6-6. Thermal shutdown circuit
This circuit triggers the latch circuit when the frame temperature of the hybrid IC exceeds 140
(typ).
The temperature is actually sensed by the control IC, but it also works against overheating of the
MOS FET as the MOS FET and the control IC are mounted on the same lead frame.
6-7. Overvoltage protection circuit
This circuit triggers the latch circuit when the VINvoltage exceeds 22.0V(typ).
Although it basically functions as protection of the VINterminal against overvoltage, since the VIN
terminal is supplied from the drive winding of the transformer and the voltage is proportional to the
output voltage, it also prevents overvoltage at the secondary output which is caused when the
control circuit is open circuited or by some other event. In this case, the secondary output voltage
at the time when the overvoltage protection is on can be obtained from the following equation.
Output voltage V out in normal operation
Vout(OVP) 22.5V(typ)
VINterminal voltage in normal operation
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ACEC
