GaN COTS CVT

Status

Completed
Status date

2015-11-13
Activity Code

4F.067

Objectives

The objective of this project is to investigate the suitability of commercially available GaN enhancement mode FET for space power switching electronics. This project is peculiar to telecom applications being a flight DC/DC converter, fed by the nowadays common 100V satellite bus and with a power level of 600W. Small converters like POL (Point of Load) are clearly out of scope. We focused on 200V rated GaN components with a high current capability with the true enhancement mode or cascode assembly.

The main steps were:

A product survey

It has been performed in 2013 on components suitable for GaN power switching (transistors and components specific to GaN power conversion like drivers).

Component procurement and preliminary evaluation

The relevant parts have been procured with a lot of difficulties (availability problems). Their preliminary performances have been measured.

Design, manufacturing and testing of GaN switching converter:

The breadboard has been based on a converter: The resonant SMART. It has been designed with GaN FET components, including the feedback control loop. Simulations have been performed prior manufacturing and the Elegant Breadboard has been intensively tested (also in temperature).

Final Elegant Bread Board picture.

SYSTEM ARCHITECTURE

The architecture proposed in this project is based on the DUAL EPC application. It is a resonant SMART : it consists in a power buck followed by a resonant push-pull.

The resonant push-pull uses a High Voltage transformer followed by High Voltage rectifiers and High Voltage filter capacitors.

The feedback control loop has been also included in the breadboard.

Benefits

The GaN components are promising parts: one of the main advantages is their switching speed. They are able to turn “ON” 100V in 2 ns.

Thanks to their performances, we are able, in the overall GaN DUAL EPC converter, to drastically reduce the mass ( lower size of all magnetic components and half of high voltage capacitors values) while keeping an efficiency (at ambient temperature) similar to the efficiency of a “classical” DUAL EPC (made with silicon components).

Features

As the GaN technology is not mature enough at manufacturer level, we cannot foresee yet to use those components in space applications, in particular in our EPC equipment.

Nevertheless, as the market is still growing, we continue to perform an active survey.

Plan

The first phase consisted in selecting the components:

We performed a market survey in order to identify several manufacturers /sources.

Then, we tried to purchase the parts but did not manage to get samples from all the manufacturers we chose.

We selected the components after the analysis of the datasheets and the complementary testing we performed.

Afterwards, we selected a converter topology based on one of our applications and we built small switching cells breadboards in order to make an evaluation.

The second phase consisted in designing, implementing and manufacturing the breadboard (converter) and then testing it.

Current status

The project is now achieved. The results obtained are conform with our expectations. One of the first conclusion is that GaN is a very interesting component, very fast but not yet mature for space activities.

Nevertheless, as the market is still growing, we continue to perform an active survey.