VBAT
0
. Charging to the battery
101
completes when the charging current ICHG decreases from its predetermined charging current ICHGM and finally runs out.
Since the charging control device
100
and the battery
101
are connected via connectors, switches and the like, there are resistance elements such as contact resistances and the like at connecting portions of the connectors and the like. A wiring resistance of connection wiring itself is also arranged together with the contact resistance at a connecting portion and a parasitic resistance RLS
1
is inserted at a connecting path. Since charging current ICHG flows in the battery
101
through the parasitic resistance RLS
1
, voltage drop &Dgr;VLS occurs when charging current ICHGM in a constant current control state flows. As a result, battery terminal voltage VBAT lowers by the voltage drop &Dgr;VLS, compared with output voltage VO at the charging-control-device output terminal VO. The charging control device
100
carries out constant voltage control with respect to output voltage VO at the charging-control-device output terminal VO. Therefore, as constant current charging control further goes on and battery terminal voltage VBAT gets higher, output voltage VO at the charging-control-device output terminal VO gets higher. And then, at a point where the charging-control-device output terminal VO reaches full charging voltage VBAT
0
, output charging control is switched from constant current control to constant voltage control.
However, the battery terminal voltage VBAT does not reach full charging voltage VBAT
0
of the battery
101
at this point but is charged up to voltage level lowered by voltage drop &Dgr;VLS from the full charging voltage VBAT
0
. That is, constant charging control is supposed to conduct high-speed charging control primarily, however, the voltage drop &Dgr;VLS due to the parasitic resistance RLS
1
shortens constant charging control time. Along with that, it takes long to fully charge the battery
101
, which is problematic.
FIG. 14
shows the battery charging characteristics of the conventional regulator circuit
100
. In the regulator circuit
100
, charging current ICHGM flows to the parasitic resistance RLS
1
during the constant current control period. Thereby, output voltage VO of the charging-control-device output terminal VO has a voltage value higher by the voltage drop &Dgr;VLS compared with battery terminal voltage VBAT. Consequently, before the battery terminal voltage VBAT reaches a value of predetermined voltage VBAT
0
in a full-charging condition, the charging control manner is switched from constant current charging control to constant voltage charging control. As a result, a constant current charging control period gets shorter than original one. Subsequent charging control is made in accordance with constant voltage charging control and the battery terminal voltage VBAT is further charged by the drop voltage &Dgr;VLS. However, the constant voltage charging control is conducted in a manner that charging-control-device output terminal VO which has already reached full charging voltage VBAT
0
is kept at voltage VBAT
0
. Therefore, a switching duty of the PMOS driver Tr
1
must be lowered inevitably. Accordingly,

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