Automatic ranging current shunt

• US 7,276,893 B2
• Filed: 02/28/2005
• Issued: 10/02/2007
• Est. Priority Date: 02/28/2005
• Status: Active Grant

• Current Assignee: Keithley Instruments, Inc.
• Original Assignee: Keithley Instruments, Inc.
• Inventors: Goeke, Wayne C., Banaska, John G.
• Primary Examiner(s): Nguyen; Ha Tran
• Assistant Examiner(s): Nguyen; Trung Q.
• Application Number:
  US11/067,953
• Publication Number:
  US 20060192547A1
• Time in Patent Office: 946 Days
• Field of Search: None
• US Class Current: 324/115
• CPC Class Codes: G01R 15/09 Autoranging circuits

Abstract

A range-changing circuit includes an array of graduated impedances in serial relationship, and a voltage sensing and limiting switch across one of said impedances. The switch limits the voltage across said one of the impedances in response to a voltage sensed by the switch.

Claims

1. A range-changing circuit for a measurement device having a desirable range, said circuit comprising:

an array of graduated impedances in serial relationship; and

a voltage sensing and limiting switch across one of said impedances, wherein said switch limits the voltage across said one of said impedances in response to a voltage sensed by said switch and thereby provides a voltage in said desirable range across another of said impedance.

2. A circuit according to claim 1, wherein said switch includes a zener diode.

3. A circuit according to claim 1, wherein said switch includes a mosfet.

4. A circuit according to claim 3, wherein the channel of said mosfet is in series with a bias voltage, said bias voltage determining said voltage limit.

5. A circuit according to claim 1, wherein said switch includes a back-to-back pair of zener diode.

6. A circuit according to claim 1, wherein said switch includes a back-to-back pair of mosfets.

7. A circuit according to claim 1, wherein said switch is guarded.