Bipolar power supply

[jplebre]

Wouldn't the screws possibly short? I bought a couple of clip on heathsinks, ideas of which is preferable?
I tried a double sided board once (for actual circuit traces) and it went terribly but since it's only for the heatsinks I don't need to be exact and it's actually a good idea!

@egasimus looks like it has more filtering (more caps) It also has a resister that fixes an issue with the 79xx not conducting when no load is present.

Beginning to think I might add one myself.

Any ideas on this one?

Also, about the filter caps - when enough filtering is enough?

Cheers
J

[Pablo1234]

Diminishing returns on filtering would be a decent answer. their will be a point where adding capacitors adds more cost and reduces the ripple in smaller degrees, it has a lot to do with current draw also. I typically use 2 4400uF Electrolytic caps and 1uF Ceramic for each side. I also do a 5V rail on mine though so you may not want as much capacitance.

Wouldn't the screws possibly short? I bought a couple of clip on heathsinks, ideas of which is preferable?

if you look at my drawing I have the negative voltage as the pad/copper back to mount the regulator to isolated from ground, its on both top and bottom.

top traces - component side


Bottom traces

[DavenPaget]

Diminishing returns on filtering would be a decent answer. their will be a point where adding capacitors adds more cost and reduces the ripple in smaller degrees, it has a lot to do with current draw also. I typically use 2 4400uF Electrolytic caps and 1uF Ceramic for each side. I also do a 5V rail on mine though so you may not want as much capacitance.

Wouldn't the screws possibly short? I bought a couple of clip on heathsinks, ideas of which is preferable?

if you look at my drawing I have the negative voltage as the pad/copper back to mount the regulator to isolated from ground, its on both top and bottom.

top traces - component side


Bottom traces

I was so stupid to think 1 LM78XX can do more then 1A , with my overkill heatsinking , but i hope it can , since it will most likely stay at  25C .
Then i forgot i used 1N4007 diodes . :\
Oh well , if i need more amperage i would need to connect another "module" .
1A is pretty much enough ( 1A per rail , my xformer (50VA) and bridge rect does 4A ) .

[jplebre]

@Pablo I think the data sheet of my 7915 has an error then. It says back connected to i/p
http://pdf1.alldatasheet.com/datasheet-pdf/view/22633/STMICROELECTRONICS/L7915CV.html

Anyone else had the issue that the guys on MFOS had of the negative Reg not working without load? I can just use kirchoff law to calculate what size resistor to add?

[DavenPaget]

@Pablo I think the data sheet of my 7915 has an error then. It says back connected to i/p
http://pdf1.alldatasheet.com/datasheet-pdf/view/22633/STMICROELECTRONICS/L7915CV.html

Anyone else had the issue that the guys on MFOS had of the negative Reg not working without load? I can just use kirchoff law to calculate what size resistor to add?

There's no problem with the datasheet .
Oh i haven't tested mine yet , but i guess it's fine , each of my pedals do at least 8ma .

[Pablo1234]

yes the data sheet is correct, if you look at my drawing the copper pad is the input voltage.

[DavenPaget]

yes the data sheet is correct, if you look at my drawing the copper pad is the input voltage.

You basically had the entire board as the ground ? Sorry i have not seen someone do a double layer here .

[Pablo1234]

no the Ground and negative input voltage pads are on both sides. I do dual layer all the time, I use proppelors alot for logic and controls and with that much I/O it would suck to try it on 1 layer, dual layers make everything simpler.

[jplebre]

Slightly OT, but how to you line up your 2 layers?? :S

now back on topic, if I wanted to add some sort of fuse (say that I'm plugging it to something that is shorted, so I'd like to protect the power supply) how would I go about it? would I need 1 per rail?
http://uk.farnell.com/littelfuse/60r010xu/polyfuse-ptc-radial-0-1a/dp/1822246

My guess would be before the Vregs, after the caps. But what about the negative supply? There isn't any polarity either, right?

[DavenPaget]

Slightly OT, but how to you line up your 2 layers?? :S

now back on topic, if I wanted to add some sort of fuse (say that I'm plugging it to something that is shorted, so I'd like to protect the power supply) how would I go about it? would I need 1 per rail?
http://uk.farnell.com/littelfuse/60r010xu/polyfuse-ptc-radial-0-1a/dp/1822246

My guess would be before the Vregs, after the caps. But what about the negative supply? There isn't any polarity either, right?

Wouldn't it be better to be before the transformer ? protects the transformer too .

[jplebre]

Stopping it on the secondary side would also protect the transformer, no?
Just It would stop current on that side?

Also, I've put them on secondary side because someone told me we shouldn't mess about with the primary side.

Any opinions anyone?

