Calling all electronics gurus! Need help with DC supply design.

**taggalucci** · 05-10-2011, 18:24

My plan is to use a single-ended 24v SMPS. From this, I wish to run:

some 12v DC fans (assuming I can run them in serial-linked pairs)
a DC-DC step-down 24v to 8v switching converter running all diode drivers and interlock signal
an isolated DC-DC converter providing -24V for scanner amps
+24V for scanner amps

I want to use the smallest and least components necessary which is why I am not opting for two or more SMPSs.

Would the DC fans produce any electrical noise that would need to be filtered and what would you suggest if so?

Will I need to consider any additional electronics to achieve a desirable supply to the diode drivers and scanner amps?

Have I completely lost my mind thinking this would even be possible?!

Thanks in advance

**-bart-** · 05-11-2011, 02:15

I would be hesitant to run 12v dc fans in series on 24v.
If one becomes stuck or wears out sooner than its counterpart, the voltage will be distributed uneven, possibly causing an overvoltage on the other.
There are solutions for this problem, otoh 24v fans are out there too.

**dnar** · 05-11-2011, 02:24

Originally Posted by -bart-

I would be hesitant to run 12v dc fans in series on 24v.
If one becomes stuck or wears out sooner than its counterpart, the voltage will be distributed uneven, possibly causing an overvoltage on the other.
There are solutions for this problem, otoh 24v fans are out there too.

This is true, I have been through this lately with a new product...

At the end of the day, I would prefer to use dedicated supplies. +/-24V SMPSU are a plenty and come with most galvos.

A single 12V supply could then power your fans and with a simple switching step down regulator provide +8V also.

I am using a 12V SMPSU to provide 9V (via the adjustable trimpot) for my Blue module.

If your set on building a step down buck regulator, I can highly recommend the National Semi "Simple Switchers". They used to sell eval boards, and that might be just the ticket!

See here: http://www.national.com/analog/power...tcher#appnotes

and here: http://www.national.com/vcm/national...sign_guide.pdf

PM me if you need any more info or help.

**hivelaser** · 05-11-2011, 04:34

I am looking for something like this too... or any link to a small 12V PSU.

**taggalucci** · 05-11-2011, 04:53

Thanks guys, I'll have another think about this in light of your suggestions.

I'll be in touch by PM Wayne, thx mate

I expect I'll do this tomorrow now.

**dnar** · 05-11-2011, 06:28

Originally Posted by taggalucci

Thanks guys, I'll have another think about this in light of your suggestions.

I'll be in touch by PM Wayne, thx mate

I expect I'll do this tomorrow now.

No worries mate.

**Banthai** · 05-11-2011, 07:30

Hi ya taggalucci

the other thing to think about when using a single PSU is for instance .....that if a diode should fail short circuiting the PSU the whole laser projector is dead ... but with seperate diode Power supplies if the red diode fails ... the other colour diodes keep going and the show goes on ... with slightly less colours

but you can still finish the show and get paid ( if you are doing a pro show )

also best to run the fans on correct supply (same as above) should a fan short circuit then you have 24v feeding the others and they will also blow ...

hope this helps ... Karl

**flecom** · 05-11-2011, 08:27

also a lot of fans will induce noise into their power source, so its best to avoid putting them (or anything else for that matter) on your galvo power supply

if you are concerned about size making an external power supply is your best bet...

**dsli_jon** · 05-11-2011, 12:55

Hey Sir Tag...

I personally love the 'EOS' line.... http://www.eospower.com/open-frame-ac-dc.aspx in-particular, the WLT200 is great http://www.eospower.com/open-frame-a...spx?prodid=410 ...as it has a 'separate' 12V integrated for cooling-fans, and these puppies are so tiny, the classic +/- 24V two-supply array takes-up about as much space as just *one* of most cheaper enclosed-supplies... and they are just bulletproof - they are pricey little buggers, but I can almost guarantee you'll never replace them!

If cost must be a driving-factor, I've found the 'MeanWell' TP-150D... http://www.ecopacpower.com/category.php?catid=1 (scroll-down to the TP-100 and 150D...) to be a good-value, since it has +5, +24 and +12, all at more than-ample currents... If that form-factor is *still* not small-enough, and cost is critical, the MP-series from MW is also worth a look, since you should be able to build-up an all-in-one supply to give you 2x +24Vs (and you make them the +/- w a com, as-usual...) and 1x +5V and 1x +12V via the 'cards'... those are really nice-style supplies...

