DEMETER

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Revision as of 06:22, 8 August 2008 by PE1RGE (Talk | contribs) (Design Ideas)

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Demeter - HPSDR Power Supply & Tiny Demeter

Project Leader: Jeroen, PE1RGE

"Demeter" is the project-name for the HPSDR power supply. Although power supplies are widely available, Demeter will be specifically designed for the HPSDR project.

On the 13th of June 2008, Tiny Demeter is added to the Demeter page. Tiny Demeter has a simpler design. Tiny Demeter will be more suitable for experimenters and allow us to gain some experience before constructing Demeter.

Further information will be presented on this page when it becomes available.

73 Jeroen PE1RGE

Result of the discussion on the HPSDR mailing-list (11th June 2007):

DEMETER SPECIFICATIONS

Input

 13.8 Volt DC (always 13.8 V or is there a supply range, see remark below)
 110 Vac (mains)
 230 Vac (mains)
 Battery (13.8 Volt) input with automatic switchover

Input connector

 Powerpole connector for DC 13.8 Volt
 Mains connector: National standard

Output voltages

 Remote switchable voltages
 +5 Volt @ …. Amps
 +12 Volt @ ….. Amps
 -12 Volt @ ….. Amps

Standby supply (for GPS-engine and OCXO)

 Constant on
 +5 Volt
 +15 Volt
 +24 Volt (depends on OCXO used, if possible user definable/adjustable)

Output connector

 ATX-connector
 DIN 41612 (Atlas connectors)

Protection

 Input protection (high/low voltage, polarity)
 Output protection (current limiting, voltage crowbar)

Monitoring

 ·	Input voltage
 ·	Output voltage
 ·	Output currents
 ·	Temperature

Power supply communication

 Atlas backplane
 USB-bus
 1 wire interface (controlled by a board on Atlas)
 Dumb-interface using the pins T7 and T8 on the Atlas

Connection to the HPSDR

 Using the ATX power connector, communication via the USB bus
 Using the DIN41612 connector using the Atlas backplane for communication

Position of the power supply

 On the Atlas backplane
 In a separate box (outside/inside Pandora)

HPSDR configuration

 Ozymandias - interface module
 Mercury – receiver (5V @ 500mA, 12V @ 200mA, -12V not used)
 Penelope – transmitter (5V @ 300mA, 12V @ 200mA, -12V not used))
 Alexiares - RF Bandpass Filters
 Gibraltar - frequency standard
 Epimetheus - antenna and other switching
 Measured: Ozy + Janus: +12v @ 200mA, +5v @ 180 ma, -12v @ 70 ma

Questions/remarks

 Switching or Linear?
 Internal/External?
 Power dissipation (Convection cooling/ forced air-cooling)?
 Do we need computer monitoring of voltages and currents?
 Include an USB-HUB (use one of the ports for the power supply communication)?
 Configuration (to use or not to use the SDR-1000)? People who use it in combination with the        
 SDR-1000 need less power from the power-supply and are using a custom built supply or the SDR-1000 
 power supply.
 Will the 13.8Volt really be 13.8Volt or “something” between 11.0 Volt and 15 Volt?  In other
 words: How many people are going to use the HPSDR mobile?
 Linear (A “lot of heat”, not “green”, easy to construct and trouble-shoot)
 Switching (Less heat, more “green”, more noise, more difficult to construct)
 Transformers:
 From my opinion there will always be a normal mains-transformer, both in the switching and the 
 linear power supply option. Building a switcher for 110Vac/230Vac is too dangerous and
 complicated (safety regulations) for (less experienced) home-builders. The switcher will be
 situated in the low-voltage part.

