[sdiy] Help, I'm Desperate! (Charge Injection with DG408)

Richie Burnett rburnett at richieburnett.co.uk
Wed Dec 12 19:54:18 CET 2018


Probably represents the bare minimum.

It depends how much you want to filter out the HF switching carrier. 

-Richie,

Sent from my Xperia SP on O2

---- Guy McCusker wrote ----

>On Wed, Dec 12, 2018 at 4:21 PM <rburnett at richieburnett.co.uk> wrote:
>
>> One switch's control signal has duty ratio ramping down from 100% to 0%,
>> whilst another switch's control signal has duty ratio ramping up from 0%
>> to 100%.  (Use whatever control law you want for the crossfade:  Linear,
>> Constant power, etc...)  Only two PWM streams are active and need to be
>> generated at any given time so shouldn't be too demanding on a low-end
>> micro.
>
>Thanks for spelling it out.
>
>This is exactly the control regimen that the Richter circuit achieves
>with the LM3914 and dithering oscillator. In that circuit the LM3914
>outputs were used to drive vactrols which attenuate the input to the
>summing amplifier but it seems to me one could use them to drive the
>switches in this design instead. Richter's oscillator runs at 44kHz,
>which is presumably fast enough for this design too?
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