The simplistic Salas low voltage shunt regulator - Page 618 - diyAudio
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Old 12th September 2013, 04:35 PM   #6171
mravlca is offline mravlca  Slovenia
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Hi there!

I am working on a small project and I would like to know if I may expect any oscilations with selected components?
Also I have searched thread a bit for 2sk170 smd replacement and found for BF862. Would this be suitable replacement?
Maximum current that I will be using with this circuit is 400mA~500mA and 5V, so I am guessing that CCS resistor should be >1.5ohm....

BR,
Ales
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Old 13th September 2013, 05:38 AM   #6172
Salas is offline Salas  Greece
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BF862 is OK for SMD replacement. Select no more than 0.6V pinch off sample for Q7. Avoid C5.
Use IRF9610 as Q1 for much better Ciss. Moderate Q5 for up to 5mA IDSS with some source resistor. R7=10R maybe not enough gate stopper in practice.
IRF9530 has better Crss for Q2 when gfs will not be significantly different from the 9540 at this low Id (comparatively low as 50W MOSFETs can go).
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Old 16th September 2013, 03:42 PM   #6173
mravlca is offline mravlca  Slovenia
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Quote:
Originally Posted by Salas View Post
BF862 is OK for SMD replacement. Select no more than 0.6V pinch off sample for Q7. Avoid C5.
Use IRF9610 as Q1 for much better Ciss. Moderate Q5 for up to 5mA IDSS with some source resistor. R7=10R maybe not enough gate stopper in practice.
IRF9530 has better Crss for Q2 when gfs will not be significantly different from the 9540 at this low Id (comparatively low as 50W MOSFETs can go).
Thank you for your reply Salas. I have made changes according to your advice, but I don't know exactly how to moderate Q5, in current attached picture Q6.

Thank you again.

Best Regards,
Ales
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Old 16th September 2013, 03:46 PM   #6174
Salas is offline Salas  Greece
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Rs between Q6 source pin and R7,Q3 node. What output voltage range is destined for? If its for low Vo you may avoid it.
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Old 16th September 2013, 03:55 PM   #6175
Salas is offline Salas  Greece
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P.S. The practical problem with those JFETs is they don't come graded and are tiny to handle for selecting IDSS. You would not want more than 10mA anywhere for current noise, self dissipation, and Vref values scaling issues. Especially in Q5 for keeping its Vp up to a 0.6V limit also. So make some kind of jig arrangement to can select them and provide copper area for their G to dissipate on the PCB.
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Old 16th September 2013, 08:20 PM   #6176
mravlca is offline mravlca  Slovenia
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Quote:
Originally Posted by Salas View Post
Rs between Q6 source pin and R7,Q3 node. What output voltage range is destined for? If its for low Vo you may avoid it.
I plan to use it for 5V(~500mA) and also for 3.3V(100~200mA).

Quote:
Originally Posted by Salas View Post
P.S. The practical problem with those JFETs is they don't come graded and are tiny to handle for selecting IDSS. You would not want more than 10mA anywhere for current noise, self dissipation, and Vref values scaling issues. Especially in Q5 for keeping its Vp up to a 0.6V limit also. So make some kind of jig arrangement to can select them and provide copper area for their G to dissipate on the PCB.
I already made PCB in such way that they all lay on ground plane.

BR,
Ales
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Old 16th September 2013, 08:34 PM   #6177
Salas is offline Salas  Greece
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Low Vo will help the semiconductors dissipation levels then. Still the 847C HFE/IC curves look better at lower IC. 2-3mA.
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Old 17th September 2013, 05:53 AM   #6178
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sorry for keep messing it up (both your circuit and the thread) but i caused a short somewhere that overheated the transformer momentarily and after that the shunt produces hiss. intensity of the hiss seem dependent on the v adjust resistor pot.

what components should i troubleshoot first? could the hum come from the trafo itself if it has shorted a wire somewhere?

edit: never mind, the transformer was faulty. how does this introduce hiss into the circuit?

Last edited by PreSapian; 17th September 2013 at 06:09 AM.
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Old 17th September 2013, 07:48 AM   #6179
Salas is offline Salas  Greece
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Maybe the pot is hit. Change that first.
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Old 17th September 2013, 02:20 PM   #6180
mravlca is offline mravlca  Slovenia
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Quote:
Originally Posted by Salas View Post
Low Vo will help the semiconductors dissipation levels then. Still the 847C HFE/IC curves look better at lower IC. 2-3mA.
So it would be better to add Rs between Q6 source pin and R7,Q3 node to achieve better hfe of BC847C?

BR,
Ales
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