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Scalable PSU/regulator GB

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#506
Hi Bob

As always you are being most helpful.
May I wish you the best in 2007 and a happy diy year.

Are you ordering BC556C and 546C?
I can get plenty of the B-variant over here but they have a different gainfactor. Don't know what that would do to the performance.
Are you by any chance also ordering the MJE's? Can't get those either.

I'll also ask KRO where he gets his.
 
#507
I'm not ordering, I still have a few thousand BC546C and 556C from PSU round 1. I'm not planning to order any MJEs anytime soon - I have enough for now, but unfrtunately just a few extra. I always seem to smoke a couple along the way. 🙁
 
#512
I was wondering whether this regulator would be able to handle high currents if I replaced the TO220 device with a TO247 or TO3 device rated at >100W, >10A? I was thinking what would happen if one fixed such a device on a large heatsink and used short copper wire to connect the three legs to the PCB.

Would it work? And would one get a few amperes of current through the device?
 
#513
The other issue that you would run into would be the rectifiers. Jumper as appropriate and and feed it DC (with additional capacitive filtering)and you ***should*** be OK to a couple of amps.

The rectifiers are the limiting factor in the current design. Depending on your applied voltage and acceptable junction temperature with a 50 mm heat sink you can probably get a couple amps out of it safely without going to a TO-247. You can also mount the MJE to the bottom without trimming the leads and mount the whole assembly to a larger sink.

You could also use a MOSFET for the pass device with a little ingenuity.
 
#514
BobEllis said:
The other issue that you would run into would be the rectifiers. Jumper as appropriate and and feed it DC (with additional capacitive filtering)and you ***should*** be OK to a couple of amps.
Click to expand...
You're spot on, as always, but then I guess there are those 1N540x series devices which will give me more than a couple of amps and still fit on your PCB, won't they? (But once that's done, the smoothing caps will become a bottleneck, and so on.) Your suggestion of taking the bridge and caps off-board is neater... it'll give me much wider latitude.

Basically, since people have been reporting surprise at the temperature of the TO220 device, I thought I'd just ask whether this easy swap will work. I'll redesign the PCB if needed.

You could also use a MOSFET for the pass device with a little ingenuity.
Click to expand...
What would be the ingenuity needed? Would I need to fit some stabilising gate resistors/caps and the like? MOSFETs had occurred to me, but I thought that a big BJT would be just as good for this design.
 
#515
Startup problem again

I finally got around to building my complete filter setup.

After checking and switching on everything worked fine.Checked sound quality by ear and its fine too. No noise or hum at all.

I decided to do some sound measurements the next day but to my suprise the PSU's didn't start up.Sometimes the positive side failed,sometimes the negative side.Disconnecting the powersuply from the filterboards made the PSU start after a second or so.

Reconnecting the powerleads after the PSU started sometimes worked and sometimes stopped the PSU again.
It seems the inrush current from the filterboards is to great for the PSU.
I use 220uF on the filterboards and 4.7uF tantalums as bypass for the opamps.
When connecting the powerleads after the PSU has started the inrush current is strong enough to "weld" the wires together.
When the filterboards are operating they draw about 80 mA per rail with no signal (6 opamps per board).
I use a 30VA toroid and the ac is about 18 Volts.Any suggestion on limiting the inrush current from the filterboards?

kr05998
 
#516
Kro,

There are some things you can test.

I think your problem is related to the amout of µF you have on the filterboards.

Try changing R4 and R19 to 1.2-1.3k or maybe even 1.5k this may be enough to let the regulator start with your extra start load.

If this does not help, please report back

Sorry for my late answer 🙁

\Jens
 
#517
Kro -

Another solution might be lift one end of R4 and R19. This means the reference doesn't get the clean voltage it normally does and the short circuit protection is gone. To restore the clean power, add a diode between the resistor and the pad it came from. Of course the diodes should be oriented to allow current to flow once the reg starts.

I'm going to try a regulator set using J511s (4.7 mA current regulators) in place of R3/R18 and eliminating R4/R19. Not that I can measure if it makes a difference 😉

Bob
 
#519
PSU starting

I have increased R4 to 1.5 k. This helps but i have to wait a couple of minutes between startups.When switched on to soon one of the rails won't start.
I'll try putting a 1 ohm resistor in series with the rails.

btw. i simulated the capacitance with the correct esr in spice.
The startup current is over 15A for a few miliseconds.

kro5998
 
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