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Old 16th June 2007, 08:00 AM   #1
jarthel is offline jarthel  Australia
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Default high DCR secondary (power transformer)

here's what I used: 500V 42ohm (as mentioned in the lundahl website) -> bridged rectifier -> 100uF -> 10H 36ohm (from lundahl website as well) -> 200uF -> 100mA current load

I was playing around PSUD2 and it seems to me that high DCR secondary (I changed 42 to 250) for the B+ supply have a "smoother" transition before the voltage stabilizes. Though at the expense of lower voltage and voltage stabilizes a bit longer.

With the lower DCR, there is some "ringing" (a term I got from reading Bas Horneman's DIY mag) but the voltage stabilizes faster and you get higher voltage.

The article from the dIY mag has also said higher DCR is better.

Is there a way to get rid of this "ringing"? how about using resistors in series with the secondary (before the diode)?

Thank you for the replies
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Old 16th June 2007, 08:54 AM   #2
Gluca is offline Gluca  Italy
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voltsecond's site
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Old 16th June 2007, 10:44 AM   #3
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What voltage are you aiming for?

I used more or less the same setup:
LL1651 -> 2x40? -> HEXFRED brigde -> 2x40? -> 3.9F -> LL1673 15H -> 220F

I surrounded the brigde with 40? resitors, used four of them to spread the heat.


You can find my thoughts on this here:
Power supply

Some remarks:
- Lundahl chokes are air-gapped, this means that you should select the current you will use. Do NOT use a choke with higher current capability just to be safe.
- Use the choke in a common mode configuration (see Lundahl docs).
- Enlarging the first cap will not reduce the hum, it will cause higher peak currents in the bridge.
- Use snubber caps across the bridge (22nF).
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