26 replies to this topic

[Altitude]

So I have always wondered how to effectively move away from the C64 PSU and I have recently been turned on to switching 5V regulators as a good way to deal with high voltage drops that would normally get a 7805 blazing hot.

What I am using is a TI PT78ST105 regulator. Not the cheapest thing in the world but its a brilliant piece of kit. I have tested it with 5V 1.5 amp load being fed a 18V DC input voltage and the thing barely gets luke warm. I ran the same test with a 78S05 (the 2 amp one) and it overheated and shut down in seconds. Pretty nifty.

The way I have that box configured is the switching reg is face down (the black little thing next to the 7809) and is fed from a 12V DC adapter. Rewiring is kept to a minimum by wiring by just patching the output back to the normal 5V line and removing the rectifier and bridging.

With everything stuffed and 8 8580s installed (and the fan running) I was drawing 800 mA total so I am using a 1A 12V DC supply to run everything. No noise at all to suggest there is a switching vReg there and in fact, background noise sounds better than the C64 brick I was using previously.



The result:

Edited by Altitude, 26 February 2012 - 19:16.

[ilmenator]

Just checked with Reichelt, they don't seem to have that model, but the TSR-1 series from Traco Power seems to be equivalent (not sure about the noise, though). And it is only 8,80 Euros, which is rather cheap if you consider the savings for a single voltage (12V) power supply.

[Altitude]

Thats how I see it. There are ones on ebay also. These switch so fast than any ripple is eaten up by the smoothing caps

[Shuriken]

It's a nice solution. The PT78ST105 has a slightly higher switching freq (600 kHz) over the Traco (500 kHz). And the PT78ST105 has a little more headroom if people have a display which uses a bit more. Downside is it is a little more expensive then the Traco.

Edited by Shuriken, 27 February 2012 - 17:25.

[technobreath]

Have u guys ever hooked a scope to this psu solution? Looks very interesting, if it doesnt make noise what so ever...

Getting away with one transformer only is a nice thought...

[orange_hand]

Hi,

was there a change on the PCB required ? Traces to be cut or additional wires ? Would be great if you could explain what needs to be done in detail (preferably with some pictures :-) ).

Cheers
orange

[Altitude]

The only thing that was added was two jumper wires. I'll try to do up a wiring diagram/pic

[orange_hand]

Hi,

another question: While searching at mouser.com I got the following ones:

PT78ST105H
PT78ST105V
PT78ST105S
PT78ST105ST

Package Suffix (last one or 2 chars):
V = Vertical Mount
S = Surface Mount
H = Horizontal Mount
ST = ?

Which of those is the right one ? Did you use the PT78ST105H ?

Cheers
orange

[smashtv]

Package Suffix (last one or 2 chars):
V = Vertical Mount
S = Surface Mount
H = Horizontal Mount
ST = ?

ST = Surface mount in tape and reel packaging (Qty. 200)

[Altitude]

I used the V but use the H since I had to yoga the legs to get it to lay flat

[technobreath]

@ smashtv. Hehe, u smashed that right in there. With the fine adjustment hammer even...

What's the thing here? Is this a powersupply or just a twist on the regular psu circuitry on the standard PCBs?

[Altitude]

Its a 5V regulator that can take a high input voltage efficiently so you can use a single 12V DC supply (or a 15V if you want +12 regulated rails) to power the whole thing instead of the the c64 supply. It uses the existing power components on the board, just wired differently.

Edited by Altitude, 29 February 2012 - 03:32.

[Altitude]

Just to follow up on this thread, I've been working on my sid and took a few pics to show the wiring:

The +/- are wired to the outside 2 pins of the 7 pin din connector (normally the AC pins)

Edited by Altitude, 01 April 2012 - 02:36.

[Blatboy]

This is pretty darn awesome.

Would the wiring you did change for a type B PS section? (Mine will use 5V and 12V)

In my brain it would seem you would need more than one input, like the C64 brick does, for multiple voltage rails. Of course, I'm somewhat new so I may be thinking this completely wrong.

Thanks

Edited by Blatboy, 06 April 2012 - 15:18.

[Blatboy]

Or would you just split the juice coming in from a 15V DC supply, and use both a PT78ST105 and a PT78ST112? Probably not, as that would split the current too, and 500mA (assuming a 1A supply) prob wouldn't be enough, right? Plus, I'm not sure there would be room for two of those big regulators on the board...

