The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

[xrk971]

A member asked me if the SLB could be used to provide 7A current at 22Vdc output at the load. Jhofland ran the sims and it appears that everything is still within design limits as long as we are using it at the lower voltage and that there is limited adjustment of the output voltage with the pot. It should be used to adjust the cap Mx to “eat” about 1v of AC ripple at the second cap. So this is about 3Vdc drop. But do not use for higher voltages than 22v at 7A. This is almost at the limit of the ripple current rating on the first cap.

You may know what Class A amp uses 7A at +/-22v.

The BJT pass transistors need plenty of heatsink though at 21W each.

Also, you should probably parallel the big power resistors, say two 0.22R side by side or use a 10W however you can fit them as they will get hot.

 

[pinnocchio]

Received my set of PCBs along with the speaker protection. Thanks X!

 

[xrk971]

Well that was pretty quick delivery to Canada. Let me know how the packaging for the SSR’s faired.

 

[pinnocchio]

The SSR seem to be in perfect shape! Will be testing them shorlty since I have three amps to try. Thanks!!!!

 

[aljordan]

Does the green color of LEDs D1 and D2 play any role in the circuit or can I sub them out for another color?

Thanks

 

[Shawnstium]

They are just for indication. Only time the color matters is if you need a certain voltage drop, like when LEDs are used for cathode biasing of a tube.

 

[aljordan]

They are just for indication. Only time the color matters is if you need a certain voltage drop, like when LEDs are used for cathode biasing of a tube.

Thanks for the info!

 

[Harry3]

The idea was to have those positions available in case we see oscillation - but will initially leave unpopulated. As I said, our earlier tests with the CFP cap Mx had issues with oscillation. We will redo the simulation though to make sure performance is not too negatively impacted.

Just to confirm - do you populate both C24 (47pF) and C17 (1000uF) or do you leave C24 out if the SLB does not oscillate?

 

[xrk971]

The 1000uF cap is the cap that is being “multiplied” so you need that. The 47pF cap is good insurance. I would install it just in case. More important are R17 and R18, don’t make them any lower than 2.2R. 10R is very safe, 4.7R is good moderate value. It sets the gain of the ripple reduction.

 

[Harry3]

Thanks for the explanation - understand about the cap (1000uF) that's being multiplied.

 

[meanie]

May I know if anyone can pass me a copy of the SLB (single rail) BOM.
I can't find it on page 1.

 

[Vunce]

@meanie,
The SLBSR uses the same components as the positive side of the dual rail SLB.

 

[meanie]

Thanks Vunce,

I worked that out, just that the component numbering is different between the single and double rail pcbs.

 

[xrk971]

SLB SR Schematic, BOM, etc are here:
The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB

 

[meanie]

Hi X,

Can i substitute the main caps with 22mF instead of 15mF?
As i have some on hand.

Thanks

 

[xrk971]

Yes, but technically you should check with an O-scope to see if the ripple current under load is not exceeded. We designed 15,000uF for 5A load. So maybe 3A load can be 22,000 uF. Higher the cap, larger the ripple current.

 

[jimk04]

Would one use an SR SLB for a class d such as 3255? Or does class d have good enough PSRR to render this project overkill for that application?

 

[xrk971]

Not overkill but there are less expensive ways to get sufficient (and quiet) power for the TPA3255. An 800w 38v (can be tweaked to 50v) SMPS for LEDs can work very well.

If you must go with a linear PSU with a trafo and rectifier the SLB single rail can work well to provide a “hum free” linear PSU with much smaller bulk caps.

I have used Class D amps with a convention trafo, bridge and bulk caps - I can hear the mains hum.

 

[jimk04]

Thanks X.

I do have linear psu into 3255. Sounds brilliant but I feel my psu could be better. Slight hum with no music. It's a cheap ebay rectifier board and caps.

 

[meanie]

Received the SLB pcbs!

Thanks X