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sumotan 15th August 2019 08:19 AM

DCR requirments for Chokes
Hi Guys,
A quick question, voltage drop aside, are there different dcr requirements between LC vs CLC supplies when using tube rectifiers ?


claudiomas 15th August 2019 09:34 AM

adeguate gap for choke imput filter
i use to modify hammond 190 gap and potting thems
also oversize current
or ask to Sowter UK

sumotan 15th August 2019 09:46 AM

Thank you kindly Claudiomas, oh no Im no looking for high ma, just wanted to know if requirements of dcr for LC & CLC is different. Btw beautiful projects that you've build.
With your compact designs, may I ask how do you counter EMI ?

Thank you again

claudiomas 15th August 2019 10:22 AM

each tube data select adeguate inductance for input choke with low DCR but read Sowter page, : "choke input filter chokes provide somewhat better regulation of the power supply though are much larger."Please specify the inductance and DC current capability you need. You can also specify the D.C. resistance or leave this to us. In this case it will be determined by the current rating of the wire but we will thicken up the wire to minimize the resistance if we have space on the bobbin. If you specify a resistance value the choke may be larger. We can design chokes for choke input or capacitor input filters. If you specify a choke for a choke input filter we need to know the rms ac voltage feeding the rectifier output as the choke must support this voltage. The choke in a capacitor input filter only sees a small ripple voltage. Chokes for choke input filters are generally at least 50% larger. "

we live with EMI but i use to pour epoxy inside HT transformers and choke bells or potting input choke and adeguate rotation before drill mounting holes. ground line short , RC tuning, wire resistors and good caps

sumotan 15th August 2019 10:25 AM

Thank you kindly Claudiomas.

claudiomas 15th August 2019 10:30 AM

I just really understood the question low DCR for choke input is essential otherwise saturation for filter choke DCR can go high if well proportioned this is what I have always remarked

sumotan 15th August 2019 10:34 AM

Thank you again .

Keit 15th August 2019 02:28 PM

Generally, there are no particular requirements of for dc resistance in power supply chokes for tube equipment, regardless of choke input or capacitor input. The higher the DCR the better the filtering (hum suppression) but given the inductance dominates, you'll never notice, and the worse the regulation. But is not at all critical, especially if the output stage is Class A.

If you specify a choke on the basis of the amount of DC it must carry and the inductance required at that current, you won't go far wrong.

A possible exception is where a shunt capacitor is used across the choke in a phase cancellation scheme - this can give very low ripple with small components. This technique is rarely used.

sumotan 15th August 2019 02:54 PM

Thank you kindly Keit . Shunt capacitor across the choke, do you mean connected cross from input to output of choke ???

Keit 15th August 2019 03:15 PM

Sumotan: Yes, connected to the two connections of the choke. This means the ripple AC goes thru the choke and gets phase retarded, and through the capacitor and gets phase advanced. If you get the phases arriving at the choke output end in opposition, the AC component is cancelled out, but only at one frequency (120 Hz in American countries and Japan; 100 Hz elsewhere).

It's rarely used because with it the design must match the supply frequency (no good for export), because it passes any hash/noise from the mains straight through, and also because if the DC load varies, as the inductance of a choke depends on the DC flowing in it, the cancellation is hardly ever perfect. The capacitor must be chosen to match the choke inductance, DCR, and core loss. A mismatch can makes things a lot worse instead of better.

But you see it occasionally, so I thought I would mention it because if I didn't some smarty pants would bring it up as an exception to the rule that choke DCR doesn't matter much in practice.

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