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Development of the World's first chip multilayer ceramic PTC thermistor
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Murata has developed a ceramic PTC thermistor ("POSISTOR") (*1) with the world's first multilayered structure. The PRG21 series has the smallest size in the industry (2.0 x 1.25 x 0.9 mm), to provide resistance of 0.2 ohms with non-operating current of 0.5 A (at an ambient temperature of 60°C) |
To ensure the PTC characteristic in a multilayered structure, the PTC thermistor needs to use a base metal (Ni) for the internal electrodes, but it is very difficult to fire this base metal and ceramics together without oxidation, due to ceramics having a higher firing temperature.
Murata solved this problem by pursuing State-of-the-art pulverizing and firing technology for these materials. Taking advantage of this successful development, Murata can provide a small and low resistance chip ceramic PTC thermistor, whose characteristics exceed the limit of those using conventional monoplate structure.
Since the PRG21 series provides high thermal stability and reliability (a recognized feature of ceramic technology PTC devices), it can substantially expand the application range of Circuit Protection components.
These products contain no lead (Pb). It can be mounted with lead-free solder (typically, Sn-Ag-Cu), and is applicable for reflow soldering at 260°C max.
Background
With the trend toward functional sophistication of general electronic equipment, there are increasing needs for circuit protection components that can protect circuits from an overcurrent caused by excessive load and incorrect wiring of peripheral equipment. For certain equipment, it is compulsory to use circuit protection components (for example plug-and-play function under the USB standard).
PTC thermistors used for circuit protection are required to provide low resistance under normal conditions to prevent signal attenuation or power consumption. On the other hand, with the recent advances in miniaturization of electronic equipment, PTC thermistors must also be smaller. To meet such needs Murata has commercialized the PRG21 series chip multilayer ceramic PTC thermistor.
Terminology
*1 PTC thermistor ("POSISTOR")
PTC is the abbreviation for "Positive Temperature Coefficient". PTC thermistors provide a positive temperature coefficient, increasing its resistance in relation to a temperature rise. When an excessive current flows through a circuit, the resistance will sharply increase by heat generation, to limit the current flowing through the circuit.
PTC thermistors also provide a self-reset function, allowing the resistance to be restored to the original low level after the cause of overcurrent is removed and heat generation stops. Unlike current fuses, PTC thermistors will not melt so they can be used repeatedly as a circuit protection component.
*2 Non-operating current
"Non-operating current" indicates the amount of current that can continuously flow through a circuit without activating a PTC thermistor. As a PTC thermistor provides lower resistance in inactivated conditions, the non-operating current becomes larger.
Features
- Size: 2.0 x 1.25 x 0.9 mm
- Resistance: 0.2 ohms
- Non-operating current: 0.5 A (at ambient temperature of 60°C)
- Structure: Multilayer structure
- Internal electrode: Ni
- High thermal stability (No characteristic change when mounted to PCB)
- High reliability
- New model contains no lead (Pb)
- Applicable to reflow soldering at 260°C max.
Applications
- USB equipment
- Power supply circuits
- PC-related and other general electronic equipment
For more information on the full range of Murata products available from Anglia please call +44 (0)1945 474747 or email info@anglia.com
