In flyback converters a transient response is the feedback loops response to a sudden change at the flyback output. This sudden change at the output is likely due to a switching load or high noise across the flyback output. A feedback loop with a good transient response will respond quickly to any changes in the output condition by modifying its feedback signal, I_{FB(secondary)}, through the optocoupler diode accordingly. The PWM controller will respond to this new signal by regulating the output voltage back to its programmed value. In applications with a switching load, it's desirable to have a quick transient response, and the speed of this response will be determined by the gain of the shunt reference, which will vary from device to device. The larger this transconductance gain of the chosen shunt reference is, the quicker the cathode current, and thus the optocoupler feedback current, will change. Figure 2-5 shows the transconductance gains of several shunt references that will be explored in greater detail in Section 4.4.