The **TH405** generally refers to a specific series of **NTC (Negative Temperature Coefficient) Thermistors**. These components are widely used in electronic circuits for temperature sensing, compensation, and protection. --- ### 1. What is a TH405? A TH405 is a thermal resistor where the electrical resistance **decreases** as the temperature **increases**. It is typically a glass-encapsulated or epoxy-coated bead that provides high sensitivity to thermal changes. ### 2. Technical Specifications While specific parameters can vary by manufacturer (such as Amphenol or Shibaura), common characteristics include: | Parameter | Typical Value | Description | | :--- | :--- | :--- | | **Resistance (R25)** | 5kΩ to 100kΩ | Standard resistance measured at 25°C. | | **B-Constant** | 3400K - 4500K | Represents the slope of the resistance-temperature curve. | | **Operating Temp** | -40°C to +125°C | The functional heat range for the component. | | **Tolerance** | ±1% to ±5% | Accuracy level of the resistance value. | | **Dissipation Constant** | ~2.0 mW/°C | Power required to raise the part's temp by 1°C. | --- ### 3. Key Electronic Functions The TH405 serves several critical roles in a circuit: * **Temperature Measurement:** Combined with a voltage divider and an ADC (Analog-to-Digital Converter), it allows microcontrollers to read ambient or surface temperatures. * **Thermal Protection:** Used in battery packs (like Li-ion) to trigger a shutdown if the cells overheat during charging. * **Temperature Compensation:** Offsets the effects of temperature changes on other components (like crystals or transistors) to maintain circuit stability. ### 4. Typical Circuit Implementation In most designs, the TH405 is placed in a **Voltage Divider** configuration: ```cpp // Basic logic for reading a TH405 with an Arduino/MCU Vout = Vcc * (R_thermistor / (R_fixed + R_thermistor)) ``` * **Vcc:** Input voltage (e.g., 5V). * **R_fixed:** A precision resistor (usually 10kΩ) used as a reference. * **Vout:** The analog voltage that changes based on temperature. --- ### 5. Common Applications * **HVAC Systems:** Monitoring air and fluid temperatures. * **Automotive:** Engine coolant or intake air temperature sensors. * **Consumer Electronics:** Overheat protection in laptop power supplies and 3D printer heat blocks. * **Medical Devices:** Skin temperature probes and digital thermometers. ---