NCP1028 ON Semiconductor, NCP1028 Datasheet - Page 18

• Manufacturer Part Number: NCP1028
• Description: High?voltage Switcher For Medium Power Offline Smps
• Manufacturer: ON Semiconductor

measurement as long as the NTC and the optocoupler are
not activated. As soon as the secondary optocoupler senses
an OVP condition, or the NTC reacts to a high ambient
In Figure 31, Q1 is blocked and does not bother the BO
Figure 31. Adding a comparator on the BO pin offers a way to latch-off the controller.
Figure 32. If the BO pin is lifted up to VLATCH, the controller permanently latches off.
Vout
NTC
V
CC
Q1
Vbulk
http://onsemi.com
Rupper
Rlower
NCP1028
BO
18
temperature, Q1 base is brought to ground and the BO pin
goes up, permanently latching off the controller. Figure 32
depicts the converter behavior in case of total latch-off.
+
VBO
+
Vlatch
+
+
-
-
IBO
←
20 ms
RC
To permanent
latch
V
BO
DD