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Class D Switching Power Amplifiers and Power D/A conversion

Charging and playing TPA3110 at the same time ?
Charging and playing TPA3110 at the same time ?
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Old 26th June 2018, 09:45 PM   #1
oxl is offline oxl  Denmark
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Default Charging and playing TPA3110 at the same time ?

Hi,

I want to use a small, compact TPA3110 2X15W Digital Stereo Bluetooth Audio Amplifier Power Amp Board TE675 together with 3x18650 lithium batteries (in a Dayton Audio KAB-BE). But how can I connect it so it can play while charging the batteries at the same time

Regards
Ole

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Old 26th June 2018, 11:21 PM   #2
FauxFrench is offline FauxFrench  France
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Hej Ole,

It is possible. You connect the amplifier to the batteries and a current source (as charger) to the batteries as well. The current from the current source has to exceed the current drawn by the amplifier in average.
If you are afraid that the charging current may pull the battery voltage above the maximum supply voltage to the amplifier, use a shunt regulator to bleed off excessive voltage.
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Old 27th June 2018, 11:48 AM   #3
oxl is offline oxl  Denmark
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Hej Faux,


What kind/size of shunt exactly ? I assume that the voltage of the power adapter has to be higher than the 12v of the batteries ? Dayton Audio use a 19v power adapter, but 12v batteries.
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Old 27th June 2018, 04:04 PM   #4
wwenze is offline wwenze  Singapore
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Don't sweat the details of voltage (unless they're out of spec, in that case seriously sweat).

These amps can operate from anywhere between 8V to 26V.

The below is typically good enough.

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Old 27th June 2018, 05:08 PM   #5
oxl is offline oxl  Denmark
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Not sure I quite understand the diagram. What is the charger ? What diodes to use ?
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Old 27th June 2018, 07:53 PM   #6
oxl is offline oxl  Denmark
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Is the charger just a 12v voltage regulator or what ?
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Old 27th June 2018, 08:48 PM   #7
FauxFrench is offline FauxFrench  France
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Hej Ole,

The "Charger" is a current source circuit that operates from the 19V power line. At the cathodes of the two diodes, the amplifier is connected. The upper diode serves to supply the amplifier directly from the 19V line when that line is powered. At the same time the batteries are charged, through the "Charger" current source circuit, from the 19V line.
If the 19V power line is low, the amplifier is feed via the lower diode from the batteries.

It is important that the charging current to the batteries remains below the maximum charging current the batteries can stand. I looked at one brand of 18650 batteries and they have a maximum charging current just above 1A. If you connect the amplifier (like I suggested for a start) directly to the batteries (without diodes) and charge the batteries directly with the amplifier connected, the charging current should be no more than 1A. 1A because you cannot rely on the amplifier drawing any significant current. But, if the amplifier actually draws 1.5A, the charging current (1A) is not even sufficient to feed the amplifier and the last 0.5A has to be taken from the batteries (no charging but actually discharging).

The slightly more complex circuit proposed by WWense has the advantage that the battery charging current is not the residual of the charger current when the amplifier current has been subtracted. With this circuit, the amplifier can draw as much current as the 19V line can supply, and the charging current to the batteries can be set independently and does not depend on the amplifier current. It is a well conceived circuit.

Did that help on the understanding?

I assume 19V is for four 18650 elements.

Last edited by FauxFrench; 27th June 2018 at 09:07 PM.
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Old 27th June 2018, 10:00 PM   #8
oxl is offline oxl  Denmark
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No, the 19v was just something I saw from Dayton Audio. I only want to use three 18650 (12,1 v). Do you imply that the power supply should also just be 12v ?

I am still unsure what a "charger" curcuit actually is (can you show a picture of a 12v charger) ? But it must somehow have separate input and output, otherwise the anodes of the two diodes would be directly connected.
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Old 28th June 2018, 03:19 AM   #9
wwenze is offline wwenze  Singapore
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Please use a proper li-ion battery charging circuit with and not just a constant-current source. Li-ion does not work well with a simple constant-current source.

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Charging Lithium-Ion Batteries – Battery University

...in fact no battery works well with a simple constant-current source, if you simply consider what happens when the battery is already fully-charged and you're still trying to push a current into it. That being said, most real-life chargers are a combination of constant-current + constant-voltage at the same time, or rather current-limited + voltage-limited. Battery charger ICs are widely-used and capable.

If in doubt, just buy a li-ion battery charger instead of making one from scratch.
1, 2 or 3 cells Lithium ion Battery 2A Charger Module 18650 Charging PCB SY6912 699901026556 | eBay

Last edited by wwenze; 28th June 2018 at 03:33 AM.
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Old 28th June 2018, 04:23 AM   #10
oxl is offline oxl  Denmark
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OK Thanks. So I should use the 3 cells Lithium ion Battery Charger together with two diodes and a 19V 1-2A power supply ? Do I need under/over-volt protection too ?
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