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 Class D Switching Power Amplifiers and Power D/A conversion

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doctormord
diyAudio Member

Join Date: Oct 2007
Quote:
 Originally Posted by doctormord If you choose 10k for the upper Resistor, the lower is: 10k/8 485=1.18k so choose 1.2k

If you choose 10k for the upper Resistor, the lower is: 10k/8.485=1.18k so choose 1.2k.

Powerrating:
PVDD=32V

Current into TPS380X or MCP120 is negligible. We only calculate for the combined voltage divider.

10k+1.2k=11.2k

Current is then:

32V/11.2k=0.0028571429A or 2.86mA

Power follows I^2*R, so for the 10k:

2.86mA^2 * 10k = 82mW -> 1/10W is fine

for the 1.2k:

2.86mA^2 * 1.2k = 9.82mW -> 1/10W is more than fine

Nothing to worry about. The zener conducts only at overvoltage and is then roughly limited to

P_zener = U_zener * ((PVDD - U_zener)/R_upper)

Because differential resistance of the diode is much smaller than R_lower (1.2k) and R_upper (10k)

For 40V overvoltage we have:

P_zener = 4.7V * ((40V-4.7V)/10k) = 17mW

The upper resistor would need a power rating of:

P = ((40V-4.7V)^2)/10k = 125mW = 1/8W

If this overvoltage will occur for long time. If it's just pulses, 1/10W is still fine.

Someone correct me please if I'm wrong.
__________________

 14th July 2018, 11:23 AM #732 doctormord   diyAudio Member     Join Date: Oct 2007 @forestsgump, may you post a good quality picture/photo of the corresponding section on your board I may use for annotation and posting on my website? I don't have any of these boards on the bench. __________________
forestsgump
diyAudio Member

Join Date: Dec 2017
Quote:
 Originally Posted by doctormord @forestsgump, may you post a good quality picture/photo of the corresponding section on your board I may use for annotation and posting on my website? I don't have any of these boards on the bench.
Want to say word of appreciation for Doctormord, also DarkOne -
It is people like you - cared to lend a helpful hand, which kept diyAudio and many enthusiasts going!

Doctormord, after you are done posting, if can could help by sharing a link of your website i can reference exactly what pin to mod? thks.
Attached Images
 20171216_113202.jpg (1.00 MB, 465 views) FX502Spro-Disassembled-Heatsink2.jpg (208.6 KB, 479 views)

Last edited by forestsgump; 14th July 2018 at 01:51 PM.

forestsgump
diyAudio Member

Join Date: Dec 2017
1 more close-up picture, if it helps
Attached Images
 20171216_110003.jpg (994.5 KB, 456 views)

 14th July 2018, 11:01 PM #735 doctormord   diyAudio Member     Join Date: Oct 2007 Thanks for the compliments and pictures. Would be great if you can take them front/back with heatsink removed to see all traces and bias with much (soft) light to keep noise and exposure time low to have it nice and sharp. This amp doesn’t feature a voltage supervisor at all. (Or am i blind?) Then i will put all annotations in where to patch. Thanks a lot. __________________
forestsgump
diyAudio Member

Join Date: Dec 2017
2 more, hope this helps.
Attached Images
 FX502Spro-Disassembled-Heatsink1.jpg (236.4 KB, 446 views) FX502Spro-Disassembled-Heatsink3.jpg (169.4 KB, 434 views)

 15th July 2018, 12:10 AM #737 doctormord   diyAudio Member     Join Date: Oct 2007 Bottom side is super, now the same from the front and we're set. (Without heatsink, full board) __________________
 15th July 2018, 12:14 AM #738 doctormord   diyAudio Member     Join Date: Oct 2007 Btw. can you see any solder in the bottom sides via drills right under the chip? Looks like they haven't soldered the thermal pad to the board. __________________
 15th July 2018, 06:08 AM #739 zenit70   diyAudio Member   Join Date: Feb 2013 Location: Sicily Hello everyone Is there a 6-channel version of the tpa3255 amp ready to buy? I would like to give a multiamplification to my three-way speakers Thanks for the reply
 15th July 2018, 07:37 AM #740 doctormord   diyAudio Member     Join Date: Oct 2007 3e-Audio does now sell 3Ch. boards with 2 TPA3251 per board. You’ll find them on ebay. __________________

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