Series regulator circuit
A series regulator circuit that enables accurate detection of the rising of an output voltage even when the output voltage fluctuates. The series regulator circuit uses an operational amplifier including a first constant current source, first and second transistors for distributing the current of the first constant current source, and a third transistor connected to the second transistor The gate terminals of the first and second transistors are respectively supplied with a reference voltage and a negative feedback voltage. Output of the operational amplifier is amplified by an amplifier. A fourth transistor forms a current mirror circuit with the third transistor. A second constant current source forms a current comparator with the current that flows to the fourth transistor. A connection node of the fourth transistor and the second constant current circuit is connected to the input terminal of an inverter. The output from the inverter is used as a power-up detection signal. The current value of the second constant current source is less than a current value il of the constant current source and greater current value [i1]/2.
1 . A series regulator including an operational amplifier incorporating a differential means formed by a first transistor and a second transistor, which distribute current of a first constant current source, wherein the series regulator circuit outputs an output voltage in accordance with an output of the operational amplifier, the series regulator circuit comprising:
a variable current source for outputting current having a current value that is proportional to current flowing to the first transistor or the second transistor; and
a second constant current source for forming the variable current source and a current comparator;
wherein the first transistor has a control terminal supplied with a reference voltage, the second transistor has a control terminal supplied with a negative feedback voltage that is based on the output voltage, and current that is in accordance with the voltage difference between the negative feedback voltage and the reference voltage flows to the first transistor and second transistor;
the second constant current source generates current having a predetermined current value, which is in the range of the current output from the variable current source, from when entering an activated state in which the reference voltage is supplied to when the negative feedback voltage and the reference voltage become equal to each other; and
voltage at a connection node of the variable current source and the second constant current source is used to output a power-up detection signal.
2 . The series regulator circuit according to claim 1 , wherein the variable current source includes:
a third transistor connected to the first transistor or the second transistor and incorporated in the operational amplifier; and
a fourth transistor forming a current mirror circuit with the third transistor and connected to the second constant current source.
3 . The series regulator circuit according to claim 1 , wherein:
the variable current source generates current having a current value that is proportional to the first or second transistor that stops the flow of current in the activated state; and
the predetermined current value of the second constant current source is a value that is greater than zero and less than one half the current generated by the first constant current source.
4 . The series regulator circuit according to claim 1 , wherein:
the operational amplifier has an output terminal connected to an amplifier for amplifying an output of the operational amplifier; and
voltage at the output terminal of the amplifier is the output voltage.
5 . The series regulator circuit according to of claim 1 , wherein the first and second constant current sources are connected to a power supply voltage line, and the variable current source is connected to a drive voltage line.
6 . The series regulator circuit according to claim 1 , wherein the first and second constant current sources are connected to a drive voltage line, and the variable current source is connected to a power supply voltage line.