An arguably better replacement for the resistor in a CRC power supply - R21 PS module

[codyt]

It is only SUP70101 burned by thermal load.

Received a few pieces of SUP70101 this morning and I've swapped a new piece into the suspect channel. Everything back to normal! Thanks again for your help with this, Tombo. 🙏 🙏 🙏

 

[tombo56]

Great to hear that everything is OK.

 

[codyt]

Quick question, @tombo56 - let’s say I’m wanting to shave another volt off my B+. Aside from the extra dissipation required of the pads pass MOS, is their any penalty in running R21 with a Vdrop of, say, 3v?

 

[tombo56]

No penalty past increased power dissipation. SUP70101 is rated for 375 W dissipation, but limited heat conducting surface of TO-220 case limits that in practice. With a good heatsink and thermal interface, I would limit dissipation to 30 W max.

 

[gsrchrisu]

Just wanted to confirm that Tta004 and Ttc004 are substitutes for ksa1381 and ksc3503. Not sure Mouser or Newark are every gonna deliver these 1381's LOL

 

[tombo56]

TTC004B/TTA004B are very good replacements for KSC/KSA in case of R21 circuit.

 

[gsrchrisu]

Awesome thank you for the quick reply

 

[codyt]

Another quick question for you, @tombo56 . I'm hoping to make a bipolar supply based on that dual mono motherboard I made a while back. Reading your earlier comments it seems pretty straightforward – would the attached schematic do the job?

 

[tombo56]

Yes, that’s the right way to connect two same polarity supplies as a bipolar supply.

 

[tombo56]

@codyt
On the second look I've noticed connection points marked as R21-G. 😳 Several coffees do wonders.

I suppose that are connection points for R21 module reference ground wires?

In that case, for the second R21 supply that has role as the negative supply, reference ground wire has to be connected to the actual ground of that module, which is on your schematic marked as V-.

 

[codyt]

Perfect, thanks Tombo. Those ground references were the part I was unsure of - I should have led with that, sorry 🙂

 

[poseidonsvoice]

@Vunce, @tombo56,@codyt,@ItsAllInMyHead

Hi fellas I’m currently building up 4 R21 regulators (2 positive and 2 negative) but I am having a heck of a time finding the Ohmite heatsink referenced in the BOM. Mouser p/n: 588-PA-T21-38E

Any tips for substitutions or where I can find it since it works so well in making the design very compact with Prasi’s LT4320/TO220 CRC PSU?

Of course if you have extra, please pm, I’ll buy them!

Thanks,
Anand.

 

[birdbox]

I think you can just buy the dual clip and take one clip off and put the remaining one in the middle.

PA-T22-38E

 

[codyt]

@Vunce, @tombo56,@codyt,@ItsAllInMyHead

Hi fellas I’m currently building up 4 R21 regulators (2 positive and 2 negative) but I am having a heck of a time finding the Ohmite heatsink referenced in the BOM. Mouser p/n: 588-PA-T21-38E

Any tips for substitutions or where I can find it since it works so well in making the design very compact with Prasi’s LT4320/TO220 CRC PSU?

Of course if you have extra, please pm, I’ll buy them!

Thanks,
Anand.

I have a pair I can send you, if that helps. Just PM me your address. I’ve not found substitutes, though the second set I built I mounted them to the chassis heat sinks (probably a slightly uncommon approach, and also the standalone PSU version).

 

[Vunce]

Sorry Anand, no extra's in my stash.
I didn't use those sinks after the initial quad of R21's were built.

 

[tombo56]

I think you can just buy the dual clip and take one clip off and put the remaining one in the middle.

PA-T22-38E

Excellent advice!
Even Mouser has some: https://hr.mouser.com/ProductDetail/Ohmite/PV-T22-38E?qs=gZXFycFWdAOMPpG1BKBMpA==

@poseidonsvoice
Check post #139 for the right R7 value, depending which MOSFET you have for the negative supply.

 

[poseidonsvoice]

Does C5 for R21N stay as 33 picofarads or should I change that to 47 pf as well?

Thanks,
Anand.

 

[tombo56]

It should stay at 33pF.
47 pF is only with SUP60061EL-GE.