15V to 13V regulator

[hifisucks]

Hello, I just bought a 230VAC/15VAC transformator and just cant figure out how get the 15V down to 13V...
Its going through a rectifier and some 20000uF to feed a small Class D amp...
So, I can only test it without load... I dont want to hook up the amp before I know what will feed in to the amp...
Any suggestions?

 

[Osvaldo de Banfield]

15V AC, rectified are about 20VDC. For a Class D amp I would use a buck regulator like L4970 series, and synchronized to the amp to minimize noise and EMI.

 

[hifisucks]

Thanks for your reply! But I must say that I used a switching regulator and had bad interfearances in my analog radio through the amp...
Tried also a 12V lead gel battery and all was good...
Dont know what to do...
Is there a old school methode without useing a switching regulator?

 

[mvs0]

Thanks for your reply! But I must say that I used a switching regulator and had bad interfearances in my analog radio through the amp...
Tried also a 12V lead gel battery and all was good...
Dont know what to do...
Is there a old school methode without useing a switching regulator?

Do you have more details on the specs of this class-D amp?
min/max power voltage (no seperated plus and minus supply needed?)
max current

 

[hifisucks]

Its a SMSL SA-S3... with the TA2021b chip...
Specific:
T-Amp IC Tripath TA2021B
Output Power 2 x 25W @ 4ohm, 2 x 13.5W @ 8ohm
Dynamic Range 100dB
Power Efficiency 81% @ 25W, 4ohm, 88% @ 13.5W, 8ohm
Audio input: RCA x 1
Power socket (5.5mm/2.5mm) x 1
Circuit board : 1.6mm thick, full-fiber, deep golden

 

[Osvaldo de Banfield]

The chip's data sheet says absolute maximum 16V and 14V typ., so a regulator must be used. Any linear approach will loose (20 - 14) / 14 = 0.42, so the net efficiency will be only 0.58. Again, a PWM reg will enhance it to more than 85%.

 

[hifisucks]

But FM radio is a must... so I must use linear power supply...

 

[Osvaldo de Banfield]

Then, a Class AB amplifier is also a must. Why do you think that a Class D amp has no interference into radio and a PWM regulator does?

 

[hifisucks]

I can only say, that with my 12V battery the sound was great without audible interferences...
So I conclude that a decent made linear power supply could do it also...
Or am I wrong?

 

[Osvaldo de Banfield]

How long are the cables between battery and amp? How long will be the wires from the amp to linear reg?

 

[hifisucks]

The cable from battery to amp is 20cm... cable length will be 20cm or maybe 15cm...

 

[Osvaldo de Banfield]

Respectfully, how skilled are you making electric/electronic circuits?

 

[mvs0]

Its a SMSL SA-S3... with the TA2021b chip...
Specific:
T-Amp IC Tripath TA2021B
Output Power 2 x 25W @ 4ohm, 2 x 13.5W @ 8ohm
Dynamic Range 100dB
Power Efficiency 81% @ 25W, 4ohm, 88% @ 13.5W, 8ohm
Audio input: RCA x 1
Power socket (5.5mm/2.5mm) x 1
Circuit board : 1.6mm thick, full-fiber, deep golden

would do something like thisbut with only one 3055:
(and smaller caps, 4700uF should do it)

An externally hosted image should be here but it was not working when we last tested it.

 

[Osvaldo de Banfield]

Making the mat, the chip says 25W @ 4Ω, does not say if is only one or both channels simultaneously. Lets suppose that is single channel only (Worst case). Then, I = √(25W/4Ω) * 2ch * √2 = 4√3 = 6.9Amper peak. So U will need a power supply capable of deliver about 10Amper. A couple of TIP36 plus a LM317 may do the job.

 

[jan.didden]

With music, 6.9A peak will translate to maybe 2A average, tops ...
An LT1085 followed with a hefty cap will do.
The xformer wouldn't support more anyway.

Jan

 

[hifisucks]

Thats okay... I am not very skilled into electronics...
hanks for your concern and ideas!
Christoph

 

[Osvaldo de Banfield]

In this case, search for a regulator board capable of 10 amper peak, and 14V output. You must think in a large heat sink for it. There must be some kit of this kind available in your town. Also, think of buying a small trafo output, say, one of about 10VAC @6-7Amps.-

 

[Vovk Z]

With music, 6.9A peak will translate to maybe 2A average, tops ...
An LT1085 followed with a hefty cap will do.

If 1085, than 1084 or 1083 could be better.

 

[hifisucks]

Found an transformer with 13.5VDC and 10-12Amps...
I will try this...
Thanks!
Christoph

 

[Osvaldo de Banfield]

(13.5V * √2 ) - 2 * 0.7V = 17.7V, it is still over maximum ratings. You will destroy the amp. Search for a 12V transformer, it is rather common.