Midibox PSU

Design Concepts
1

Hi all,

Ater my recent “success” with my 9v/5v/GND PSU, and in an attempt to give something back to the MidiBox community, I’m designing a PSU that delivers +12v -12v +9v +5v and GND, so every MBHP module currently available can be powered from it, with clean filtered current.  I’ve created a schematic for it (and I’m not very expirienced with electronics, so all comments are welcome!):

The goal is for it to consist of parts that are easily available, for example new from Reichelt, so anybody can build a good, stable PSU capable of powering all modules without the need for complicated tricks and/or unreliable second-hand stuff (after 2 malfunctioning C64 PSU’s this has been a big wish for me, I can’t imagine nobody else would :slight_smile: ).

I’ve tried to build a PCB from the schematic, but as I don’t know the right dimensions of the components, I think that’s not very useful yet.

I’ve looked at my own wishes when designing this thing, and that is to have in 1 box: 4x Core, 4x SID, 3x DOUT+LEDs, 2xDIN, Backlit LCD, LTC, AOUT, additional Filters. I’ve estimated the total load not to exceed 2A, but I believe proper heatsinking of the 7812, 7809, and 7805 are a must. I’m not sure if this schematic could also be used for MidiBox LC, as I haven’t studied it’s power requirements, any advise is welcome.

I’ve read that a Toroid/Ringkern Trafo delivers the cleanest current of all trafo’s. At Reichelt there is this trafo: :“RKT 8012 - Ringkerntrafo, 80 VA, 2x 12 V, 2x 3,33 A”. Is that a good choice, or are there better suitable ones in their catalogue that I haven’t found yet? It’s priced at 15,65 euro.

Hope to hear from you guys soon!

Cheers,  Alex.

[edit]

Found this one: “RKT 5012 - Ringkerntrafo, 50 VA, 2x 12 V, 2x 2,08 A” - it’s 2x 2,08 A instead of the 3,33A of the other one, should be enough I guess. Price is 12,30 euro - 3,70 euro lower.

There’s also this one: “RKT 3012 - Ringkerntrafo, 30 VA, 2x 12 V, 2x 1,25 A”. I’m not sure if it can deliver enough current. It’s price is 11,95 euro, only 35 cents cheaper than the 2,08A so I think the 2,08 A is preferrable anyway.

Also lightly modified the schematic, replaced the +9v and +5v 4 1x2 SIL headers with 1 2x4 DIL headers, and replaced the +12v 1x2 SIL header with a 2x5 DIL header (for adittional 4x SID6581). Maybe I should extend the +12v to a 2x6 DIL and the -12 to a 2x2 DIL, so AOUT(LC) and OPL3 can be attached at the same time.

[/edit]

[update]

Alle images were moved to the WIKI: http://www.midibox.org/dokuwiki/northernlightx

[/update]

2

Hi there!

Do I see that wrong? The schematic is only partly visible. The right side is cutted away somehow… fix?

In most apps (W/O LC or motorfaders!!) the current load won´t even succeed 1A pretty sure. If you´re going for bigger stuff with one than one core you´re probably able to go above the 1A mark, but normally a wallplug with 500 mA is enough (the BIG sucker still is the LCD with up to 300 mA). So the 1,25A Trafo should be enough, too.

The LC will suck a lot more and many people already built their own PSU´s for that.

I also built a few PSU´s, but after a while I recognized that it´s not worth the work. I do NOT want to bring down your work in any part (!!!). But normally you can power a MB with a 9V/1A wallplug very well and they cost appr. the same as the trafo alone would cost… Just as a small sidehint to think twice before building the PSU by yourself.

On the other hand it´s TOTALLY something else if you need symmetric voltages (-12/GND/+12). There are nearly no wallplugs for that and you are better of with building them by yourself (so your schematic just shows the right stuff!).

So: Where´s the PCB? ;D ;D ;D :wink:

Thnx and greetz!

3

Hi there!

Do I see that wrong? The schematic is only partly visible. The right side is cutted away somehow… fix?

In most apps (W/O LC or motorfaders!!) the current load won´t even succeed 1A pretty sure. If you´re going for bigger stuff with one than one core you´re probably able to go above the 1A mark, but normally a wallplug with 500 mA is enough (the BIG sucker still is the LCD with up to 300 mA). So the 1,25A Trafo should be enough, too.

The LC will suck a lot more and many people already built their own PSU´s for that.

I also built a few PSU´s, but after a while I recognized that it´s not worth the work. I do NOT want to bring down your work in any part (!!!). But normally you can power a MB with a 9V/1A wallplug very well and they cost appr. the same as the trafo alone would cost… Just as a small sidehint to think twice before building the PSU by yourself.

On the other hand it´s TOTALLY something else if you need symmetric voltages (-12/GND/+12). There are nearly no wallplugs for that and you are better of with building them by yourself (so your schematic just shows the right stuff!).

So: Where´s the PCB? ;D ;D ;D :wink:

Thnx and greetz!

