Constant-current control device and related control method

A constant-current control device for a power supply, wherein the power supply includes a primary side switch and a secondary winding, the primary side switch is configured to receive a control voltage to be selectively conductive or open, the constant-current control device comprising:

• a voltage waveform detector, configured to generate a discharging period signal based on a first feedback voltage and the control voltage, and the discharging period signal associated with a period of discharging time of the secondary winding;
• and
• a constant-current controller, coupled to the voltage waveform detector, including an integrator, a first current source and a second current source, wherein the integrator is configured to receive one of the first current source and the second current source to generate an integrator result voltage based on the discharging period signal and a current detecting voltage, the current detecting voltage is related to a secondary winding current value flowing through the secondary winding, and the secondary winding current value is positively related to a secondary winding output current value of the power supply;
• wherein when the integrator is configured to receive the first current source and a variation trend of the integrator result voltage is different from an integration trend of the first current source, and when the integrator result voltage reaches a second boundary voltage, the integrator is switched to receive the second current source;
• wherein when the integrator is switched to receive the second current source and the variation trend of the integrator result voltage is same as an integration trend of the second current source, and when the integrator result voltage reaches a first boundary voltage, the integrator is switched to receive the first current source.