Series regulator

Details Series regulator Series regulator

2001-12-21

2004-03-23

Riley, Shawn (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

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

C323S280000

Reexamination Certificate

active

06710584

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a series regulator that is used for obtaining a stabilized power source in a compact device like a portable telephone.
BACKGROUND OF THE INVENTION
Series regulators are provided in the form of ICs using bipolar transistors and unipolar transistors. Series regulators using bipolar transistors will be explained below as an example.
FIG. 5
is a circuit diagram showing a basic structure of a conventional series regulator. As shown in
FIG. 5
, a power transistor
503
is connected in series between an input terminal
501
to which a non-stabilized voltage Vin output from an external starting voltage source is applied and an output terminal
502
to which a stabilized voltage Vout is output. Input ends (emitters) of transistors E
1
, E
2
and E
3
that constitute a bias current circuit are connected to a line that connects the input terminal
501
and an input end (emitter) of the power transistor
503
.
The transistor E
1
and the transistors E
2
and E
3
that are in diode connection have their control ends (bases) connected in common to constitute a current mirror circuit. A constant-current source
504
is provided between an output end (collector) of the transistor E
1
and the ground. An output end (collector) of the transistor E
2
is connected to a reference voltage circuit
505
and a negative-phase input end of an amplifier
506
. An output end (collector) of the transistor E
3
is connected to a bias input end of the amplifier
506
.
A series circuit of resistors R
1
and R
2
is provided between a line that connects an output end (collector) of the power transistor
503
and an output terminal
502
and the ground. A control end of the reistors R
1
and R
2
is connected to a positive-phase input end of the amplifier
506
. An output end of the amplifier
506
is connected to a control end (base) of the power transistor
503
.
In the series regulator having the above structure, when the external starting voltage source has started operation, a constant bias current is supplied to the reference voltage circuit
505
based on a current mirror operation of the transistors E
1
and E
2
, and a reference voltage is supplied to the amplifier
506
from the reference voltage circuit
505
. At the same time, a bias current is supplied to the amplifier
506
from the transistor E
3
, and the amplifier
506
starts the operation of changing the internal resistance of the power transistor
503
. The output voltage of the power transistor
503
is supplied to the amplifier
506
after being divided by the series circuit of the resistors R
1
and R
2
.
As a result, the amplifier
506
changes the internal resistance of the power transistor
503
based on the result of a comparison between the magnitude of the reference output voltage and the magnitude of the divided voltage, and output a stable constant output voltage Vout from the output terminal
502
. As explained above, according to the conventional series regulator, the reference voltage circuit
505
and the amplifier
506
operate based on the bias current supplied from the input side.
However, when the power source of the external starting voltage source is turned on, the output voltage, that is, the input voltage Vin of the series regulator, varies in many cases, as shown in
FIG. 6
, for example. In this case, according to the conventional series regulator, the reference voltage circuit and the amplifier operate by receiving a supply of a bias current that varies following the variation in the input voltage Vin. Therefore, there occurs a fluctuation in the reference voltage, and a ripple is generated in the output voltage Vout as shown in FIG.
6
. This becomes one of factors that aggravates a ripple removal ratio.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a series regulator capable of reducing a ripple voltage that appears in the output voltage due to a variation in the input voltage during a normal operation after a stable voltage has been obtained following the turning-on of the power source, and capable of improving a ripple removal ratio of the series regulator.
The series regulator according to one aspect of the present invention comprises: a power transistor connected in series between an input terminal to which a non-stabilized voltage is applied and an output terminal; an amplifier for changing an internal resistance of the power transistor based on a result of a comparison between an output voltage of the power transistor and a reference voltage, and outputting a stabilized constant voltage to the output terminal; a first bias current circuit for generating a bias current to be supplied to a reference voltage circuit that generates the reference voltage, based on a non-stabilized voltage applied to the input terminal; a resistance voltage dividing circuit for generating a divided voltage of a predetermined value from an output voltage of the power transistor; an output voltage detecting circuit including a first transistor to a control end of which there is applied a conversion voltage of a bias current that the first bias current circuit supplies to the reference voltage circuit; and a second transistor to a control end of which there is applied the divided voltage, wherein the output voltage detecting circuit having a differential structure such that the second transistor is turned on and the first transistor is turned off when the divided voltage has reached a value of the conversion voltage; a second bias current circuit for generating a bias current to be supplied to the reference voltage circuit in response to the on-operation of the second transistor, based on an output voltage of the power transistor; and a bias switching circuit for stopping a bias-current supply operation of the first bias current circuit in response to a starting of the operation of the second bias current circuit.
Thus, when a non-stabilized voltage has been applied to an input terminal, a bias current is supplied to a reference voltage circuit from a first bias current circuit provided at the input side. Then, an amplifier starts the control of a power transistor. In an output voltage detecting circuit, a first transistor is applied with a conversion voltage of a bias current at its control end, and is turned on. When the output voltage of the power transistor rises, and a value of a divided voltage generated by a resistance voltage dividing circuit has reached a value of a conversion voltage of the bias current, a second transistor is turned on in the output voltage detecting circuit. Therefore, a second bias current circuit starts supplying a bias current to the reference voltage circuit. At the same time, a bias switching circuit operates to stop the bias-current supply operation of the first bias current circuit.
The series regulator according to another aspect of the present invention comprises: a power transistor connected in series between an input terminal to which a non-stabilized voltage is applied and an output terminal; an amplifier for changing an internal resistance of the power transistor based on a result of a comparison between an output voltage of the power transistor and a reference voltage, and outputting a stabilized constant voltage to the output terminal; a resistance voltage dividing circuit for generating a divided voltage of a predetermined value from an output voltage of the power transistor; a first bias current circuit for generating a bias current to be supplied to a reference voltage circuit that generates the reference voltage, based on a non-stabilized voltage applied to the input terminal, the first bias current circuit for supplying a bias current to the reference voltage circuit during a period while a first transistor to a control end of which a conversion voltage of the bias current is applied is in on-operation; and a second bias current circuit for generating a bias current to be supplied to the reference voltage circuit, based on an output voltage of the power transistor, the second bias current circui

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