m00dawg

Multi-Tap Transformers Versus Voltage Regulators?

119 posts in this topic

Wow that was very helpful and make sense! At least I think it does :) I've included a quick schematic of what I think you're saying.

yes that's what I meant :)

2200uF -> 330uF -> 330nF -> Regulator -> 330nF -> 100nF

I'd suggest something like:

2200uF -> (maybe 47uF, although not really needed) -> 330nF -> Reg -> 100nF -> e.g. 10 or 47 uF (some small electrolytic does make sense here) -> if you like, another 100nF (also not really needed but maybe doesn't hurt).

Should I tweak that a bit for the 7805 since it's input is not being fully rectified (looks like it could be half-wave if I'm not mistaken)?

no it's still full-wave, because "the GND is full-wave" in relation to the center tap :)

By the way, thanks a ton for the great explanation. If you lived where I did, I'd totally go buy you a beer :) I hope, at least for now, my thanks, admiration, and gratitude are enough (and that extends to everyone who has helped!)

no problem, just keep us posted about your results/experiences :)

S

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I'd suggest something like:

2200uF -> (maybe 47uF, although not really needed) -> 330nF -> Reg -> 100nF -> e.g. 10 or 47 uF (some small electrolytic does make sense here) -> if you like, another 100nF (also not really needed but maybe doesn't hurt).

To dive in a bit more, after the regulator, why a 100nF followed by a 47uF? In other words, why not have the 47uF first and then the 100nF after? I assume it's to help better filter noise but I'm not exactly sure why?

As for keeping everyone posted about my results, you can bet on that! I plan on making a nice, pretty, printed board of this thing when it's all said and done and would be more than happy to post my final schematic and board designs for all to use. I think there's a definite need for a clear alternative to the C64 PSU for those that can't get one or just want an alternative that's easier to work with, so hopefully someone can find all this work useful.

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To dive in a bit more, after the regulator, why a 100nF followed by a 47uF? In other words, why not have the 47uF first and then the 100nF after? I assume it's to help better filter noise but I'm not exactly sure why?

the small caps around the regulator are there to prevent that the regulator starts to oscillate. Don't ask me about why exactly this could happen etc, this is just the standard implementation from the 78xx datasheet. But as long as both capacitors are in direct neighbourhood of the regulator, the order won't matter much.

S

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*smacks forehead* duh! I should've remember that!

That said, I have updated the original schematic with the modifications. Will give it a go either today or sometime this weekend hopefully and let ya know what comes of it!

4251_sch_png3e87fcea16fc9d196178418d675f

4251_sch_png3e87fcea16fc9d196178418d675f

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Sorry, I've been away for a while.

The good news, I have a job now! It's a 2+ hour drive each way, so I don't get much free time.

Multiple capacitors: Why?

2 reasons..

A Big cap and a little cap: Big cap filters the power, little cap is much more effective for high frequency noise.

A bunch of big caps: Will fit in a low-profile case better than one cap that is the sum of them all.

That's especially useful if you are fitting your toy into a 1U rack mount.

Have Fun,

LyleHaze

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you've got the rotation of the rectifier wrong - the diodes must always poit towards the + rail :)

And the upper cirquit should be the one with the 7809.

But looks good otherwise - good luck :)

S

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Doh! You're right! Oversights on my part. Fixed on my schematic. Will definitely let you know how it goes! Definitely looking forward to this weekend! I can't really do much work on my MB-6582 without this part squared away.

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Moo: More changes,

Assuming that's a Bipolar supply (+ and -)

The transformer center tap is GROUND for both regulators.

The + side of the bridge (both cathodes together) goes to 7805 input.

The - side of the bridge (both Anodes together) goes to the 7905 input.

http://www.midibox.org/dokuwiki/lib/exe/detail.php?id=pga%3Abuildregbrd&cache=cache&media=pga:txandbridge.gif

CAUTION: the 78xx series are "In, Gnd, Out" pin order. The negative 79xx series ARE DIFFERENT!!

Have Fun,

LyleHaze

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Assuming that's a Bipolar supply (+ and -)

Not quite. It's a power-supply designed to replace the C64 power-supply in that it offers +5VDC and +9VDC. So I'm using the center-tap to half the voltage so that I'm jot jamming a ton of volts down the 7805's throat. I actually thought about making a supply that was 1:1 compatible (namely, it outputs 9VAC and 5VDC) so it could be used as a direct replacement. I opted not to go that route so that I could do some additional filtering. I am still going to try and make it almost pin-compatible so projects can be more easily modified to use it if need be.

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I'm afraid we're not there yet.

You'll have full-wave rectified DC to IC1 (5V reg)

You'll be feeding something resembling AC to IC2.

Don't order the PC board until you've thoroughly checked this out.

Have Fun,

LyleHaze

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I'm afraid we're not there yet.

You'll have full-wave rectified DC to IC1 (5V reg)

You'll be feeding something resembling AC to IC2.

no I don't think so. I've already explained what happens here - would you mind reading the rest of the thread before giving more comments? And if you still think it won't work, please explain why.

S

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Seppoman:

This was the first time in weeks I've had time to post.

Sorry if I didn't read it all thoroughly.

Regarding the final version of the circuit, It's not the way I'm used to seeing it, but if you say it will work, I believe you.

