I'm designing a PSU that will make use of one of these linear transformers which has in input of 230V and an output of 24V with a 5% ripple.
Before I'm told "design your own linear transformer, don't buy a prebuilt one" I want to be clear that this is my first build working with mains AC and while this transformer will never be as good as one I build from scratch it will be a LOT safer for me. There are only two points I can mess up the mains connection and electrocute myself rather than several! Once I've build a few of these successfully I'll consider building one from scratch!
OK, now the boring explanation is out of the way this is my rough plan. I have stupidly noisy USB power on my main PC. With an alternative PC and much less powerful A2020 Tripath amp (15Wper channel) I don't even get a whisper from my DAC. On my main PC with STR-DN1050 AV reciever I get a 2000hz sawtooth pulsing buzz even with the DAC volume turned down low (In fact adjusting the volume makes no difference to the noise). This really spoils the listening experience! My conclusion is that dirty USB power is the problem which the sony then amplifies. Even if it isn't, I have several other projects in the pipeline that will need their own PSU so this will be a good learning experience.
The 5V DC output will be rated at 3A (Yes, LM2596 needs a heatsink at 3A). I'll split the data lines from the USB, run the existing power across a dummy load (47k ohm resistor?) and put the clean 5VDC in its place.
My questions are:
1. Do I need the "L3" inductor in my design - does the ground need filtering?
2. What values of inductance do I need to "L1", "L2" and (if applicable) "L3". How do I calculate these on my own later for other voltages and ICs?
3. What values and types (film, ceramic, polypropelene, electrolytic) should "C1", "C2", "C3" and "C4" be for maximum ripple smoothing and noise filtering? Is there any benefit in adding more than 3 capacitors in parallel after the IC?
4. To simulate a dummy load on usb (so it doesn't turn off) is a 47k ohm resistor ok?
5. Is there an easy way to feed 2 or more USB devices from this clean 5VDC - how do I isolate them electronically? If I can isolate them completely without introducing more noise I could run 4+ 500mA USB devices on clean power or feed a small class D amp from the single PSU...
6. How would I build a version that had multiple output feeds, eg a) +5VDC, b) +15,-15VDC, c)+12VDC - while keeping each output electrically isolated? Doing this would mean I could power a USB DAC, OpAmp chip/headphone amp and 2020A Tripath 15/15W class D amp (I seriously love this little amp, it's almost tubelike!) from a single clean PSU. What ICs would I need for this?
7. Allowing for the capacitors and ICs to eat some power, if I wanted 3A on the +12V and 500mA on each the other two power connections, what ampage at 24V transformer would I need? Would 3A at 24V cover it?
8.What Rectifier diode would you suggest? Is it strictly necessary?
9. Anybody got opinions on shielded USB cables? I've seen them range in price from the £4 or so here to almost £200! If anybody has experience with them I would love to hear about it. Bare in mind, I'm a cheapskate though and highly unlikely to spend more than £10 on a USB cable!
Before I'm told "design your own linear transformer, don't buy a prebuilt one" I want to be clear that this is my first build working with mains AC and while this transformer will never be as good as one I build from scratch it will be a LOT safer for me. There are only two points I can mess up the mains connection and electrocute myself rather than several! Once I've build a few of these successfully I'll consider building one from scratch!
OK, now the boring explanation is out of the way this is my rough plan. I have stupidly noisy USB power on my main PC. With an alternative PC and much less powerful A2020 Tripath amp (15Wper channel) I don't even get a whisper from my DAC. On my main PC with STR-DN1050 AV reciever I get a 2000hz sawtooth pulsing buzz even with the DAC volume turned down low (In fact adjusting the volume makes no difference to the noise). This really spoils the listening experience! My conclusion is that dirty USB power is the problem which the sony then amplifies. Even if it isn't, I have several other projects in the pipeline that will need their own PSU so this will be a good learning experience.
The 5V DC output will be rated at 3A (Yes, LM2596 needs a heatsink at 3A). I'll split the data lines from the USB, run the existing power across a dummy load (47k ohm resistor?) and put the clean 5VDC in its place.
My questions are:
1. Do I need the "L3" inductor in my design - does the ground need filtering?
2. What values of inductance do I need to "L1", "L2" and (if applicable) "L3". How do I calculate these on my own later for other voltages and ICs?
