DCDC for RF Equipment

Objectives

Other than the general technical goals the main objectives of this R&D project are to develop, test and qualify DC/DC converters for RF equipment which will:

  • Be flexible with respect to the application and platform interfaces,
  • Be compatible with all orbits : GEO Telecom, other potential applications on LEO or MEO orbits,
  • Have significantly lower cost than our actual solution of LPLC plus external circuitry, or than competitors such as EMS (a Canadian Company) or others offer,
  • Meet the volume and mass constraints (reduced with respect to our actual LPLC based solution,
  • Meet the efficiency targets despite the requirement for series regulators on a large number of outputs (very low output noise constraints),
  • Ensure simple mechanical and thermal interfaces despite the relatively high power losses and associated dissipative components.

The RF application serving as a basis for this project was that of a transponder for which 2 types of DCDC converter, differing mainly in power level (33W and 7W) are required as indicated by the following diagram:


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The general constraints are, however, applicable to most RF equipment.

Challenges

The key issues solved by the project are:

  1. Compatibility with a wide input voltage range (20V to 50V) and a wide range of input bus EMC constraints, i.e. multi-platform,
  2. High regulation precision for up to 5 output voltages from a single converter,
  3. Very low output ripple and noise requirements, e.g. 2mVrms on certain outputs,
  4. Sequencing between the negative voltage and 2 or 3 of the other, positive, outputs,
  5. Good efficiency, particularly for the Rx converter which operates continuously, often in a low power mode (2W),
  6. Integrated solution,
  7. Competitive cost.

Benefits

An integrated DCDC for RF solution compatible with a wide range of platforms given the wide input voltage range compatibility, as well as the input EMC approach consisting of applying the most stringent of the different EMC CE/CS requirements.

The simple mechanical implementation (all components, including power elements, are mounted on the PCB) also allows the design to be independent of the user mechanical development as long as the fixation points and thermal conductivity at those fixation points are respected.

Features

The two types of converter are both based on a forward topology, the higher power converter (Tx) using the forward active clamp (FAC) variant. The basic functional diagrams are shown below:

Figure 1: TX DC/DC Converter block diagram


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Figure 2 : RX DC/DC Converter block diagram


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With respect to the physical interfaces the DCDC converters are provided as open board solutions, i.e. no mechanical housing or other element, with the main bus interfacing to the board via a dedicated sub-D connector while all other input or output connections are provided via solder pads at PCB level. The thermal and mechanical interfaces are ensured via the fixation points of the PCB’s.

Images of the resulting boards are provided below:

RX DCDC Converter

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TX DCDC Converter

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Plan

The following activities were foreseen:

  1. Design, development and analysis of 2 separate DCDC’s characterised notably by 2 different output power levels: one for a RF transmitter (Tx / 33W) and one for a RF receptor (Rx / 7W),
  2. Manufacturing of 2 EQM’s, 1 Tx DCDC and 1 Rx DCDC,
  3. Qualification testing of the 2 EQM’s: functional, performance, EMC, vibration, mechanical shock, thermal vacuum and humidity tests.

All activities have been successfully completed.

 

Current status

All activities are completed. The qualification of the 2 EQM’s was completed on the 4th December 2009. The TRB/DRB was held on the 09/02/2010.

Contacts

Status date

Tuesday, December 7, 2010 - 13:28