Ray Ring's High-Efficiency Amplifier Design Drives a QRP Ham Transmitter From a 4V Lithium Battery

Engineer Ray Ring has published a design for a high-efficiency amplifier, capable of working at very low supply voltages, and proven its capabilities by building a QRP transmitter capable of operating from a 4V lithium battery.

"This is an example of a high efficiency QRP transmitter designed to work at very low supply voltages (3v-5v)," Ring explains. "It can produce 2 watts at 4 volt supply @ 70% efficiency. It uses small, inexpensive switching MOSFETs. The primary requirement for these MOSFETs is low output capacitance, a VDS of >20V, a logic level VGS and a drain current rating of a couple amps."

"Unlike a Class E amplifier, this design requires no special alignment, providing for multi-band operation easily. Only the output filter consisting of a L Network and Pi network in series need to be changed for a given band. It is tolerant of all kind of load conditions including infinite Z and maintains efficiency when poorly matched. While this circuit utilizes a microcontroller, display and clk generator, the logic buffer can operate from any oscillator source so the amplifier can be adapted to simpler designs."

A schematic which uses the amplifier in a simple 2W QRP transmitter, capable of running from a 4V lithium battery or external 5V power source and driven by a PIC18 microcontroller, has been published to Ring's website Circuit Salad, while a video demonstration is available on YouTube.