SHINDENGEN

ELECTRIC MFG.CO.,LTD

- 8 -

2.2

Zero current detection

Master

This IC detects the control coil voltage to turn on the switching device. The Z/C pin determines

turn-on timing.

As shown in Fig. 7, the main switch activates when the Z/C pin voltage drops below the zero

detection voltage (0.5 V). The main switch is turned on after every switching cycle once the

energy of the choke coil is fully discharged (i.e., a current-critical operation is performed).

Hysteresis of +1 V is added to the zero detection voltage to increase noise resistance. Unless a

voltage exceeding +1.5 V is applied to the Z/C pin, the switch operates in the restart cycle (150 μs).

This IC incorporates an on-dead timer. This function disables the on-trigger for a period

(Tondead) after the gate-off signal is turned on, thereby preventing unintended operations due to

ringing generated at gate-off. A ringing voltage may be generated at gate-off, resulting in

detection of the on-trigger and turning on the switch before the current critical point.

See Section 4.5 for constants for the components around the Z/C pin.

Z/C pin voltage

0.5V

Hysteresis

1V

Zero detection

voltage

0V

Diode current

Main switch VDS

0V

0A

0A

Main switch IDID

Tondead

Fig. 7 Turn-on timing (Z/C pin)