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Howto: TeddyCap

With most (small) transformers, CRCRC will be good enough. The internal resistance of the transformer is higher than the first R anyhow.

Teddy
 
You can use less than that, but then the dropout due to the internal impedance, the smoothing capacitors, and the load will be larger and the noise at the input of the TeddyRegs will be higher. 30VA works well too. I even managed to make it work well with a 15VA, but I recommend 50VA to be on the safe side. It's still very small comparing to the 500VA HiCap transformer...
 
OK thanks Teddy. The TeddyCap does look fairly essential as far as I can see. The output of my 30VA transformer, bridge rectifier and a single smoothing capacitor looks like this:

psu01.jpg


Even the TeddyReg has difficulty removing these peaks, and the TeddyCap should get rid of most of them. But what is the cause of the noise at about 26kHz shown above? Is this switching noise from the bridge rectifier? It seems odd that its frequency is so high.

Andy
 
Looks like a resonance. I'd be interested to see the effect of 4 x 0.01uF ceramic caps in parallel with each diode in the bridge for a start. Or try schottkies.
 
jamadlavy said:
Answering this question made me realise I should try the RCRCRC again, My system has evolved so much since then that maybe I'd get different results ?? I'll post my findings later. Eric
Click to expand...

Hi Eric,
I know this is an old thread, but did you try the RCRCRC schema again? What where your findings?
Joe
 
teddy_pardo said:
The first "R" is redundant, the internal impedance of the transformer is sufficient

Teddy
Click to expand...

Thanks Teddy, got the message about first R being redundant. I have an 80VA toroidal with two 18V secondaries fto use with a JFET Buffer at +–15V, drawing about 10mA per channel.

I already have four 10uH air core chokes that I could use in place of the resistors. I also have some nice 0R47 2W MF resistors that I could use. So I am trying to decide whether the go with CRCRC or CLCLC (three 2200uF caps per rail).

Any thoughts about whether the inductors are a worthwhile improvement?

Thanks,

Joe
 
Any chance someone could point me to a suitable transformer...?
I'm not exactly sure what I'm looking for, I know a 50Va C core is the ticket, but it's the output voltage and current rating I'm unsure about....any help would be greatly appreciated.
Cheers.
 
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