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Chip Amps Amplifiers based on integrated circuits

TDA7575B - helping understand
TDA7575B - helping understand
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Old 17th July 2018, 01:53 PM   #1
dutamete is offline dutamete  Latvia
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Default TDA7575B - helping understand

I am searching to build small amplifier for 4ohm subwoofer in car.
I found this chip-amp and it have single channel mode, but all info in datasheet about single channel mode is for 1ohm load.
What i am missing? What would be power for 4ohm load in single channel mode?

Datasheet: https://www.st.com/resource/en/datasheet/tda7575b.pdf
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Old 17th July 2018, 02:10 PM   #2
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If you're running in a car without any boost converter than you can assume your supply volts are close to those in the datasheet (14.4V) hence your output into 4R will be around 22W.
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Old 17th July 2018, 02:13 PM   #3
dutamete is offline dutamete  Latvia
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I understood that those values are for dual channel mode.
I thought, that paralleling the outputs into a single channel will result in higher output, as this chip have option like this.
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Old 17th July 2018, 02:39 PM   #4
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Paralleling isn't designed to give higher output into the same impedance (it cannot since the output is voltage limited by the supply), rather its designed to give higher power output (more current) into a lower impedance.
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Old 17th July 2018, 05:39 PM   #5
dutamete is offline dutamete  Latvia
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Thank You for clear answers.
Maybe do you know some other options with more power @14.4V and 4ohm load?
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Old 17th July 2018, 07:45 PM   #6
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> more power @14.4V and 4ohm load?

Power is limited by supply voltage and load impedance. (And that we define Audio power as Sine RMS.)

Take a simple amplifier fed 14V. Its output can (ideally) swing zero V to 14V. Or 14V peak to peak. Which is 5V Sine RMS. (5V^2)/4r is 6 Watts.

In practice, non-ideal devices always lose several tenths of a Volt each way. I would expect 4 Watts, 4Vrms, 11.2V p-p, so about 3V of total losses. (That's 4 Watts "clean". You can always drive it harder. Car-sound also likes a "10% THD" spec, which is gross clipping, but is indeed often tolerable for partying. The 10%THD spec on a basically clean efficient amplifier clearly exceeds clipping.)

4 Watts aint enough for a loud car. (Also this form needs a large capacitor to block the steady 7V DC of the amplifier.)

If you rig *two* of these 14V amps, back-to-back, with *opposite* signal polarity, "BTL", you can approach 28V p-p, 10Vrms, 25 Watts, which in a real world works out near 22W clean 28W in obvious clipping (and 40W-50W "Max power", totally clipped, which can be a guide for the thermal rating of your loudspeakers in heavy abuse, or when using audio amplifier to cook sausages). BTL also avoids the need of big capacitors.

At the SAME supply and load, the only differences between chips is the losses. Older low-price chips settled for 17W @ 14.4V 4r. This super-chip reaches 22W same feed and load. This is a mere 1.1dB difference for a nine buck!! chip compared to a $4 chip.

You can't BTL again. At this point you have two choices:

Raise the supply voltage
Lower the load impedance

In battery work, raised voltage is not trivial.

Lowering the load is *often* a good path. Four 4r 25W 6" speakers may be the same cost as one 4r 12" 100W speaker. Put them in parallel for 1 Ohm. Look for an amp that is beefy enough to drive 1 Ohm (such as TDA7575).

Another path specific to "12V" work is Car-Audio. "Trunk amps" have a voltage converter and audio amps all pre-made and sold at competitive prices, far cheaper than you could build such a thing. They come from 60W to 2,500W.
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Old 17th July 2018, 08:30 PM   #7
Kshishtoff is offline Kshishtoff
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Quote:
Originally Posted by dutamete View Post
Maybe do you know some other options with more power @14.4V and 4ohm load?
You can buy TDA1562q. Its power is up to 70 watts. But it's expensive. And you will also need high-capacity capacitors for circuit assembly. They are also quite expensive.
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Old 17th July 2018, 11:47 PM   #8
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My outline of 12V amplifiers above does not cover the strange new way the TDA1562 works. Two large caps "lift" the supply rails to cover short-term peaks.

The TDA1562 contains a mono class-H BTL output power amplifier. At low output power, up to 18 W, the device operates as a normal BTL amplifier. When a larger output voltage swing is required, the internal supply voltage is lifted by means of the external electrolytic capacitors. Due to this momentarily higher supply voltage the obtainable output power is 70 W.
In normal use, when the output is driven with music-like signals, the high output power is only needed during a small percentage of time. Under the assumption that a music signal has a normal (Gaussian) amplitude distribution, the reduction in dissipation is about 50% when compared to a class-B output amplifier with the same output power. The heatsink should be designed for use with music signals. If the case temperature exceeds 120 C the device will switch back from class-H to class-B operation. The high power supply voltage is then disabled and the output power is limited to 20 W.


At best, this "lift" could approach 4X the power of BTL with the same supply and load, over 80 Watts. Lift-losses account for the 70W 4r 14.4V number in the spec. The time that lift-power is available (for specific lift caps) is not given? A couple 4,700uFd will cover many musical peaks.
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Old 20th July 2018, 09:29 PM   #9
dutamete is offline dutamete  Latvia
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TDA1562q is obsolete and i cant find any reputable distributor which sells them.
Ordering from China will end up with fake...
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