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NCP1239KD65R2G

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26
NCP1239
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16
If the V
CC
capacitor is first dimensioned to supply the
controller for the traditional 5 to 50 ms until the auxiliary
winding takes over, no-load standby requirements usually
cause it to be larger. The HV start-up current source is then
a key feature since it allows keeping short start-up times with
large V
CC
capacitors (the total start-up sequence duration is
often required to be less than 1 s).
When the DSS mode is enable (NCP1239JD65), the V
CC
voltage is maintained between V
CC(on)
and V
CC(min)
by
turning the HV start−up current source on and off. This
function can be used only during transient load or in light
load condition. The HV current source cannot supply the
controller in Fixed−frequency operation otherwise the die
will overheat. As a result, an auxiliary voltage source is
needed to supply V
CC
during normal operation.
BROWN-OUT CIRCUITRY
For the vast majority of controllers, input line sensing is
performed via a resistive network monitoring the bulk
voltage or the incoming ac signal. When in the quest of low
standby power, the external network adds a consumption
burden and deteriorates the power supply standby power
performance. Owing to its proprietary high-voltage
technology, ON Semiconductor now offers onboard line
sensing without using an external network. The system
includes a 90-MW resistive network that brings a minimum
start-up threshold and an auto-recovery brown-out
protection. Both levels are independent from the input
voltage ripple. The brown-out thresholds are fixed (see
levels in the electrical characteristics table), but they are
designed to fit most of standard ac-dc converter
applications. The simplified internal schematic appears in
Figure 33 while typical operating waveforms are drawn in
Figure 34 and Figure 35.
Figure 33. A Simplified View of the Brown-Out Circuitry
L1
N
EMI
Filter
Vbulk
Rbo_H
Rbo_L
HV
GND
BO_OK
VBO
When the HV pin voltage drops below the V
BO(off)
threshold, the brown-out protection trips: the controller
stops generating DRV pulses once the BO timer elapses.
V
CC
is discharged to V
CC(min)
by the controller
consumption itself. When this level is reached, the HV
current source is activated to lifts V
CC
up again. At new
V
CC(on)
, BO signal is again sensed. If V
HV
>V
BO(on)
, the
parts restarts. If the condition is not met, no drive pulse is
delivered and internal IC consumption brings V
CC
down
again. As a result, V
CC
operates in hiccup mode during a BO
event.
NCP1239
www.onsemi.com
17
Figure 34. BO Event during Normal Operation
BO_OK = "0"
è
Drive pulse stops
V
cc(on)
V
cc(off)
V
cc(min)
v
cc
(t)
BO(t)
BO_OK = "0"
BO_OK = "1"
t
t
v
DRV
(t)
No pulse area
BO_OK = "1"
V
cc
hiccup waiting
BO signal
Figure 35. BO Event before Start-Up
BO no OK
è No drive pulse
BO_OK = "1"
è
Wait the next V
cc(on)
for
fresh start-up sequence
V
cc(on)
V
cc(off)
V
cc(min)
First drive pulse
v
cc
(t)
V
cc
hiccup waiting
BO signal
V
cc(inhibit)
BO(t)
BO_OK = "0"
BO_OK = "1"
t
t
NCP1239
www.onsemi.com
18
OVER POWER PROTECTION
Over Power Protection (OPP) is a known means to limit
the output power runaway at high mains. Several elements
such as propagation delays and operating mode explain why
a converter operated at high line delivers more power than
at low line. NCP1239 senses the input voltage via HV pin.
This line voltage is transformed into a current information
further applied to the current sense pin (CS). A resistor
placed in series from the sense resistor to the CS pin will
create an offset voltage proportional to the input voltage
variation. An added current sink will ensure a zero OPP
current at low line (125 V dc), leaving the converter power
capability intact in the lowest operating voltage. Figure 36
presents the internal simplified architecture of this OPP
circuitry.
Figure 36. Over Power Protection is Provided via the Bulk Voltage Present on HV Pin
CS
HV sample
& sampling
HV detection
HV
ROPP
Rsense
offset
To CS
comparator
L1
N
EMI
Filter
Vbulk
Iopp
OPP current
generation
Vfb
The HV voltage will be transformed into a current equal
to 67.5 mA when the HV pin is biased to 125 V. However,
there is an internal fixed sink of 67.5 mA. Therefore, the net
current flowing into R
OPP
is 0 at this low-voltage input
(≤ 125 V dc), ensuring an almost non-compensated
converter at low line: at a 115-V rms input (162 V dc), the
current from the OTA block will induce a 87.5-mA current,
turning into a 20-mA offset current flowing into R
OPP
. Now,
assume a 260-V rms input voltage (365 V dc), the controller
will generate an offset current of:
365 @ 0.54 u * 67.5 u + 130 mA
(eq. 8)
Assume we need to reduce the maximum peak current
setpoint by 250 mV to limit the maximum power at the
considered 260-V rms input. In that case, we will need to
generate a 250-mV offset across R
OPP
. With a 130-mA
current, R
OPP
should be equal to:
250 m
130 u
+ 192 kW
(eq. 9)
A small 100−220-pF capacitor closely connected between
the CS and GND pins will form an effective noise filter and
nicely improves the converter immunity. Now, with this
1.92-kW resistance, the low-line 20-mA offset current will
incur a 38-mV drop, which, in relationship to a 800-mV
maximum peak, generates a small 5% reduction. Assuming
a full DCM operation, the power would be reduced by 0.95
2
or 9.75% only. Please note that the OPP current is clamped
for a HV pin voltage greater than 365 V dc. Should you lift
the pin above this voltage, there will be no increase of the
OPP current.
The offset voltage can affect the standby power
performance by reducing the peak current setpoint in
light-load conditions. For this reason, it is desirable to cancel
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P26

NCP1239KD65R2G

Mfr. #:
Buy NCP1239KD65R2G
Manufacturer:
ON Semiconductor
Description:
Switching Controllers NCP1239K, 65KHZ
Lifecycle:
New from this manufacturer.
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