Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2001-02-07
2002-07-16
Patel, Rajnikant B. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S326000
Reexamination Certificate
active
06420857
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to phase compensation for providing a transient response characteristic which does not depend on load current of a regulator.
2. Description of the Related Art
FIG. 4
shows a constitution of a conventional regulator. A reference voltage power supply
201
supplies constant voltage Vref to an inverted input terminal of a transconductance amplifier
202
. An output of the transconductance amplifier
202
is connected to the gate of a PMOS output driver transistor
204
and a phase compensating RC network
203
constituted by a resistor
208
and a capacitor
209
. The source of the PMOS output driver transistor
204
is connected to an input terminal IN and the drain is connected to an output terminal OUT. The output terminal OUT is connected with a load resistor
207
and a capacitor
206
and a voltage dividing circuit
205
constituted by resistors
210
and
211
. The voltage dividing circuit
205
supplies voltage produced by dividing output voltage VOUT to a noninverting input terminal of the transconductance amplifier.
When a resistance value of the resistor
208
constituting the phase compensation RC network
203
is designated by notation R
208
and a capacitance value of the capacitor
209
is designated by notation C
209
, frequency fz of a zero point for phase compensation constituted by R
208
and C
209
, is calculated by the following equation.
fz
=
1
2
π
·
R208
·
C209
(
1
)
When a resistance value of the load resistor
207
is designated by notation R
207
and a capacitance value of the load capacitor
206
is designated by notation C
206
, frequency fp of a pole constituted thereby is calculated by the following equation.
fp
=
1
2
π
·
R207
·
C206
(
2
)
As is apparent from Equation (2), in accordance with a variation in the load resistor
207
, the frequency fp of the pole is also changed. Meanwhile, as is apparent from Equation (1), the frequency fz of the zero point for phase compensation is a fixed value.
When load current is large, the load resistor
207
becomes small and accordingly, by Equation (2), the frequency fp of the pole is moved to a high frequency side. Further, when the load current is small, the load resistor
207
becomes large and accordingly, by Equation (2), the frequency fp of the pole is moved to a low frequency side.
FIG. 5
shows frequency characteristics of the regulator when the load current is large and when the load current is small.
As shown by
FIG. 5
, when the load current is large, unity gain frequency at which voltage gain of the regulator becomes
1
, becomes high, conversely, when the load current is small, the unity gain frequency becomes low. When the unity gain frequency is changed by the load current in this way, the transient response characteristic depends on the load current, which is not preferable. Particularly, when the load current is small, the unity gain frequency is low and accordingly, the transient response characteristic is deteriorated.
SUMMARY OF THE INVENTION
In order to resolve the above-described problem, according to the invention, there is carried out an improvement in which by varying a frequency of a zero point for phase compensation in accordance with load current, a variation in a frequency band of a regulator is restrained such that transient response does not depend upon the load current.
According to the invention, by generating current in proportion to load current by a load current detecting transistor connected in parallel with an output driver transistor for supplying current to a load and changing a resistance value of a variable resistance portion by the current, a frequency of a zero point for phase compensation is varied.
An improvement is carried out by varying the frequency of the zero point for phase compensation in accordance with the load current, thereby, a variation in a frequency band of a regulator is restrained without depending upon the load current such that transient response does not depend upon the load current.
REFERENCES:
patent: 5648718 (1997-07-01), Edwards
Adams & Wilks
Patel Rajnikant B.
Seiko Instruments Inc.
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