The simplistic Salas low voltage shunt regulator - Page 43 - diyAudio
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Old 11th June 2009, 04:47 AM   #421
Salas is offline Salas  Greece
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With 24V Zener you get about 24.7-25V. 28V you quote is fishy. That much goes to Q1's gate with about 33V DC In and accounting the Leds drop. Maybe you got Q1 wrongly wired. The Mosfets are G,D,S from left to right as you face them and you can read the part numbers. S is the arrow pin on the schematic. Please check everything again.
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Old 11th June 2009, 04:51 AM   #422
Salas is offline Salas  Greece
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Quote:
Originally posted by staggerlee


How about a 22v zener?


Click the image to open in full size.

That will give about 23V, that Zener number shown was a leftover when drawing. 1N4749A is the correct part.
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Old 11th June 2009, 05:14 AM   #423
jam is offline jam  United States
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mikelm,

I am not condemming CFP's but if you notice not many of the worlds best designers use CFP's. Most of them have avoided them because of potential problems.

Sometimes getting a CFP to work requires a heroic amount of compensation(which usually damages it's sonic qualities) and I myself try to aviod any circuitry that is on the verge of instability even if my choice has slightly higher distortion.

Countless papers have been written on the subject but no one has come up wiyh a total solution. CFP's enclosed in feedback loops can be particularly problematic. CFP's have their place but in most cases they can be subsituted for another design element that sounded better (note I said sounded not measured)

Regards,

Jam
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Old 11th June 2009, 05:32 AM   #424
iko is offline iko  Canada
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Quote:
Originally posted by mikelm
I use irf9530 successfully for current source - so far so good

I used two matched zvp3310a's in parallel for shunt.

had some oscillation - ran out of time - needs more work

I'll report if I get it working
Try a 100pF ceramic cap on the B-C pins of the NPN driver. Also, try different NPNs if you have them around. I successfully used 2SC828s, 2N3904, etc.
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Old 11th June 2009, 05:45 AM   #425
Salas is offline Salas  Greece
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Complementary Feedback Pair, generally hates parallel current elements. Much more prone to oscillate. If suggestions like double stoppers, big output cap, and what Iko said fail, try a single heavier and slower Mosfet instead of the 2X TO-92 ZVPs.
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Old 11th June 2009, 05:47 AM   #426
Salas is offline Salas  Greece
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Quote:
Originally posted by jam
CFP's have their place but in most cases they can be subsituted for another design element that sounded better (note I said sounded not measured)

Regards,

Jam
I agree for AF amps, where the distortion spectrum shape counts more than the CFP's lower %. For DC regulation, CFP mates well.
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Old 11th June 2009, 08:46 AM   #427
Tham is offline Tham  Malaysia
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Hi Salas,

Checked and found out that I did not connect the emitter (BC550C) to the drain of IRFP9240. Other areas seemed to be correctly connected. However, the output now measures just over 12VDC

I used the schematic on post #255 which is for 37VDC output. Do I need to make changes to component values on that schematic to get 24VDC?

Regards

Tham
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Old 11th June 2009, 09:43 AM   #428
Salas is offline Salas  Greece
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Are you sure that you don't have just a 12V Zener by mistake?
No, you don't need more changes than a DC In about 30-35V and a Vref of 24V. I.e. a 24V Zener or 2X12V in series.
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Old 11th June 2009, 09:49 AM   #429
Tham is offline Tham  Malaysia
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Hi Salas,

It is a 1N4749A. I use BC550 and I will just turn it the other way to see if it is the culprit.
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Old 11th June 2009, 09:52 AM   #430
Salas is offline Salas  Greece
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BC550 goes CBE from left to right as you face it with legs down, flat side front.
Attached Images
File Type: gif 550.gif (7.2 KB, 804 views)
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