Resonant push-pull switching power amplifier

• US 5,327,337 A
• Filed: 09/01/1992
• Issued: 07/05/1994
• Est. Priority Date: 09/01/1992
• Status: Expired due to Fees

• Current Assignee: FB Commercial Finance, Inc. (FB Corp. (Missouri))
• Original Assignee: Broadcast Electronics, Inc. (Elenos Srl)
• Inventors: Cripe, David W.
• Primary Examiner(s): Dougherty, Thomas M.
• Application Number:
  US07/937,700
• Time in Patent Office: 672 Days
• Field of Search: 363/134, 363/24, 363/97
• US Class Current: 363/134
• CPC Class Codes: H02M 3/3372 of the parallel type
• CPC Class Codes: Y02B 70/10 Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

A highly efficient, tuned, switching power amplifier has components in a circuit configuration which minimizes switching losses and stored energy within the circuit. The circuit includes a pair of switches operating at the carrier frequency at substantially 50% duty. The switches are coupled through a transformer to a load, with the circuit being tuned, taking the particular load into account, so as to minimize the power loss in the switches by ensuring that immediately prior to, and during each, transition of each switch from its non-conducting (off) state to its conducting (on) state, both the voltage across the switch and the first derivative with respect to time of the voltage across the switch are substantially zero.

Claims

1. An apparatus of the tuned switching type for generating alternating current output power, for use with a load representable as a series combination of a load capacitance, a load inductance and a load resistance, said apparatus comprising:

first and second active switching devices each having a low-impedance on state and a high-impedance off state and each having a controlled path having one end connected to a common circuit point;

means for driving said first and second switching devices between said on and off states in alternation at substantially 50% duty;

a coupling transformer having a primary winding with opposite ends respectively connected to the other ends of said controlled paths of said respective switching devices, said primary winding having a center tap, with a source of d.c. power being connectable across said center tap and said common circuit point, said transformer having a secondary winding forming an output of the apparatus, and across which an output signal is generated, and connectable to said load, said output signal having a fundamental frequency;

each controlled path of said first and second switching devices having a parallel capacitance associated therewith, the parallel capacitances of each of said first and second switching devices being equal, said parallel capacitances each having a value which is 0.0386 divided by the product of the fundamental frequency and said load resistance; and

said coupling transformer and said parallel capacitances forming, in combination with said load, a resonant circuit means for creating respective waveforms across said first and second switches for causing the voltage across the controlled path of each switch at the end of said off state to be substantially zero, the voltage across the controlled path of each switch to be substantially zero during a time that switch is in transition from said off state to said on state, and for causing the first derivative with respect to time of the voltage across the controlled path of each switch to be substantially zero at the end of said off state.

2. An apparatus of the tuned switching type for generating alternating current output power, for use with a load representable as a series combination of a load capacitance, a load inductance and a load resistance, said apparatus comprising:

first and second active switching devices each having a low-impedance on state and a high-impedance off state and each having a controlled path having one end connected to a common circuit point;

means for driving said first and second switching devices between said on and off states in alternation at substantially 50% duty;

a coupling transformer having a primary winding with opposite ends respectively connected to the other ends of said controlled paths of said respective switching devices, said primary winding having a center tap, with a source of d.c. power being connectable across said center tap and said common circuit point, said transformer having a secondary winding forming an output of the apparatus, and across which an output signal is generated, and connectable to said load, said output signal having a fundamental frequency;

each controlled path of said first and second switching devices having a parallel capacitance associated therewith, the parallel capacitances of each of said first and second switching devices being equal;

an RF choke connected in series with said center tap of said primary winding of said coupling transformer, said RF choke having an inductance which is greater than twice the square of the voltage of said d.c. power source divided by the product of the fundamental frequency and the desired output power of said apparatus; and

said coupling transformer and said parallel capacitances forming, in combination with said load, a resonant circuit means for creating respective waveforms across said first and second switches for causing the voltage across the controlled path of each switch at the end of said off state to be substantially zero, the voltage across the controlled path of each switch to be substantially zero during a time that switch is in transition from said off state to said on state, and for causing the first derivative with respect to time of the voltage across the controlled path of each switch to be substantially zero at the end of said off state.