Starfire

Custom Power Supply for mb6582

235 posts in this topic

Good tip. Lesson: assumption is the mother of all f***ups. I'm very glad until now I only inquired about prices because I was planning to order this morning; great timing dude! :thumbsup:

I'll go ahead and dig into some datasheets then, basically anything switching above 50KHz (I know human ears often dont go beyond 22KHz but let's assume Philips knew what they were doing when deciding that 44.1KHz was the right bandwitdh to use when they developped the CD) is out of the audible spectrum, above 94KHz is out of the recording spectrum as well and thus (theoretically) better. Aside from the guys who record at 192KHz but I don't believe any switcher is that fast. Besides, if it really adds something to your recording to go to 192KHz/32bit instead of 94KHz/32bit is a whole different discussion.

I am going to build a Switching PSU which uses 260kHz frequency. For modern switchers its even possible to do higher frequencies. 1mHz is achievable.

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BTW don't forget to buy the matching Molex connector for the primary and secondary side of the PSU.

Ah good point! I haven't totally decided yet on what I should do :) I am going to design the intermediate power board for the 7809 regulator for the SIDs and filtering caps to see how small I can make that. I suspect that won't take much space at all and would still be smaller than my original linear PSU design (based off your original design) and a lot more efficient power-wise.

Edited by m00dawg

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Ah good point! I haven't totally decided yet on what I should do :) I am going to design the intermediate power board for the 7809 regulator for the SIDs and filtering caps to see how small I can make that. I suspect that won't take much space at all and would still be smaller than my original linear PSU design (based off your original design) and a lot more efficient power-wise.

I have ordered a LM2675 for the 9V and a LM2676 for the 5V part. Since they are 90% efficient i don't expect much heat. Component choice is a bit more tricky then with a linear one though.

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Ah wow when you said you were building your own switcher, I was a tad skeptical but I forgot about switched regulators (duh :P). I dunno for me having a PSU that is ready-made and has all the protection built-in seems like a good way to go. I made a tiny board for the extra tantalum filtering caps and a 7809 and it's only 1.25 x 1.30 in which is pretty tiny and may be sufficient.

Hell I dunno what I'm going to do :) I already have a linear design that, while it lacks some of the protection stuff discussed earlier in this thread, seems to look pretty solid (and isn't much more complicated than my own PSU I was using previously). I don't like the idea of loosing 50% of my PSU efficiency due to heat - I could bring that down with transformers but then the design gets pretty big.

I don't think I can make a switching supply much smaller than my linear design, save for the lack of a big transformer (?) so for me it's other a ready-made PSU + a tiny filtering/regulating board; or a linear PSU option.

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it's only 1.25 x 1.30 in

including mounting holes? I tend to forget those when prototyping on veroboard and man that is annoying...

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Yep including 3mm mounting holes, although I thought of forgoing it and just using an insulator on the bottom just because the holes account for 1/4th of the space :)

By the way, Shuriken is correct - some of the switching regulators I found do indeed switch at 1MHz which is plenty. Looks like in order to get 9V, though, might have to get an adjustable regulator (which is the LM2675 Shuriken mentioned). to switch down to 9V. I suppose that's an option over using the 7809 in my setup, although 12 -> 9V for the SIDs probably isn't bad enough to be worried about heat (I'm going to secure it to the chassis anyway).

Edited by m00dawg

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Yep including 3mm mounting holes, although I thought of forgoing it and just using an insulator on the bottom just because the holes account for 1/4th of the space :)

By the way, Shuriken is correct - some of the switching regulators I found do indeed switch at 1MHz which is plenty. Looks like in order to get 9V, though, might have to get an adjustable regulator (which is the LM2675 Shuriken mentioned). to switch down to 9V. I suppose that's an option over using the 7809 in my setup, although 12 -> 9V for the SIDs probably isn't bad enough to be worried about heat (I'm going to secure it to the chassis anyway).

The heat is probably not a problem. As the load is pretty low. But i figured will i was at it, make the whole thing completely switched. At 1A max it produces so little heat, it comes in a DIP8 or similar smd package. The pcb is very small if you go by the ref. design national semi gives you in the datasheet.

The bigger 3A brother comes in a TO220 package but can be cooled with a small TO220 heatsink.

