Output protection scheme for unipolar constant current source

• US 5,067,045 A
• Filed: 05/30/1989
• Issued: 11/19/1991
• Est. Priority Date: 07/01/1987
• Status: Expired due to Fees

• Current Assignee: Square D Company (Schneider Electric SE)
• Original Assignee: Square D Company (Schneider Electric SE)
• Inventors: Schweiger, Thaddeus J.
• Primary Examiner(s): Pellinen, A. D.
• Assistant Examiner(s): JACKSON, STEPHEN W
• Application Number:
  US07/358,746
• Time in Patent Office: 903 Days
• Field of Search: 361/56, 361/26, 361/91, 361/110, 361/111, 330/207 P, 330/278, 389/331, 389/412
• US Class Current: 361/56
• CPC Class Codes: H02H 9/04 responsive to excess voltage lightning arrestors H01C7/12, H01C8/04, H01G9/18, H01T

Abstract

A protection circuit for the output stage of an operational amplifier may utilize two diodes and two resistors. A circuit for protecting electronic components from the voltage on the cable has an operational amplifier having the signal connected to an input, a diode oriented to conduct the signal from an output of the operational amplifier to the cable, and a diode for shunting a voltage, of a polarity opposite the polarity of the signal, from a first conductor of the cable to a second conductor of the cable, and at least one resistor for limiting current flow to the second diode.

Claims

1. A protective circuit protecting electronic components transmitting an unipolar time varying signal from extraneous surge voltages on a cable, comprising:

unipolar output means for providing an output conductive path for a signal voltage driven into said cable, and for blocking the extraneous voltages having a first polarity on said cable from entering said output means;

shorting means for essentially shorting the extraneous voltages having a second polarity on said cable from a first conductor of said cable to a second conductor of said cable.

2. The apparatus, as in claim 1, wherein said output means comprises:

an operational amplifier having said signal applied to an input; and

a diode driven by an output of said operational amplifier; and

said cable is driven by a current flowing through said diode.

3. The apparatus as in claim 1 wherein said shorting means is a diode in forward conduction, said diode only in a conduction state when said second polarity extraneous voltage is present.

4. A protective circuit protecting electronic components transmitting an unipolar time varying signal from extraneous voltages on a cable comprising:

an operational amplifier having said unipolar signal connected to an input;

a diode oriented to conduct said unipolar signal from an output of said operational amplifier to said cable, and to block extraneous voltages of the same polarity but of greater magnitude than said unipolar signal; and

a second diode for essentially shunting a voltage of a polarity opposite the polarity of said unipolar signal from a first conductor of said cable to a second conductor of said cable.

5. The apparatus as in claim 4 further comprising:

at least one resistor to limit current flow through said second diode.

6. A protective circuit protecting electronic components transmitting an unipolar time varying signal to a cable from extraneous surge voltages on the cable, comprising:

unipolar output means for providing an output conductive path through a first terminal and a second terminal for a signal voltage driven into said cable, and for preventing the extraneous voltages having a first polarity on said cable from applied to said output means, said output means being self actuated by said signal and by said extraneous voltage;

shorting means for essentially shorting the extraneous voltages having a second polarity on said cable, said shorting means connected between said first terminal and said second terminal, said shorting means being self actuated by said extraneous voltage.

7. The protective circuit of claim 6 wherein said unipolar output means comprises:

an operational amplifier having said signal applied to an input; and

a diode driven by an output of said operational amplifier; and

said cable is driven by a current flowing through said diode.

8. The apparatus, as in claim 7 wherein said shorting means is a diode forward biased by the extraneous voltage having a second polarity.

9. A protective circuit protecting electronic components transmitting an unipolar time varying signal to a cable from extraneous surge voltages on the cable, comprising:

an operational amplifier having said unipolar signal connected to an input which transmits signal current conducted by said cable;

a blocking diode in series with said operational amplifier oriented to conduct said unipolar signal from an output of said operational amplifier, in a designed forward conduction mode, to said cable through a diode output terminal, and to block extraneous voltage of the same polarity but of greater magnitude than said unipolar signal by having a relatively high peak inverse voltage to prevent said blocking diode from conducting in an undesired reverse conduction mode; and

a shorting diode essentially shunting a voltage of a polarity opposite the polarity of said unipolar signal in a forward conduction mode connected between said operational amplifier input and said diode output terminal, said shorting diode being of the same diode type as that of said blocking diode.

10. The protective circuit of claim 9 further including:

at least one limiting resistor in series with said shorting diode reducing the amount of current conducted by said shorting diode, connected in a manner which avoids applying the voltage developed across said at least one limiting resistor across said operational amplifier and said shorting diode.

11. The protective circuit of claim 10 wherein said at least one limiting resistor is an input limiting resistor and an output limiting resistor, said input limiting resistor is connected between said input and a first conductor of said cable, and said output limiting resistor is connected between said output terminal and a second conductor of said cable.

12. The protective circuit of claim 9 wherein:

said shorting diode can not affect said unipolar signal.

13. A cable driving and protective circuit transmitting an unipolar time varying signal to a cable and protecting the cable driving and protective circuit from extraneous surge voltages on the cable, comprising:

an operational amplifier having an input and an output, and having said unipolar signal connected to an input, said operational amplifier transmitting unipolar signal current to said cable;

a blocking diode connected to the output of said operational amplifier oriented to conduct said unipolar signal from the output of said operational amplifier, in a designed forward conduction mode with a low forward voltage drop, to said cable through a diode output terminal, and to block extraneous voltage of the same polarity but of greater magnitude than said unipolar signal by having a relatively high peak inverse voltage to prevent said blocking diode from conducting in an undesired reverse conduction mode; and

a shorting diode essentially shunting a voltage of a polarity opposite the polarity of said unipolar signal in a forward conduction mode connected between the input of said operational amplifier and the output terminal of said diode said shorting diode being of the same diode type as that of said blocking diode.