G540 inputs question

[aystarik]

Mariss,
Some early schematics of "chip drive" showed that inputs of G540 are pulled up to 12V.
What happens if I connect TTL/CMOS output to such input (i suppose current G540 has the same pull)?
Chip in question is a single Schmitt trigger SN74LVC1G17, spec says what VOUT should not be greater than 5.5V...

Thanks,
Alex

[Mariss Freimanis]

The inputs are pulled up to 12VDC via 2.2K resistors in series with optoisolator LEDS. The sink current is 5mA to operate the inputs. You will have to use an open collector NPN to go from 5V logic to the G540 12V input.

Take the 74LVC output to a 4.7K resistor.
Take the resistor to the base of a PN2222A or similar.
Take the PN2222A emitter to GND (G540 term 12).
Take the PN2222A collector to the G540 input.

Mariss

[aystarik]

Mariss, thanks for such detailed answer!
Really appreciate your work.