Proposal for a
New Type of ATX PC PSU

 

Summary:
   
Most PC users have a number of accessories which require separate low voltage power supplies in the form of "wall warts". Many also have Uninterruptible Power Supplies (UPS) which take up space and are costly. This is a proposal to integrate these several functions into the PCís PSU thereby gaining in convenience and saving cost and space. This would require implementing certain (loose) standards.

Introduction:
   
Initially, power supply units (PSU) for desk PCs were simply black boxes which provided certain output voltages at certain amps and nothing more was required. With the arrival of the ATX standard the PC PSU started interacting with the main part of the computer. The ATX PSU provides a certain standby power to the main board and some daughter boards and peripherals so that some functions remain active and the main power supply can be switched on or off by these devices. This is a start in a certain direction but the possibilities are much greater than whet is currently being done.
    Notebook computers have long ago integrated power management into the main computer rather than having it be an isolated function of the power supply. Desk PCs can and should do the same thing as it provides more and better features and would result in a reduction in manufacturing and usage costs.
    We will propose here to develop a new, expanded, PC PSU which, in addition to those functions already provided by the standard ATX PSU (namely standby power and fan control) would also provide other functions such as:

  1. Supply at low voltage (12 V?) for external peripherals such as flat displays, audio speakers, external modem, router, etc.
  2. Provide surge suppression protection not only for the mains power line but also for the modem and ethernet lines.
  3. Provide backup power supply in case of a mains power outage. Many computer have an external, separate, Uninterruptible Power Supply (UPS) which is a function the PC PSU can assume with advantage.
  4. Provide signaling to the main board about the state of different relevant parameters like main power failure, battery charge, etc. The main computer can then control the PSU in an integrated fashion with the rest of the PC's power management policies.

Function #1: Power Supply to Peripherals (PSP).
   
The average PC user has several wall type adapters to power accessories like speakers, printer, external modem, scanner, etc. More importantly, todayís flat LCD displays also require little power and have an additional, external, power adapter. It makes no sense to have a separate AC power adapter for each item. If the power supply voltage for all these accessories was standardized at, say, 12 V, then they could all be supplied power directly by the computerís PSU which would result in some advantages:

  1. Gain in convenience as the wall adapters disappear.
  2. Gain in convenience as the PC controls the power supply to all accessories and switches them off when the PC is turned off.
  3. Saving in cost as the wall adapters are no longer required.
  4. Saving in cost and gain in convenience as accessories are powered world wide at the standard low voltage rather than different voltages depending on the country. This dispenses with the need to ship adapters of different voltages to different countries.
  5. Saving energy as the computer controls the power supply to the accessories and turns them off when the PC is off.

Implementation of Function #1:
   
This function would be very easy to implement because all that is required is to fit the PCís PSU with one or more lowvoltage output connectors and provide power to them, probably with some protection or limit, say, 5 Amps in total. Although is seems unlikely, some form of filtering may be convenient if there is any chance that the accessories could introduce transients into the PSU.
    The PSU would have a number of low voltage jacks (say 4) which would be standardized and situated in the rear of the PSU so that they would be accesible to the end user. The powered accessories would then come with a cable suitable for the connector adopted rather than the standard wall adapter and the end user would plug them into the PSU. This would produce a much neater installation as well as convenience and savings in manufacturing costs and in energy usage over the life of the system.
    A possibility would be for the main board to control this output so that it was only turned on after the main board had powered up successfully. Even further, they could be controlled individually and integrated in the PC's power management scheme. One would be designated for the display and the PC would control the power supply to the display, etc.

Function #2: Surge Suppression Protection (SSP).
   
There is no question that this is a desirable function to have as it would protect vital parts of the PC which are subject to damage from spikes. The question is whether this function can advantageously be included in the PSU or whether it is better left to an external protector such as is done at present. The pros and cons would have to be studied and evaluated. It is possible that the PSU should include protection only for the power line and then leave the protection for the phone and ethernet lines to outside devices. This is not of major importance but including this function in the PSU would result in greater protection and in a neater system appearance as the external devices disappear. It could be that the protection for the phone and Ethernet lines could be installed in the PC box but separate from the PSU.

Function #3: Uninterruptible Power Supply (UPS).
   
Many PC users have a UPS which will provide a cleaner AC power supply to the PC, avoiding voltage spikes and micro-cuts as well as providing power for some minutes, enough to save the work being done, in the event of a power outage. But this setup has important drawbacks:

  • There is an intermediate power conversion to the mains frequency (60/50 Hz) which is costly and wasteful. This is unnecessary if the UPS function is integrated into the PC. Now that the display is also powered at low voltage there is no need to generate AC at the mains voltage and the UPS-PSU combination can generate the required low voltages directly.
  • A traditional UPS duplicates many parts of the PSU and it would make more sense to integrate them both in one unit which would result in fewer parts needed. This in turn would mean savings in manufacturing costs as well as increased reliability.
  • Requires the UPS to have a separate, intelligent control which can be assumed by the PC.
  • For an integral power management by the PC the UPS must communicate with the PC via a data cable which is usually a serial or USB connection.
    We therefore see that it makes great sense to combine the PC PSU and UPS into a single unit. For convenience we will call a combined UPS-PSU unit an "Uninterruptible Power Supply Unit" or UPSU for short.
    With respect to power management a desk PC with a UPSU would function just like a notebook. When a power outage occurs the computer continues to function and the time available depends on the capacity and state of charge of the battery. The PC will be aware of the main power outage and of the reserve time remaining and will take appropriate action (save work, shut down, etc.) at each crucial point as it has been instructed.

The characteristics of an UPSU would be:

  1. Housed similarly to a standard ATX PC PSU in the computer case.
  2. The UPSU can function with or without a battery. With a battery it provides UPS function, without a battery it provides normal PSU function.
  3. The backup battery is external to the UPSU but can be housed in the computer case for relatively small sizes. For bigger sizes it would be external.

Implementation of Function #3:
   
There are multiple types of circuit designs which could be used to implement this function. Ordinary ATX type PSUs are of the fly-back switching type and would need only a little additional circuitry to provide this function.
    The physical layout also admits several variations. If the battery is large then it would go in a separate box and be connected to the UPSU by a cable but a smaller battery could be housed in the PC box which would make it more tidy and convenient. It could go in an enclosure where it would be inserted from the front of the box:

Or it could be inserted from the rear:

Function #4: Integrated Power Management (IPM).
   

Implementation of Function #4:
   

Conclusion:
   
Adding these two functions to PC power supplies is cost effective and would result in savings in manufacturing costs and in energy usage. The additional cost of the PSU would be partially or totally offset by the saving of several power adapters so it should not mean a significant cost increase. The battery would be an optional item for the user and would always cost a fraction of the cost of a complete UPS. PCs equipped with UPSU would have a significant marketing advantage and should not cost much more than traditional PCs.
    Manufacturers and assemblers of whole systems would be in the best position to exploit this concept as they could ship complete systems which would have the necessary cables and not have the unnecessary AC adapters.