EEVblog Electronics Community Forum

Electronics => Beginners => Topic started by: julian1 on August 23, 2022, 12:22:43 pm

Title: simple 74hc inverter not working in ltspice
Post by: julian1 on August 23, 2022, 12:22:43 pm

I cannot get a simple ltspice 74hc04, or 74hc14 inverter to output an inverted waveform.

More complicated models such as 74hc74 flip/flop appear Ok.

Title: Re: simple 74hc inverter not working in ltspice
Post by: Ian.M on August 23, 2022, 12:44:40 pm

Increase 'DRIVE' logic high voltage to min. 70% of Vcc to meet 74HC family input thresholds!

Code: [Select]

PULSE(0 5 1us 10ns 10ns 25us 50us 7)

Title: Re: simple 74hc inverter not working in ltspice
Post by: julian1 on August 23, 2022, 12:52:47 pm

I can't believe I did that. Thank you!

Title: Re: simple 74hc inverter not working in ltspice
Post by: Ian.M on August 23, 2022, 12:58:20 pm

Its a frequent trap for young players in the real world as well.   When trying to interface a 3.3V MCU output to 5V logic, 70% of 5V Vcc is 3.5V, so if using 74HC its pure luck whether or not it works!!