Synchronous rectification control device, method for synchronous rectification control, and insulated type switching power supply

A synchronous rectification control method comprising:

• a step of detecting winding voltages including a process that detects an edge of a first winding voltage of a first section of windings in a secondary side of a transformer and a process that detects an edge of a second winding voltage of a second section of windings, in the secondary side of the transformer;
• a step of measuring a period between the edges detected in the step of detecting the winding voltages;
• a step of estimating an OFF timing for a synchronous rectification switch based on the period obtained in the step of measuring the period,
• a step of starting a charging of a capacitor at a constant current when the edge of falling down of the first winding voltage is detected;
• a step of turning the synchronous rectification switch to an ON state after an arbitrary delay time from the start of charging;
• a step of holding a voltage of the capacitor when the edge of rising up of the second winding voltage is detected;
• and
• a step of starting a discharging of the capacitor at a constant current when the edge of falling down of the second winding voltage is detected and turning the synchronous rectification switch to an OFF state when the voltage of the capacitor falls down to a threshold voltage that determines an OFF timing.

An insulated type switching power supply in which a primary side and a secondary side are insulated by a transformer, the switching power supply having a synchronous rectification control device and comprising:

• means for detecting winding voltages that detects an edge of a first winding voltage of a first section of windings in a secondary side of the transformer and an edge of a second winding voltage of a second section of windings in the secondary side of the transformer;
• means for measuring a period between the edges detected by the means for detecting the winding voltages;
• and
• means for estimating an OFF timing for a synchronous rectification switch based on the period obtained by the means for measuring the period,
• means for switch ON control for starting a charging of a capacitor at a constant current when the means for detecting the winding voltages detects the edge of falling down of the first winding voltage and for turning the synchronous rectification switch to an ON state after a predetermined delay time from the start of charging;
• means for holding a voltage of the capacitor when the means for detecting the winding voltages detects an edge of rising up of the second winding voltage;
• and
• means for switch OFF control for starting a discharging of the capacitor at a constant current when the means for detecting the winding voltage detects an edge of falling down of the second winding voltage and for turning the synchronous rectification switch to an OFF state when the voltage of the capacitor falls down to a threshold voltage that determines an OFF timing.