Power control system with zero voltage switching

A power control system with zero voltage switching for implementing a function of flyback power conversion, comprising:

• a power controller comprising a power pin, a ground pin, a primary side driving pin, a voltage sensing pin, an auxiliary driving pin and an auxiliary winding sensing pin, the ground pin connected to a ground level;
• a rectification unit for receiving and rectifying an external input power to generate a rectified power, the rectification unit electrically connected to the ground level through a rectification auxiliary capacitor;
• a power unit for receiving the external input power to generate a power voltage, the power controller receiving the power voltage through the power pin to operate;
• a transformer unit comprising a primary side winding, an auxiliary winding, and a secondary side winding electromagnetically coupled together, an end of the primary side winding connected to the rectification unit for receiving the rectified power;
• a primary side switch unit comprising a drain connected to the other end of the primary side winding, a gate connected to the primary side driving pin, and a source connected to the voltage sensing pin;
• a current sensing unit, an end of the current sensing unit connected to the voltage sensing pin, the other end of the current sensing unit connected to the ground level, the voltage sensing pin generating a current sensing signal;
• an auxiliary switch unit comprising a drain connected to the rectification unit for receiving the rectified power, a gate connected to the auxiliary driving pin, and a source connected to an end of the auxiliary winding and the auxiliary winding sensing pin, the other end of the auxiliary winding connected to the ground level, the source of the auxiliary winding generating an auxiliary winding voltage corresponding to a drain voltage of the drain of the primary side switch unit, the drain of the primary side switch unit further connected to the ground level through an auxiliary capacitor;
• and
• an output unit having an end connected to an end of the secondary side winding for generating an output power to supply a load connected to the output unit, and the other end connected to the ground level, the other end of the secondary side winding connected to the ground level,
• wherein the power controller executes a zero voltage switching control process to generate a primary side driving signal and an auxiliary driving signal, the primary side driving signal is transmitted to the gate of the primary side switch unit through the primary side driving pin, the auxiliary driving signal is transmitted to the gate of the auxiliary switch unit through the auxiliary driving pin, the primary side driving signal is a pulse width modulation (PWM) signal having a PWM frequency and provided with a turn on level and a turn off level for periodically turning on and off the primary side switch unit, the turn on level is sustained for a turn on time, the turn off level is sustained for a turn off time, the PWM frequency is dependent on a loading level of the load, the turn on time is dependent on a voltage of the output power, and the zero voltage switching control process comprises:
• detecting and determining whether the auxiliary winding voltage is lower than a knee when the auxiliary switch unit is turned off and then the primary side switch unit is turned off;
• determining a demagnetization time when the auxiliary winding voltage is lower than the knee, and then calculating a turn on delay time, the demagnetization time referring to a period from the time when the primary side switch unit is turned off to the time when the auxiliary winding voltage is lower than the knee;
• driving the auxiliary driving signal to turn on the auxiliary switch unit after the turn on delay time, and then setting, changing, or calculating an auxiliary turn on time;
• after the auxiliary turn on time, driving the auxiliary driving signal to turn off the auxiliary switch unit, and then calculating a separate time;
• and
• driving the primary side driving signal to turn on the primary side switch unit after the separate time, the turn off time substantially comprising the demagnetization time, the turn on delay time, the auxiliary turn on time, and the separate time.