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Proposal - Power Supply Architecture

This page outlines some of the problems with the current CyberJacket power supply arrangements and proposes a different architecture which should improve reliability and performance. This architecture also lends itself to future developments such as standby power, and incorporating additional modules.

Current Power Related Problems

  1. Battery life - currently well under two hours dependant on activity
  2. Noise/spikes on supplies (e.g. >200mV on 5v line)
  3. Insufficient power to use backup batteries on GPS (causes CPU to crash)
  4. Currents over 2A flowing in jacket with attendant losses and interference
  5. Suspected interference between CPU and GPS (and dGPS?)
  6. Amount of cabling required for parallel circuits and power distribution
  7. Battery monitor designed for 12v working (partly modified for 6v)
  8. Excessive voltage conversion e.g. 6v to 5v to 12v to 5v for GPS sub-module

Proposal

It is proposed to adopt a 12v supply and distribution system. This will have the following immediate advantages:

  1. Extends battery life - batteries will be able to discharge to a lower voltage before system fails
  2. Distribution currents will be halved reducing losses and interference
  3. Batteries can be connected in series reducing cabling and fuses in shoulder pockets
  4. Battery monitor works as originally designed

The block diagram below shows the proposed arrangement.

The advantages of this layout are:

  1. Reduction in noise/spikes on supplies resulting from parallel distribution
  2. Sufficient power to use backup batteries on GPS
  3. Lessens possibility of interference between CPU and GPS (and dGPS?)
  4. Less cabling required for power distribution
  5. Voltage conversion happens only where it is needed
  6. Voltage conversion can be customised to the particular module e.g. the PC/104 PSU is appropriate for the CPU, while the Maxim boards can be used for other modules
  7. Easier to isolate and debug modules
  8. Easily expandable to include future developments
  9. Other?

Disadvantages:

  1. Additional voltage convertor(s) is needed
  2. Poorer weight distribution
  3. Other?

Conclusion & Recommendation

Advantages significantly outweigh disadvantages and will help us progress towards Christmas objective - let's do it!

cnr 8/12/98


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