Isolated output system for a class D switching-mode amplifier

• US 3,899,745 A
• Filed: 04/26/1974
• Issued: 08/12/1975
• Est. Priority Date: 04/26/1974
• Status: Expired due to Term

• Current Assignee: Fletcher James C Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Martial A. Honnell
• Original Assignee: Fletcher James C Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, Martial A. Honnell
• Inventors: Honnell, Martial A., Fletcher, James C. Administrator of the National Aeronautics and Space (N/A)
• Primary Examiner(s): Kaufman, Nathan
• Application Number:
  US05/464,723
• Time in Patent Office: 473 Days
• Field of Search: 330/27A,10 307/261,262
• US Class Current: 330/251
• CPC Class Codes: H03F 3/217 Class D power amplifiers; Switching amplifiers
• CPC Class Codes: H03F 3/38 DC amplifiers with modulator at input and demodulator at output; Modulators or demodulators specially adapted for use in such amplifiers switched capacitor amplifiers H03F3/005

Abstract

A Class D amplifier for the amplification of signals having unipolar or bi-polar direct current, or alternating current, content comprising positive and negative signal channels and including a transformer-coupled output circuit for each channel which includes a switching circuit which effects isolation of the nonoperating channel from the operating channel as a function of signal polarity.

Claims

1. A Class D amplifier comprising:

input signal means responsive to an input signal for providing a first signal output corresponding to the positive polarity content of said input signal and a second signal output corresponding to the negative polarity content of said input signal;

first and second pulse-width modulators, said first modulator being responsive to said first output for providing a chain of first output pulses wherein the width of each pulse is proportional to the instantaneous level of said first output, and said second modulator being responsive to said second output for providing a chain of second output pulses wherein the width of each pulse is proportional to the instantaneous level of said second output;

a DC power source;

a first output stage comprising;

first switching means comprising a two-terminal switched circuit responsive to the presence of a said first output pulse for presenting a closed circuit and otherwise presenting an open circuit, a first transformer comprising a primary winding and at least one secondary winding, connecting means connecting said power source in series with said primary winding and said two-terminal switched circuit, and second switching means comprising a two-terminal switched circuit in series with said secondary winding and being responsive to a discrete polarity output of said transformer for providing a first stage output from said first secondary winding of a first polarity and responsive to the release of stored energy previously supplied through said primary winding to the core of said first transformer, and otherwise said second switching means blocking current flow through said secondary winding;

a second output stage comprising;

third switching means comprising a two-terminal switched circuit responsive to the presence of a said second output pulse for presentIng a closed circuit and otherwise presenting an open circuit, a second transformer comprising a primary winding and at least one secondary winding, connecting means for connecting said power source in series with said primary winding of said second transformer and said two-terminal switched circuit of said third switching means, and fourth switching means comprising a two-terminal switched circuit in series with said secondary winding of said second transformer and being responsive to a discrete polarity output of said second transformer for providing a second circuit output from said secondary winding of said second transformer of a second polarity responsive to the release of stored energy previously supplied through said primary winding of said second transformer to the core of said second transformer and otherwise said fourth switching means blocking current flow through said secondary winding of said second transformer; and

filter means coupled to receive said first and second circuit outputs of said first and second output stages for eliminating pulse switching occurrences and thereby recreating an amplified replica of said input signal.

2. A Class D amplifier as set forth in claim 1 further comprising a first diode in circuit between said second switching means and said filter means polarized to pass current from said first output stage only in a first direction and a second diode in circuit between said fourth switching means and said filter means polarized to pass current only in a second direction, whereby current flow between said output stages are blocked and said output stages are isolated one from the other.

3. A Class D amplifier as set forth in claim 2 wherein each said transformer includes a second secondary winding and wherein:

said second switching circuit comprises a transistor, the collector-emitter circuit of which is connected in circuit with said first secondary transformer winding of said first transformer and the base-emitter circuit of which is connected in circuit with said second secondary winding of said first transformer; and

said fourth switching means comprises a transistor, the emitter-collector circuit of which is connected in circuit with said first secondary winding of said second transformer and the base-emitter circuit of which is connected in circuit with said second secondary winding of said second transformer.

4. A Class D amplifier as set forth in claim 2 wherein said amplifier includes an electrical resistance load and said filter means comprises an electrical capacitor connected in parallel with said resistance load.

5. A Class D amplifier as set forth in claim 2 further comprising negative feedback means interconnected between said filter means and said input signal means for reducing distortion products generated within said amplifier.