The simplistic Salas low voltage shunt regulator - Page 600 - diyAudio
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Old 12th May 2013, 05:20 AM   #5991
vgeorge is offline vgeorge  Greece
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Quote:
Originally Posted by Salas View Post
Try a Zener reference. Any, even 18V to check. If its not oscillation and the cap does not have a problem it should go Vz+VFled+2Vbe=Vo. Zener cathode orientation vice versa to LED.
Here is one I made with the 3055VL. Target was to get 35 Vout. Vin was 43V. I had a problem in the beginning to get more than 15V with the 5K trimmer and I had to go up to 15 - 20K to reach the desired voltage. But could not get the voltage to be stable and not to drift. Maybe due to thermal issues (4404 too close to the heatsinks?), or due to my stash of 4403 which seemed to be higher Hfe. Changed the trim and led you see on the pictures (also removed the zip tie on the lower pair) with some combination of zeners and diodes and is stable right now. Also tried an 640 in place of the 3055VL but here was no difference in the drift.
Could not listened to it yet as I am too busy at the moment, will see when I get some time.
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Old 12th May 2013, 05:55 AM   #5992
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thank you Salas and vgeorge

4403 are far away from Mosfets - I don't have heatsinks at all because I test only for 20 sec
I am almost sure that there Is no oscillation - why It will work to 14 V and not more
will see with a led string or zener

BTW I removed Vref filtering cap
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Old 12th May 2013, 06:49 AM   #5993
vgeorge is offline vgeorge  Greece
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20 seconds maybe not enough time to reach the desired voltage, even without the Vref cap. Put some sinks even small ones and test for a few minutes.
You can even do a combination of leds zeners and diodes.
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Old 12th May 2013, 07:56 AM   #5994
Salas is offline Salas  Greece
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@ Vgeorge:
3055VL is under 2V VGS at that bias so it would take a big resistor. Still it climbed.
@ Samoloko:
There was a connection error in that Eagle test layout around the output Mosfet pins so follow the schematic and not the vias blindly.
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Old 12th May 2013, 08:23 AM   #5995
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Salas
you already told me about that - thank you
I think output fet Is connected correct for positive - drain to other fet drain, source - to gnd
now I have 9 leds In string + 1 K as a Vref
output Is 14 Vdc leds does not light
there Is an error but don't know where
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Old 12th May 2013, 08:29 AM   #5996
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by dimkasta View Post
I have added a 1000uF FR cap on the shiga entry and things are down to

Click the image to open in full size.

No patience right now to experiment with lower values and different types...
When I start wrapping things up, I will also up the CCS current a bit
I would use inspired guesswork to suggest the Shiga has not got properly designed decoupling built in to the correct locations and of the correct sizes/types.
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Old 12th May 2013, 08:30 AM   #5997
vgeorge is offline vgeorge  Greece
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Quote:
Originally Posted by Salas View Post
@ Vgeorge:
3055VL is under 2V VGS at that bias so it would take a big resistor. Still it climbed.
What I meant was that even with the 640, the resistor value was higher than what samoloko used.
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Old 12th May 2013, 09:59 AM   #5998
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I would use inspired guesswork to suggest the Shiga has not got properly designed decoupling built in to the correct locations and of the correct sizes/types.
You would probably be right...

I plan on separating some more stuff with their own PSUs... we ll see...
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Old 12th May 2013, 10:43 AM   #5999
AndrewT is offline AndrewT  Scotland
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It's not PSUs, it's decoupling.
The faster signals change the more important decoupling becomes.
Digital signal processing cannot operate properly without a lot of both MF and HF decoupling.
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Old 12th May 2013, 11:19 AM   #6000
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Still with such complex devices with fast twitching motors and digital controllers divided in many subsystems, decoupling should be able to fix some stuff but probably not all when there is only 1 PSU...
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