DIY Powersupply with +12v, -12v, +9v, -9v, 5v and variable voltage output ?

[SPoT_D]

Hi all,

Because i'm done with juggling a bunch of separate power supplies in a somewhat experimental setup (guitar, pedals, arduino and eurorack combination) I'm looking to build a power supply that can handle it all. There are plenty of examples online on how to build a supply for -12v to +12v, but I don't see many that have an added +9 -9 or added to that. Now since I'm a bit worried that doing it wrong will cause problems with overheating regulators or stuff like that, I was wondering if any of you have made such a power supply before or can point me into the right direction?

Do I ad  (-)9v regulators in series or parallel to the 12v ones?
Can I ad a 7805 and a LM713 to a bipolar supply like this:


(I have a 220 to 18+18 volt transformer and a KBL410 rectifier, in case that information helps)

[ElectricDruid]

I've done something very similar to what you're suggesting. My version had +/-15V rather than +/-12V. I added 5V and (later on) 3.3V regulators in parallel to get handy voltages for running PIC and dsPIC microprocessors.

It works well enough, but the 5V and 3.3V regulators do get hot because of the hefty volt drop across them. In an ideal world, I'd be able to find a transformer with a tap for the 5V supply. I'm sure there are such things, but I didn't find one. I sometimes need more power than my current supply can provide, so I've been thinking about building another, and I was wondering about using two transformers for the new one - one to do the bipolar audio supply (so a 18-0-18 like you have) and a separate one to do the logic supply. That would save the regulators from getting so hot. Obviously it will make the thing bigger and heavier, but since it only sits at the back of my workbench and never gets moved that's not a huge problem.

So I'd say go for it, but make sure you've got decent heatsinks, and make sure your lower-voltage regulators are well over-specced so you're not pushing them too hard because they'll have a lot to do just burning spare volts into heat as it is!

[merlinb]

I've been thinking about building another, and I was wondering about using two transformers for the new one - one to do the bipolar audio supply (so a 18-0-18 like you have) and a separate one to do the logic supply. That would save the regulators from getting so hot. Obviously it will make the thing bigger and heavier, but since it only sits at the back of my workbench and never gets moved that's not a huge problem.

Have you considered using a couple of SMPS? You can follow these with buck regulators to get the voltage down close to where you need it, efficiently. then use linear regulators for the final step to get quiet outputs.

[SPoT_D]

I've done something very similar to what you're suggesting. My version had +/-15V rather than +/-12V. I added 5V and (later on) 3.3V regulators in parallel to get handy voltages for running PIC and dsPIC microprocessors.

It works well enough, but the 5V and 3.3V regulators do get hot because of the hefty volt drop across them. In an ideal world, I'd be able to find a transformer with a tap for the 5V supply. I'm sure there are such things, but I didn't find one. I sometimes need more power than my current supply can provide, so I've been thinking about building another, and I was wondering about using two transformers for the new one - one to do the bipolar audio supply (so a 18-0-18 like you have) and a separate one to do the logic supply. That would save the regulators from getting so hot. Obviously it will make the thing bigger and heavier, but since it only sits at the back of my workbench and never gets moved that's not a huge problem.

So I'd say go for it, but make sure you've got decent heatsinks, and make sure your lower-voltage regulators are well over-specced so you're not pushing them too hard because they'll have a lot to do just burning spare volts into heat as it is!

Could you show me how you wired it up?
Would it work to distribute the heat if i ran the 5 volt regulator after the 9 volt one? So have the 12 volt regulators run parallel to the 9 volt ones, and the 5 volt regulators in series with the 9 volt ones?
Also: if I would put 2 +9v regulators parallel would that work?   so I'd get output jacks like  [+12 -12] [+9 -9] [+9] [+5] (all these with a common ground)

[Mark Hammer]

One can simply cascade a series of 3-pin regulators, in descending manner, bearing in mind that they always need at least 2V more at their input than they can provide at their output.  So  The output of +12V can feed a +9V regulator, whose output can feed a +5V regulator.  If you want to go super-deluxe, you can start with +/-15V, and extract 12, 9, and 5 from that, with positive regulators taking their feed off the positive line and negative taking theirs off the negative line.

