2018 red edition exxos PSU specs

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2018 red edition exxos PSU specs

Post by exxos » Fri Oct 05, 2018 5:08 pm

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The latest PSU from exxos. The "red edition". Featuring highly efficient high power modern switch mode chips from one of the leading manufacturers, Texas Instruments.

PCBs optimised for maximum cooling and uses heavier weight copper than most general PCBs. This not only keeps resistance down which helps increase efficiency and reliability. It also greatly aids in the cooling of the switch mode controllers as the heat can be transferred away much more efficiently with a heavier weight copper. As the PCB is used as a heatsink, there is no need to bolt the regulators onto the metalwork like my previous design.

I have done away with all the electrolytic's apart from the large bulk capacitance. This means there are practically no components to fail or degrade over time. I now use ceramic capacitors which give much better performance and they are practically indestructible.

I have moved over to the much larger flat coil inductors. These is practically no voltage drop as the resistance is near zero and this increases efficiency and reduces heat output. While these inductors are a little overkill in this design, manufactures does not currently make a smaller version. However while these are rated as 30amp parts, the inductance only remains stable up until about 10amps. This of course still gives the design a good amount of headroom as the max output on the 5V rail is 6amps. These are certainly not "toy inductors" which just about every PSU I have seen uses. The inductance will remain ultra stable and not impact reliability or stability of the power supply regardless of load conditions.

Another good feature about this design is the operating frequency is a lot higher so we can have much tighter control over regulation and use smaller value inductors and capacitors. A huge advantage of this is that lower inductances is that the reaction time of current surges is reduced dramatically. Generally we are forced to use higher value inductors which inherently give better regulation figures, but they also become more sluggish to instantaneous power requirements (such as floppy motor powering up etc). So this power supply manages to get the best of both worlds.

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10uH parts are used.


The 5V,12V,0V output holes have been increased in size to accept larger cables easier. I have also increased the amount of holes so they can be used to power other devices if needed.

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The four leftmost holes are 5Volts output.
The six middle holes are 0V.
The two rightmost holes are 12V output.

The 4 PSU mounting holes (each corner of the PCB) have been increased in diameter to help aid in fitting to various metal power supply bases.

As the power supply is more efficient it can run higher amperage easier and more efficiently . Typically 5V rail can deliver up to 6 Amp RMS, the 12V rail can deliver to 3 Amps RMS. However the total output VA is not exceed 40VA.

For example:

3A x 5V = 15va
2A x 12V = 24va
15 + 24 = 39va.

4A x 5V = 20va
1A x 12V = 14va
20 + 14 = 38va.

5V can deliver 6amps max. (30va)
12V can deliver 3amps max. (36va)
Total output must not exceed 40va.

Note: A typical STF/Falcon pulls about 1.8amps on the 5V rail and generally almost no load on the 12V rail.. For example 5V at 1.8amps is only 9va and we have 40va available. So there is plenty of headroom to power just about anything.

(PSU must be operated with minimum 1amp load else fuse may blow due to the peak voltage charging of the main reservoir capacitor)

The power supply has many modes of protection. It has short circuit and overcurrent protection where it will rapidly enter hiccup mode where there is a cycle by cycle current limit until the fault is resolved. The chips will also shut down upon seeing any under or over voltages on any of the inputs or outputs.

Secondly we have the classic crowbar protection circuit which monitors the 5V,12V rails and the main DC supply coming from the transformer typically 15VDC (20V max). Should either the 5V or 12V rail increase more than approximately 0.5V it is assumed there is some problem and the crowbar activates which blows the fuse and immediately cuts power to the whole board. So equipment attached to this power supply have maximum protection possible.

While this power supply does not have a ripple filter which is normally customary like a my previous design, this new power supply topology does not require a ripple filter and can achieve extremely good regulation like my previous design.

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Test was done using a x10 probe with 4.5amps loading on the 5V rail.

Typically 2mV (0.002V) ripple which is as good as things are likely ever going to get. Noise figure is approximately 18mV (0.018V). To put it in perspective the original Atari power supplies were easily over 200mV (0.2V) noise.

So while my previous design was totally awesome, I have managed to make this power supply even more awesome by increasing efficiency and amperage output while also reducing the amount of electrolytic's used.

