Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-11-20
2003-03-11
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06531853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a DC—DC converter and, in particular, to a DC—DC converter, which utilizes a switching regulator inputted with and selectively driven by a voltage of a battery power source, a power source for obtaining DC power by rectifying AC power or an AC adapter and which has a wide dynamic range of an input voltage and can stabilize an output voltage thereof even when the power source voltage is varied. In the following description, the power source for generating DC power by rectifying AC power or the AC adapter will be referred to as “AC power source”.
2. Description of the Prior Art
In a conventional portable electronic device such as a portable audio equipment, a personal computer, a PHS (Personal Handyphone System), a portable telephone set or a PDA (Personal Digital Assistance), etc., it has been usual to utilize a DC—DC converter constructed with a switching regulator for obtaining a predetermined power source voltage by efficiently performing a power conversion.
FIG. 2
shows a construction of an example of a conventional switching regulator used for the DC—DC converter.
In
FIG. 2
, the switching regulator
10
includes an error amplifier (Err)
11
, a reference voltage generator circuit
12
, a PWM pulse generator circuit
13
, which includes a comparator
13
a
and a triangular wave generator circuit
13
b,
a driver
14
, a switching circuit
15
constructed with a P channel MOSFET Q and a Schottky diode D connected in series with the P channel MOSFET Q. The series circuit of the P channel MOSFET Q and the Schottky diode D is provided between a power source line +Vcc connected to an input side DC power source and ground GND.
The switching regulator
10
further includes an output capacitor C provided between an output terminal
16
and ground GND and a solenoid L is connected between a junction of the MOSFET Q and the Schottky diode D and the output terminal
16
. In this case, a value of the solenoid L is in the order of 10 &mgr;H and a capacitance of the output capacitor C is about 150 &mgr;F, for example. The switching regulator
10
further includes a resistive voltage divider circuit
17
constructed with a series connection of resistors R
1
and R
2
, which are provided between the output terminal
16
and ground GND. A detection voltage Vs detected by the resistive voltage divider circuit
17
is fedback to the error amplifier
11
. The detection voltage Vs is compared by the error amplifier
11
with a reference voltage Vref generated by the reference voltage generator circuit
12
and a resultant voltage difference Ve (error detection signal) is inputted to the comparator
13
a
of the PWM pulse generator circuit
13
.
The resistive voltage divider circuit
17
for generating the output voltage is constructed with the series circuit of the resistors R
1
and R
2
and a speed-up circuit for reducing a time period from an operation start time of the DC—DC converter
10
up to a time at which the DC—DC converter
10
becomes in a steady operation state. The speed-up circuit comprises a CR time constant circuit
17
a,
which is a series circuit of a resistor and a capacitor and is connected in parallel to the resistive voltage divider circuit
17
and functions to set a PWM driving gain.
The error amplifier (Err)
11
includes a phase correction circuit
18
composed of a series circuit of a capacitor C
1
and a resistor R
3
and a capacitor C
2
connected in parallel to the series circuit of the capacitor C
1
and the resistor R
3
. The phase correction circuit
18
is connected between one of input terminals of the error amplifier
11
and an output terminal thereof and constructs a negative feedback circuit functioning to prevent oscillation of the error amplifier
11
when the PWM drive gain is increased.
The comparator
13
a
of the PWM pulse generator circuit
13
compares a triangular wave signal generated by the triangular wave generator circuit
13
b
with the error voltage Ve to slice the tooth wave by the error voltage to thereby generate a PWM pulse signal, which is supplied to the driver
14
. The driver
14
ON/OFF controls the transistor Q according to a width of the PWM pulse and generates a reduced voltage at the output terminal
16
when the DC—DC converter
10
is of a drop type. When the DC—DC converter is of a boost type, a boosted voltage, which is generated by a fly-back pulse, appears at the output terminal
16
.
Incidentally, the Schottky diode D is a flywheel diode for returning a current, which flows out from the solenoid L when the transistor Q is turned OFF, to the solenoid L.
As described, the transistor Q of the DC—DC converter
10
is ON/OFF controlled such that the voltage Vs divided by the resistive voltage divider circuit
17
becomes coincident with the reference voltage Vref to make the output voltage at the output terminal
16
coincident with the constant voltage Vo to thereby stabilize the output voltage.
The input side power source line +Vcc, whose voltage Vcc is equal to Vin, is usually connected to a battery as shown by a dotted line. In a portable, notebook type personal computer, etc., however, one of a battery power source and an AC power source is selected by means of a power source switching circuit and utilized as the input side power source.
In a PWM control circuit for performing such operation, a range of the input power source voltage Vin is limited and its dynamic range is relatively narrow. The reason for this is that, in order to stabilize the output voltage when the input power source voltage is lowered, the PM control is performed such that a ratio of the ON period of an output transistor of the driver
14
to the OFF period thereof is set to, for example, 80% or more, so that a variation range of the pulse width with respect to a variation of the error voltage Ve is restricted and saturated. Therefore, it becomes difficult to satisfactorily perform a control operation with respect to a variation of the output voltage when the power source voltage is lowered. On the other hand, in the portable, notebook type personal computer, etc., in which one of the battery power source and the AC power source is selectively utilized as the input side power source by the power source switching circuit, the input power source voltage when the AC power source is used is usually higher than that of the battery. Therefore, when the AC power source is used, the variation of the power source voltage is larger than that when the battery is used, so that it becomes necessary to regulate the power source voltage in a wider range. Further, when the power source voltage is increased, the PWM control is performed in a level of the triangular wave in the vicinity of a summit thereof, contrarily to the case mentioned above. Therefore, it becomes difficult to perform a satisfactory control with respect to a variation of the output voltage when the power source voltage is lowered, similarly to the case mentioned above.
In order to obtain a stable output voltage under the circumstances, it is preferable that the PWM control is performed for the input power source voltage Vin in a level in which duty cycle is in a range from 30% to 70%.
As a control system capable of obtaining some dynamic range with respect to the input power source voltage Vin, there is the current mode PWM control system in which the PWM control is performed by current comparison. However, since, in such system, a detection resistor is inserted in series with a switching transistor Q, power loss is increased and a current comparator circuit, etc., are required additionally, so that there are problems of high cost and low power conversion efficiency.
On the other hand, in the conventional portable electronic device such as a notebook type personal computer, the output power source voltage is lowered in a standby state or a sleep mode thereof. On the contrary, in a case where luminance of a liquid crystal display thereof is set high, it is necessary to generate high output voltage
Berhane Adolf Deneke
Mattingly Stanger & Malur, P.C.
Rohm & Co., Ltd.
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