The simplistic Salas low voltage shunt regulator - Page 512 - diyAudio
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Old 8th July 2012, 03:37 PM   #5111
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Why have you connected collector BC547 to GND? you have to follows exaqctly Salas schematic.
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Old 8th July 2012, 03:46 PM   #5112
Salas is online now Salas  Greece
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Quote:
Originally Posted by studiostevus View Post
Funny stuff here... My 4 salas shunts seemed to be working correctly.... However one of them has a problem: the bc547 gets really hot and eventually burns (after several hours)

Specs:
Bib version, but on my own pcb, using irf610 for ccs and irf620 for shunt
Vout=15v
Vin=25v
Ccs=130mA
Iload=50mA tda1541a

Any ideas?

The other 3 regs on the board (5v, -5v, 3.6v) all work fine
See if the 170 on top of it feeds it too much current. Could that 170 got shorted dead? See if something oscillates in the particular unit if all its semis are healthy.
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Old 8th July 2012, 06:53 PM   #5113
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Quote:
Originally Posted by merlin el mago View Post
Why have you connected collector BC547 to GND? you have to follows exaqctly Salas schematic.
The GND connection I mean is the 'S0' connection. This connection is according to the schematic.
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Old 8th July 2012, 06:57 PM   #5114
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Quote:
Originally Posted by Salas View Post
See if the 170 on top of it feeds it too much current. Could that 170 got shorted dead? See if something oscillates in the particular unit if all its semis are healthy.
Do you mean U$22 in my schematic?

I have replaced it yesterday, as I thought it was the reason for the trouble I had. It turned out that the BC547 was the problem. After I replaced it (yesterday), regulation was back, however after listening to the unit for some hours today, again the voltage was drifting upwards as the bc547 got hotter and hotter...
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Old 8th July 2012, 07:45 PM   #5115
Salas is online now Salas  Greece
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U$23
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Old 9th July 2012, 03:47 AM   #5116
agussug is offline agussug  Indonesia
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@Studiostevus : What BC547 did you use?
@Salas : Is it possible to see oscillation without oscilloscope?

Regards
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Old 9th July 2012, 04:22 AM   #5117
Salas is online now Salas  Greece
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If you move a portable AM radio over an oscillating circuit it can pick it up given its strong and high enough. Not reliable, kinda Mad Max world solution.
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Old 9th July 2012, 05:04 PM   #5118
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Quote:
Originally Posted by agussug View Post
@Studiostevus : What BC547 did you use?
Regards
Plain BC547's...

I just noticed that on both my negative regs, the bc547's get really hot
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Old 9th July 2012, 05:36 PM   #5119
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I just checked on the scope: the -15V reg (the troubling one) is absolutely not stable. The output voltage moves irregularly down, on the scope visible as the trace pulling several mV's down. It's very irregular, i can't see any particular pattern, it's more like flickering, and goes instantly
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Old 9th July 2012, 05:54 PM   #5120
Salas is online now Salas  Greece
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The error amp or the Vref must be having an intermittent condition. Any semi for that matter.
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