Consider the Schmidt trigger circuit shown below.
A triangular wave which goes from $-12 \mathrm{~V}$ to $12 \mathrm{~V}$ is applied to the inverting input of the $\text{OPAMP}$. Assume that the output of the $\text{OPAMP}$ swings from $+15 \mathrm{~V}$ to $-15 \mathrm{~V}$. The voltage at the non-inverting input switches between
- $-12 \mathrm{~V}$ and $+12 \mathrm{~V}$
- $-7.5 \mathrm{~V}$ and $+7.5 \mathrm{~V}$
- $-5 \mathrm{~V}$ and $+5 \mathrm{~V}$
- $0 \mathrm{~V}$ and $5 \mathrm{~V}$