Re:Low THD PWM audio amp, DIY friendly
by amluto on Sunday January 15, 2023 @11:58AM
(#34390874)
Not at all my expertise, but:
The good class D amplifiers are closed-loop control systems. They don’t just create a output a fixed sequence of highs and lows for a given piece of music — they determine when to switch based on some combination of the input signal, the observed output voltage and current, and various state variables (for example, for protection). And they operate at frequencies of several megahertz, possibly with rather high precision pulse widths needed.
So one could do this with an ADC, a microcontroller, and a single output bit, but it would need to run the ADC at quite high frequency and possibly have multiple input channels (for current and voltage). This sounds expensive.
A TPA3255 costs $12.50 (qty 1 from Digikey). Add a dollar or two a nice DAC. I don’t think a 20-bit ADC, a DSP running at a couple hundred MHz, and most of the same driver and power circuitry that’s already in the TPA3255 would come out at the same price.
The good class D amplifiers are closed-loop control systems. They don’t just create a output a fixed sequence of highs and lows for a given piece of music — they determine when to switch based on some combination of the input signal, the observed output voltage and current, and various state variables (for example, for protection). And they operate at frequencies of several megahertz, possibly with rather high precision pulse widths needed.
So one could do this with an ADC, a microcontroller, and a single output bit, but it would need to run the ADC at quite high frequency and possibly have multiple input channels (for current and voltage). This sounds expensive.
A TPA3255 costs $12.50 (qty 1 from Digikey). Add a dollar or two a nice DAC. I don’t think a 20-bit ADC, a DSP running at a couple hundred MHz, and most of the same driver and power circuitry that’s already in the TPA3255 would come out at the same price.