Radiation Tolerant LED PSU

Power supply unit for emergency lamps that may need to be used in areas with radiation. The power supply consists of a transformer, a diode bridge, capacitors and an optional voltage stabilisation device. It converts a 207V to 253V 50Hz AC to a stable DC voltage and current, as required by the LED load.

Note: It is possible to increase the radiation hardness of the power supply by a factor of up to 10x by replacing the Si diodes with SiC based diodes. This has not yet been implemented in the reference design, but is on our list for future improvements.

Project status: In production.

Video summary of the project [http://cds.cern.ch/record/2135181\]

Functional specifications

Technical Requirements:

Input Voltage: 230V AC RMS
Voltage Tolerance: +/-10%
Input Frequency: 50Hz
Frequency Tolerance: +/- 0.5Hz
Maximum power: 7W (measured at input terminals)
Voltage Output: As LED requirements
Current Output: As LED requirements
Earthing Regime: IT
Relevant standards to be observed: IEC 61000-3-2, EN 55015, EN 50082-1, EN 50082-2

Whilst the standard conditions of the electrical network dictate 230V AC with a margin of +/-10, due to cabling constraints within radiation exposed areas it would be considered advantageous should the supply continue to operate below the -10 threshold. Please note that compliance with the standards requires the power supply to be installed within a suitable enclosure, it is assumed this will be the responsibility of those manufacturing the power supply and integrating it within their existing products.

The power supply consists of a transformer, a diode bridge, capacitor(s) and optional voltage stabilisation device. It converts 50Hz AC voltages from 207V RMS to 253V RMS to a stable DC voltage, as required by the LED load. The power supply is designed to supply the current requirements of the connected LED load.

The Altium PCB schematics in the zip file provided for download comprise three versions:
1) Unregulated design for a single LED (e.g. Cree XR-E)
2) Regluated design for a single LED, requiring the LHC4913 radiation resistant voltage regulator IC. This is a CERN developed part provided by ST and may not be available for everyone.
3) Unregulated design for three LED string (higher output voltage due to modified resistor configuration).

Radiation resistance:
The radiation-hard voltage regulator L4913 was developed by ST Microelectronics in collaboration with CERN to satisfy the radiation requirements of the LHC (Large Hadron Collider). Its radiation hardness has been extensively tested using X-rays, 60Co, and a pion beam. The regulator appears to tolerate TID (total ionizing dose) levels above 100 Mrad, and 1 MeV equivalent neutron fluence above 1.9×1015 cm-2. The radiation resistance of the regulated designs should be equivalent to these levels, with the unregulated design significantly exceeding these levels. Luminaires based on these designs are now installed in activated parts of the accelerator complex and their performance is being monitored on an ongoing basis.

Please note that the radiation resistance of the LED's (or other connected equipment) themselves, and their light output and lifetime in a radioactive environment, may not reach the levels of reliability provided by this power supply. Now that the power supply design has been released this is a current research topic for this project.

Block diagram

Project information

Contacts

Commercial producers

Luminaires based on earlier versions of this design (using the same principles) are produced by the following companies:

Comatelec (FR)
- one luminaire
Thorlux (UK) - three types of luminaire for different situations

Project Development

James Devine - CERN - General question about project
Jean Marie Foray - CERN - Engineer (2009-2014)

Project Status

Date	Event
27-05-2011	Initial testing of commerical prototypes for LED emergency lighting in radiation environment
04-07-2011	Development of technical solution following test outcomes
05-03-2012	Production and test of solutions based on design principles by Thorlux & Comatelec
15-06-2013	First test installations at CERN LHC7 and Linac 4
30-09-2014	First deployment in CERN TDC2/TCC2 underground zone
09-03-2016	Release of updated PSU under CERN OHL
01-02-2019	Installation within CERN PSB accelerator completed

J Devine March 2016

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