NCP1015 ON Semiconductor, NCP1015 Datasheet - Page 9

• Manufacturer Part Number: NCP1015
• Description: Self-supplied Monolithic Switcher For Low Standby-power Offline Smps W/out Ovp
• Manufacturer: ON Semiconductor

expressed by:
formula topology:
be computed:
parameter section gives a typical duty-cycle D of 13%,
precluding any lethal thermal runaway while in a fault
condition.
DSS Internal Dissipation
drain pin. In the Flyback-based converters, this drain level
can easily go above 600 V peak and thus increase the stress
on the DSS startup source. However, the drain voltage
evolves with time and its period is small compared to that of
the DSS. As a result, the averaged dissipation, excluding
capacitive losses, can be derived by:
The rising slope from the latch-off level up to 8.5 V is
The time during which the IC actually pulses is given by:
Finally, the latch-off time can be derived using the same
From these three definitions, the burst duty-cycle D can
Feeding the equation with values extracted from the
The Dynamic Self-Supplied pulls the energy out from the
D +
P
DSS
D +
ICC1 @
P
t
t
+ ICC1 @t V
DSS
t
latch
start
sw
t
start
+ DV2 @ C
+ V
+ DV1 @ C
+ DV3 @ C
) t
ICC1
DV2
Figure 15. NCP1015 Facing a Fault Condition (V
DV2
ICC1
in
t
Tstart
ICC2
sw
sw
IC1
)
@ ICC1
) t
DV1
IC1
DS(t)
latch
)
ICC2
DV3
u
Tsw
http://onsemi.com
(eq. 2)
(eq. 3)
(eq. 4)
NCP1015
TLatch
9
where leakage effects have been removed:
derived by additive square area calculation:
1 V Ripple
Figure 16 shows a typical drain-ground wave-shape
By looking at Figure 16 the average result can easily be
By developing Equation 5 we obtain:
t
t
off
on
Figure 16. A Typical Drain-ground Waveshape
Vds(t)
where Leakage Effects are Not Accounted for
can be evaluated by:
can be expressed by:
Latch-off
Vin
Level
t V
t V
ton
Vr
DS(t)
DS(t)
in
= 150 Vdc)
u+ V
u+ V
Tsw
toff
t
t
off
on
in
in
+ I
+ I
* V
@ (1 * D) ) V
p
p
@
@
in
dt
L
V
V
L
@
p
r
p
in
t
t
on
sw
) V
r
r
@
@
t
t
off
sw
t
t
sw
off
(eq. 5)
(eq. 6)
(eq. 7)
(eq. 8)
t