For safety's sake, one is advised to use the larger 1amp regulators, simply because you don't know which of those outputs will be asked to provide the most current.

What I would ask the real EE types to answer here, however, is what sort of components are wise to place between the successive regulators.  We all see how a medium-size electro is normally placed between input and ground for typical 3-pin regulators, with a smaller electro and non-polarized to ground on the output.  But all those examples presume the circuit takes its feed from a transformer, and only one stage of regulation is involved.  One generally doesn't see what ought to happen when the output of one level of regulation is then down-regulated.

[SPoT_D]

One can simply cascade a series of 3-pin regulators, in descending manner, bearing in mind that they always need at least 2V more at their input than they can provide at their output.  So  The output of +12V can feed a +9V regulator, whose output can feed a +5V regulator.  If you want to go super-deluxe, you can start with +/-15V, and extract 12, 9, and 5 from that, with positive regulators taking their feed off the positive line and negative taking theirs off the negative line.

For safety's sake, one is advised to use the larger 1amp regulators, simply because you don't know which of those outputs will be asked to provide the most current.

What I would ask the real EE types to answer here, however, is what sort of components are wise to place between the successive regulators.  We all see how a medium-size electro is normally placed between input and ground for typical 3-pin regulators, with a smaller electro and non-polarized to ground on the output.  But all those examples presume the circuit takes its feed from a transformer, and only one stage of regulation is involved.  One generally doesn't see what ought to happen when the output of one level of regulation is then down-regulated.

Thanks.
So to sum it up, You think that something like this will work:

Just not sure what caps to use and if it needs something like a resistor or diode somewhere?

[davent]

For a power supply, +/- 18, 15, 12, 9, 6, 5v, you could use  heatsinked 317 & 337 regulators with a 1x6 rotary switch for each to change out the resistor that sets the output voltage.

I've used cascaded regulators as well.
dave

[R.G.]

Cascaded regulators spread the heat load out over all the regulators in the chain. Another dodge is to use resistors in series with the low voltage linear regulators to eat up the heat. You calculate the resistor values to soak up all but about 3V above the  low voltage regulator's output at its maximum current. This leaves most of the heat in the resistor instead of the regulator. A 3.3V regulator is likely to have a 100ma, 500ma, or 1A maximum current, so the resistor calculations are not too arduous.

As Merlin notes, you can use step down regulators to wipe off some of the excess voltage in a non-dissipative manner. This works well as long as you are careful about wiring, decoupling, and grounding to keep the switching module's noise out of the output of the linear reg. A linear reg does a reasonable job of reducing the noise in the regulated line after a switcher, but can't do anything about ground noise from the switcher, so you have to do the grounding right.

But we always have to do that right, yes?   

[Fancy Lime]

Hi there,

I have been pondering building something similar but with a different approach. I would like isolated power supply outputs to reduce ground loop noise problems. As Jack Orman pointed out in this thread
https://www.diystompboxes.com/smfforum/index.php?topic=122714.msg1158201#msg1158201
you can use DC-DC converters to isolate and at the same time step the voltage up or down. It is not very efficient but probably more efficient than essentially "burning" voltage in a regulator. I'm not sure though, needs calculating. Anyway, what this technique gets you, is a number of isolated outputs with a wide range of voltages of your choosing. That is IF you can get the right DC-DC converters, which I have not been able to track down so far. 9V seems to be the problem here. There seem to be 5V and 12V converters (to and from) aplenty on the market. I know 9V converters exist, I just haven't found a source yet (not spending an awful lot of time searching). So what you need then, is a strong DC powersupply with the right DC output to feed the inputs of your converters. I would go with 2A or more and 12V but it obviously depends on your requirements. With isolated DC outs, you don't care if it is, say, +12 or -12, because there is no DC path between them. As a bonus, the isolated outs can be bridged, so that you get e.g. 24V from bridging two 12V outputs.

