Do any PCE systems use >5V anywhere?

[SamIAm]

AC adapters are often poorly made, including official ones, and generally waste a lot of energy. Many older adapters are begging to have pricey new high-value smoothing capacitors put in them, too, because their original ones are at death's door.

I've been thinking of getting a single high-quality switch-mode power supply to use with all of my consoles. I know that 9V is safe to go with for virtually all systems, and it's what the popular Retro DC Powered supply uses. However, it seems to me that 7.5V is a smarter solution for any console that runs entirely on 5V from a 7805 regulator. You throw away less energy at the regulator and generate less heat, on top of 7.5V supplies themselves being cheaper at high amp ratings. 7805s only need 7V at their inputs to work.

The question is, is there anything out there (PCE or otherwise) that actually needs more than that? Or is everything everywhere running on 5V from a 7805?

[ClodBusted]

This meets my interest as well.

Remember, there are two 7805's in a Duo, each hooked up to their own extruded heatsink. From looking at photos on the web, I see only one 7805 in PCE and Turbografx-16 consoles, and it seems to be connected to a large metal shield for heat dissipation.

I could try hooking up my Turbo Duo to the lab power supply once again, to test it against 7.5 V.
When the console would need 1 A at 10 V = 10 W, I'd expect it to need 1,3 A at 7.5 V to get the same wattage. I can test this by using the current limiter of the power supply and playing a CD game, where I noticed the current draw is at peak when loading from the disk. When the console draws more power than the limiter allows, the lab power supply will switch to constant current mode, the voltage drops and the console will reset itself.

[soop]

This meets my interest as well.

Remember, there are two 7805's in a Duo, each hooked up to their own extruded heatsinks. From looking at photos on the web, I see only one 7805 in PCE and Turbografx-16 consoles, and it seems to be connected to a large metal shield for heat dissipation.

I could try hooking up my Turbo Duo to the lab power supply once again, to test it against 7.5 V.
When the console would need 1 A at 10 V = 10 W, I'd expect it to need 1,3 A at 7.5 V to get the same wattage. I can test this by using the current limiter of the power supply and playing a CD game, where I noticed the current draw is at peak when loading from the disk. When the console draws more power than the limiter allows, the lab power supply will switch to constant current mode, the voltage drops and the console will reset itself.

Interested to know the outcome of this.  Actually, I'd be interested to know on a core/white unit too.  Wish I had a variable PSU.  I might put one on my wishlist.

[SamIAm]

If the whole CD unit and everything else in all PCE incarnations is running on 5V from a 7805's output (or two 7805s), then lowering the voltage on said 7805's input should result in less current drawn by the total system.

7805 is not very efficient. A lot of energy is wasted in the form of heat.

Heat generated = (input voltage – 5) x output current

If we have a system with input 15 volts and output current required is .5 amperes, we have:
(15 – 5) x 0.5 = 10×0.5 =5W;

5W energy is being wasted as heat, hence an appropriate heatsink is required to disperse this heat. On the other hand, energy actually being used is:

(5 x 0.5Amp) = 2.5W.

So twice the energy that is actually utilized is wasted. On the other hand, if 9V is given as input at the same amount of load:

(9-5) x 0.5 = 2W

2W energy will be wasted as heat.

So, if supplying 10V shows the system drawing 1000mA at peak usage, then supplying 7.5V should conveniently show a draw of 750mA. The system beyond the 7805 should only be using 500mA in either case.

I'm very much inclined to think that nothing is using the AC adapter's output directly because it can have a huge ripple on it - easily 1Vp-p in some cases. The best way to go is to simply check the circuitry of various console PCBs, though.

If everything really is just using 5V, then the really ballsy and probably redundant thing to do would be to remove the 7805 and feed the system a very stable 5V. You'd have to use a good quality power supply and maybe add some extra decoupling capacitors, but you'd be using half the energy of an AC adapter and you would not waste anything while the system is off.

The power savings are so small that it's not really worth going that far. If 7.5V works, though, you might as well get it over 9V.

[SamIAm]

Protection diodes before the 7805.

That's why 7.5V won't work. The SFC/SNES has one, and I bet PCE hardware does, too. These cause a 0.7-0.8V drop, which means a 7.5V supply can't give a 7805 the 7V it needs.

8V power supplies don't really exist except as custom parts, so 9V it is.

[ClodBusted]

I noticed that voltage drop of approx. 1 V between the DC jack and the regulators when I probed my Turbo Duo last time. Thanks for letting us know why this occurs.

[soop]

I learned something!