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I have an 8-LED array driven by an 8-channel source driver (TD62783AP) controlled from an 8-bit shift register (74HC4094).

When it comes to dimming the LEDs using PWM, I came up with two solutions, and I was wondering if one was better than the other:

  • I can PWM the Output Enable pin of the shift register
  • I can PWM the supply VCC of the source driver

Which one, if any, would be best, and why ?

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I would say you should apply the PWM signal to the OE pin of the shift register because the driver is not designed to have a voltage level at the inputs higher than the supply voltage due to the clamp diodes at the input.

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