E-L4981A

Overview

The L4981A is a fixed-frequency average current mode power factor corrector (PFC) pre-regulator designed for high efficiency AC-DC power supplies. It operates with a switching frequency of 100 kHz and supports universal mains input voltages ranging from 85V to 265V without line switching. The device integrates a precise 2% on-chip voltage reference, error amplifier, under-voltage lockout, and soft-start functionality. It provides overvoltage and overcurrent protection, with the overcurrent level programmable via a simple resistor. The IC utilizes BCD 60II technology and features a high-current bipolar and DMOS totem-pole output gate driver.

Feature Summary

• Fixed frequency average current mode PWM control for minimum noise sensitivity
• Integrated overvoltage and overcurrent protection mechanisms
• Precise 2% on-chip voltage reference available externally
• Universal input mains compatibility without line switch

Applications

• AC-DC Power Supply Units for server infrastructure
• Telecommunications equipment power systems
• High efficiency-mode power supply designs requiring sinusoidal line current consumption

Procurement Notes

Verify the specific suffix 'AD' or 'D' against the required package type, as the base model L4981A typically corresponds to DIP-20 while the 'D' variant indicates SOIC-20 surface mount. Confirm that the design requires fixed frequency operation rather than line-modulated frequency, which is characteristic of the L4981B variant. Ensure the application circuit includes the necessary external components for the average current mode control loop and that the input voltage range aligns with the specified 85V to 265V universal mains specification.

Selection Notes

Select this component when a fixed switching frequency is required to simplify input filter design compared to modulated frequency alternatives. It is suitable for applications demanding a power factor up to 0.99 with limited line current distortion. The integrated protections reduce the need for external safety circuits. Consider the L4981B if variable frequency operation is preferred to optimize filter size, or if higher precision overcurrent limiting via an external divider is necessary instead of the resistor-programmable limit found in the L4981A.

Part Context

The L4981 series represents STMicroelectronics' solution for power factor correction in pre-regulators. The L4981A specifically offers fixed-frequency operation, distinguishing it from the L4981B which uses line-modulated frequency. Both variants share the core average current mode architecture but differ in frequency control strategies. This family is part of ST's broader portfolio aimed at improving system efficiency and meeting certification requirements like 80 PLUS for power supplies.

Replacement Considerations

The L4981B serves as a functional alternative within the same family, offering line-modulated frequency operation instead of fixed frequency. Designers must account for differences in frequency control and overcurrent programming methods when substituting.