Features

• Suitable for protecting circuit boards.
• Flameproof construction in a ceramic case, resistant to humidity and insulation.
• For high resistance values, the winding cores can be replaced by power film cores.
• Excellent anti-surge characteristics and accurate fusibility.

Product Positioning and Core Applications

The SQF series is a thermal fuse cement resistor that combines resistance and thermal protection functions in one component. It is designed for circuit boards where resistor performance and thermal fuse protection are required within the same protection circuit.

As a fusible resistor, the SQF series provides resistance during normal circuit operation while supporting thermal fuse protection under specified abnormal conditions. Its anti-surge characteristics and available rated current and functioning temperature options allow engineers to select a suitable configuration according to circuit protection requirements.

The ceramic case and flameproof construction also make the series suitable for circuit protection designs where flameproof structure, insulation and resistance to humidity are required.

Electrical and Mechanical Specifications

The product data specifies test conditions for insulation resistance, dielectric withstand voltage, short-time overload, temperature cycling, load life and moisture-proof load life. Model-specific rated current, functioning temperature, resistance range and dimensions are provided in the product specification section.

Application Areas

PCB Circuit Protection

The SQF series can be used in circuit board protection circuits where a resistor and thermal fuse function are required in the same component. Engineers can select the appropriate fusible resistor configuration according to resistance value, rated current and rated functioning temperature.

Electronic Circuit Protection

For electronic circuit protection, the SQF series can be applied to circuits requiring a combination of resistance, anti-surge characteristics and thermal fuse protection. The flame proof resistor construction uses a ceramic case and incorporates insulation and humidity-resistant characteristics.

Surge and Overload Protection

For circuits exposed to short-duration surge or overload conditions, the SQF series provides anti-surge characteristics together with specified short-time overload capability. The product data specifies a short-time overload test at 10 times rated wattage for 5 seconds, while the Power Film version uses 5 times rated wattage for 5 seconds.

Moisture-Exposed Circuit Environments

For circuit protection applications where humidity is an environmental consideration, the moisture proof resistor characteristics can be evaluated using the specified moisture-proof load-life test. The test condition is 40°C, 95% RH for 500 hours, with resistance change limited to ΔR/R ≤5%.

Selection Considerations

The SQF series is available with 3A, 5A and 10A rated current options, together with rated functioning temperatures of 132°C, 145°C and 185°C. Selection should consider resistance value, rated wattage, ambient operating temperature and the required thermal protection conditions of the circuit.

When the resistor is operated at ambient temperatures above 25°C, the rated power must be derated according to the specified derating curve.