حفاظت مدار فیوز خودبازگشت (پی‌تی‌سی)

Product Attributes

Introduction

At its most fundamental level, a Bel PTC consists of a block of polymeric material containing conductive filler, bonded between two conductive planar terminals. At currents below the device's IHOLD rating, and at temperatures below 100°C, the PTC maintains its resistance below the R1 MAX rating. As the device temperature approaches 130°C — whether due to elevated ambient temperature or current exceeding its ITRIP rating — the volumetric expansion of the filled polymer disrupts most of the conductive pathways formed between the terminals by chains of adjacent filler particle contacts, causing the device resistance to increase sharply by several orders of magnitude. At this elevated "tripped" resistance, only sufficient leakage current flows to maintain internal heating that keeps the device "held" in the tripped state (approximately 125°C) until power is interrupted. Once power is removed, the PTC core cools and contracts, allowing the conductive chains to re-form and returning the device to its low-resistance state. The catalog data for each device specifies a "typical power" value. This is the power required at 23°C for a tripped device to dissipate heat to the surrounding environment at exactly the rate needed to maintain the tripped state. By Ohm's Law, power can be expressed as: W = E² / R. Therefore, the approximate resistance of a "tripped" PTC can be determined by: R = E² / W, where "E" is the voltage across the PTC (typically the open-circuit voltage of the supply) and "W" is the typical power value for the specific PTC. Since the function of the PPTC is to maintain a constant internal temperature, its apparent resistance will vary with applied voltage and, to a lesser extent, with ambient conditions.

Features

• Low holding current
• Solid state
• Radial lead product for applications up to 60VDC
• Operating (holding current) range: 50mA - 3.75A
• Maximum voltage temperature range: 60VDC, -40°C ~ 85°C

Applications

Various electronic devices