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Old 30th April 2013, 09:31 PM   #2231
Salas is offline Salas  Greece
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Red leds duo are part of the voltage reference parallel floating sense circuit. Not meeting the force lines locally or afar means no juice & no lights.
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Old 30th April 2013, 10:15 PM   #2232
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Thanks Salas - that makes a world of sense. No pun intended. That is exactly my problem; I wasn't comprehending how sensing works. I think I've got it now.
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Old 5th May 2013, 12:48 PM   #2233
Armand is offline Armand  Norway
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I am simulating the circuit in Proteus and trying to understand why you are using a 1R resistor on the base of the BC550C. The current flowing there is in the nA area and hence also the voltage. In simulation there is no sigificant reduction in noise on the output before it reaches 100 ohm. Can it simply be omitted?
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Old 5th May 2013, 12:57 PM   #2234
Salas is offline Salas  Greece
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I have it there as reserve compensation position in case of an odd load. For curtailing the OLG 0 point with a higher value as band aid. Less bandwidth is less total noise integration also. For self noise purposes when using the normal BW I kept it near zero. 1 Ohm used is for not to bother forming wire for a jumper. It could be a jumper all the same.
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Old 5th May 2013, 01:42 PM   #2235
Armand is offline Armand  Norway
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OK. Thank you.
A smaller resistance on the MOSFET's is somehing I have playing around with. It will increase the bandwith but there might be instability issues? How far can we go??
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Old 5th May 2013, 01:59 PM   #2236
Salas is offline Salas  Greece
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100 Ohm maybe. Its a juggling act depending on specific load reactivity also. Layout issues stopper too. Its doing rather well for a biggish gamut as it is. There was careful balancing, subjective also. If you have it sounding worse than a 317 then there is something wrong with interfacing or EMI is abundant coupling over long sense runs. If all is well its "wow!" better than a 317. That's an easy test for all, mainly for the non techies. Its a wide bandwidth shunt reg not a series chip or a discrete passer, this one is as plug and play as a shunt goes, still look twice when applying.
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Old 17th May 2013, 10:35 AM   #2237
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Hi all,

I've just built 3 of the Salas BiB modules from the latest GB, 2 Irf +- and 1 Bjt based. These are to power twisted pear kit: a buffalo II dac and legato 3.1 IV (previously powered by placid HD's).

I have been working to 5v/580ma on bjt for the dac and 15v/300ma for each IV channel, shunting around 80/100ma based on previous measurements (from placids). The dac bjt is up and running and appears to be stable, all as you would expect.

The IV Irf shunts are not behaving as I would expect though. It is quite likely that I have got something wrong in the calcs as this was a bit of a learning curve for me, but anyway. At the moment I only have the resistors to test with a dummy load of 90r for each: 166ma load (not ideal but) and this all appears to work ok (all leds/correct V) and I measure r101 (8r2) and get 304ma (2.5v/8r2). However, on connecting to the legato, for both shunts, the out V drops to 2v and current out is at 0.

Would I be right to suspect that this is saying - 'not enough current' for the legato?
[An anomaly is that with the placid BP in, that will do a similar thing if too much current goes in (more than 100ma over), V drops to 6-7v]

Someone has already pointed me towards separating the two circuits (as Andrew T discusses somewhere here) and testing the CSS. Im have not looked in depth about where exactly to disconnect/short ATM, but I am not in a rush and will take time to understand it before attempting. I could try some other r101 resistors of course, but would like to understand what is going on before messing about. If I have made any errors in what I have said I would be very grateful to hear your comments.

Many Thanks,
Lucas
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Old 17th May 2013, 12:37 PM   #2238
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My methodology is to leave the load resistor in place, assuming enough 'free' current, and jumper to the device itself, see if it powers up appropriately.

I've lost a few volts in one project, and it was oscillating. It did not drop as much as yours by percentage. if you have a scope you could try that.
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Old 17th May 2013, 01:20 PM   #2239
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Hi, I'm putting together a red baron dac.

I need 2x shunt regs - 5v + 3.3v. Where should I add my name in the spreadsheet?


Ok, I think I'm in the right spot.

Last edited by merlin2069er; 17th May 2013 at 01:24 PM.
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Old 17th May 2013, 02:56 PM   #2240
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Hi Salas

I've built a 5.25V, 1.0A reg for my BIII and other devices. I loaded the reg with a variable dummy load and found that the output voltage only stable up to 5-600mA than it dropped when increased the load current. I am using a 1 Ohm for R101.
Is there anything wrong?
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