Power control system for periodically and selectively energizing or shorting primary windings of transformers for controlling the output voltage across a common secondary winding

• US 4,717,889 A
• Filed: 09/02/1986
• Issued: 01/05/1988
• Est. Priority Date: 09/02/1986
• Status: Expired due to Fees

• Current Assignee: Electro-Voice Inc (Robert Bosch GmbH)
• Original Assignee: Electro-Voice Inc (Robert Bosch GmbH)
• Inventors: Engelmann, Rudolph H.
• Primary Examiner(s): BEHA JR, WILLIAM
• Application Number:
  US06/902,934
• Time in Patent Office: 490 Days
• Field of Search: 363/17, 363/43, 363/16, 363/131, 363/90, 323/301, 323/247, 323/328, 323/258, 323/345, 323/343, 323/361, 330/10, 330/297
• US Class Current: 330/297
• CPC Class Codes: H03F 1/0227 using supply converters

Abstract

A power supply includes a plurality of transformers with individual primary windings, having one end connected in common, respectively, the transformers sharing a secondary winding; a switching network for (1) applying alternate polarity DC voltages to the commonly connected ends of the primary windings over each half-cycle of a clock signal, and relative to these commonly connected ends of the primary windings, (2) applying the same or opposite polarity DC voltages individually to the other ends of the primary windings, over each half-cycle of the clock signal, and in different combinations dependent upon the amplitude or level of a command signal at any given switching time, for producing a pulsed AC waveform in the secondary winding that is amplitude modulated by the command signal.

Claims

1. A method for processing an electrical quantity in a system including a plurality of transformers each having a primary winding, each sharing a common secondary winding, comprising the steps of:

A. selectively shorting given ones of said primary windings; and

B. periodically connecting the remaining ones of said primary windings in parallel across a source of current for passing pulses of current through each one of these said primary windings in a given direction, for inducing an electrical quantity of desired value and waveshape in said secondary winding.

2. The method of claim 1, further including the step of selectively changing the combination of effective and ineffective ones of said primary windings for changing the level of either the secondary voltage or current to a new desired level.

3. The method of claim 1, further including the steps of:

(C) selectively changing the combinations of effective and ineffective ones of said primary windings, and repeating steps (A) and (B) for inducing a voltage into said secondary winding that approximates the waveform of a command signal; and

(D) rectifying the AC voltage developed across said secondary winding for obtaining a DC voltage that is amplitude modulated by said command signal.

4. The method of claim 1, further including the steps of:

selecting one of said primary windings to serve as an idle voltage primary winding; and

passing current through said idle voltage primary winding alternately and successively, in a periodic manner, in opposite directions through said primary winding, for inducing an idle voltage in said secondary winding.

5. An amplitude modulated power supply comprising:

a source of direct voltage

a plurality of transformers each having a primary winding, and each sharing a common secondary winding;

switching means for (1) selectively shorting either one or a combination of said plurality of primary windings, and (2) periodically connecting in parallel with one another and with said source of direct voltage the remaining ones of said plurality of primary windings for causing pulses of current to flow through these windings in a given direction, thereby causing voltage pulses of desired amplitude, polarity, and duration to be induced into said secondary winding; and

wherein said control means includes ROM based waveform generator means for producing said AC command signal.

6. The amplitude modulated power supply of claim 5 further including rectifier means connected to said secondary winding for rectifying said amplitude modulated voltage pulses to produce a DC output voltage that is a discrete amplitude modulated DC representation of said AC command signal, whereby each discrete voltage level of said amplitude modulated DC output voltage represents an instant amplitude value of said command signal.

7. The amplitude modulated power supply of claim 5, wherein said plurality of transformers are each provided by laminated cores for switching frequencies below 2 kHz, tape wound cores for frequencies from about 2 kHz to 20 kHz, and ferrite cores of either toroidal, pot, or E-core configuration for frequencies above 20 kHz.

8. The amplitude modulated power supply of claim 5, wherein said control means includes:

rectifier means for full-wave rectifying said command signal;

analog-to-digital (A/D) converter means for converting said rectified command signal, varying on a continuum to a digitized command signal;

oscillator means for providing a plurality of clock signals;

switch driver means responsive to both said digitized command signal and to at least one clock signal from said oscillator means, for providing a plurality of control signals for operating said switching means.

9. The amplitude modulated power supply of claim 8, wherein said switching means includes:

first switch means responsive to said one clock signal being either "high" or "low" for applying either -E volts or +E volts, respectively, to one end of each one of said plurality of primary windings connected in common therebetween;

AC common means for terminating the other end of a selected one of said plurality of primary windings to an AC ground reference point;

a plurality of second switch means responsive to individual ones of said control signals being either "high" or "low" for applying either -E volts or +E volts, respectively, to the other ends of the other ones of said plurality of primary windings;

said switch driver means providing said control signals over each half-cycle of operation for (1) operating selected ones of said second switch means in phase with said first switch means, for rendering ineffective the primary windings associated with the selected ones of said second switch means, and (2) operating the other ones of said second switch means out of phase with said first switch means, for producing said voltage pulses of desired polarity, amplitude, and duration in said secondary winding, the amplitude of said voltage pulses being related to the combination of shorted primary windings at any given time.

