Browse Prior Art Database

Zero Voltage Switching HF Stairstep Power Amplifier

IP.com Disclosure Number: IPCOM000112389D
Original Publication Date: 1994-May-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 86K

Publishing Venue

IBM

Related People

Carpenter, BA: AUTHOR [+3]

Abstract

This invention disclosure describes a power amplifier circuit which runs on a single power input voltage, has higher efficiency, and simpler magnetics than previously known circuits.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Zero Voltage Switching HF Stairstep Power Amplifier

      This invention disclosure describes a power amplifier circuit
which runs on a single power input voltage, has higher efficiency,
and simpler magnetics than previously known circuits.

      Stairstep power amplifiers are known.  The theory behind them
is that for the stairstep waveshape, the second through eighth
harmonics can be eliminated if the amplitudes and timing are
precisely controlled.  Existing stairstep power amplifiers use two
power supplies and a complex 5 winding transformer to produce the
stairstep waveform.  The drawack of this implementation is that
efficiency is limited by several R-C snubbers and by the need to
clamp the transformer to ground.  Thus, all energy in the circuit is
dissipated twice each cycle, this is necessary to keep the circuit
from ringing during the zero voltage portions of its cycle.  As a
result, the prior art amplifiers show an efficiency of only 68%, with
a resistive load.  Since the load is not always resistive, efficiency
is further reduced.

      The invention shows a new and better means to produce a
stairstep waveform.  The schematic is shown in Fig. 1.  The essence
of the invention is to use two zero voltage switching full bridge
phase-controlled power chains.  Timing information for the eight
switches is shown in Fig. 2.

      The two bridges operate off of the same power input, and the
proper transformer ratios are 1:1 and 1:(0.618) as the two chains'
outputs are summed to give the proper waveform.

      The ZVS phase-controlled full bridge is used in the A-12
program power supply.  Note that the zero voltage portion is produced
by clamping the primary of the power transformers back to the power
supply, thus "recycling" reactive power instead of merely dissipating
it.  For this reason, this amplifier has superior efficiency.

      The circuit has three major advantages over the prior art.
This amplifier is intended for use in high frequency sonar systems
(such as advanced mine detection system, HF...