Current limiter for power line communication amplifier

• US 4,645,956 A
• Filed: 09/11/1984
• Issued: 02/24/1987
• Est. Priority Date: 09/11/1984
• Status: Expired due to Fees

• Current Assignee: ABB Power T&D Co Inc (ABB Limited)
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Shuey, Kenneth C.
• Primary Examiner(s): Miller, Stanley D.
• Assistant Examiner(s): ROSEEN, RICHARD R
• Application Number:
  US06/649,461
• Time in Patent Office: 896 Days
• Field of Search: 307/270, 307/491, 307/362, 307/297, 307/546, 307/549, 307/557, 307/562, 307/200 A, 323/313, 323/316, 323/317, 328/172-175
• US Class Current: 327/318
• CPC Class Codes: H04B 3/58 Repeater circuits

Abstract

A current limiter is provided which responds to the magnitude of the output current signal from a power amplifier. A full wave rectified signal is provided in response to the magnitude of the current output signal and is used as an input to a comparator. The other input of the comparator is a voltage reference signal that represents a maximum desired current level for the output current signal of the power amplifier. When the output current signal exceeds its reference level, a signal is provided which is used as an input to an exclusive-OR gate which has, as its other input, a modulated square wave signal. The effect of the exclusive-OR gate is to notch the square wave modulated signal in such a way so as to alter its shape. The altered square wave carrier signal causes the MOSFETs of the power amplifier to switch on and switch off at additional occurrences which has the effect of reducing the maximum current level of the output current signal being output by the power amplifier.

Claims

1. An apparatus for limiting an output current of a power amplifier which has a modified phase modulated signal at its input, comprising:

first means for providing a first signal, said first signal being representation of said output current;

second means for providing a second signal, said second signal being representative of a reference magnitude;

means for comparing said first signal and said second signal, said comparing means being configured to provide a third signal, said third signal being indicative of a first occurrence when said first signal exceeds said second signal; and

means for altering a phase modulated signal as a function of said third signal, said altering means providing said modified phase modulated signal at an output which is connected as an input to said power amplifier, said altering means comprising an exclusive-OR gate having as its inputs said phase modulated signal and said third signal.

2. The apparatus of claim 1, wherein:

said first signal providing means comprises a current transformer.

3. The apparatus of claim 1, wherein:

said second signal providing means comprises a resistive voltage divider.

4. The apparatus of claim 1, wherein:

said comparing means comprises a comparator having an inverting input electrically connected with said first signal providing means and a noninverting input electrically connected with said second signal providing means.

5. The apparatus of claim 1, wherein:

said first signal providing means comprises a current transformer;

said second signal providing means comprises a resistive voltage divider;

said comparing means has an inverting input electrically connected with said first signal providing means and a noninverting input electrically connected with said second signal providing means; and

said altering means comprises an exclusive-OR gate having as its inputs said phase modulated signal and said third signal.

6. The apparatus of claim 5, further comprising:

a full wave rectifier electrically connected between a secondary winding of said current transformer and said inverting input of said comparing means.

7. A power amplifier, comprising:

means for switching from a positive voltage to a negative voltage in response to a modified phase modulated signal magnitude, said switching means being configured to alternate its output waveform magnitude between positive and negative levels to form a sinusoidal current signal;

first means, connected to an output of said power amplifier, for providing a first signal representative of said sinusoidal current signal, said first means comprising a current transformer;

means for rectifying said first signal;

second means for providing a reference signal representative of a preselected current magnitude;

means for comparing said first signal and said reference signal, said comparing means being configured to provide a second signal having logic levels which represents a result of a comparison of the magnitudes of said first signal and said reference signal; and

means for changing a phase modulated signal based on a preselected logical level of said second signal and outputting said modified phase modulated signal.

8. The amplifier of claim 7, wherein:

said second reference signal providing means comprises a voltage divider.

9. The amplifier of claim 7, wherein:

said comparing means comprises a comparator having an inverting input electrically connected with said first signal providing means and a noninverting input electrically connected with said second providing means.

10. The amplifier of claim 7, wherein:

said changing means is an exclusive-OR gate having said phase modulated signal and said second signal as its inputs.

11. A current limiter for a switching power amplifier that has a phase modulated input and a current signal output, comprising:

a current transformer electrically connected with the current signal output of said amplifier;

a full wave rectifier electrically connected with a secondary winding of said current transformer, said rectifier producing a first signal representative of said current signal output;

a resistive voltage divider producing a preselected reference signal;

a comparator having its inverting input electrically connected to said first signal and its noninverting input electrically connected to said reference signal, said comparator providing an output representative of relative magnitudes of said first signal and said reference signal; and

an exclusive-OR gate having at its inputs said phase modulated input and said output of said comparator, said exclusive-OR gate having its output electrically connected with the phase modulated input of said power amplifier.