PSUs are available from my store..

https://www.exxoshost.co.uk/atari/last/storenew/#0095

Fitting remains almost the same as previously.. Please see the link below for wiring the primary of the transformer. http://www.exxoshost.co.uk/atari/last/p ... htm#PSUFIT

Please note, there are no regulators to fit to the metalwork on this new power supply design. You should leave in place the plastic insulation sheet (whereas before it had to be removed to mount the regulators)


ADDENDUM
Later production runs of this PSU design moved to a normal "green PCB". All the PSU's with the "large inductor coils" and SMT regulators are all basically the same PSU regardless of PCB colour. There are PCB revisions done each batch, and these are stamped on the PCB on the top left. Revisions are generally only to aid in the reliability of manufacturing and not performance or spec related changes.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Re: 2018 red edition exxos PSU specs

Post by exxos » Sun Jul 14, 2019 10:46 am

Pinouts of the low voltage side of the PSU.

NOTE that the pinout arrangement is the same as the older PSU types (TO220 based regulators, blue PCB) just there is a second row of holes for power on later editions.

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4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Re: 2018 red edition exxos PSU specs

Post by exxos » Sun Sep 15, 2019 10:45 pm

WHY THE FUSE BLOWS

This comes up now and then so let me explain why the fuse can blow. The fuse only generally blows because of some fault condition relating to how it is being used, not because the PSU itself has a fault! These are protection circuits, there are there to keep things from exploding like your £1,000+ Falcon under huge mains surges etc! Of course most issues are generally "self inflicted" by people not reading the instructions :)


OPERATING THE PSU WITH NO LOAD

If you power up the PSU without load resistors or the ST connected, then its possible the over voltage protection will trigger and blow the fuse. This is because without a load, there is nothing to suck power out of the large capacitor on the board and its voltage rises beyond 20volts and blows the fuse. Why the hell does it do that ? Because it's a protection circuit! The regulator chips (or at least the 5V one) has a maximum input voltage of 20 volts. So if I allowed the voltage to rise to that level or above , it could blow the 5volt regulator.

The overvoltage protection could also trigger if the mains input voltage goes very high even under load. Such as 270VAC for the 230V model. At some point the protection circuit has to kick in right ? Where do you draw the line ? 250V ? 300V ? The circuit will blow the fuse if the voltage exceeds a safe level. This circuit is there to protect your PSU and your ST or Falcon from mains surges!


FUSE BLOWING AND TRANSFORMER MELTING HOT

Some people manage to run the 110V PSU on 230V which doubles the input voltage to the PSU. As such if the voltages happen to be a safe region the fuse may not blow but generally it will. If the transformer is being run on twice the input voltage, it will get VERY hot very fast and will start to smell or even smoke after a couple of minutes. The transformer doesn't generally come to harm, just let it cool down for a hour before powering it up again.


FUSE BLOWING INTERMITTENTLY UNDER LOAD

Aside from high mains surges, generally this has been realised to be relating to the old ST PSU connector. While I mention to recycle the old ST power connector, I generally do not recommend this anymore. I myself had a issue of the fuse blowing (its actually the same as the OPERATING THE PSU WITH NO LOAD topic). A bad PSU connector will have a bad contact and likely cause your ST to intermittently crash along with intermittently blowing the PSU fuse. I had this issue with one ST connector, I tried cleaning it with IPA etc, it did not help. I replaced it with one of my new ST PSU connectors and the problem did not return.


SHORTING OUT THE PSU

The PSU has automatic overcurrent protection circuits so its unlikely you will blow the fuse by shorting it out. When a short condition is detected the PSU will enter a low current state until the short is removed.

If you short out the 12V output to the 5V output, then its likely the 5V over voltage protection circuit will kick in and blow the fuse. Of course we don't want to feed 12V into the 5V rail on a £1,000 falcon do we ? So again the fuse will blow to protect from such a fault.


WHAT IS THE FUSE TYPE ?

The fuse is just a generic 20mm 4amp quick blow fuse.
DO NOT USE ANY OTHER TYPES. Placing a higher current fuse or a "anti-surge" fuse will not help with fuse blowing issue at all! If anything you may well just end up causing damage to the PSU. The fuse is there to protect your PSU and machine from various fault conditions. So don't screw with its values!



OTHER STUFF


12V VERY LOW ABOUT 8 VOLTS

Some people manage to run the 230V PSU on 110V. Generally the 5V will output fine, but the 12volts will likely be low around 8volts.


CAN'T YOU USE A AUTO RESET FUSE ?

Generally these can take up to several seconds to trip. A fuse can blow in a quarter of a second in general. So unless there are some very high speed auto reset fuses out there, I will not be adding them to the PSU.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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