SSLV1.1 builds & fairy tales

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B

Backbones

Member
Joined 2008
AndrewT said:
if you plan to use a shunt regulator then the CCS feeding the shunt must deliver more current than the worst case maximum demand of the client circuit (FM4).

If 30mApk is the worst case demand then the CCS should be set for 30+X mA.
X can be any value >=1mA. I would suggest you aim for setting the CCS in the range 60mA to 100mA.

Note that the FM4 has a compartment housing the 3pin regulator. One does not have much room to fit in a BiB.
Click to expand...

Thanks Andrew,
In fact I don't think it does draw 30mA. I measured the voltage across another power supply resistor on a Pi filter and it was 0.05V for a 0.27ohm resistor. I think it is drawing more like 0.185A. I have wired up the Salas regulator and it sound very good but I now can't get more than 9.7V output. Earlier whilst testing on a 390ohm resistor for the load I got bang on 12V but of course that had assumed 30mA draw.
I have 8.2ohm 3W resistor on the input side with the voltage reg configuration of 1 diode, 1k resistor and 5K pot (only one I had available).
Any suggestions would be gratefully received.
Chris
 
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B

Backbones

Member
Joined 2008
Just carried out a few experiments with the voltage adjustment area and it seems that at these currents, the voltage is largely unresponsive to alterations in the potentiometer position. So I assume I'll have to increase the current via R301. Could I get away with 7W, 4.7ohm resistor here (Maplin don't have the 3.9ohm)?
Chris
 
A

AndrewT

R.I.P.
Joined 2004
First, one must set the CCS current !

If there is insufficient current, at any time no matter how short a time period that might be, then the shunt has no current to regulate with and the output voltage falls, while all the capacitors release their stored energy to try to meet that current demand.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
The main constant current source is around the IRF9610 first Mosfet in line. There you set its steady current available with R101 etc. There is a 4th LED position to aid you if you don't have small resistors, read the last page of the guide rev.2 available for download at post#1 this thread.
 
B

Backbones

Member
Joined 2008
OK if I understand this correctly. For the green LEDs there is a 2.1v drop per diode which if we use four equals 8.4V. Looking at the ID/VGS chart for a projected value of CCS (150mA above peak current for FM4 which is 200mA + 150mA= 350mA) we get for 350mA a Vgs of 4.8. Subtract from 8.4V=3.6V. Current resistor is 8.2ohms. V/R=3.6/8.2 equals 0.43A, which exceeds my requirements. So if I add another green diode with the current resistor I should be alright.
Hard work these threads all of a sudden.
Chris
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
P.S. Sticking the 8R2 you have available along with 4 green LEDS should get you comfortably above your load needs, around 340mA give or take. Just solder it in, and by measuring the drop across it, you will be able to figure out the current by dividing that voltage drop with 8.2.
 
P

PET240

Member
Joined 2010
I prefer centigrade.....my winter was shorts and shirt for most of it. In my experience pieces of paper are just that, doesn't mean the person that has it is any good with it!
Don't know what qual's Salas has, but he be one of the most helpful gent I've found anywhere, I'm a electrician by trade, self employed in Industrial Machines Contracting, would love to offer the service you guys do.
Thanks Very Much!
 
B

Backbones

Member
Joined 2008
I'd take a GCSE in electronics anyday over a degree in interior decoration at the University of LaLa! Trouble is you can probably get more money as an interior decorator.
Anyway back to the real business of this thread. One more diode and we have a working PSU fixed at 12V. The mosfet, however, is running a little hotter than I would like (about 55deg) so I'll have to find a bigger heatsink.
Thanks for all the help.
Chris
 
B

Backbones

Member
Joined 2008
Not really. As I am new to this game I am minded to stay about the 55c level because of Nelson Pass designs and I know no better. Going back to the FM4 there was a 7812 reg in there taking a 22VDC input from the tuner's transformer and it didn't have a heatsink. It must have run very hot indeed and there are references to problems with the reg in the repair manual, however, it did run for very long periods all the same.
Chris
 
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