The simplistic Salas low voltage shunt regulator - Page 253 - diyAudio
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Old 23rd May 2010, 06:03 PM   #2521
pidesd is offline pidesd  Canada
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i m no expert, but is it not recommended to add holes for to-220 mosfet too?

Last edited by pidesd; 23rd May 2010 at 06:06 PM.
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Old 24th May 2010, 11:05 AM   #2522
tubo is offline tubo  Philippines
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Quote:
Originally Posted by Salas View Post
Try this one. I don't like to go so low in Voltage output, near the Mosfet Vgs margins, but this one looks like working alright on the simulator. Try it, I haven't tried for 5V before. Its inexpensive to make p2p and see if it will do well for you.

hey guys,

will the regulator be able to power a squeezebox touch which has a 5v 3amp requirement? what do i need to replace on the scheme to output 3amp?thanks
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Old 24th May 2010, 11:15 AM   #2523
Salas is offline Salas  Greece
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V1.0 has done 3A at 13V for a T-Amp. The dissipation at 5V is almost 1/3rd than that, so I guess its possible. Its only Rset that needs go low value and you need substantial sinking. Since that post many used it at 5V for digital. DACEND, DVBPROJECT's 1541 REF, Merlin El Mago on Buffallo remote sensed, etc.
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Old 24th May 2010, 11:58 AM   #2524
tubo is offline tubo  Philippines
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if i understand it correctly i just need adequate sinking ? i believe 6 ohm for the rset with a 12v supply. and 10 ohm for rset with a 15v supply.

Last edited by tubo; 24th May 2010 at 12:01 PM.
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Old 24th May 2010, 12:09 PM   #2525
Salas is offline Salas  Greece
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Is it the 3LED CCS? Shoot for Iset=2V/Rset roughly.
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Old 24th May 2010, 02:06 PM   #2526
massimo is offline massimo  Italy
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Originally Posted by THKL View Post
@Massimo: would you advise to use a groundplane "net" (how is that kind of groundplane called, btw?) or leave the ground trace alone?
I thought the groundplane could add some screening, but I'm no analogue wizard...
I don't think GP is necessary in analog pcbs, and, as pointed out by Salas, a solid GP is like adding a big cap. If you want it, use a grid or net, but better without IMO.

Verify hole size: if you vary hole size for each components, the pcb price goes up. Consider that through hole plaiting reduces the actual size by 0.1 -0.15 mm. Small bjt/fet pads are still too small for me. Easy to destroy them if you have to desolder a component.

Move 33 pf cap to the left (on top of 1k resistor) in order to reduce track lenght. Its pitch can be 5 mm or smaller if you use a good ceramic component.
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Old 24th May 2010, 03:45 PM   #2527
THKL is offline THKL  Germany
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Thanks for all the feedback.

I designed a new PCB for the LED-reference BJT-cascode and tried to incorporate all the feedback.
The small transistor pads have been increased (they now only have 0.3mm space between them - I don't think that it'll be a good idea to further reduce it - any comments, maximo?)
Due to popular request I also added TO220 holes to the PCB layout.
The new design looks cleaner IMHO.

Since the new design does not require IDSS sorting, can go for higher input voltages and performance is the same as the older version, this new design will become the standard design I will be working on.

@Salas:
1.) Somewhere in the thread it was mentioned that LED-reference could be used in the remote sensing and adjustment part, too. Does that improve overall quality? (There seems to be enough space left in the new design so that I could even add in that option with a "daughterboard".)

2.) I understood correctly that the performance of the LED-reference version is at least the same as the one with 2SK170/2N2559, did I?

3.) At the moment the circiut contains BC560B and BC560C. Can't one model be used for all without compromising performance?
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File Type: gif Salas LED Negative PCB.gif (36.7 KB, 415 views)
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Old 24th May 2010, 03:50 PM   #2528
THKL is offline THKL  Germany
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Quote:
Originally Posted by massimo View Post
Move 33 pf cap to the left (on top of 1k resistor) in order to reduce track lenght. Its pitch can be 5 mm or smaller if you use a good ceramic component.
If I remeber right, Salas advised on using a Silver Mica 33p and I took the footprint from the datasheet. I don't know about performance of different capacitors there, but I'm eager to learn and changing the pitch is not a big deal...
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Old 24th May 2010, 03:59 PM   #2529
Salas is offline Salas  Greece
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3.Yes, use 550B-560B for those CCS TO-92s, so some will not stick out for hfe too much. Had no problems with mixing B or C, or all being C, but the B grade is more conservative around 300 hfe.
2. Yes, equivalent. BJT or FET cascode same PSRR.
1. LEDs are for fixed reference on a daughter board if you fancy. In that case you should have to jumper the source to ground of the trimmer controlled JFET, because the LEDS are going to need stronger current to be happy. They are stiff, will not come up thermally anymore than +/-0.4V, the resistor will slide with the small Jfet current coming to thermal final -but stay then-. Also less impedance. A bit different subjectively than a resistor Norton ref. Semis are active things. Much of a hassle for 24V, not recommended there since you will also lose noise performance gradually with number, but nice in the 5V.

P.S. Don't know if TO-220 will work equally well given the extra length to gate stoppers in your last iteration. But they can always get soldered directly to legs and just leave their other leg lengthier to is pad.
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Old 24th May 2010, 04:00 PM   #2530
Salas is offline Salas  Greece
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Quote:
Originally Posted by THKL View Post
If I remeber right, Salas advised on using a Silver Mica 33p and I took the footprint from the datasheet. I don't know about performance of different capacitors there, but I'm eager to learn and changing the pitch is not a big deal...
C0G/NP0 recommended equally.
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