Constant voltage power supply with normal and standby modes

Abstract

A first constant voltage circuit includes an operational amplifier having a reference voltage applied to a first input terminal thereof and a voltage obtained as a result of an output voltage being divided applied to a second input terminal thereof, and controls an output transistor with an output of its operational amplifier. A second constant voltage circuit includes an operational amplifier having a reference voltage applied to a first input terminal thereof and a voltage obtained as a result of the output voltage being divided applied to a second input terminal thereof, and controls the output transistor with an output of its operational amplifier, a current consumption of the second constant voltage circuit being smaller than a current consumption of the first constant voltage circuit. A switching part is provided for each of those operational amplifiers and makes connection and disconnection between an output terminal of the operational amplifier and the output transistor. A switching logic circuit controls the switching units so that the first constant voltage circuit is connected to the output transistor when the load is in the operation condition but the second constant voltage circuit is connected to the output transistor when the load is in the standby condition.

1. A constant voltage power supply supplying power to a load having an operation condition and a standby condition switched to one another, comprising:
 a first constant voltage circuit applying a first reference voltage to a first input terminal of a first operational amplifier and a voltage obtained as a result of an output voltage being divided to a second input terminal of said first operational amplifier, and controlling an output transistor with an output of said first operational amplifier;  
 a second constant voltage circuit applying a second reference voltage to a first input terminal of a second operational amplifier and a voltage obtained as a result of the output voltage being divided to a second input terminal of said second operational amplifier, and controlling said ouptut transistor with an output of said second operational amplifier, a current consumption of said second constant voltage circuit being smaller than a current consumption of said first constant voltage circuit;  
 a switching part provided for said first and second operational amplifiers and switching connection between output terminals of said operational amplifiers and said output transistor; and  
 a switching logic circuit controlling said switching part so that said first operational amplifier is connected to said output transistor when said load is in the operation condition but said second operational amplifier is connected to said output transistor when said load is in the standby condition.  
 
     
     
       2. The power supply as claimed in  claim 1 , wherein:
 said first and second operational amplifiers have the same circuit configuration; and  
 said first operational amplifier employs at least one transistor having a current supply capability larger than that of at least one transistor employed by said second operational amplifier.  
 
     
     
       3. The power supply as claimed in  claim 1 , wherein said first operational amplifier has a buffer transistor having a large current supply capability at an output stage in comparison to said second operational amplifier. 
     
     
       4. The power supply as claimed in  claim 1 , wherein said switching logic circuit controls said switching part so that both said first and second operational amplifiers are connected to said output transistor for a period after the condition of said load is switched. 
     
     
       5. The power supply as claimed in  claim 1 , wherein:
 said first and second constant voltage circuits comprise interrupting circuits which interrupt passing-through currents thereof, respectively; and  
 said switching logic circuit also controls said interrupting circuits so as to turn on the interrupting circuit of said first constant voltage circuit and turn off the interrupting circuit of said second constant voltage circuit when said load is in the operation condition but turn off the interrupting circuit of said first constant voltage circuit and turn on the interrupting circuit of said second constant voltage circuit when said load is in the standby condition.  
 
     
     
       6. The power supply as claimed in  claim 5 , wherein said switching logic circuit controls said switching part and said interrupting circuits so that both said first and second operational amplifiers are connected to said output transistor and also the interrupting circuits of both said first and second constant voltage circuits are turned on for a period after the condition of said load is switched. 
     
     
       7. A constant voltage power supply supplying power to a load having an operation condition and a standby condition switched to one another, applying a reference voltage to a first input terminal of an operational amplifier and a voltage obtained as a result of an output voltage being divided to a second input terminal of said operational amplifier, and controlling an output transistor with an output of said operational amplifier, said power supply comprising:
 a parallel circuit of two transistors provided in a current path of said operational amplifier and having different current capacities; and  
 a switching logic circuit controls said parallel circuit so that the transistor of said parallel circuit having a larger current capacity is turned on when said load is in the operational condition but the transistor of said parallel circuit having a smaller current capacity is turned on when said load is in the standby condition.  
 
     
     
       8. The power supply as claimed in  claim 7 , wherein said switching logic circuit controls said parallel circuit so that both transistors of said parallel circuit are turned on for a period after the condition of said load is switched. 
     
     
       9. A constant voltage power supply comprising:
   a first constant voltage circuit applying a first reference voltage to a first input terminal of a first operational amplifier and a voltage obtained as a result of an output voltage being divided to a second input terminal of said first operational amplifier, and controlling a first output transistor with an output of said first operational amplifier;        a second constant voltage circuit applying a second reference voltage to a first input terminal of a second operational amplifier and a voltage obtained as a result of the output voltage being divided to a second input terminal of said second operational amplifier, and controlling a second output transistor with an output of said second operational amplifier; and        a part switching between outputs of said first constant voltage circuit and said second constant voltage circuit, and wherein said power supply is arranged such that a current consumption of said second constant voltage circuit is smaller than a current consumption of said first constant voltage circuit.      
     
     
       10. The power supply as claimed in  claim 9 , wherein:
   said first and second operational amplifiers have the same circuit configuration; and        said first operational amplifier employs at least one transistor having a current supply capability larger than that of at least one transistor employed by said second operational amplifier.      
     
     
       11. The power supply as claimed in  claim 9 , wherein said first operational amplifier has a buffer transistor having a large current supply capability at an output stage in comparison to said second operational amplifier.  
     
     
       12. The power supply as claimed in  claim 9 , wherein:
   said first and second constant voltage circuits comprise interrupting circuits which interrupt passing - through currents thereof, respectively; and        said interrupting circuits are controlled so as to turn on the interrupting circuit of said first constant voltage circuit and turn off the interrupting circuit of said second constant voltage circuit in a predetermined first condition, but turn off the interrupting circuit of said first constant voltage circuit and turn on the interrupting circuit of said second constant voltage circuit in a predetermined second condition.      
     
     
       13. A constant voltage power supply comprising:
   a first constant voltage circuit applying a first reference voltage to a first input terminal of a first operational amplifier and a voltage obtained as a result of an output voltage being divided to a second input terminal of said first operational amplifier, and controlling an output transistor with an output of said first operational amplifier;        a second constant voltage circuit applying a second reference voltage to a first input terminal of a second operational amplifier and a voltage obtained as a result of the output voltage being divided to a second input terminal of said second operational amplifier; and        a part switching between outputs of said first constant voltage circuit and said second constant voltage circuit, and wherein said power supply is arranged such that a current consumption of said second constant voltage circuit is smaller than a current consumption of said first constant voltage circuit.