BLF369 BLF369

Designers seeking to generate high output power in broadcast and radar systems are nonetheless hoping to do so in the smallest device/circuit footprint possible. For HF/VHF broadcast and UHF radar markets, the new BLF369 LDMOS transistor from Philips Semiconductors is not only compact, but also delivers a generous 500 W CW output power from HF through 500 MHz.

Fast pulse rise and fall times result in large differential current-versus-time (di/dt) values for a device. This is multiplied by whatever inductance is present between the device and the power supply. All of this results in a large voltage swing within the device itself given by V = L di/dt, where V is the voltage swing within the device and L is the inductance between the device and the bias supply.

When evaluating a power transistor for processing a particular type of pulsed waveform, the rise and fall times of the waveform should be well known in order to accurately evaluate a device for that application. Once the specification of the pulse waveform is known, the device should be tested with a waveform that has a rise and fall time AT LEAST as quick as used in the real application.

The SOT800A-housed BLF369, although an unmatched device, was optimized for UHF prior to testing. It was evaluated with est gear from Agilent Technologies (www.agilent.com): an HP8648C signal generator and HP8990A peak power meter. At 440 MHz, device gain was typically 12 dB from 100 to 500 MHz, with 500 W output power across that range. Test conditions included dual drain voltage supplies of +32 VDC and quiescent current draw of 500 mA for each supply. Compression is slight even at 500 MHz, indicating raw power capability.