CHARGING CIRCUIT FOR WRIST WATCH HAVING SOLAR BATTERY

• US 3,731,474 A
• Filed: 12/27/1971
• Issued: 05/08/1973
• Est. Priority Date: 12/29/1970
• Status: Expired due to Term

• Current Assignee: Yuki Tsuruishi
• Original Assignee: Yuki Tsuruishi
• Inventors: Tsuruishi, Yuki
• Primary Examiner(s): Wilkinson, Richard B.
• Assistant Examiner(s): Jackmon, Edith C. Simmons
• Application Number:
  US05/212,297
• Time in Patent Office: 498 Days
• Field of Search: 58/23R,23A,23C,5DR 250/215X 307/202
• US Class Current: 368/205
• CPC Class Codes: G04C 10/02 the power supply being a radioactive or photovoltaic source
• CPC Class Codes: H02J 7/35 with light sensitive cells
• CPC Class Codes: Y02E 10/56 Power conversion systems, e.g. maximum power point trackers
• CPC Class Codes: Y10S 136/293 Circuits

Abstract

In a wristwatch having therein a solar battery and a secondary battery charged by said solar battery, a charging circuit prevents too high a current from flowing when the solar battery is strongly illuminated. Provision is also made for preventing overcharge of the secondary battery.

Claims

1. A timepiece powered by a solar battery comprising a secondary battery, first circuit means connecting the positive terminal of said solar battery with the positive terminal of said secondary battery and connecting the negative terminal of said solar battery with the negative terminal of said secondary battery for charging said secondary battery, a diode in said first circuit means for preventing reverse current flow through said solar battery when the voltage of said secondary battery exceeds the voltage of said solar battery, transistor means connected with the collector-emitter path thereof in parallel with said solar battery, and second circuit means connecting the base of said transistor means to said first circuit means for sensing the current flowing in a portion of said first circuit so that an increase in current flow through said solar battery causes an increase in current through said transistor means emittercollector path, the increase in current through said transistor means emitter-collector path being such as to prevent excessively high current flow through said secondary battery and to prevent overcharge of said secondary battery.

2. A timepiece as defined in claim 1, wherein said transistor means is of the PNP type, with the emitter thereof connected to the anode of said diode and the base thereof connected to the cathode of said diode.

3. A timepiece as defined in claim 2, wherein said second circuit means includes a resistor.

4. A timepiece as defined in claim 2, wherein said second circuit means includes a diode having its anode connected to the base of said transistor.

5. A timepiece as defined in claim 1, wherein said first circuit means has therein said diode with its anode connected to the positive terminal of said solar battery and a first resistor connected at one end to the cathode of said diode and at the other end to the positive terminal of said secondary battery, said transistor means being of the PNP type, said transistor means emitter being connected to the junction of said first resistor and said diode and a second resistor connected between said transistor means collector and to the negative terminals of said batteries, said second circuit means for sensing the current in a portion of said first circuit means including a means connecting the base of said transistor means to the junction between said first resistor and said positive terminal of said secondary battery.

6. A timepiece powered by a solar battery comprising a secondary battery, first circuit means connecting the positive terminal of said solar battery with the positive terminal of said secondary battery and the negative terminal of said solar battery with the negative terminal of said secondary battery, a diode in said first circuit with its anode connected to the positive terminal of said solar battery, transistor means having its collector-emitter path extending from the anode of said diode tO the negative terminals of said batteries, and second circuit means connecting the base of said transistor means and said first circuit means.

7. A timepiece as defined in claim 6, wherein said second circuit means comprises a resistor and a thermistor in series, the resistor being connected to the positive terminal of said solar battery, the thermistor being connected to the negative terminal of said solar battery, the base of said transistor being connected to the junction between said resistor and said thermistor.

8. A timepiece as defined in claim 6, wherein said transistor is of the PNP type.