The NCP1337 combines a true current mode modulator and a demagnetization detector which ensures full Borderline/Critical Conduction Mode in any load/line conditions together with minimum drain voltage switching (Quasi−Resonant operation). The transformer core reset detection is done internally, without using any external signal, due to the Soxyless concept. The frequency is internally limited to 130 kHz, preventing the controller to operate above the 150 kHz CISPR−22 EMI starting limit. By monitoring the feedback pin activity, the controller enters ripple mode as soon as the power demand falls below a predetermined level. As each restart is softened by an internal soft−start, and as the frequency cannot go below 25 kHz, no audible noise can be heard. The NCP1337 also features an efficient protective circuitry which, in presence of an overcurrent condition, disables the output pulses and enters a safe burst mode, trying to restart. Once the default has gone, the device auto−recovers. Also included is a bulk voltage monitoring function (known as brown−out protection), an adjustable overpower compensation, and a VCC OVP. Finally, an internal 4.0 ms soft−start eliminates the traditional startup stress.
The NCP1337 PWM current‑mode controller is designed for free‑running quasi‑resonant operation in AC‑DC adapters, battery chargers and other consumer electronics. It integrates a demagnetization detector, internal soft‑start, and a dynamic self‑supply that allows direct connection to the high‑voltage rail.
Key features include a maximum switching frequency of 130 kHz, 500 mA peak current drive, 4 ms internal soft‑start, brown‑out detection on Pin 1, over‑voltage protection on the VCC pin, and built‑in over‑current and over‑power compensation circuits. The device is offered in PDIP‑7 and SOIC‑7 packages and meets Pb‑free compliance.
| Maximum Switching Frequency | 130 kHz |
|---|---|
| Peak Current Drive (Sink Capability) | 500 mA |
| Internal Soft‑Start Duration | 4.0 ms |
| Operating Temperature Range | -40 °C to +125 °C |
| Maximum Junction Temperature | 150 °C |
The controller’s internal frequency is limited to 130 kHz.
Pin 1 monitors the input voltage; if it falls below the brown‑out threshold (≈500 mV), the controller disables the output until the voltage rises again.
The internal soft‑start lasts 4.0 ms before the controller begins normal operation.