Efficient power amplifier for high capacitive devices

• US 4,628,275 A
• Filed: 07/29/1985
• Issued: 12/09/1986
• Est. Priority Date: 07/29/1985
• Status: Expired due to Fees

• Current Assignee: Rockwell International Corporation
• Original Assignee: Rockwell International Corporation
• Inventors: Long, Steven M., Skipper, John D.
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US06/759,717
• Time in Patent Office: 498 Days
• Field of Search: 330/10, 330/102, 330/105, 330/207 A, 330/251
• US Class Current: 330/10
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence
• CPC Class Codes: H10N 30/802 Drive or control circuitry or methods for piezoelectric or electrostrictive devices not otherwise provided for

Abstract

An efficient power amplifier for high-capacitive device C2 in load string 10. The load string 10 includes a reference capacitor C3, a resistor R1, and an inductor L1. A large capacitor C1 is connected to load string 10 through high voltage power bridge 28. A current sensing feedback 30 is utilized to produce a triangular waveform of current in load string 10 for causing charge to be alternatively removed from capacitor C1 and delivered to device C2 through inductor L1 and then returned to capacitor C1 with any losses replenished by the dc power source. A voltage sensing feedback 14 is used to modulate the triangular current waveform. The power amplifier behaves as a stable linear dc coupled operational amplifier delivering a large reactive current with only slight losses.

Claims

1. A power amplifier circuit for driving a high-capacitive device, comprising:

a load string including inductive means connected to said device;

capacitive means connected to said load string, wherein during operation of said circuit said inductive means exchanges energy between said device and said capacitive means;

a dc power source for charging said capacitive means;

means for producing a full wave alternating triangular waveform of current in said load string including,

current sensing means connected to said load string, and

comparing means connected to said current sensing means for comparing current circulating in said load string to equal and opposite polarity reference levels so that equal charge is alternately removed from said capacitive means and delivered to said device through said inductive means then returned to said capacitive means with any losses replenished by said dc power source;

means connected to said load string for sensing charge contained in said high capacitive device and to modulate said full wave alternating triangular current waveform;

whereby, said amplifier behaves as a stable linear dc coupled single pole operational amplifier delivering a large reactive current with only slight losses.

2. The amplifier circuit, according to claim 1, wherein said charge sensing and modulated waveform production means includes:

a reference capacitor connected in series with said load string;

means for summing the voltage across said reference capacitor with an external input voltage said summation resulting in a first error signal;

a first amplifying means for amplifying said first error signal; and

means associated with said amplifying means to introduce phase lead or lag for insuring closed loop stability.

3. The amplifier circuit, according to claim 2, wherein said triangular waveform producing means includes:

a resistor in series with said load string;

second amplifying means for developing dc reference voltages;

means for summing the voltage across said resistor with said first error signal and said dc reference voltages said summation resulting in a second error signal;

first and second comparators for comparing said second error signal;

a plurality of field-efficient transistors connected to said circuit whereby when some of said transistors are ON current flows in one direction through said device and when others are ON the current flows in the reverse direction; and

flip-flop means connected to said comparators and to said transistors for turning the appropriate transistors ON and OFF, and holding the ON/OFF state;

whereby, when the current in said resistor exceeds a comparison level said first comparator presets or clears said flip-flop means to reverse the current flow and when the current in said resistor again exceeds the comparison level said second comparator switches and changes the flip-flop state to again reverse the current flow, thereby resulting in a triangular waveform through said load string.

4. The amplifier circuit, according to claim 3, further including:

a plurality of optically and electrically isolated drive circuits each drive circuit connected to each of said field-effect transistors, said drive circuits for isolating the field-effect transistor drive signls from the rest of said amplifier circuit.

5. The amplifier circuit, according to claim 3, wherein said plurality of field-effect transistors includes a first pair of MOSFETS which when ON allow current to flow in one direction through said load string on one half-cycle and a second pair of MOSFETs which when ON allow current to flow in a reverse direction through said load string.

6. The amplifier circuit, according to claim 5, further including:

a resistor, capacitor, diode combination connected to each of said MOSFETs, so that each MOSFET turns ON slow and OFF fast to prevent an occasion where a MOSFET pair is on for a short period but long enough to place a direct short across said capacitive means.

7. The amplifier circuit, according to claim 6, further including diodes connected to said MOSFETs to steer reverse current that would otherwise flow through each MOSFET bulk diode.

8. The amplifier circuit, according to claim 7, further including zener diodes connected to said MOSFETs to limit any voltage spikes to levels below the MOSFET breakdown voltage to prevent device failure.

9. The amplifier circuit, according to claim 3, further including small capacitors connected to said comparators to filter spurious noise.

10. The amplifier circuit, according to claim 1, wherein said capacitive means includes two capacitors connected in series.

11. The amplifier circuit, according to claim 10, further including:

a second capacitive means connected to said load string; and

a second inductive means connected to said second capacitive means for blocking high frequency noise, whereby, the modulation frequency content of the output signal of said amplifier is reduced.

12. The amplifier circuit, according to claim 1, wherein said dc power source includes:

a bridge rectifier; and

a center tapped transformer connected to said bridge rectifier for producing a bipolar dc output.

13. A power amplifier circuit for driving a high-capacitive device requiring high voltage drive, comprising:

a load string containing a plurality of elements in series, said elements including;

said high-capacitive device,

a reference capacitor grounded at a first end,

a resistor grounded at a first end, and

an inductor,

capacitive means connected to said load string for storing energy during operation, said inductive means exchanging energy between said device and said capacitive means;

a feedback connection from a second end of said reference capacitor to a follower amplifier and then to a summing amplifier, said summing amplifier connected to a voltage input of said power amplifier so that the voltage at the output of said summing amplifier is proportional to the difference between said input voltage and the voltage across said reference capacitor;

first and second voltage generating amplifiers connected to said follower amplifier and said summing amplifier and also connected to a feedback connection from a second end of said resistor, said first voltage generating amplifier for providing a low impedance dc voltage as a positive reference, said second voltage generating amplifier for providing a lower impedance negative reference voltage of equal magnitude;

a first comparator for comparing the summation of said negative reference voltage, the outputs from said follower amplifier and said summing amplifier, and the voltage across said resistor with ground;

a second comparator for comparing the summation of said positive reference voltage, the outputs from said follower amplifier and said summing amplifier, and the voltage across said resistor with ground;

flip-flop means connected to said first and second comparators, said flip-flop means for determining the path for current flow through a power bridge, said power bridge for directing the magnitude and direction of current flow through said load string;

whereby, during operation of said power amplifier a modulated, full wave alternating, triangular waveform of current is produced in said load string for causing charge to be alternately removed from said capacitive means and delivered to said device through said inductive means then returned to said capacitive means, said power amplifier behaving as a stable linear dc coupled operational amplifier delivering a large reactive current with only slight losses.

14. The power amplifier, according to claim 13, wherein said power bridge includes:

a transformer for converting line power to high voltage power;

a plurality of diodes for rectifying said high voltage power so that high voltage dc is stored on said capacitive means;

a plurality of field-effect transistors so arranged and connected to said circuit whereby when some of said transistors are ON current flows in one direction through said device and when others are ON the current flows in the reverse direction; and

a plurality of optically and electrically isolated drive circuits each drive circuit connected to each of said field-effect transistor and to said flip-flop means, said drive circuits for isolating the field-effect transistor drive signals from the rest of said amplifier circuit.