Application Note: A Broadband, 500-Watt, Push-Pull Amplifier

By Ben Caccavale, Spectrum Devices

This application note describes a reference design for a power amplifier that provides continuous operation in the 2 to 30 MHz HF band, achieving 500 watts with a minimum gain of 14 dB. The module uses a push-pull design, which reduces even order harmonics. Operating at 50 volts, this reference design uses broadband 9:1 impedance transformers and negative feedback to maintain a gain flatness of 1 dB across the frequency band. A built-in bias power supply allows for Class AB operation. A 1,700- watt power amplifier system can be realized by combining four power modules with a broadband four-way splitter and combiner. The push-pull power module uses Spectrum Devices' HF50- 220 bipolar power transistors and can be modified to use the thermally enhanced HF50-250 power transistors.