D-type headphone drive

Other Hardware General Electronics
1

555 Timer can be used as a PWM / D amplifier for instruments or other applications; it can work within 4.5V to 16V supply voltage range, and can output 200 mA drive currents. The audio signal is transmitted to the CV (control voltage) pin of the [555 timer](https://www.utmel.com/blog/categories/integrated circuit/what-is-a-555-timer). Can a D-type headphone drive based on 555 timer can be used as a practical amplifier?

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o4YBAGBlfhGAfbVvAABXQ56b6As976.jpg

2

Why would you use an NE555 for that. To enjoy distortion?
There is a whole range of dedicated class-D amplifier chips on ebay.
PAM8403, PAM8406, PAM8610, etc.
Starting from about $2.
Leo..

3

I don't know if that will work or not...

I'm sure the 555 can be used as an oscillator but I think most class-D amplifiers are more complicated with some kind of a transistor/MOSFET output-driver and a feedback-circuit to "control" the signal. And there is usually an inductive "smoothing filter" so you can get a nice clean analog output. (Some cheap designs skip the inductor and rely on the speaker coil.)

The output should rest at 0V (with silence) and then swing positive & negative with the AC audio signal.

4

DVDdoug:
The output should rest at 0V (with silence) and then swing positive & negative with the AC audio signal.

Most small class-D amplifiers use two amps in bridge mode (mid-voltage on the speaker), so the DC blocking cap can be avoided (which might be more expensive than a second amp).
That also gives (almost) 4x the power for the same supply voltage.
Leo..

5

I guess in theory it could be used as a limited bandwidth class D amplifier.

However:

  • Typical class D amplifiers have more complex output filtering.
  • Your dynamic range will be quite limited.
  • The input to output transfer function is not very linear, will result in a lot of weird distortion (i.e. not the usual clipping or crossover distortion)
6

The CMOS versions of the 555 will give better performance I think, being significantly faster - in general
a 7555 outperforms a 555 in most areas and needs much less severe decoupling on the supply (the original
555 needs 470uF or so to reduce the heavy shoot-through spikes it otherwise puts on the rail).

The sport of adapting a 555 to as many possible applications as can be dreamt up is a thing in itself. Or is
it an art?

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