Cheers

[EATyourGuitar]

http://search.digikey.com/us/en/products/CC3-1212DF-E/445-2472-ND/920432

http://search.digikey.com/us/en/products/CC6-1212DF-E/445-2488-ND/920448

you wont find better specs at a better price for a small footprint assembled and tested DC to bipolar DC module. I will be using one of these for a 9.55VDC visual sound one spot powering some synth circuits in a pedal. its also great for increasing the gain and headroom of an op-amp. the smaller one is 100ma per rail. the one spot is 500ma. no problem.

I have seen all those AC to bipolar supplies posted everywhere and they are all similar in concept. you convert AC 110 to AC 12V or 16V. then you rectify each rail.. filter with huge caps. use 3 pin regulators for the end game. thats all good and great if you supply the wall wart with the pedal. I found some cheap wallwarts on jameco. there is a strip board version of the MFOS supply if you already have the transformer. its posted on electro-music forum.

remember kids, don't kill yourself building power supplies

[jplebre]

http://search.digikey.com/us/en/products/CC3-1212DF-E/445-2472-ND/920432

http://search.digikey.com/us/en/products/CC6-1212DF-E/445-2488-ND/920448

you wont find better specs at a better price for a small footprint assembled and tested DC to bipolar DC module. I will be using one of these for a 9.55VDC visual sound one spot powering some synth circuits in a pedal. its also great for increasing the gain and headroom of an op-amp. the smaller one is 100ma per rail. the one spot is 500ma. no problem.

I have seen all those AC to bipolar supplies posted everywhere and they are all similar in concept. you convert AC 110 to AC 12V or 16V. then you rectify each rail.. filter with huge caps. use 3 pin regulators for the end game. thats all good and great if you supply the wall wart with the pedal. I found some cheap wallwarts on jameco. there is a strip board version of the MFOS supply if you already have the transformer. its posted on electro-music forum.

remember kids, don't kill yourself building power supplies

Need to look into those for pedals. This is for a rack unit with preamp, eq, compressor etc that I'm putting together from different schems. I do need a stable power supply. I can't go really higher than 15 because of one of the JFet's I'm using, so that wouldn't be good for me (I still need the AC conversion and tbh I'd like to design a safe'r power supply - hence taking the time in this forum, with very lovely people, to try and understand the schemos I found better, and to put them together to build a better one

[EATyourGuitar]

if you are putting 110AC mains wiring inside the unit there is a lot to consider. I'm no expert so I'll leave it up to you to find good information. remember that if you dont do it right, you could die or burn down someones studio or house. if you can't do it right or your not sure if you did it right then don't do it.

[jplebre]

Actually, I'm putting 240v
I live on the other side of the pond 

Bump on the fuses: The rack will have an IEC lead i/p with fuse holder on the live terminal BUT I will still be doing testing. I built the small bear Wall Wart (240VAC to 9VDC) and it had a fuse on the + side of the secondary.
Any ideas? Fuse on both the + and - side on secondary or just a fuse on the primary? would the secondary also protect the transformer?

[Pablo1234]

you absolutely must use a fuse from the cord to the primary on all live wires, if its 240VAC single phase, this means a live and a neutral you only need one on the live side. If however you are doing 220 2 phase, that's 2 110VAC 180 Deg out of phase then you need one on both live wires. Almost every country is different and you really should look at how primary wiring is done in your country. Al ot of people add MOV's to their primary side also and a switch rated at your country line voltage and current draw is a must also. this is kinda where you start and finish your design, the regulation is secondary to the safety of the unit.

you can fuse the secondary side but its not required.

[Pablo1234]

Slightly OT, but how to you line up your 2 layers?Huh? :S

its not as hard as you might think. first you need to get your margins on the printer consistent from print to print, I use 4.5 on my brother laser printer and measure them on each print job. If it prints consistently withing +/- .005" then your ok and just mirror the top layer.

its helpful and more reliable to have a form to set everything up, I have a small 6" x 6" piece of sheet metal with a 90 deg bend on the top and side for alignment. you put the bottom print job facing up into the form then the dual side board then the top print job facing down and if its all pushed into the corner it will line up every time. then you just set your iron on it till its all stuck together and you can then move it about to really iron it together.

you must also make sure that your boards are square and straight.

Another option is too print out the bottom layer, lay it over the board and drill 2 holes, on in the top right corner and one in the bottom left corner. then you stick a needle through the printouts of the top laser print job that correspond to the board drill holes and ling it up then iron it on till its stuck and do the same for the bottom. this is how I used to do it and its not as difficult as it sounds.

[jplebre]

you absolutely must use a fuse from the cord to the primary on all live wires, if its 240VAC single phase, this means a live and a neutral you only need one on the live side.

this is the one I'm using - 2 birds in one stone - full on IEC lead wich is what 19" rack equipment generally use, allowing me to earth the chassis straight there, and built in fuse holder.
http://www.rapidonline.com/SearchResults.aspx?kw=23-2100