Placing a Zener diode in parallel with the secondary output is another good way to ensure the secondary output voltage stays within a certain range of regulation. The benefit of adding this component is that it will clamp the secondary at the desired voltage, while a preload resistor can be subject to drift due to the magnitude of the input voltage. In this particular application, selecting a Zener with a breakdown voltage of 3.3 V can result in a more tightly regulated secondary output voltage. A resistor can be added in series to the Zener diode to limit current and ensure the power rating of the Zener is not exceeded.