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Class D Switching Power Amplifiers and Power D/A conversion

TPA3255 - all about DIY, Discussion, Design etc.
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Old 14th July 2018, 11:19 AM   #731
doctormord is offline doctormord  Germany
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Quote:
Originally Posted by doctormord View Post
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.
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Old 14th July 2018, 11:23 AM   #732
doctormord is offline doctormord  Germany
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@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.
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Old 14th July 2018, 01:47 PM   #733
forestsgump is offline forestsgump
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Quote:
Originally Posted by doctormord View Post
@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.
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File Type: jpg FX502Spro-Disassembled-Heatsink2.jpg (208.6 KB, 479 views)

Last edited by forestsgump; 14th July 2018 at 01:51 PM.
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Old 14th July 2018, 03:03 PM   #734
forestsgump is offline forestsgump
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1 more close-up picture, if it helps
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Old 14th July 2018, 11:01 PM   #735
doctormord is offline doctormord  Germany
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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.
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Old 14th July 2018, 11:57 PM   #736
forestsgump is offline forestsgump
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2 more, hope this helps.
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File Type: jpg FX502Spro-Disassembled-Heatsink3.jpg (169.4 KB, 434 views)
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Old 15th July 2018, 12:10 AM   #737
doctormord is offline doctormord  Germany
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Bottom side is super, now the same from the front and we're set. (Without heatsink, full board)
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Old 15th July 2018, 12:14 AM   #738
doctormord is offline doctormord  Germany
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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.
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Old 15th July 2018, 06:08 AM   #739
zenit70 is offline zenit70  Italy
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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
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Old 15th July 2018, 07:37 AM   #740
doctormord is offline doctormord  Germany
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3e-Audio does now sell 3Ch. boards with 2 TPA3251 per board. You’ll find them on ebay.
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