AC adapter having a function for lowering and heightening an adapter voltage

• US 7,071,655 B2
• Filed: 02/26/2004
• Issued: 07/04/2006
• Est. Priority Date: 07/09/2003
• Status: Expired due to Fees

• Current Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Original Assignee: Mitsumi Electric Co., Ltd. (MinebeaMitsumi Inc.)
• Inventors: Murakami, Kouji, Hamai, Hidetoshi
• Primary Examiner(s): Berhane, Adolf Deneke
• Assistant Examiner(s): GRANT, ROBERT J
• Application Number:
  US10/789,498
• Publication Number:
  US 20050007069A1
• Time in Patent Office: 859 Days
• Field of Search: 320/149, 320/160, 320/146
• US Class Current: 320/149
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/00714 in response to battery charging or discharging current
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage
• CPC Class Codes: H02M 1/0009 Devices or circuits for detecting current in a converter
• CPC Class Codes: H02M 3/33523 with galvanic isolation between input and output of both the power stage and the feedback loop

Abstract

Disposed in a secondary side circuit of an AC adapter (10A), a−ΔI detection circuit (45) detects that a charging current (Ic) lowers less than a set current value to produce a detected signal. A voltage control circuit (42A) operates so as to repeat the steps of gradually lowering an adapter voltage (V_ADP) and of heightening the adapter voltage in response to the detected signal.

Claims

1. An AC adapter for use in charging a secondary battery which is contained in or mounted on a main body, said AC adapter comprising:

a primary side circuit for turning, by using a switching element, an input DC voltage applied to a primary winding of a transformer on and off;

a secondary side circuit for rectifying and smoothing an AC voltage induced in a secondary winding of said transformer to produce an adapter voltage;

a voltage control circuit for detecting a variation of said adapter voltage to produce a voltage control signal;

a constant current control circuit for detecting a charging current flowing in said secondary side circuit to produce a constant current control signal;

a photocoupler for feeding said voltage control signal and said constant current control signal as a feedback signal back to said primary side circuit;

a switching control circuit for controlling, in response to said feedback signal, on and off of said switching element; and

detection means, disposed in said secondary side circuit, for detecting when said charging current decreases to less than a set current value due to a drastic decrease of said charging current to produce a detected signals;

wherein said voltage control circuit repeats operations comprising gradually lowering said adapter voltage and increasing, in response to said detected signal, said adapter voltage by a predetermined voltage, so that said AC adapter carries out a constant voltage charging with a necessary minimum voltage difference which is a potential difference between said adapter voltage and a battery voltage of said secondary battery on a constant current charging.

2. An AC adapter as claimed in claim 1, wherein said main body comprises a portable telephone set.

3. An AC adapter as claimed in claim 1, wherein said predetermined voltage is equal to 100 millivolts.

4. An AC adapter as claimed in claim 1, further comprising a reference voltage generating circuit for supplying a reference voltage to said voltage control circuit, said voltage control circuit controlling said adapter voltage so as to change said adapter voltage by changing said reference voltage by said reference voltage generating circuit.

5. An AC adapter as claimed in claim 4, wherein said main body comprises a portable telephone set.

6. A method of charging, by using an adapter voltage, a secondary battery which is contained in or mounted on a main body, said method comprising the steps of:

a) gradually lowering said adapter voltage;

b) increasing said adapter voltage by a predetermined voltage when a charging current flowing through said secondary battery is less than a set current value due to a drastic decrease of the charging current; and

c) repeating said steps a) and b), whereby constant voltage charging is carried out with a necessary minimum voltage difference which is a potential difference between the adapter voltage and a battery voltage of the secondary battery on a constant current charging.

7. A method as claimed in claim 6, wherein said predetermined voltage is equal to 100 millivolts.