For DC-DC, I've always had good-success with Vicor micro-bricks http://www.vicr.com/cms/home/product...cro-converters but I've never tried using a DC-DC for the -24... not sure how the 'load-balance' would behave..

But

for these as nice, clean, isolated DC-smackdowns

Anyhoo, my bet would be on the EOSs... hope this helps...

cheers..
j

**taggalucci** · 05-11-2011, 17:59

Thanks guys for your responses so far

BTW, much of this idea is inspired by j4cbo and his post here.

Originally Posted by -bart-

I would be hesitant to run 12v dc fans in series on 24v.
If one becomes stuck or wears out sooner than its counterpart, the voltage will be distributed uneven, possibly causing an overvoltage on the other.

Very good point. I actually forgot that the 24V SMPS I have in mind has an isolated 12V @ 1A rail for fans - doh! I take it this should remove the fans from being an issue in this discussion?

Originally Posted by dnar

PM me if you need any more info or help.

Done! ...and I'm throwing a few things out here as well for the sake of this thread.

Originally Posted by Banthai

the other thing to think about when using a single PSU is for instance .....that if a diode should fail short circuiting the PSU the whole laser projector is dead ... but with seperate diode Power supplies if the red diode fails ... the other colour diodes keep going and the show goes on ... with slightly less colours

but you can still finish the show and get paid ( if you are doing a pro show )

This is really for a "cheap" n cheerful compact satellite projector, so total failure from one colour blowing is not really an issue, but I would want to know that adequate protection existed in the circuit to isolate such a failure from damaging other components. Assuming 3 FlexMod P3s were in use running a diode or two each, could a diode failure cause any damage to the P3 driving it, any of the other 2 P3s, the DC-DC step down converter running all 3 or the SMPS itself?

Originally Posted by flecom

also a lot of fans will induce noise into their power source, so its best to avoid putting them (or anything else for that matter) on your galvo power supply

As above, assuming an isolated 12V rail for fans, would fan noise continue to be an issue?

This would leave trying to extract 8V from the 24V supply prior to setting up a -24V rail with the isolated DC-DC converter. Would you expect noise to affect the galvos from doing this?

Originally Posted by flecom

if you are concerned about size making an external power supply is your best bet...

Ah, but my challenge is to get the whole lot in one box!

Originally Posted by dsli_jon

I personally love the 'EOS' line.... http://www.eospower.com/open-frame-ac-dc.aspx in-particular, the WLT200 is great http://www.eospower.com/open-frame-a...spx?prodid=410 ...as it has a 'separate' 12V integrated for cooling-fans, and these puppies are so tiny, the classic +/- 24V two-supply array takes-up about as much space as just *one* of most cheaper enclosed-supplies... and they are just bulletproof - they are pricey little buggers, but I can almost guarantee you'll never replace them!

If cost must be a driving-factor, I've found the 'MeanWell' TP-150D... http://www.ecopacpower.com/category.php?catid=1 (scroll-down to the TP-100 and 150D...) to be a good-value, since it has +5, +24 and +12, all at more than-ample currents... If that form-factor is *still* not small-enough, and cost is critical, the MP-series from MW is also worth a look, since you should be able to build-up an all-in-one supply to give you 2x +24Vs (and you make them the +/- w a com, as-usual...) and 1x +5V and 1x +12V via the 'cards'... those are really nice-style supplies...

Thanks for those links Jon, they look like great PSUs (especially the EOS ones), a little "big" though!

I'm trying to avoid a 2 SMPS array to get the +/-24v, especially if I then need another for the 8V and 12V. I already have the SMPS that came with the scanners (too big for my liking though!)

Originally Posted by dsli_jon

For DC-DC, I've always had good-success with Vicor micro-bricks http://www.vicr.com/cms/home/product...cro-converters

Hmm, they look pricey (nice, but pricey)! I'm thinking about something like this http://www.x-on.com.au/details-new.a...&p=PTN78020WAH at a better price and as per j4cbo's experience.

Originally Posted by dsli_jon

I've never tried using a DC-DC for the -24... not sure how the 'load-balance' would behave..

But

for these as nice, clean, isolated DC-smackdowns

j4cbo's using a Mean Well PSD-30B-24 for this. I'd be interested in his perspective on this.

Also, would there be a way to "load-balance" such an arrangement if this was a problem?

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