Portable computer containing bidirectional current blocking MOSFET for battery disconnect switching

• US 6,087,740 A
• Filed: 01/14/1998
• Issued: 07/11/2000
• Est. Priority Date: 11/30/1993
• Status: Expired due to Term

• Current Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Original Assignee: Siliconix Incorporated (Vishay Intertechnology Incorporated)
• Inventors: Williams, Richard K.
• Primary Examiner(s): Gaffin, Jeffrey
• Assistant Examiner(s): FLEMING, FRITZ M
• Application Number:
  US09/006,774
• Time in Patent Office: 909 Days
• Field of Search: 307/43, 307/45, 307/46, 307/66, 307/85-87, 307/112, 307/113, 307/125, 307/130, 307/131, 307/139, 327/425, 327/434, 327/534, 327/537, 361/760, 361/761, 361/807
• US Class Current: 307/125
• CPC Class Codes: G06F 1/26 Power supply means, e.g. regulation thereof for memories G11C
• CPC Class Codes: H02J 1/10 Parallel operation of dc sources
• CPC Class Codes: H02J 7/0024 Parallel/serial switching of connection of batteries to charge or load circuit
• CPC Class Codes: H02J 7/0031 using battery or load disconnect circuits H02J9/002 takes precedence
• CPC Class Codes: H02J 7/0034 using reverse polarity correcting or protecting circuits mechanical means of polarity protection H02J7/0045
• CPC Class Codes: H02J 9/061 for DC powered loads
• CPC Class Codes: H03K 17/0822 in field-effect transistor switches
• CPC Class Codes: H03K 17/687 the devices being field-effect transistors
• CPC Class Codes: H03K 17/6874 in a symmetrical configuration
• CPC Class Codes: H03K 17/693 Switching arrangements with several input- or output-terminals, e.g. multiplexers, distributors logic circuits H03K19/00; code converters H03M5/00, H03M7/00

Abstract

A bidirectional current blocking switch is disclosed. The switch includes a four-terminal MOSFET in which there is no source-body short. The voltages applied to the source and drain terminals are both higher than the voltage applied to the body terminal (for an N-channel) device so that the source-body and drain-body junction of the MOSFET never become forward-biased. The switch of this invention is particularly useful for switching a cascaded set of batteries in a portable computer.

Claims

1. A portable computer comprising:

a first battery;

a second battery;

a power supply bus;

a first switch connected in a first current flow path between said first battery and said power supply bus;

a second switch connected in a second current flow path between said second battery and said power supply bus;

wherein said first switch comprises a first MOSFET, said first MOSFET being formed in a semiconductor die and comprising a first source region of a first conductivity type, a first drain region of said first conductivity type, a first body region of a second conductivity type opposite to said first conductivity type separating said first source and drain regions, a first gate separated by a first dielectric layer from a first channel region of said first body region, neither said first source region nor said first drain region being shorted to said first body region, said first body region being connected to a reference voltage and said first source and drain regions being connected in said first current flow path; and

wherein said second switch comprises a second MOSFET, said second MOSFET being formed in said semiconductor die and comprising a second source region of said first conductivity type, a second drain region of said first conductivity type, a second body region of a second conductivity type opposite to said first conductivity type separating said second source and drain regions, a second gate separated by a second dielectric layer from a second channel region of said second body region, neither said second source region nor said second drain region being shorted to said second body region, said second body region being connected to said reference voltage and said second source and drain regions being connected in said second current flow path.

2. The portable computer of claim 1 further comprising an AC/DC converter connected through a third switch to said power supply bus, said third switch being substantially similar in structure to said first and second switches.

3. The portable computer of claim 2 further comprising a terminal for connecting said power supply bus to an external backup battery.

4. The portable computer of claim 1 further comprising a terminal for connecting said power supply bus to an external backup battery.

5. The portable computer of claim 1 further comprising a battery charger connected through a third switch to said first battery, said third switch being substantially similar in structure to said first and second switches.

6. The portable computer of claim 5 further comprising a fourth switch for connecting said battery charger to said second battery, said fourth switch being substantially similar in structure to said first and second switches.

7. The portable computer of claim 5 wherein an input terminal of said battery charger is connected to a terminal of said portable computer to be connected to a power main.

8. The portable computer of claim 5 further comprising an AC/DC converter connected through a fourth switch to said power supply bus, said fourth switch being substantially similar in structure to said first and second switches.

9. The portable computer of claim 5 wherein an input terminal of said battery charger is connected to an output terminal of said AC/DC converter.

10. The portable computer of claim 9 further comprising a terminal for connecting said power supply bus to an external backup battery.