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 s 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 s 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.

Features

• 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 s Minimum TOFF for NCP1207A,

4.5 s 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.)