3. What values and types (film, ceramic, polypropelene, electrolytic) should "C1", "C2", "C3" and "C4" be for maximum ripple smoothing and noise filtering? Is there any benefit in adding more than 3 capacitors in parallel after the IC?
4. To simulate a dummy load on usb (so it doesn't turn off) is a 47k ohm resistor ok?
5. Is there an easy way to feed 2 or more USB devices from this clean 5VDC - how do I isolate them electronically? If I can isolate them completely without introducing more noise I could run 4+ 500mA USB devices on clean power or feed a small class D amp from the single PSU...
6. How would I build a version that had multiple output feeds, eg a) +5VDC, b) +15,-15VDC, c)+12VDC - while keeping each output electrically isolated? Doing this would mean I could power a USB DAC, OpAmp chip/headphone amp and 2020A Tripath 15/15W class D amp (I seriously love this little amp, it's almost tubelike!) from a single clean PSU. What ICs would I need for this?
7. Allowing for the capacitors and ICs to eat some power, if I wanted 3A on the +12V and 500mA on each the other two power connections, what ampage at 24V transformer would I need? Would 3A at 24V cover it?
8.What Rectifier diode would you suggest? Is it strictly necessary?
9. Anybody got opinions on shielded USB cables? I've seen them range in price from the £4 or so here to almost £200! If anybody has experience with them I would love to hear about it. Bare in mind, I'm a cheapskate though and highly unlikely to spend more than £10 on a USB cable!
Attachments
Last edited:
1/ L3, not required.
2/ No L1. L2 needs to be 68uH.
3/ 220uF 35V. No, no need other than maybe a 100nF close to the output.
4/ Don't know what you mean.
5/ Noise doesn't matter as the threshold point is usualy 30% or 60% of rail.
6/ Read the data sheet http://www.ti.com/lit/ds/symlink/lm2596.pdf
7/ Convert to V/A or power and then work backwards.
8/ It depends on power requirements but 1n400* or 1n540* range will probably cover it.
9/ They don't need to be shielded as the noise rejection is excellent. Don't waste your money!
2/ No L1. L2 needs to be 68uH.
3/ 220uF 35V. No, no need other than maybe a 100nF close to the output.
4/ Don't know what you mean.
5/ Noise doesn't matter as the threshold point is usualy 30% or 60% of rail.
6/ Read the data sheet http://www.ti.com/lit/ds/symlink/lm2596.pdf
7/ Convert to V/A or power and then work backwards.
8/ It depends on power requirements but 1n400* or 1n540* range will probably cover it.
9/ They don't need to be shielded as the noise rejection is excellent. Don't waste your money!
Stop.
Don't get confused between transformer and Power Supply Unit.
Don't try to build your own transformer !
You can assemble your own PSU.
Have a look at the TNT and ESP sites.
Solid State Power Amplifier Supply Part 1
Linear Power Supply Design
Just curious: why on Earth would any Home Audio fan use one of these very heavy duty INDUSTRIAL supplies ?
Which I guess must cost an arm and a leg because they certainly must pass *rigorous* tests.
3 phase transformers?
400V primaries? (some even 415/440/460/480/500 VAC primaries).
Sounds like buying a Formula 1 car just to do the grocery shopping.
Technically nothing against, of course, just that they sound like the definition of overkill.
That said, they are probably way cheaper than Audiophile approved supplies using silver wound transformers, insulated with Emperor Ming's robe silk, beeswax, and with iron forged out of King Arthur's sword.
Which I guess must cost an arm and a leg because they certainly must pass *rigorous* tests.
3 phase transformers?
400V primaries? (some even 415/440/460/480/500 VAC primaries).
Sounds like buying a Formula 1 car just to do the grocery shopping.
Technically nothing against, of course, just that they sound like the definition of overkill.
That said, they are probably way cheaper than Audiophile approved supplies using silver wound transformers, insulated with Emperor Ming's robe silk, beeswax, and with iron forged out of King Arthur's sword.
Your schematic shows a 12V regulator yet your lines say 5V on them.
I think your problem may actually be a ground loop, which a separate supply won't fix. You can buy USB isolators for about 20 quid.
I think your problem may actually be a ground loop, which a separate supply won't fix. You can buy USB isolators for about 20 quid.
- Status
- Not open for further replies.