10. The amplitude modulated power supply of claim 9, wherein the combination of said first switch means, AC ground means, and selected one of said plurality of primary windings responsive to said one clock signal, cause a pulse train of minimum amplitude pulses to be induced into said secondary winding for providing an "idle voltage" regardless of the operation of said second switch means.

11. The amplitude modulated power supply of claim 10, wherein said common reference means includes first and second capacitors connected in series between said first and second terminals of said source of DC voltage, said reference point being the common connection between said capacitors.

12. The amplitude modulated power supply of claim 5, wherein said predetermined frequency is greater than 20.0 kHz, and said plurality of transformers include:

a first plurality of stacked ferrite cores upon each of which a primary winding is individually wound;

a second plurality of stacked ferrite cores upon which stack said secondary winding is wound; and

means for inductively coupling together said first and second plurality of stacked ferrite toroid cores.

13. The amplitude modulated power supply of claim 12 wherein said coupling means consists of a one-turn closed loop of copper tubing inserted through the first and second plurality of stacked ferrite toroid cores.

14. The amplitude modulated power supply of claim 8, wherein said rectifier means includes:

first and second operational amplifier means each having a non-inverting terminal, an inverting terminal, and an output terminal;

a reference potential connected to said non-inverting terminal of said first operational amplifier means;

first and second input resistors each having one end for receiving said command signal, and another end connected to said inverting terminal of said first operational amplifier, and non-inverting terminal of said second operational amplifier, respectively;

a feedback resistor connected between said inverting and output terminals of said first operational amplifier means;

a capacitor connected in parallel with said feedback resistor;

a direct connection between the inverting input and output terminals of said second operational amplifier, to form a voltage follower;

first and second diodes having commonly connected anode electrodes, said first diode having a cathode electrode connected to the output of said comparator means, said second diode having a cathode electrode;

second and third diodes having commonly connected anode electrodes, and cathode electrodes connected to the output of said second operational amplifier and cathode electrode of said second diode, respectively;

a load resistor connected between the cathode electrode of said second diode and a source of reference potential, said full-wave rectified AC command signal being developed across said load resistor; and

first and second terminating resistors connected from the common connections of the anodes of first and second diodes, and third and fourth diodes, respectively, each to a source of voltage.

15. The amplitude modulated power supply of claim 8, wherein said analog-to-digital converter means includes:

a voltage comparator having a non-inverting terminal for receiving said full-wave rectified AC command signal from said rectifier means, an inverting terminal, and an output terminal;

binary digital counter means including an up/down terminal connected to said output terminal of said comparator means, a clock terminal for receiving one of said plurality of clock signals from said oscillator means, and an output terminal;

digital-to-analog (D/A) ladder network means including an input terminal connected to the output terminal of said counter means, and an output terminal connected to the inverting terminal of said comparator means; and

latch means including an input bus connection to the output of said counter means, for temporary storage of binary digital count outputs from said counter as a stable digital command signal;

said D/A means providing a feedback signal to said comparator means for ensuring in closed load manner that the digital count from said counter means is an accurate digital representation of the level of said rectified AC command signal which is the reference for the comparator means, whereby the output of said comparator means goes high whenever said feedback signal is lower in level than said rectified command signal, for causing said counter means to count up, and the output of said comparator means goes low whenever said feedback signal is higher in level than said rectified command signal, for causing said counter means to count down.

16. The amplitude modulated power supply of claim 5, wherein said AC command signal is a fixed amplitude waveshape, and said power supply further includes means for selectively adjusting the amplitude of said waveshape for configuring the power supply as a variable output transformer.

17. The amplitude modulated power supply of claim 5, wherein said control means includes ROM based waveform generator means for producing said AC command signal.

18. The amplitude modulated power supply of claim 6, wherein said AC command signal consists of an audio signal, and said DC output voltage from said rectifier means is applied as a DC power source for an audio amplifier amplifying said audio signal, whereby the power efficiency of said audio amplifier is enhanced.

19. A power conversion system comprising:

transformer means having a plurality of first cores each with an individual primary winding, a second core with a secondary winding, and means for electromagnetically coupling said first cores with said second core for transforming voltage/current relationships between said plurality of primary windings and said secondary winding in combination;

a source of DC voltage;

switching means for periodically both (1) shorting selected ones of said primary windings, and (2) individually applying said DC voltage source in one polarity across each of the unshorted ones of said primary windings in one-half cycle of operation, and in opposite polarity over the next half-cycle of operation, for periodically inducing desired levels of pulsed voltage and current in said secondary winding;

means for producing a plurality of signals for controlling the level of voltage across and magnitude of current through said secondary winding;

control means for operating said switching means at a predetermined frequency and responsive to said plurality of signals for producing said voltage/current pulses in said secondary winding.