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Easy Class D, redux




 
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Author Topic: Easy Class D, redux  (Read 402 times)
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km6sn
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« on: May 26, 2020, 05:03:53 PM »

Hi All,
having already ordered two of the  TPA3116D2 2x50W Class D Stereo from parts express,
JB enlightened me that they may not do what I want.

After studying the data sheet, I have come up with reasonable design goals:

1. Use tpa3118d2 in mono  mode, 2 channels, w/ .2 ohm balancing resistors
2. switch at 500 khz.
3. Vdd at 17v (5v+12v)
4. Carrier Vdd 8.5v , 1.54A
5. RF deck at 6ohms
6. carrier power 12w (enough to drive the 3-500 one-holer)
7. pep 48W , 48W audio required

The choice of RF deck impedance is a tradeoff between

A. lowering the resistance until the stereo amp can produce enough distortion-less power, and
B. minimizing the RF deck losses by keeping the R high.

I will keep you posted on the progress.  I would appreciate any thoughts on this approach.
Thanks, and
73,
Rod

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M0VRF
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« Reply #1 on: May 27, 2020, 12:58:24 AM »

Hi Rod, PBTL is obtained by grounding an input, mentioned in the data sheet. There are versions that have this facility but guess you can mod the ones you have?

BTW, there are so may versions of the TPA3116D2 amp now it's ridiculous!

The one you want is this;

https://www.alibaba.com/product-detail/Factory-Price-high-power-digital-power_60348535823.html

Altho' advertised it's no longer available and you'll get the op-amp version so just remove it!

I based a product around the original version that had PBTL links under the PCB along with space for a type 'M' regulator so you could drop the 24V to 12V (say) for powering the Oscillator section of the class E (or D!) generator. Made a really sweet unit.
What happens.....CH changes the design for no good reason and fits an op-amp to the front end with a dumb filter with a huge dip in the mid range!
I tried to reverse engineer the circuit and gave up finding that removing the op-amp gave a perfectly flat response albeit at a lack of gain, just had to drive it harder to get the required O/P.

If anyone is interested, this design is an idea driver for most valve linears and the BLF188XR, 12W carrier with 24V depending on your RF stage of course, I use single ended class E.

Being direct PWM, the modulated audio response is flat from 20Hz to 10KHz.

Regards.

JB.
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