Electrical transmission or interconnection systems – Plural load circuit systems – Control of current or power
Reexamination Certificate
2002-09-27
2004-11-02
Patel, Rajnikant B (Department: 2838)
Electrical transmission or interconnection systems
Plural load circuit systems
Control of current or power
C307S037000, C307S069000, C323S318000, C327S530000
Reexamination Certificate
active
06812590
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to the field of power supply circuit technology; in particular, to a power supply circuit suitable as an internal power supply of a liquid crystal driver IC.
BACKGROUND OF THE INVENTION
A power supply circuit as a conventional liquid crystal driver IC circuit is indicated by symbol
102
in FIG.
3
.
Symbol V
DD
in FIG.
3
and
FIGS. 1 and 2
to be described later indicates a positive voltage line connected to a positive voltage source of 3V or so, and symbol V
EE
indicates a negative voltage line connected to a negative voltage source of −15V or so. In addition, symbol V
SS
is the ground potential.
The power supply circuit
102
has output transistor
111
, amplifier
112
, voltage detection circuit
120
, and reference voltage circuit
125
.
The output transistor
111
is configured with a p-channel MOS transistor, its source terminal is connected to positive voltage line V
DD
, and its drain terminal is connected to external output terminal
128
. Its gate terminal is connected to the output terminal of amplifier
112
.
Load
127
and voltage detection circuit
120
are connected to external output terminal
128
, whereby when output transistor
111
becomes conductive as amplifier
112
outputs a low signal, a current is supplied to load
127
. At this time, the voltage of external output terminal
128
is divided by resistor elements
121
and
122
in detection circuit
120
and input as detection voltage V
S
to the inverted input terminal of amplifier
112
.
Reference voltage circuit
125
is connected to the non-inverted input terminal of amplifier
112
in order to input reference voltage V
ref
output from reference voltage circuit
125
.
When detection voltage V
S
is higher than reference voltage V
ref
, the output voltage of amplifier
112
increases, the current driver capability of output transistor
111
drops, and the current flow therein drops, so that the voltage of external output terminal
128
drops.
On the contrary, when detection voltage V
S
is lower than reference voltage V
ref
, the output voltage of amplifier
112
decreases, the current driver capability of output transistor
111
increases, and the current flow therein increases, so that the voltage of external output terminal
128
increases.
The voltage of external output terminal
128
is regulated to a fixed voltage by the negative feedback operation of amplifier
112
in said manner.
In terms of the configuration of reference voltage circuit
125
, reference voltage circuit
125
has bias circuit
140
and voltage generator circuit
130
.
The bias circuit
140
is configured by connecting diode-connected p-channel type MOS transistor
141
in series with resistor element
142
, and the differential voltage between positive voltage line V
DD
and ground voltage V
SS
is applied to bias circuit
140
. Here, a voltage obtained by subtracting the operating voltage of MOS transistor
141
from the differential voltage is applied to resistor element
142
.
Because the voltage of positive voltage line V
DD
is almost fixed, a constant voltage is applied to resistor element
142
, and a constant current of a fixed amount flows therein. Said constant current also flows into MOS transistor
141
.
Reference voltage generator circuit
130
has p-channel type MOS transistor
131
and n-channel type MOS transistor
134
.
P-channel type MOS transistor
131
includes a current mirror circuit together with diode-connected MOS transistor
141
in bias circuit
140
, and a current proportional to the current flowing in diode-connected MOS transistor
141
flows into said MOS transistor
131
.
In addition, n-channel type MOS transistor
134
is diode-connected, and a current flows therein from MOS transistor
131
constituting the current mirror circuit. As a result, a constant voltage close to the threshold voltage is generated at both ends of diode-connected n-channel type MOS transistor
134
.
The constant voltage serves as reference voltage V
ref
and is input to the inverted input terminal of amplifier
112
.
In the case of power supply circuit
102
, its current supplying capability needs to be determined according to the maximum current consumption by load
127
. Because said load
127
is an internal logic circuit provided in a liquid crystal driver IC, and the size of output transistor
111
needs to be increased, the power consumption of power supply circuit
102
is difficult to decrease.
In addition, because amplifier
112
requires an internal capacitor for phase compensation, a large area is needed, resulting in high cost.
The present invention was created to solve the problems of the prior art, and its objective is to present a low power consumption, reduced size power supply circuit.
SUMMARY OF INVENTION
In order to solve the problems, the power supply circuit of the present invention is provided with a current supply circuit having a first current supplying element connected in parallel to a current supply terminal and a second current supplying element configured with a transistor, a detection circuit containing a clamping circuit provided with multiple diode circuits and connected in series with the current supply circuit in order to output a detection signal according to the voltage at the current supply terminal, and a control circuit having the second current supplying element, a first transistor including a current mirror, a second transistor which becomes conductive or non-conductive according to the detection signal, and a third transistor connected in series with the first transistor in order to control the conduction status of the first transistor according to the conduction status of the second transistor.
Also, in the power supply circuit of the present invention, it is desirable that a bias circuit which outputs a bias voltage be provided, and that the bias voltage be applied to the control terminal of the transistor of first current supplying element.
Moreover, it is desirable that the bias circuit have a fourth transistor which includes a current mirror together with the first current supply circuit, and that the control circuit have a fifth transistor which constitutes a current mirror circuit together with the fourth transistor while supplying supply current to the second transistor.
The power supply circuit of the present invention is included in the diode circuits that are by diode-connecting MOS transistors, and the diode circuits are connected in series to form the clamping circuit; and the diode-connected MOS transistors form a current mirror together with the second transistor (detector transistor).
The detector transistor enters either a conductive or a shut-off status according the status, that is, either conductive or shut-off, of the clamping circuit, whereby the conduction status of the first transistor (driver transistor) is controlled in order to control the operation of the second current driver element.
In addition, the clamping circuit has a function to maintain the voltage value at the current supply terminal at an almost fixed voltage.
REFERENCES:
patent: 6005434 (1999-12-01), Tsukikawa et al.
Lee Yong-hwan
Nishimizu Manabu
Okada Yoshinori
Brady W. James
Patel Rajnikant B
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
LandOfFree
Power supply circuit does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power supply circuit, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power supply circuit will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3329556