I'm reading the datasheet for the HCPL3700M AC/DC to Logic Interface Optocoupler. In a test circuit diagram, it shows a pulse generator connected to both the AC and DC pins (see attached).

  • Why would it need to go to both?
  • Why is the pulse connected to the ground on the logic side? Is the purpose not to keep higher voltage AC separated from the logic side?

schematic test circuit

The datasheet can be found here: https://www.mouser.com/datasheet/2/308/HCPL3700M-1306568.pdf


  • \$\begingroup\$ Why is the pulse connected to the ground on the logic side? ... the AC side is not connected to the same ground \$\endgroup\$ – jsotola Nov 27 '19 at 0:09

This is just a pulse speed test circuit to minimize measurement errors with a common ground and simple DC positive pulse input.

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Although intended for line frequency it's max. toggle rate of 4kHz is not speedy by design in order optimize transistor parameters for high current gain yet low bandwidth. Yet with all the optical coupling loss factors the hFE or CTR is still < 1.


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