Hi pay_c

in my browser (opera) there’s a horizontal scrollbar at the bottom of my post so you can see the rest of the schematic. Please let me know if that works, if not I’ll remake the picture in a smaller footprint.

You are totally right: for small midiboxes a common wallwart is sufficient, but I’m not aiming at that :wink:

I’m aiming for the boxes that need -12v (OPL3, AOUT) and/or a double voltage that is difficult to create with new parts (e.g. +12v/+5v for multiple 6581 SIDs, your 7805 will get hot enough to fry an egg if it has to remove 7 volts, but you already knew that).

My experiences with C64 PSU’s are BAD to say the least, so I wanted NEW stuff I can trust on. Also, in my own box I’m going to need all 4 voltages, and I believe other people will also want to add AOUT to their SID boxes, and for them this PSU design will be what they are looking for, I believe.

The PCB I’ll have to recreate, I don’t have the correct part footprint, and without that it’s worthless anyway. Will give it a shot tonight maybe.

Cheers,  Alex.

4

Looks good to me (not that I know electronics too well), and it sounds like you’ve got a hell of a plan here - A C64 PSU will be an average of 20 years old, so there’s obviously gonna be a few dead ones around, and the good ones may not stay that way for long. The idea of a universal MB power supply is awesome, and it could even be a cool addition to the MBHP - MBHP_PSU anyone?

5

Ok, so you already got the point! Cool! ;D

Aaaaaaah! THERE´s the scrollbar! CEWL! :wink:

So i totally agree. Just some minor errors/suggestions/whatever:

  • I can´t read the negative voltage regulator - it´s a 7912, right?

  • you really don´t want to use 10 mF caps, right? Those will be F****ING huge! ;D :wink: Meant 10uF, right?

  • I think 1000 Ohm for the LED is a little much @5 volts, 220 Ohms would be better for a “normal” LED. Unless you´re using a low-current LED?

And just as a small hint: Go through the Eagle tutorial shortly! It´s really worth the time! E.g. u can rip up all those GND-wires by using the grounding symbol (wrong-way T-like thingy) and so keep the schematic a bit easier to understand.

Good luck & much of fun with the PCB (I dooo like etching) & greetz! :slight_smile:

6
  • I can´t read the negative voltage regulator - it´s a 7912, right?

Yes, thats a 7912, I based the +12/-12v part of the schematic on the OPL3 PSU schematic on uCApps.de

  • you really don´t want to use 10 mF caps, right? Those will be F****ING huge! ;D :wink: Meant 10uF, right?

I don’t see mF, does anybody see mF???  ;D (Fixed)

  • I think 1000 Ohm for the LED is a little much @5 volts, 220 Ohms would be better for a “normal” LED. Unless you´re using a low-current LED?

I’m using a high intensity LED, but I don’t want to blind the audience, so I mount a 1K resistor. For the schematic I agree woth you though, so I’ve replaced it with a 220 Ohm resistor.

And just as a small hint: Go through the Eagle tutorial shortly! It´s really worth the time! E.g. u can rip up all those GND-wires by using the grounding symbol (wrong-way T-like thingy) and so keep the schematic a bit easier to understand.

I already understand how to route the tracks (took me some time, ratsnest rules!) but for me, the ground wire makes it more understandable! I’m really an electronics n00b. Last night I learned for the fiorst time that on the PCB it doesn’t matter in what order the components are placed (e.g. ceramic cap between el. cap and rectifier, instead of behind the el.cap as in the schematic)! So I’ll check the dimensions of the parts tonight, update the schematic with the right parts, and build a PCB in eagle. I’ll post it when it’s finished.

I’ll leave the trafo off the board, no need to waste that space. Any suggestions on how to mount a Ringkern Trafo in an enclosure (exept for ducttape :slight_smile: )?

Good luck & much of fun with the PCB (I dooo like etching) & greetz! :slight_smile:

Thanks, and if you’re etching anyway, maybe do a sprare board for me?  :wink: :-*

Cheers,  Alex.

7

Hey, I see you’ve been working on this behind my back  ;D

You can do this with one less rectifier, just connect the two center leads of the trafo together to earth and connect the positive side of the rectifier to the positive line and the negative side to the negative line.

It should look a bit like this

http://1176neve.tripod.com/id26.html

8

Hi,

I’ve updated the schematic with the “one rectifuer only” design mendelt came up with. Then I selected parts at Reichelt, and implemented the correct measurements of those parts in Eagle. I’ve been working on the PCB for a few hours (and I should’ve been sleeping) but I hope it was worth it. I’ve exported the board as a picture:

The space around the regulators is intentionally left open for proper heatsinking (although the 7912 probably will not get hot at all).

Any commenst/suggestions?

9

Hi NorthenLightX!

Just two small things: Did you only use the top layer as routing? Normally you would use the bottom layer for that, but doesn´t matter to much.

Open up the manual for Eagle and search for “Copper fill” - that´s the thing for filling up the empty spaces with the GND.

