Constant voltage power supply with normal and standby modes

• US 6,236,194 B1
• Filed: 08/04/2000
• Issued: 05/22/2001
• Est. Priority Date: 08/06/1999
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Yoshii, Kohji, Manabe, Shinya
• Primary Examiner(s): STERRETT, JEFFREY L
• Application Number:
  US09/633,148
• Time in Patent Office: 291 Days
• Field of Search: 323/282, 323/284, 323/273, 323/274
• US Class Current: 323/274
• CPC Class Codes: G05F 1/565 sensing a condition of the system or its load in addition to means responsive to deviations in the output of the system, e.g. current, voltage, power factor G05F1/563 takes precedence
• CPC Class Codes: G05F 3/242 with compensation for device parameters, e.g. channel width modulation, threshold voltage, processing, or external variations, e.g. temperature, loading, supply voltage

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 operatioanal 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 operatioanal 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 amplifiers 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.

Claims

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 output 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 operatioanal 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.