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Old 12th December 2012, 03:26 PM   #251
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Quote:
Originally Posted by KlipschKid View Post
Hello again,

I just realised it might be far easier and more effective to replace the string of diodes with a 12V zener, so this would drop about 12.7V ? So 21V in and 8.3V out. This would be fine for my application. Would the higher voltage drop cause any issues, except of course the need for a heatsink on Q2 ?
To use that schematic you need to turn the zener upside down and add a 5mA resistor from it's bottom to ground. However this way the Kmultiplier will still track the input voltage. Is this the desired effect? I don't think so, and I would rather replace the upper two diodes with a 5mA resistor, and put the zener below in series with a diode to put the output less than a diode away from 12V.

One of the reasons the Kmultiplier works is because it normally has such low Vce. With 2V Vce the output transistor can handle its max Ic within SOA. However you won't get this benefit if you step a 21V supply down to 12V, so mind the inrush and output dissipation. If the output dissipates more than 2W you'll need a heatsink.

Here is a version of the Kmultiplier for a fixed output voltage. Choose the Zener for whichever output voltage you need and size R5/6 for 5mA of current.

Merlin, I think it is safe to put in the lineamp box. However if you are going to swap power supplies at any point I would put it in the supply box because it needs the 220R/220u RC up front to limit inrush.
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Last edited by keantoken; 12th December 2012 at 03:30 PM.
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Old 12th December 2012, 03:34 PM   #252
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Many thanks keantoken.
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Old 12th December 2012, 11:58 PM   #253
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Kean,

You are so helpful - thank you. I've got it sorted in my head now so thank you very much. I greatly appreciate your help.

In my case, there'll be just under 8V across R5 (20.5V in, - 12.7V for the diode+zener) so 1.6K resistor.

I've ordered parts and I found some ME210/200 too, so I'll let you know when I've tried this out.

I'm also very interested in an smd version so I hope someone will do a pcb ....

Here are Farnell's part codes if anyone needs them :

1084508 BD139-16 STMICROELECTRONICS

1084566 BD140-16 STMICROELECTRONICS

1126461 MJE210G ON SEMICONDUCTOR

1126460 MJE200G ON SEMICONDUCTOR

9556109 1N4004RL ON SEMICONDUCTOR

1228215 BC337-25 FAIRCHILD SEMICONDUCTOR

1853514 BC327-25 FAIRCHILD SEMICONDUCTOR

1782479 1N4148TR FAIRCHILD SEMICONDUCTOR

Last edited by KlipschKid; 13th December 2012 at 12:10 AM.
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Old 13th December 2012, 03:02 PM   #254
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@keantoken
Can't get 2SA1930, could you let me know other to replace?
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Old 13th December 2012, 05:12 PM   #255
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You can use the 2SC4793/A1837 pair, since you have low current it will work better.
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Old 13th December 2012, 05:39 PM   #256
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Quote:
Originally Posted by keantoken View Post
You can use the 2SC4793/A1837 pair, since you have low current it will work better.
Still Farnell & RS don't have here in Europe.
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Old 13th December 2012, 05:54 PM   #257
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Can you get BD139/140 from ST? Genuine 2SD669/B649?
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Old 13th December 2012, 08:37 PM   #258
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Quote:
Originally Posted by keantoken View Post
Can you get BD139/140 from ST? Genuine 2SD669/B649?
Yes BD139/140 from RS, only to be sure BD139 to replace 2SA1930 & BD140 to replace BC337, right?

Can't get 2SD669/B649.

Last edited by merlin el mago; 13th December 2012 at 08:40 PM.
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Old 13th December 2012, 09:04 PM   #259
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I have have bought 1930/5171 from Mouser

funny, I just now found a Poland supplier
http://www.micros.com.pl/25,about-micros-firma.html
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Old 13th December 2012, 09:19 PM   #260
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No, if you can't find BC337 replace it with BC5xxC.

Make sure the BD139/140 are from STMicro if you can, or maybe Fairchild.
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