Have Fun,

LyleHaze

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lyle, sorry I didn't want to sound rude - just in my impression you sounded still too much set on thinking of it as a regular bipolar supply cirquit. From theory I'd say it should definitely work but I didn't try it out in reality yet. I'm playing a bit with a cirquit simulator now (http://www.falstad.com/circuit/) and so far it looks like it should work that way. It seems like some larger capacitor value on the primary side wouldn't hurt if  the cirquit should supply more than a few hundred mA, so maybe a second 2200uF cap could be added.

S

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Seems like it works, though I did have to add more capacitance like you mentioned (the LED on the 6V side showed a dip in current otherwise). That's a pretty awesome little tool, by the way!

The drop in current does seem to indicate that using multiple rectifiers might be a way to go as well. I really don't mind adding more capacitors though. The only issue I see is current draw. The 5V rail is going to be pushing more current than the 9V. Wilba's estimates put it at around 1A if memory serves.

What's interesting is that I built my circuit that I was using previously and it sort of explains a bit of what was going on (and why I was probably blowing fuses). I'm going to keep playing around with this thing and then perhaps see about testing it.

4262_Picture_3_png704e81a963470bf9fbcf13

4262_Picture_3_png704e81a963470bf9fbcf13

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Seppo:

Likewise, I may have come off a bit wrong.

No offense intended, and I have taken none either.

This week has been stressful in ways I have not yet figured out, but it's nice to be working again anyway.

All:

Have a great weekend,

LyleHaze

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Ok I built the thing and it seems to be working like a champ! I haven't yet used it to power my current MidiBox yet, though, but there's no shorts, no blown fuses, both LEDs light up, and the output is +5 and +9VDC. I'll throw some pictures up soon, but for now, I need a break :)

BTW, that really simple and easy to use circuit simulator (which I use a lot too) can be found at http://www.falstad.com/circuit/

FYI, seppoman posted the link already two posts ago :)

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i took a look, and first impulse was to think you needed another bridge rectifier, but second look it seems this is better since it should balance the load on the two halves of the secondary.  i'd love to see a scope shot of the outputs, maybe i'll build one... will be a while though...

my .0047 ucents

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The more I think about it, the better I like it.

After a nice long 2.5 hour drive home, it makes much better sense.

Big thanks to Seppoman for being patient with me.

Oh, and I'd rather see a scope shot of the regulator INPUTS. the outputs would be boring as hell to look at if they are working. :-)

This does NOT "balance" the load on the secondary.

The current from the "top half" will be the supply for the 9v regulator, and the current on the "bottom half" will be the sum of the current of both regulators. I think.

I don't know enough about transformers to say if that might be a problem or not.

Enjoy Life,

LyleHaze

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It's about 15V on the 9V side (before the regulator) and 7V on the 5V side (also before the reg). Working on pictures right now, although I only have a multimeter. No oscope coolness or anything :)

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So I don't want to flood the forum with pictures of this thing, but here's 4. Two are what lylehaze wanted to see, namely the voltage before the regulators. The 3rd is a shot of basically everything after it has been installed and the 4th one is the box all closed up and ready to be used.

I should point out that I haven't yet tested this with beyond the multimeter and 2 blue LEDs on the inside of the box. I need to finish making the cable to connect to my MB-SID. I've basically settled on a 7-pin DIN to resemble the C64 connector (with similar pin-outs is the plan, though obviously it won't work properly as a drop-in replacement though that wouldn't be hard to do). I ordered the wrong 7-pin panel mount DIN connector so, for now, the cable just is knotted inside the box.

I'll let you know how those adventures go as soon as I get that far :) I hope to test it tomorrow but it took longer to build the circuit than I thought.

Note that, if all goes well, I'll be making a printed board for this whole thing. As you can see from the pictures, I'm not so great at soldering on a prototyping board :) Plus a printed board looks way more awesome (and should take up less room, or at least let me match up the holes in whatever case I end up going with - either the blue on or, perhaps, one a bit smaller. And I can use some hardy Molex connectors for the power in and outs.

One final question if I may. The power connector is a 3 prong and I'm not currently using that 3rd prong for anything. I know it's earth ground (and is there to protect oneself from stupid things) but I'm not sure how to connect it, even if at all.

(by the way, if anyone wants to see more pics, though they aren't terribly interesting, I'm throwing them up on my website)

4265_DSC_0097_jpg017272c529f27c63c185933

4267_DSC_0099_jpg36a1885e5b71c1008adadd2

4269_DSC_0102_jpg04746b21894749b46eccc4d

4271_DSC_0109_jpg021aabe0bc880c8a99e94a5

4265_DSC_0097_jpg017272c529f27c63c185933

4267_DSC_0099_jpg36a1885e5b71c1008adadd2

4269_DSC_0102_jpg04746b21894749b46eccc4d

4271_DSC_0109_jpg021aabe0bc880c8a99e94a5

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Oh one more note...the caps I used aren't exactly what we've been discussing. I was running low on spare caps so I made a few substitutions. For the final design, I may use a slightly modified design as well (given what we discussed with the +5V side possibly needing a bit more capacitance).

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So I don't want to flood the forum with pictures of this thing, but here's 4.

(by the way, if anyone wants to see more pics, though they aren't terribly interesting, I'm throwing them up on my website)

Don't be shy man, chuck em up here :) You never know when some dude will be hoping to see it later....

Good luck with the final tests!

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...

This does NOT "balance" the load on the secondary.

...

I don't know enough about transformers to say if that might be a problem or not.

these two lines don't go so well together...

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