NCP1280_05 ONSEMI [ON Semiconductor], NCP1280_05 Datasheet - Page 12

• Manufacturer Part Number: NCP1280_05
• Description: Active Clamp Voltage Mode PWM Controller for Off-Line Applications
• Manufacturer: ONSEMI [ON Semiconductor]

DSS mode is provided by C
sized such that a V
maintained while the outputs are switching and the
converter reaches regulation. Also, the V
(from 11 V to 7 V) must be greater that the soft−start charge
period to assure the converter turns ON.
If the device operates in the DSS mode, power dissipation
should be controlled to avoid exceeding the maximum
power dissipation of the controller.
reaches 11 V, the controller initiates a soft−start cycle.
Figure 31 shows the relationship between the UV/OV
voltage, the outputs and the soft−start voltage.
V
Power to the controller while operating in the self−bias or
The startup circuit is rated at a maximum voltage of 700 V.
Once the UV or OV condition is removed and V
in
Figure 29. Recommended V
Disable
I
START
UV/OV Voltage
V
V
V
AUX(on)
AUX(off)
OUT2
OUT1
AUX
I
V
AUX
V
V
AUX
0 V
0 V
0 V
0 V
OV
UV
AUX
I
START
AUX
voltage greater than 7 V is
C
AUX
. Therefore, C
AUX
Configuration
I
AUX
supply
To auxiliary supply
Figure 30. UV/OV Fault Timing Diagram
discharge time
AUX
must be
http://onsemi.com
AUX
NCP1280
12
Line Under/Overvoltage Shutdown
overvoltage shutdown (UV/OV) circuits. The under voltage
(UV) threshold is 1.52 V and the overvoltage threshold
(OV) is 3.61 V, for a ratio of 1:2.4. If the input voltage range
exceeds the pre−set OV threshold, the OV function can be
disabled by connecting a Zener from this pin to ground. The
Zener voltage should be less than 3.6 V.
resistor divider from the input line. The resistor divider must
be sized to enable the controller once V
required operating range. If the UV or OV threshold is
reached, the soft−start capacitor is discharged, and the
outputs are immediately disabled with no overlap delay as
shown in Figure 30. Also, if an UV condition is detected, the
5.0 V Reference Supply is disabled.
enable/disable function. Biasing the UV/OV pin below its
UV threshold disables the converter.
The NCP1280 incorporates line undervoltage and
The UV/OV circuit can be biased using an external
The UV/OV pin can also be used to implement a remote
UV or OV Fault
Propagation delay to
outputs (t
UV
or t
in
OV
is within the
)