Also, the GND should be on the same side on all connections - but that´s also just a very small thingy. :slight_smile:

Greetz!

10

This would be great for modular builders.  Sticky?

11

Hi NorthenLightX!

Just two small things: Did you only use the top layer as routing? Normally you would use the bottom layer for that, but doesn´t matter to much.

Open up the manual for Eagle and search for “Copper fill” - that´s the thing for filling up the empty spaces with the GND.

Also, the GND should be on the same side on all connections - but that´s also just a very small thingy. :slight_smile:

Greetz!

it looks like I did, doesn;t it? oops…  :-[

I will copper fill the thing when it’s finished.

Why should the GND be the same direction? that way I get all kind of unwanted routing problems… ???

12

OK, some more changes will be implemented:

  • Bridge rectifier will be replaced by discrete diodes (avalable bridge rectifiers might not fit the pcb-holes correctly, diodes always fit)

  • Mendelt currently is researching a design change to try to get the regulators less hot (not the use of bigger heatsinks). Fortunately, he knows more about electronisc than I do. Results will be posted as usual.

Cheers,  Alex.

13

This is great  8)

14

Why should the GND be the same direction? that way I get all kind of unwanted routing problems… ???

Ooooops! Didn´t know that, sorry!  ;D

New design?  8) Looking forward! (MBPSU coming up ;D ;D ;D - really good work NorthernLightX!!!)

15

Update:

the 10uF caps have been replaced by 22uF caps. Diodes are in place.

I’m looking forward to receive Mendelt’s findings, last time I spoke with him he suggested placing the 7809 and 7805 directly after the big filtercaps, with a 5w 5Ohm resistor…I don’t really understand it all but fortunately he knows his stuff :slight_smile:

Cheers,  Alex.

16

[edit]

Images removed due to design flaw. Will post new ones below.

[/edit]

This is the final version so far.

I am really content with the board, it was fun actually, like a puzzle :slight_smile:

The regulators are placed in a line, Mendelt’s suggestion was to make it possible to use the case (if it’s aluminium for example) as a huge heatsink. I needed some space on the edge of the board for routing, so I’m not sure if that’s possible, still a good piece of aluminium could function as a nice heatsink for all 4 regulators.

I’ve also taken pay-c’s advise into account, and all SIL headers have the GND on the same side now, exept for the 3 legged headers, where GND is the middle pin.

More last minute changes: the 330n WIMA film capacitors where exchanged for 220n Kerko’s - Mendelt suggested that Kerko’s are much better at filtering higher frequencies than the film caps.

The 2 resistors are placed to keep the 7809 and 7805 cooler. How this works exactly, and if I’ve placed them right, I don’t know. They are 2W 10Ohm resistors in parallel, forming a 4W 5Ohm resistance.

Any comments are still very welcome! If the design is approved, I’ll release the Schematic and .BRD file to the community, along with a Reichelt partlist. Total costs of the PSU are about 20 euro (including 2x 12v Toroid transformer @ 2A, excluding heatsink and PCB) when ordered from Reichelt.

Cheers,  Alex.

17

Nice work guys. Once it’s all final and documented etc, I think this module would make a great addition to the MBHP.

18

Hi!

The 2 resistors are placed to keep the 7809 and 7805 cooler. How this works exactly, and if I’ve placed them right, I don’t know. They are 2W 10Ohm resistors in parallel, forming a 4W 5Ohm resistance.

These resistors become part of the “load” on that particular branch of the power and cause voltage drop before voltage enters the regulator - this helps regulators run cooler. (Less voltage to “regulate” - less power to dissipate as heat)

One word of warning:

Don’t connect 7912 directly to the same heatsink as 78** regulators. The metal tab (and the middle pin) is voltage input here. Use insulator and plastic screw.

Moebius

19

These resistors become part of the “load” on that particular branch of the power and cause voltage drop before voltage enters the regulator - this helps regulators run cooler. (Less voltage to “regulate” - less power to dissipate as heat)

One of my co-workers, who is also fairly skilled with electronics, pointed out that my schematic is flawed, and so the board is useless too! I have to put the resistors in series with the input of the 7809 and 7805. I will correct this asap, in the meantime the current pictures will be removed temporarily, sorry.

One word of warning:

Don’t connect 7912 directly to the same heatsink as 78** regulators. The metal tab (and the middle pin) is voltage input here. Use insulator and plastic screw.

Moebius

Thanks for the warning, I indeed did not take that into account! The 7912 will not become all that hot though, not much stuff makes use of the -12V anyway, and since I’ll have to redesign the board anyhow, I’ll put it in a separate space.

Cheers,  Alex.

20

Learned a lesson the hard way: Pay attention to the ratings on your components. I was building a PSU for my SID and used a 16V 1000uF cap, unfortunately I didn’t read the rating properly and hooked it up to 24V. Around 20 seconds later it went BOOM. Smoke and bits of capacitor everywhere….Lesson learned!  ;D

-Dave