Altitude Posted February 26, 2012 Report Posted February 26, 2012 (edited) 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 January 27, 2017 by Altitude Quote
ilmenator Posted February 26, 2012 Report Posted February 26, 2012 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. Quote
Altitude Posted February 26, 2012 Author Report Posted February 26, 2012 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 Quote
Shuriken Posted February 27, 2012 Report Posted February 27, 2012 (edited) 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 February 27, 2012 by Shuriken Quote
technobreath Posted February 27, 2012 Report Posted February 27, 2012 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... Quote
orange_hand Posted February 28, 2012 Report Posted February 28, 2012 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 Quote
Altitude Posted February 28, 2012 Author Report Posted February 28, 2012 The only thing that was added was two jumper wires. I'll try to do up a wiring diagram/pic Quote
orange_hand Posted February 28, 2012 Report Posted February 28, 2012 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 Quote
smashtv Posted February 28, 2012 Report Posted February 28, 2012 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) Quote
Altitude Posted February 28, 2012 Author Report Posted February 28, 2012 I used the V but use the H since I had to yoga the legs to get it to lay flat Quote
technobreath Posted February 28, 2012 Report Posted February 28, 2012 @ 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? Quote
Altitude Posted February 29, 2012 Author Report Posted February 29, 2012 (edited) 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 February 29, 2012 by Altitude Quote
Altitude Posted April 1, 2012 Author Report Posted April 1, 2012 (edited) 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 January 27, 2017 by Altitude Quote
Blatboy Posted April 6, 2012 Report Posted April 6, 2012 (edited) 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 April 6, 2012 by Blatboy Quote
Blatboy Posted April 6, 2012 Report Posted April 6, 2012 (edited) 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 April 6, 2012 by Blatboy Quote
Blatboy Posted April 6, 2012 Report Posted April 6, 2012 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? Quote
technobreath Posted April 9, 2012 Report Posted April 9, 2012 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. Quote
Altitude Posted April 18, 2012 Author Report Posted April 18, 2012 (edited) 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/lit/ds/slts059a/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 April 18, 2012 by Altitude Quote
technobreath Posted April 18, 2012 Report Posted April 18, 2012 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. Quote
latigid on Posted February 17, 2013 Report Posted February 17, 2013 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)! Quote
Shuriken Posted February 17, 2013 Report Posted February 17, 2013 As an alternative maybe the Recom R-78-1.0 series? Quote
latigid on Posted February 17, 2013 Report Posted February 17, 2013 It has a maximum output of 1 A, is this enough to power an MB-6582? Quote
Shuriken Posted February 17, 2013 Report Posted February 17, 2013 Well then use the Recom R-78Bxx-1.5 ... Quote
Altitude Posted March 11, 2013 Author Report Posted March 11, 2013 (edited) 1A is plenty for the 5V rail Liking the look of their +/-12V Step up transformers as well. Could be a slick way of powering some CV stuff http://www.mouser.com/ds/2/468/REC3-SRW_DRW_Z_Hx-26530.pdf Edited March 11, 2013 by Altitude Quote
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