Cheers,
Andy

[Mark Hammer]

One can simply cascade a series of 3-pin regulators, in descending manner, bearing in mind that they always need at least 2V more at their input than they can provide at their output.  So  The output of +12V can feed a +9V regulator, whose output can feed a +5V regulator.  If you want to go super-deluxe, you can start with +/-15V, and extract 12, 9, and 5 from that, with positive regulators taking their feed off the positive line and negative taking theirs off the negative line.

For safety's sake, one is advised to use the larger 1amp regulators, simply because you don't know which of those outputs will be asked to provide the most current.

What I would ask the real EE types to answer here, however, is what sort of components are wise to place between the successive regulators.  We all see how a medium-size electro is normally placed between input and ground for typical 3-pin regulators, with a smaller electro and non-polarized to ground on the output.  But all those examples presume the circuit takes its feed from a transformer, and only one stage of regulation is involved.  One generally doesn't see what ought to happen when the output of one level of regulation is then down-regulated.

Thanks.
So to sum it up, You think that something like this will work:

Yeah, pretty much.

Just not sure what caps to use and if it needs something like a resistor or diode somewhere?

You and me both, pardner.

BTW, if I have understood the original request, it is not to be able to provide ONE single output voltage that is switch selectable, but rather something like what many power bricks now do, which is several different supply voltages, simultaneously, to different devices with different needs.  E.g., this thing needs +/-9V, that thing needs +12V, and that other thing needs +5V

[ElectricDruid]

Just not sure what caps to use and if it needs something like a resistor or diode somewhere?

You and me both, pardner.

I've used 1N4004 diodes, one from the regulator output back to the input (for +ve regulators - reverse for negative), and one across the output. I no doubt copied this from some power supply schematic I saw somewhere because I no longer remember what they were supposed to do or protect against!
<goes to check>
Actually, it looks like I got it from the datasheet. The diode around the regulator protects it from a shorted input. They also show the diode across the output, but I can't find the explanation for that one on a quick scan through. They look like "belt and braces" rather than essential to me. For a power supply I think I'd probably go with belt and braces.

http://www.ti.com/lit/ds/symlink/lm7800.pdf

I also like to add a resistor+LED to keep an eye on the output. If one of the regulators goes into a thermal shutdown because you're hammering it, you can see straight away that's what's happened. Plus "more pretty lights = better", of course...

[Ice-9]

Just not sure what caps to use and if it needs something like a resistor or diode somewhere?

You and me both, pardner.

I've used 1N4004 diodes, one from the regulator output back to the input (for +ve regulators - reverse for negative), and one across the output. I no doubt copied this from some power supply schematic I saw somewhere because I no longer remember what they were supposed to do or protect against!
<goes to check>
Actually, it looks like I got it from the datasheet. The diode around the regulator protects it from a shorted input. They also show the diode across the output, but I can't find the explanation for that one on a quick scan through. They look like "belt and braces" rather than essential to me. For a power supply I think I'd probably go with belt and braces.

http://www.ti.com/lit/ds/symlink/lm7800.pdf

I also like to add a resistor+LED to keep an eye on the output. If one of the regulators goes into a thermal shutdown because you're hammering it, you can see straight away that's what's happened. Plus "more pretty lights = better", of course...

The diode around the regulator in/out also protects it from  a higher voltage on the output in reference to the input, for example if you remove power from the input a large cap on the output can hold the voltage higher than the input for a period of time, while this usually won't be a problem it can damage the regulator.

[SPoT_D]

Thanks for the replies guys. I have ordered a bunch of parts and will soon start prototyping, Please keep those tips comming

Another dodge is to use resistors in series with the low voltage linear regulators to eat up the heat. You calculate the resistor values to soak up all but about 3V above the  low voltage regulator's output at its maximum current.

I think I can do this with the first regulator (18 to 12), but is it wise to do  in the steps after that?

