The time it takes to switch from the off state to the on state is known as the on delay time ton, and the time it takes to make the transition from on state to Toff state known as the off delay time Toof As illustrated in Figure 2-26, the on delay time ton is the sum of the delay time Td and the rise time tr The delay time ta is the time interval it takes for the collector current to rise from 0% to 10% of its final value. The rise time tr is the time interval it takes for the collector current to rise from 10% to 90% of its final value. The on delay time is