PWM Current--Mode
Controller for Free Running
Quasi--Resonant Operation
The NCP1207A/B combines a true current mode modulator and a
demagnetization detector to ensure full borderline/critical Conduction
Mode in any load/line conditions and minimum drain voltage switching
(Quasi--Resonant operation). Due to its inherent skip cycle capability,
the controller enters burst mode as soon as the power demand falls
below a predetermined level. As this happens at low peak current, no
audible noise can be heard. For the NCP1207A, an internal 8.0 ms timer
prevents the free--run frequency to exceed 125 kHz (therefore below the
150 kHz CISPR--22 EMI starting limit), while the skip adjustment
capability lets the user select the frequency at which the burst foldback
takes place. For the NCP1207B, the internal timer duration is reduced to
4.5 ms to allow operation at higher frequencies (up to 200 kHz).
The Dynamic Self--Supply (DSS) drastically simplifies the
transformer design in avoiding the use of an auxiliary winding to
supply the NCP1207A/B. This feature is particularly useful in
applications where the output voltage varies during operation (e.g.
battery chargers). Due to its high--voltage technology, the IC is
directly connected to the high--voltage DC rail. As a result, the
short--circuit trip point is not dependent upon any VCC auxiliary level.
The transformer core reset detection is done through an auxiliary
winding which, brought via a dedicated pin, also enables fast
Overvoltage Protection (OVP). Once an OVP has been detected, the
IC permanently latches off.
Finally, the continuous feedback signal monitoring implemented
with an overcurrent fault protection circuitry (OCP) makes the final
design rugged and reliable.
. Free--Running Borderline/Critical Mode Quasi--Resonant Operation
. Current--Mode with Adjustable Skip--Cycle Capability
. No Auxiliary Winding VCC Operation
. Auto--Recovery Overcurrent Protection
. Latching Overvoltage Protection
. External Latch Triggering, e.g. Via Overtemperature Signal
. 500 mA Peak Current Source/Sink Capability
. Undervoltage Lockout for VCC Below 10 V
. Internal 1.0 ms Soft--Start
. Internal 8.0 ms Minimum TOFF for NCP1207A,
4.5 ms Minimum TOFF for NCP1207B
. Adjustable Skip Level
. Internal Temperature Shutdown
. Direct Optocoupler Connection
. SPICE Models Available for TRANsient Analysis
. These are Pb--Free and Halide--Free Devices
Typical Applications
. AC/DC Adapters for Notebooks, etc.
. Offline Battery Chargers
. Consumer Electronics (DVD Players, Set--Top Boxes, TVs, etc.)
. Auxiliary Power Supplies (USB, Appliances, TVs, etc.)