Power source supplying circuit and method comprising a constant-voltage control arrangement

• US 6,194,873 B1
• Filed: 01/26/2000
• Issued: 02/27/2001
• Est. Priority Date: 01/26/1999
• Status: Expired due to Term

• Current Assignee: Lenovo Innovations Ltd Hong Kong (Lenovo Group Ltd.)
• Original Assignee: NEC Corporation
• Inventors: Matsushita, Akimasa
• Primary Examiner(s): Tso, Edward H.
• Application Number:
  US09/491,468
• Time in Patent Office: 398 Days
• Field of Search: 320/123, 320/124, 320/125, 320/134, 320/136, 320/137, 320/162
• US Class Current: 320/137
• CPC Class Codes: G05F 1/575 characterised by the feedback circuit

Abstract

In a power source supplying circuit for supplying a load with an external power source voltage supplied from an external power source terminal thereof, a backflow check diode and a current limiting resistor are disposed in a side of the external power source terminal out of a charging control transistor. The power source supplying circuit further comprises a constant voltage control circuit for controlling the charging control transistor and a battery voltage monitoring feedback resistor connected to the load.

Claims

1. A power source supplying circuit for supplying a load with an external power source voltage supplied from an external power source terminal thereof, said power source supplying circuit comprising a backflow check diode, a current limiting resistor, and a charging control transistor, wherein said backflow check diode and said current limiting resistor are disposed in a side of said external power source terminal out of said charging control transistor, said power source supplying circuit further comprising:

a current detection circuit, connected between both ends of said current limiting resistor, for detecting a current flowing said current limiting resistor on the basis of a potential difference between the both ends of said current limiting resistor to produce a current detected signal;

a charging control circuit, connected to said current detection circuit and supplied with a battery presence or absence detected signal, for controlling said charging control transistor in response to the current detected signal and the battery presence and absence detected signal;

a feedback resistor having an end connected to said load; and

a constant-voltage control circuit, connected to another end of said feedback resistor, for controlling said charging control transistor so as to make a voltage supplied to said load a constant voltage, thereby always supplying a constant stable voltage to said load although a load current of said load varies.

2. A power source supplying circuit as claimed in claim 1, wherein said load comprises a radio apparatus.

3. A power source supplying circuit as claimed in claim 1, wherein said charging control transistor consists of a P-channel metal oxide semiconductor field effect transistor having a source electrode connected to an end of said current limiting resistor, a drain electrode connected to said load, and a gate electrode which is connected to said constant-voltage control circuit and said charging control circuit.

4. A method of supplying a load with an external power source voltage supplied from an external power source terminal, said method comprising the steps of:

applying the external power source voltage through a backflow check diode and a current limiting resistor;

controlling, using constant-voltage control means, a dropped voltage to which the external power source voltage is dropped by said backflow check diode and said current limiting resistor so as to make the dropped voltage a constant voltage; and

supplying the constant voltage to said load, thereby always supplying said load with a constant stable voltage although a load current of said load varies.

5. A power source supplying circuit for supplying a load through a backflow check diode with a voltage supplied from an external power source terminal, said power source supplying circuit comprising constant-voltage control means disposed between said backflow check diode and said load, thereby always supplying said load with a constant stable voltage although a load current of said load varies.

6. A power source supplying circuit as claimed in claim 5, wherein said constant-voltage control means comprises:

a constant-voltage control transistor having main electrodes which are connected to said backflow check diode and said load, respectively;

a feedback resistor having an end connected to said load; and

a constant-voltage control circuit, connected to another end of said feedback resistor, for controlling said constant-voltage control transistor so that a voltage supplied to said load becomes a constant voltage.

7. A power source supplying circuit as claimed in claim 6, wherein said constant-voltage control transistor consists of a P-channel metal oxide semiconductor field effect transistor having a source electrode connected to a cathode electrode of said backflow check diode, a drain electrode connected to said load, and a gate electrode connected to said constant-voltage control circuit.

8. A method of supplying a load with an external power source voltage supplied from an external power source terminal, said method comprising the steps of:

applying the external power source voltage through a backflow check diode;

controlling, using constant-voltage control means, a dropped voltage to which the external power source voltage is dropped by said backflow check diode so as to make the dropped voltage a constant voltage; and

supplying the constant voltage to said load, thereby always supplying said load with a constant stable voltage although a load current of said load varies.