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Old 30th September 2012, 05:24 PM   #11
GaryB is offline GaryB  United States
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Quote:
Originally Posted by yagoolar View Post
Two setups were tested - same result.
I recently built one of these tracking preregs and it works fine.
Looking at your circuits, the values look a bit odd. Here are some specific comments.

1) The 1000uf cap at the output of the 1st regulator isn't needed although it shouldn't cause any problems.

2) The resistors around the 2nd regulator look odd. What voltage are you trying to regulate? Compare your circuit to the referenced circuit. They don't look the same.

3) The value of R6 (top circuit) or R2 (bottom circuit) = 6.3ohms is much too low. Typical values should be 100 - 240 ohms. Similar comment for R7 in the top circuit.

--Gary
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Old 30th September 2012, 05:33 PM   #12
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I didn't notice that. The cap on the reg2 adjust pin has got to go. Or at least shunted with a resistor.
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Old 30th September 2012, 05:37 PM   #13
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Increased caps value in voltage doubler to 19,4mF+19,4mF and voilá - ripple voltage went down 0,9 mV rms at R load!
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Old 30th September 2012, 05:49 PM   #14
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I want to regulate filament current for 6B4G/6C4C -> 6.3V @ 1A. Cold cathode filament is actually 3.5 ohm measured.
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Old 30th September 2012, 05:52 PM   #15
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Quote:
Originally Posted by sofaspud View Post
I didn't notice that. The cap on the reg2 adjust pin has got to go. Or at least shunted with a resistor.
Why remove? It improves ripple rejection by 20 dB according to datasheets. What shunt resistor value?
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Old 30th September 2012, 06:01 PM   #16
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My bad; it actually is shunted by a resistor. D'oh!
But at least at answered the question posed to me.
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Old 30th September 2012, 06:03 PM   #17
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So now we learn it is a current regulator you want to build. Carry on.
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Old 30th September 2012, 06:05 PM   #18
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Yep. It is shunted it is 8 pm in PL already, but in US is still quite early ...
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Old 30th September 2012, 06:09 PM   #19
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So now we learn it is a current regulator you want to build. Carry on.
Er, I wrote it in the subject. Too much or too little alcohol
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Old 30th September 2012, 06:11 PM   #20
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It's not that early.
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