30 kVA LF/VLF power amplifier module

A high reliability RF power amplifier module (PAM) has been developed for high power LF/VLF transmit systems applications. The PAM is intended for operation in the 14 to 160 kHz frequency range for driving highly reactive loads. It uses a full-bridge configuration of high power field effect transistors (FETs). The PAM replaces four of the current 7.5 kVA modules developed for airborne applications resulting in a reduction in parts count, increased efficiency and increased power output. The new PAM provides efficiencies greater than 90 percent when operating into a reactive load of 70 degree phase angles and greater than 98 percent when operating into a resistive load. A low inductance power and RF interconnect bus structure is employed along with metal oxide semiconductor field effect transistor (MOSFET) power hybrid switching assemblies to minimize switching losses and reduce voltage transients. Protection features have been provided to preclude over current, over temperature and loss of the low voltage power on the RF input drive from causing damage or erroneous operation. Remote control and monitoring is provided through an EIA RS-485 bus interface, allowing RF output control and reporting of status conditions. The RF and control interfaces utilize opto-isolators to provide noise immunity for operation in high noise environments. Cooling is provided by means of a forced air, high performance heat sink assembly resulting in low operating temperatures and high efficiency. The PAM provides an output of thirty kVA into a resistive or reactive load when operating from a 330 V DC source and can be combined with additional modules to form a transmitter power amplifier capable of delivering up to 2 MW to an antenna system.