The simplistic Salas low voltage shunt regulator - Page 320 - diyAudio
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Old 11th November 2010, 12:12 PM   #3191
AndrewT is offline AndrewT  Scotland
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post3176
What is Vce of Q9?
With high mains voltage could Vce rise above specified rating?
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Old 11th November 2010, 12:47 PM   #3192
Salas is offline Salas  Greece
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He substituted for BC546 he wrote. With 70Vin 50Vout and his current given his voltage over R15 1k in the source he must be having around 40V across Q9 and 50mW I would estimate.
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Old 11th November 2010, 12:51 PM   #3193
AndrewT is offline AndrewT  Scotland
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the problem is that the resistor ladder fixes the emitter of Q9 @ ~24V.
The supply rising to 80Vdc, when mains is high, puts a high Vce across Q9.
I do not think he realises that.
Changing the ratios of the resistor ladder could help alleviate that problem, or simply looking at the range of worst case supply voltages that one expects the circuit to survive with.
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Old 11th November 2010, 12:55 PM   #3194
Salas is offline Salas  Greece
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By stating he put BC546 there (Vceo=65V), he must have had it in mind?

Quote:
Originally Posted by klewis View Post
...and a few modifications for the higher Vin - 6.8k R14 and R4, changed Q9 and Q2 to BC546C from BC550C,...

Ken
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Old 11th November 2010, 01:18 PM   #3195
klewis is offline klewis  United States
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Quote:
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By stating he put BC546 there (Vceo=65V), he must have had it in mind?
Hi Salas and Andrew,

Thanks for your help and thoughts. I turned the Vout up to 60, it took a while ( 10 minutes or so) for the Vout to stop climbing up. I adjusted it back down to 60 several times. Measured temp at Q1 at about 50 deg C and the second mosfet at almost 60 deg C. My heat sink was definately warm and is probably too small.

The LED glowed normally. I will hook the shunt up to the scope tonight and see if its oscillating.

Yes, I was concerned that I would exceed the Vceo of Q9 hence the BC546.

Ken
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Old 11th November 2010, 01:25 PM   #3196
AndrewT is offline AndrewT  Scotland
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the cascode (q9) will remove much of the temperature variation in the CCS due to mains voltage changes.
The drift you have found must then be in the Shunt stage or the series FET.
Big sinks will have a profound effect on reducing temperature drift with mains variation.
Further "warm up" drift will tend to zero since the CCS passes by definition constant current.
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Old 11th November 2010, 03:32 PM   #3197
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Yes.... Those white sonicaps are really excelent.... Similar tone to Mundorf MKP but without the trebble grit.
Platinum teflons maximum value only to 1uF but 0.047uF for RIAA must be excellents.
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Old 11th November 2010, 06:54 PM   #3198
klewis is offline klewis  United States
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I went back into the simulation and looked at some of the heat dissipation issues and realized that I have been underestimating just how hot this thing will get. So, several of my concerns were unfounded. For example at this voltage with 100ma load and 200ma current, the shunt mosfet makes over 14w of heat. And my 1k load resistor makes 3.6w of heat. I'm going to take it back to 130ma of current by changing the 3.3 ohm to 5 ohm and see if that doesn't solve some of voltage rise issues.

Ken
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Old 11th November 2010, 07:25 PM   #3199
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Originally Posted by merlin el mago View Post
Platinum teflons maximum value only to 1uF but 0.047uF for RIAA must be excellents.
Might be good but we must consider the size... and the cost.
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Old 11th November 2010, 08:26 PM   #3200
Salas is offline Salas  Greece
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Default The V1.2R example schematics

Phew, lots of drawing.
Attached Images
File Type: gif 1V2RposLow.gif (9.8 KB, 4265 views)
File Type: gif 1V2RnegLow.gif (8.9 KB, 3486 views)
File Type: gif 1V2RposMedium.gif (9.4 KB, 3705 views)
File Type: gif 1V2RnegMedium.gif (8.9 KB, 4671 views)
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