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Any guess on the cost and complexity of that homebrew switching PSU? I like the DIY idea, but I need to have some success this time... everytime I run into major difficulties with the DIY projects I shelf the whole shizz and pickup one of my other hobbies... Maybe better for me to just order one of those 20€ (plus €25 S&H) babies and get going while I'm on this roll... Just thinking out loud :ermm:

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It will be faster and not much more expensive i am guessing. Not sure about the last bit, but way sure on the first. I know your MB6582 has been covered on quite a lot of dust, so i think it would be a good idea to just order a psu.

If you check the datasheets of LM2675 and LM2676 its not that complex. If you download the program LM267X Made Simple it will even calculate all the components. I checked if it was correct according to the formulas in the datasheet. And what do you know, it is correct :shifty:

The problem is most components recommended are SMD. I looked for through hole stuff at reichelt....and still ended up with smd. For the caps you need low esr parts which are a bit more expensive.

Edited by Shuriken

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The problem is most components recommended are SMD. I looked for through hole stuff at reichelt....and still ended up with smd. For the caps you need low esr parts which are a bit more expensive.

Low ESR is no issue, I ordered loads of those a few days ago for some other projects that are scheduled for imminent completion :angel:

I consider myself adequate enough as far as soldering wires and through-hole are concerned, SMD however is a big nono for me, I'm not going down that path. ordering it is then, I hope they get back to me soon.

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Ah SMD isn't that bad :)

As far as low ESR, what would you folks recommend? I know tantalum tends to offer low ESR. Anything else? Capacitance values matter much here as well? What I have done to this point is based off what I read from the PDFs I linked on this thread a while ago. Seems that Tantalum would do the trick for anything close to the audio spectrum (and perhaps further out though I haven't seen any data on that).

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Ah SMD isn't that bad :)

As far as low ESR, what would you folks recommend? I know tantalum tends to offer low ESR. Anything else? Capacitance values matter much here as well? What I have done to this point is based off what I read from the PDFs I linked on this thread a while ago. Seems that Tantalum would do the trick for anything close to the audio spectrum (and perhaps further out though I haven't seen any data on that).

Depends on how much space you got on your board. I'd stay off tantalums unless they are *really* needed since they have this tendency to self-incinerate every once in a while. If you can, I'd say use low ESR Sanyo or Nichicon electrolytic caps instead.

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Depends on how much space you got on your board. I'd stay off tantalums unless they are *really* needed since they have this tendency to self-incinerate every once in a while. If you can, I'd say use low ESR Sanyo or Nichicon electrolytic caps instead.

The datasheet, recommends using Panasonic HFQ (replaced with FC)series, Nichicon PL, Sanyo MV-GX or equivalent elcos. The recommended tantalums are hard to get and atleast here only available through mouser or digikey.

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@olga42:

It seems like the majority of folks on this forum hate tantalums :) They are, however, fairly good at filtering HF noise. I think even the low ESR electrolytics were tested (see some of those PDF links earlier in this post, though I'm not sure which page they are on so you may have to do some digging/searching) and tantalums were still much preferred. I think using them past the regulated section of a PSU should help avoid their explosive tendencies since, by that time, the voltage should be quite stable.

Regardless, I'll look again at the low ESR electrolytics. I have heard Panasonic is a great brand to go with from multiple places so that's probably a safe bet...as far as aluminum electrolytics go :)

@Shuriken

I assume you won't have more luck with a US-based store, but alliedelec.com has quite a few tantalums as well as Panasonic (and others) caps. I typically use them for more common parts (mostly since they are close by and shipping is uber fast usually).

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@olga42:

It seems like the majority of folks on this forum hate tantalums :) They are, however, fairly good at filtering HF noise. I think even the low ESR electrolytics were tested (see some of those PDF links earlier in this post, though I'm not sure which page they are on so you may have to do some digging/searching) and tantalums were still much preferred. I think using them past the regulated section of a PSU should help avoid their explosive tendencies since, by that time, the voltage should be quite stable.

Regardless, I'll look again at the low ESR electrolytics. I have heard Panasonic is a great brand to go with from multiple places so that's probably a safe bet...as far as aluminum electrolytics go :)

@Shuriken

I assume you won't have more luck with a US-based store, but alliedelec.com has quite a few tantalums as well as Panasonic (and others) caps. I typically use them for more common parts (mostly since they are close by and shipping is uber fast usually).

