BATTERY CHARGING AND DISCHARGING BY USING A BI-DIRECTIONAL TRANSISTOR

• US 20100277125A1
• Filed: 07/16/2010
• Published: 11/04/2010
• Est. Priority Date: 01/21/2003
• Status: Active Grant

• Current Assignee: Microsemi Corporation (Microchip Technology Incorporated)
• Original Assignee: Microsemi Corporation (Microchip Technology Incorporated)
• Inventors: Ferguson, Bruce R.
• Granted Patent: US 8,193,779 B2
• Time in Patent Office: Days
• US Class Current: 320/128
• CPC Class Codes: H02J 2207/30 Charge provided using DC bus or data bus of a computer
• CPC Class Codes: H02J 7/0047 with monitoring or indicating devices or circuits
• CPC Class Codes: H02J 7/007182 in response to battery voltage
• CPC Class Codes: H02J 7/04 Regulation of charging current or voltage

Abstract

A battery charger for an electronic device receives current limited power from an external power source, such as a Universal Serial Bus power interface. The battery charger can linearly regulate a charging current to an internal battery and limit the charging current so as not to demand current in excess of what the external power source can provide. A bi-directional pass element coupled between a system power terminal and the internal battery controls the charging current and effectively isolates the internal battery from a system load during charging of the battery while providing a low impedance path from the internal battery to the system load during discharging of the battery.

Claims

1. A battery charger comprising:

a first input configured to accept DC power from an AC adapter;

a second input configured to accept DC power from a Universal Serial Bus power interface;

a first output configured to provide power to a system load;

a second output configured for connection to a battery;

a bi-directional pass element coupled between the first output and the second output, wherein the bi-directional pass element conducts a charging current in a first direction to the second output during charging of the battery and conducts a discharging current to a second direction from the second output during discharging of the battery; and

a charging controller configured to regulate the charging current of the bi-directional pass element based on the current flow from the Universal Serial Bus power interface.

2. The battery controller of claim 1, wherein the bi-directional pass element is a P-channel enhancement mode MOSFET.

3. The battery controller of claim 2, wherein the P-channel enhancement mode MOSFET comprises a configurable body contact.

4. The battery controller of claim 1, further comprising a comparator coupled across the bi-directional pass element to sense the voltage polarity of the bi-directional pass element and to connect a body contact accordingly.

5. The battery controller of claim 1, further comprising a switching diode coupled across the bi-directional pass element to assist in a transient response of the battery.

6. The battery controller of claim 5, wherein the bi-directional pass element comprises a body contact that connects to a channel terminal with a relatively higher voltage during a shutdown mode to prevent current flow in a body diode and to disconnect the battery.

7. The battery controller of claim 1, further comprising a bi-directional pass element driver that controls a gate voltage with respect to a body terminal of the bi-directional pass element to control the level of the charging current or the discharging current.

8. The battery controller of claim 1, further comprising:

a current sensor that outputs a current sense voltage indicative of the level of current supplied by the Universal Serial Bus power interface; and

an error amplifier that compares the current sense voltage to a reference level and overrides a feedback control signal to reduce the charging current when the current sense voltage exceeds the reference level.

9. The battery charger of claim 1, further comprising:

a first isolation circuit coupled in series between the first input and the first output to prevent current flow in a reverse direction to the first input;

a first bypass transistor coupled across the first isolation circuit;

a second isolation circuit and a current sensing circuit coupled in series between the second input and the first output, wherein the second isolation circuit is connected in parallel with the first isolation circuit to the first output, and wherein the second isolation circuit prevents current flow in a reverse direction to the second input, and the current sensing circuit measures the current flow from the Universal Serial Bus power interface; and

a second bypass transistor coupled across the second isolation circuit, wherein the first bypass transistor and the second bypass transistor are selectively enabled to couple an output of the AC adapter or an output of the Universal Serial Bus power interface to the first output.

10. The battery charger of claim 1, wherein the primary power source is provided by an AC adapter and the secondary power source is provided by the Universal Serial Bus power interface.

11. The battery charger of claim 1, further comprising a current limiter coupled between the Universal Serial Bus power interface and the second input to ensure that a supply current is less than a predetermined level.

12. The battery charger of claim 1, wherein the battery controller automatically enters a discharge mode when a supply current exceeds a predefined level.

13. The battery charger of claim 1, further comprising a dual input source selector connected to the first input and the a second input, wherein the dual input source selector selectively couples the DC power from the AC adapter or the DC power from the Universal Serial Bus power interface, the dual input source selector configured to automatically disconnect the DC power from the Universal Serial Bus power interface when the DC power from the AC adapter is available.

14. The battery charger of claim 1, wherein the battery controller linearly regulates charging current and limits charging current to ensure that a supply current is less than a reference level.

15. The battery charger of claim 14, wherein the reference level is selectable from a plurality of predefined limits.