Demeter.jpg

Demeter block diagram legenda: 1. Standby transformer – Used for the GPS and OCXO 2. Standby rectifier and buffercapacitor 3. Switch – Switches between mains and battery power 4. Linear regulator 5. Overvoltage protection 6. Solid state (?) mains power switch 7. Power transformer 8. Power rectifiers and buffercapacitors (positive + negative voltage) 9. Switch – Switches between battery, mains and external power 10. Step-up converter 11. Linear regulator +12Volt 12. Overvoltage protection +12Volt 13. Charger (optional) 14. Step-down converter 15. Linear regulator +5Volt 16. Overvoltage protection +5Volt 17. Inverter – generates negative supply from the positive supply 18. Switch – Switches between inverter and mains power 19. Linear regulator –12Volt 20. Overvoltage protection –12Volt 21. Passive filter 22. Overvoltage protection for U++ (Could be used for a PA) 23. USB-Hub – one port used for communication with Demeter 24. PIC controller 25. Temperature sensor(s) 26. Analog to digital converter (for voltage and current) 27. Analog multiplexer 28. Controlled fan (forced air cooling)


Tiny Demeter

Based on the Teamspeak Session from 31st of May 2008 the idea arose to develop a simpler power supply. The working title for this supply became Tiny Demeter.

This supply could be handy for: - experimenters - people who want a simple configuration - temporary solution unitl Demeter becomes available

Tiny Demeter uses the station power supply as main-source. It expects a fairly well regulated 13.6 till 13.8Volts. From this voltage it will generate:

  • +12V @ 1Amp
  • +5V @ 1.5Amp
  • -12V @ -0.3Amp

Current rating can be increased by adding multiple regulating power transistors.

The regulators for Tiny Demeter (and Demeter) will be build from discrete components. The reason for this are the following:

  • It allows "current scaling", by adding more power transistors the current handling can be increased
  • A discrete regulator gives better temperature stability
  • A discrete regulator gives lower output-noise

From the basic idea of having just a few linear regulators the following extras were added:

  • Input voltage monitor; This will warn the user when the input power source voltage is too low. (If the input voltage is below a certain threshold the +12V stability cannot be guaranteed, probably causing problems in the HPSDR system.)
  • Temperature regulator/monitor; Due to the nature of linear regulators the power dissipation will be around 15 Watts (without extra regulating transistors).
  • Crow-bars for each supply voltage; For added safety
  • Shunt-resistors to measure the current for each supply-voltage
  • Input protection circuit; probably consists of a fuse and a diode OR a fuse and an electronic switch (switch only closes when the input voltage has the right polarity).

The board itself will have a:

  • An ATX 20pin power connector attached to its PCB, so it plugs in directly on Atlas

OR

  • An ATX 20pin power connector attached to a short cable and mounting brackets which can be used to mount Tiny Demeter on the mounting holes of Atlas

The proposed schematic block-diagram can be found below:

Block Diagram

Tiny Demeter block-diagram

TinyDemeter2.jpg


Design Ideas

Here some references are made to components and ideas which I have in mind for the Tiny Demeter design:

* Transformers for the switcher:

  • www.bourns.com/pdfs/pm600_610_620_series.pdf
  • www.cooperbussmann.com/3/CoiltronicsFinder.html

* Linear regulator

  • discrete: see schematic below
  • Linear Technology LT3080

* Crow Bar

Crowbar.jpg This image shows the (basic) schematic diagram of the crowbar circuit. Component values are for a voltage around 20V. . .

The principle of the regulator with the discrete components:

Regulator.pdf

The best topology for the switcher has to be determined. At this moment a Push-Pull configuration looks very promising. This will generate the least harmonics as the duty-cycle of the switcher is close to 50%. To get an idea of a push pull switcher one can look here: http://sound.westhost.com/project89.htm

Please note: THIS IS NOT THE DESIGN FOR DEMETER, ONLY AN EXAMPLE OF THE TOPOLOGY.

Preliminary design

The following documents contain a part of the design of Tiny Demeter. "Tiny Demeter design.pdf" contains (some) engineering notes. The file "Schematic Prints.pdf" contains the schematic of the switcher, however without the correct values for the components. You can use it to get a general idea of the DC/DC converter design. More details of the design will be added soon!

Design notes: Tiny_Demeter_design.pdf

Preliminary (partial) design: Schematic_Prints.pdf

--PE1RGE 08:36, 1st August 2008 (PDT)