EPCs

Sequenced power converters (also known as EPCs) for FET RF amplifiers need outputs which operate so that the negative (gate) voltage appears first and remains on last. This is because the gate of the RF amplifier FET is enhanced at zero voltage, so the gate must always be negative before the drain voltage is applied.

MDI has designed and manufactured many types of radiation tolerant EPCs, both as complete hermetic hybrid units up to 100 watts as well as assemblies of hybrid modules that can produce sequenced outputs of hundreds of watts, even up to a kilowatt.

Since MDI manufactures standard DC-DC converters able to operate at all the popular satellite bus voltages, our EPCs are also available for all the same bus voltages.

The key features of a typical design are as follows:

• Depending on power level, the power stage topology can be a current mode flyback, a phase staggered current mode flyback or a full bridge
• Input-output isolation is achieved using magnetic coupling
• GaN FETs are used for the power switches
• Output sequencing of the positive outputs is achieved with rad hard output transistor switches
• On-off control can be done by pulse command (latching relay) or by inhibit/enable

When power is removed intentionally or unintentionally, a hold up capacitance internal to the converter supplies the negative output while the positive outputs decay.

To eliminate overshoot when the main output is connected through the transistor switch, the turn on rise time is carefully controlled. This rise time is essentially constant over temperature, aging and radiation effects.

When the negative output exceeds its threshold value (typically 90% of the final value), a delay starts. The customer may specify the nominal delay, which can range from 10 milliseconds to 100 milliseconds. Following the delay, the two transistor switches close, applying the positive voltages to the load. To eliminate overshoot when the main output is connected through the transistor switch, the turn on rise time of the transistor is carefully controlled. This rise time is essentially constant over temperature, aging and radiation effects. The turn off rise time is minimized.