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Class D Switching Power Amplifiers and Power D/A conversion

7498E BTL Mode Question
7498E BTL Mode Question
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Old 14th January 2020, 06:12 AM   #81
Sera26 is offline Sera26  Hungary
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Ok, I understand and great thank you for professional support


Do you think this can be a possible solution to avoid additional problem during usage?


30A 900W Mono Amplifier Speaker Protection Board Module Single Channel AC 12~15V | eBay
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Old 14th January 2020, 12:17 PM   #82
FauxFrench is offline FauxFrench  France
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Originally Posted by Sera26 View Post
Ok, I understand and great thank you for professional support


Do you think this can be a possible solution to avoid additional problem during usage?


30A 900W Mono Amplifier Speaker Protection Board Module Single Channel AC 12~15V | eBay
Hi Sera,
Unless you have important problems with start-up or shut-down "plop" in the speakers, I would do nothing.
The reason is that class D amplifiers (like yours) should have a load on the output all the time when powered, in particular during start-up. Without a load, you risk damaging the amplifier due to the LC output filter. Class D chips have various MUTE and the like facilities to suppress the start-up and shut-down "plop".
Such relay boards were designed for and very useful in class AB amplifiers. Class AB amplifiers can be operated without a load and far the majority of class AB chips have no "plop" damping features. The relay circuit connects the speakers only after the "plop" at start-up and before the "plop" at shut-down.

Last edited by FauxFrench; 14th January 2020 at 12:21 PM.
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Old 14th January 2020, 12:30 PM   #83
Sera26 is offline Sera26  Hungary
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Dear FauxFrench,


frankly say the speaker is still on the way so I can make a final decision only after first test later.
Real reason of showing this protection board was an own experience because I have built another boombox system with TPA3116D2 (2.1 channel) a few month ago and had serious "plop" at start-up and shutdown. This protection board (in 2.1 version) solved this issue after installation so I thought it can be a solution in this case also. But as you recommended, I will test the new configuration firstly and then comes the decision.
Thank you very much for your assistance again.

Last edited by Sera26; 14th January 2020 at 12:32 PM.
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Old 14th January 2020, 01:03 PM   #84
FauxFrench is offline FauxFrench  France
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Hi Sera,
In the very start of the TPA3116D2 Giga-thread TPA3116D2 Amp (postings #1 and #2) it is described how a guy ruined his TDA3116D2 amplifier by not having a load connected. "ddapkus" was working for TI and explains the problem.
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Old 14th January 2020, 01:08 PM   #85
Sera26 is offline Sera26  Hungary
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Ok, I'll check it, thanks.
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Old 14th January 2020, 07:12 PM   #86
Think is offline Think  Netherlands
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7498E BTL Mode Question
Has anyone tried lower impedance loads with TDA7498E in PBTL? like a 2ohm sub woofer? It might well be that it can't play sinewaves but that it has no problems with music as it has a crest factor. (much lower average power/heat) At lower voltages like 24v this should work for sure as max power is about the same as 3Ohm and 36V.



I'm running a TPA3251 (also max 36v 3ohm but in BTL) at 24V 2.0 Ohm per channel with a dual coil subwoofer. Runs fine and I will run it with a 7S 29V 10Ah battery later. 29V should put out about 2x200W instead of 2x135W with 3ohm loads. (3e audio 4 channel dual TPA3251 chip, $75 is great quality/value)
I read reports about TPA3116 and TPA3118 being fine with lower then specified impedance at max (24) voltage.
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Old 14th January 2020, 07:23 PM   #87
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by Think View Post
Has anyone tried lower impedance loads with TDA7498E in PBTL? like a 2ohm sub woofer? It might well be that it can't play sinewaves but that it has no problems with music as it has a crest factor. (much lower average power/heat) At lower voltages like 24v this should work for sure as max power is about the same as 3Ohm and 36V.
Reading the datasheet, you can use 2 Ohm loads but you need to reduce the supply voltage to 24V due to current limitation. You will only get 140W out while 3 Ohm should leave you 220W.
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Old 15th January 2020, 09:16 AM   #88
Sera26 is offline Sera26  Hungary
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Quote:
Originally Posted by FauxFrench View Post
Hi Sera,
Unless you have important problems with start-up or shut-down "plop" in the speakers, I would do nothing.
The reason is that class D amplifiers (like yours) should have a load on the output all the time when powered, in particular during start-up. Without a load, you risk damaging the amplifier due to the LC output filter. Class D chips have various MUTE and the like facilities to suppress the start-up and shut-down "plop".
Such relay boards were designed for and very useful in class AB amplifiers. Class AB amplifiers can be operated without a load and far the majority of class AB chips have no "plop" damping features. The relay circuit connects the speakers only after the "plop" at start-up and before the "plop" at shut-down.

Dear FauxFrench,


just another question concerning to this project.
What would be the recommended size of power supply for this PBTL/4 ohm spekaer combination? DC 36V/10A can be enough?
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Old 15th January 2020, 10:19 AM   #89
FauxFrench is offline FauxFrench  France
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Quote:
Originally Posted by Sera26 View Post
Dear FauxFrench,


just another question concerning to this project.
What would be the recommended size of power supply for this PBTL/4 ohm spekaer combination? DC 36V/10A can be enough?
A quick calculation: 36Vp across a 4 Ohm load means 36V/1.414 = 25.5Vrms. Then, the power calculation in 4 Ohm -> 25.5Vx25.5V/4 Ohm = 162W. The power supply has a capacity of 36Vx10A = 360W. You can assume a class D amplifier to have an efficiency above 85%. Thus, 162W in the load means less than 162W/0.85 = 191W consumption at the amplifier supply terminals. You need (less than) 191W from the power supply and you have a power capacity of 360W. The 36V/10A power supply is more than sufficient.

Last edited by FauxFrench; 15th January 2020 at 10:22 AM.
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Old 15th January 2020, 11:59 AM   #90
Sera26 is offline Sera26  Hungary
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Originally Posted by FauxFrench View Post
A quick calculation: 36Vp across a 4 Ohm load means 36V/1.414 = 25.5Vrms. Then, the power calculation in 4 Ohm -> 25.5Vx25.5V/4 Ohm = 162W. The power supply has a capacity of 36Vx10A = 360W. You can assume a class D amplifier to have an efficiency above 85%. Thus, 162W in the load means less than 162W/0.85 = 191W consumption at the amplifier supply terminals. You need (less than) 191W from the power supply and you have a power capacity of 360W. The 36V/10A power supply is more than sufficient.

OK, thank you very much for calculation and confirmation
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