Constant-voltage circuit
View Patent ↗A start signal (STA) at “H” causes a current to flow through a constant-current portion ( 10 ) and control voltages to be produced at nodes (N 1 , N 2 ) for biasing of a reference voltage portion ( 20 ) and an output portion ( 30 ), respectively. This allows a predetermined current to flow through the reference voltage portion ( 20 ), and a reference voltage (VRF) to be output at a node (N 4 ). With the start signal (STA) at “L”, only a constant-voltage device ( 22 ) provides a reference voltage (VRF 1 ), whereas the start signal (STA) at “H” causes the constant-voltage devices ( 22,23 ) to be connected in parallel to provide a reference voltage (VRF 2 ). The reference voltage (VRF) is amplified at an output portion having a differential amplifier arranged in the voltage follower connection to output an internal voltage (VOUT) corresponding to the reference voltage (VRF).
1. A constant-voltage circuit comprising:
a constant-current portion for allowing an electric current to start flowing, when a start signal is in an active state, to output a first control signal and a second control signal of predetermined levels, respectively, and continue outputting said first and second control signals after said start signal is in an inactive state;
a reference voltage portion for outputting a first reference voltage in response to said first control signal while the start signal is in said inactive state and for outputting a second reference voltage higher than said first reference voltage in response to said first control signal while said start signal is in said active state; and
an output portion for outputting a constant internal voltage corresponding to either one of said first and second reference voltages output from said reference voltage portion in response to said second control signal.
2. The constant-voltage circuit according to claim 1 , wherein
said output portion includes switching means for outputting an externally applied supply voltage as said constant internal voltage irrespective of said second control signal and said first or second reference voltages when a mode signal designating a high-load mode is in an active state.
3. The constant-voltage circuit according to claim 1 , wherein
said constant-current portion comprises:
a first transistor connected between a first node for outputting said first control signal and a source potential, the conduction state of said first transistor being controlled by said first control signal;
a second transistor connected between a second node for outputting said second control signal and the source potential, the conduction state of said second transistor being controlled by said first control signal;
a third transistor connected between said first node and a third node, the conduction state of said third transistor being controlled by said second control signal;
a resistor connected between said third node and a ground potential;
a fourth transistor connected between said second node and the ground potential, the conduction state of said fourth transistor being controlled by said second control signal; and
a fifth transistor connected between said first node and said third node, the conduction state of said fifth transistor being controlled by said start signal,
said reference voltage portion comprises:
a sixth transistor connected between a fourth node, for outputting said first and second reference voltages, and the source potential, the conduction state of said sixth transistor being controlled by said first control signal;
a first constant-voltage device connected between said fourth node and the ground potential, and
a second constant-voltage device to be connected in parallel to said first constant-voltage device when said start signal is in said active state, and
said output portion comprises:
a differential amplifier having a non-inverting input terminal provided with one of said first and second reference voltages, an inverting input terminal connected to an output node for outputting said internal voltage, the bias current of said differential amplifier being controlled by said second control signal;
a seventh transistor connected between the source potential and said output node, the conduction state of said seventh transistor being controlled by an output signal from said differential amplifier; and
an eighth transistor connected between said output node and the ground potential, the conduction state of said eighth transistor being controlled by said second control signal.
4. The constant-voltage circuit according to claim 1 , wherein
said constant-current portion comprises:
a first transistor connected between a first node for outputting said first control signal and a source potential, the conduction state of said first transistor being controlled by said first control signal;
a second transistor connected between a second node for outputting said second control signal and the source potential, the conduction state of said second transistor being controlled by said first control signal;
a third transistor connected between said first node and a third node, the conduction state of said third transistor being controlled by said second control signal;
a first resistor connected between said third node and a ground potential;
a fourth transistor connected between said second node and the ground potential, the conduction state of said fourth transistor being controlled by said second control signal; and
a fifth transistor connected between said first node and said third node, the conduction state of said fifth transistor being controlled by said start signal,
said reference voltage portion comprises:
a sixth transistor connected between a fourth node, for outputting said first and second reference voltages, and the source potential, the conduction state of said sixth transistor being controlled by said first control signal;
a first constant-voltage device connected between said fourth node and the ground potential; and
a second constant-voltage device to be connected in parallel to said first constant-voltage device when said start signal is in said active state, and
said output portion comprises:
a differential amplifier having a non-inverting input terminal provided with one of said first and second reference voltages, an inverting input terminal connected to a fifth node, the bias current of said differential amplifier being controlled by said second control signal;
a seventh transistor connected between the the source potential and an output node for outputting said internal voltage, the conduction state of said seventh transistor being controlled by an output signal from said differential amplifier,
a second resistor connected between said output node and said fifth node,
an eighth transistor connected between said fifth node and the ground potential, the conduction state of said eighth transistor being controlled by said second control signal, and
a ninth transistor connected in parallel to said first resistor, the conduction state of said ninth transistor being controlled by said start signal.
5. The constant-voltage circuit according to claim 3 , wherein
said output portion includes a switching transistor connected between the source potential and said output node, the conduction state of said switching transistor being controlled by a mode signal.
6. The constant-voltage circuit according to claim 4 , wherein
said output portion includes a switching transistor connected between the source potential and said output node, the conduction state of said switching transistor being controlled by a mode signal.