BTW, if I have understood the original request, it is not to be able to provide ONE single output voltage that is switch selectable, but rather something like what many power bricks now do, which is several different supply voltages, simultaneously, to different devices with different needs.  E.g., this thing needs +/-9V, that thing needs +12V, and that other thing needs +5V

exactly.

The diode around the regulator protects it from a shorted input. They also show the diode across the output, but I can't find the explanation for that one on a quick scan through. They look like "belt and braces" rather than essential to me. For a power supply I think I'd probably go with belt and braces.

http://www.ti.com/lit/ds/symlink/lm7800.pdf

I also like to add a resistor+LED to keep an eye on the output. If one of the regulators goes into a thermal shutdown because you're hammering it, you can see straight away that's what's happened. Plus "more pretty lights = better", of course...

Yeah I'll put the parallel diodes in.
According to a datasheet i found, the ones on the output are explained as "A clamp diode should be used at the output of the MC78xx to prevent potential latch−up problems whenever the output of the positive regulator (MC78xx) is drawn below ground with an output current greater than 200 mA"
I'm not yet sure what to do there. I think most pedals or modules have those kind of diodes already build in for reverse voltage protection, right? But I guess I could put them in just in case.

I have 5 to 6 regulators, so if i'm going to put LEDs in for al those, there will be no shortage of pretty lights

[PRR]

> I think I can do this with the first regulator (18 to 12), but is it wise to do  in the steps after that?

Why not?

I have a tree. I need 2x9 joists so I cut it like that.

Floor framed, on to the walls. I need some 2x4 studs so I rip the joists smaller.

Window trim, need 3/4" boards, I rip the leftovers to trim boards.

Build a panel door. Need 1/4" dowels for joints. I rip and turn trim-boards to dowels.

Eat lunch. Meat/celery strings in my teeth. Whittle a dowel into a toothpick.

Going back to the electronics: your project manager should be aghast at all these different supplies. Can't you rationalize to a smaller number of different supplies? As the house project shows, sometimes you can't. But another problem in electronics: all dem wires!! Put three or four bipolar supplies in one box, you have nine or a dozen wires to connect (and connect wrong, or short). As bad as my house telephone wires. Needs some thought before you get in a tangle.

[SPoT_D]

I have made a little prototype (with lots of sockets to try out caps). power looks to be 0,3 volts under the expected voltages. Is this normal behavior for cascaded voltage regulators?

I'm also still looking in a variable power supply that goes from +9 to +3. Could i run it parallel with the 9v regulator after the 12v one? or would i need to run that part completely separate from the cascaded part? 

[ElectricDruid]

I have made a little prototype (with lots of sockets to try out caps). power looks to be 0,3 volts under the expected voltages. Is this normal behavior for cascaded voltage regulators?

I'd say no. A voltage regulator is supposed to give a fixed out, as long as you give it the required input. Is the 12V input high enough for the regulator you're using? (Some require a few volts drop, but that does sound a bit much).

I'm also still looking in a variable power supply that goes from +9 to +3. Could i run it parallel with the 9v regulator after the 12v one? or would i need to run that part completely separate from the cascaded part?

Again, as long as you've got enough "extra volts" on the input voltage above the +9V, it should be fine.

This is why people invented "Low Drop Out" (LDO) regulators. They don't need such a large difference between the input voltage and the output voltage to function correctly. Assuming of course that that is what your problem is here, which is not certain.

T.

[SPoT_D]

I just doesn't seem to work.. If i cascade the regulators, there are major voltage drops nowhere near the expected values..

Does anyone have any idea?

[davent]

What are the voltages on the inputs of the  +/-12v regulators?
dave

[SPoT_D]

What are the voltages on the inputs of the  +/-12v regulators?
dave

Around 7v. Around 5v on the 7809 out and around 3v on the 7805

If I do not cascade the 12v regulators, they act as expected giving +-12.2v out

[davent]

What are the voltages on the inputs of the  +/-12v regulators?
dave

I still have the same question, input voltages of the 7812 & the 7912, or the output of the transformer. You need at least +/-14.5v on the inputs according to the datasheet.
dave