NCP1207A ON Semiconductor, NCP1207A Datasheet - Page 8

• Manufacturer Part Number: NCP1207A
• Description: PWM Current-Mode Controller
• Manufacturer: ON Semiconductor

architecture where the switch−off time is dictated by the
peak current setpoint whereas the core reset detection
triggers the turn−on event. This component represents the
ideal candidate where low part−count is the key parameter,
particularly in low−cost AC/DC adapters, consumer
electronics, auxiliary supplies, etc. Thanks to its
high−performance
NCP1207A incorporates all the necessary components /
features needed to build a rugged and reliable Switch−Mode
Power Supply (SMPS):
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The NCP1207A implements a standard current mode
Transformer core reset detection: borderline / critical
operation is ensured whatever the operating conditions
are. As a result, there are virtually no primary switch
turn−on losses and no secondary diode recovery losses.
The converter also stays a first−order system and
accordingly eases the feedback loop design.
Quasi−r esonant operation: by delaying the turn−on
event, it is possible to re−start the MOSFET in the
minimum of the drain−source wave, ensuring reduced
EMI / video noise perturbations. In nominal power
conditions, the NCP1207A operates in Borderline
Conduction Mode (BCM) also called Critical
Conduction Mode.
Dynamic Self−Supply (DSS): due to its Very High
Voltage Integrated Circuit (VHVIC) technology,
ON Semiconductor’s NCP1207A allows for a direct pin
connection to the high−voltage DC rail. A dynamic
current source charges up a capacitor and thus provides
a fully independent V
result, there is no need for an auxiliary winding whose
management is always a problem in variable output
voltage designs (e.g. battery chargers).
Overvoltage Protection (OVP): by sampling the plateau
voltage on the demagnetization winding, the
NCP1207A goes into latched fault condition whenever
an over−voltage condition is detected. The controller
stays fully latched in this position until the V
cycled down 4.0 V, e.g. when the user un−plugs the
power supply from the mains outlet and re−plugs it.
External latch trip point: by externally forcing a level
on the OVP greater than the internal setpoint, it is
possible to latchoff the IC, e.g. with a signal coming
from a temperature sensor.
Adjustable skip cycle level: by offering the ability to
tailor the level at which the skip cycle takes place, the
designer can make sure that the skip operation only
Introduction
High−Voltage
CC
level to the NCP1207A. As a
technology,
APPLICATION INFORMATION
CC
is
http://onsemi.com
the
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Dynamic Self−Supply
V
can easily describe the current source operation with some
simple logical equations:
sketch offers the necessary light.
Figure 12. The Charge/Discharge Cycle Over a 10 mF
CC
The DSS principle is based on the charge/discharge of the
To better understand the operational principle, Figure 12’s
occurs at low peak current. This point guarantees a
noise−free operation with cheap transformer. This
option also offers the ability to fix the maximum
switching frequency when entering light load
conditions.
Overcurrent Protection (OCP): by continuously
monitoring the FB line activity, NCP1207A enters burst
mode as soon as the power supply undergoes an
overload. The device enters a safe low power operation
which prevents from any lethal thermal runaway. As
soon as the default disappears, the power supply
resumes operation. Unlike other controllers, overload
detection is performed independently of any auxiliary
winding level. In presence of a bad coupling between
both power and auxiliary windings, the short circuit
detection can be severely affected. The DSS naturally
shields you against these troubles.
POWER−ON: IF V
is ON, no output pulses
IF V
OFF, output is pulsing
IF V
ON, output is pulsing
Typical values are: VCC
bulk capacitor from a low level up to a higher level. We
V
CC
CC
RIPPLE
decreasing > VCC
increasing < VCC
= 2 V
V
ON
CC
CC
VCC
< VCC
Capacitor
OFF
OFF
OFF
ON
= 12 V, VCC
OFF
Output Pulses
= 12 V
THEN Current Source is
THEN Current Source is
VCC
THEN Current Source
ON
= 10 V
OFF
ON
= 10 V