5D-9 Negative Temperature Coefficient Thermistor

5D-9 Negative Temperature Coefficient Thermistor is a crucial passive component for thermal sensing and current limiting in a variety of electronic circuits. This particular NTC thermistor features a nominal resistance of 5 Ω at 25°C and utilizes its Negative Temperature Coefficient property to provide effective inrush current suppression. Consequently, as the device heats up due to current flow, its resistance drops rapidly, transitioning from a high cold resistance to a very low operating resistance, thereby protecting power supplies and sensitive components from harmful initial current surges. Furthermore, its robust 9 mm diameter and leaded design make integration simple for power conditioning applications and temperature monitoring circuits where stability and cost efficiency are essential. Therefore, designers frequently specify the 5D-9 for consumer electronics and industrial equipment that require reliable power-up protection.

Key Features:

• Inrush Current Limiting: Effectively suppresses high transient currents during the power-up sequence, protecting relays, switches, and capacitors.
• Negative Temperature Coefficient (NTC): Resistance decreases predictably as the ambient or operating temperature increases.
• High Power Handling: Designed to withstand large current surges and dissipate heat efficiently during operation.
• Ceramic Disc Construction: Offers a stable, durable, and highly reliable structure for demanding operational environments.
• Through-Hole Mounting: Axial leaded construction simplifies assembly and provides secure mounting on standard PCBs.

Technical Specifications:

• Nominal Resistance (R₂₅): 5 Ω (±20%) at 25°C
• Thermal B-Constant (B_25/50): ≈ 2800 K (Determines the relationship between resistance and temperature)
• Maximum Steady State Current (I_max): 3 A (The maximum current the device can sustain continuously)
• Dissipation Factor (δ): ≈ 12 mW/°C (Indicates heat dissipation capability)
• Operating Temperature Range: −50°C to +175°C
• Time Constant (τ): ≈ 40 seconds (Rate of thermal response)

Mechanical Specifications:

• Body Diameter (D): 9 mm
• Lead Style: Radial Leads
• Coating: Epoxy Resin (Often Black)
• Construction: Highly stable pressed ceramic disc

Dimensions:

• Disc Diameter: 9.0 mm
• Lead Length (Each): ≈ 20 mm
• Lead Pitch: 5.0 mm
• Lead Diameter: ≈ 0.6 mm
• Body Thickness: ≈ 4.0 mm

Pinout and Wiring:

• Lead 1 (Input): Connect this lead in series with the AC or DC power line entering the circuit (e.g., connected to the fuse or rectifier bridge input).
• Lead 2 (Output): Connect this lead to the part of the circuit you need to protect (e.g., the charging capacitor bank or DC bus).
• Wiring Note: Always install the 5D-9 in series with the line voltage. In short, as the circuit powers up, the NTC limits the initial current; after a few seconds, it conducts freely as its resistance drops to a negligible level.

Datasheet Reference:

• Download Ametherm 5D-9 NTC Thermistor Datasheet

Commonly Used in:

• Switch Mode Power Supplies (SMPS): Essential protection for the bulk filter capacitors in SMPS circuits.
• Motor Drives: Providing initial current damping to protect motor windings and associated electronics during startup.
• LED Power Drivers: Used to limit inrush current to prevent premature failure of high-power LED drivers.

Applications:

• Power Supply Protection: Offers a cost-effective, self-resetting alternative to fuses for preventing excessive startup current.
• Soft Start Circuits: Implements a temporary high resistance to ensure a controlled and gradual rise in operating voltage and current.
• Temperature Measurement: While primarily used for current limiting, the device can also serve as a basic, low-precision temperature sensor.

Equivalent Models:

• SCK055 (Semitec): A functionally similar 5 Ohm, 5A ICL thermistor, frequently used as a direct cross-reference.
• B57164K0500K000 (EPCOS/TDK): A 5 Ω NTC thermistor from a major manufacturer offering similar performance characteristics.
• MZ6-05D9: Various manufacturer’s general part number for the 5 Ohm, 9 mm diameter Inrush Current Limiter.

Package Includes:

• 1 x 5D-9 Negative Temperature Coefficient Thermistor (5 Ω, 3 A, 9 mm)