Hmm, akshually the tantalums are of better performance for this application, but given their volatile tendencies wrt voltage spikes, I'd say stay off them unless you have:

a) need for this performance or

b) a tightly defined operating environment or

c) you can absorb the cost delta

In this case I'd say that c) doesn't apply since it's DIY and you won't exactly use thousands. The other conditions still apply though. Guess I just like to play it safe when DIY-ing and use rule of thumb. Please consider not bringing a howitzer to a knife fight :flowers:

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Yeah but, again, if you're using them as a post filter after the regulation phase of a PSU then it's a non-issue typically because, unless something really bad happens, the voltage past the regulator will be stable or nil meaning it is easy to predict what types of tolerances you will need for the tantalum. The data-sheet for the LM2675 includes a tantalum for the input so I could see that possibly being more of an issue depending on what is being used to feed the regulator. If it's the output of another, regulated, supply, however, then it's basically a non-issue.

Again, unless something goes really wrong :)

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Yeah but, again, if you're using them as a post filter after the regulation phase of a PSU then it's a non-issue typically because, unless something really bad happens, the voltage past the regulator will be stable or nil meaning it is easy to predict what types of tolerances you will need for the tantalum. The data-sheet for the LM2675 includes a tantalum for the input so I could see that possibly being more of an issue depending on what is being used to feed the regulator. If it's the output of another, regulated, supply, however, then it's basically a non-issue.

Again, unless something goes really wrong :)

I've gotten away with sticking tantalums in far worse places, but... I was also concerned with the safety of people since this being a DIY forum we shouldn't make assumptions about the skills of various persons building this. Metal oxide vapors are nasty. Have a go either way - rolling your own switcher is a good training exercise :sorcerer:

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Yeah I'm debating on building my own switcher, but I can't imagine being able to do it in a smaller space than I could buy one. I think if I was building my own PSU, I would just go the linear route since I already have that designed and have a prototype board ready to go for it. *shrug* I haven't decided what I should be doing yet :) But I have time anyway since I need to finish my final space measurements and need to start populating a new MB-6582 baseboard.

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I just found this topic and had an interesting read through all the various options mentioned. I was struggling with how to make the power supply and actually, the project hasn't moved from the shelve since then.

The idea of a switched power supply appeals to me, as three different transformers (as I was planning) combined with maybe a bit more safety (the crowbar-circuit mentioned here earlier seems like a decent option) will take a lot of space and money (which kept me from building one). I researched a bit more on opinions for switched power supplies and found that there are people who praise technology for making switched power supplies that are equally noise-less as linear power supplies. I also found people who throw all switched power supplies away and replace them with linear ones, because the switched ones are evil. So that doesn't get me any further.

I know that the SID isn't whispering quiet and that if synth manufacturers use switched power supplies all the time, maybe I could do so as well. Naturally they have budget as a heavy factor to consider, but even synths like the Andromeda and Prophet 08 use switched power supplies if I recall correctly..

Building my own switching power supply is not an option, I doubt that I can design something with less noise than a stock power supply, even when using a higher switching frequency, as layout and choice of parts seem to be a bigger issue than with a lineair design..

Therefore I lean towards the RPT-60 at this moment, together with a 7809 and some extra smoothing caps on all lines. I'm going to give it some thought during a good night's sleep...

Edit: not sure why I wrote all of this down. Seems to be an elaborate way to show my enthousiasm for this topic.. ;)

Edited by Flying Panther

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A good thing then that I ordered two RPT-60B instead of one, so you can buy the extra one from me :)

(I just ordered before the weekend and haven't heard anything back yet though, so bare with me)

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A good thing then that I ordered two RPT-60B instead of one, so you can buy the extra one from me :)

(I just ordered before the weekend and haven't heard anything back yet though, so bare with me)

If you're sure you don't need that extra one yourself, that would be perfect! But I don't want to be responsible for one of your projects not having a power supply.. :angel:

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No I bought 2 because of the exorbitant shipping and handling costs (the unit costs €22 on the website, the S&H is €25 :mad: ). So now it's about €33,50 per unit instead of €47 for one. The FM doesn't need that much power anyway so I can build a linear supply for it with parts I already have in stock.

