A power off delay circuit includes a first diode with an anode receiving input power and a boost transformer circuit connected to a cathode of the first diode. The boost transformer circuit outputs power signals to a load circuit, and includes a capacitor, a primary winding, a first secondary winding, and a second secondary winding. The capacitor is charged when an input power is on, and discharges when the input power is off. The first secondary winding boosts power flowing through the primary winding and the first switch branch to charge the capacitor via the third switch branch when the input power is on. The capacitor discharges via the second secondary winding and the fourth switch branch when the input power is off, and the primary winding boosts discharging power of the capacitor, and outputs boosted discharging power to the load circuit via the second switch branch.