Brain working hard on new concepts... sorry for thinking out loud...

Edited by Blatboy, 06 April 2012 - 16:03.

[Blatboy]

Ok. Now I'm probably pushing it, but I'll push it.

In my collection of power supplies, I found one from an old Jaz drive. It has DC outputs on 5V/1A and 12V/.75A rails. It's not a grounded plug. Would it be a workable solution to use this? Is that enough ampage? I wouldn't even need regulators on the board, would I? Would that me a safer solution than the C64 brick?

[technobreath]

Yo alti, where did u buy the vreg? And does it really use the same caps as the 78xx vreg? And what kinda heat sink do u use. Please forgive me for not looking too close on the picture, as I am watching from my phone.

If this works and doesn't make switching noise, that's a very nice find! And I want it hehe.

[Altitude]

Sorry, forgot about this thread

..
Would the wiring you did change for a type B PS section? (Mine will use 5V and 12V)

Nothing. Just use a 7812 in place of the 7809, same wiring

Or would you just split the juice coming in from a 15V DC supply, and use both a PT78ST105 and a PT78ST112? Probably not, as that would split the current too, and 500mA (assuming a 1A supply) prob wouldn't be enough, right? Plus, I'm not sure there would be room for two of those big regulators on the board...

You could, but it would be a bit of a waste of $$ since all you really need is a DC adapter that has enough juice to power the +12V regulator. You can use a linear one (7812)

Ok. Now I'm probably pushing it, but I'll push it.

In my collection of power supplies, I found one from an old Jaz drive. It has DC outputs on 5V/1A and 12V/.75A rails. It's not a grounded plug. Would it be a workable solution to use this? Is that enough ampage? I wouldn't even need regulators on the board, would I? Would that me a safer solution than the C64 brick?

Maybe. If its pretty small its probably a SMPS which may or may not be fine. Test it with load on another circuit and see how it behaves

Yo alti, where did u buy the vreg? And does it really use the same caps as the 78xx vreg? And what kinda heat sink do u use. Please forgive me for not looking too close on the picture, as I am watching from my phone.

If this works and doesn't make switching noise, that's a very nice find! And I want it hehe.

I got it from Mouser. Its a drop in replacement for a 7805 and no heatsink is necessary (it does not really get hot at all). The existing caps for the 5V rail are probably overkill but I left them in anyway. It makes no noise that I can hear at all, it switches at 600 kHz so that is well outside of anything of concern. Here is the doc: http://www.ti.com/li...9a/slts059a.pdf

I have now used this thing in my MBsid, MB808 (which was REALLY bad thermally, 18V input to the 7805 BIG heatsink needed) and my 9090 (which was almost as bad as the MB808, 15V input) and it has worked perfectly in all 3 cases.

I mentioned this in another thread but I'll repeat it here also: These are 85-90% efficient regulators vs 78xx which are about 55% efficient. I did a test to compare the performance of these vs a 78xx by generating a 1.5A load (bank of LEDs) driven by the PT78 and a 78S05 (the 2A one) at varying input voltages. I had no heat sink on the 78S05 and that thing got too hot to touch in seconds at a low input voltage (7.5V) and went into thermal shut down at anything above 12V (and was scary hot). The PT78 was barely warm to the touch at 18V at the input at its maximum load (1.5A). I was sold on these after that

Edited by Altitude, 18 April 2012 - 04:06.

[technobreath]

Hehe, seems like nice vreg. I can see why you tested it with no heatsink, but that will of course only give the results we know from before, of course a 78xx will need a heatsink... Hehe

Buy when it comes to the switching noiseless statement. I don't say you are wrong, but I need more scientific data than one person that says "it works fine" hehe, I will order one myself, build a test circuit and scope the thing myself, that is if pete isn't already on that hehe.

[latigid on]

I am looking at a Mouser order right now, the PT78ST105H is obsolete, but there seems to be a pin compatible replacement with slightly better ripple characteristics and a lower input voltage (7 V, if you need it).

 

It is # 78SR105HC which is currently being made obsolete. Mouser have under 500 units remaining so get in quick (or find another alternative)!