Plus the order hasn't yet been confirmed so I could also just buy 3 now :)

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The diodes around the regulators are there for protection of the regulator incase of input short. The diodes on the output are (old skool) there for the protection of the phenomenom called latchup. As the sid chips are old style CMOS chips they are vunerable to this.

This design is much like Roland's design for the Juno 60. Which holds a lot of 4000 series cmos chips.

When the C64 PSU fails the 5V regulator will put out something like 10V. Since you have 30 euro chips behind it, a 1 euro circuit can make the difference. So i figure you spend a few bucks to safe you from spending a lot of bucks makes sense.

The crowbar circuit is there for when the regulator fails. If i look at the datasheet of the mc3423 it can also help with current limiting.

After reading a bit more into this, I get the idea behind the crowbar circuit. That might be a very useful safety measure. I also get the diode around the regulator (although the datasheet states that when capacitors behind the regulator arent over 10nF the diode isn't necessary, it might not hurt to put it in either).

What I don't really get is the latchup protection. The only application of a diode that I found was between two different power sources of a CMOS, not between the GND and V+. Not that I'm questioning your setup, but I'm trying understand what you did.

In this case (with a diode between GND and V+), when GND accidentally gets a voltage spike of more than 0.3V, it will flow to the V+ rail, right? But what if that is, say in a worst-case scenario something above 10V. Then you have 10V passing from GND to V+, which might damage the SID as it can only withstand 9V. Wouldn't it then be much safer to leave the 10V on the GND-rail and let that current blow a fuse or something?

Also, will the diode do it's work properly when fitted right after the PSU? In all documented cases I found, the extra components were fitted right before the CMOS that needed protection from latchup.

Could you explain the phenomenon a bit more and as well your solution to this? Because I feel like I'm missing some key point in the whole latchup matter. :)

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For the Meanwell RPT-60B (sitting nicely on my desk now, thanks NorthernLightX!), some extra electronics are needed to provide me with additional smooting (which is mainly a precaution, as the power supply itself seems to have a lot of smoothing capacitors already), but more importantly needs to convert +12V into +9V for the 8580 Sids.

This is the schematic I've come up with so far:

post-4703-006426600 1302898996_thumb.png

I'm not sure if I implemented the latchup protection right, as I still don't really understand what's going on (I just copied from what was posted earlier).

I will be using the modular SID boards, which will be connected to +5/AGND and +9 (which has no AGND to prevent ground loops on the SID-board). Now, if I understand correctly, to prevent latchup directly before the SID-chip, a diode needs to be placed between +9V and the AGND connected to the SID (coming from the +5/AGND rail). Also, I saw Shuriken used 1N4004 diodes in his schematic, but wouldn't a 1N4001 be sufficient as well (as 50V is quite a lot)? And could I maybe also use the 1N4148 here, or are those too small?

Also, I'm thinking of using a metal film and a ceramic 0.1uF capacitor on each rail, as they both provide different smoothing caracteristics (so I figured they will complement eachother). And when using this schematic, is there any advice on the smoothing capacitors on the SID boards? I intend to leave the whole regulating circuit out on the SID-board (rectifier, capacitors, regulator, capacitors), but I'm thinking, would it help protect the SID in any way to leave the (last) 0.1uF capacitor on the 9V input of the SID?

All thoughts are appreciated! :)

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I don't think you need the latchup on the regulated DC outs from the Mean-Well? I doubt they hurt anything though but the Mean-Well has safety features on it as well. As far as the filtering caps, yes they can compliment each other though you may want to look at tantalums in replacement or addition to ceramics. They tend to handle HF noise a better. Some people on the forums hate them, but as long as you pick out a properly rated cap I doubt there is anything to be concerned with. They have lower tolerances to voltage than electrolytics and are a bit more expensive but likely worth it if you really want to attenuate HF noise.

Leaving caps on the SID side is probably not going to protect it but may help give you more stable power or at least won't hurt anything. The .1uF is likely more for the regulator. Speaking of, be sure to check the datasheets for the regulator you are using since they often have very good information about capacitor choice and location.

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