Retro gaming consoles power supplies ratings

[VEGETA]

Hello,

We talked in another thread about ripple and noise requirements for retro gaming consoles and devices (scalers, etc..) and different opinions spawned between designers, and was agreed that a dedicated thread is best. Therefore this thread is created.

What is considered to be "good" ripple\noise figure you think for such devices? I saw people assuming 100mV p-p is considered excellent while it may not be the case since video signal itself is just 1v and analog signals are so affected by noise and ripple. is it really seen or appear on final video on screen? how much is perceptible? what about audio signals? also, stuff about low frequency ripple vs high frequency ripple and which is worse...etc. all these questions and more are basis for discussion.

So, for respected designers and fellow engineers, please state your opinion.

[Guspaz]

While I'm not a hardware designer, I wanted to touch on a sort of more philosophical aspect. Many modern retro devices like scalers have USB power input. As soon as you do that, use a generic standardized input, you're inviting the user to use a variety of different power supplies. Either because you didn't ship one with your product, or because they lost the original power supply, or because there was something more convenient to them (like using a TV's USB ports for power, or the USB-port built-in to a powerbar or wall socket, or using a charging hub). As such, any device that chooses to use USB power should be more tolerant of (that is, have better filtering) lower quality power input.

tl;dr: if you use USB power input on your device, the onus is on your device to supply good power, not the power supply.

[VEGETA]

While I'm not a hardware designer, I wanted to touch on a sort of more philosophical aspect. Many modern retro devices like scalers have USB power input. As soon as you do that, use a generic standardized input, you're inviting the user to use a variety of different power supplies. Either because you didn't ship one with your product, or because they lost the original power supply, or because there was something more convenient to them (like using a TV's USB ports for power, or the USB-port built-in to a powerbar or wall socket, or using a charging hub). As such, any device that chooses to use USB power should be more tolerant of (that is, have better filtering) lower quality power input.

tl;dr: if you use USB power input on your device, the onus is on your device to supply good power, not the power supply.

Everyone agree on this, but the point is how much ripple and noise exactly is considered good or bad? I saw on HDretrovision third-party page that they posted 100mv p-p PSU being good for retro gaming which surprised me due to 100 mV being very high value. Therefore I posted this dedicated thread.

USB is usually low power and can be filtered more easily than high current barrel jack inputs of 12v for example. These wall-mounted PSUs will have at least 80-150 mV p-p ripple and noise but at a slightly low frequency which is better filtered with elec. caps.

I would really like to see someone posting noise and ripple figures of full load measurement of OEM PSUs of PS2, Dreamcast, etc... to see what the manufacturers themselves choose to have. I wish someone participates in that since I can't really.

[VEGETA]

I've looked into other methods of implementing power supply in designs which are big in size, like video scalers... and thought of something like Meanwell IRM series of AC-DC power modules. IRM-20-5 (20 watts, 5 volts) or IRM-20-12 (20 watts, 12 volts) module is about 12$ and has maximum of 200 mv p-p ripple which is bad, but the testing report of actual usage reported < 50mV p-p with very little capacitance. Plus it is 65 kHz frequency, so putting simple LC or even just elec caps is going to enhance it further.

this way you can get reasonably good to really nice noise\ripple performance with relatively cheap price... you would need to include a wall-adapter which will cost more anyway. this way you can just supply a 1$ "figure-8" AC cable and that is that.

obviously this solution is not suitable to small-sized USB powered designs.

I really hope this thread collects opinions from all designers.

[marqs]

Whether PSU ripple is visible / audible also depends quite a lot on the device it's connected to, e.g. are the rails directly supplying DAC/ADC and how much filtering there is on-board. I remember seeing PSU related AV noise at least on N64s (late rev or 3rd party PSUs) and Amigas (dried caps etc.). Obviously using cheap SMPS wall PSUs with classic consoles that were designed to be used with linear supplies (SNES, MD etc.) can be a bad idea even if the consoles have 7805s or similar on-board to regulate into lower internal voltage. I don't have one specific number for acceptable ripple in this context, but in general I'd consider 1-2% ripple not too bad, especially if it's on low frequency (<100kHz).

[VEGETA]

Whether PSU ripple is visible / audible also depends quite a lot on the device it's connected to, e.g. are the rails directly supplying DAC/ADC and how much filtering there is on-board. I remember seeing PSU related AV noise at least on N64s (late rev or 3rd party PSUs) and Amigas (dried caps etc.). Obviously using cheap SMPS wall PSUs with classic consoles that were designed to be used with linear supplies (SNES, MD etc.) can be a bad idea even if the consoles have 7805s or similar on-board to regulate into lower internal voltage. I don't have one specific number for acceptable ripple in this context, but in general I'd consider 1-2% ripple not too bad, especially if it's on low frequency (<100kHz).

So for 5v it is 50~100 mV p-p?

You put a good note about those consoles which run using linear regulators, but I've seen that most consoles especially stuff like Dreamcast, PS1, PS2, etc.. use a flyback converter design which is very typical. this design is usually having multiples of very big filtering capacitors at the output stage, and also relatively low switching frequency which is suitable to be filtered by those big elec. caps.

the main board will also have many Linear regulators which are very good at PSRR at low frequencies. I remember PC engine has a 7805 regulator which is fed by a power brick, the official power brick is just a stepdown transformer, therefore pure linear operation. Neo geo AES probably have a SMPS on-board but with very heavy inductors and caps.

I feel like this area of retro gaming hardware should have more attention.