Squeezebox power supply

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Thanks ;)
Any advice for the other components values in this shematic ?
 

Attachments

  • enpower.gif
    enpower.gif
    8.4 KB · Views: 724
You would only need the top half, the part with the LM317. You can also use the LM338, but i don't think you need the headroom.

I have a Roku soundbridge with a Meanwell smps with some filter caps. A slight improvement, more discernable with headphones. Probably going linear would have more positive results. All the best.

Chuck.
 
OK, thanks, it's more precise for me now.
It will be Pinkmouse's shematic, with his recommandation of the LM338 in a TO3 can. Angchuck'link gives me 220 Ohms for R1, and 660 Ohms for R2 withe the LM317. Will it be the same for the LM338 ?
Can you help me with the choice of the transformer ? toroïdal or other ? 9V 25VA ?
 
close to prefect ...

... I would be quite satisfied with one of these myself.

" ... It will be Pinkmouse's shematic, with his recommandation of the LM338 in a TO3 can. Angchuck'link gives me 220 Ohms for R1, and 660 Ohms for R2 withe the LM317. Will it be the same for the LM338 ? ..." Yes, similar circuits / chips that use the same basic resistor ratios.

" ... Can you help me with the choice of the transformer ? toroïdal or other ? 9V 25VA ? ..."

Preference would be the torridal type, but there is a plathora of "standard" transformers to chose from. Your target voltage should closely match the specifications for best results from the LM338 = 9 to 15 VDC from the diode bridge (Vin for the LM338) ... so a 9 Volts AC secondary times 1.414 ~= 12.xx volts (the peak voltage from the diode bridge = input AC volts times square root of 2 ~= 1.414 [... which would make this an almost ideal 12 Volt battery charges as well]).

As for the transformer power rating, I like a two to one safety ratio (others may have other preferences) ... so, output power = volts DC times current = 5 VDC times 2.x Amps ~=12 to 14 Watts ... times two for safety and lower heat ~= 25 Watts = 25 VA.

:smash:
 
That snubbing cap ... at C4 is a great idea = stabilizes the voltage reference.
Yes, but actually , it's a bit more interesting than that. To be pernickety, it doesn't[/] stabilise the voltage reference but plays impedance tricks that the internal error amp likes.

The reference voltage is based on holding an accurate 1.25v across the upper resistor. This is multiplied by (R2/R1) to get an output voltage of 1.25*(1+(R2/R1)). What C4 does is reduce 'noise gain': to AC signals the voltage gain tends towards (0/R1) - since the cap looks like a very low impedance at HF. This is where the much better ripple rejection shown in the 317/338 datasheets comes from. So, big hint: make Z of C4 much smaller than R2 at twice your AC Mains frequency; 100uF can be better than 10uF.

Better yet, if you can replace R2 with somethig like a zener diode*, you'll get lower noise all the way down to DC - because the dynamic impedance of the zener will much lower than the required value of R2 (just 1-5ohms insteead of 1-2Kohms, say). So it mimics the action of a truly enormous cap at C4 without the potential for damage, or cost. Use a zener in series with a normal diode (anode to 0v), and you get nearly-perfect temperature compensation for free, too :)


*Output voltage will of course be (Vz+1.25)v
 
great report ...

" ... Better yet, if you can replace R2 with somethig like a zener diode ... Use a zener in series with a normal diode (anode to 0v), and you get nearly-perfect temperature compensation for free, too ..."

This is also a neat trick to get closer to a particular desired Zener diode voltage ... each series "regular" silicon diode adds 0.6 Volts to a Zener's value ... so a 3.8 Volt Zener in series with two silicon diodes = 5.0 Volts with (as you say) thermal stabization ! ... and a well regulated 5.0 it will be.

(a trick on cheap solar cell power supplies to fix regulated output at 10.2 V. for a nine volt metal halyde battery. ... 9.0 volt Zener plus two diodes = no overcharging. On 12 volt lead acid batteries = 12 v. Zener + two diodes = 13.2 = no boiling of the battery.)

:smash:
 
A question please :

Can the Nazar PS design near this one above could be good enough ? (IIRC it is near the same but BC transistor as currrent follower after the LM regulator !)

Need also a 9 V for my SB Duet as well !

PS : are red led not better than zener here for those few voltages (question of course not statment) ?
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.