Constant voltage circuit

Abstract

A current source generates a reference current. A first transistor is a depletion-type MOSFET arranged such that one terminal thereof is connected to the current source and its gate is connected to its source. A second transistor is an enhancement-type MOSFET arranged such that one terminal thereof is connected to the other terminal of the first transistor, the other terminal thereof is connected to a fixed voltage terminal, and its gate and drain are connected. A third MOSFET is an enhancement-type P-channel MOSFET arranged such that one terminal thereof is connected to the current source, the other terminal thereof is connected to the fixed voltage terminal, and its gate is connected to a connection node connecting the first and second transistors. A constant voltage circuit outputs at least a voltage that corresponds to the gate voltage of the third transistor or a voltage that corresponds to the gate voltage thereof.

1 .- 6 . (canceled) 
     
     
         7 . A comparator configured to make a comparison between a first voltage and a second voltage, and to generate an output voltage which represents the comparison result, the comparator comprising:
 a differential pair configured to receive, as input signals, the first voltage and the second voltage;   a tail current source configured to supply a tail current to the differential pair;   a load circuit connected to the differential pair;   a source follower comprising a current source and an output transistor arranged on a path of the current source, and configured such that the turn-on degree of the output transistor changes according to a current that flows through a transistor that is one component of the differential pair; and   a constant voltage element arranged between the transistor that is one component of the differential pair and the control terminal of the output transistor.   
     
     
         8 . A comparator according to  claim 7 , wherein the constant voltage element comprises a MOSFET arranged such that the gate thereof is connected to the drain thereof. 
     
     
         9 . A comparator according to  claim 7 , wherein the constant voltage element comprises a diode. 
     
     
         10 . (canceled) 
     
     
         11 . A voltage monitoring circuit configured to compare a voltage to be monitored with a predetermined reference voltage, the voltage monitoring circuit comprising:
 a constant voltage circuit configured to generate the reference voltage; and   a comparator according to  claim 7 , configured to compare the voltage to be monitored with the reference voltage.