Salas SSLV1.3 UltraBiB shunt regulator

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Salas

Salas

diyAudio Chief Moderator
Joined 2002
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I just measured a couple of 100uF/25V Silmic II for 100kHz ESR and its about 0.2 Ohm so that or the 50V type should be adequate for C3 ESR in UBiB I guess. But keep the term "guess" since I did not apply a Silmic II in C3 position. But for C2 its ESR value does not destabilize anything so you are free to exchange whatever brand and type you like.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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3 Ohm will give about 0.2A constant current. ICCS=0.58V/R to 0.6V/R in usual builds. What's left from that number when subtracting you load's current pull spec will be shunted to ground through M2. Output voltage times that gives you M2 dissipated power in Watt. M1 Will burn 0.2A times (Vin (at C1) - Vout) in Watt. Consider the calculated dissipation figures vs your available sinks. If your load is of lowish current consumption, thus allowing much extra to burn, use higher R1. But always leave at least 0.1A shunt current to burn out on M2 for good UBiB shunt reg working spec.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
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Not too much but you could possibly live well with 3.3 Ohm or 3.9 Ohm resistor too (CCA 175mA or 150mA). Because Vout is generally low with digital applications, M2's dissipation in Watt does not multiply fast with few more mA. Its mainly about what you can afford burning on M1 vs your sinking allowances. If you also employ an unnecessarily high voltage transformer for the situation, then M1 burns even more.
 
M

manniraj

Member
Joined 2012
A quick question regarding my Ultra BiB negative board. I have built my 1.3 version of psu boards and running into an issue with the negative board. With the load resistor I am able to get a max output voltage of -9.5v and the trimmer turns are to the max. Turning other side reduces the voltage. So I have changed the Vrr to 100k as well as 50k but still cannot increase the voltage. I have now removed the Vrr and still the same issue.

So I removed the load resistor and now I can easily set the voltage to -12v which is my intended purpose to power the Soekris DAC. So I presume that my IDSS values are fine as I can set the output voltage. What could be the issue with my R1 at 3.9R 3w and load resistor is 62R 22w?

The positive board with the same load resistor works fine and I could set it to +12v.

Thanks
 
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manniraj

Member
Joined 2012
Yes I have the RCORE transformer rated at 0-15v *2 which was being used since last 5 years with the Salas BiB 1.1 version without any issues. I am using the same transformer now with the 1.3 version of PSU boards. The positive works fine but not the negative board and confused in terms what might be wrong.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
@manniraj

First don't use the load resistor you now use but one with higher value or none at all because it overloads the output and brings it to current limit. That is why the voltage comes down with it.

The positive setting of UBiB for Soekris normally has higher current limit due to smaller R1 because that DAC has more positive current spec. So it sounds normal that the negative reg will limit first when with a heavy dummy load.

The 1.1 reg used higher constant current for its own good performance so the same heavy dummy load did not use to bring it down.
 
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