ncp1608d ON Semiconductor, ncp1608d Datasheet - Page 19

• Manufacturer Part Number: ncp1608d
• Description: Critical Conduction Mode Pfc Controller Utilizing Ota
• Manufacturer: ON Semiconductor

Overvoltage Protection (OVP)
active PFC stages to react to changes in output load or input
voltages slowly. Consequently, there is a risk of overshoots
during transient conditions (i.e. startup, load steps, etc.).
For reliable operation, it is critical that overvoltage
protection (OVP) prevents the output voltage from
exceeding the ratings of the PFC stage components. The
NCP1608 detects excessive V
driver until V
the PFC stage component ratings. A comparator connected
to the FB pin provides the OVP protection. The maximum
PFC output voltage (the OVP voltage that activates an OVP
fault) is calculated using Equation 13:
V
Where V
Figure 43 depicts the operation of the OVP circuitry.
Undervoltage Protection (UVP)
is forced to equate to the peak of the line voltage. The
NCP1608 detects an undervoltage fault if V
low, such that V
the drive and error amplifier are disabled. The UVP feature
protects the application if there is a disconnection in the
power path to C
is disconnected.
using Equation 17:
V
out(OVP)
out(UVP)
The low bandwidth of the feedback network causes
When the input voltage is applied to the PFC stage, V
The output voltage that causes a UVP fault is calculated
OVP
+
+ V
V
V
/V
out
OVP
REF
UVP
bulk
REF
FB
decreases. OVP ensures that V
@ V
@ R
is less than V
(i.e. C
is the OVP detection threshold.
REF
out1
V
out(OVPL)
@ R
bulk
@
R
is unable to charge) or if R
R
out
out1
out2
out2
UVP
OVP Fault
V
voltages and disables the
V
out(OVPL)
+
@
) R
out(OVP)
@ R
R
. During an UVP fault,
R
DRV
V
out2
out2
FB
out
FB
V
V
) R
) 1
OVP
REF
@ R
out
FB
FB
@ V
is unusually
out
Figure 43. OVP Operation
) 1
REF
is within
(eq. 13)
(eq. 17)
http://onsemi.com
out1
* V
out
OVP(HYS)
19
inadvertently triggered by the 100 Hz or 120 Hz ripple of
V
Equation 14:
Where V
ripple and f
ensure that V
NCP1608 attempts to restart and to ensure noise immunity.
The output voltage at which the NCP1608 attempts a restart
(V
Open Feedback Loop Protection
against open feedback loop conditions by including OVP,
UVP, and FPP. Figure 44 illustrates three conditions in
which the feedback loop is open. The corresponding
number below describes each condition shown in
Figure 44.
out
The C
V
The OVP logic includes hysteresis (V
The NCP1608 features comprehensive protection
out(OVPL)
ripple(peak-peak)
. The minimum value of C
1. UVP Protection: The connection from R
2. OVP Protection: The connection from R
C
V
@ R
ripple(peak−peak)
bulk
the FB pin is open. R
to ground. The UVP comparator detects an UVP
fault, the drive and error amplifier are disabled.
the FB pin is open. R
V
10 V and R
The OVP comparator detects an OVP fault and
the drive is disabled.
ripple(peak-peak)
out
bulk
w
out1
) is calculated using Equation 16:
line
. The ESD diode clamps the FB voltage to
out
2 @ p @ V
value is sized to ensure that OVP is not
@
is the ac line frequency.
R
has sufficient time to discharge before the
R
out2
out2
is calculated using Equation 15:
out1
v 2 @ V
) R
ripple(peak−peak)
@ R
limits the current into the FB pin.
is the peak−to−peak output voltage
FB
FB
P
) 1
out2
out1
out(OVP)
out
pulls down the FB pin
pulls up the FB pin to
bulk
@ f
* V
is calculated using
line
@ V
out
OVP(HYS)
out
out1
out2
(eq. 16)
(eq. 14)
(eq. 15)
to
) to
to