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Old 13th November 2012, 11:22 AM   #11
vingenz is offline vingenz  Italy
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Today I improved the voltage drop and sagging (~410vdc @ max volume) decreasing first cap value (down to 40uF) and adding a 470R resistor between first cap and choke. I've tried to increase the first cap value, but the sagging was too much. Heres the schematic:
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Old 13th November 2012, 12:01 PM   #12
DF96 is offline DF96  England
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If increasing a reservoir cap value increases sagging then this may be a sign that the transformer has high resistance. Or it could be a sign that something is not right.
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Old 13th November 2012, 12:39 PM   #13
macboy is offline macboy  Canada
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Your 1000V diodes are not quite sufficient. You have a 744 VAC transformer, so the the peak voltage (per side) is 1052V! Don't forget that during the other half of the AC cycle, the voltage on the diode anode will swing to the negative side. Opposed to the positive voltage on the cap (and cathode), you are approaching and likely exceeding the 1000V breakdown voltage. And that's without accounting for component tolerances, slightly hot line voltage, etc. It is possible that the diodes are at least partly conducting in reverse and taking some charge out of the cap. Try to find something with higher breakdown voltage.

Last edited by macboy; 13th November 2012 at 12:42 PM. Reason: typo
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Old 13th November 2012, 01:33 PM   #14
vingenz is offline vingenz  Italy
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I' ve already tried to put 2x1n5408 in series each side but nothing change. secondary DC resistance is about 150 ohm.
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Old 13th November 2012, 01:55 PM   #15
jrenkin is offline jrenkin  United States
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How about the DCR of your choke?
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Old 13th November 2012, 02:09 PM   #16
vingenz is offline vingenz  Italy
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Quote:
Originally Posted by jrenkin View Post
How about the DCR of your choke?
100 ohm
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Old 13th November 2012, 02:45 PM   #17
Yvesm is offline Yvesm  France
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A pair of 6L6GC powered at 450V and loaded with 5600 ohms can deliver some 50W and draws 230mA from the B+ to do that.
With such HI DCR values for the transformer and the choke, (150 + 100 that is 250 ohms) a minimum of 57V of B+ drop is . . . normal

Enter thoose values in PSUD and check yourself.

Yves.
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Old 13th November 2012, 02:58 PM   #18
jrenkin is offline jrenkin  United States
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I guess I am a little confused on your design. The first picture only shows the transformer, diodes and one capacitor. The second shows more, but now has an extra CR filter in front. With a transformer DCR of 150, choke DCR of 100, AND an additional 470R in the way, you have a mess.
Start over, model it in PSUD. Start with a more standard CLC plan and model the load as a current sink. Make sure you input the correct values for your iron, and play with it until you get reasonable results and make sure components like the diodes and capacitors can handle the large voltage swings.
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Old 13th November 2012, 03:29 PM   #19
vingenz is offline vingenz  Italy
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On psud2 simulation, the issue is the secondary dc resistance that doesn't allow me to use big capacitor.
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Old 13th November 2012, 03:56 PM   #20
DF96 is offline DF96  England
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Don't forget to include the transformed primary resistance too. I think PSUD2 has a calculator for that.
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