UC3842B

DC DC Switching Controllers Overview

The UC3842B is a fixed-frequency current mode PWM controller designed for offline and DC-DC converters. It features an internally trimmed oscillator, precision reference, and under-voltage lockout with thresholds of 16V (on) and 10V (off). The device supports duty cycles approaching 100% and includes a high-current totem pole output stage capable of sourcing or sinking peak currents. Operating frequencies are guaranteed at 250kHz, with capabilities up to 500kHz. Start-up current is less than 0.5mA.

DC DC Switching Controllers Feature Summary

• Current mode control architecture with internal trimming for precise frequency and duty cycle regulation
• Under-voltage lockout mechanism ensuring stable operation during power transitions
• High-current totem pole output stage optimized for driving N-channel MOSFETs
• Integrated latching PWM protection for cycle-by-cycle current limiting

DC DC Switching Controllers Applications

• Offline flyback converter designs
• Forward converter topologies
• DC-to-DC step-down regulator circuits
• Battery charger power supplies

DC DC Switching Controllers Procurement Notes

Verify the manufacturer marking on the component surface to distinguish between UMW and other producers such as STMicroelectronics or onsemi, as pinouts and electrical characteristics may vary slightly between sources. Confirm the package type matches the required PCB footprint, typically SOP-8 or DIP-8. Ensure the specific suffix indicates the correct temperature range and lead finish before finalizing procurement orders.

DC DC Switching Controllers Selection Notes

Select the UC3842B when applications require near 100% maximum duty cycle capability, distinguishing it from the UC3844B which limits duty cycle to below 50%. This model is suitable for off-line applications due to its higher UVLO thresholds compared to the UC3843B. Engineers should consider the current mode control benefits for improved line regulation and simpler compensation networks in high-power density designs.

DC DC Switching Controllers Part Context

The UC3842B belongs to the UC284xB family of control ICs, which share common internal circuitry including the oscillator and error amplifier. While the UC3842B and UC3844B share identical UVLO thresholds, they differ significantly in duty cycle control logic. The UC3842B lacks the internal toggle flip-flop found in the UC3844B, allowing for continuous high-duty cycle operation essential for certain transformer-based power supply architectures.

DC DC Switching Controllers Replacement Considerations

The UC3842BN from STMicroelectronics serves as a direct functional substitute within the same series. Verify that the replacement maintains the 16V/10V UVLO thresholds and 100% duty cycle capability. Cross-reference pin assignments to ensure compatibility with existing PCB layouts.