Battery charger with control circuit

• US 5,694,025 A
• Filed: 04/23/1996
• Issued: 12/02/1997
• Est. Priority Date: 04/23/1996
• Status: Expired due to Term

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Oglesbee, John W., Geren, Michael D.
• Primary Examiner(s): TSO, EDWARD H
• Application Number:
  US08/636,486
• Time in Patent Office: 588 Days
• Field of Search: 320/5, 320/12, 320/49, 320/50, 320/51, 320/53, 320/54, 363/21, 363/84, 363/89
• US Class Current: 320/137
• CPC Class Codes: H02J 2207/20 Charging or discharging characterised by the power electronics converter
• CPC Class Codes: H02J 7/02 for charging batteries from ac mains by converters
• CPC Class Codes: H02M 1/0006 Arrangements for supplying an adequate voltage to the control circuit of converters
• CPC Class Codes: H02M 7/217 using semiconductor devices only
• CPC Class Codes: Y10S 320/29 Transformer having plural secondaries

Abstract

A battery charger (10) is provided with a power supply (26) which is energized by a main winding (22) and a bias winding (24) on the secondary side (18) of an input transformer (14). The charger switches a main voltage level provided at a main voltage output (28) according to a pulse width modulation scheme, and has an output section (36) for filtering the switched voltage. A power switch (38) is coupled between the output section and the main voltage output, and is driven by a bias switch (48) coupled between the control terminal (50) of the power switch, and a bias voltage output (30), which provides a bias voltage level that is higher then the main voltage level by a minimum delta.

Claims

1. A battery charger for charging a battery, comprising:

a power supply, having a return line, for providing a main voltage level at a main voltage output, and a bias voltage level at a bias level output, the bias voltage level being higher than the main voltage level;

an output section for filtering a switched voltage and providing a regulated current to the battery;

a power switch, having a control terminal, coupled between the main voltage output and the output section for switching the main voltage level thereby providing the switched voltage;

a control circuit having a bias switch for switchably connecting the control terminal of the power switch with the bias level output; and

a control network coupled to the control terminal of the power switch.

2. A battery charger as defined by claim 1, wherein the power switch is an N channel MOSFET.

3. A battery charger as defined by claim 1, wherein the output section comprises:

an inductor coupled in series between the battery and the power switch;

a freewheel diode coupled between the power switch and the return line of the power supply; and

an output filter capacitor coupled in parallel with the battery.

4. A battery charger as defined by claim 1, wherein the power supply comprises a transformer having a primary side and a secondary side, the secondary side having a main winding for providing voltage to the main voltage output, and a bias winding for providing voltage to the bias level output.

5. A battery charger as defined by claim 4, wherein said bias winding is coupled in series with said main winding.

6. A battery charger for charging a battery, comprising:

a transformer having a secondary side having a main winding and a bias winding, the main winding providing voltage for a main voltage output, the bias winding providing voltage for a bias level output, the bias level output having a bias voltage level which is higher than a main voltage level at the main level output;

an output section, having a series inductor and a shunt freewheel diode, for filtering a switched voltage and providing a regulated current to the battery;

a power switch, having a control terminal, coupled between the output section and the main voltage output for providing the switched voltage to the output section; and

a control circuit, having a bias switch coupled between the control terminal of the power switch and the bias voltage output.

7. A battery charger as defined by claim 6, wherein the main winding and the bias winding are coupled in series.

8. A battery charger as defined by claim 7, further comprising a bias rectifier coupled to the bias winding, and a main rectifier coupled to the main winding.

9. A battery charger as defined by claim 6, wherein the power switch is a transistor.

10. A battery charger as defined by claim 9, wherein the transistor is a N-channel MOSFET.

11. A battery charger as defined by claim 6, further comprising a control network coupled to the control terminal of the power switch.

12. A battery charger as defined by claim 11, wherein the control network is a pull down resistor.

13. A battery charger as defined by claim 11 wherein the control network comprises an emitter follower.