Power generation circuit
In a power generation circuit configured by a voltage follower amplifier, a selector is provided inside of an operation amplifier. When a standby mode is released, a bias voltage in a constant current source is applied to a gate of a PMOS, and during a normal operation, an output voltage of a differential amplifier stage is applied to the gate of the PMOS. This favorably allows only the constant current to flow to a stable capacity after the standby mode is released, and prevents the flow of a large amount of current so that the power supply voltage is not dropped in value that much. The power generation circuit configured as such thus can prevent an inrush current from flowing to the stable capacity at startup without reducing the power supply efficiency and without complicating the circuit configuration.
1 . A power generation circuit, comprising:
a constant current source stopping, with a connection to a power supply terminal receiving a power supply voltage, under a control of a first control signal that is at a first logic level in a standby mode and is changed to a second logic level when the standby mode is released, operation as a supply of the power supply voltage is cut off when the first logic level is provided, starting operation as the supply of the power supply voltage comes when the second logic level is provided, and generating a constant bias voltage and outputting a constant current;
a differential amplifier stage amplifying, with a connection to the power supply terminal, when the constant current is provided, a difference between an input voltage and a voltage of an output terminal connected with a stable capacity, and outputting a resulting amplified voltage;
an output transistor flowing, with a connection between the power supply terminal and the output terminal, a power supply current to the output terminal with control exercised over continuity based on a voltage of a control node; and
a control device which applies, to the control node, under a control of a second control signal that is at a third logic level when the standby mode is released and is changed to a fourth logic level after a predetermined length of time passes, a predetermined voltage that increases an ON-resistance value when the output transistor is put in continuity when the third logic level is provided, and applies the output voltage of the differential amplifier stage to the control node when the fourth logic level is provided.
2 . The power generation circuit according to claim 1 , wherein
the control device is configured by a selection circuit that receives the bias voltage and the output voltage of the differential amplifier stage, and when the third logic level of the second control signal is provided, selects the bias voltage as the predetermined voltage for application to the control node, and when the fourth logic level of the second control signal is provided, selects the output voltage of the differential amplifier stage for application to the control-node.
3 . The power generation circuit according to claim 2 , wherein
the selection circuit is configured by a transistor selector that receives the bias voltage and the output voltage of the differential amplifier stage, and based on the second control signal, selects either the bias voltage or the output voltage of the differential amplifier stage for output to the control node.
4 . The power generation circuit according to claim 1 , wherein
the control device is configured by a constant current transistor circuit that is connected between the power supply terminal and the control node, and when the third logic level of the second control signal is provided, is put in an ON state and supplies a constant current to the control node for biasing the control node to the predetermined voltage, and when the fourth logic level of the second control signal is provided, is put in an OFF state and applies the output voltage of the differential amplifier stage to the control node.
5 . The power generation circuit according to claim 4 , wherein
the constant current transistor circuit includes a first transistor under a control of the second control signal over continuity, and a second transistor under a control, over continuity, for use for the constant current source, of a voltage on a signal line connecting the output terminal of the differential amplifier stage and the control node, and
the first and second transistors are connected in series between the power supply terminal and the signal line.
6 . The power generation circuit according to claim 1 , wherein
the output transistor is a MOS transistor in which a source electrode and a drain electrode are connected between the power supply terminal and the output terminal, and a gate electrode is connected to the control node.
7 . The power generation circuit according to claim 6 , wherein
the predetermined voltage has a value in a vicinity of (VCC−Vt) (where VCC denotes the power supply voltage, and Vt denotes a threshold voltage of the MOS transistor).
8 . The power generation circuit according to claim 1 wherein
the constant current source, the differential amplifier stage, and the output transistor are configured by a voltage follower amplifier circuit.
9 . A power generation circuit, comprising:
a constant current source stopping, with a connection to a power supply terminal receiving a power supply voltage, under a control of a first control signal that is at a first logic level in a standby mode and is changed to a second logic level when the standby mode is released, operation as a supply of the power supply voltage is cut off when the first logic level is provided, starting operation as the supply of the power supply voltage comes when the second logic level is provided, and generating a constant bias voltage and outputting a constant current;
a differential amplifier stage amplifying, with a connection to the power supply terminal, when the constant current is provided, a difference between an input voltage and a voltage of an output terminal connected with a stable capacity, and outputting a resulting amplified voltage;
an output transistor flowing, with a connection between the power supply terminal and the output terminal, a power supply current to the output terminal with control exercised over continuity based on a voltage of a control node; and
control means for applying, to the control node, under a control of a second control signal that is at a third logic level when the standby mode is released and is changed to a fourth logic level after a predetermined length of time passes, a predetermined voltage that increases an ON-resistance value when the output transistor is put in continuity when the third logic level is provided, and applying the output voltage of the differential amplifier stage to the control node when the fourth logic level is provided.
10 . The power generation circuit according to claim 9 , wherein
the control means is configured by a selection circuit that receives the bias voltage and the output voltage of the differential amplifier stage, and when the third logic level of the second control signal is provided, selects the bias voltage as the predetermined voltage for application to the control node, and when the fourth logic level of the second control signal is provided, selects the output voltage of the differential amplifier stage for application to the control node.
11 . The power generation circuit according to claim 10 , wherein
the selection circuit is configured by a transistor selector that receives the bias voltage and the output voltage of the differential amplifier stage, and based on the second control signal, selects either the bias voltage or the output voltage of the differential amplifier stage for output to the control node.
12 . The power generation circuit according to claim 9 , wherein
the control means is configured by a constant current transistor circuit that is connected between the power supply terminal and the control node, and when the third logic level of the second control signal is provided, is put in an ON state and supplies a constant current to the control node for biasing the control node to the predetermined voltage, and when the fourth logic level of the second control signal is provided, is put in an OFF state and applies the output voltage of the differential amplifier stage to the control node.
13 . The power generation circuit according to claim 12 , wherein
the constant current transistor circuit includes a first transistor under a control of the second control signal over continuity, and a second transistor under a control, over continuity, for use for the constant current source, of a voltage on a signal line connecting the output terminal of the differential amplifier stage and the control node, and
the first and second transistors are connected in series between the power supply terminal and the signal line.
14 . The power generation circuit according to claim 9 , wherein
the output transistor is a MOS transistor in which a source electrode and a drain electrode are connected between the power supply terminal and the output terminal, and a gate electrode is connected to the control node.
15 . The power generation circuit according to claim 14 , wherein
the predetermined voltage has a value in a vicinity of (VCC−Vt) (where VCC denotes the power supply voltage, and Vt denotes a threshold voltage of the MOS transistor).
16 . The power generation circuit according to claim 9 wherein
the constant current source, the differential amplifier stage, and the output transistor are configured by a voltage follower amplifier circuit.