In continuous mode, the primary switching current starts from a certain amplitude, then rises to a peak value, and then quickly returns to zero. Its switching current waveform is trapezoidal. This indicates that in continuous mode, the next switching cycle has an initial energy because the energy stored in the high-frequency transformer is not all released in each switching cycle. The use of continuous mode reduces the primary peak current Ip and RMS current IRMS, reducing the power consumption of the chip. However, the continuous mode requires an increase in the primary inductance Lp, which leads to an increase in the size of the high-frequency transformer. In summary, the continuous mode is suitable for smaller power TOpSwitches and larger size HF transformers.

The switching current in discontinuous mode rises from zero to a peak and then falls to zero. This means that the energy stored in the high-frequency transformer must be completely released during each switching cycle, with a triangular switching current waveform. The discontinuous mode has larger values of Ip and IRMS, but requires less Lp. Therefore, it is suitable for the use of TOpSwitch with larger output power with smaller size high frequency transformer.

(1) Basic feedback circuit;

(2) Improved basic feedback circuit;

(3) Optocoupler feedback circuit with voltage regulator;

(4) Optocoupler feedback circuit with TL431.