STMicroelectronics has introduced an inrush current limiter for use in off-line power converters that use half-controlled rectifier bridge (HCRB) circuits. Typical applications are in high-density power adapters, high-end TV power supplies and in open-frame switch-mode power supplies.
Many AC/DC power converters use a rectifier bridge and filtering capacitor to condition the incoming AC mains to drive a DC/DC converter. But when the AC mains is first applied to the converter, the current needed to charge the filtering capacitor is so large it can blow the converter's inline fuse and trip the mains circuit breaker. This inrush current can be handled by over-specifying the protection circuits, but this is not cost-effective.
A better approach is to include a current limitation circuit that does not cause large losses and that avoids creating a hot spot on the PCB, which could affect the power supply's reliability. The circuit should also be able to instantly limit the inrush current during repetitive on/off cycles of the mains and be immune to power line disturbances generated when the power supply is turned on. Ideally, the current limiter should also be small.
The STIL02-P5 and STIL04-P5 current limiters are designed to meet these requirements. Each monolithically integrates two unidirectional switches in one package. They are built using a robust planar manufacturing process, known as ASDTM, which is especially useful for this application since it produces parts that overcome the traditional trade-off in using SCRs between noise (dV/dt) immunity and power losses.
The benefits of the STIL parts include low power consumption Ipt of 20mA, and high noise immunity (dV/dt) greater than 500V/µs at a Tj of 150°C. The parts also have low reverse current losses and include a pilot driver for the power switches.
The STIL should be used as part of an AC rectification bridge design that mixes diodes and SCRs to produce a half-controlled rectifier bridge (HCRB). This circuit topology makes it possible to limit the inrush current with greater efficiency and integration than with traditional inrush current limitation circuits.
The advantages of using the HCRB with STIL current limiters over traditional inrush current limiters include reduced power loss, higher efficiency, reduced size and absence of hot spot during nominal operation. Additionally, when coupled to a PFC boost regulator, the STIL offers high responsiveness during AC on/off cycles. The STIL also sustains high repetitive forward and reverse on-state voltages up to 700V.
The STIL02-P5 and theSTIL04-P5 are designed for use in power supplies with output power inferior to 150W and 250W respectively. Both products are offered in the PENTAWATT HV2 package.
