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naik_mc · 23rd January 2008, 06:14 AM

i would like to know what will happen when the output of a basic CMOS inverter is connected to the ground

kchriste · 23rd January 2008, 06:24 AM

Depends on the inverter. 74HC04? 74HCT04? 4049?
Nothing will happen if the input is tied high.

Papabravo · 23rd January 2008, 06:59 AM

I think you already know the answer. With the input low the output will try to source current into the grounded output. The chip may get quite warm and fail.

audioguru · 23rd January 2008, 08:36 PM

It depends on the output current from the type of Cmos IC.
A CD4069 inverter has a typical current into a short of only 4ma when its supply is 5V. Its output transistors can dissipate a max power of 100mW so the 20mW in this case is safe. When the supply is 10V then the typical current into a short is 20mA so the resulting 200mW power dissipation might fry its output transistor.

74HCxx high-speed Cmos ICs have a max allowed output of 25mA but will try to feed 60mA into a short then will fry.

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23rd January 2008, 06:14 AM	(permalink)
naik_mc	cmos i would like to know what will happen when the output of a basic CMOS inverter is connected to the ground

23rd January 2008, 06:24 AM	(permalink)
kchriste	Depends on the inverter. 74HC04? 74HCT04? 4049? Nothing will happen if the input is tied high. __________________ --- The days of the digital watch are numbered. ---

23rd January 2008, 06:59 AM	(permalink)
Papabravo	I think you already know the answer. With the input low the output will try to source current into the grounded output. The chip may get quite warm and fail. __________________ We never have time to do it right; but we always have time to do it over.

23rd January 2008, 08:36 PM	(permalink)
audioguru	It depends on the output current from the type of Cmos IC. A CD4069 inverter has a typical current into a short of only 4ma when its supply is 5V. Its output transistors can dissipate a max power of 100mW so the 20mW in this case is safe. When the supply is 10V then the typical current into a short is 20mA so the resulting 200mW power dissipation might fry its output transistor. 74HCxx high-speed Cmos ICs have a max allowed output of 25mA but will try to feed 60mA into a short then will fry. __________________ Uncle $crooge