Vdd and vss are exchanged

Hi,

What happens when Vdd and vss are exchanged. Please explain me by taking the example of cmos inverter circuit.

Thanks.

Swapping VDD and VDD normally results in a damaged device, no matter whether its an inverter or any other kind of circuit.

Brian.

Substrate diodes and dedicated protection diodes are forward biased with inverted power supply. If the supply source is able to exceed the maximum diode current, the device is destroyed.

Most standard IC's are built with a process that generates a parasitic substrate diode.
This diode is normally reverse biased with the proper polarity of the applied supply voltages.
As noted, a reverse polarity supply will forward bias this diode, thus the current will be limited only by the power supply current limit and/or the resistance in the circuit, which is normally enough to zap the circuit.

I remember way (way) back when, a fellow engineer had one of those new-fangled 741 op amps (cost about $30 at the time, I think) wired up in a breadboard circuit. He applied power, but the circuit wouldn't work. He then touched the op amp metal case, and suddenly jerked away with a burnt finger. Yup, the power was wired in reverse and the op amp was toast (literally).

Thanks Fvm and crutschow for better explaining!